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KCSE Biology Questions and Answers Form 1 - Biology Form One Notes

KCSE Biology Questions and Answers - Biology Questions and Answers Form 1

Biology Notes Form 1

Introduction to Biology

Biology is a branch of science that deals with the study of living things. There are diverse forms of life on earth ranging from the invisible microscopic living things to the gigantic life forms. It aims at explaining the living world in terms of scientific principles.

It is important to note, however, that living things interact with the non living things in the environment as Well. Biology, therefore also entails the study of non living things as well.

The role of human beings in shaping the environment is also investigated in biology.

In summary, biology deals with the study of origins, types, nature, growth, development, interactions and maintenance of all life forms on earth.

Branches of Biology

Biology is such a broad field of knowledge. It is divided into two broad branches

1. Zoology- This is a branch of biology that deals with the study of animal life.

2. Botany- This is a branch of biology that deals with the study of plant life.

Within the two branches, there exist even smaller branches because the branches (botany and Zoology) are very wide and complex.

The smaller branches of biology include:

a) Ecology- This is the study of the interrelationships between organisms and their environment. Ecology aims at establishing how organisms are related to each other and their environment.

Ecology is further subdivided into smaller branches. These can be forest ecology, marine ecology, rangeland ecology etc.

b) Genetics- This sub-branch of biology deals with the study of inheritance and variation. It deals with the study of how variations (differences) occur between parents and their offspring. It is also concerned with how various characteristics are passed on from parents to offspring.

c) Entomology- This is the study of insects.

d) Parasitology- This is the study of parasites.

e) Physiology- This deals with the study of the functions of various structures of an organism. It deals with the processes that take place in the body of organisms.

f) Anatomy- The study of the internal structure of organisms

g) Microbiology- This is the study of microorganisms

h) Bacteriology- The study of bacteria

i) Ornithology- This is the study of birds

j) Itchthology-This is the study of fishes

This list is in-exhaustive as there are very many other branches of biology.

Importance of biology

  • The study of biology is very important. The knowledge acquired from this study can benefit an individual in myriad ways. The study of biology is important in that:

  • The knowledge acquired from the study of biology can be very helpful in solving environmental problems such as food shortage, poor health services, pollution and environmental degradation.

  • The study of biology can grant one an entry into various careers such as medicine, veterinary medicine, animal husbandry, horticulture and dentistry.

  • The study of biology leads to development of scientific skills which are very useful in life. These include skills of observing, identifying, recording, classifying, measuring, analyzing and evaluating. These skills can enable one learn how to make right choices and lead an improved life.

  • Through the study of biology man learns the causes of human, plant and human diseases and how best these diseases can be prevented and cured.

  • Biological knowledge acquired in the study of biology is very useful in enhancing international cooperation. Some biology related international conventions include:

    > Joint development of HIV/AIDS vaccine by Kenyan and British scientists.

    > The coordinated fight against Severe Acute Respiratory Syndrome involving scientist all over the world.

    > The fight to save the ozone layer from depletion through various international agreements such as the Kyoto protocol.

    > Management of resources through international treaties such as the CITES (Convention against International Trade on Endangered Species).

    Characteristics Of Living Things

    Living things share a lot of characteristics in common. These characteristics are discussed below.

    a) Nutrition

    Nutrition is the process by which living things obtain and assimilate (utilize) nutrients. Living things require nutrients for various purposes; growth, repair of worn out tissues and for provision of energy. Plants manufacture their own food using light energy, carbon (IV) oxide, water and mineral salts through the process of photosynthesis. Conversely, animals feed on already manufactured foods from plants and other animals.

    b) Respiration

    Respiration is the process by which food substances are chemically broken down to release energy. During respiration, oxygen is used while energy, carbon (IV) oxide and water are released. Respiration occurs in all living cells.

    The energy produced in living things is very useful as it enables the living things carry out some of their physiological processes.

    The energy is also required for growth and development, movement and repair of worn out tissues.

    c) Gaseous Exchange

    Gaseous exchange refers to the process by which living things exchange oxygen and carbon (IV) oxide across the respiratory surfaces. Animals always take in air rich in oxygen and give out air rich in carbon (IV) oxide.

    Carbon (IV) oxide is a waste product of chemical reactions in the body. Animals require oxygen for respiration. Gaseous exchange, therefore, enables animals obtain oxygen for respiration and get rid of carbon (IV) oxide, a waste product.

    Plants, however, require carbon (IV) oxide for photosynthesis during the day. They give away oxygen as a by-product. The plants equally require oxygen for respiration and give away carbon (IV) oxide.

    d) Excretion

    This is the process by which living things separate and eliminate the waste or harmful materials resulting from chemical reactions Within the cells. These harmful waste products of metabolism maybe toxic to the body if they are left to accumulate in the cells of the living things

    e) Growth and Development

    Growth refers to an irreversible increase in size and mass while development refers to the irreversible change in complexity of the structure of living things. Growth and development of living things is essential as it enables the living things to attain maximum size that can enable them to perform their functions and roles.

    f) Reproduction

    This is the process by which living things give rise to new individuals of the same kind. All living things reproduce. Reproduction is essential as it leads to perpetuation of species and it avoids extinction of certain animals and plants.

    g) Irritability

    This is the ability of living things to perceive (detect) changes in their environment and respond to them appropriately. Living things respond to changes in temperature, humidity, light, presence or absence of certain chemicals.

    Response of organisms to these changes is crucial as it enables them to escape from harmful stimuli. Ability to detect changes in the environment also enables organisms to obtain resources in their environment.

    h) Movement

    Movement refers to change is position (displacement) of a part or parts of an organism. Movement in plants includes folding of leaves, closing of flowers and growing of shoots towards light. The change of position of an entire organism from one position to another is locomotion.

    Study questions

    a) Motor vehicles move, use energy and produce carbon dioxide and water. Similar characteristics occur in living organisms yet motor vehicles are not classified as living. List the other characteristics of living things that do NOT occur in motor vehicles.

    b) Give the name to the study of:

  • The cell

  • Micro—organisms

  • The study of differences between parents and their offspring

  • The study of relationships between organisms and their environment.

    Collection of Specimen

    We have defined biology as the study of living things. For effective study, a biologist may have to collect some living things or some parts of living things for observation and analysis. The living things or parts of living things that are used for biological study are called specimens.

    Biological studies always take place in laboratories. A laboratory is a building or a room that is designed and equipped for scientific studies.

    Collections of living things especially animals may not be very easy. Some of the animals are not easy to catch while some are quite dangerous. Knowledge on proper specimen collection and handling of is very important. We will discuss some of the apparatus used in specimen collection.

    a) Sweep net- This is used for catching flying insects.

    b) Fish net- This is used for trapping small fish and other small Water animals.

    c) Pooter- This is used for sucking small animals from rock surfaces or barks of trees.

    d) Bait trap- This is used for attracting and trapping small animals including rats.

    e) Pit fall trap- This is used for catching crawling animals.

    f) Pair of forceps- This is an apparatus used for picking up small crawling animals e.g. stinging insects.

    g) Specimen bottles- These are bottles used for keeping collected specimen. They are of different sizes depending on the size of the specimen being studied.

    h) Magnifying lens- This is used to enlarge small objects. A hand lens is a common magnifying lens used in the laboratory. The magnifying power of the hand lenses is always indicated on the lens e. g. X10, X5, X8. The magnifying power of a lens shows how many times the image will be enlarged compared to the object.

    How to use a magnifying lens

    To use a magnifying lens, place the object to be enlarged on the bench. Hold the magnifying lens on one hand and while closing one eye, move the lens towards the object until the image comes into clear focus.

    If a magnifying lens is used to make a drawing of a specimen, the magnification of the drawing will have no relation with the size of the drawing.

    The magnification of the drawing can be calculated using the formula shown below.

    Drawing magnification: Length of drawing divided by Length of the actual object

    The sign of “times” must come before the magnification value e. g. X10, X5, X15 etc.

    Precautions During Collection and Observation of Specimen

    While collecting specimen for observation, a biologist should play close attention to the following:

  • Collect only the number of specimen you need; do not collect more than you need.

  • Do not harm the specimen during the capture/collection exercise.

  • Do not destroy the natural habitat of the specimens.

  • Handle dangerous/injurious specimens with care. Such injurious specimens can be stinging plants or insects. Forceps and hand gloves should be used in such cases.

    Comparison Between Plants and Animals

    Plants

  • most posses chlorophyll which gives them their green color. Chlorophyll is very useful in the process of photosynthesis
  • their cells have cellulose cell walls
  • they respond slowly to changes in their environment
  • plants are immobile
  • they lack specialized excretory organs

    Animals

  • they lack chlorophyll content hence feed on already manufactured food materials
  • their cells lack cellulose cell walls
  • they respond quickly to changes in their environment
  • most animals move around in search of food, shelter and mates
  • have complex excretory organs

    Chapter Two: Classification 1

    Introduction

  • Biology has been defined as the study of living things (living organisms). Even though all living things share similar characteristics discussed in the introductory chapter, the living things exhibit a lot of differences.

    In particular, animals and plants are all living things yet they differ in many aspects. Amongst animals and plants also there exist a lot of differences.

    There are millions of different plant and animal types exhibiting a range of differences. This created a need for a classification system of living things to make study of the living organisms easier.

  • Classification refers to the grouping of living organisms according to their structure.
  • In classification, organisms that share a lot of similarities are placed under one group referred to as a taxon (plural: taxa).

  • Other than the similarities, grouping of the organisms also takes into account the evolutionary relationships (phylogeny) of the organisms. It is believed that all organisms once had a common ancestor (theory of evolution). During classification, organisms that are believed to have evolved along the same line of evolution are placed in one taxon.

  • The scientific study of classification is known as taxonomy. A biologist studying taxonomy is a taxonomist.

  • In classifying organisms taxonomists to a great extent rely on the use of external observable features of organisms.

    External features of plants used in classification

  • The rhizoids as in moss plant

  • Fronds in ferns

  • The type of root; tap root, adventitious, fibrous, prop, buttress roots.

  • Stem presence and type.

  • Presence or absence of flowers

  • Type of leaves; simple or compound; leaf venation- parallel or net work veined.

  • Presence and types of fruits and cones.

    External features of animals used in classification

  • Tentacles in hydra

  • Body covering- feathers, scales, hair or fur

  • Shells in snails

  • Wings in birds

  • Proglotids in tapeworms

  • Mammary glands in mammals

  • Locomotory structures

  • Body pigmentation

    Importance of Classification

  • Classification systems improve our ability to explain relationships among things.

  • Classification helps in identifying living organisms into their correct groups for reference

  • Classification helps in avoiding chaos and confusion when dealing with animals as it arranges the information on organisms in an orderly manner.

  • Classification brings together living organisms with similar characteristics together but separate those with different features.

  • Taxonomic systems provide relatively stable, unique, and unequivocal names for organisms

  • It makes the study of such a wide variety of organisms easy.

  • It projects before us a good picture of all life forms at a glance.

  • It helps us understand the interrelationship among different groups of organisms.

  • It serves as a base for the development of other biological sciences such as biogeography etc.

  • Various fields of applied biology such as agriculture, public health and environmental biology depend on classification of pests, disease vectors, pathogens and components of an ecosystem.

    Historical background of Classification

  • In the past, scientists used to classify organisms based on personal conveniences. They heavily relied on very few observable features. There was no standard classification system as each and every scientist would classify organisms in a way that would suit his intentions.

  • In particular, living organisms were simply classified as plants or animals. The plants were also classified as herbs, trees, shrubs. Animals were also grouped into herbivores, carnivores and omnivores.

  • Some biologists would also classify plants as:

    a) Edible or non edible

    b) Flowering or non-flowering

  • The modern classification systems take into account the evolutionary relationships between living organisms. It has overcome the many weaknesses of the artificial (traditional) classification systems.

  • From the original parents, arose new groups of organisms that went under structural changes that enabled them to live in different habitats. The structural changes account for the great diversity of living organisms observed today.

  • Carolus Linnaeus, a Sweddish biologist is largely credited for his significant contribution to the development of the modern classification system.

    Taxonomic Units of Classification

  • Taxonomic units of classification refer to the groups or taxa into which organisms are placed as a matter of convenience.
  • Grouping of organisms in these groups is based on easily observable characteristics that are common in that group.
  • Living organisms which share a lot of characteristics are placed in the same group.
  • Each taxonomic unit reflects the position of an organism in relation to the others in the classification scheme.
  • In a classification scheme, a hierarchy of groups is recognized and it proceeds from the first largest and highest group, the kingdom to the smallest and lowest unit, the species.
  • There are seven taxonomic units of classification.

    1. Kingdom

    2. Phylum (animals)/division (plants)

    3. Class

    4. Order

    5. Family

    6. Genus

    7. Species

    All living organisms are classified into five major kingdoms:

    a) Kingdom Monera- This is composed of microscopic unicellular organisms mainly bacteria e.g amoeba.

    b) Kingdom Protoctista- This kingdom is comprised of members who are microscopic. Though, some are large enough to be seen with the naked eyes.

    Members of this kingdom include algae and protozoa.

    c) Kingdom Fungi- Members of this kingdom comprises the mushrooms, toadstools, moulds and yeast.

    d) Kingdom Plantae- This kingdom comprises the moss plant, ferns, maize plants, hibiscus, meru oak tree etc.

    e) Kingdom Animalia — Members of this kingdom include the tapeworms, hydra, fishes, human beings, lizards, earthworms etc.

    In hierarchy of classification, a kingdom is further divided into several phyla (plural of phylum) or divisions (in plants). Within the phyla or divisions, organisms are further sorted out into groups known as classes based on their similarities and mode of life.

    Each class is further subdivided into small groups called orders based on structural similarities. Orders subdivide into families which subdivide into genera (plural for genus).

    Genera are then subdivided into smaller units of classification called the species.

    Species is the smallest unit of classification whose members share many similarities and can freely interbreed to give rise to fertile or viable offspring.

    Members of a particular species can, however, exhibit various differences e. g. differences in skin colour or body forms. Within the species, organisms can further be classified based on the differences in colour or forms.

    In humans, this gives the races, in animals the term used is breed while in plants, variety is preferred. In bacteria, the term strain is used to describe the variant forms.

    Members of different but very closely related species can breed but the resulting offspring will be sterile (infertile). In particular, a mule is a sterile offspring between a horse and a donkey.

    Moving from kingdom to species, it is important to note that the number of organisms in each taxon decreases. The similarities, however, increase as one moves from kingdom to species.

    Scientific Naming of Living Organisms

  • Scientific naming involves assigning an organism two names in Latin language. The naming system was developed by Carolus Linnaeus in the 18th century.
  • Organisms always have common names and scientific names. Common names are local names by which the organisms are known in the vernacular languages. In particular, a cat is an English name, mbura is a luo name, paka is a Swahili name etc. these names differ across cultures and cannot be used by scientists to communicate across the world. This makes sharing scientific knowledge on organisms very difficult. There was need for a common language and this led to development of scientific language in latin.
  • Latin was the preferred language since it was the first language of civilization that was widely spoken at that time. Similarly, latin language is a dead language hence not subjected to a lot of changes. The scientific names are, therefore, static.
  • Scientific names are the valid names by which organisms are known all over the world.
  • In scientific naming, an organism is assigned a specific name that is unique. The specific name adopts two names. This implies that the specific scientific name of an organism has two names. This double naming system is known as binomial nomenclature.
  • In binomial nomenclature, an organism is assigned its genus name and species name.
  • Assigning of scientific names to living organisms is governed by a definite set of rules which are internationally recognized and referred to as binomial nomenclature which literally means the rule of double naming system.

    Rules of Binomial Nomenclature

    Binomial nomenclature requires that:

    a) The first part of the scientific name is that of the genus name which should begin with a capital letter. The second name is that of species. The species name should be written in small letters e. g.

    a) Maize- Zea mays

    b) Lion- Panthera leo

    c) Leopard- Panthera pardus

    d) Domestic dog- Canisfamiliaris

    e) Human being- Homo sapiens

    b) When printed in books and other printed works, the scientific names should be printed in italics. However, in handwritten manuscripts and typed works, the genus and species names should be lined separately.

    Printed work- Homo sapiens

    c) The specific name is frequently written with the name of the scientist who first adequately described and named the organism e. g. Balanus balanoides Linneaus. d) Scientists must give a latinised name for a newly described animal or plant species where a Latin name is missing e,g.

    Aloe kilzfiensis- A type of aloe found in kilifi

    Meladogyne kikuyuensis- A nematode found in kikuyu.

    Origin of scientific names

    Scientific names assigned to organisms can be:

  • Descriptive
  • Geographical
  • Commemorative

    Chapter Three: The Cell

    Introduction

  • The bodies of living organisms are made up of small microscopic units called cells. The cells make up the structures of the living organisms and are responsible for carrying out various biological processes in the bodies of the living organisms.
  • Some organisms are made up of a single cell only e.g. amoeba and other bacteria in the kingdom monera. These organisms are known as unicellular organisms.
  • Other organisms are composed of many cells and are said to be multicellular. Most plants and animals are multicellular.
  • A cell is the basic functional unit of an organism.
  • Being very small, the cell cannot be seen with a naked eye. A powerful magnifying instrument is required. The microscope is used to view the cells.
  • Development of the light microscope
  • In 1650, Zacharias Jansen invented the compound microscope which combines two lenses for greater magnification.
  • In 1665, Robert Hooke used an improved compound microscope to observe cells.
  • Between 1650 and 1700, Anthony Van Leewenhoeck developed a better microscope with lenses which provided a greater magnification. He used the microscope to view nuclei and unicellular organisms including bacteria.
  • The development of the electron microscope in 1930s significantly improved microbial studies. Through this microscope, it was possible to study very finer details of structures.

    The Light Microscope

  • This is the most commonly used microscope in schools and institutions that do not focus on very fine details of the internal structures of cells.
  • The light microscope uses a beam of light to illuminate the specimen being studied.
  • A microscope is a delicate and expensive instrument that should be handled with care. It is imperative to understand the parts and functions of various parts of a microscope.
  • In a light microscope, the eye piece and the objective lenses both contribute to the magnification of the specimen.
  • The total magnification of the specimen viewed under a light microscope will be given by:

  • Magnification: Eyepiece lens magnification X Objective lens magnification
  • In particular, if the eyepiece lens magnification is X10 and objective lens magnification power is X8, then the total magnification of the specimen would be:

    Magnification=Eyepiece magnification X Objective lens magnification

    = 10 X 8

    =X80.

    Figure 1. The light microscope

    Handling and Care of the Microscope

    Part of the microscope: Limb

    function: supports the body tube and stage

    Base:

    function: provides firm and steady support to the microscope

    Body tube:

    function: holds the eyepiece and the revolving nose piece

    Coarse adjustment knob:

    function: raises or lowers the body tube through longer distances to bring the image into sharper focus

    Fine adjustment knob:

    function: raises or lowers the body tube through smaller distances to bring the image into sharper focus. it is mostly used with the high power objective lens

    Diaphragm:

    function: an aperture that regulates the amount of light passing through the condenser to illuminate the specimen

    Eye-piece:

    function: contains a lens which contributes to the magnification of the specimen under review

    Objective lens:

    function: bring image into focus and magnifies it.

    Mirror:

    function: reflects light through the condenser to the object on the stage

    Revolving nose piece:

    function: holds the objective lenses in place and enables the change from one objective lens to the other

    Condenser:

    function: concentrates light on the object on stage

    Stage:

    function: flat platform where specimen on the slide is placed.it has two clips to hold the slide into position

    The following rules should be observed when handling the microscope:

    > Always use both hands when carrying the microscope. One hand should hold the base to provide support while the other hand holds the limb.

    > Never place the microscope too close to the edge of the working bench or table.

    > Do not touch the mirror or the lenses with your fingers.

    > Dirty lenses should be cleaned using a special soft lens tissue paper or tissue paper moistened with ethanol. The other parts of the microscope may be cleaned using a microscope.

    > Do not wet any part of the microscope.

    > Make sure the low power objective lens clicks into position in line with the eye piece before and after use.

    > After use, always clean and store the microscope in a safe place, free from moisture and dust.

    How to use the Microscope

  • Place the microscope on the bench with the stage facing away from you.
  • Turn the low power objective lens until it clicks into position.
  • Ensure that the diaphragm is fully open.
  • Look through the eye-piece with one eye; meanwhile adjust the mirror under the stage to ensure that maximum light can pass through. The circular area seen is referred to as the field of view.
  • Again look through the eyepiece while adjusting the mirror under the stage to ensure that sufficient light is passing through the specimen.
  • Use the coarse adjustment knob to bring the low power objective lens to the lowest point.
  • Viewing through the eye-piece, turn the coarse adjustment knob gently until the specimen comes into focus.
  • Use the fine adjustment knob to bring the image into sharp focus. Make a drawing of what you observe.
  • For higher magnifications, turn the medium power objective lens into position and adjust the focus using the coarse adjustment knob. For sharper images, use the fine adjustment knob.
  • If finer details are required, turn the high power objective lens into position; now use only the fine adjustment knob to bring the details into sharper focus.

    Cell Structures as seen under the Light Microscope

  • The structures within the cell are referred to as organelles. Some of the cell organelles that can be observed under the light microscope include the cell wall, cell membrane, cytoplasm, nucleus, vacuole and chloroplasts.
  • These cell organelles perform specific functions within the cell.

    Figure 2 Plant and animal cells as seen under the light microscope

    The cell as seen under the Electron Microscope

  • The electron microscope is more powerful than the light microscope. It uses a beam of electrons to illuminate the specimen instead of light as in the case of light microscope.
  • Electron microscope can magnify an object up to 500,000 times.
  • It also has a very high resolving power. Resolving power is the ability to distinguish between separate things which are close to each other.
  • The high resolving power makes the electron microscope a very important research tool in microbiology.
  • Through the electron microscope, very fine details of the cell can be observed.

    Figure 4. The plant cell

    Structure and Functions of the Cell Organelles

    Cell membrane

  • The cell membrane, also known as plasma membrane or plasmalemma consists of three layers when viewed under the electron microscope. The three layers are composed of one layer of phospholipid sandwiched between two protein layers.
  • It is flexible and has pores. The cell membrane is important in that:
  • It encloses the cell contents.
  • It allows for selective movement of materials in and out of the cells. The pores allows materials particularly of small molecular size to move in and out of the cells

    Cytoplasm

  • Cytoplasm consists of a fluid medium in which chemical reactions take place. It contains dissolved substances.
  • organelles and other inclusions such as starch, glycogen, fat droplets and many other dissolved substances.
  • Cytoplasm is not static; it undergoes a movement known as cytoplasmic streaming.
  • It provides a suitable medium for cellular reactions to take place.

    c) Mitochondrion

  • Mitochondrion is a sausage shaped organelle that provides sites for respiratory reactions that yield energy for the cell. Mitochondria is thus, referred to as the powerhouse of the cell.
  • It is bound by two membranes. The inner membrane is greatly folded into cristae to increase surface area for respiration.
  • The arrangement and number of mitochondria in a cell depends on the cell energy requirements. Cells that require large amounts of energy contain high amount of mitochondria.
  • Such cells include muscle cell, sperm cell, apical meristem cells, and kidney cell.

    > Mitochondria are self replicative that is they can divide to form new ones.

    Figure 5. The Mitochondrion (Animal)

    Figure 6, (generalize(lmage23 mitochondrion Structure)

    d) Endoplasmic Reticulum

  • Endoplasmic reticulum appears as a series of interconnected channels, running throughout the cytoplasm.
  • Their membranes are continuous with the outer membrane of the nuclear membrane.
  • Some endoplasmic reticula have granules called ribosomes on their surfaces and are referred to as rough or granular endoplasmic reticula. Endoplasmic reticula that are not associated with ribosomes are called smooth endoplasmic reticula.
  • The rough endoplasmic reticulum transports proteins while the smooth endoplasmic reticulum transports lipids.
  • Generally, endoplasmic reticula also act as storage areas for synthesized molecules such as enzymes. They also contribute to mechanical support.

    e) Ribosomes

  • These are spherical in shape. While some are bound to the endoplasmic reticula, some ribosomes are scattered within the cytoplasm (free ribosomes). Their largest dimension is 25 nanometres.
  • They are synthesised in the nucleolus.
  • They form sites for protein synthesis.

    f) Lysosomes

  • These are spherical sac-like organelles bound by a single membrane. They contain lytic enzvmes which break down large molecules. destroy Worn out oraanelles or even the entire cells.
  • Lysosomes also play crucial role in digestion in unicellular organisms.
  • The lysosomes are also vital in breakdown of bacteria and other harmful microbes that might have been ingested in food. This explains their high relative abundance in injured or infected cells.
  • The membrane of the lysosomes are intact. This is important because if the enzymes leak out, they may destroy the whole cell.

    g)Golgi bodies/Golgi apparatus

  • These are stacks of membrane bound tube like sacs. They are found close to the cell membrane.
  • Golgi bodies perform the following functions:

    1) They package and transport glycoproteins.

    2) They are involved in secretion of synthesized proteins and carbohydrates.

    3) They manufacture lysosomes.

    Note: Golgi bodies are abundant in cells that are active in secretion. For instance pancreatic cells which secrete enzymes and the nerve cells which secrete neurotransmitter substances.

    h)Centrioles

  • These are rod shaped structures located just outside the nuclear membrane.
  • They take part in cell division and also in the formation of cilia and flagella in lower organisms.
  • Plant cells lack centrioles.

    i) Chloroplasts

  • Chloroplasts are egg-shaped structures surrounded by two membranes and contain a gel- like stroma through which runs a system of membranes that are stacked together to form grana.
  • The granum contains chlorophyll which traps light energy that is used during photosynthesis.
  • It is in the chloroplasts that photosynthesis takes place.

    j) Vacuoles

  • These are sacs that are filled with fluid called cell sap. Vacuoles vary in size.
  • Animal cells contain small vacuoles which may be numerous in the cells while plant cells contain one large centrally placed vacuole.
  • Sap vacuoles store sugars and salts thereby contributing to the osmotic properties of the cell. This influences how materials move in and out of the cell.
  • In some unicellular organisms, food vacuole stores and digests food substances while the contractile vacuole excretes unwanted materials from the cell.

    k) Cell wall

  • This is the rigid outer cover of plant cells and some lower organisms.
  • In plants it is composed of cellulose fibres.
  • Cell wall is important in that:

    1. It gives plant cells their definite shape

    2. It provides mechanical support and protection against mechanical injury.

    3. The cell wall allows gases, water and other substances to pass through it.

    i) Nucleus

  • Nucleus is a double membrane bound structure made up of a viscous fluid known as nucleoplasm in which nucleolus and chromatin materials are suspended. The nuclear membrane has minute pores, nuclear pores which allow materials to move in and out of the nucleus.
  • Nucleus controls all the activities of the cell.
  • Nucleolus is responsible for manufacture of ribosomes while chromatin contains hereditary materials.
  • Nucleus generally takes a sperical or oval shape.

    Comparison between Plant Cells and Animal Cells

    While there exist many similarities between plant and animal cells, there are a number of differences.

    Plant cells

  • usually large
  • regular in shape
  • has a cell wall
  • usually has a large central vacuole
  • cytoplasm and nucleus are usually located towards the periphery of the cell
  • some have chloroplast
  • usually more store oil, starch and proteins
  • has no centriole

    Animal cells

  • smaller in size
  • irregular in shape
  • has no cell wall
  • usually has no vacuole but when present,they are often temporary and small structures within the cytoplasm
  • cytoplasm occupies most space in the cell with the nucleus usually centrally placed
  • has no chloroplast
  • stores glycogen and fats
  • has centrioles

    Estimation of Cell Size

    The light microscope can be used to estimate the size of a cell. Most cells have diameters smaller than a millimeter. Due to this, cell sizes are always measures in smaller units.

    These are micrometres and nanometers. These units of measurements are related as shown below.

    1 millimeter (mm) = 1000 micrometres (pm).

    1 micrometer (pm) = 1000 nanometres (nm).

    Procedure in cell size estimation

  • One requires a microscope, transparent ruler marked in millimeters and a prepared slide of cells.
  • With the low power objective lens in place, keep a transparent ruler on the stage of the microscope.
  • Focus so that the millimeters marks on the ruler are seen as thick dark lines.
  • Estimate the diameter of the field of view by counting the one millimeter spaces between the first mark and the last one across the field of view. Count only the spaces between two thick dark lines.
  • Convert the diameter of the field of view from millimeters to micrometres.
  • Remove the ruler and place the prepared slide of cells.
  • Count the number of cells along the diameter of the field of view.
  • Calculate the diameter of one cell using the formula:

    cell diameter = diameter of the field of view in micrometers divided by number of cells.

    Cell Specialization. Tissues. Organs and Organ Systems

    Cell Specialization/Cell Differentiation

  • This refers to the process by which a cell becomes structurally modified to perform specific functions
  • While cells have a basic outline, they become differentiated to perform specific functions
  • In particular, the root hair cell has extended surface for absorption while the sperm cell has a tail-like extension for swimming towards the ovum.

    Tissues

  • A tissue is a group of cells of a particular type that are grouped together to perform the same function.

    a) Tissue types in animals

    1. Epithelial tissue- This is a thin continuous layer of cells for lining and protection of internal and external surfaces.

    2. Skeletal muscle- This is a bundle or sheets of elongated cells with fibres that can contract. Its contraction and relaxation brings about movement.

    4. Blood tissue- This is a fluid containing red blood cells, white blood cells and platelets.

    The main functions of blood tissue are transportation of nutrients and gases as well as protection of the body against infections.

    5. Connective tissue- This tissue consists of strong fibres that connects other tissues and organs thereby holding them in position.

    b)Tissue types in plants

    1. Epidermal tissue- This is a single thin layer of cells covering the outer surfaces. It protects inner tissues of plants from mechanical damage and infection.

    2. Palisade tissue- This is a group of cells rich in chloroplasts containing chlorophyll. It has a site for the absorption of light energy and manufacture of food by photosynthesis.

    3. Parenchyma tissue- This tissue consists of special thin walled irregularly shaped cells. They form packaging and storage cells.

    4.Conducting tissue/Vascular bundle- This tissue consists of xylem and phloem. Xylem conducts water and dissolved mineral salts in a plant while phloem conducts food substances in solution.

    Organs

  • An organ is a group of specialized tissues that are grouped together to perform a common function.

  • Organs in animals include:

    a) Heart- composed of connective, muscle, epithelial and blood tissues.

    b) Kidney- Composed of connective, epithelial and muscle tissues

    c) Brain- Composed of epithelial, connective tissues

    d) Lungs- Composed of epithelial, connective tissues.

  • Organs in plants include:

    a) Roots- composed of epidermal, conducting and parenchyma tissues.

    b) Flowers- This is composed of epidermal, conducting tissues.

    c) Stem- Composed of conducting, parenchyma, and epidermal tissues and palisade tissues in some cases

    d) Leaves- Composed of palisade, conducting and epidermal tissues.

    Organ system

    This is a group of organs Whose functions are coordinated and synchronized to perform the same function.

    Organ systems are more pronounced in animals than in plants

    Organ systems in animals include

    a) Digestive system composed of organs such as oesophagus, stomach, intestines and their associated glands.

    b) Circulatory system composed of the heart, blood vessels (arteries, veins, capillaries). c) Excretory this is composed of kidney, liver, and blood vessels.

    d) Respiratory system composed of trachea, bronchus, and lungs.

    e) Reproductive system composed of the reproductive organs and associated glands.

    f) Nervous systems composed of the brain, spinal cord, eye, ear organs.

    Chapter Four: Cell Physiology

    Introduction

  • Physiology refers to the branch of biology that deals with the study of functions and activities of life or of living matter such as organs, tissues or cells. It aims at understanding the mechanism of living.
  • In simpler terms, physiology refers to the processes and functions that take place inside the body cells of organisms.
  • Cell physiology refers to the study of functions of the cell structures. The cell structures perform various functions of life. In particular:

    a) Chloroplasts play a vital role in carbohydrate synthesis.

    b) Mitochondrion produces energy required to carry out life processes.

    c) Ribosomes manufacture of proteins.

  • These physiological processes require various raw materials for them to take place.
  • For photosynthesis to occur, carbon (IV) oxide, mineral salts and water have to be taken into the chloroplasts.
  • For respiration (energy production) to take place, food substrate such as glucose and oxygen have to be taken into the mitochondrion. Energy, carbon (IV) oxide, water and alcohol (in plants) are some of the end products of respiration.
  • Some of the end products of the physiological processes such as carbon (IV) oxide can be harmful when allowed to accumulate in the cells. They, thus, have to be eliminated from the cells.
  • This implies that there is a constant flow of materials in and out of the cells and the cell organelles where these physiological processes are taking place. There is a constant movement of materials across the cell membrane in the cells.
  • This chapter discusses the properties of the cell membrane and the processes through which materials move in and out of the cells.

    Structure of the membrane

  • A membrane is a surface structure that encloses the cell and cell organelles.
  • The membranes include the cell membrane, tonoplasts, nuclei membrane, mitochondrial membrane and chloroplast membrane.
  • The membranes have a common basic structure which regulates the movement of materials in and out of the cells.
  • The cell membrane is made up of a phospholipid layer sandwiched by two protein layer (it is a lipoprotein layer) the overall thickness of the cell membrane is about 7.5 nm thick.
  • The membrane is perforated by small pores that allow the passage of substances in and out of the cells.

    Properties of the cell membrane

    a) The cell membrane is semi permeable- The pores that occur on the cell membrane allows the passage of the small size molecules but does not allow the passage of the large sized molecules.

    Such a membrane is said to be selectively permeable or semi-permeable. In particular, when a cell is surrounded by a dilute sugar solution, the small sized water molecules will enter the cell but the larger sugar molecules will not pass through the cell membrane.

    In contrast, the cell wall is permeable as it allows both sugar and water molecules to pass through it; it has larger pores. This property of selectively permeability enables the cell membrane to select what enters and leaves the cell.

    b)The cell membrane is sensitive to changes in temperature and pH- Cell membranes are made up of protein. Proteins are adversely affected by extreme changes in temperature and pH.

    Changes in temperature and pH will alter the structure of the cell membrane thereby hindering the normal functioning of the cell membrane. High temperature denatures (destroys) the proteins thereby impairing the functions of the cell membrane.

    c)The cell membrane possesses electric charges- The cell membrane has both positive and negative charges. These charges affect the manner in which substances move in and out of the ells. The charges also enable the cell to detect changes in the environment.

    Physiological Processes of the Cell membrane

  • In this section, we discuss the various physiological processes through which materials move in and out of the cells across the cell membrane.
  • Materials move in and out of the cells through three main physiological processes:

    a) Diffusion

    b) Osmosis

    c) Active transport

    Diffusion

  • From kinetic theory, matter is made up of particles that are in continuous random motion.
  • In solids, the particles are at fixed positions and can only vibrate at these fixed positions.
  • In liquids and gases, the particles are loosely held and are free to move from one region to another randomly. This movement of gas or liquid particles is observed to be from regions of high concentration to a region of low concentration. The process by which particles move from a region of high concentration to a region of low concentration is known as diffusion.
  • In particular, the scent of a flower or perfume experienced by an individual is as a result of the flower scent particles or perfume particles move from a region of high concentration.
  • Diffusion occurs until the regions have an even concentration of the liquid or gas particles.
  • The difference in concentration of particles between the region of high concentration and region of low concentration is known as the diffusion gradient/concentration gradient.

    Demonstration of the process of diffusion using_potassium manganate (VII)

    Requirements: potassium manganate (VII) crystals, glass tubing, 100 cm3 beaker and water.

    Procedure

    a) Hold the glass tubing vertically in a beaker so that one end of the tubing rests on the bottom of the beaker.

    b) Cautiously and quickly drop a crystal of potassium manganate (VII) through the upper opening of the glass tubing.

    c) Close the upper hand of the glass tubing with the thumb.

    d) Half fill the beaker with water.

    e) Carefully withdraw vertically the glass tubing so that the crystal is left undisturbed at the bottom of the beaker.

    f) Record your observations for the first 15 minutes.

    g) Explain your observations.

    Expected observations

  • After some time, the purple colour of the potassium manganate (VII) spread throughout the water and eventually all the water turned purple.

    Explanation

  • The crystals of potassium manganate (VII) are highly concentrated with the potassium manganate (VII) particles. The potassium manganate (VII) particles break away from the crystals, dissolve in water and then diffuse through the water until they are evenly distributed.

    The Role of Diffusion in Living Organisms

    a) In Plants

    Diffusion plays an important role in plants in that:

  • It helps in absorption of mineral salts from the soil to the plant. Most salts dissolve in soil water. For those salts whose concentration in soil water is higher that their concentration in the cell sap of root hair cells, they move into the root hair cells through diffusion. Plants require mineral salts for numerous life processes.
  • Diffusion plays a role in gaseous exchange in plants. The respiratory gases (oxygen and carbon (IV) oxide) diffuse across the stomata and lenticels of plants.
  • Diffusion also contributes to the transportation of manufactured food materials from the leaves to other parts of the plant.

    b) In Animals

    In animals diffusion plays the following important roles

  • It helps in the absorption of digested food materials in the alimentary canal. End products of digestion such as amino acids and glucose diffuse across the wall of the ileum into the blood for transport to other parts of the animal body.
  • Diffusion also plays a significant role in gaseous exchange in animals. In animals, gaseous exchange occurs at certain structures known as respiratory surfaces.

    These include the skin, gills, lungs, tracheal system and the cell membrane (in unicellular organisms). Gaseous exchange at these surfaces occurs through the process of diffusion.

  • Diffusion is important in excretion of nitrogenous wastes especially in unicellular animals.

    Factors affecting the rate of Diffusion

    a) Diffusion gradient

  • A greater diffusion gradient between two points increases the rate of diffusion. Increasing the concentration of diffusing molecules also increases diffusion gradient with corresponding regions hence increases the rate of diffusion.

    b) Surface area to volume ratio

  • Rate of diffusion directly depends on the surface area to volume ratio. The greater the surface area to volume ratio, the greater the rate of diffusion will be. Conversely, low surface area to volume ratio results in a low diffusion rate.
  • This implies that diffusion rate is greater in small organisms than the large organisms. This is because the small organisms have a large surface area to volume ratio. As a result, most of their body parts are closer to the external surrounding leading to faster diffusion.
  • Small organisms can, therefore, depend on diffusion alone as a means of transporting foods, respiratory gases and waste products.
  • To large organisms, diffusion alone is inadequate as a means of transport of foods and excretion. They have an additional transport system.
  • Organisms always lose heat to the surrounding through diffusion. This implies that small animals lose a lot of heat to the surrounding compared to the large animals.

    c) Thickness of membranes and tissues

  • The thicker the membrane or tissue, the lower the rate of diffusion. This is because the distance covered by the diffusing molecules is greater through the thicker membranes.
  • The rate of diffusion is higher in thinner membranes.

    d) Size of molecules

  • Small and light molecules diffuse much faster than the heavy and large sized particles.

    e)Temperature

  • An increase in temperature increases the energy content of the diffusing particles; thereby causing them to move faster, this implies that the rate of diffusion increases with increase in temperature.

    Osmosis

  • Osmosis is a process by which solvent molecules move from a region of high concentration (dilute solution) to a region of low concentration (concentrated solution) through a semi permeable membrane.
  • Osmosis can be described as a special type of diffusion since it involves movement of solvent (Water) particles from a region of high concentration to a region of low concentration.

    Demonstration of Osmosis Using a Visking Tubing

    Requirements

    5OOcm3 beaker, visking tubing, a piece of thread, glass rod, concentrated sugar solution, 500 cm3 distilled Water.

    Procedure

    1. Into the beaker, put 350 cm3 of the distilled water.

    2. Dip the visking tubing in water to moisten it. Open the visking tubing and tie one end with the thread provided.

    3. Half fill the visking tubing with the sugar solution provided and then tie the open end of the tubing. Ensure no sugar solution spills out of the tubing.

    4. Immerse the visking tubing into the distilled water in the beaker and suspend it using the glass rod provided.

    5. Leave the set up for about 30 minutes.

    6. Record your observations.

    7.Explain the observations made.

    Observations

  • The visking tubing became swollen indicating that its cell contents increased. The amount of water in the beaker decreased. This implies that water moved from the beaker into the visking tubing.

    Explanation

  • The visking tubing contains both sugar and water molecules. The beaker contains a higher concentration of water molecules than the visking tubing. The water molecules diffused from the beaker (where they are highly concentrated) into the visking tubing (where they are lowly concentrated).

    Even though there is a higher concentration of sugar molecules in the visking tubing, they were not able to diffuse out of the visking tubing due to their large molecular sizes. The visking tubing is semi permeable.

  • Other than visking tubing, dialysis tubing or cellophane are also other semi permeable membranes that can be used in this experiment.

    Osmosis explained

  • When two separate solutions are separated by a semi permeable membrane, there will be movement of water molecules from their region of high concentration (dilute solution) to a region of low concentration (the highly concentrated solution) across the semi permeable membrane. The semi permeable membrane does not allow movement of solute particles across it.
  • The movement of the water molecules continues until the separate solutions have the same concentrations.
  • Solutions with the same concentrations are referred to as isotonic solutions. The solutions are said to be isotonic to each other.
  • A lowly concentrated solution (dilute solution) is referred to as a hypotonic solution. A hypotonic solution has less of the solute molecules but more of the solvent molecules.
  • A highly concentrated solution with more of the solute particles but less of the solvent particles is referred to as a hypertonic solution.
  • When isotonic solutions are separated with a semi permeable membrane, there will be no net movement of solvent molecules to any of the solutions since they have the same concentration of solvent molecules.

    Osmotic pressure

  • When a concentrated solution is separated from distilled water by a semi permeable membrane, the concentrated solution will develop a force with which it draws water through the semi permeable membrane from the distilled water.
  • Osmotic pressure refers to the force with which a concentrated solution draws water to itself.
  • An osmometer is an instrument used to measure the osmotic pressure.

    Osmotic potential

  • This is a measure of the pressure a solution would develop to withdraw water molecules from pure water when separated by a semi permeable membrane.

    Water Relations in Animals

  • As discussed earlier, the cell membrane is semi permeable. Let us discuss what would happen if an animal cell say red blood cell is placed in solutions of varying concentrations

    a) Red blood cell in hypotonic solution e. g. distilled water

  • Distilled water has a higher concentration of water molecules compared to the red blood cell cytoplasm.

    When a red blood cell is placed in a hypotonic solution, water will move into the cell through osmosis. The cell will swell and burst. Swelling of red blood cell when placed in a hypotonic solution is referred to as haemolysis. The cell is said to be haemolysed.

    b) Red blood cell in hypertonic solution

  • A hypertonic solution has a low concentration of water molecules compared to the red blood cell cytoplasm.

    Water will, therefore, be drawn out of the cell into the hypertonic solution. The cell will shrink and become small. The cell is said to be crenated.

    The process by which animal cells shrink and become smaller when placed in hypertonic solutions is referred to as crenation.

    c) Red blood cell in isotonic solution

    When placed in an isotonic solution, the cell remains unchanged. This is because there will be no net inflow or outflow of water between the cell and the solution.

    Note:

  • When the cell becomes haemolysed or crenated, its functioning is impaired. This implies that the body fluids and blood plasma surrounding the cells must be kept at the same concentration as the animal cells.

    This will prevent bursting or shrinking of the cells that would otherwise impair their physiology.

  • The body has a mechanism through which these concentrations are maintained at a nearly same concentration.

    Water Relations in Plants

  • Water relations in plant cells differ with that in animal cells.
  • A plant cell has both a cellulose cell wall and cell membrane. The centre of the cell contains vacuole with sap. The sap is a solution of salts and sugars and is bound by a membrane, the tonoplast.
  • The cell membrane and tonoplast are semi permeable while the cellulose cell wall is fully permeable.

    a) Plant cell in hvpotonic solution e. g. distilled water

  • If a plant cell is placed in water or hypotonic solution, the cell will draw water from the hypotonic solution through osmosis causing the cell to distend.
  • The cellulose cell wall is rigid and does not allow plant cells to burst as in the case of animal cells.
  • As the cell gains more water, the vacuole enlarges and exerts an outward an outward pressure on the cell wall called turgor pressure.
  • The turgor pressure increases as more water is taken into the vacuole causing the cell to stretch until the cell cannot stretch any more. The cell becomes firm and is said to be turgid.
  • Turgor pressure is the outward pressure that the cell cytoplasm exerts on the cell wall as it gains more water through osmosis.
  • When the cell wall is being stretched towards the outside, it will develop a resistant pressure to stretching that is equal and opposite to turgor pressure called wall pressure. b) A glam cell in a hygertonic solution

  • When placed in a hypertonic solution, the plant cell will lose water to the solution through osmosis. As the water moves out of the cell, the cell starts to shrink, becomes less rigid or flabby and is said to be flaccid.
  • It the cell loses more water, its contents reduce in size and the plasma membrane pulls away from the cell wall towards the centre. The process through which plant cells lose water, shrink and become flaccid is called plasmolysis.
  • Plasmolysis can be reversed when a flaccid cell is placed in distilled water in a process called deplasmolysis.

    Wilting

  • Plants always lose water to the atmosphere through transpiration and evaporation.
  • Simultaneously, the plant cells lose water and draw more from the soil.
  • Wilting is a phenomenon that occurs when plant cells lose more water than they draw from the soil making the plant cells to lose their turgor pressure and droop.
  • At night, plants always recover from wilting since stomata are closed and water loss through evapotranspiration is significantly reduced.
  • Where water supply from the soil is inadequate, the plants may fail to recover from wilting and instead undergo permanent wilting.

    Role of Osmosis in Organisms

  • Absorption of water from the soil-The root hair cell of plants absorbs water from the soil through osmosis. Osmosis also helps in distribution and movement of water from the roots to other parts of the plant.
  • Osmosis plays an important role in support in herbaceous plants and young seedlings. When the cells of these plants take in water through osmosis, the cells become firm or rigid and thus gain support.
  • Osmosis plays a role in opening and closing of stomata in plants- The guard cells surrounding the stomata synthesize glucose through photosynthesis in the presence of light.

    As glucose accumulates in the guard cells, the osmotic pressure of the guard cells increase making them to draw water from adjacent cells through osmosis. When the guard cells become turgid, they bulge outwards leading to opening of the stomata.

    Opening of the stomata is crucial as it allows for gaseous exchange in plants. At night, there is no glucose synthesis.

    The glucose available in the guard cells is respired on leading to reduction of glucose and consequently reduction in osmotic pressure. The guard cells lose turgidity and close the stomata.

  • Osmosis also plays a role in feeding in insectivorous plants- These plants live on nitrogen deficient soils and trap insects from whence they obtain the nutrients. These plants possess special structures that suddenly change their turgor pressure when disturbed.

    The change in turgor pressure enables the special structures to rapidly close thereby trapping the insects.

  • Osmosis also plays a role in osmoregulation in animals
  • In kidney tubules of animals, water is withdrawn from the tubules into the body cells through osmosis through the tubular walls. This enables animals to maintain the osmotic pressure of the body fluids.

    Factors Affecting the Rate of Osmosis

  • Concentration of solutions and concentration gradient. Osmosis is greater when the separated solutions have a greater difference in osmotic pressure. In summary, the greater the concentration gradient, the greater the rate of osmosis and vice versa.
  • Temperature-An increase in temperature would increase the rate of osmosis as it increases the energy content of the molecules.
  • Thickness of the membranes-The thicker the membrane the lower the rate of osmosis while the rate of osmosis is greater through thinner membranes.

    Active Transport

  • Active transport refers to the process through which substances are moved across the cell membrane and against a concentration gradient.
  • Diffusion and osmosis alone do not account for movement of substances in and out of the cells. In particular, there are some mineral salts that occur at low concentrations in the soil water than in the cell sap.

    Some of these mineral salts cannot be absorbed by the plants through diffusion. A mechanism that would move them into the cells against the concentration gradient will be useful.

  • Active transport requires energy. This is unlike diffusion and osmosis that only depend on concentration gradient for them to take place.
  • It is postulated that there are protein carrier molecules on the cell membrane that aid in the moving these substances across the membrane. These carrier molecules combine with the substances being transported across the membrane and then move them from one side of the membrane to the other side.
  • Cellular intake of solutes is largely through active transport.

    Role of active transport in living organisms

  • Active transport is important in living things in that:
  • It helps in re-absorption of sugars and some salts by the kidney to the bloodstream.
  • It helps in absorption of some mineral salts from the soil by roots.
  • Absorption of digested food from alimentary canal of animals into the bloodstream.
  • It leads to accumulation of substances into the body to offset osmotic imbalance in arid and saline environments
  • It plays a role in excretion of waste products from body cells.

    Factors affecting the rate of Active Transport

  • Most factors that affect active transport are those factors that would affect the energy production process in living cells.
  • These include:

    a) Oxygen concentration

    Oxygen is required in respiration process that yields energy for active transport. Under low oxygen concentration, the rate of respiration will be low hence there will be production of little energy leading to low rate of active transport. Increase in oxygen concentration translates into a higher energy production leading to high rate of active transport.

    b) Change in pH

    Change in pH affects the respiratory process which is enzyme controlled. Respiratory enzymes require optimum pH for their efficient activity. Extreme pH conditions will increase lower the rate of active transport since the enzymes controlling respiration Will be denatured.

    c) Glucose concentration

    Glucose is the chief respiratory substrate. At low glucose concentration, there will b less production of energy leading to decreased rate of active transport. Rate of active transport increases with increase in glucose concentration due to increase in the rate of energy production.

    d ) Temperature

    Temperature affects the enzyme controlled respiration process. At low temperatures, the enzymes are inactive hence the rate of respiration will be low resulting into low rate of active transport since there will be less production of energy. An increase in temperature increases the rate of respiration since the enzymes become more activated. At temperatures beyond 40 degrees celcius, the enzymes become denatured, respiration stops and so does active transport.

    e) Presence of metabolic inhibitors e. g. cyanide.

    These are substances which act as metabolic poisons. They stop the rate of respiration leading to production of no energy. Active transport is, thus, stopped.

    Nutrition Plants And Animals

    Introduction

  • Nutrition refers to the process by which living organisms obtain and assimilate (utilize) nutrients. It is one of the fundamental characteristics of living things. The nutrients obtained are useful to the living organisms in many ways:

    a) The nutrients are required for growth and development of the living organisms.

    b) The nutrients are required for energy provision as they are broken down to release energy.

    c) They nutrients are also required for repair of worn out tissues

    d) Nutrients are required for synthesis of very vital macromolecules in the body such as hormones and enzymes.

    Modes of nutrition

    There are two main nutrition modes:

    a) Autotrophism mode of nutrition through which living organisms manufacture their own food from simple inorganic substances in the environment such as carbon (IV) oxide, water and mineral ions. Organisms that make their own food through this mode are autotrophs.

    b) Heterotrophism mode of nutrition in which living organisms depend on already manufactured food materials from other living organisms. Heterotrophs are the organisms that feed on already manufactured food materials.

    Autotrophism

    In this mode of nutrition, organisms manufacture their own food from readily available materials in the environment. These organisms use energy to combine carbon (IV) oxide, water and mineral salts in complex reactions to manufacture food substances. Depending on the source of energy used to manufacture the food, there are two types of autotrophism:

    a)Chemosynthesis

    This is the process whereby some organisms utilize energy derived from chemical reactions in their bodies to manufacture food from simple substances in the environment. This nutrition mode is common in non green plants and some bacteria which lack the sun trapping chlorophyll molecule.

    b) Photosynthesis

  • This is the process by which organisms make their own food from simple substances in the environment such as carbon (IV) oxide and water using sunlight energy.
  • Such organisms often have chlorophyll which traps the required sunlight energy.
  • This mode of nutrition is common in members of the kingdom Plantae. Some protoctists and bacteria are also photosynthetic.

    Importance of Photosynthesis

    1. Photosynthesis helps in regulation of carbon (IV) oxide and oxygen gases in the environment.

    2. Photosynthesis enables autotrophs make their own food, thus, meet their nutritional requirements.

    3. Photosynthesis converts sunlight energy into a form (chemical energy) that can be utilized by other organisms that are unable to manufacture their own food.

  • Photosynthesis largely occurs in the leaf. To understand the process of photosynthesis, it is important to understand the leaf structure.

    External leaf structure

  • Externally, the leaf has a petiole through which it attaches to the leaf branch or stem, lamina- the broad flat surface, margin- the outline and the leaf apex.
  • The leaf margin can be smooth, dentate, serrated or entire.
  • The size of a leaf depends on its environment. Plants in arid areas have small sized leaves with some leaves reduced to needle like shape.

    This helps reduce the rate of water loss in such plants. However, the plants in areas of water abundance have broad leaves to enable them lose the excess Water.

    a) Cuticle

  • This is the outermost layer of the leaf.
  • It is a thin non-cellular, Waxy, transparent and waterproof layers that coats the upper and lower leaf surfaces.

    Functions of the cuticle

    a) Being waterproof, it minimizes water loss from the leaf cells to the environment through transpiration and evaporation.

    b) It protects the inner leaf tissues from mechanical damage.

    c) It prevents entry of pathogenic microorganisms into the leaf.

    b) Epidermis

  • This is the outermost one cell thick layer covering upper and lower leaf surfaces. Its cells are flattened and lack chloroplasts.

    Functions of the epidermis:

    a) It protects the leaf from mechanical damage.

    b) It also protects the leaf from entry of disease-causing microorganisms.

    c) It secretes the cuticle.

  • There are many small pores on the epidennis known as stomata (singular-stoma) through which exchange of materials occur. The opening and closing of the stomata is controlled by the guard cells. Each stoma is controlled by two guard cells.
  • The guard cells have chloroplasts and are bean shaped. They have thicker inner cell wall and thinner outer cell wall.

    Adaptations of the guard cells

  • They have deferentially thicker walls to enable them bulge as they draw water through osmosis from the neighboring cells making them to open the stomata.
  • They contain chloroplasts that manufacture sugars which increase osmotic pressure of the guard cells. As they draw water through osmosis, they bulge making the stomata to open.

    c) Palisade mesophyll

  • This is the chief photosynthetic tissue in plants. Its cells are regular in shape.
  • Its cells contain numerous chloroplasts for photosynthesis.
  • Their close packing and location just below the epidermis enables them to trap maximum sunlight for photosynthesis.
  • Location of palisade layer on the upper surface explains why upper leaf surfaces are greener than the lower surfaces.

    d) Spongy mesophyll layer

  • This layer contains loosely arranged irregular cells. This leaves large airspaces between the cells which permits free circulation of gases carbon (IV) oxide and oxygen into the photosynthetic cells. Spongy mesophyll cells contain fewer chloroplasts compared to palisade cells.

    e) Vascular bundle/tissue

  • This is found in the midrib and leaf veins. Vascular bundle is made of phloem and xylem tissues. Xylem tissues conduct Water and some dissolved mineral salts from the roots to other plant parts while phloem translocates manufactured food materials from photosynthetic areas to other plant parts.

    Chloroplast

  • This is the organelle in which photosynthesis takes place. It is an oval shaped double membrane bound organelle.
  • Internally, it is made up of membranes called lamellae suspended in a fluid filled matrix called stroma.
  • Lamellae forms stacks at intervals called grana (singular-granum). Chlorophyll molecules are contained in the grana.
  • Within the stroma. fat droplets, lipid droplets and starch grains are found.
  • The strona contains enzymes and forms the site Where light independent reactions take place.

    Adaptations of the leaf to photosynthesis

  • The leaf has a flat snd broad lamina to increase surface area for trapping sunlight energy and for gaseous exchange.
  • The leaf has numerous stomata through which photosynthetic gases diffuse.
  • The leaf is thin to reduce the distance through which carbon (IV) oxide has to diffuse to the photosynthetic cells.
  • The palisade mesophyll cells contain numerous chloroplasts which contain chlorophyll molecules which trap sunlight energy for photosynthesis.
  • The photosynthetic mesophyll is located towards the upper surface for maximum absorption of sunlight energy.
  • The leaf has an extensive network of veins composed of xylem which conducts water to the photosynthetic cells and phloem to translocate manufactured food materials to other plant parts.
  • The epidermis and cuticle are transparent to allow light to penetrate to the photosynthetc cells.

    Raw materials for photosynthesis

  • Water
  • Carbon (IV) oxide

    Conditions for photosynthesis

  • Light energy
  • Chlorophyll

    Photosynthesis Process

  • Photosynthesis is a complex process that involves a series of reactions. It can be summarized into two main reactions.

    a)Light reaction/Light stage

  • This is the first stage of photosynthesis. It occurs in the presence of light. Without light it cannot take place.
  • Light stage occurs in the grana of the chloroplasts.
  • During light stage, two fundamental processes occur:

    i) Photolysis of water

  • This refers to the splitting of water molecules using sunlight energy to give hydrogen ions and oxygen gas.
  • This is aided by the fact that the grana contain chlorophyll molecules that trap sunlight energy for photolysis.
  • The oxygen gas produced can either be released into the atmosphere or be utilized by the plant for respiration.

    Water-- Hydrogen atoms + Oxygen gas

    ii) Formation of adenosine triphosphate (ATP)

  • Some of the sun light energy is used to combine Adenosine Diphospate molecule in the plant tissues with a phosphate molecule to form Adenosine Triphosphate (ATP). ATP is an energy rich molecule that stores energy for use in the dark stage when sunlight energy could be unavailable.

    ADP + P = ATP

  • The hydrogen ions and ATP formed during light stage are later used in dark stage.

    b) Dark reaction/Dark stage

  • These reactions are light independent. The energy that propels these reactions are derived from the ATP formed during light stage.
  • Also known as carbon (IV) oxide fixation, dark stage involves combination of carbon (IV) oxide molecule with hydrogen ions to form a simple carbohydrate and a water molecule.
  • Dark reactions take place in the stroma.

  • Other food materials are then synthesized from the simple sugars through complex synthesis reactions.
  • The simple sugar formed in dark stage is quickly converted to starch which is osmotically inactive. When a lot of simple sugars accumulate in the chloroplasts, osmotic pressure of the guard cells would increase causing the guard cells to draw a lot of water through osmosis. This makes the guard cells to bulge and open the stomata. This can result into excessive water loss.
  • To prevent, this, the simple sugars are quickly converted to starch. To test whether photosynthesis has taken place in a leaf, therefore, a test for presence of starch and not simple sugars is carried out.

    Testing for starch in a leaf

    Requirements

  • Iodine solution
  • Methylated spirit/alcohol
  • Boiling tube
  • Droppers
  • Water
  • White tile
  • Fresh leaf
  • Means of heating
  • Timer

    Procedure

  • Detach a leaf that has been exposed to light for about six hours. This duration ensures that the leaf has photosynthesized.
  • Put the leaf in boiling water for 10 minutes. This kills the protoplasm, denatures the enzymes and stops any chemical reactions in the leaf.
  • Remove the leaf and put it in a boiling tube containing methylated spirit or alcohol and boil in a water bath. Methylated spirit is highly flammable hence should be boiled indirectly. Boiling with methylated spirit or alcohol decolourises the leaf (removes the chlorophyll). This ensures that the leaf becomes white so that colour changes can be observed easily when iodine is added.
  • Remove the leaf and wash off in hot water to remove methylated spirit and to soften the leaf.
  • Spread the leaf on a white tile and add drops of iodine solution onto the leaf and observe.

    Observations

  • If there is formation of blue black patches on the leaf then starch is present
  • If the yellow/brown colour of iodine persists on the leaf then starch is absent in the leaf.

    Factors affecting the rate of photosynthesis

    a) Carbon (IV) oxide concentration

  • While the concentration of carbon (IV) oxide in the atmosphere is fairly constant at 0.03%, an increase in carbon (IV) oxide concentration translates into an increase in the rate of photosynthesis up to a certain point when the rate of photosynthesis becomes constant.

    At this point, other factors such as light intensity, water and temperature become limiting factors.

    b)Light intensity

  • The rate at of photosynthesis increases with an increase in light intensity up to a certain level. Beyond the optimum light intensity the rate of photosynthesis becomes constant. To this effect, plants photosynthesize faster on bright and sunny days than on dull cloudy days.
  • Light quality/wavelength also affects the rate of photosynthesis. Most plants require red and blue wavelengths of light for photosynthesis. Light duration also affects photosynthesis rate.

    c)Temperature

  • Photosynthesis is an enzyme controlled process. At very low temperatures the rate of photosynthesis is slow because the enzymes are inactive. As temperature increases, the rate of photosynthesis increases because the enzymes become more active.

    Rate of photosynthesis is optimum at (35-40) °C. Beyond 40°C the rate of photosynthesis decreases and eventually stops since the enzymes become denatured.

    d) Water

  • Water is a raw material for photosynthesis. At extreme level of water shortage, rate of photosynthesis will be severely affected.

    Experiment to investigate the gas produced during photosynthesis

    Requirements

  • Water plant e.g. elodea, spirogyra, Nymphea (water lily), glass funnels, beakers, small wooden blocks, test tubes, wooden splints and sodium hydrogen carbonate.

    Procedure

    a) Set up the apparatus as shown in the figure below

    b) Place the set up in the sunlight to allow photosynthesis to take place.

    c) Leave the set up in the sun until sufficient gas has collected in the test tube.

    d) Test the gas collected with a glowing splint.

    e) Record your observations.

    Note:

  • In this experiment, sodium hydrogen carbonate is added to the water to boost the amount of carbon (IV) oxide in the water since water has a low concentration of carbon (IV) oxide.
  • A water plant is also selected because Water plants are adapted to photosynthesis under the low light intensity in water where terrestrial plants cannot easily photosynthesize.
  • This experiment can also be used to investigate the factors affecting the rate of photosynthesis:

    1) Carbon (IV) oxide concentration: Carry out the experiment using different amounts of dissolved sodium hydrogen carbonate e. g 5 g, 10g, 15g, 20g and examine the rate at which the gas collects.

    2) Light intensity: An artificial light source can be used. Illuminate the plant and vary the distance between the set up and the light source While recording the time it takes for the gas jar to fill or counting the number of bubbles peer unit time.

    3) Temperature: carry out the experiment at varying temperatures and record the rate at which the gas collects.

    Experiments on factors necessary for photosynthesis

    Light

    Requirements

  • Methylated spirit, iodine solution, water, white tile, droppers, beaker, source of heat, boiling tube, light proof material e.g. aluminium foil, potted plant and clips. Procedure
  • Cover two or more leaves of a potted plant with a light proof material.
  • Place the plant in a dark place for 48 hours (keeping the plant in the dark for 48 hours is to ensure that all the starch in it is used up. This makes the leaves ideal for investigating whether starch would form in the experimental period. This is called destarching).
  • Transfer the potted plant to light for 5 hours.
  • Detach and uncover the leaves and immediately test for starch in one of the covered leaves and one that was not covered.

    Carbon (IV) oxide

    Requirements

  • Sodium hydroxide pellets, flask, jelly Procedure

  • Destarch the plant for 48 hours
  • Place a few pellets of sodium hydroxide in the flask
  • Bore a hole in the cork of the same size as the petiole of the leaf being used
  • Cut the cork lengthwise. Chlorophyll

  • For this experiment, a variegated leaf is required. This is a leaf in which some patches lack chlorophyll.
  • These patches could be yellow. They lack chlorophyll hence photosynthesis does not take place in them.

    Procedure

  • Detarch or remove variegated leaf that has been exposed to light for at least three hours.
  • Draw a large diagram of the leaf to show the distribution of the chlorophyll
  • Test the leaf for starch and record observations.

    Chemicals Of Life

  • These are chemical compounds that constitute the living organisms.
  • Biochemistry is the branch of biology that deals with the study of the chemicals of life and their reactions.
  • Chemicals of life include carbohydrates, proteins and lipids.

    Carbohydrates

  • Are compounds of carbon, hydrogen and oxygen in the ratio of 1:2: l.
  • They have a general formula (CH2O)n where n represents the number of carbon atoms.
  • Carbohydrates are grouped into three categories:

    Monosaccharides

  • These are the simplest carbohydrates.
  • They include glucose, fructose, galactose.
  • Their general formula is C6H12O6.

    Properties of Monosaccharides

  • They are sweet tasting
  • They readily dissolve in water
  • They are crystallisable
  • They are reducing sugars; monosaccharides reduce blue copper (II) sulphate in Benedict’s solution to red brown copper (I) oxide when heated.

    Note:

  • Most fruits are sweet tasting because they contain a lot of monosaccharides.
  • Monosaccharide units can be combined to form complex carbohydrate molecules through a process known as condensation. Water molecules are produced in the process. Functions
  • They are the chief respiratory substrate. They are broken down to release energy in the body.
  • They are condensed to form complex important carbohydrates.

    Disaccharides

  • These are complex sugars formeed by linking two monosaccharide units through condensation.
  • They have a general formula CHHZZOH. The bond that holds two monosaccharide units is called glycosidic bond.
  • Examples of disaccharides include:

  • Maltose-common in germinating seeds
  • Sucrose-fruits and sugar cane. Sucrose is the form in which carbohydrates are transported in plants
  • Lactose- found in milk

    Properties of Disaccharides

  • They are sweet tasting
  • They are crystallizable
  • They are water soluble
  • While they are non reducing sugars, some such as maltose is sugar reducing and is known as a complex reducing sugar.
  • They can be broken down into their constituent monosaccharide units through hydrolysis. Hydrolysis is the process through which complex molecules are broken down in the presence of water molecules.
  • In living systems, hydrolysis is carried out by enzymes. However, in the laboratory, hydrolysis can be carried out by boiling the disaccharide in dilute aid such as hydrochloric acid.

    Functions

  • They are hydrolyzed into monosaccharides and respired on to yield energy
  • They are the form in which carbohydrates are transported in plants due to their soluble and inert nature.

    Polysaccharides

  • These are formed through linking of numerous monosacchride units through condensation.
  • Their general formula is (C6H10O5),, where n is a very large number.

    Properties of polysaccharides

  • They are non sweet
  • They do not dissolve in water
  • They are non crystalline
  • They are non-reducing sugars

    Examples of polysaccharides

    a) Starch- Made by linking numerous glucose molecules. It is a form in which carbohydrates are stored in plants.

    b) Glycogen- Is a storage carbohydrate in liver and muscles of animals. It is broken down to glucose in animals when blood glucose falls.

    c) Cellulose- This is a structural polysaccharide in plants. It is a component of the cell wall

    d) Chitin- A structural carbohydrate found in cell wall of fungi and arthropod exoskeletons

    Functions of polysaccharides

  • They are storage carbohydrates; their insolubility and inertness makes them ideal for storing carbohydrates.
  • They are structural carbohydrates e. g. cellulose forms the plant cell walls
  • They can be hydrolyzed into monosacharides and be broken down to release energy

    Lipids

  • These are compounds of carbon, hydrogen and oxygen. However, they contain lesser oxygen but higher hydrogen compared to carbohydrates.
  • Building units for lipids are fatty acids and glycerol. To synthesize a molecule of lipid, three fatty acids and a glycerol molecule are linked through a condensation reaction.
  • There is one type of glycerol but numerous fatty acids
  • There are different types of fatty acids. The property of a lipid therefore depends on the type of fatty acids that link up with the glycerol.
  • There are complex lipids such as phospholipids, steroids, waxes and cholesterol. These also form through condensation.

    Properties of lipids

  • Fats easily change to oil when heated while oils easily solidify when cooled.
  • They are insoluble in water but readily dissolve in organic solvents such as chloroform to form emulsions
  • They are inert hence can be stored in tissues of organisms.

    Functions

  • They are a source of energy when oxidized. They yield more energy compared to carbohydrates when oxidized per unit weight. However, they are less preferred as source of energy because they require a lot of oxygen to oxidize. In addition, they are insoluble hence not easy to transport to respiratory sites.
  • They are a source of metabolic water. When oxidized, they yield a lot of metabolic water. This explains why some desert animals such as camels store large quantities of fat in their bodies.
  • Lipids offer protection to internal organs as they are deposited around them to act as shock absorbers.
  • Lipids provide heat insulation when stored underneath the skin as they are poor conductors of heat hence do not conduct heat away from the body. Organisms in cold areas tend to be short and plump as they have fatter fat adipose.
  • Lipids form structural compounds for instance phospholipids in cell membrane.
  • Complex lipids such as waxes in leaves help minimize water loss through transpiration.
  • Some lipids mediate communication between cells

    Proteins

  • These are compounds of carbon, hydrogen and oxygen. In addition, they also contain nitrogen and sometimes phosphorous or sulphur or both. Some proteins molecules contain other elements. In particular, haemoglobin contains iron.
  • Proteins are made up of amino acids. There are about twenty known amino acids. Amino acids are of two kinds:

    a) Essential- These are those amino acids that cannot be synthesized by the body systems hence have to be supplied in the diet.

    b) Non essential- These are amino acids that can be synthesized by the body mechanisms hence do not need to be supplied in the diet.

  • An amino acid has an amino group, carboxyl group, hydrogen atom and an alkyl, R group. Amino acids differ from each other by the alkyl group.

  • Proteins are of two kinds:

    a) First class proteins- Contain all essential amino acids

    b) Second class proteins- Proteins lack one or more essential amino acids

    Protein synthesis

  • Two amino acids combine through a condensation process to form a dipeptide molecule Several amino acids link up to form a polypeptide chain. Proteins are made up of long chain polypeptides.
  • Properties of a protein depend on the type of amino acids present in its chain and the sequence in which the amino acids link up in the polypeptide chain.

    Properties of Proteins

  • They dissolve in Water to form colloidal suspensions in which the particles remain suspended in water.
  • They are denatured at temperatures beyond 40°C. Strong acids, bases, detergents and organic solvents also denature proteins.
  • They are amphoten'c- possess both basic and basic properties.
  • This property enables them to combine with other non protein substances to form conjugated proteins such as:
  • Mucus- Protein plus carbohydrate
  • Haemoglobin- Protein plus iron

    Functions of proteins

    a) They are structural compounds of the body. Cell membrane is protein in nature. Hair, nails and hooves are made up of protein keratin.

    b) Proteins are broken down to release energy during starvation when all carbohydrate and lipid reserves are depleted.

    c) Functional proteins play vital roles in metabolic regulation. Hormones are chemical messengers while enzymes regulate the speed of metabolic reactions.

    d) Proteins such as antibodies provide protection to the body against infections

    e) Some protein molecules are transport molecules. Haemoglobin molecule plays a crucial role in transportation of respiratory gases.

    f) Proteins play a vital role in blood clotting e. g. fibrinogen.

    g) Contractile proteins such as actin and myosin bring about movement.

    Enzymes

    What are enzymes?

  • Are organic catalysts that are protein in nature and regulate the rate of metabolic reactions.
  • They speed up or slow down the rate of metabolic reactions but to not get used up in the process.

    Types of enzymes

    a) Extracellular: Are produced within the cells but used outside the cells e. g. digestive enzymes.

    b) Intracellular: Are enzymes produced and used within the cells e. g. respiratory enzymes.

    Importance of Enzymes

  • They speed up the rate of chemical reactions that would otherwise be too slow to support life.
  • Some enzymes take part in synthesis/building of useful complex substances such as DNA.
  • Digestive enzymes breakdown complex food substances into simple foods that can be utilized by the cells.
  • Some metabolic enzymes such as catalase play a vital role in detoxification (making poisonous substances less harmful.

    Enzyme nomenclature

  • Two systems of naming enzymes have been adopted.

    a).Trivial naming

  • This is where an enzyme is named by the scientist who discovered it.
  • In trivial naming all enzyme names end in prefix —in.

    Examples

  • Pepsin (Theodor Schwann, German physiologist -1836).
  • Ptyalin (Anselme Payen, a French chemist- 1833).
  • Trypsin.

    b). Use of suffix -ase

  • Enzymes are assigned names by adding suffix -ase to the food substrate acted by the enzyme or by adding the suffix to the reaction being catalyzed by the enzyme.

    Substrates

  • Amylose (starch) ............ ..amylase.
  • Lipids .......................... ..lipase.
  • Protein ....................... .. protease.
  • Carbohydrate ........... . . . . . . ..carbohydrase.
  • Lactose ......................... ..lactase

    Processes/Reactions

    Hydrolysis .................... ..hydrolase

    Reduction ..................... ..reductase

    Oxidation ...................... ..oxidase

    Mechanism of action of Enzymes

  • Enzymes are not used up during metabolic reactions. They do have “active sites” through which the substrate molecules bind to the enzymes. The reaction is then catalyzed and the end products released. The enzyme is free to bind with another substrate molecule. The enzymes can be used again and again.

    Properties of Enzymes

  • They are protein in nature; hence affected by temperature and pH.
  • They are substrate specific e. g. maltase cannot digest sucrose.
  • They are efficient in small amounts since they are re-used in the reactions.
  • They mostly take part in reversible reactions.
  • They regulate the rate of metabolic activities but are not used up.

    Factors affecting enzyme activity

  • Temperature.
  • pH.
  • Substrate Concentration.
  • Enzyme Concentration.
  • Enzyme co-factors and co-enzymes; Fe, Mg, Zn, Cu ions.
  • Specificity.
  • Enzyme inhibitors.

    a)Temperature

  • At low temperatures, kinetic energy of enzymes and molecules are low. There are few collisions leading to low enzyme activity.
  • As temperature increases, the kinetic energy of the enzyme and substrate molecules increases leading to increased collisions hence increase in enzyme activity.
  • Enzyme activity is optimum at (35 -40)°C.
  • Beyond 40 °C the rate of enzyme activity decreases and eventually stops. This is because enzymes get denatured and their active sites get destroyed.

    b)pH

  • Enzymes work best under different pH conditions.
  • Some enzymes work best under alkaline conditions e. g amylase. Some also work better under acidic conditions e. g. pepsin. However, most intracellular enzymes work better under neutral conditions.
  • Altering the pH conditions would affect enzyme activity.

    c)Enzyme Specificity

  • A particular enzyme will only act on a particular substrate or will only catalyze a particular reaction.
  • For instance, sucrase enzymes can only breakdown sucrose.

    d)Substrate Concentration

  • Assuming all other factors are constant, t low substrate concentration, the rate of enzyme activity is low.
  • Increase in substrate concentration increases the rate of enzyme activity since more active sites of the enzymes will be occupied and there will also be an increase in enzyme- substrate collisions leading to increased reaction.
  • The reaction increases up to a point at which it becomes constant. At this point, all active sites are utilized. The enzymes become the limiting factor of reaction. Increasing enzyme concentration would increase the rate of enzyme activity.

    e) Enzyme Concentration

  • An increase in enzyme concentration increases the rate of enzyme reaction up to a level beyond which the rate of reaction becomes constant.
  • At low enzyme concentration, rate of enzyme activity is low because there are fewer sites and also fewer enzyme-substrate collisions that would lead to reactions.
  • Increasing enzyme concentration increases rate of enzyme activity since there will be an increase in number of active sites and enzyme-substrate collisions.
  • At optimum enzyme concentration, substrate concentration is the limiting factor. Increasing substrate concentration increases the rate of reaction.

    f) Enzyme co-factors

  • These are inorganic substances which activate enzymes.
  • Without them, most enzymes would not function properly.
  • Co- factors include mineral ions like iron, magnesium, copper, manganese, zinc as well as vitamins.
  • They are used again and again since like enzymes, they do not get used up during the reactions.

    g) Co-enzymes

  • These are organic molecules that are required by some enzymes for their efficient functioning. Some enzymes will not function without them.
  • Most co-enzymes are derivatives of vitamins.

    Examples

    NAD- Nicotine Adenine Dinucleotide.

    FAD- Flavine Adenine Dinucleotide.

    NADP- Nicotine Adenine Dinucleotide Phosphate.

    h) Enzyme inhibitors

  • These are chemical substances which slow down or eventually stops enzyme activity.
  • They are of two types:

    1. Competitive

    2. Non- competitive

    Competitive inhibitors

  • These are chemical substances which are structural analogs of the substrates i.e. they take up the shape of the substrates and compete for the active sites of the enzymes.
  • They bind with the enzymes and do not disentangle easily (they stay in the enzyme active site for a long time) thereby slowing down the rate of enzyme activity.
  • The reaction can be increased by increasing the substrate concentration.

    Non competitive inhibitors

  • These are inhibitors that do not resemble the substrate molecules but they combine with the enzyme at any site other the active site and alter the structure of the active site of the enzyme. The normal substrate, therefore, fails to bind to the active site leading to decreased rate of reaction.
  • Note that these substances do not compete for the active sites of the enzymes.
  • The enzymes are destroyed permanently hence the effect cannot be reversed.

    Examples of non competitive inhibitors

    Heavy metals (such as lead, mercury, silver), Cyanide, organophosphates such as malathion.

    Heterotrophism

  • This is a mode of nutrition in which organisms take in already manufactured complex food substances such as carbohydrates, proteins and lipids.
  • Heterotrophs are organisms that feed on already manufactured food substances.
  • These substances are broken down in the bodies of the Heterotrophs into simple soluble food substances that can be absorbed and be utilized by the cells.

    Modes of Heterotrophism

  • There are four main heterotrophic modes on nutrition:
  • Holozoic- Where organisms ingest, digest and assimilate solid complex food substances.
  • Saprophytism — Where organisms feed on dead decaying matter causing decomposition.
  • Parasitism- a feeding association in which one organism (parasite) feeds on or obtain nutrients on another organism, the host.
  • Symbiosis/Mutualism- An association where two organisms live together and mutually benefit from each other.

    a) Parasitism

  • There are two main types of parasites:
  • Endo parasites- Live inside the host
  • Ecto-parasites- Found on the external surface of the host.
  • The parasite benefits but the host does not. Some of the parasites cause diseases to the hosts and damage their tissues thereby weakening them.

    b) Symbiosis

  • In saprophytism, both organisms benefit:
  • Symbiotic relationships include

    > Rhizobium and leguminous plants: rhizobium fixes nitrogen for the legume while the bacteria obtains manufactured food from the legumes.

    > Lichen: association of fungi (absorbing water and nutrients) and algae (manufacturing food for the association.

    > Catalase digesting bacteria and ruminants.

    Dentition

  • Large animals depend on complex manufactured food substances.
  • These food substances once ingested must be broken down to simpler forms that can be utilized by the cells. The breakdown is both physical and chemical.
  • Most of the large animals have teeth to enhance physical breakdown of the complex food substances.
  • Dentition refers to the description of types of teeth, their arrangement and specialization.

    Types of Dentition

  • Homodont dentition: Teeth arrangement and description where an organism has teeth of the same size and shape. Fishes and birds have homodont dentition.

  • Heterodont dentition: where an organism has teeth of different sizes and shapes that is incisors, canines, premolars and molars. Heterodont dentition is common with mammals and reptiles.

    a) Incisors

  • Are flat and chisel shaped with sharp ridged edges for cutting and biting food.
  • They have one root.

    a. Canines

  • Are conical teeth with sharp pointed edges modified for seizing and tearing prey among carnivores.
  • They have one root

    b. Premolar and molar

  • They have cusps on their surface to suit their grinding action.
  • Premolars have two roots.
  • Molars have either two or three roots.

    Classes of Holozoic Heterotrophs

  • Holozoic heterotrophs are classified according to the type of food they consume.
  • These are:

    a) Herbivores: heterotrophs that exclusively feed on vegetation.

    b) Carnivores: heterotrophs exclusively feed on flesh.

    c) Omnivores: heterotrophs that feed on both flesh and vegetation.

  • Dentition of heterotrophs is based on the kind of food they consume.

    Dental Formula

  • This is the of the number, type and position of teeth in the jaws of animals
  • Number of teeth recorded represents half the total teeth in the upper and lower jaws.
  • The teeth names are abbreviated as

    a) i-incisors.

    b) c-canines.

    c) pm-premolars.

    d) m-molars.

  • An animal was found to have no incisors and canines on the upper jaw. It had six premolars and four molars on the upper jaw. On the lower jaw, it had eight incisors, no canines, six premolars and six molars.

    a) Write down its dental formula.

    b) State its mode of feeding.

    c) Give a reason.

    Herbivores

  • Most do not have upper incisors. Instead they have a homy pad against which grass is pressed and cut by the lower incisors.
  • They have a long tongue that assists in the cutting and moving food.
  • They have a gap in the lower jaw separating canines from premolars known as diastema which allows the tongue to manipulate food.
  • Herbivore teeth have open enamel which allows for continuous growth to replace worn out surfaces due to grinding.
  • Their incisors are wedge shaped to cut grass and vegetation together with the horny pad
  • The jaws have movable joints to allow the sideways movement of lower jaw to facilitate grinding of grass.

    Carnivores

  • Their incisors are chisel shaped and closely fitting to seize the prey.
  • Their canines are long, conical and curved to hold, kill and tear the prey.
  • Some of their premolars in the lower and upper jaw are modified into specialized carnassial teeth which have smooth sides and sharp edges to slice through flesh and crush bones
  • Premolars and molars are broad with cusps for crushing bones.
  • Their jaws are attached to powerful muscles that move the jaws up and down
  • Carnivores are adapted to fast running by possessing well developed leg muscles.

    Dental Diseases

    a) Dental Carries

  • Caused by lack of hard food, too much sweet or sugary food, lack of calcium in diet, lack of vitamin D, lack of cleaning teeth and general ill-health. The bacteria in the mouth break down the sugars to form energy and organic acids. The acids corrode the enamel.

    b) Periodontal Diseases

  • Caused by lack of vitamins A and C, lack of massage of the gums and imperfect cleaning of gums.
  • The gums become flabby and soft so they do not support the teeth. Common in adults than children.

    Are of two types:

    a) Gingivitis- Characterized by reddening of gums, bleeding and pus in the gums.

    b) Pyorrhea- The teeth become loose due to infection of the fibres holding the teeth in the sockets.

    Dental Hygiene

  • Proper teeth care requires:
  • Regular cleaning or brushing teeth after every meal
  • Avoid eating too much sugary foods.
  • Eating hard foods e. g. raw carrots, cassava, yams, sugar cane.
  • Eating diet rich in calcium, phosphate and vitamins A, C and D.
  • Teeth should be used for their correct purpose.
  • Regularly visit the dentist if necessary.

    Digestion

  • The process through which complex food substances is broken down physically and chemically into simpler food substances that can be absorbed by body cells.
  • However, small molecules like those of vitamins, mineral salts and water are directly absorbed into the bloodstream without undergoing digestion.
  • Digestion occurs in the mouth, stomach, duodenum and ileum.
  • There are glands also associated to the digestive system. These include the pancreas, gall bladder, salivary glands.

    Digestion in the mouth

  • At the mouth both physical and chemical digestion takes place.
  • The food is mechanically broken down by the teeth through grinding and chewing. This process is called mastication.
  • Mastication reduces the food into small size to increase the surface area for enzymatic action.
  • The tongue helps in manipulation of the food as it mixes the food with the saliva secreted from the salivary glands. The salivary glands are:

    a) Sublingual salivary gland; beneath the tongue

    b) Sub mandibular gland: under the jaw

    c) Parotid gland: Found in the cheeks in front of the ears.

  • All the glands have ducts through which saliva is directed to the mouth.
  • The tongue also rolls the food into small round masses called boluses. The boluses are then pushed to the back of the mouth to initiate the swallowing process. The boluses are then moved to the stomach via oesophagus. Movement is facilitated by a wave of muscular contractions of longitudinal and circular muscles of the oesophagus known as peristalsis.
  • There is a flap of cartilage, epiglottis which closes the wind pipe (trachea) during swallowing.

    Digestion in the stomach

  • Upon swallowing, the boluses move down the gullet to the stomach. The boluses enter the stomach via the cardiac sphincter (a muscular valve).
  • The stomach has thick circular and longitudinal muscle layers which contract and relax to produce movements that mix the contents of the stomach. The mixing process is known as churning and results in formation of a fluid called chyme
  • Arrival of food in the stomach stimulates secretion of the hormone gastrin which stimulates the gastric glands in the stomach walls to secrete gastric juice which contains:

    a) Pepsinogen-This is activated to pepsin which breaks down proteins to peptides.

    b) Rennin- Digests caseinogens protein in milk to casein (curd).

    e) Hydrochloric acid- This:

  • Activates pepsinogen to pepsin
  • Provides a favorable medium for action of the enzymes rennin and pepsin
  • Kills some bacteria ingested with food.

    d) Mucus- Forms a protective barrier to the stomach wall against corrosion by the HC1. Mucus is secreted by goblet cells in the epithelial membrane of the alimentary canal.

    Duodenum

  • The chyme then passes down to the Duodenum through pyloric sphincter.
  • Duodenum is the first section of the small intestine. In humans it measures about 25-38 cm. the chyme is let down into the duodenum in small quantities.
  • Secretions that contribute to digestion at the duodenum are received from:

    a) Gall bladder in the liver- Secretes bile.

    b) Pancreas- Secrete hormones and digestive enzymes.

  • Arrival of food in the duodenum stimulates secretion of

    i. Secretin hormone from the pancreas: Secretin stimulates secretion of pancreatic juice into the duodenum

    ii. Cholecystokinin from the duodenal wall: This stimulates secretion of bile from the gall bladder.

  • Pancreatic juice contains:

    a) Pancreatic amylase- This facilitates breakdown of the remaining starch into maltose

    b) Trypsin- Digests proteins into peptides.

    c) Pancreatic juice-Digests lipids into fatty acids and glycerol

    d) Sodium hydrogen carbonate- This:

    Provides alkaline medium for activity of the duodenum enzymes.

  • It also neutralizes the acidic chyme.
  • The bile juice contains bile salts that include sodium glycocholate and sodium taurocholate. These salts:

    i. Aid in emulsification (breakdown of fat molecules into tiny fat droplets to increase surface area for digestion).

    ii. The salts also provide a suitable alkaline medium for action of the duodenal enzymes.

    iii. In addition they neutralize the acidic chyme.

    Digestion in the ileum

  • Ileum is the final part of the small intestine.

  • The inner cells contain secretory cells some of which secrete mucus while some secrete an alkaline fluid known as succus entericus (intestinal juice). The arrival of chyme in ileum stimulates secretion of intestinal juice which contains:

    a) Maltase: speeds up breakdown of maltose to glucose

    b) Sucrase: speeds breakdown of sucrose to glucose and fructose

    c) Peptidase: speeds breakdown of peptides to amino acids

    d) Lipase: speeds breakdown of lipids to fatty acids and glycerol.

    e) Lactase: speeds breakdown of lactose to glucose and galactose.

    f) Polypeptidase: speeds breakdown of plypeptides into amino acids

    Note:

    The mucus secreted by the goblet cells lubricates food along the alimentary canal and also protect the canal from being digested by enzymes.

    At the end of digestion in the ileum, the resulting watery emulsion is called chyle; it contains soluble end products of digestion ready to be absorbed.

    Absorption

  • This is the process through which the soluble end products of digestion diffuse into the cellular lining of the villi.
  • Absorption of micronutrients such as water soluble vitamins, mineral salts and alcohol are absorbed at the stomach. Alcohol is equally absorbed here without undergoing digestion.
  • Most absorption of end products of digestion occurs in the ileum.
  • Molecules of amino acids and glucose pass through the epithelial lining and capillary walls into the blood system by active transport.
  • The capillaries drain into the hepatic portal vein where the absorbed products are transported to the liver before they are circulated to other body parts.
  • The fatty acids are absorbed into the lacteals of the villi which drain into the lymphatic vessels. The lymphatic vessels later join the blood circulatory system which transports them to other body parts.
  • The ileum is adapted to absorption in many ways

    a) It is long to provide a large surface area for absorption

    b) It has a narrow lumen so as to bring the digested food into close contact with the walls of the ileum for easier absorption

    c) It is highly coiled to slow down movement of food thus allowing more time for digestion and absorption of food.

    d) The inner surfaces have numerous villi and microvilli to increase surface area for absorption of end products of digestion.

    e) The epithelial lining is one cell thick to reduce the distance through which digested food diffuses.

    f) Has a dense network of blood capillaries into which digested food materials diffuse to increase transport and thus maintain a steep concentration gradient.

    g) Have lacteal vessels in the villi for absorption of fatty acids and glycerol.

    Egestion

    > This is the process through which the undigested and indigestible food substances are eliminated from the body. Caecum and Appendix

  • While these have no roles in man, they play vital roles in the ruminant animals and other herbivores.
  • They contain some bacteria which secrete cellulose enzyme. These enzymes digest cellulose since most digestive systems cannot secrete cellulose digesting enzyme. The bacteria and the herbivores are in a symbiotic relationship. Assimilation

  • This is process of incorporation of the end products of digestion into the cell metabolism.
  • It involves utilization of the end products of digestion into various uses.

    a) Glucose

  • Oxidized to release energy
  • Excess glucose is stored under the skin to provide heat insulation
  • Glucose is used to synthesize complex polysaccharide such as cellulose that is an important structural compound in plants.

    b) Fatty acids and glycerol

  • Oxidized to release energy
  • Combine to form neutral fats stored under the skin to provide heat insulation
  • Used to build structures

    c) Amino acids

  • Used to synthesize proteins for general body growth
  • Oxidized during starvation to release energy.

    Vitamins

  • These are organic chemical compounds that are essential for a healthy body.
  • Some are synthesized in the body through the action of some microorganisms while some are also obtained in fresh fruits and vegetables.
  • Vitamins are destroyed when foods are excessively cooked. They are required in small quantities.
  • They play vital roles in metabolic reactions. Some act as co-enzymes while some influence the intake of certain substances. In particular, vitamin C influences uptake of iron while vitamin D influences absorption of calcium ions in the gut.
  • Lack of vitamins in the body results into abnormities that manifest through various deficiency diseases. These deficiency diseases can be corrected by inclusion of the deficient vitamins in the diet or taking the vitamin supplements.
  • There are two classes of vitamins owing to their solubility:

    a) Fat soluble vitamins- They dissolve in fats and are often stored in the liver. Include Vitamins A, D, E, K.

    b) Water soluble vitamins- Dissolve in water. Include vitamins B1, B2, B5, B12 and C.

    Vitamin A (retinol)

    main food source

  • liver, milk, eggs,cold liver oil, carrots, fresh green vegetables uses in the body

  • for vision especially at night
  • protects skin and cornea from drying or becoming scaly deficiency disease symptoms

  • poor night vision
  • sore eyes
  • dry scaly skin and cornea
  • reduced resistance to diseases

    Vitamin B1 (thiamine)

    main food source

  • ground nuts, beans, unpolished cereals, egg-yolk, milk, liver, kidney

    uses in the body

  • cell respiration
  • proper growth in children

    deficiency disease symptoms

  • general weakness
  • retarded growth in children
  • beriberi-wasting of muscles and swelling of feet and legs

    Vitamine B2 (riboflavine and nicotinic acid)

    main food source

  • green veges, yeast extracts, groundnuts, unpolished cereals, egg-yolk, milk, liver, kidney

    uses in the body

  • cell respiration
  • normal skin health and function

    deficiency disease symptoms

  • pellagra-skin disorders
  • sore and bleeding in mouth and gum

    Vitamin B5 (pentathonic acid)

    main food source

  • like B1 and B2 but more in eggs

    uses in the body

  • cell respiration
  • proper function of nervous system and alimentary canal

    deficiency disease symptoms

  • malfunctioning od nervous system and digestive system Vitamin B12 (cobalamine)

    main food source

  • liver, beef, kidney

    uses in the body

  • formation of blood cells

    deficiency disease symptoms

  • pernicious anaemia-low blood count

    Vitamin C (absorbic acid)

    main food source

  • fresh citrus fruits, green vegetables, mangoes, pawpaw and tomatoes

    uses in the body

  • protection against infections

    deficiency disease symptoms

  • scurvy-bleeding of mouth and gum
  • anemia
  • swellings of skin
  • poor healing of wounds
  • reduced resistance to infection

    Vitamin D (calciferol)

    main food source

  • milk, fish, liver, egg-yolk, formed in skin in presence of sunlight

    uses in the body

  • formation and hardening of bones and strong teeth
  • absorption of calcium and phosphorus

    deficiency disease symptoms

  • rickets-an abnormal bone formation in children
  • soft and brittle bones in adults

    Vitamin E (tosopherol)

    main food source

  • egg-yolk, green vegetables and vegetable oil

    uses in the body

  • necessary for normal fertility in some animals
  • cell metabolism

    deficiency disease symptoms

  • sterility in some animals

    Vitamin K (quinone)

    main food source

  • liver, green veges, unpolished cereals, egg-yolk

    uses in the body

  • necessary for blood clotting

    deficiency disease symptoms

  • excessive bleeding

    Mineral salts

  • These are important inorganic compounds containing elements required for essential body functioning. Depending on body requirements, mineral salts are of two classes:

    a) Macro-nutrients: Nutrients required in large quantities. These include nitrogen, sulphur, phosphorous, calcium, sodium, iron and magnesium.

    b) Micro-nutrients: Nutrients required in small quantities. Include copper, manganese, boron, iodine and cobalt.

    Element: Nitrogen

    source

  • meat, milk, egg, fish, other proteins

    function in the body

  • synthesis of proteins
  • formation of cell, tissue and structures

    deficiency symptoms

    -

    Element: Phosphorous

    source

  • protein foods

    function in the body

  • synthesis of proteins
  • bone and teeth formation
  • ATP formation

    deficiency symptoms

  • rickets-poorly developed bones

    Element: Calcium

    source

  • green veges, milk, cheese

    function in the body

  • blood clotting and muscle contraction
  • formation of bone and teeth

    deficiency symptoms

  • muscle cramps
  • rickets

    Element: Iodine

    source

  • iodinised table salt, cheese, sea fish such as cold and salmon

    function in the body

  • formation of thyroxine hormone
  • regulate rate of energy production

    deficiency symptoms

  • goiter- swelling of thyroid glands in the neck region

    Element: Potassium

    source

  • Liver, beef, veges, milk, egg

    function in the body

  • transmission of nerve impulses
  • proper heart functioning
  • growth and maintenance

    deficiency symptoms

  • mascular cramps
  • twitching and weakness
  • irregular heart beats

    Element: Iron

    source

  • liver, eggs, veges

    function in the body

  • formation of hemoglobin in red blood cells
  • role in respiration

    deficiency symptoms

  • anemia

    Element: Sodium

    source

  • table salt, green veges, milk, fish

    function in the body

  • maintaining osmotic balance of the body fluids
  • transmission of nerve impulses
  • regulation of blood pressure

    Element: Chlorine

    source

  • table salt

    function in the body

  • maintaining osmotic balance of the body fluids
  • transmission of nerve impulses

    Element: Sulphur

    source

  • Protein foods

    function in the body

  • protein synthesis
  • formation of body tissues

    Element: Magnesium

    source

  • present in almost all foods

    function in the body

  • bone and teeth formation
  • activates enzymatic activities in the body
  • proper functioning of the nerves and muscles
  • activating B vitamins
  • insulin secretion and functioning
  • energy production
  • making of new cells

    deficiency symptoms

  • muscles tremors and convulsions
  • fatigue
  • nervousness

    Roughage

  • This is the indigestible material in food. Mainly composed of cellulose from plant cell walls.
  • They are found in full cereals, fresh fruit fibres like lemons, oranges, mangoes and vegetables.

    Importance of roughage

    a) It rubs against the walls of the alimentary canal stimulating secretion of digestive enzymes and mucus to lubricate the epithelial lining.

    b) Roughage enhance peristalsis since as they rub against the walls of the alimentary canal, they stimulate contraction and relaxation of the muscles.

    c) Roughage is an absorbent; it extracts water from the alimentary canal making the fecal matter bulky and moist hence can be easily propelled by peristaltic movements. This prevents constipation.

    Factors affecting energy requirements in humans

    Discuss how the following factors affect energy requirements in humans:

  • Basal metabolic rate
  • Occupation
  • Health of an individual
  • Age
  • Sex
  • Body size
  • Environmental temperature

    KCSE Biology Questions and Answers Form 2 - Biology Form Two Notes

    K.C.S.E ONLINE REVISION

    BIOLOGY NOTES FORM 2

    1. a) i) Define transport

  • Movement of substances from one pan of the body to another

    ii) Explain the necessity of transport in plants and animals

  • make nutrients move from one point to another

  • movement of respiratory gases i.e. oxygen and carbon IV oxide

  • elimination of metabolic wastes

  • movement of hormones

  • movement of water

  • movement of salts

  • movement of enzymes

    b) i) Describe the structure and function of root hair

  • root hairs are found near the root tip

  • they are cells with elongated finger-like projections which are in contact with soil particles

  • they are permeable to water and mineral salts hence are used to absorb Water and mineral salts

  • There large number offers a large surface area for absorption of water and mineral salts.

    ii) State ways in which the root hairs are adapted to their functions

  • the root hair is long/narrow/numerous to increase surface area for absorption of water and mineral salts

  • many mitochondria in cytoplasm to supply energy for active transport of mineral salts

  • are thin walled to speed up rate of absorption of Water and mineral salts

    c) i) Compare the internal structure of a dicotyledonous root and a monocotyledonous root

    Monocot root

    ii) State the similarities and differences between a dicotyledonous and monocotyledonous root

    Similarities

  • both used for anchorage and absorption of water and mineral salts

  • both have root hairs, epidermis, pericycle, cortex, endodermis and vascular bundles

  • (xylem and phloem)

  • both may be used to store food/storage organs

    Differences

    Monocotyledonous

  • phloem and xylem are arranged in ring form alternately

  • pith present

    Dicotyledonous

  • phloem lies between radial rays of central xylem(star shaped)

  • pith absent

    iii) Compare the internal structure of a monocotyledonous and dicotyledonous stem

    Monocotyledonous stem

    Dicotyledonous stem

    i) Give the similarities and differences between a monocotyledonous and dicotyledonous stem

    Similarities

  • both are used for protection

  • both conduct water, salts and food

  • both have epidermis, cortex, pericycle and vascular bundles

    Differences

    Monocotyledonous

  • vascular bundles are many and scattered

  • some have hollow pith or pith is absent

  • no cambium layer therefore cannot
  • undergo secondary growth very
  • little cortex

    Dicotyledonous

  • vascular bundles are few and arranged in a concentric ring near the epidermis

  • pith large and well developed

    State the differences between the internal structure of a root and a stem.

  • no cambium layer therefore cannot

  • undergo secondary growth

  • very little cortex

  • presence of cambium therefore
  • undergoes secondary growth

  • cortex has several layers of cells

    c) i) Name the transport structures of a flowering plant

  • xylem vessels and tracheids transport water and mineral salts from the soil

  • Phloem vessels translocate manufactured food from leaves to other parts of the body

    ii) State the ways in which xylem vessels are adapted to their function

  • lignified/thickened to prevent collapsing

  • narrow to facilitate capillary

  • no cross walls for continuous flow/column of water

  • have bordered pits for lateral movement of water

    a) i) Why do flowering plants need water?

  • photosynthesis

  • transport

  • turgidity w h helps in plant support

  • solvent i.e. medium for chemical reactions

  • cooling effect during transpiration

  • seed germination

    ii) Describe the movement of water from the soil to the leaves of a tall plant

  • Soil water exists as a thin film in the soil, between soil particles

  • the concentration of cell sap of root hair is greater than that of the surrounding solution in the soil, thus drawing the Water molecules across the cell wall and cell membrane into the root hair by osmosis

  • water drawn into the root hair cell dilutes the cell sap making it less concentrated than that in the adjacent cortex cells of the root

  • due to osmotic gradient water moves from the root hair cells into the cortex by osmosis, from cell to cell by osmosis, across the endodermis by active transport into xylem vessels of the root that conduct water into xylem vessels of the stem into xylem vessels of the leaves

    Stem

  • Once in the stem water moves up the plant aided by the narrowness of the xylem vessels (capillary), root pressure, attraction of water molecules to each other (cohesion).

  • Attraction of water molecules to the Walls (adhesion) from the stem water enters the xylem of leaves

  • water moves in the xylem vessels of the stem in a continuous (uninterrupted) water column up to the tree leaves

    Leaves

  • once in the leaves water moves into the mesophyll cells by osmosis as water vaporizes from the spongy mesophyll cells their sap becomes more concentrated than the adjacent cells as the result water flows into the cell from other surrounding cells which in turn takes in water from xylem vessels within the leaf veins this creates a pull(suction force) called transpiration pull that pulls a stream of water from xylem vessels in the stem and roots .

  • The transpiration pull maintains a continuous column of water from the roots to the leaves.

    iii) Name the process by which mineral salts enter into a plant

  • active transport

  • diffusion

    i) Explain the forces that make water and mineral salts move through a plant

  • mineral salts are taken up due to diffusion because of the concentration gradient between the mineral ions in sap and those in soil solution

  • active transport involves energy in form of ATP due to respiration which forces mineral salts through a plant against a concentration gradient

  • water moves by osmosis through a semi-permeable membrane of root hairs and between cells of stem

  • in stem water moves by cohesion(attraction of water molecules to each other)

  • it also moves by adhesion(attraction of water molecules to walls)

  • capillarity is due to narrowness of xylem vessels

  • transpiration pull occurs When Water vapour evaporates from sub-stomatal chambers into the air

  • root pressure is a force that pushes Water up the stem from the roots and causes guttation /exudation

    ii) Explain the uptake of mineral salts by plants

  • plants require mineral salts for metabolism and proper functioning of their bodies

  • mineral salts are taken up from the soil into the root hairs in form of solution by active

  • transport which requires energy

  • active transport involves substances called carriers taken up together with water and are then carried to the stems and leaves

  • the main process involved in uptake and movement of mineral salts is active transport

    b) i) What is transpiration?

  • loss of water from plant to the atmosphere

    ii) Name the sites through which transpiration takes place in a plant

  • stomata (stomatal transpiration)

  • lenticels (lenticular transpiration)

  • cuticle(cuticular transpiration)

    iii) State the importance of transpiration to plants

  • cooling the plant

  • transport of water

  • transport of mineral salts

  • excretion of excess Water from plants

    excess transpiration causes wilting

    i) Explain the structural factors that affect the rate of transpiration in plants

  • number of stomata i.e. the more the stomata the higher the rate and vice versa

  • turgidity of the guard cells which control the opening and closing of stomata when they are open transpiration rate is high

  • size of leaves where the larger the surface area the higher the rate of transpiration

  • leaf fall leads to lower rate of transpiration and also drying of leaves reduces rate of transpiration

  • Thin cuticle reduces distance through Which water vaporizes hence increase transpiration rate. Absence of cuticle also increase rate of transpiration

    ii) Explain the environmental factors that affect rate of transpiration in plants

  • high temperature increases rate of transpiration and low temperature reduces the rate

  • humidity when high increases rate and when low reduces the rate

  • transpiration rate is higher in moving air (wind) than in still air

  • high light intensity increases internal temperature hence higher rate of evaporation leading to higher rate of transpiration

  • availability of water in the soil leads to more absorption hence more loss to the atmosphere

  • atmospheric pressure when high leads to more evaporation and when low leads to low rate evaporation of water

    iii) State the structural differences between xylem vessels and sieve tubes

  • sieve tubes have cross wall while xylem vessels have none

  • xylem vessels are lignified while sieve tubes are not

  • Sieve tubes have cytoplasm elements while xylem vessels have none.

    iv) State the adaptations of plants which enable them to reduce water loss

  • thick waxy cuticle

  • reduced leaf size/thorns/spines

  • shedding of leaves

  • Sunken stomata. Water vapour accumulates in the depression of stomata lowering the water vapour concentration gradient leading to lower rate of evaporation

  • rolling of leaves

    v) State the factors that cause increase in the rate of transpiration from leaves

  • increased light intensity

  • low relative humidity

  • temperature

    vi) Explain how drooping of leaves on a hot sunny day is advantageous to a plant

  • reduces surface area exposed to sun reducing cuticular transpiration

    c) Explain how aquatic and terrestrial plants are adapted to deal with problems of transpiration

    a. Mesophytes

  • they grow in soils with enough water

  • water loss is perfectly balanced by absorption of more from the soil

  • no special adaptations

    b. Xerophytes

  • they grow in dry conditions

  • root grow very deep to absorb water

  • succulent/fleshy leaves to store water

  • few stomata which are sunken

  • thickened waxy cuticle

  • leaves are hairy and often folding

  • some leaves are needle-like/spines or scales

  • leaf surfaces are reduced i.e. small leaves

  • all these adaptations are to reduce water loss

    c. Hydrophytes

  • plants that grow in water

  • presence of sclereids

  • leaves are broad

  • leaves have many stomata on upper side only (none on the lower surface)

  • some leaves float on water

  • absence or reduced leaf cuticle

  • large air spaces

  • some leaves are submerged

  • poorly developed or reduced vascular bundles

    d) i) What is translocation

  • transfer of manufactured food substances to the parts where they are required

    ii) Name the tissue which is responsible for translocation of manufactured food in flowering plants

  • phloem tissue

    iii) Name the processes that bring about the translocation of manufactured food

  • active transport

  • Diffusion

  • Mass flow

  • Cytoplasmic streaming

    iv) Draw a labeled diagram to represent phloem tissue

    ii) State the functions of the labbeled structures cytoplasmic strands

  • translocation

    Companion cell

    supply nutrients to sieve tube element

  • supply energy for translocation

  • regulates activities of tube cells/elements

    Sieve tubes element

  • conduct food down the stem

    iii) name the compounds that are translocated in phloem

  • sugars

  • amino acids

  • hormones e.g auxins

  • oils/lipids

  • resins

  • vitamins

    Describe an experiment you would carry out in order to demonstrate that phloem transports manufactured food substances in a plant

    a. Ringing experiment

  • cut a ring in the bark including the phloem from the stem of a woody plant

  • phloem is found next to or just beneath the bark

  • observe daily for some time(more than three weeks)

  • a swelling of the bark appears above the ring

  • this is due to accumulation of food from leaves

  • the bark of a second similar plant is removed carefully leaving the phloem intact

  • a swelling does not appear

    ii) Use the radio-active tracers

  • plant is exposed to carbon containing radio-active carbon C14

  • C14 is found in the end products of photosynthesis

  • It is finally detected in phloem

  • C14 is found to move in both directions

    iii) Collecting exudate from stylets of aphids

  • aphids feed on certain plant phloem using their stylets

  • aphid mouth parts are dissected using a sharp razor

  • exudes from the mouth parts are collected and then analyzed

  • sucrose is found to be a major component of the exudates

  • this proves that phloem translocates manufactured food substances

    e) Describe an experiment you would carry out to demonstrate that xylem transports water

    i. Either

  • cut a stem of a young plant or twig of a tree under water

  • or else uproot a young herbaceous plant and wash the soil gently

  • put some water in a beaker and add a dye i.e. eosin or red ink and place the cut stem or young plant in a beaker

  • leave for time e. g. between 20 minutes and one hour

  • cut a thin section of stem or leaf

  • mount it on a slide and examine under a microscope

  • observe and note the distribution of the dye or ink

  • the dye appears only in the xylem vessels

    ii. OR

  • use radio-active tracers, C14 in form of carbon

  • ring a plant then put it in a container containing radio-active phosphorous solution

  • The radio-active phosphorus is later detected in the leaves.

    2. a) i)List the components of animal transport systems

  • system of blood vessels in which materials are circulated round the body

  • blood, a fluid medium which contains dissolved substances and cells

  • the heart, a pumping mechanism which keeps blood in circulation

    ii) Distinguish between closed and open circulatory systems

  • closed system has blood vessels through which blood moves eg vertebrates

  • open system has no blood vessels hence blood is in direct contact with tissues e. g arthropoda

    iii) What are the advantages of the closed circulatory system over open circulatory system?

  • Closed system has continuous vessels hence able to generate high pressure

  • Circulates blood over longer distance

  • Circulates blood at a faster rate

  • Efficient transport of nutrients and waste products

  • Animals are more active

    iv) Distinguish between single circulatory system and double circulatory system Single circulatory

  • blood passes through the heart once in a complete circuit of the body

  • Double circulation

  • blood enters the heart twice in a complete circulation

  • Pulmonary circulation from the heart to lungs and back

  • Systemic circulation from the heart to body systems and back

    b) i) Describe the general layout of the transport system in mammals

  • blood which is a fluid tissue of the body carrying food substances, oxygen, carbon IV oxide and metabolic wastes

  • arteries which are elastic tubes carrying blood from the heart to cells

  • veins which are blood vessels carrying blood away from the cells to the heart

  • capillaries which are extremely numerous and are microscopic channels connecting arteries to veins

    ii) Describe the structure and function of the mammalian heart

  • the heart is a four-chambered hollow muscle located in the thoracic cavity

  • it consists of two small receiving chambers, the atria(auricles) and two larger pumping chambers, the auricles

  • the left ventricles is the most powerful and has the thickest walls

  • this is because it is the chamber which pumps blood throughout the body

  • each time it contracts, blood is forced out into the elastic arteries(aorta)

  • blood moves on to the capillaries

  • from capillaries blood moves to veins and back to the heart through the vena cava

  • from vena cava it enters into right auricle which contracts and pumps blood into the right ventricle

  • right ventricle pumps blood into the lungs through the pulmonary artery

  • blood releases carbon IV oxide to lungs and picks oxygen then returns to left auricle

  • left auricle pumps blood into left ventricle

  • left ventricle then pumps blood into the aorta and into arteries, starting the process all over again

  • both auricles contract simultaneously while both

    iii) Explain how the mammalian heart is adapted to performing its functions

  • the heart is made of muscles that contract and relax synchronously without requiring nervous stimulation

  • nerve supply however, determine contraction strength and frequency

  • the heart is divided into four chambers

  • The right atrium is connected to the right auricle. It receives blood from the whole body.

  • The blood is pumped from the left atrium to the right ventricle

  • To avoid flow back into the right atrium, a valve is present between the two chambers

    the tricuspid valve

  • The right ventricle pumps blood to the lungs

  • This is facilitated by the presence of pulmonary artery

  • A valve is also present to avoid blood flowing back from the pulmonary artery to the right ventricle

  • Blood from the lungs enters the heart through the pulmonary vein into the left atrium.

  • When the left atrium contracts, blood flows into the left ventricle

  • Blood will not flow back into the left atrium because of the presence of bicuspid valve(mitral)

  • The left ventricle is connected with the aorta and when it contracts, blood flows into the aorta for distribution into the whole body

  • The heart muscle surrounding the left ventricle is thicker than that surrounding the right ventricle to be able to generate enough pressure to push blood to the whole body

  • A pace-maker is present in the heart muscle to initiate and synchronise contractions.

  • For the heart muscle to be well nourished and be provided with enough oxygen and carbon IV oxide removal, it is supplied with blood by the coronary arteries and drained by the coronary veins

    iv) Explain why blood leaving the lungs may not be fully oxygenated

  • under ventilation of the lungs

  • blockage of alveoli (air sacs)

  • high cardiac frequency i.e. high rate of pumping of blood in the heart

    e) Describe the structure and functions of the blood vessels

    i. Arteries

  • carry away blood from the heart

  • carry oxygenated blood except pulmonary artery which takes blood from the heart to lungs for oxygen

  • have thick, muscular walls

  • are elastic

  • have narrow lumen

  • all these adaptations are required to withstand high pressure caused by heartbeat

    ii. Capillaries

  • link arterioles and venules to arteries and veins

  • small in diameter to increase pressure resistance for materials to filter out

  • thin walled as they consist of a single layer of cells to allow diffusion of substances e.g leucocytes to tissues

  • thin walled to allow presence of intercellular spaces

  • large number i.e. numerous to provide a large surface area for exchange of materials

  • have sphincter muscles at the junction of the arterioles and capillaries to control movement of blood into them

  • lie close to the body for easy exchange of materials

    iii. Veins

  • carry blood back to the heart

  • all carry deoxygenated blood except pulmonary vein that carries blood from the heart to lungs

  • have thinner Walls than arteries

  • have valves to prevent back flow of blood

  • have wide lumen

    b) i) State the ways in which the composition of blood in the pulmonary arterioles differs from that in the pulmonary venules

    pulmonary arterioles

  • deoxygenated
  • high carbon iv oxide
  • low oxygen
  • more nutrients

    pulmonary venules

  • oxygenated
  • low carbon iv oxide
  • high oxygen
  • less nutrients

    ii) Give the reasons why pressure of blood is greater in the arterioles than I the veins of mammals

  • blood is pumped to the arteries by the heart at high pressure

  • blood pressure in veins is reduced by capillary resistance

  • arteries have narrow lumen which maintains high pressure/veins have wide lumen which reduces pressure

  • arteries have more/thicker muscular walls which generate pressure/veins have less/thinner muscular walls which reduce pressure

    iii) Name the common heart diseases in humans

  • thrombosis

  • antheroma

  • arteriosclerosis

  • varicose veins

  • cerebral vascular thrombosis

    c) i) State the functions of mammalian blood

  • transport of substances

  • defense against diseases

  • clotting

  • temperature regulation

    ii) Describe how mammalian blood components carry out their functions Plasma

  • transport dissolved food substances like glucose, amino acids, fatty acids and glycerol from small intestines to liver and other body tissues

  • transports hormones, enzymes from secretory glands to tissues when required

  • transports carbon IV oxide to lungs and urea from tissues to the kidneys

  • distributes heat

  • bathes the tissues allowing for exchange of materials

  • contains protein fibrinogen and pro-thrombin which take part in blood clotting

    Red blood cells (Erythrocytes)

  • transports oxygen from the lungs to body tissues in form of haemoglobin

  • transport carbon IV oxide from body tissues to the lungs in form of bicarbonates

    White blood cells (leucocytes)

  • engulf foreign bodies

  • produce antibodies for defense against disease

  • produce antitoxins which neutralize bacterial toxins

    Blood platelets (thrombocytes)

  • produce an enzyme called thrombokinase/thromboplastin necessary for blood clotting

  • prevents loss of blood, water and mineral salts

    iii) State the Ways in which the red blood cells are adapted to their functions

  • many per unit volume hence carry more oxygen and carbon IV oxide

  • biconcave in shape to provide large surface area for absorption of oxygen and carbon IV oxide

  • absence of nucleolus hence more haemoglobin to carry sufficient oxygen and carbon IV oxide

  • alter shape to be able to pass through the narrow lumen of capillaries to deliver or supply oxygen and carry away carbon IV oxide

  • have haemoglobin with high affinity for uptake of oxygen and carbon IV oxide

    iv) State the structural differences between a red blood cell and a white blood cell.

    Red blood cells

  • has hemoglobin

  • smaller size

  • lacks nucleus

    White blood cells

  • not pigmented

  • larger size

  • nucleated

    v) State the functional differences between a red blood cell and a White blood cell

    Red blood cell

  • Transports oxygen and carbon IV oxide

    White blood cell

  • Protects body against harmful pathogens

    How does the heart increase blood flow to some parts of the body during exercise

  • stronger contractions

  • faster contractions/heartbeat

    Explain how oxygen and carbon Iv oxide are transported in the blood

    Oxygen

  • oxygen concentration is higher in lungs(alveoli) that in blood

  • oxygen in the alveoli dissolves in the film of moisture and diffuses through thin epithelial and capillary walls into plasma and red blood cells

  • the oxygen combines with haemoglobin to form oxyhaemoglobin

  • blood then becomes oxygenated

  • blood from lungs then travels to all body tissues where the oxyhaemoglobin breaks down to form oxygen and haemoglobin

  • haemoglobin is transported back to the lungs to collect more oxygen while the oxygen in capillaries diffuses into body cells for respiration

  • respiration produces carbon IV oxide

    Carbon IV oxide

  • carbon IV oxide produced during respiration diffuses out of cells into blood plasma and red blood cells due to concentration gradient

  • carbon IV oxide and water fonn carbonic acid carbamino compounds with haemoglobin

  • in the presence of carboxyl anhydrase enzyme, hydrogen carbonate is carried in blood to the lungs

  • in the lungs the hydrogen carbonate dissociates to liberate carbon IV oxide which diffuses into alveolar cavity due to concentration gradient

  • from alveolar space carbon IV oxide is expelled during expiration

    Most carbon IV oxide is transported from tissues to lungs within the red blood cells and not in the blood plasma. Give the advantages of this mode of transport.

  • PH of blood is not altered/homeostasis is maintained

  • Within the red blood cell is an enzyme, carbonic anhyrase which helps in fast loading(combining) and offloading of carbon (iv) oxide

    d) i) what is blood clotting?

  • process in which blood components clump together to prevent loss of blood from an injured/cut vessel

    ii) Name a protein, vitamin, an enzyme and a mineral element involved in blood clotting

  • Protein — fibrinogen/prothrombin

  • Vitamin - k/quinine

  • Enzyme — thrombokinase/thromboplatin/thrombin

  • Mineral element — calcium

    iii) describe the blood clotting process

  • enzyme thromboplastin produced in the platelets of damaged tissues converts plasma

  • protein prothrombin into thrombin in the presence of calcium ions

  • thrombin converts another plasma protein fibrogen into fibrin in the presence of vitamin K

  • fibrin is insoluble

  • fibrin forms fibres which form a meshwork that forms a clot

  • prothrombin thromboplastin thrombin

  • calcium ion

  • Fibrinogen thrombin fibrin clot

  • vitamin K

    iv) State the role of blood clotting on wounds

  • prevents blood/body fluids from being lost

  • conserves water and salts

  • prevents entry of microorganisms/pathogens

  • regulates body temperature

  • enables wound to heal faster

    v) Explain why blood flowing in blood vessels does not normally clot

  • Presence of anticoagulant in blood

  • e) i. list the major types of human blood groups

  • O, with neither B nor A antigen

  • AB, with both A and B antigens

  • A, with type A antigen

  • B, with type B antigen

    iii. Explain the meaning of :

    Universal donor

  • a person who can donate blood to any other blood group without agglutination/clumping

  • this is usually blood group O

  • however this person cannot receive blood from other blood groups except group O

    Universal recipient

  • can receive blood from all blood groups without agglutination

  • this is usually blood group AB

  • however, can only donate blood to group AB

    iii) What is the difference between rhesus positive and Rhesus negative blood samples?

  • rhesus positive blood has the Rhesus (Rh) antigen

  • rhesus negative lacks the Rhesus antigen

    vi) What is blood transfusion?

  • Introduction of blood from one person to another

    v) Under what conditions would blood transfusion be necessary in people?

  • during accidents

  • during surgery in hospitals

  • bleeding mothers when giving birth

    vi) How can low blood volume be brought back to normal?

  • transfusion

  • taking fluids

  • eating iron rich food/taking iron tablets

    How may excessive bleeding result in death?

  • Anaemia/low blood volume/loss of iron/low red blood cells count/low haemoglobin leading to low oxygen, loss of nutrients and dehydration.

    State the precautions that must be taken before blood transfusion

  • blood must be disease free

  • sterilized equipment must be used

  • blood of the recipient and that of the donor must b compatible to both ABO and rhesus factor

  • Fresh blood must be used.

    j) i) What is immunity?

  • Resistance to disease by organisms

    ii) Distinguish between natural and acquired immunity

  • natural immunity is inherited/transmitted from parent to offspring/inborn/innate

  • Acquired immunity is developed after suffering from a disease or through vaccination.

    iii) What are allergic reactions?

  • Excessive sensitivity and reaction of an individual to certain substances in environment e.g. dust, pollen, perfumes, smoke etc.

    vi) How does an allergic reaction occur?

  • the substances act as antigens

  • an antigen-antibody reaction occurs on surface of cells

  • the cells release a substance called histamine

  • the histamine causes irritation, itching and may stimulate nasal discharge

    ii) State the role of vaccination against certain diseases

  • protect body against infectious diseases

  • prevent spread/transmission of certain diseases

  • diseases for which vaccination is given include tuberculosis, poliomylitis,measles,
  • whooping cough, diphtheria

    3. a) i) What is gaseous exchange?

  • The continuous exchange of oxygen and carbon Iv oxide between the organism and environment

    ii) Why is gaseous exchange important to organisms?

  • to supply oxygen necessary for energy production

  • to remove carbon IV oxide produced during respiration

  • To remove Water vapour.

    b) i) name the structure used for gaseous exchange by plants

  • stomatal pores/stomata

  • lenticels

  • cuticle

  • pneumatophores

    ii) Briefly describe the structure of stomata

  • are minute pores found in leaf epidermis

  • each consists of a slit-like opening

  • Each is bordered by two large, bean-shaped guard cells.

  • Guard cells contain chloroplasts, unlike the other epidermal cells which enable photosynthesis to occur

  • Inner walls of guard cells are thicker than the outer cells

    iii) State the factors which affect stomatal opening

  • water which when low stomata close and when high stomata keeps open

  • light as stomata open in bright light and close in darkness

  • temperature

    iv) Name the theories suggesting the mechanism of opening and closing of stomata

  • interconversion of starch and sugar

  • pH theory

  • mineral ion concentration

    v) Describe the mechanism of opening and closing of stomata

  • stomata close at night and open during daytime

  • This comes about due to changes in turgidity as a result of pH changes in guard cells.

  • In the dark carbon Iv oxide accumulates in the intercellular spaces

  • This raises concentration of carbonic acid

  • The pH drops (pH lowered)

  • Enzymes convert sugar into starch in guard cells

  • Osmotic pressure in guard cells is lowered

  • Water moves out of guard cells by osmosis making cells lose turgidity hence become flaccid

  • The stomata close

  • During day time there is photosynthesis hence the production of sugar, carbon IV oxide concentration is lowered, pH increases, guard cells become turgid causing stomata to open.

  • During the day potassium ions concentrate in guard cells, raising their osmotic pressure and causes then to open

  • In the night the concentration of potassium ions decreases increasing osmotic pressure in guard cells therefore causes stomata to open.

    i) What is the advantage of having stomata open during daytime and having them closed at night?

  • opening in the daytime allows diffusion of carbon IV into the leaf for photosynthesis to take place and allows diffusion of oxygen out of the leaf

  • transpiration also takes place, thus cooling the leaf and facilitating uptake of water and mineral slats

  • Closing in the night is to conserve water in the plant especially when there is not enough water available in the soil.

    c) i) State the ways in which leaves of plants are adapted to gaseous exchange

  • presence of stomata for faster gaseous exchange

  • intercellular spaces/air spaces in the leaf for movement/circulation of air

  • film of moisture around the surface of cells for easy diffusion

  • broad/flattened shape to increase surface area

  • thin lamina to reduce distance of diffusion

  • exposed to air for easy diffusion

    ii) Describe how gaseous exchange takes place in terrestrial plants

  • Gaseous exchange takes place in spongy mesophyll

  • During the day air diffuses into large air spaces of spongy mesophyll through stomata

  • The carbon iv oxide in the air diffuses into the photosynthesis oxygen is produced

  • Some of the oxygen diffuses out of the leaf through stomata

  • During the night air diffuses out of air spaces of spongy mesophyll

  • The air dissolves into film of moisture

  • The oxygen in the air diffuses into cells and is used in respiration during which carbon iv oxide is produced

  • The carbon iv oxide diffuses out of the leaf through stomata due to diffusion/concentration gradient

  • At night carbon iv oxide accumulates in the leaf since photosynthesis does not take place

  • Some gaseous exchange also takes place through cuticle

  • Gaseous exchange occurs through epidermis of young leaves and stems

  • The cork cells at lenticels are loosely packed

  • Gaseous exchange takes place between cork and atmosphere within the loosely packed cell

    iii) State the ways in which floating leaves of aquatic plants are adapted to gaseous exchange

  • stomata found only on upper dermis to allow efficient gaseous exchange

  • presence to aerenchyma tissues/large air spaces to enable it float/buoyancy/storage of air

  • absence of cuticle to enhance gaseous exchange

    iv) How is aerenchyma tissue adapted to its function?

  • has large airspaces which store gases/for gaseous exchange/buoyancy

    v) Explain stomatal distribution in plants of different habitats

  • land plants have their stomata mainly on the lower side to reduce water loss but if on both sides then upper side has very few

  • water plants, floaters, have stomata on upper side to enhance water loss

  • in dry areas, plants have leaves with sunken stomata to reduce water loss by transpiration
  • Plants in wet areas have stomata equally distributed on both sides.

    d) i) List the types of respiratory surfaces of animals

  • cell membrane in unicellular organisms e. g. amoeba

  • gills in fish

  • tracheal system

  • skin, buccal cavity and lungs in amphibians

  • lings in mammals

    ii) State the characteristics of respiratory surfaces in animals

  • moist thin walled/thin membrane/thin surface

  • Highly/richly vascularised/numerous blood vessels/Well supplied with blood vessels.

  • Large surface area

    iii) Describe gaseous exchange in protozoa

  • example is amoeba

  • small and have large surface area

  • oxygen diffuses into the organism and carbon IV oxide diffuses out into Water

  • simple diffusion of gases is enough to meet its respiratory requirements

    e) i) Make a labeled drawing of a fish gill

    ii) How is a fish gill adapted to its function?

  • large surface area due to many filaments

  • extensive vascularisation due to capillaries, for gaseous exchange

  • thin filaments to facilitate diffusion of gases

  • presence of rakers to filter solid particles

  • gill bar is bony, hard and firm to support the filaments and rakers and for attachment of filaments and rakers

    iii) Discuss gaseous exchange in bony fish

  • example is tilapia

  • the mouth opens and the floor of the mouth is lowered so that the volume in the mouth is increased and pressure is lowered

  • water then enters into the mouth cavity

  • the mouth is closed and the floor of the mouth raised so that the volume is reduced this raises the pressure, forcing water over gills and out through the operculum

  • As water passes over the gills oxygen diffuses due to concentration gradient (partial pressure) into the blood stream.

  • In the body tissues, carbon IV oxide diffuses into the blood (due to concentration gradient, and is transported to the gills and diffuses out into the water.

    iv) What is counter-flow system?

  • Where water in which the fish lives flows in opposite direction across the gill.

    vi) What is the advantage of counter-flow system?

  • maintains a diffusion gradient so that there is maximum uptake of oxygen

  • oxygen continues diffusing into blood and carbon iv oxide into Water

    f) i) Describe the mechanism of gaseous exchange in terrestrial insects

  • example is cockroach

  • air in the atmosphere contains oxygen

  • air is drawn into the body of the insect through the spiracles due to movement of abdominal muscles

  • these movements cause the opening of spiracles

  • air moves through the trachea to tracheoles

  • oxygen moves from the tracheoles into body cells by diffusion due to concentration gradient

  • carbon iv oxide in the tissues diffuses into tracheoles due to concentration gradient

  • From tracheoles carbon IV oxide moves into trachea and out through the spiracles into the air.

    ii) State how traceholes are adapted to gaseous exchange

  • thin walls of tracheoles

  • moist surface

  • large surface area due to numerous tracheoles

    g) i) What is breathing?

  • Any process which speeds up the rate of gaseous exchange between an animal and its surrounding.

    ii) Name the structures in humans that are used in gaseous exchange

  • nose

  • larynx

  • epiglottis

  • trachea

  • lungs

  • pleural membrane

  • pleural cavity

  • diaphragm muscles

    iii) Describe the mechanism of gaseous exchange in a mammal

    Breathing in

  • external intercostals muscles contract while internal intercostals muscles relax, raising then ribcage upwards and outwards

  • muscles of the diaphragm contract hence it flattens

  • the volume of the thoracic cavity increases while pressure decreases

  • higher air pressure in the atmosphere forces air into lungs through the nose

    Breathing out

  • external intercostals muscles relax while internal intercostals muscles contract, moving the ribcage downwards and inwards

  • muscles of the diaphragm relax hence the diaphragm assumes dome shape

  • the volume of the thoracic cavity decreases while pressure increases

  • the higher pressure forces air out of the lungs through the nose

    iv) Explain how mammalian lungs are adapted to gaseous exchange

  • large number of alveoli that increase surface area

  • moist inner surface of alveoli for dissolving oxygen/gases to facilitate exchange of gases

  • through alveolar cavities and blood

  • thin walls of alveoli to allow efficient/faster diffusion of gases

  • rich capillary/blood supply on alveolar surface to transport oxygen away from the lungs and carbon IV oxide to the lungs

    v) Name the features of alveoli that adapt them to their function

  • have large surface area/spherical shaped

  • numerous/many to increase surface area

  • one cell thick

  • moist surface for air to diffuse

  • highly vascularised/numerous capillaries

    vii) How is the trachea of a mammal suited to its function?

  • has a ring of cartilage which keeps it open at all times

  • cilia that move mucus/particles to the top of the trachea i.e. into larynx for removal

  • mucus to trap dust, solid particles and microorganisms

  • hollow for passage of air

    viii) State the advantages of breathing through the nose rather than through the mouth

  • nose has hairs to filter solid particles

  • it has mucus lining to trap dust particles

  • the nose has cells sensitive to smell for survival

  • it warms the air before it reaches the lungs

    ix) Give the conditions under which the carbon iv oxide level rises above normal in mammalian blood

  • vigorous exercise

  • emotions/stress

  • disease infection

    x) Explain the physiological changes that occur in the body to lower the carbon iv oxide level back to normal when it rises

  • heartbeat/cardiac frequency increases to pump blood faster carbon iv oxide from the tissues and supply more oxygen

  • ventilation rate/rate and depth of breathing increases to take more oxygen and remove carbon iv oxide from the lungs

  • arterioles to take in more oxygen and remove carbon iv oxide from the lungs

  • arterioles dilate leading to faster flow of blood to and from body tissues

    h) i)Describe the factors which control the rate of breathing in humans

  • breathing movements usually occur unconsciously

  • it is controlled by the medulla oblongata part of the brain situated at the breathing centre

  • medullar oblongata is in the brain

  • respiratory centre transmits impulses to the diaphragm through phrenic nerves

  • carbon iv oxide concentration in the blood determines the breathing rate

  • if carbon iv oxide is less, the brain is triggered to decrease breathing rate

  • cardiac frequency decreases and the arterioles constrict

  • therefore carbon iv oxide level is raised

  • this brings back to normal level of breathing and carbon iv oxide level increases/is more

  • the brain is triggered to increase breathing rate

  • cardiac frequency is increased

  • there is vasodilation of arterioles

  • carbon iv oxide level falls

  • therefore the normal level is attained and carbon iv oxide is removed faster

    ii) Name the respirator diseases

  • asthma

  • bronchitis

  • whooping cough

  • pneumonia

  • tuberculosis

    4. a) i) Define respiration

  • the oxidation/breakdown of food within cells to release energy

    ii) Explain the significance of respiration in living organisms

  • it yields energy (ATP)

  • this energy enables organisms to move, grow, excrete and reproduce

    iii) Where does respiration take place?

  • in the mitochondria

    b) i) Draw and label a mitochondrion

    ii) State the most important function of mitochondria

  • to produce Adenosine triphosphate (ATP) which is the energy source of the Whole cell

    iii) Give the functions of the labeled parts

    Outer membrane

  • controls what enters and What leaves mitochondrion

    Cristae

  • also called inner membrane

  • increase surface are for attachment of enzymes

  • this is Where cellular oxidation reactions occur

    Matrix

  • enzymes are located here

  • other reactions occur here

    c) Explain the roles of enzymes in respiration

  • they catalyse reactions i.e. speed up respiration

    d) i) What is aerobic respiration

  • respiration in the presence of oxygen

    ii) Give a word equation for aerobic respiration

  • glucose + oxygen - Water + carbon iv oxide + energy

    iii) What are the end products of aerobic respiration?

  • energy

  • carbon iv oxide

  • water

    e) i) What is anaerobic respiration

  • occurs in the absence of oxygen e. g. yeast and certain bacteria release energy in the absence of oxygen

    ii) What are obligate anaerobes?

  • are completely independent of oxygen

    iii) What are facultative anaerobes?

  • can survive both in the presence and absence of oxygen also called partial anaerobes

    iv) State the Word equation representing anaerobic respiration in plants

  • Glucose ethanol + carbon (iv) oxide + energy

    v) Name the end products of anaerobic respiration in plants

  • alcohol/ethanol

  • carbon iv oxide

  • energy

    g) i) Give a word equation of anaerobic respiration in animals

    Glucose —> lactic acid + energy

    ii) Name the end products of respiration in animals when there is insufficient oxygen supply

  • lactic acid

  • energy

    iii) Why is there a high rate of lactic acid production during exercise?

  • the demand for oxygen is more than supply leading to anaerobic respiration

    iv) Why does lactic acid level reduce after exercise?

  • lactic acid is oxidized to form carbon iv oxide and water

  • some is converted to glucose

  • some is converted into glycogen

    v) State why accumulation of lactic acid during vigorous exercise lead to an increase in heartbeat

  • lactic acid is poisonous to tissues and must be removed

  • to increase supply of oxygen to tissues

    State the economic importance of anaerobic respiration

  • brewing of alcohol

  • biogas production

  • compost manure formation

  • silage formation

  • baking bread

  • production of dairy products

  • fermentation of milk

  • sewage treatment

  • Fermentation of tea in industries.

    What is oxygen debt?

  • amount of oxygen required to convert accumulated lactic acid to water, carbon IV oxide and energy

    h) i) What is respiratory quotient(RQ)?

  • ration of carbon IV oxide produced to oxygen consumed

    RQ = volume of CO2 produced

    volume of oxygen consumed

    ii) Why are respiratory quotient important

  • their calculation assists in identifying the kind of substrate being used in respiration

    iii) Name the respiratory substrates

  • carbohydrates

  • fats

  • proteins

    iv) Why does anaerobic respiration of a given substrate yield a smaller amount of energy than aerobic respiration?

  • Some energy locked up in intermediate products like ethanol in plants and lactic acid in animals

  • substrate is completely oxidized in aerobic respiration

    iv) Explain the disadvantages of anaerobic respiration

  • Less energy produced in anaerobic respiration since food is partially oxidized while in
  • aerobic respiration food is completely oxidized.

  • Some metabolic wastes accumulate in cells affecting cellular functions

  • Ethanol produced in plants poisons the tissues while lactic acid produced in animals

  • causes muscle fatigue/muscle cramp and may stop muscle contraction

  • Such intermediate wastes are not produced in aerobic respiration

    v) Mention the types of experiments carried out for respiration

  • germinating seeds which yield energy in form of heat

  • animals produced heat when they respire

  • yeast cells respire to produce heat

    5. a) i) Define the following terms

    Excretion

  • the process by which organisms get rid of waste products which result from chemical process which occur in living cells

    Secretion

  • the process by which organisms produce substances which are useful to the body, by glands

    Egestion

  • removal of indigestive materials from the body

    Homeostasis

  • maintenance of constant internal environment

    ii) Explain Why excretion is necessary in plants and animals

    -products of excretion are usually harmful while some are toxic

    - if allowed to accumulate in the cells they would destroy tissues and interfere with normal metabolism

    - They are therefore removed through excretion

    b) i) Describe how excretion takes place in green plants

  • carbon IV oxide, oxygen and water diffuse through the stomata, lenticels and hydathodes

  • some toxic wastes are convened into non-toxic substances

  • these are deposited in certain tissues of the plant or stored in aging stmctures

  • resins and tannins are exuded through the bark of stem or lost during leaf fall

    ii) Why do plants lack complex excretory structures like those of animals?

  • plants have lower rates of metabolism

  • plants excrete non-poisonous products derived from carbohydrate metabolism unlike animals which produce toxic wastes derived from protein metabolism

  • plants re-use some of their wastes like nitrogenous wastes used in protein synthesis

  • plants store waste products in roots, fruits and leaves

    ii) State the excretory products of plants and some of their uses to humans

  • caffeine from tea and coffee is used in medicine and as a stimulant which is harmful to humans

  • quinine used for treating malaria

  • cocaine derived from leaves of cocoa plant used as a stimulant by addicts or as a local anesthesia, also causes damage to the brain, may cause addiction if not well used and is an illegal drug

  • Tannins derived from barks of acacia (wattle bark) trees are used to make ink and tanning (softening) of leather.

  • Nicotine got from leaves of tobacco plant stimulates the central nervous, may cause addiction if much is used or consumed. It is used to make cigarettes, cigars and is poisonous. It is a precursor of lung cancer

  • Cannabis sative(bhang) is used to make drugs

  • Gum derived from glues is used for sticking substances and making certain jellies

  • Rubber, a product of latex, got from rubber plant is sued to make tyres and synthetic fibres

  • Morphine from opium poppy plant is a narcotic and illegal drug as it causes addiction

  • Khat and miraa are used as stimulants

  • Colchicines used in inducing polyploidy, cancer therapy, treatment of gouts in small quantities

  • Papain used as meat tenderizer

    c) i) Describe excretion in unicellular organisms

    -examples are amoeba and paramecium

    -They have to remove waste products such as carbon IV oxide and nitrogenous substances e. g urea and ammonia

    - These diffuse from the body surface into the surrounding Water

    - Diffusion is due to large surface area

    ii) List excretory organs and products of mammals

  • kidney excretes urea, water and salts

  • skin excretes Water, slats and urea

  • lungs excrete carbon IV oxide and water

  • liver excretes bile salts

    d)i) Draw and label a mammalian skin

    ii) Explain how the mammalian skin is adapted to its functions

    the skin is made up of dermis and epidermis

    Epidermis

  • it is made up of three layers

  • the outermost layer, comified layer is made up of dead cells that prevent entry of microorganisms, prevent physical damage and dessication

  • granular layer made of living cells gives rise to cornified layer

  • malpighian layer is made up of actively dividing cells that give rise to new epidermal cells/granular layer it contains melanin that protects the body against ultra violet rays(radiations)

    Dermis

  • has several components

  • Has sweat gland which produce sweat through sweat pores on the skin and the sweat evaporates cooling the body by lowering body temperature. When it is cold, no sweat is produced, conserving water

  • sweat contains water, sodium chloride, uric acid and urea hence the skin acts as an excretory organ

  • Has hair. The hair stands erect to trap air when temperature is low to reduce loss/insulation. It lies flat to allow heat loss when temperature is high.

  • Has nerve endings which are sensitive to stimuli such as heat, cold, pain, pressure and touch

  • Has subcutaneous fat/adipose fat that insulates the body against heat loss

  • Has arteries and capillaries (blood vessels) that supply food and oxygen and remove excretory products. Arterioles vasodilate when temperatures are high to lose heat by radiation, and convention. Arterioles constrict when temperatures are low to conserve heat i.e. reduce heat loss

  • Has sebaceous glands which secrete sebum, and antiseptic and water repellant that prevents drying and cracking the skin by making the skin supple

    e) What is the role of lungs in excretion?

  • during respiration oxygen is used up in the body cells to produce energy

  • carbon IV oxide is produced as a by-product

  • the carbon IV oxide must be eliminated from the body

  • elimination is through the lungs

  • also, water vapour is formed and must be removed

  • this removal is through the lungs

  • the lung is therefore considered as an excretory organ as it removes carbon IV oxide and water vapour which are by-products of respiration

    f) State the functions of the liver

    i. Excretion

  • in this function the liver is aided by the kidney

  • deamination i.e. excess amino acids converted into urea and uric acid which is transported to skin and kidney for removal

  • detoxification where harmful substances are converted into harmless ones in the liver and transported to kidneys for removal

  • breakdown of worn out blood cells and haemoglobin and the residue excreted through the
  • kidney to give urine a yellow tinge

  • Breakdown of sex hormones after they have performed their function and the wasted are
  • released through the kidney and bile.

    ii) Homeostasis

  • regulation of blood glucose

  • the normal amount of glucose in blood is about 90mg/ 100

  • increase in blood sugar is detected by cells of the pancreas which secrete insulin

  • insulin stimulates the liver to convert excess glucose to glycogen

  • further excess glucose is converted to fats until the normal blood sugar level is attained

  • Excess glucose is oxidized to carbon IV oxide, water and energy. Excess glucose is also used in respiration

  • decrease in blood sugar level below normal level is detected by the pancreas, which secretes glucagon which stimulates the liver to convert glycogen to glucose until the normal sugar level is attained

  • fats, amino acids are converted to glucose

  • it also leads to reduced oxidation of glucose

    Deamination

  • excess amino acids are deaminated by the removal of amino group

  • the amino group is converted to ammonia

  • ammonia combines with carbon IV oxide to form urea

  • urea is excreted in urine through the kidney

  • Detoxification

  • poisonous substances are converted to less harmful compounds

  • Thermal regulation

  • maintenance of body temperature

  • heat is generated in the liver by chemical activities

  • the heat is distributed

    g) i) Draw a labeled diagram of mammalian nephrone

    ii) Describe how the human kidney functions

  • the afferent arterioles, which is a branch of the renal artery, supplies blood to the glomerulus

  • the afferent arteriole has a wider diameter than the efferent arteriole

  • this difference in diameter of afferent and efferent vessels causes high pressure leading to ultra filtration

  • the walls of the blood capillaries are one cell thick hence glucose, amino acids, vitamins,

  • hormones, salts, cratinine, urea and water filter into Bowman’s capsule to form glomerular filtrate

  • white blood cells, red blood cells, plasma proteins (such as globulin) and platelets are too large to pass through the capillary walls hence remain in blood capillary

  • the filtrate flows into proximal convoluted tubule where amino acids, vitamins and all glucose are selectively reabsorbed back into the blood stream

  • many mitochondria provide energy for reabsorption of these substances against a concentration gradient by active transport

  • the glomerular filtrate flows into the loop of Henle

  • water in the descending loop moves by osmosis into the blood capillaries

  • sodium chloride is actively pumped from the ascending arm of the loop of Henle into the blood capillaries

  • the glomerular filatrate flows into the distal convoluted tubule

  • water and salts are reabsorbed from distal convoluted tubule into blood capillaries

  • the glomerular filtrate flows into collecting tubule (duct) from where more Water is reabsorbed into blood stream

  • antiduretic hormone influences the amount of Water reabsorbed depending on osmotic pressure of blood

  • the glomerular filtrate from collecting duct, now referred to as urine, is emptied into pelvis and ureter into bladder and out of body through urethra

  • urine consists of excess water, slats and nitrogenous wastes

    iii) State the adaptations of proximal convoluted tubule to its function

  • folded to increase surface area for absorption thin epithelium to reduce distance of diffusion micro-villi on inner

  • lining to increase surface area for absorption folded to reduce speed of flow for efficient absorption numerous mitochondira to provide energy for reabsorption dense capillary network to transport reabsorbed products

    iv) Name the common kidney diseases

  • nephritis

  • kidney stones(renal calculi

  • cystitis

  • oedema

  • kidney failure

    6. a) i) Why is homeostatic control necessary?

  • this provides a constant internal environment so that the cells of the body have the optimum (best) condition for their survival

    ii) What is internal environment?

  • immediate surrounding of body cells

  • refers to tissue fluid within an organism

    b) i) Why is constant body temperature maintained by mammals?

  • most enzymes in the body function within a narrow range of temperature

  • high temperature denatures enzymes

  • low temperature inactivates and inhibits enzymes

    ii) Explain the advantage gained by possessing a constant body temperature

  • animals remain active despite fluctuations in environmental temperature

  • higher chances of survival in various environments ie they colonize various environments

  • chemical processes in their body continues at an optimum rate

    iii) How do mammals regulate body temperature?

  • the body temperature of a mammal is kept constant

  • to maintain this temperature the mammal must be able to balance its heat loss against the heat gain

  • body temperature is controlled by the hypothalamus, a specialized part of the brain

  • changes in the temperature within the body and the surrounding are detected by the hypothalamus it transmits impulses to the skin and the blood stream in response to temperature changes hypothalamus acts as a thermostat for the body

  • a mammal loses heat by breathing out, urine, feaces, skin by radiation and by evaporation of sweat.

  • A mammal generates heat by the activity of its muscles, by general metabolism in respiration, or chemical activities

  • In hot conditions the hypothalamus stimulates responses that increase heat loss from the body hence lowering the body temperature

  • Such responses include sweating, vasodilation, keeping its hair flat on the surface of skin and reduction of metabolic rate

  • In cold conditions the hypothalamus stimulates responses that generate heat gain in the body and reduce heat loss to the environment

  • Such responses include shivering, vasoconstriction, raising its hair to trap a layer of air around the skin because still air is a good insulator of heat and by generation of heat by increasing metabolic rate.

    iv) Why does body temperature of a healthy person rise up to 37 C on a hot humid day?

  • sweat evaporation is reduced hence cooling is less therefore more heat is retained in the body causing temperature to rise

    v) Name the structures in the human body that detect external temperature changes

  • temperature receptors (end bulb corpuscles e. g. bulb of Krause (warmth) and organ of Ruffinni (cold)

  • heat (thermal) receptors

    vi) State the advantages that organisms with small surface area to volume ratio experience over those with larger

  • heat loss slow hence their body temperature can increase to intolerable levels

  • Heat gain from surrounding slower hence may remain inactive for a long time.

  • Need specialized and complex transport system and also gaseous exchange system

    Explain why individuals with smaller sizes require more energy per unit body weight than those with larger sizes.

  • surface area to volume ratio is higher in smaller individuals than larger ones, therefore smaller heat is lost faster by smaller ones than larger ones

  • they therefore require more energy per unit body weight to maintain body temperature

    c) i) What is the meaning of osmoregulation?

  • mechanism which regulates osmotic pressure of internal environment of an organism

  • the regulation/maintenance of salt/solute-water balance of an internal environment

    ii) State the importance of osmoregulation

  • Maintenance of constant level of water and slats (osmotic pressure) for optimum/suitable conditions for metabolism suitable for cellular functions

    iii) State the ways by which desert mammals conserve water fewer glomeruli longer loop of Henle

  • excretion of dry feaces or concentrated urine

  • hump for fat to be metabolized to give metabolic water for use

  • nocturnal, burrowing, aestivate or hibernate

  • sweat glands few or absent

  • more ADH (vasopressin)

    iv) Explain why some desert animals excrete uric acid rather than Water

  • uric acid is less toxic than ammonia, hence elimination of uric acid requires less water

  • than ammonia therefore more water conserved

  • uric acid being less toxic is safer to excrete where there is less water/desert

    v) Explain why eating a meal with too much salt leads to production of a small volume of concentrated urine

  • the concentration of salts in the blood rises leading to production of more ADH hence higher rate of water reabsorption by kidney tubules

    vi) Explain how marine fish regulate their osmotic pressure

  • swallow plenty of sea water to increase amount of water in the body

  • have chloride excretory cells in their gills to remove excess salts

  • eliminate nitrogenous wastes in form of trimethalamine oxide which requires little water for elimination

  • few/small glomeruli thus slow filtration rate in the kidneys

  • retain nitrogenous wastes in form of urea to raise osmotic pressure of body fluids

    d) i) What is the biological significance of maintaining a relatively constant sugar level in a human body?

  • body cells are surrounded by tissue fluids that are isotonic/same osmotic pressure as cytoplasm

  • if sugar level is high/hypertonic, cell will lose water by osmosis to the surrounding, thus increasing the concentration of the contents

  • this changes the physiology of the cell

  • if the blood sugar is lower than the normal, the cytoplasm gains water by osmosis,

  • diluting the cell contents, thus altering the physiology of the cell

    ii) Discuss the role of the following hormones in blood sugar control

    Insulin

  • insulin is produced when there is increase in blood sugar concentration

  • it converts glucose to glycogen which is in the liver or muscle thus lowering sugar level

    Glucagon

  • when glucose level decreases glucagon is produced, which causes the breakdown of glycogen to glucose thus raising blood sugar level

    e) Explain the part played by antidiuretic hormone in homeostasis

  • Produced when there is less water (high osmotic pressure above normal level of salt concentration) in the blood.

  • It acts on kidney tubules (nephron) thus increasing water reabsorption from tubules to the blood stream, thus restoring osmotic pressure

  • When there is more water(lower osmotic pressure) or decreased salt concentration in blood, little or no ADH is produced, less water reabsorbed hence water loss in urine (more dilute urine) hence raising the osmotic pressure in body fluids/blood

    f) What is the role of blood clotting in homeostasis?

  • when a blood vessel is cut, there is exposure of blood platelets to the air

  • this triggers fibrinogen to be converted to fibrin

  • the fibrin forms a clot that prevents body fluids e. g. blood from being lost

  • therefore the clot conserves water and salts in the body

    g) Describe the role of the following hormones in homeostasis

    i. Aldosterone

  • concerned with regulation of ionic balance

  • secreted by the cortex of adrenal glands

  • it increases sodium ion uptake by the gut and promotes the reabsorption of sodium ions (and therefore water) in the kidneys)

  • this is accompanied by elimination of potassium ions

  • this raises the overall level of sodium and lowers the overall level of potassium in the blood

  • as sodium ions are absorbed in the blood, chlorine ions follow so as to neutralize the effect of sodium ions

  • the production of aldosterone is regulated by the concentration of sodium ions which has an inhibiting effect, and a fall in sodium ions has a stimulating effect on the adrenal cortex

  • the flow of aldosterone is stimulated by the adreno-cortic-tropic hormone (ACTH) produced in the anterior of the pituitary gland however, the main method of control is dependent on the fact that adrenal cortex itself is somehow sensitive to the relative concentration of potassium and sodium in the blood

    ii. Adrenaline

  • produced by adrenal glands

  • in high concentrations, it increases hydrolysis of glycogen and increases blood sugar

  • it is usually released in emergency cases to increase glucose level for respiration

  • this releases energy for the emergency

    h) i) Distinguish between diabetes mellitus and diabetes insipidus

  • diabetes mellitus is a condition resulting from insufficient production of insulin causing hyperglucaemia and presence of glucose in urine

  • diabetes insipidus is a condition whereby less or no antidiuretic hormone is secreted hence a high volume of water is passed out in urine in a condition called diuresis

    ii) How can high blood sugar level in a person be controlled?

  • administer insulin

    iii) Why does glucose not normally appear in urine even though it is filtered in the mammalian Bowman’s capsule?

  • glucose molecules are actively reabsorbed in the proximal convoluted tubules

    iv) When is glycogen which is stored in the liver converted into glucose and released into the blood?

  • after activity/when blood sugar (glucose) falls below normal

  • when glucagon

  • stimulates the liver/when glucagon is produced

  • after strenuous/vigorous activity

  • during starvation

    v) How would one find out from a sample of urine whether a person is suffering from diabetes mellitus?

  • test or react urine in Benedict’s solution

  • positive result i.e. orange or red precipitate

  • Positive result is an indication of diabetes mellitus

    KCSE Biology Questions and Answers Form 3 - Biology Form Three Notes

    Biology Questions and Answers Form 3

    1. a) i) What is meant by the term binomial nomenclature?

  • scientific system of naming organisms using the generic(genus) and specific (species)

    ii) State briefly the general principles of classification of living organisms

  • scientific names must be in Latin or should be latinised
  • family names are formed by adding the suffix “idea” to the stem of the genus e.g the genus Rana become Ranaidea
  • generic names should be a single unique name

    b) State the main characteristics of the five kingdoms of organisms

    i. Monera

  • e.g. bacteria
  • unicellular (single celled)
  • prokaryotic (genetic material not surrounded by membrane)
  • cell Wall without cellulose
  • lack most organelles
  • small in size (microscopic)

    ii. Protista(protoctista)

  • single celled(unicellular)
  • eukaryotic (most cell organelles present)
  • when cell Walls are present have no cellulose
  • e.g. protozoa and algae
  • usually microscopic

    iii. Fungi

  • have hyphae (which form mycelia)
  • absence of chlorophyll
  • have rhizoids (lackroots, leaves, stem)
  • have spore forming structures (sporangia)
  • e.g. mucor, rhizopus

    iv. Plantae

  • most are green/contain chlorophyll
  • autotrophic/feed by photosynthesis
  • cells have cellulose cell walls
  • respond slowly to stimuli (tropism)
  • lack locomotion (are stationary)
  • indefinite growth (at meristems)
  • lack specialized excretory structures

    v. Animalia

  • cells do not have cell walls
  • most carry out locomotion
  • heterotrophic
  • fast response to stimuli (tactic)
  • have specialized excretory structures

    c) Describe the economic importance of:

    i. Fungi

  • some cause decay to our food
  • some cause diseases to humans and animals e. g. ringworms
  • may be used as food e. g. mushrooms, yeast
  • some are used in production of antibiotics e. g. penicillin, chloromycin, streptomycin
  • yeast is used in brewing industry, baking and source of vitamin B
  • many cause diseases to our crops e. g. late blight
  • important in recycling nutrients in soil since they cause decay of organic matter
  • mycorrhizal association in forest development may help in Water intake/absorption
  • help in nitrogen fixation

    ii. Bacteria

  • are useful in the manufacture of antibiotics
  • silage formation,
  • fermentation of cheese, butter, milk yoghurt
  • curing of tea, tobacco and retting flax
  • formation of vitamin B12 and K
  • enzymes such as amylase and invertase
  • hormones such as insulin '
  • vinegar, acetic acid, lactic acid, citric acid
  • in septic tanks and modern sewage Works make use of bacteria
  • biogas production
  • saprophytic bacteria are used in compost decomposition or cause decay
  • symbiotic bacteria are used in compost decomposition or cause decay
  • symbiotic bacteria in herbivores/ruminants help in digestion
  • some diseases in animals/humans and plants are caused by bacteria
  • many bacteria cause‘ food spoilage/decay
  • nitrifying and nitrogen fixing bacteria increase soil fertility/make nitrates available
  • denitrifying bacteria reduce soil fertility/convert nitrates into nitrogen/reduce nitrates

    d) State the main characteristics of the following division of kingdom plantae

    i. Bryophyte

  • e.g. mosses and liverworts
  • presence of rhizoids
  • lack of vascular tissues (lack phloem and xylem)
  • body pans not differentiated into root, stem, leaves
  • capsule or seta
  • gametophyte generation dominant.

    ii. Pteridophyta

  • e.g. ferns
  • has true roots, stems and leaves
  • fond with sori on under-surface
  • vascular tissues present
  • sporophyte generation is dominant

    iii. Spermatophyte

  • photosynthetic
  • well differentiated into roots, stems and leaves
  • well developed vascular system
  • seed bearing plants

    e) Name sub-divisions of spermatophyte and state the characteristics of each class

    i. Gymnospermae (cornifers)

  • naked seeds (exposed
  • are all woody trees
  • reproduce by means of cones
  • show xerophytic characteristics
  • xylem have tracheids but lack vessels
  • phloem lacks companion cells ~
  • single fertilization
  • pollen lands directly on ovules

    ii. Angiospermae (flowering plants)

  • reproduce by flowers
  • seeds enclosed (in fruits)
  • flowers bisexual hence double fertilization
  • herbaceous
  • pollen grains land on stigma of pistil
  • xylem contains vessels
  • phloem contains companion cells
  • ovules contained in ovary

    iii. Name the classes and state characteristics of angiospermae

    Dicotyledonae

  • two seed leaves
  • network venation of leaves
  • regularly arranged vascular bundles
  • tap root system
  • broad leaves
  • secondary growth occurs

    Monocotyledonae

  • one seed leaf
  • parallel venation of leaves
  • irregularly arranged vascular bundles
  • fibrous root system
  • narrow leaves
  • sheath like leaf stalk (petiole)
  • no secondary growth

    iv)State the importance of plants

  • balancing carbon IV oxide and oxygen in the atmosphere during photosynthesis and respiration influence water cycle
  • reduce soil erosion by bind soil particles together
  • useful products e. g. food, medicine, timber, paper and clothing
  • habitat ( e. g. forests and grassland) for animals which may also be tourist attraction earn money from sales of products
  • aesthetic value/beauty e. g. flowers, shade/shelter, live fences, windbreaks
  • Some are harmful e. g. poisons, weeds, injurious (stinging nettles, thorns), water hyacinth

    f) i) Give the general characteristics of phylum arthropoda

  • jointed appendages
  • presence of exoskeleton
  • triploblastic and coelomate
  • segmented body
  • bilateral symmetry (similar halves)

    ii. State the characteristics of the following classes of arthropoda

    Diplopoda

  • the millipedes
  • two pairs of legs per segment
  • many segments
  • terrestrial habitat
  • body cylindrical and long
  • herbivorous
  • one pair of antennae

    Chilopoda

  • the centipedes
  • one pair of legs per segment
  • many segments
  • terrestrial habitat
  • body long and ventro-dorsally flattened
  • carnivorous
  • last pair of legs pointing backwards with poison claws called maxillipedes
  • one pair of antennae

    Insecta

  • three body pans i.e. head thorax, abdomen
  • six legs/three pairs of legs
  • a pair of compound eyes
  • presence of wings
  • a pair of antennae

    Crustacean

  • two body parts
  • segmented body
  • have pincers (modified legs) to catch prey
  • have hard exoskeleton
  • a pair of compound eyes

    Arachnida

  • body divided into two parts( abdomen and cephalothorax)
  • simple eyes
  • eight legs (four pairs of legs)

    iii) State the economic importance of insects

    Beneficial effects

  • food supply
  • important in food chains
  • pollinators
  • biological control of pests and other organisms
  • aesthetic value
  • contribute to decomposition e. g. litter feeders like beetles

    Harmful effects

  • pests
  • vectors
  • dirt and disease carriers
  • injurious e.g. stings and bites g) i) State the general characteristics of chordate

  • notochord
  • dorsal slits (pharyngeal cleft during development)
  • bilateral symmetry
  • triploblastic (three layer body-ectoderm, mesoderm and endoderm)
  • clear cut head formation
  • multilayered epidermis
  • post anal tail
  • closed circulatory system
  • segmented muscle blocks(myotomes)
  • single pair of gonads

    Give the characteristics of the following classes of chordate

    Pisces

  • presence of fins for locomotion
  • two chambered heart *
  • presence of overlapping scales ~
  • presence of gills or operculum for gaseous exchange
  • presence of lateral line for protection
  • streamlined body
  • poikilothermic (body temperature varies with that of environment)

    Amphibian

  • partially live in fresh Water and partially on land
  • poikilothermic
  • pentadactylous with two pairs of limbs
  • webbed feet for locomotion in water
  • body streamlined
  • heart is three chambered
  • moist skin for gaseous exchange

    Reptilia

  • scales on body
  • poikilothermic
  • homodont teeth except tortoise and turtle
  • all have limbs except snakes
  • skin is dry
  • oviparous (lay eggs)
  • no pinna (external ear)
  • three chambered heart 9crocodile has four chambers)
  • skin not glandular
  • no mammary glands

    Aves

  • the birds
  • homoeothermic (constant body temperature)
  • four chambered heart
  • streamlined body for locomotion in air
  • skin dry and covered by feathers
  • scales on legs
  • hollow bones
  • oviparous (lay eggs)
  • mouths modified into beaks

    Mammalian

  • hair on the body
  • homoeothermic
  • viviparous (give birth to live young) eXcept a few
  • have mammary glands
  • glandular skin e.g. sweat glands, sebaceous glands
  • four chambered heart
  • pinna (external ear)
  • two pairs of pentadactyl limbs
  • presence of diaphragm
  • have salivary glands

    a) i) What is a dichotomous key?

  • A biological device (tool) which enables one to identify an organism by progressively opting between two alternative observable characteristics

    i. State the necessity of using a dichotomous key

  • used to identify organisms quickly and accurately
  • by following the statements in the key we are able to identify each organism on the basis of a characteristic which is not to be found in other specimens

    ii. List the rules followed in constructing a dichotomous key

  • use observable characteristics only
  • start with major characteristics, placing organisms into two groups at each stage
  • use a single characteristics at a time
  • use contrasting characteristics at each stage e.g 1(a) short, 1(b) tall
  • avoid repeating the same characteristics

    iv) Describe the procedure of using a dichotomous key. Make a list of major features of the characteristics to be identified

  • look at the features of similarities
  • look at the features of differences between the organisms
  • we can then be able to identify the organisms by distinguishing one from another
  • the key uses a method of elimination by following statements that are correct only for the organism

    iv You are provided with a specimen kale leaf. Use the dichotomous key below to identify the taxonomic group to which the specimen belongs. Show the steps (number and letter) in the key that you followed to arrive at the identify of the specimen

    1 a) Leaf broad....... Go to 2

    b) Leaf narrow....... Araicaria

    2 a) Leaf parallel vein....... Cynodon

    b) Leaf net veined....... Go to 3

    3 a) Leaf with one lobe (simple Leaf)....... Go to 4

    b) Leaf with many lobes (compound Leaf)....... Grevellea

    4 a) Leaf Fleshy....... Kalanchoa

    b) Leaf not fleshy....... Go to 5

    5 a) Leaf petiole modified to form sheath....... Go to 6

    b) Leaf petiole not modified to form sheath....... Brassica

    6 a) Leaf purple....... Tradescantia

    b) Leaf green....... commelina

    Steps 1a, 2b, 3a, 4b, 5b

    Identify- Brassica

    v) You have been provided with four animals labeled K (mature adult housefly), L (mature adult grasshopper, M(maize flour beetle) and N(Worker termite) use the dichotomous key below to identify the specimens. Write down in the correct order, the steps (number and letter) in the key that you followed to arrive at your answer.

    Dichotomous key

    1 a) Animal with wings....... Go to 2

    b) Animal without wings....... Go to 7

    2 a) With two pairs of wings....... Go to 3

    b) With one pair of wings....... Diptera

    3 a) With membranous wings....... Go to 4

    b) Hind pair of membranous wings....... Go to 6

    4 a) With long abdomen ....... Odontata

    b) Medium sized abdomen....... Go to 5

    5 a) Wings with colored scales....... Lepidoptera

    b) Wings without scales....... Hymenoptera

    6 a) Forewings hard and shell-like....... Coleoptera

    b) Forewings hard but not shell-like....... Orthoptera

    7 a) Body horizontally flattened....... Isoptera

    b) Body laterally flattened....... Symphonopteria

    Identify the orders of the various specimen as per the table below

    Specimen Order Step followed

    K- housefly Diptera 1a, 2b

    L- grasshopper Orthoptera 1a, 2a, 3b, 6b

    M- beetle Coleoptera 1a, 2a, 3b, 6a

    M- termite Isoptera 1b, 7a

    2 a) Define the following ecological terms

    i. Ecology

  • study of the interrelationships between organisms and their environment

    ii. Environment

  • surrounding of the organism i.e. biotic or a biotic factors

    iii. Habitat

  • A specific locality (home) of a living organism with a set of factors (conditions) in which an organism lives.

    iv. Ecological niche

  • Role of an organism in its habitat e. g. feeding relationship

    v. Population

  • Number (group) of organisms of a species occupying a given habitat

    vi. Community

  • Refers to different species of (plants and animals) organisms in a given habitat (area) co- existing or interacting (living) with each other and the environment in which they live

    vii. Ecosystem

  • A community of organisms interacting with one another and the environment in which they live

    vm. Biosphere

  • The earth and its atmosphere where living organisms are found

    ix. Autecology

  • Study of a single (individual) species of plants or animals within a community, ecosystem, habitat or environment.

    x. Synecology

  • Study of natural communities (plants and animals) or populations interacting within an ecosystem.

    xi. Carrying capacity

  • maximum number of organisms an area can support without being depleted

    xii. Biome

  • geographical area with particular climatic conditions and flora and fauna
  • it constitutes many ecosystems

    xiii. Biomass

  • dry weight (mass) of a living organism in a given area
  • units of measurement are kg/m2/year

    b) i) What are abiotic factors?

  • non-living components of the ecosystem

    ii) Explain how abiotic factors affect living organisms

    Wind

  • this influences rate of water evaporation from organisms
  • therefore it affects distribution of organisms e. g. wind increases rate of transpiration and evaporation of water from the soil
  • wind is an agent of soil erosion, may break and uproot trees
  • may aid in the formation of sand dunes which can form habitats for some desert plants
  • wind disperses fruits, seeds, spores
  • wind forms waves in lakes and oceans which enhances aeration of water which replenishes oxygen concentration necessary for life
  • wind is an agent of pollination

    Temperature

  • influences rate of enzyme action in photosynthesis and other metabolic reactions in plants and animals
  • organisms function within a narrow range of temperature
  • it affects distribution of organisms
  • changes in temperature affect rate of photosynthesis and biochemical reactions e.g. metabolism and enzyme reaction
  • temperature increases rate of transpiration

    Light

  • needed by green plants and photosynthetic bacteria which are primary producers
  • animals depend on plants directly or indirectly for food
  • main source of light is the sun
  • light is necessary for synthesis of vitamin D in certain animals
  • some plants need light for flowering
  • seeds like lettuce need light for germination

    Humidity

  • amount of water vapour held by the air
  • affects the rate at which water is lost from organisms body by evaporation and stomatal transpiration
  • when humidity is low the rate of transpiration increases
  • humidity influences distribution of organisms

    pH

  • each plant requires a specific PH in which to grow (acidic, neutral or alkalinic)
  • pH affects enzyme reaction in metabolism

    Salinity

  • some ions are needed for plant and animal nutrition
  • osmoregulation implants and animals is affected by salinity Topography

  • altitude affects light, atmospheric pressure and light
  • Slope influences surface runoff, wind erosion, etc.
  • mountains affect distribution of organisms which differs in leeward side and windward side
  • mountains affect distribution of organisms which differ on lowlands and on highlands
  • mountains also form physical barriers to migration of organism and may cause isolation of species
  • background may offer camouflage to some organisms hence protection from enemies

    Rainfall (Water) or precipitation

  • amount and distribution of rainfall affect vegetation type
  • this consequently affects distribution of animals e. g. polar region water frozen hence only
  • well adapted organisms survive
  • fewer organisms found in deserts where rainfall is less
  • Water is required for seed germination, raw material for photosynthesis, solvent for mineral salts. Provides turgidity for plant support, medium for transport, disperses fruits, seeds and spores

    Pressure

  • the weight atmosphere exerts upon the earth
  • varies with altitude the higher the altitude the less the pressure
  • this variation implies change in density which directly means less oxygen for respiration and less carbon iv oxide for photosynthesis and this affects distribution of organisms

    Mineral salts (trace elements)

  • these affect distribution of plants in the soil
  • plants thrive best where elements are available
  • Plants living in soil deficient in a particular element must have special methods of obtaining it.
  • They harbor nitrogen fixing bacteria and others have carnivorous habit
  • Plant distribution influences animal distribution

    c) i) What are biotic factors?

  • refers to living organisms in an area
  • biotic environment of an organism constitutes all organisms around it, which it relates or interacts with in various ways

    ii) Give examples of biotic factors affecting ecosystems

  • feeding relationships
  • predation
  • competition
  • diseases and pests
  • human activities

    d) Discuss how the various biotic factors affect living organisms

    i. Competition

  • organisms compete with one another for food, light, water, mates and shelter
  • organisms must live together for competition for available resources
  • those which cannot cope either structurally or behaviorally will migrate or die
  • those remaining, due to better adaptations will increase in population
  • competition between members of the same species is called intra-specific competition e.g. for mates
  • Competition between members of different species is inter specific competition e. g. for food and space.

    ii. Predation

  • this is predator-prey relationship
  • predator feeds on prey hence both control the other’s population
  • Distribution of predator and prey is important as predator cannot survive without prey
  • It there is no predator the prey will increase in population beyond carrying capacity hence die due to environment depletion

    iii. Parasitism

  • an association where an organism lives in or on another living organism obtaining food(and other benefits) from it, causing harm to it (without necessary killing it)
  • parasites may kill host
  • they deprive host of food
  • make host weak by introducing diseases
  • make reproductive ability of host low hence host becomes susceptible to predation

    iv. Diseases and parasites

  • make organisms weak and susceptible to predation
  • kill organisms and reduce their population

    v. Symbiotic

    and association of organisms of different species where both benefit from the association i.e. there is mutual benefit

    vi. Human activities

  • these are human factors which have an influence on the biosphere
  • examples are road construction, industrialization, deforestation, agriculture, pollution, poaching, fishing conservation, population control
  • affect ecosystem and balance of nature

    Saprophytism

  • saprophytes are organisms which obtain organic matter in solution from dead and decaying tissues of plants and animals
  • they include saprophytic bacteria and fungi
  • they make available carbon, nitrogen and other elements form dead to living organisms
  • they are useful in recycling nutrients in nature

    e)i) What is nitrogen cycle?

  • The process by which nitrogen in the air is made available plants and animals and eventually returns to the air.

  • ii) Draw a simplified diagram representing the nitrogen cycle

    iii) Describe the nitrogen cycle

  • during thunderstorms/lightning nitrogen gas combines with oxygen to form nitrogen oxides
  • nitrogen oxides dissolve in water to form nitric acid
  • acid is deposited in the soil by rain
  • nitric acid combines with chemical substances to form nitrates or nitric acid dissociates to form nitrates which are absorbed by plants
  • symbiotic bacteria (Rhizobium) which are found in root nodules of leguminous plants fix free nitrogen to nitrates
  • free living bacteria (clostridium and Azotobacter) fix nitrogen to nitrates
  • nostoc algae (Anabaema chlorella) fix nitrogen to nitrates
  • plants use nitrates to form plant proteins
  • animals feed on plants and convert plant proteins into animal proteins
  • plants and animals die and are decomposed by putrefying bacteria, fungi(saprophytes)
  • decomposing plants, animals and nitrogenous wastes release ammonia which is converted to nitrites by Nitrosomonas and nitrococcus bacteria
  • nitrites are converted to nitrates by nitrobacter bacteria
  • nitrates in the soil can be converted to free nitrogen (denitrification) by some fungi, pseudomonas and theobaccilus bacteria generally called denitrifying bacteria

    iii. Nitrogen in the atmosphere cannot be directly utilized by plants. State two ways by which this nitrogen is made available for plant use

  • fixation by microorganisms (Rhixobium, Axotobacter)
  • fixation by electrical discharge in atmosphere i.e. conversion by thunderstorm or lightning

    f) i) Describe how energy flows from the sun through the various trophic levels in an ecosystem

  • energy from the sun is trapped by green plants during photosynthesis, producing chemical energy9food or carbohydrates
  • green plants are producers and occupy the first trophic level
  • green plants are eaten by herbivores called primary producers as they occupy the second trophic level
  • herbivores are eaten by carnivores, secondary consumers, which occupy the third trophic level
  • when organisms - plant and animals) die, fungi and bacteria which are saprophytic organisms feed on them thus causing them to decompose into simple substances e. g. mineral salts
  • these organisms are called decomposers and detrivores
  • decomposer feed on dead organic matter hence cause decomposition and decay which releases nutrients for plants, linking biotic and a biotic components
  • at all levels energy is lost through respiration

    Give the reasons for loss of energy from one trophic level to another in a food chain

  • insufficient utilization of food resources(wastage) e.g by defalcation
  • through respiration
  • through excretion e.g. urination and sweating

    Why are green plants referred to as primary producers in an ecosystem?

  • They utilize the energy from the sun to manufacture food for themselves and for subsequent trophic level (consumers) and other organisms

    vi. Explain the following terms giving suitable examples

    Food chain

  • a nutritional sequence between producers and consumers through which energy flows in a straight line i.e. linear representation of feeding relationship between different organisms in an ecosystem
  • if one consumer or the producer is removed the food chain is broken
  • arrow points to the direction of energy flow e. g. green plant herbivore carnivore decomposer

    Food web

  • complex feeding relationship Where a on more than one type of food while several herbivores feed on one type of plant
  • it is an interrelationship of many consumers are usually fewer to ensure survival of both

    Pyramid of numbers

  • this is a diagrammatic representation of numbers of organisms at each trophic level in a food chain
  • usually there are more producers than consumers
  • hence producers herbivores carnivore
  • the reason for the pyramid is because herbivores feed on many plants (producers) as camivores feed on many herbivores
  • sometimes this may not be true e. g. when many caterpillars feed on one tree or parasites on a herbivore
  • this gives an inverted pyramid of numbers

    Pyramid of biomass

  • refers to diagrammatic representation total dry weight of organisms at different trophic levels in a food chain
  • producers have greater biomass than any level of consumers progressively
  • size of organisms in successive e trophic levels increases
  • amount of individuals decreases in successive levels

    Account for the decrease of biomass in the successive trophic levels

  • fixed energy which supports living matter decreases at each successive trophic level since energy is lost by respiration and indigested (unconverted) materials hence less biomass supported at each level

    h) i) Describe the three characteristics of a population growth

  • increase in numbers
  • decrease in numbers growth rate
  • change in numbers

    Dispersion

  • spread or distribution of organisms in a habitat

    Density

  • the number of individuals per unit area

    ii) Explain how the following methods are used to estimate population of organisms

    quadrat method

  • identify the study area
  • throw or mark out the quadrat in the area of study at random
  • identify or label the various species of plants in the quadrat
  • count plants of each species
  • record the numbers
  • repeat the process
  • work out the average per quadrat for each species
  • calculate the total number of different species in the area or calculate the population for the total area of habitat Q

    Line transect

  • a string is stretched along an identified area
  • all plants touching the string are counted

    Belt transect

  • preliminary study of the study area to estimate siie or make a sketch map
  • two parallel lines (strings or ropes) running for a determined distance and width
  • count the number of organisms in the transect
  • calculate the area covered by the transect
  • calculate the number of organisms being investigated per unit area
  • repeat this process at least three times in other parts of the study area
  • find the mean number of organisms per unit area from all the belt transects
  • from this figure calculate the total population of the desired organisms in the study area

    Capture-recapture method

  • e.g. grasshoppers or fish
  • capture the grasshoppers
  • count and mark using permanent ink
  • record
  • release and allow time
  • recapture and count the marked and unmarked
  • total population is equal to the number of marked and unmarked grasshoppers in the second sample multiplied by the number of marked grasshoppers in the first sample divided by number of grasshoppers marked in the second sample that were recaptured

    2. a) Describe the adaptations of plants to various habitats

    i. Xerophytes

  • grow in areas with scarcity of water
  • roots grow deeply and extensively (widely spread) to ensure access to water
  • thick succulent stems, roots and leaves for water storage
  • photosynthetic stems take place of leaves which would lose a lot of water
  • Leaves are needle-like (reduced to spines), scaly, have sunken stomata. Some have curled (rolled) leaves. Some have thick waxy cuticle, reduced number of stomata to reduce water loss by transpiration
  • some shed leaves during dry season to reduce water loss
  • presence of thorns for protection
  • short life cycle to ensure survival
  • reversed stomatal rhythm

    ii. Hyrophytes

  • grow in places with plenty of water(waterlogged)
  • aerenchyma a tissue (airspaces) and large intercellular spaces and long fibrous roots for buoyancy (floating in water)
  • poorly developed support tissues (sclerenchyma) because water provides the necessary support
  • upper epidermis of leaves have more stomata than lower epidermis for gaseous exchange or for increased rate of transpiration
  • poorly developed conducting tissues (xylem and phloem) because plants obtain water by diffusion

    iii. Mesophytes

  • grow in well watered soils ‘(common plants)
  • no special adaptations, but depending on particular habitat, may have some adaptations
  • in forests they grow fast; tall to capture light. Have climbers while some are adapted to carry out photosynthesis in low light intensities (those that form undergrowth)
  • in places with adequate water they form broad leaves, thin cuticle and many stomata on both leaf surfaces
  • in direr regions they possess more stomata on the lower leaf surface and are deep rooted
  • some are shallow rooted and develop buttress and prop roots for support
  • some have waxy or glossy surface to reflect sun rays and drip off rain water

    iv. Halophytes

  • plants that grow in very salty soil where the salt concentration is higher than that in the plant
  • have root cells which concentrate a lot of salts in them and enable then to take in water by osmosis
  • succulent roots to store water
  • have pneumatophores (breathing roots) to take in oxygen
  • some have buttress roots for support
  • secrete excess salt by use of salt glands
  • have large airspaces in leaves and stems for buoyancy and to store air
  • capable of photosynthesis at low light intensities e.g. mangrove

    b) 1) What is pollution?

  • any process which leads to adverse or harmful changes in the environment

    ii) Explain the various human activities that have caused pollution

    Causes and effects of air pollution

  • sulphur iv oxide, hydrogen sulphide, chlorine, oxides of nitrogen produced by industries, sewage, decomposing organic matter and fumes affect gaseous exchange, makes acid rain and damage plant leaves
  • aerosols, herbicides, insecticides (agrochemicals), paint spays, acaricides and CFC’s sprayed to control diseases, pests and weeds affect respiratory organs of animals. The chemicals are residual and persistent (not easily broken down) and bring depletion of the ozone layer
  • smoke and fumes produced in areas withheavy industries, motor vehicles, fires which bum fuel, oil, wood and coal cause carbon ii oxide, poisoning affect respiratory systems and affect visibility
  • particles in smoke and fumes settle on leaves and stop photosynthesis
  • carbon iv oxide causes green house effect which causes temperature inversion as a result of heating the lower layers of atmosphere
  • sound and noise produced incessantly by machines, aeroplanes and heavy vehicles affect hearing in animals
  • dust from cement factories, quarries, dust roads settles on leaves limiting photosynthesis
  • removal of vegetation interferes with carbon cycle radio-active emissions from nuclear reactors, mines and bombs cause cancer, mutations and death.

    Control of air pollution

  • use of lead free petrol in motor vehicles, air craft, aeroplanes and petroleum engines
  • uses of smokeless fuels and electricity
  • filtration, dissolution and use of chemicals to remove harmful gases
  • factories should be erected far away from residential areas
  • use of tall chimneys
  • reduce volume or intensity of sound e. g. by use of ear muffs
  • concords should fly at higher altitudes and aeroplanes to fly high up

    State the causes, effects and methods of controlling and prop roots for support water pollution

    Causes and effects

  • agrochemicals e.g. fertilizers cause eutrophication leading to increase in animal population
  • Silting makes water surfaces shallow and silt clogs stomata and gills of fish reducing rates of photosynthesis and gaseous exchange. It also leads to reduction of algae which causes reduction of consumers i.e. animal population
  • industrial and domestic wastes contain toxic materials which kill producers and other organism while oily substances in wastes may clog gills of fish and may change pH of water oxygen solubility is also reduced by oily surfaces
  • Untreated sewage and effluents where decomposition or organic matter in sewage reduces oxygen supply and sewage provides food for bacteria increasing their population and demand for oxygen thus depriving fish of oxygen.
  • Human feaces causes eutrophication, carbon IV oxide produced by decomposition of faecal matter changes pH of water interferes with photosynthesis and may clog fish gills or block light penetration which interferes with producers thereby decreasing productivity.
  • Dumping of chemicals from industries with toxic pollutants which kill organisms
  • Spillage of oil and chemicals block oxygen and kill organisms
  • Discharge of water from industries into water body where high temperatures reduce amount of oxygen in the water causing organism to suffocate and die
  • Untreated sewage may lead to outbreak of epidemics

    Control of water pollution

  • pollution caused by domestic effluents may be controlled by treating domestic waste, using biotechnology, banning the use ofphosphate-based detergents, using plastic pipes instead of those made from lead, recycling gabbage, using biodegradable detergents.
  • Pollution caused by industrial waste may be controlled by treating/cooling industrial waste, carrying out environmental impact assessment before establishing industries
  • Oil spillage may be controlled by cleaning spilled oil biotechnology and penalizing the industry
  • individual or companies which cause oil spills/water pollution
  • Pollution caused by agrochemicals may be controlled by using mechanical control of weeds, biological control of weeds and pests, biodegradable organic fertilizer herbicides, insecticides pesticides, organic farming educate farmers on the use of correct amount of agrochemicals
  • silting may be controlled by appropriate farming practices, contour farming, reafforestation, building gabions and terracing

    iv) State the causes /effects and control methods of soil pollution

    Causes and effects

  • Air pollutants e. g. sulphur IV oxide fumes form sulphuric acid with rain water. The acid rain alters soil pH therefore affecting plants that cannot tolerate acidic soil
  • most aerosols sprayed to control pests and diseases precipitate in the soil and are taken up by plants which make its concentration many times higher, increasing the toxicity in the plants which absorb them
  • petroleum products due to spillage by oil tankers making it impossible for plant roots to obtain oxygen in oil saturated soils, therefore plants are killed
  • agrochemicals and inorganic fertilizers contain heavy metals that are not used up by plants and eventually soil microorganisms cannot inhabit the soils
  • organic matter slows down, life ceases and soil becomes exhausted
  • community, household wastes and industrial wastes disposal is a major problem in big towns and cities. commodities packaged in metal tins, rubber, plastic containers, scrap metal, glass bottles, different types of paper are nuisance to the environment, rendering it useless for agricultural purposes

    Control of soil pollution

  • use of organic farming techniques _
  • biological control of pests, diseases, parasites
  • recycling of non-degradable containers or burying them safely after use
  • controlled burning of garbage
  • treatment of human and industrial waste for safe disposal
  • avoid spilling chemicals and oil when used

    v) Define biological control give suitable examples

  • using a living organism to regulate, control or reduce the population of another organism e.g beetles to feed on water hyacinth, fish to feed on mosquito larvae.

    vi) What is eutrophication?

  • enrichment of water bodies with nutrients due to discharge of sewage leading to rapid growth of surface plants

    i) What are the effects of eutrophication?

  • enrichment of water bodies with nutrients due to discharge of sewage leading to rapid growth of surface plants

    vii) What are the effects of eutrophication?

  • The plants block light from reaching plants underneath hence no photosynthesis The plants die and decompose leading to lack of oxygen hence animals also die

    c) Describe the symptoms, mode of transmission and control of cholera, typhoid, malaria and amoebic dysentery in humans

    Cholera

    causative agent

  • Vibrio cholerae (bacterium)

    Transmission

  • Contaminated food or water
  • Spread by flies from faeces

    Symptoms

  • Intestinal pain
  • Diarrhea
  • Vomiting
  • Dehydration

    Control

  • Proper hygiene e.g boiling drinking water
  • vaccination

    Typhoid

    Causative agent

  • salmonella typhi (bacterium)

    Transmission

  • Contaminated food or water
  • Spread by flies from faeces

    Symptoms

  • Fever
  • Rashes
  • diarrhea plus blood from bowels

    Control

  • Proper hygiene e.g boiling drinking water
  • vaccination

    Malaria

    Causative agent

  • Plasmodium (protozoa)

    Transmission

  • Bite by infected anopheles female mosquito

    Symptoms

  • Fever
  • Joint pains
  • Vomiting
  • Headache
  • Anaemia

    Control

  • Killing the mosquito
  • Killing the mosquito larvae
  • Draining stagnant water
  • Clearing bushes
  • Treatment
  • Sleep under mosquito nets

    Amoebic dysentery (amoebiasis)

    Causative agent

  • Entamoeba hystolytica (bacterium)

    Transmission

  • Contaminated food or water due to improper faeces disposal

    Symptoms

  • Intestinal pain
  • Diarrhea
  • Vomiting
  • Dehydration

    Control

  • Sanitation
  • Personal hygiene
  • Cook food well
  • Treatment using drugs

    d) Discuss Ascaris lumbricoides under the following sub-headings

    i. Mode of transmission

  • through ingestion of contaminated food
  • live in intestines

    ii. Effects of parasite on the host

  • inflammation of lungs
  • pneumonia
  • produce toxic substances
  • intestinal obstruction

    iii. Adaptations

  • thick cuticle which protects it against digestion
  • lays many eggs to ensure survival
  • mouthparts for sucking partly digested food
  • lack of elaborate alimentary canal
  • tolerant to low oxygen concentration
  • two hosts to ensure survival
  • eggs have protective cover to ensure survival in adverse environments

    iv. Control and prevention

  • proper sanitation
  • wash hand after defaecation and before eating

    e) Discuss schistosoma under the following sub-headings

    i. Mode of transmission

  • through contaminated water in swamps, etc

    ii. Effects on host

  • bleeding in lungs
  • blood stained urine
  • unthriftiness

    iii. Adaptations

  • has two hosts to increase chances of survival
  • eggs have a hook like structure which raptures the walls of intestine or bladder
  • lay large number of eggs to ensure survival
  • larvae have a sucker for attachment on human skin which it digests
  • larva has a tail which it swims with in search of host in water
  • prolonged association between male and female to ensure that fertilization takes place
  • adults can tolerate low oxygen concentration (in the animal tissues)
  • adult worm secretes chemicals against antibodies
  • larvae and eggs (have glands that) secrete lytic enzymes to soften the tissues that ease penetration
  • larvae are encysted so as to survive adverse conditions

    Control and prevention

  • proper use of toilet facilities
  • boiling water before use
  • avoid bathing/washing in infected water
  • Use of molluscicides (chemicals that kill snails/biological control/clearing water weeds on which snails feed.
  • Drainage of stagnant water
  • Wearing gum/rubber boots

    3. a) i) What is reproduction?

  • process by which living organisms give rise to new members of their own species which resemble the parents

    ii) Why is reproduction important?

  • for continuity of speciesl to ensure survival of species
  • maintaining life of species
  • replace dead individuals

    iii) Name the types of reproduction

  • sexual which involves fusion of male and female gametes
  • asexual in which no gametes are involved but parts of a mature organism develops into new individuals

    b) i) What is cell division?

  • process by which cells are formed from pre-existing cells

    ii) What are chromosomes?

  • Threadlike structures found in nucleus of a cell.
  • The units called genes
  • Genes are factors that cause inheritance or determine characteristics of offspring

    c) i) What is mitosis?

  • A type of cell division that occurs during growth leading to increase in number of cells
  • all cells maintain the same chromosome constitution i.e. the diploid state

    ii) Describe the five stages of mitosis

    Interphase

  • replication of organelles
  • duplication of DNA
  • production of energy (ATP) for cell division

    Prophase

  • stage of dehydration
  • chromosomes shorten and thicken
  • chromosome replicates into two chromatids
  • chromatids joined at centromere
  • formation of spindle fibers

    Metaphase

  • chromosomes move to equator (early metaphase)
  • chromosomes line up at the equator
  • homologous chromosomes do not associate

    Anaphase

  • Chromatids separate
  • move to opposite ends (poles) of the cells

    Telophase

  • chromatids reach the poles
  • formation of two daughter cells occurs i.e. cytoplasmic division

    ii) State the significance of mitosis

  • ensures each daughter cell has same number and kinds of chromosomes as daughter cells
  • gives rise to new cells (responsible for growth)

    d) i) What is meiosis?

  • division of diploid cells to form gametes which are haploid

    ii) State the significance of meiosis

  • gives rise to gametes
  • source of variation

    iii) Give a summary of the stages of meioeis

  • First meiotic division

  • Interphase I

  • cell is in non-dividing condition
  • chromosomes appear threadlike

    Prophase I

  • chromatic material shorten and thicken
  • double stranded chromosomes appear (bivalent)
  • double stranded chromosomes pair and twist round each other (synapsis)
  • point of contact of chromosomes is called chiasma

    Metaphase I

  • paired homologous chromosomes line up at the equator

    Anaphase I

  • paired homologous chromosomes move to the poles

    Telophase I

  • paired homologous chromosomes reach the pores
  • two new nuclei are formed

    Second meiotic division

    Prophase II

  • chromosomes shorten, thicken and become visible,
  • stage of dehydration

    Metaphase II

  • movement of chromosomes to equator

    Anaphase II

  • chromatids of each chromosome separate to the poles

    Telophase II

  • reach the poles
  • four haploid daughter cells are formed

    iv) Give the similarities between mitosis and meiosis

  • both take part in cells
  • both involve division (cell multiplication)

    v) What are the differences between mitosis and meiosis?

    Mitosis

  • maintenance of chromosome number (diploid)
  • take place in somatic cells/growth
  • no crossing over/no variation
  • results in to two daughter cells
  • no pairing/no synapsis/no bivalent formed
  • a one division process of four stages

    meiosis

  • reduction halving of chromosomes (haploid)
  • occurs in reproductive cells/gonads/produces gametes
  • crossing over takes place/variation occurs
  • results in to 4 daughter cells
  • there is pairing/synapsis/bivalent
  • a two dicision process of four stages each

    d) i) What is asexual reproduction

  • formation of new individuals as a result of the fusion of two gametes
  • fusion is called fertilization

    ii) What is the significance of sexual reproduction in living organisms?

  • leads to genetic variation e. g. cross breeding which gives rise to hybrids

    iii) State the advantages of sexual reproduction

  • genetic variation
  • greater adaptability to environment by offspring
  • few bad or good traits inherited/retained
  • greater amount of dispersal is possible
  • may result in stronger offspring

    iv) Give the disadvantages of sexual reproduction

  • less certainty in egg and sperm meeting
  • low rate of survival
  • sex-linked diseases easily transmitted

    e) i) What is asexual reproduction?

  • formation of new organisms without fusion of gametes
  • occurs with only one parent
  • parts of organism develop into new individual

    ii) State the advantages of asexual reproduction

  • retention of useful characteristics/genes/traits
  • offspring establish faster/shorter life cycle
  • better chances of survival because of suitable environment

    iii) Give the disadvantages of asexual reproduction

  • lack of genetic variation
  • lowered resistance to disease ~
  • loss of hybrid vigor
  • competition for resources due to overcrowding

    iv) Explain how reproduction occurs by the following methods of asexual reproduction

    Sporulation

  • formation of spores
  • spores are small haploid cells produced by plants
  • Spores give rise to new haploid organisms
  • includes moulds, ferns, bryophytes, pteridophytes

    Budding

  • where an outgrowth arises from a parent and drops off to develop into a new organisms
  • hereditary material in the daughter cell and parent are exactly the same
  • occurs in organisms such as hydra, jelly fish, sea anemones, yeast and some fungi

    Binary fission

  • a cell splits into two new cells of equal size
  • each daughter cell grows into anew organism
  • Occurs in organisms such as amoeba, euglena, paramecium, some fungi and bacteria.

    f) i) What is a flower?

  • this is the reproductive structure which bears the reproductive pans of a plant
  • it produces seeds and fruits

    ii) Draw a longitudinal section of a labeled diagram of a flower

    iii) Give the functions of the parts of a flower

    Receptacle

  • expanded end of stalk which bears floral parts

    Calyx

  • consists of sepals
  • usually green
  • protect flower in bud

    Corolla

  • consist of petals
  • often colored or scented to attract insects

    Androecium

  • male part of flower
  • consist of stamens
  • each stamen consists of an anther containing pollen sacs
  • anther produces pollen grains which contain male gametes

    Gynaecium

  • female part of flower
  • consists of one or more carpels
  • each carpel contains one or more ovules in an ovary
  • style bearing a stigma extends from ovary
  • ovary contains female gametes which when fertilized become seeds

    iv) What is inflorescence?

  • a group of flowers borne on the same branch (main stalk)

    v) Explain the meaning of the following terms which describe flowers

    Hermaphrodite

  • one with both stamen and carpel
  • most flowers are hermaphrodite/bisexual

    Unisexual

  • have only one of carpel or stamen i.e. either male or female

    Carpelate

  • also called pistilate
  • contains only carpels hence a female flower

    Staminate

  • also called male flower
  • contains only stamens

    Dioecious plants

  • have pistilate and staminate flowers on different plants e.g. pawpaw

    Monoecius plants

  • have pistilate and staminate on one plant
  • however, pistilate and staminate occur at different plants e. g. maize

    Complete flower

  • Has all four parts i.e. Calyx, corolla, androecium and gynoecium

    Incomplete flower

  • does not have all four parts
  • at least one is missing

    vi) Explain the meaning of the following types of ovary

    Superior Q ovary occurs above other floral parts on the receptacle Inferior (epigynous) Q other floral parts arise above ovary on the receptacle

    g) i) What is pollination?

  • transfer of pollen grains from anther of a stamen to stigma of a flower

    ii) Explain the types of pollination

  • self pollination takes place when mature pollen grains of a flower fall on the stigma of the same flower
  • cross pollination takes place when pollen grains of a flower fall on the stigma of another flower of the same species

    iii) State the advantages of pollination

  • healthy offspring
  • leads to variation
  • greater chances of dispersal

    iv) List the agents of pollination

  • wind
  • water
  • insects

    v) How are flowers adapted to wind and insect pollination?

    Insect pollinated flowers (entomophilus)

  • are scented to attract insects
  • have stick stigma for pollen grains to stick on
  • are brightly coloured to attract insects ,
  • presence of nectar to attract insects
  • have nectar guides to guide insects to the nectarines
  • have nectarines to secrete nectar
  • stigmal anthers located inside the flower/tubal/funnel shaped corolla to increase chances of contact by insects
  • sticky/spiny/spiky pollen grains which stick on the body of insects and on stigma
  • large/conspicuous flowers easily seen by/attract insects
  • anthers firmly attached to the filament for insects to brush against them
  • landing platform to ensure contact with anthers and stigma
  • mimicry to attract (male) insects

    Wind pollinated flower (anemophilus)

  • anthers/stigma hang outside the flower to increase chances of pollination
  • the style/filament is long to expose stigma/anthers
  • stigma is hairy/feathery/branched to increase surface area over which pollen grains land/to trap pollen grains
  • pollen grains are smooth/dry/light/small to be easily carried by wind
  • large amount of pollen grains to increase chances of pollination
  • anthers loosely attached to filaments to enable them to sway to release pollen grains
  • pollen grains may have structures which contain air to increase buoyancy
  • flowers have long stalks holding them out in the wind

    vi) State the Ways in which plants prevent self-pollination

  • protandry(anthers/stamens mature first)
  • protagyny (pistils mature first)
  • monoecism (where male and female parts are on same plant but different parts)
  • dioecism(where male and female parts are on different plants)
  • incompatibility (self sterility)
  • heterostyly (styles at different heights)

    vii) Give the characteristics that ensure cross pollination takes place in flowering plants

  • presence of special structures that attract agents of pollination
  • protandry/dichogamy
  • protagyny/dichogamy
  • monoecism
  • self sterility
  • heterostyly

    viii) State the advantages of cross pollination

  • hybrid vigour
  • less prone to diseases
  • promotes genetic variation
  • greater evolutionary potential

    h) i) What is fertilization?

  • Fusion of male and female gametes to form a zygote

    ii) Describe how fertilization takes place in a flower

  • this follows pollination
  • pollen grain is deposited on the stigma
  • pollen grain sticks to the surface of the stigma
  • the surface of the stigma produces a chemical substance which stimulates the pollen grain to produce a pollen tube/to germinate
  • the pollen tube grows through the style tissues on which it feeds until it enters the ovary
  • the generative nucleus divides into two giving two male nuclei
  • embryo sac contains eight nuclei i.e. two synergids, egg cell, two polar nuclei and three antipodal cells
  • the pollen tube enters the embryo sac through the micropyle and one of the male nucleus fuses with the egg cell/ovum to form a zygote
  • the other male nucleus fuses with the two polar nuclei to form the triploid nuclei/endosperm)food storage used by developing embryo)
  • the pollen tube nucleus in the pollen tube disintergrates soon afterwards
  • this process is referred to as double fertilization
  • zygote grows into an embryo containing plumule, radicle and cotyledons

    iii) What is double fertilization?

  • there are two male nuclei entering embryo sac
  • one fuses with the ovum to form a zygote, while the other fuses with the polar nuclei to form a triploid primary endosperm nucleus
  • therefore there are two fusions at fertilization

    iv) Name the changes that Occur in a flower after fertilization

  • petals, stamen, calyx and style wither
  • ovary wall changes into pericarp
  • intergument changes in to seed coat/testa
  • zygote changes into embryo ‘(by mitosis)
  • primary endosperm nucleus changes into endosperm
  • whole ovule changes in to seed
  • ovary develops and grows into fruit(under the influence of gibberrellic hormone)

    b) i) Distinguish between a fruit and a seed

  • a fruit is a fertilized ovary and has two scars
  • a seed is a fertilized ovule and has one scar

    ii) How is a seed formed?

  • after fertilization, zygote grows into an embryo, primary endosperm nucleus developed into endosperm, interguments harden to form testa, hence the whole ovule becomes the seed
  • the seed loses water to become drier
  • the seed has plumule, radicle, seed leaves called cotyledons, a microphyle and a scar

    iii) Draw a labeled diagram of a seed

    iv) Describe the main parts of a seed

    Testa

  • also called seed coat
  • a tough outer covering which protects the seed from insects, bacteria etc
  • segment is the membrane inside the testa

    Hilum

  • a scar
  • spot where the seed was attached to the fruit or pod

    Micropyle

  • small hole through which water and air enter the seed

    Radicle

  • embryonic root
  • grows into the shoot system

    Cotyledons

  • embryonic leaves
  • store food for the germinating seed i.e. for plumule and radicle
  • when plumule and radicle grow, they use food stored in the cotyledon
  • in some seeds food is stored in the endosperm

    v) Draw a labeled diagram of a fruit

    vi) How is a fruit formed?

  • one of the organs that remains on the plant after pollination and fertilization is the ovary
  • within the ovary, the developing embryo produces special chemical substances that stimulate the young ovary
  • these substances also signal the start of the formation of the fruit, which is a mature ovary
  • the fruit may contain one or more seeds
  • during fruit formation the ovary increases in size while ripening or maturing
  • a true fruit is formed from the ovary of a flower after fertilization
  • it has two scars(style scar and stalk scar) and contains seeds
  • some seeds are not formed from the ovary of a flower
  • some other parts of a flower develop to form a fruit
  • such fruits are called false fruits

    vii) Explain the importance of fruits in the survival of plants

  • protect the seed against dessication, predators and adverse conditions
  • aid in seed dispersal by attracting agents of dispersal
  • stores food for the plant

    vii. Distinguish between parthenogenesis and parthenocarpy

  • parthenogenesis is development of new animals from unfertilized eggs
  • paithenocarpy is development of a fruit without fertilization

    iv) state the differences between a seed and a fruit

    A Seed

  • fertilized ovule
  • attached to the placenta through funicle
  • one scar called hilium
  • has seed coat/testa
  • seed wall undifferentiated

    fruit

  • fertilized ovary
  • attached to branch through a stalk
  • two scars (style scar and stalk scar)
  • has fruit wall/pericap
  • fruit wall is differentiated

    j. i) What is placentation?

  • arrangement of ovules within the plant ovary

    ii) Explain the following types of placentation

    Marginal

  • placenta appears as one ridge on ovary wall
  • ovules are attached to placenta in rows e. g. peas in a pod

    Basal

  • placenta formed at the base of the ovary With numerous ovules attached to it

    Parietal

  • edges of carpels fuse together
  • dividing Walls disappear, leaving one
  • have numerous seeds e. g. passion fruit
  • placenta of each carpel appears as ridge on ovary Wall

    Axile

  • edges of carpels fuse together to form a single central placenta
  • numerous ovules arranged on placenta
  • ovary divided into a number of loculi by walls of the carpel e. g.

    Free central placentation

  • edges of carpels fuse together
  • dividing was disappears leaving one loculus
  • placenta appears at base of ovary
  • has numerous ovules

    c) i) How are fruits grouped?

    Simple fruits

  • formed from a single flower or one ovary e. g. mango

    Aggregate fruits

  • consists a group of ovaries that appear on a common receptacle e. g. strawberry

    Multiple (compound) fruits

  • formed from several flowers whose ovaries fuse together after fertilization
  • form a bunch e. g. pineapple, figs
  • are always false fruits

    ii) What are succulent fruits?

  • also called fleshy fruits
  • all or part of pericarp (fruit wall) becomes juicy

    iii) Give types of juicy fruits

    Berry

  • has many seeds
  • whole pericarp is succulent e. g. orange, tomato, pawpaw

    Drupe

  • only one seed
  • pericarp divided into three layers i.e. epicarp, mesocarp(juicy) and endocarp(hard) eg mango and coconut

    Pome

  • juicy part is swollen receptacle
  • is usually a false fruit
  • example is a pear

    iv) What are dry fruits?

  • have a pericarp that is dry, hard and Woody
  • either dehiscent or indehiscent
  • called dry because they are not succulent

    v) What are dehiscent fruits?

  • split open when ripe to release seeds
  • contain many seeds

    vi) Give types of dehiscent fruits

    Legumes

  • split along two edges
  • are usually pods e.g. beans, peas, crotolaria

    Follicle

  • split on one side only e. g. Sodom apple

    Capsule

  • has several lines of Weakness/sutures
  • open in many places e.g. castor oil, cotton

    vii) What are indehiscent fruits?

  • non-splitting fruits
  • usually one seeded only

    ii) Give main types of indehiscent fruits

    Nut

  • pericarp woody, hard and thick e.g. cashew

    Achene

  • has thin, tough pericarp e.g. sunflower

    d) i) What is seed and fruit dispersal?

  • spreading of seeds and fruits away from parents so as to settle where conditions are suitable for their germination

    ii) Why is dispersal of seeds and fruits necessary?

  • prevent overcrowding
  • reduces competition for space, nutrients and light
  • colonization of new areas is made possible
  • to increase chances of survival
  • to prevent inbreeding
  • to avoid extinction due to over competition for the necessities

    iii) Explain how seeds and fruits are adapted to various methods of dispersal

    Adaptations for wind dispersal

  • they have wings, feathers or hair-like structures to increase surface area for wind to carry them easily/buoyancy
  • seeds/fruits are loosely attached on the stalks so that they can easily be released and carried away by wing
  • seeds/fruits are generally light and small sized to be easily carried by wind
  • some seeds/fruits have parachute-like structures to be easily carried b wind
  • some have censor mechanism where seeds and fruits are borne on long stalks that are loosely attached which allows swaying so that movements of capsule by wind releases the seeds

    Water dispersal seeds

  • seed mesocarp has air spaces thus light/buoyant to float hence carried by water
  • they have waterproof cover and tough pericarp protects seeds from getting soaked
  • fibrous and spongy mesocarp to easily float

    Animal dispersal seeds

  • presence of hooks for attachment to animals thus carried to other parts
  • fruits are brightly coloured, succulent and scented to attract animals
  • seed coats are hard and resistant to digestive enzymes hence seeds are dropped away from mother plant
  • large in size or borne on clusters to be easily seen

    Self dispersal/explosive

  • self opening seeds
  • they have lines of weakness called sutures for violent opening thus scattering seeds away from parent plant

    5. a) i) Distinguish between external and internal fertilization in animals

  • in external fertilization fusion of the male and female gametes takes place outside the body of the female e. g. amphibians and fish
  • in internal fertilization union of gametes occurs inside the body of the female

    ii) State the advantages and disadvantages of external fertilization

    Advantages

  • large numbers produced therefore many offspring per breeding season
  • female does not suffer gestation stress
  • mother does not need to care for the young except in a few species
  • the surviving individuals are highly selected for better survival

    Disadvantages

  • many predators surround the eggs before and after fertilization
  • fewer chances of fertilization/a lot of gametes wasted
  • embryo development at mercy of environment
  • large numbers of female gametes are required therefore female gets much exhausted

    iii) State the advantages and disadvantages of internal fertilization

    Disadvantages

  • number of gametes fewer hence less number of offspring
  • less adapted for sudden change of environment after birth
  • in mammals females suffer gestation stress

    Advantages

  • more chances of fertilization
  • fewer predators of oval/fertilized egg protected in females body
  • Stable internal environment
  • fewer gametes required

    iii) Give a reason why it is necessary for frogs to lay many eggs

  • to increase chances of survival/fertilization

    iv) Compare external and internal fertilization

    b) i) Draw and label the human male reproductive system

    ii) Describe how the mammalian male reproductive system is adapted to perform its functions

    Penis

  • is highly vascularised/spongy
  • has a sensitive glands
  • becomes erect to allow entry into the vagina

    Scrotum

  • contains the testes outside the body on whose walls the process of spermatogenesis takes place
  • the process is favored by lower temperature
  • it contains sertoli cells which nourish sperms until they are mature

    Epididymis

  • long and coiled for the purpose of sperm storage

    Vas deferens

  • muscular
  • upon contraction pushes sperms out and allows ejaculation

    Gametes

  • produced in large numbers to increase chances of fertilization
  • the sperms have a tail for swimming/large number of mitochondria to provide energy/allow swimming to reach the egg

    Accessory glands

  • are seminal vesicle, Cowper’s gland and prostate gland
  • they produce seminal fluid to provide a medium/nutrients for sperms to swim

    iii) How is the sperm adapted to perform its function?

  • acrosomes contain enzymes to digest egg membrane
  • nucleus contains genetic material
  • mitochondria produce energy to move the tail back and forth the lashing movement of the tail enables the sperm to move/propulsion in fluid medium towards the egg
  • it is streamlined for faster/easier movement/swimming to meet the egg

    c) i) Draw and label the human female reproductive system

    ii) Describe how the various structures of the human female reproductive system are adapted to their function

    Ovaries

  • have several graafian follicles that develop and burst open to release/produce mature ova
  • secretes sex hormones(oestrogen) which initiate/control development of secondary sexual characteristics
  • produce hormones oestrogen and progesterone which prepare the uterus for implantation and subsequent nourishment of the embryo

    Oviducts (Fallopian tube)

  • are thin narrow and tubular to increase flowing speed of semen containing sperms
  • are funnel shaped on the end next to ovary which enables them to receive the ovum
  • their lining contains cilia which propel the ovum towards the uterus
  • has peristaltic muscles that enable movement of zygote/ovum to the uterus for implantation
  • is fairly long to increase surface area for fertilization

    Uterus

  • is muscular for protection of developing embryo
  • has elastic wall that allows growth and development of foetus/embryo
  • has a highly vascularised endometrium that provides nutrients/gaseous exchange to developing embryo

    Cervix

  • has valves that close the lower end of the uterus to ensure continued pregnancy during gestation period
  • is capable of dilating ~
  • has narrow entrance/neck-like entrance to uterus that enables quick swimming of sperms to uterus
  • has suction mechanism that draws up/pulls sperms into uterus
  • has a “W” shape that fits well with the glands of the penis to ensure sperms are deposited at the right point

    Vagina

  • is elastic and muscular to enable good accommodation or penetration of the penis thus proper deposition of sperms and for easy parturition
  • allows menstrual flow
  • has sensitive labial walls which secrete/produce lubricating substances that
  • ensure/enable/facilitate good coition
  • capable of considerable enlargement, due to elastic muscles, to accommodate baby during parturition

    Clitoris

  • has sensitive cells for orgasm

    iii) Explain how the ovum is adapted to its function

  • nucleus contains genetic material
  • ventelline membrane encloses plasma membrane which encloses yolky cytoplasm
  • yolky cytoplasm provides nourishment
  • jelly coat protects ovum against dehydration

    iv) Explain the differences between sperm and ovum

    d) i) Explain the process of fertilization

  • a process whereby the egg and sperm are brought together and fuse to form a zygote
  • occurs in the fallopian tube after copulation
  • sperm head penetrates the outer coat of the ovum While the tail remains outside
  • penetration is due to reaction of acrosome
  • acrosome digests the vitelline membrane
  • thereafter a zygote is formed
  • zygote which is diploid undergoes rapid cell division to form a mass of cells called blastocyst
  • after fertilization a membrane forms around the ovum to prevent further entry of sperms
  • blastocyst eventually develops into an embryo

    i) Explain the process of implantation

  • this is the embedding and attaching of the embryo in the uterine wall/endometiium
  • implantation marks the beginning of pregnancy
  • sometimes implantation occurs in the oviduct Wall which is abnormal and results in ectopic pregnancy which is fatal
  • the outer wall of the blastocyst develops finger like projections which project into the uterine wall for attachment
  • the projections are called villi
  • the villi and endometrium develop into an organ that is called the placenta
  • the embryo is attached to the placenta through a cord called the umbilical cord

    State the functions of umbilical cord

  • it contains blood vessels umbilical artery, iliac arteries and umbilical veins)
  • it joins the placenta to the embryo
  • passage for nutrients other
  • passage of excretory substancess from foetus to mother for final discharge
  • gaseous exchange
  • passage of antibodies from mother to foetus, for protection of foetus against diseases

    State the role of placenta

  • exchange of gases between mother and foetus
  • exchange of nutrients and nitrogenous wastes
  • anchorage/attachment of foetus
  • produces hormones (oestrogen and progesterone)

    e) i) What is gestation period?

  • time taken from fertilization to birth/pregnancy

    ii) Explain the functions of the membranes associated with placenta

    Chorion

  • surrounds the embryo
  • has fingerlike projections that attach embryo to the uterus

    Amnion

  • contains amniotic fluid
  • fluid surrounds embryo
  • protects embryo from mechanical injury by acting as shock absorbers
  • fluid also protects embryo from dehydration
  • distributes pressure equally over embryo

    Yolk sac

  • surround the yolk
  • produces blood cells for embryo until its own liver is able to perform the task

    Allantois

  • present only for a short time
  • removes and store waste material
  • it eventually becomes the umbilical cord

    iii) Explain the events that take place to facilitate parturition

  • near birth the placenta produces less progesterone
  • oxytocin hormone is produced by posterior lobe of pituitary gland
  • because progesterone level has decreased the uterus becomes sensitive to oxytocin
  • oxytocin causes the contraction of the uterus (myometrium)
  • these contractions are called labour pains
  • just before parturition the head turns downwards
  • the contractions eventually push the baby through the vagina
  • amnion breaks and amniotic fluid is released
  • oxytocin dilates the cervix
  • foetus is expelled through cervix with head coming out first
  • finally the whole infant comes out
  • the umbilical cord is cut and the placenta is expelled as afterbirth

    iv) State the reasons why later in pregnancy the ovary will b e removed without disturbing the pregnancy

  • corpus luteum in the ovary secretes progesterone which maintains pregnancy and development of foetus after conception
  • after four months pregnancy is maintained by progesterone from the placenta

    f) i) What are secondary sexual characteristics

  • Characteristics (physiological and anatomical) that start developing at puberty due to the influence of male and female hormones

    ii) State the main secondary changes in

    Boys

  • deepening of the voice
  • growth of hair on face, pubic part, chest, legs
  • penis and testes become bigger
  • muscular development
  • sperm production begins at puberty and may continue throughout life

    Girls

  • growth of hair on pubic part and armpits
  • widening/enlargement of hips
  • development of breasts
  • menstrual cycle starts as ovaries mature
  • body acquires extra fat

    iii) Describe the role of hormones in secondary sexual characteristics in

    Boys

    Follicle stimulation hormone (FSH)

  • from pituitary
  • stimulates production of androgens(male hormones) mainly testosterone by testis

    Testosterone

  • secondary sexual characteristics

    Girls

    FHS

  • from pituitary
  • development of follicles
  • stimulates oestrogen production by ovary

    LH

  • from pituitary
  • ovulation
  • stimulates release of progesterone by ovary

    Oestrogen

  • stimulates release of LH
  • secondary sexual characteristics

    Progesterone

  • also from placenta
  • sustains pregnancy as it inhibits prolactin and oxytocin during pregnancy

    Prolactin

  • milk formation

    Oxytocin

  • parturition
  • milk ejection

    g) i) What is menstruation?

  • vaginal discharge due to disintegration of endometrium

    ii) Describe the role of hormones in the human menstrual cycle

  • it is controlled by sex hormones which are responsible for the onset of secondary sexual characteristics and also control of the menstrual cycle
  • the onset is signaled by discharge of blood/menses 14 days following the start of menstruation
  • anterior lobe of pituitary gland secretes follicle stimulating honnone(FSH)
  • Follicle stimulating hormone causes graafian follicle to develop in the ovary. It also stimulates tissues of the ovary/wall (theca) to secrete oestrogen
  • oestrogen causes repair/healing of uterine wall
  • oestrogen stimulates anterior lobe of pituitary to produce luteinising hormonge (LH)
  • LH causes ovulation. It also causes graafian follicle to change into corpus luteum. LH stimulates corpus luteum to secrete progesterone
  • Progesterone causes proliferation/thickening of uterine wall
  • Oesterogen/progesterone inhibits, the production of FSH by anterior lobe of pituitary, thus no more follicles develop and oestrogen production reduces
  • In the next two weeks progesterone level rises and inhibits production of LH from anterior lobe of pituitary“
  • The corpus lutetium stopssecreting progesterone and menstruation occurs when the level of progesterone drops
  • Anterior lobe of pituitary starts secreting FSH again.

    iii) What is menopause?

  • end of ovulation in women
  • occurs after age of 45 years
  • does not occur in males

    h) Explain the symptoms, methods of transmitting and prevention (control) of the following sexually transmitted diseases

    i) Gonorrhea

  • caused by a bacterium called neisseria gonorrhea
  • transmitted through sexual intercourse,
  • infects urethra and vaginal tract (epithelia)
  • Symptoms include pain, discharge of mucus and bad smell (females)
  • Effects include sterility, heart diseases, blindness of foetus and arthritis
  • Treatment by antibiotics
  • Control and prevention by proper sexual conduct

    ii) Herpes

  • notably Herpes simplex and H. genitalis
  • caused by virus which attacks genitalia
  • symptoms are painful sores in genitalia, skin lesions
  • transmitted in saliva, sexual intercourse and injection by drug addicts
  • no treatment

    iii) Syphilis

  • caused by bacterium called Treponema palladium
  • symptoms are painless wounds in genitalia
  • attack genitalia, nervous system, lips
  • treated by antibiotics

    iv) Trichomoniasis

  • caused by plasmodium called trichomonas
  • attacks reproductive tract
  • symptoms are itching and discharge of pus from the genitals
  • treated by antibiotics

    v) Hepatitis

  • Viral disease
  • Affects the liver
  • Transmitted through sexual intercourse
  • No known treatment

    vi) Candidiasis

  • caused by fungus called candida albicans
  • transmitted through sexual intercourse
  • symptoms include itching urethra, and vaginal discharge (odourless)
  • controlled by personal hygiene, early treatment and responsible sexual behavior

    vii) HIV/AIDS

  • caused by HIV virus
  • transmitted by sexual intercourse, blood transfusion, sharing piercing instruments from infected mother to foetus, infant and baby
  • symptoms include fever, swollen lymph nodes, night sweating, cough, weight loss, fatigue, loss of appetite, diarrhea, headache, a opportunistic infections and tumors
  • Control by responsible sexual behaviour, education, screening blood for transfusion and using sterile piercing instruments.

    6. a) Define the terms

    i) Growth

  • an irreversible change in size of a cell, organ or whole organism
  • growth is due to synthesis of protoplasm or extracellular substances

    ii) Development

  • refers to a series of changes which an organism goes through in its lie cycle
  • during development both qualitative and quantitative changes take place(involves differentiation)

    iii) Differentiation

  • refers to changes in which the cells of the body undergo and become specialised to perform specific functions

    b) i) Differentiate growth in plants and animals

    More differences between Plant Growth and Animal Growth

    Plant Growth:

    1. Growth continues throughout the life of the plant.
    2. Here the growth involves increases in the number of parts.
    3. Growth take place during definite seasons.
    4. Growing pattern is distinct each species.
    5. Plant possess well-defined growing regions.
    6. A seedling does not resemble an adult plant.
    7. A juvenile stage with distinct may be present in the life-history of a plant.
    8. Growth is by addition of new parts ahead or around the older ones.

    Animal Growth:

    1. Growth takes place for definite periods before maturity.
    2. Here it does not involve increase in the number of parts.
    3. Each species has a distinct season for growth.
    4. Growing pattern is absent.
    5. They have no such defined growing regions.
    6. The young one are identical to adults except in the body size and sexual maturity.
    7. A juvenile stage with different morphology does not occur in higher animal.
    8. Growth is diffused by all round increases in different organs of the body.

    ii) List the processes involved in growth

  • assimilation
  • cell enlargement
  • cell division(by mitosis)

    iv) List the parameters used to measure growth

  • height/length
  • dry Weight
  • number of individuals
  • volume
  • leaf area of plant

    iv) Name the patterns of growth in organisms

  • allometric and isometric
  • limited and unlimited
  • discontinuous growth

    c) i) Name the different types of growth curves

  • sigmoid curve(normal growth curve)
  • intermittent growth curve

    ii) Draw a sigmoid growth curve and explain its different phases/stages

    A-lag phase

    - Slow growth rate at first

    Organism adapting to the environment

    B-exponential phase

    - organisms already adapted

    - first growth due to birth rate that is higher than death rate

    C- Stationery phase (plateau)

    - Birth rate equals death rate (equilibrium)

    Lack of nutrients, accumulation of toxic waste products

    D-phase of decline

    - due to depletion of nutrients, accumulation of toxic wastes, lack of space

    - some individuals old hence not reproducing

    - death rate higher than birth rate

    iii) Draw an intermittent curve and explain the various stages

    A-growth

    B-no growth

    C- moulting/ecdysis

    - seen in arthropods

    - growth in in arthropods is intermittent(takes place during some time only because their hard cuticles (exoskeleton) does not expand to cause growth

    - the cuticle must be shed off first to allow further growth

    - the shedding is called ecdysis or moulting

    - when moulting has taken place animal grows but growth stops when the exoskeleton hardens again

    d) i) What is seed dormancy?

    - A state where a viable seed is incapable of germinating when all conditions are favorable.

    ii) State the biological importance of seed dormancy

    - gives embryo time to reach maturity

    - gives time for dispersal

    - allows plant to survive adverse conditions

    iii) State the factors which cause seed dormancy

    Internal factors

    - presence of abscisic acid/ABA/ presence of germination inhibitors

    - embryo not fully developed

    - absence of hormones/enzymes/inactivity of hormones/enzymes/gibberellins/cytokinins

    - impermeability of seed coat

    External factors

    - unsuitable temperature

    - absence of light

    - lack of oxygen

    - lack of oxygen

    - lack of water

    iv) Give the conditions necessary to break seed dormancy

    - scarification/scratching to make seed coat impermeable

    - vernalisation/cold treatment in some seeds like wheat

    - burning/nicking/expose to heat e.g. wattle seeds

    - destruction of germination inhibitors

    e) i) What is seed germination?

    - process by which a seed develops in a seedling

    ii) What is viability

    - ability of a seed to germinate

    iii) Discuss the various conditions necessary for the germination of seeds

    Water

    - medium for enzymatic activity

    - hydrolysis of food into simpler substances

    - medium of transport

    - softens the seed

    - acts as a solvent

    Air

    - in form of oxygen

    - oxygen is used for respiration/oxidation of food to release energy

    Suitable (optimum) temperature

    - activates enzymes involved in mobilization of food reserves

    Enzymes

    -breakdown and subsequent oxidation of food

    - conservation of hydrolyzed food products in to new plant tissues

    Viability

    - only viable seed are able to germinate and grow

    iv) Name and describe the types of germination

    Epigeal

    cotyledons are brought above the ground level during germination due to elongation of the bean seed that elongates to bring about epigeal germination

    Hypogeal

    - the cotyledons remain below the surface during germination due to elongation of epicotyl e.g maize

    vi) Account for the loss in dry weight of cotyledons in a germinating bean seed

  • food stored is mobilized/used up for respiration and growth

    vii) Describe the physiological changes that occur in a seed during germination

  • in presence of oxygen, optimum temperature and water, food reserves in the seed are hydrolysed or broken down into soluble diffusible form by enzymes
  • soluble food diffuses to the growing embryo
  • oils and carbohydrates provide energy
  • simple sugars converted to cellulose to form cell wall
  • amino acids make protoplasm
  • seed develops plumule and radicle hence germinates

    viii) Explain the biological significance of cotyledons being brought above the ground in epigeal germination

  • cotyledons have inadequate food
  • they are brought above the ground to acquire chloroplasts to carry out photosynthesis
  • before the formation of foliage leaves to supplement food supply required for growth during germination

    f) i) Distinguish between primary and secondary growth

    Primary growth

  • occurs at the apical (shoot and tip) apices regions where meristematic cells occur
  • causes plant elongation since cells divide by mitosis

    Secondary growth

  • occurs at the cambium meristems
  • Increases width (girth) of the stem

    ii) What are meristems

  • dividing cells
  • meristem means they are dividing

    iii) State the characteristics of meristematic cells

  • dense cytoplasm
  • thin cell walls
  • absence of vacuoles/cell sap

    iv) State the location and function of the following meristematic tissues

    Apical meristem

  • located at tips of roots and shoots
  • increase length of stem and roots/primary growth

    Intercalary meristem

  • found at bases of internodes
  • responsible for elongation of internodes and increase in leaf sheath in grasses

    Lateral meristems

  • found near the periphery of stem and root
  • responsible for secondary growth/growth in girth of stem and root/lateral growth
  • called cambium and constitute vascular and cork cambium

    v) Describe primary growth

  • occurs at tips of shoots and roots in the meristematic tissues of apical meristem
  • at the apex there is a zone of cell division/mitosis
  • cells elongate at elongation zone
  • the elongated cells differentiate at the region of differentiation resulting in increase in size
  • in the stems meristems give rise to leaf premodia which envelop the apex to form a bud
  • the bud protects the delicate inner cells
  • in roots the meristem is protected by root cap
  • after cells differentiate the form permanent tissues

    vi) Describe secondary growth in plants

  • also called secondary thickening '
  • only occurs in dicotyledonous plants that have cambium
  • monocotyledonous plants do not undergo secondary growth because they lack intervascular cambium
  • cambium cells divide to produce more cells on either side of the cambium
  • cells produced to the inside become secondary cambium
  • cells produced to the outside become secondary phloem
  • division of cambium cells occurs yearly producing new rings of secondary phloem and secondary xylem each year
  • intervascular cambium(cambium between vascular bundles) divide to form secondary parenchyma, thereby increasing growth of medullary rays
  • much more xylem is formed than phloem, thus pushing phloem and cambium ring outward
  • the rate of secondary growth is depended on seasons(rains) resulting in annual rings
  • cork cambium is located beneath epidermis ad is responsible for secondary thickening of the bark of perennial plants
  • cork cambium divides to form new cork(bark) tissues to accommodate increased growth on outside and secondary cortex on the inside
  • Cork cells (cells of the bark) are loosely parked at some points to form lenticels for gaseous exchange.

    vii) State the significance of secondary growth

  • increase girth or circumference of trees
  • annual rings which show seasonal growth can be used to tell the age of trees

    g) i) Describe one method which can be used to measure the average growth rate of a single leaf of a plant

    Either

    - chose/identify a young leaf (just unfolded)

    - use the same leaf throughout

    - measure (total) length of (whole) leaf

    - record

    - repeat at regular intervals until no more change occurs/constant length

    - average rate of growth is equal to total increase in length divided by the period taken to achieve full length

    Average rate of growth = total increase in length divide by period taken to achieve full length

    OR

    - choose/identify a young leaf(just unfolded)

    - use the same leaf throughout

    - trace the outline on a graph paper and work out the area

    - record

    - repeat at regular intervals until regular area

    - average rate of growth equals to total increase in area divided by the period of time taken to achieve full area

    Average rate of growth = total increase in area divide by period of time taken to achieve final area

    i) Describe how the growth of a root can be determined

    Materials

    - fine thread, marking ink, germinating bean seedlings, blotting paper, ruler marked in millimeters, pins, cork, a boiling tube and moist cotton wool

    Procedure

    - dry seedlings using blotting paper

    - place inside against the ruler marked in mm

    - dip the fine thread in waterproof ink

    - mark the radicle at equal intervals

    - pin the seedling to the cork

    - suspend the seedling into the boiling tube containing moist cotton wool

    - allow the seedling to grow for two days/some time observe the intervals with the marks

    - record your observations the Widest intervals are found in the region just behind the tip indicating/showing region of greatest growth

    iii) A boy hammered a nail in the bark of a tree at a height of 1.5 metres above the ground Four years later, the nail was found at the same height although the tree had grown 3 meters taller. Explain the above observation

    The nail was hammered at a point where vertical growth had stopped/further growth was confined to increase in width/diameter.

    Vertical growth is confined to tips/apex/vertical apical meristem

    h) i) Describe the role of hormones in growth and development of plants

  • indole acetic acid/IAA/ auxins
  • Cell division/increase in cell division
  • Tropic responses
  • Cell elongation/increases in ell elongation
  • Development of abscision layer
  • Growth of ovaries into fruits/parthenocarpy/initiates flowers
  • Inhibits growth of lateral buds/produces apical dominance
  • Stimulates adventitious/lateral roots ‘
  • Gibberellins (Gibberellic acid/GA3
  • Promote cell elongation/rapid cell division/increase in length of the internodes
  • Promote fruit formation without fertilization/parthenocarpy
  • Reduces root growth
  • Breaks seed dormancy/promotes germination

    Cytokinnins (Kinnins/Kinnetin/Zeatin)

    - breaks dormancy

    - promotes flowering

    - promotes cell division

    - stabilizes protein and chlorophyll

    - promotes root formation on a shoot

    - low concentration encourages leaf senses

    - normal concentration increases cell enlargement in leaves

    - stimulates lateral bud development

    Ethylene (ethynel C2H4)

    - accelerates ripening in fruits

    - encourages fruit fall/leaf fall

    - induces thickening in stern/inhibits stem elongation

    - promotes flowering (in pineapples)

    - promotes germination in certain seeds

    Abscisic acid (ABA) abscisin hormone/dormin)

    - causes bud dormancy

    - encourages fruit/leaf fall

    - high concentration causes closing of stomata

    - causes seed dormancy

    - inhibits cell elongation

    Traumatin

    - heals wounds by callous formation

    Florigen

    - promotes flowering

    ii) State the applications of plant hormones in agriculture

    - induce root growth in stem cuttings

    - selective weed killers

    - encourage sprouting of lateral buds

    - breaking seed dormancy

    - induce parthenocarpy

    - accelerate ripening of fruits

    - promote flowering

    - cause dormancy

    iii) Explain apical dominance

    - a phenomenon whereby production of auxins by a growing apical bud of a shoot inhibits growth of lateral buds

    - this inhibition is due to high concentration of auxins (indoleacetic acid/IAA) in apical bud

    - removal of terminal/apical bud causes development and sprouting of several buds which later develop into branches

    - applied in pruning coffee, tea and hedges

    - this leads to more yield

    iv) Describe the role of hormones in the growth and development of animal

    somatotrophin (growth hormones)

    - from anterior pituitary

    - promotes cell division

    - overproduction causes gigantism

    - underproduction causes dwarfism

    Thyroxine

    - promotes growth and metamorphosis

    - underproduction leads to a child becoming a cretin (mentally retarted)

    Androgens

    - in males

    - growth of male reproductive organs

    Oestrogen

    - in females

    - growth of female reproductive organs

    Ecdysone

    - in arthropods

    - moulting (ecdysis)

    t) i) What is metamorphosis?

    - change in form during which there are changes in structure and function in body of organism

    - prepares organism for life in a different habitat

    ii) Explain complete metamorphosis

    radical changes in the body during the life cycle of an organism

    called holometabolous development

    example is egg larva pupa adult (imago)

    occurs in animals such as butterfly and bee

    iii) What is the significance of each of the four stages in complete metamorphosis?

    Larval stage

    - feeding takes place

    - larva is quite different from adult

    - larva sheds its cuticle (exoskeleton) several times to emerge as pupa

    - dispersal stage avoids overcrowding

    Pupa

    - enclosed in a case called puparium (cocoon)

    - no feeding

    - organ formation takes place

    Adult

    - emerges from puparium

    - reproductive stage of the life cycle

    iv) Describe incomplete metamorphosis

    - called hemimetabolous development

    - changes are gradual

    - eggs develop into nymphs which develop into adults

    - nymph resembles adult but are sexually immature

    - a nymph moults several times as some parts develop before it becomes an adult

    - stage of development between one moult and another is called instar

    - occurs in insects such as locust and cockroach

    v) Name the hormones that control metamorphosis in insects

    - brain hormone responsible for moulting because it simulates production of ecdyson (moulting hormone)

    - ecdysone(moulting hormone) causes moulting

    - juvenile hormone causes moulting in larvae

    vi) State the advantages of metamorphosis in the life of insects

    - the adult and larvae exploit different niches

    - do not compete for food

    - pupa cam survive adverse pupa can survive adverse conditions eg-feeding stage

    - dispersal prevents overcrowding

    KCSE Biology Questions and Answers Form 4 - Biology Form Four Notes

    Biology Questions and Answers Form 4

    Biology Form 4 Notes

    a) i) Define the term genetics

  • the study of heredity(inheritance) and variation or study of mechanisms by which characteristics are passed from parents to offspring

    ii) List some characteristics which are inherited

  • size

  • height/length

  • colour/type

  • shape

  • yield

    iii)State the importance of genetics

  • helps to explain differences between organisms of the same species

  • helps to explain the transmission of characters from generation‘ to generation

  • improvement in livestock

  • improvement in crops

  • can be used to treat some difficult diseases

    b) i) Explain the meaning of the following terms

    Heredity

  • the resemblance among individuals related by descent

  • transmission of traits from parents to offspring

    Trait

  • also called character

  • A character of the organism e.g. type of ear, colour of eyes, height, yield etc.

    Gene

  • unit of inheritance

  • it is the heredity factor which transmits traits from parents to offspring

  • genes are located at ‘fixed points on chromosomes

  • each point is called a locus (loci)

    Allele

  • genes can exist in a series of alternative forms at a particular locus

  • allele refers to alternative forms of genes controlling a particular characteristic

    Chromosomes

  • threadlike structures found in nuclei of all plants and animals

  • they carry genes which are hereditary materials

  • they consist of substances called DNA and proteins called histosones

    DNA

  • deoxyribonucleic acid

  • substances that make up chromosomes

  • double helix(strand) molecule that contains genes

  • DNA consists of nucleotides

  • A nucleotide consists of an inorganic phosphate, ribose sugar and a base

  • There are four bases in a DNA molecule i.e. Adenine(A), guanine(G), thymine(T) and cystosine (C)

  • Ribose sugar has four bases attached to it i.e. adenine, cystosine, guanine and thymine

  • Adenine pairs with thymine while guanine pairs with cystosine

  • Nucleotide initiates and controls protein synthesis

    ii) List the types of chromosomes

  • somatic (body) chromosomes also called autosomes

  • sex chromosomes (related to reproduction)

    c) i) What is variation?

  • sequence of differences occurring among individuals of the same species

    ii) State the causes of variation in organisms

  • random assortment of genes during meiosis

  • crossing over

  • fertilization

  • doubling of chromosome numbers(mutation)

  • environmental conditions

    iii) Name the types of variation

  • Continuous variation (differences not clear cut) e. g. height, length, weight, skin colour, intelligence etc. They are quantitative and show intermediates

  • discontinuous variation(differences are clear cut) e. g. ability to roll tongue, ABO blood grouping system, RH factor, patterns of fingerprints, and ability to taste PTC. They are qualitative and have no intermediates

    iv) Explain the following terms

    Acquired characteristics

  • they are as a result of adaptations due to the environment and are not inherited Inherited characteristics

  • are passed down to offspring during sexual reproduction

    Genotype

  • genetic constitution of an individual/genetic makeup

    Phenotype

  • characteristics of an individual observed or discernible by other means i.e. observable character

    Dominant gene (character)

  • expressed in the phenotype when homozygous or heterozygous

    Recessive gene

  • only expressed in homozygous state

    Homozygous

  • when two alleles are identical e.g. LL,ll

    Heterozygous

  • when two alleles are different at a particular locus e.g. Ll

    F1 and F2

  • Fl means first filial generation i.e. the first generation produced when two varieties can be crossed

  • F2 means second generation i.e. product of offspring or from F1 generation

    d) i) Explain Mendels first law of inheritance

  • also called law of segregation

  • it states that genes are responsible for the development of individual characters

  • these characters are transmitted individually without any alterations

  • Only one character from a contrasting pair can be carried in a gamete, hence only one character can be inherited.

    ii) Give an example of this law

  • In an experiment, Drosophila (fruit fly) with long wings were crossed with those having short wings. Assume letter L denotes gene for wing size. The gene for long wings is dominant to that for short wings

  • the genes for dominant are LL and for recessive ll.

  • State the expected results for the first cross

    iii) What is monohybrid inheritance?

  • when inheritance of one character is studied one at a time e.g. wing size only

  • the F2 generation (when selfed) always gives a phenotypic ratio of 3:1 and a genotypic ratio of 1:2:1 in a complete dominance

    i) What is complete dominance?

  • refers to where only one dominant character is expressed while the other character which is recessive is not expressed in the heterozygous state e. g. the case of wing size above e) i) What is meant by co dominance?

  • When genes produce independent effects when heterozygous/none of the genes is dominant over the other/where two or more alleles does not show complete dominance/recessiveness due to the failure of any allele to be dominate in a heterozygous condition.

    ii) Give an example of co dominance

    In a certain plant species, some individual plants may have only white, red or pink flowers. In an experiment a plant with white flowers was crossed with a parent with red flowers. Show results of Fl generation. Use letter R for red gene and W for white gene.

    If the plants form F1 were selfed, work out the phenotype ratio for the F2 generation Phenotypic ratio 1 red:2 pink: 1 white

    Genotypic ratio 1:2:1

    f) i) What is a test cross?

  • A cross between an individual showing a character for a dominant gene(that is homozygous or heterozygous) with a homozygous recessive individual

    OR

  • a cross between individual(organism) of unknown genotype with a homozygous recessive individual

    ii) State the importance of a test cross in genetics

  • helps in determining the genetic constitution/genotype of an organism

    iii) What are multiple alleles?

  • a set of more than two alleles that may determine a character

    example is blood group which can be determined by any two of three alleles i.e. A,B and O

    iv) Explain the inheritance of ABO blood groups

  • in humans blood groups are determined by three alleles i.e. A,B and O

  • it is only possible to have two genes at a time

  • genes A and B are co-dominant while gene O is recessive to genes A and B

  • Give a worked example using parents with heterozygous blood groups Ao and BO

    ii) Explain the inheritance of Rhesus factor (Rh) in human beings

  • in humans blood is either Rh positive or Rh negative

    people who have Rh antigen are Rh(+ve) while those without Rh antigen in their blood are Rh(-ve)

  • Rh(+ve) is due to a dominant gene while the recessive gene causes lack of Rh factor.

  • When a person who is homozygous dominant marries a person who is homozygous

    recessive the result is as shown below

    Let the gene for dominant Rh factor be R while gene for recessive be r

    iii) How is sex determined in human beings .

  • there are two sex chromosomes in humans, x and y

  • males are xy and females are xx

  • in females all ova have x chromosome

  • in males 50% of sperms contain x chromosomes While 50% of sperms contain y

    chromosome

  • when a sperm containing x chromosome fuses with an ovum this results into a girl

  • when a sperm containing y chromosome fuses with an ovum the result is a boy

  • an example is given below

    g) i) What does the term linkage mean?

    - These are genes which occur together on a chromosome and are passed to offspring without being separated ii) Define the term sex-linked genes

  • genes carried in the sex chromosome that are transmitted along with genes that determine sex

    iii) What is meant by the term sex linkage?

  • genes are located on the sex chromosome

  • they are transmitted along with those that determine sex

    iv) Name the sex-linked traits in humans

  • colour blindness

  • haemophilia

  • Hairy ears. pinna, nose

  • Baldness

  • Duchene muscular dystrophy (DMD) muscular wasting

    v) Give an example of a sex linked trait in humans on:

    Y Chromosome

  • tuft of hair sprouting from pinna/baldness

    X Chromosome

  • colour blindness/haemophilia

    vi) In humans red-green colour blindness is caused by a recessive gene C, which is sex- linked. A normal man married to a carrier Woman transmits the trait to his children. Show the possible genotypes of the children.

    Let C represent the gene for normal colour vision (dominant)

    Let c represent the gene for colour blindness

    Parental phenotype Norman man x carrier woman

    iv) State the importance of sex linkage

    possible to determine sex of day old chicks

    v) Haemophilia is due to a recessive gene. The gene is sex-linked and located on the x chromosome. The figure below shows sworn offspring from phenotypically normal parents

    What are the parental genotypes?

  • XY and XhX

    Work out the genotypes of the offspring

    h) i) What is mutation?

  • sudden change in the structure of DNA at a particular locus/chromosome/ gene

    ii) Describe how mutations arise

  • mutations arise due to alterations in normal number of chromosomes

  • change in a portion of a chromosome affecting one or more genes
  • by chromosomal aberration e.g. dleltion/duplication/substitution/inversion/translocation/crossing over

  • caused by mutagenic agents e. g. radiation (x-rays, ultra violet light, gamma rays) and chemicals e. g. mustard gas/colchicines

    iii)State the factors that may cause mutation

  • these are chemicals and radiations

    Radiations Effects

    X-rays gene/chromosome alteration

    Ultra violet rays structural distortion of DNA

    Chemicals Effect

    colchicines prevents spindle formation

    Cyclamate chromosome aberrations

    Mustard gas chromosomes aberrations

    Nitrous acid adenine in DNA is deaminated so behaves like guanine

    Acridone orange addition and removal of bases of DNA

    Formaldehyde

    iv) State the characteristics of mutations

  • arise suddenly

  • are unpredictable

  • random

  • generally rare

  • may breed true

  • some are desirable while others are lethal

    v) Explain chromosomal mutation

    - Change in nature, structure or number of chromosomes

    vi) Explain how the following types of chromosomal mutations occur

    Duplication

  • a section of a chromosome is repeated/replicates

  • therefore genes are repeated

    Inversion

  • occurs when chromatids break at 2 places and when rejoining the middle piece rotates and joins in an inverted position

    Deletion

  • portion of a chromosome is left out after it breaks off

  • alters number and sequence of genes

    Translocation

  • occurs when a section of a chromatid breaks off and becomes attached to another chromatid of another chromosome

    Non-disjuntion

  • Failure of homologous chromosomes/sister chromatids to separate/segregate during meiosis

    Polyploidy

  • where number of chromosomes double or triple

  • beneficial in plants due to the following

  • increased yields/hybrid vigour//heterosis

  • resistance to pests

  • early maturity

  • resistance to drought

  • resistance to diseases

    vii) What are gene mutations?

  • an alteration in the structure of a gene

    i) Explain how the following occur during gene mutation

    Deletion

  • some bases/nucleotides of a gene are removed

    Inversion

  • the order of some bases/nucleotides of a gene is reversed

    Insertion

  • addition of a base between two existing bases

    Substitution

  • a portion of a gene is replaced by a new portion

    ii) Name the disorders in humans caused by gene mutation

  • albinism

  • sickle cell anaemia

  • achondroplasia/chondordystorphic dwarfism

  • haemophilia

  • colour blindness

  • phenylketonuria

    I. State the practical applications of genetics

    i. Breeding programmes (research)

  • high yielding/hybrid vigour/heterosis

  • resistance to diseases

  • resistance to drought/salinity

  • early maturing

    ii. Genetic engineering

  • genetic manipulation to produce desired characteristics

    iii. Law

    - legal questions of paternity knowledge of blood groups or blood transfusion

    iv) Genetic counseling

  • aimed at reducing harmful traits e.g. albinism, congenital idiots, colour blindness e.t.c

    v) Others

    - Pre-sex determination

    Understanding human evolution and origin of other species.

    2. a) i) Explain the meaning of evolution

  • a gradual change in living organisms from simple life forms to more complex forms over a long period of time.

    ii) Differentiate organic evolution from chemical evolution as theories of origin of life

  • organic evolution refers to the emergence of present forms of organisms gradually from pre-existing forms (some of which no longer exist)

  • chemical evolution explains the origin of life as having occurred when simple chemical compounds reacted to form the simplest life forms

    iii) What is special creation?

  • maintains that the whole universe and all living organisms came into being due to the act of a supernatural being

    b) Discuss the various kinds of evidence for evolution

    i) Fossils

  • fossils are remains of organisms preserved in naturally occurring materials for many years

  • they give evidence of types of plants/animals that existed at certain geological age/long ago/millions of years ago

  • gives evidence of morphological/anatomical/structural changes that have taken place over a long period of time e. g. human skull, leg of horse

    ii) Comparative anatomy

  • gives evidence of relationship among organisms/gives evidence of a common ancestry of a group of organisms

  • organisms have similar structures/organs performing the same function e. g. digestive system] urinary system/nervous system/vestigial structures and vertebrate heart

  • Divergence where the basic structural form is modified to serve different functions e.g. vertebrate forelimb/beak structure in birds/birds feet/parts of a flower. These are called homologous structures

  • homologous structures have a common embryonic origin but are modified to perform different functions e.g. the pentadactyl limb
  • adaptive radiation is a situation where organism have a homologous structure with common embryonic origin which is modified to perform different functions to adapt organisms to different ecological niches/habitats e.g. beaks of Darwinian finches(birds)

  • Convergence is where different structures are modified to perform a similar function e.g. wings of birds and insects/eyes of humans and octopuses. These are called analogous structures

  • Vestigial structures are greatly reduced in size and have ceased to function e.g. human appendix/caecium/coccix in humans, wings of kiwi (flightless bird), presence of hind limb pad in python, halters in insects, human hair nictitating membrane in human eye, human ear muscle, pelvic girdle in whale and third digit of wing of bird.

    iii) Comparative embryology

  • some embryos of different animals appear very similar thus showing relationship and possibility of a common ancestry

  • e.g. different classes of vertebrates larvae of annelida and mollusca are similar (tocophere)

    iii) Comparative serology/physiology

  • these show biochemical and immunological comparisons of blood groups/components to show immunological similarities of tissues therefore showing relatedness of different organisms

  • e.g. antigen antibody reactions, human blood groups/Rh factor reveal some phylogenic relationship among organisms/common ancestry

    iv) Geographical distribution

  • organisms differ in various geographical regions

  • present continents are thought to have been a large land mass joined

  • together/pangea/Eurasia/Gondwanaland

  • present continents drifted apart from one land mass/continental drift

    as a result of continental drift isolation of organisms occurred bring about different patterns of evolution

  • organisms in each continent evolved along different lines hence emergence of new species/divergence/convergence

    Examples

  • marsupials in Australia

  • llama, jaguar, panther in S. America

  • lion, camel in Africa

  • I tiger in Asia

    vi) Cell biology (cytology)

  • structures and functioning of cells are similar

  • occurrence of organelles e.g. mitochondria in all cells/both plant and animal cells

  • these point at a common ancestry

    c) i) State the evolutionary characteristics that adopt human beings to the environment

    - Brain

    - Eyes

    - Upright posture/bipedal locomotion

    - prehensible arm/hand

    - Speech

    ii) State the ways in which Homo sapiens differs from Homo habilis

  • standing upright/erect posture

  • intellectual capacity/higher thinking capacity/bigger brain/higher brain capacity

  • communication through language/speech

    d) i) Explain Larmarck’s theory of evolution

    - Inheritance of acquired characteristics/environment induces production of a favorable trait which is then inherited

    ii) Explain why Lamarck’s theory of evolution is not accepted by biologists today

    - evidence does not support Lamarck’s theory

    - acquired characteristics are not inherited/inherited characteristics are found in reproductive cells only

    iii) Explain Darwin’s theory of evolution

    - inheritance of genetically acquired characteristics

    - a character happens to appear spontaneously which gives advantage to an organism therefore adapted then inherited through natural selection

    e) i) What is natural selection?

    - Organisms with certain characteristics are favoured by the environment

    Such organisms tend to survive and produce viable offspring

    Others not favored are eliminated from subsequent generations

    ii) With examples, explain how natural selection takes place

    - organism with certain characteristics are favored by their environment

    - such organisms tend to survive and produce viable offspring

    - others not favored are eliminated from subsequent generations

    - as the environmental conditions change the survival value of a character may alter with time so that characteristics which were favored may no longer have advantage and other characters may then become favorable

    - if a favorable character is inherited, then offspring produce generations which are better adapted to survive in a population

    - more offspring are produced than can survive which results in struggle for survival - the fittest survive

    iii) State the advantages of natural selection to organisms

    - assist to eliminate disadvantageous characteristics/perpetuates advantageous characteristics

    - allows better adapted organisms to survive adverse changes in the environment/less adapted organisms are eliminated

    iv) State the ways in which sexual reproduction is important in the evolution of plants and animals

    - brings about useful variations/desirable characters

    - variations make offspring better adapted for survival/more resistant to diseases

    - may lead to origin of new species

    v) Explain the significance of mutation in evolution

    - Mutation bring about variation which can be inherited

    - Some of these variations are advantageous to the organism

    - Others are disadvantageous

    - The advantageous variations favour the organism to compete better in the struggle for survival

    - This results into a more adapted organism to its environment or new species/varieties

    - Those with disadvantageous characters will be discriminated against therefore eliminated from the population/death/perish

    vi) Plain why it is only mutations in genes of gametes that influence evolution

    - gametes form the new offspring

    vii) How would you prove that evolution is still taking place?

    - resistance of organism to antibiotics, pesticides and drugs

    - new varieties of bacteria are resistant to certain antibiotics such as penicillin

    - houseflies and mosquitoes are resistant to DDT

    vii) Explain why some bacteria develop resistance to a drug after they have bee subjected to it for some time

    - bacteria mutates/develops a new strain/chemical composition is altered hence is able to produce enzymes/chemicals which degrade the drug rendering it non-susceptible to the drug

    - the new strain is favoured by selection pressure natural selection

    f) How has industrial melaninism i.e. peppered moth contributed towards the mechanism of evolution

    - This is an example of natural selection

    - The peppered moth exists in two distinct forms, the speckled white form (normal form) and a melanic form (the black/dark)

    - They usually rest on leaves and barks of trees that offer camouflage for protection

    - Originally the “speckled white” form predominated the unpolluted area of England

    - This colouration offered protection against predatory birds

    - Due to industrial pollution tree barks have blackened with soot

    - The white form underwent mutation

    - A black variety/mutant emerged suddenly by mutation

    - It had selective advantage over the white forms that were predated upon in the industrial areas

    - The speckled white form is abundant in areas without soot/smoke

    3. a) i) Define irritability, stimulus and response irritability

    -also called sensitivity

    - Responsiveness to change in environment

    Stimulus

    A change in the environment of organism which causes change in organism’s activity

    Response

    - change in activity of an organism caused by a stimulus

    ii) State importance of irritability to living organisms

    - Adjusting to environmental conditions. Sensitive/defect/responding

    iii) List the examples of external stimuli to organisms

    - air/oxygen (aero)

    - light(photo)

    - osmotic pressure (osmo)

    - current (Rheo)

    - chemical concentration (chemo)

    - \water/moisture (hydro)

    - Touch/contact (hapto/thigmo)

    - Gravity/soil (geo)

    - Temperature (thermo)

    b) i) What are tactic responses?

    - response in which whole organism or its motile parts move e. g. gamete

    ii) What causes tactic responses?

    - caused by unidirectional stimulus

    - usually doesn’t involve growth

    - response is either positive or negative

    - named according to source of stimulus

    - e.g phototaxis, aerotaxis, chemotaxis

    iii) State the importance of tactic response to:

    Members of kingdom protista

    - move towards favorable environment/move away from unfavorable environment

    - move towards their prey/food

    Microscopic plants

    - escape injurious stimuli/seek favorable habitats

    iv) Name the type of response exhibited by:

    Euglena when they swim towards the source of light

    - phototaxis

    - sperms when they swim towards the ovum

    - chemotaxis

    v) State the advantages of tactic responses to organisms

    - to avoid unfavorable environment/injurious stimuli

    - escape from predators

    - to seek favorable environment

    - to seek for food/prey

    c) i) Define the term tropism

    - growth movement of plants in response to external unilateral/unidirectional stimuli

    ii) Explain the various types of tropism in plants

    Phototropism

    - growth movements of plant shoots in response to unilateral sources of light

    - the tip of the shoots produce auxins down the shoot

    - light causes auxins to migrate to outer side/darker side causing growth on the side away from light hence growth curvature towards source of light roots are negatively phototrophic

    Geotropism

    - response of roots/pans of a plant to the direction of force of gravity

    - auxins grow towards the direction of force of gravity causing positive geotropism in roots while shoot grows away from force of gravity (negatively geotrophic)

    Thimotropism/Haptotropism

    - growth response of plant when in contact with an object

    - contact with support causes migration of auxins to outer side causing faster growth on the side away from contact surface

    - this causes tendrils/stem to twin around a support

    Hydrotropism

    - growth movement of roots in response to unilateral source of water/moisture

    - the root grows towards the source of water/ positively hydrotropic while leaves are negatively hydrotropic

    chemostropism

    - growth movement of parts of plant to unilateral source of chemicals

    - the chemicals form a gradient between two regions e.g. pollen tube growing towards the ovary through the style

    iii) State the ways in which tropisms are important to plants

    - expose leaves/shoots in positions for maximum absorption of sunlight for photosynthesis

    - enables roots of plants to seek/look/search for water

    - enables plant stems/tendrils to obtain mechanical support especially those that lack woody stems.

    - enables roots to grow deep into the soil for anchorage

    - enables pollen tube grow to embryo sac to facilitate fertilization

    iv) Explain the differences between tropic and tactic responses

    Tropism

    -growth curvature in response

    -slow

    -influenced by hormones

    Taxes

    -locomotory response

    -fast

    -external influence

    d) The diagram below represents growing seedlings which were subjected to unilateral light at the beginning of an experiment

    i) State the results of P, Q and R after S days

    - P will bend/grow towards light

    - Q will remain straight/have little or no growth

    - R will remain/grow straight/grow upwards

    ii) Account for your results in (i) above

    P- Growth substance/growth hormone/IAA/auxin are produced by the stem tip

    - they move (downwards and get distributed) to the side away from light where they cause rapid/more growth/cell division/elongation that results in bending

    Q- Source of auxin has been removed

    R- The auxins cannot be affected by light because the tip has been covered

    iii) If the tin foil were removed from the tip of seedling R, what results would be observed after two days

    - it will bend/grow towards light

    iv) State the expected results after 3 day is if the box were removed

    - all seedlings will grow straight/upwards

    e) In an experiment to investigate a certain aspect of plant response, a seedling was placed horizontally as shown in diagram I below. After seven days the appearance of the seedling was as shown in diagram 2

    Account for the curvature of the shoot and root after the seven days

    i) Shoot

    - auxins accumulate on the lower side of the seedling due to gravity

    - high concentration of auxins in shoot stimulates faster growth causing more elongation on the lower side than the upper side hence curvature occurs upwards

    ii) Root

    - the high concentration of auxins inhibits growth hence the upper side with less auxins grows faster than the lower side therefore the curvature occurs downwards

    f) What is etiolation?

    - phenomenon exhibited by plants when grown in darkness

    - such plants are pale yellow due to absence of chlorophyll, have small leaves, long stems/hypocotyle and slender stems

    - plants exhibit etiolation to reach light/obtain light

    - this is a survival response

    4. a) i) What is coordination in animals

    - The linking together of all physiological activities that occur in the body so that they take place at the night time and in the correct place

    ii) Name the main systems for coordination in animals

    - Nervous system/sensory system

    - Endocrine (hormonal system)

    iii) List the components of the mammalian sensory system

    - Central nervous system (CNS), brain & spinal cord

    - Peripheral nervous system (PNS) cranial and spinal nerves

    - Sense organs

    - Autonomic nervous system (ANS) nerve fibers and ganglia

    iv).Explain the terms receptors, conductors and effectors

    - Receptors are structures that detect stimuli i.e. sense organs

    - Conductors transmit impulses from receptors to effectors e. g. neurons

    - Effectors are the responding parts e.g. muscles, glands

    v) What are the functions of the central nervous system?

    - provides a fast means of communication between receptors and effectors

    - coordinates the activities of the body

    vi) State the differences between somatic and autonomic systems of peripheral nervous system

    - Somatic is concerned with controlling the conscious or voluntary actions of the body i.e. skin, bones, joints and skeletal muscles

    - the autonomic (automatic) nervous system controls involuntary actions of internal organs, digestive system, blood vessels, cardiac muscles and glandular products.

    b) i) What is a neurone?

  • the basic unit of the nervous system

  • also called nerve cell

  • conducts impulses

  • include monitor sensory and relay neurons

    ii) Name the parts of a typical neurone and state the functions of each part

  • cell body/centron contains nucleus and cytoplasm

  • axon transmits impulses away from cell body

  • dendrites relays impulses across adjacent neurons

  • myelin sheath insulates axon and speeds up transmission of impulses

  • schwan cells forms myelin sheath and aid in nutrition and regeneration of axon

  • node of ranvier occur between schwan cells, where axon is not covered, speeds up impulse transmission

  • nissils granules contain mitochondria that provide cell body with energy for metabolic process

    i) Describe the structure and function of a motor neurone

  • motor neurone relays impulses from CNS (brain/spinal cord) to effectors ( muscles/glands)

    ii) Describe the structure and of sensory neurone

  • sensory neurone relays receptors (sense organs) to CNS

    iii) State structural differences between motor and sensory neurons

  • Cell body in motor neurone is terminal (at the end) and inside central nervous system.

  • Cell body in sensory neurone is terminal but has axon at both ends (bipolar)

    iv) Describe the structure and function of a relay neurone

  • also called intermediate/internucial/associate/connector/interneurone

  • locate inside central nervous system and spinal code

  • usually lack myelin sheath

    c) State the function of the major parts of the human brain

    i) Cerebrum

  • called forebrain

  • occupies most of the brain

  • consists of four lobes each with specific function

  • temporal lobe controls taste smell hearing learning and memory

  • partial lobe controls sensory output and touch

  • occipital lobe controls vision, motor output and speech

  • frontal lobe controls personality, learning thought and speech

  • also has parts called thalamus and hypothalamus

  • thalamus helps to sort sensory information

  • hypothalamus controls hunger, heartbeat body temperature and aggression

    ii) Mid brain

  • quite small in humans

  • relay centre for audio and visual information

  • also involves in some sight, hearing and orientation responses

    i) Hind brain

  • consists of cellebral and medulla oblongata

  • cerebellum is responsible for coordinating impulses, posture and balance, motor coordination and muscle tone

  • medulla oblongata controls heartbeat, blood pressure breathing rate, coughing and sneezing

    a) i) What is reflex action?

  • an automatic response to an external stimulus e. g. sneezing or Withdrawing hand from a hot object

    ii) Describe a reflex action that will lead to the Withdrawal of a hand from a hot object

  • Receptors in the skin respond to stimuli. Arestimulated

  • an impulse is transmitted through the sensory neurone, across a synapse to the central nervous system (White matter), through the relay neurone into grey matter, then to the motor neurone and finally to the effect muscle which contracts

  • the hand is then withdrawn

    iii) Explain how an impulse is transmitted across the synapse (gap)

  • impulse initiates release of transmitter substance acetylcholine at the end of the sensory neurone

  • acetylcholine diffuses across the synapse and generates an impulse in the next neurone

    ii) Briefly describe the transmission of a nervous impulse across a neuro-muscular junction

  • impulse arrives at synoptic knob and causes vesicle to move to the pre-synaptic membrane

  • vesicle discharges transmitter substance into synaptic cleft

  • transmitter substance/acetylcholine diffuses across the cleft and attaches to post-synaptic membrane

  • the membrane is depolarized, generating the action potential

    iii) What are the functions of a synapse?

  • allows transmission of nerve impulses from neurone to neurone

  • ensures nerve impulses travel in only one direction W

  • in the brain they store information/memory

    b) i) What is a conditioned reflex?

  • A response caused by a unilateral stimulus (associated stimulus) which substitutes the normal stimulus

    ii) Explain a conditioned reflex

  • it is automatic

  • it involves the spinal cord

  • it is usually learned e. g. writing, cycling, dancing

  • it involves the interaction of highly specialized centers of the brain with a large number of neurone necessary to bring about conditioning

  • example is experiments carried out by Pavlov using dogs

    iii) Compare a simple reflex action with a conditioned reflex

    c) i) What are endocrine glands?

  • ductless glands that produce hormones in animals

  • hormones are chemical substances which help to coordinate the functions of the body

    ii) State the functions of hormones in animals

  • regulate growth and development

  • control behavior during breeding

  • proper functioning of cells

  • regulate metabolic activities

    iii) Name the main endocrine glands, their secretions and functions in the human body

  • Gland: Thyroid

    Hormone:

    Thyroxine

    Function:

    increases the rate of metabolism

  • Gland: Parathyroid

    Hormone:

    Parathyroid hormone

    Function:

    regulates calcium and phosphate levels

  • Gland: Pituitary

    Hormone:

    growth hormone

    Function:

    regulates growth of the body

    gonadotrophic hormone

    Function:

    stimulates the growth of male and female organs

    lactogenic hormone (prolactine)

    Function:

    stimulates secretion of milk after child birth

    thyrotropic hormone( TSH)

    Function:

    proper functioning of thyroid glands/thyroxine production

    adrenocorthicotropic hormone (ACTH)

    Function:

    stimulate release of adrenal cortex hormone

    oxytocine hormone

    Function:

    regulates blood pressure

    stimulates smooth muscles

    stimulates contraction of uterus during child birth

    aids flow of milk from mammary glands

    follicle stimulating hormone (FSH)

    Function:

    causes maturition of egg in females

    stimulates sperm production in male

    Vasopressin (ADH) antidiuretic hormone

    Function:

    regulates water balance by kidney

  • Gland: adrenal

    adrenaline (epinephrine hormone)

    Function:

    for emergency

    prepares body to cope up with stress

    aldosterone hormone

    Function:

    maintain balance of salt and water in blood

    cortisone hormone

    Function:

    break down the stored proteins to amino acids

    aids in the break down of adipose tissue

    regulates sugar levels in the blood

    prevents inflammation

    sex hormone

    Function:

    supplements sex hormones produced by gonads

    promotes development of sexual characteristics

  • Gland: Pancreas

    Hormone:

    insulin

    Function:

    regulates levels of sugar in blood

    enables liver to store sugars

    glucagon

    Function:

    regulates levels of sugar in blood

  • Gland: ovaries

    Hormone:

    oestrogen Function:

    causes secondary sexual characteristics in female

    prepares the uterus for pregnancy

    progesterone Function:

    growth of mucus lining of uterus

    maintains the uterus during pregnancy

  • Gland:testes

    Hormone:

    androgen testosterone

    Function:

    causes secondary sexual characteristics in male

  • Gland: stomach cells

    Hormone:

    gastrin

    Function:

    stimulates release of gastric juice

  • Gland:intestinal cells

    Hormone:

    secretin

    Function:

    stimulates secretion of pancreatic juice

    iv) Give the differences between nervous and endocrine (hormonal) communication

    nervous

  • response confined to effector organs( localized target)
  • speed of response is rapid
  • nervous impulse through nerve/nerve cells/neurons
  • duration of response is short
  • speed of transmission is rapid
  • transmission is electrical

    hormonal(endocrine)

  • response more widespread (various targets)
  • response less rapid
  • hormones transferred through blood
  • persistent for long
  • speed of transmission is slower
  • transmission is chemical

    v) State the effects of over secretion and under secretion of adrenaline and thyroxine in humans

    g) i) Define the following terms

    Drug

  • a substance that causes a change in body function

    Drug abuse

  • indiscriminate use of drugs without minding their side effects

  • misuse or wrong use of drugs

    ii) State the types of drugs, examples and side effects

    Sedatives

  • also called depressant

  • a drug that decreases the action of the central nervous system

  • reduce anxiety, and tension, induce sleep and act as muscle relaxants

  • when abused they cause withdrawal effects such as anxiety, delirium and death

  • includes barbiturates, other sedatives, tranquilizers and alcohol

    Pain-killers

  • suppress centers of pain in the brain

    Hallucinogens

  • given to people with hallucination or mentally ill patients to calm then down

  • when abused they lead to a feeling of confusion, agitation, depression and violent behavior that can lead to murder or suicide

  • examples include valium, LSD, bhang, narcotics and cannabis

    Stimulants

  • drugs that temporarily increase the action of the central nervous system

  • they create a feeling of alertness, wakefulness, a sense of self confidence and well being

  • used to decrease fatigue and mild depression

  • when abused they cause feelings of persecution, hallucination and addiction

  • include amphetamines, cocaine, caffeine, miraa and nicotine

    iii) State the general effects of drug abuse on human health

  • damage to body organs e. g. liver cirrhosis

  • drug addiction

  • impaired judgment resulting in clumsiness

  • socio-economic problems e. g. crime, loss of jobs, divorce, prostitution, HIV/AIDS

    may cause poor health

    h) i) List the special sense organs in mammals and the major function of each

    - Eye for sight

    - Ear for hearing and balance

    - Nose for smell

    - Skin for touch, temperature detection, pain detection

    iii) How is the human eye adapted to its function?

  • conjunctiva is thin/transparent/tough to allow light to pass through/to protect the eye Sclerotic layer is made up of (collagen) fibers/fibrous. It maintains shape of the eyeball/protects the eye

  • cornea is transparent/curved thus refracts light rays/allows light to pass through

  • Choroid is a layer of tissue with black pigment/dark pigment. Prevents internal reflection of light in the eye/contains blood vessels that supply oxygen/nutrients/remove (metabolic) wastes from the eye

  • retina has cones/rods for bright colour vision/low light vision

  • yellow spot has a high concentration of cones for accurate vision/visual acuity

  • Blind spot has no cones and rods. Place where optic nerve leaves/enters the eye

  • optic nerve has (sensory) nerve fibers for transmission of impulses to the brain (for interpretation)

  • Lens is biconvex/made up of elastic material/transparent. Adjust focus on far or near objects allow light to pass through/for refraction of light rays

  • ciliary body is made up of muscle fibers glandular which contract/relax to change shape

  • suspensory ligaments are inelastic to hold lens in position/attach it to ciliary body

  • iris(is the coloured part of the eye it) has radial and circular muscles which control size of pupil

  • pupil is the small hole at the centre of iris through which light passes into the eye

  • aqueous humor is a fluid through which oxygen/nutrients pass to the comea/lens/maintains shape of the eyeball/refracts light rays

  • vitreous humor is a fluid which maintains shape of eye/refracts light rays

    iii) What is accommodation of the eye?

  • ability of the eye to adjust to bring an image from a near or far object into sharp focus on the retina

    iv) Explain how an eye viewing a near object adjusts to viewing a far object

  • ciliary muscles relax

  • suspensory ligaments become taut/tight

  • lens decreases curvature/becomes thinner

  • radial muscles relax

  • circular muscles contract

  • size of pupil decreases to reduce amount of light

    v) What changes occur in the eye if it changes from observing an object at a distance to one at a closer range?

    - ciliary muscles contract

    - Tension in suspensory ligaments reduces/relaxes slackens

    - Lens bulges/thickens/increases curvature

    - Radial muscles contract

    - Circular muscles relax

    - Size of pupil becomes large to allow in more light.

    viii) State the changes which would take place in the eye if a person in a dark room had lights switched on

  • circular muscles contract and radial muscles relax

  • pupil becomes small to allow less light into the eye

    ix) Explain how the eye forms an image

  • the mammalian eye works like a camera

  • light rays enter the cornea pass through the pupil, aqueous humor, lens and vireous humor

  • light rays are refracted by the aqueous and humor and lenses

  • finally light falls on the retina to form an image

  • the image is real and invened and smaller than object, back to front/reversed

  • Retina forms a fine image when light rays reach it.

    x) Name the defects of the eye and state how they can be corrected

    Short sight (Myopia)

  • eye cannot focus on far objects

  • image is formed in front of the retina because light rays converge in front of retina

  • the lens is too thick, curve and eyeball too long

  • corrected by wearing concave/biconcave/lenses

  • these lenses diverge light rays onto retina

    Long sight (Hypermetropia)

  • eye lenses are unable to focus because they are flat, thin and weak hence unable to focus image on the retina

  • they are unable to accommodate/change the focal length

    near image is formed behind the retina but a distant one is correctly focused on the retina

  • corrected by wearing convex/biconvex/converging lenses

    Presbyopia

  • occurs in old age hence called old sight

  • caused due to loss of elasticity of lenses, weakness of ciliary muscles hence lack of focus of light rays

  • this causes long sight

  • corrected by wearing biconvex/convex/converging lenses

    Squinting

  • eyeballs are uncoordinated/do not turn at the same time

  • eye muscles move in different directions

  • this makes accommodation and focusing difficult

  • corrected through surgery

    Astigmatism

  • surface of cornea is uneven

  • leads to weak focus of light raise on retina

  • corrected by using cylindrical lenses/lenses with combined curvature

    xi) State the advantages of having two eyes in human beings

  • stereoscopic vision

  • gives a wider angle of binocular vision

  • if one is damaged human is not blinded

    i) What are the functions of the human ear?

  • hearing

  • maintaining body balance and posture

    iv) How are the structures of the human ear suited to perform the function of hearing?

  • Pinna is funnel shaped allows collection of sound waves and channels them down the auditory canal/auditory mateus

  • auditory canal is a tube that concentrates and directs sound waves to tympanic membrane/tympanum/eardrum

  • Eardrum is thin and tight. It sets into vibration/vibrates/converts sound waves into vibrations

  • the vibrations are transmitted to the ear ossicles/malleus, incus and stapes that amplify the sound vibrations

  • the vibrations are then transmitted to the fennestra ovalis/oval window

  • Oval window is a membrane which amplifies/transmits vibrations to the fluids (perilymph and endolymph) then to cochlea.

  • The cochlea is coiled to occupy a small space and accommodate a large number of sensory cells

  • The sensory cells/hairs (in the cochlea) are set into vibrations/stimulated producing nerve
  • impulses in the auditory nerve

  • Impulses in the auditory nerve are transmitted to the brain for interpretation for hearing

  • Eustachian tube connects the inner ear to the throat. It equalizes air pressure in the middle ear with the atmospheric air pressure (in outer ear)

  • Fennestra rotundus/round window dissipates/discharges/discards vibrations from inner ear to middle ear

    iii) Explain how the structure of the human ear performs the function of balancing

  • there are three semi-circular canals/utriculus/succulus/vestibular apparatus arranged in planes at right angles to each other

  • at the end of each canal is a swelling called ampulla which contains receptors

  • the movement of the head causes movement of the fluid/endolymph in at least one canal

  • the fluid movement causes stimulation of the receptors/sensory hairs

    sensory impulses are generated

  • the auditory nerve transmits the impulses to the brain for interpretation for the position of body/posture/balance

    iv) State what would happen if the auditory nerve was completely damaged

  • deafness

  • loss of body balance

  • impulse not transmitted to the brain

    5. a) i) What is support?

  • to support is to carry part of the weight/mass of an organism

    ii) What is locomotion?

  • progressive change in the position of an organism

    iii) State the importance of support systems in living organisms

  • they provide a framework for the body of organisms and help to determine their shape

  • provide land animals with means for support to their weights against gravity

  • organs are attached to the skeleton for support and stability to avoid entanglement and crushing each other

  • they protect very important and delicate organs whether inside or outside the body e. g. eyes, heart

  • in large plants the rigid trunks of trees support the greater mass of leaves and fruits

    iv) State the importance of locomotion in animals

  • in search of food

  • Search for mates

  • escaping predators

    b) i) Name the tissues in higher plants that provide mechanical support

  • Sclerenchyma

  • collenchyma (not lignified)

  • xylem/tracheids and vessels

    ii) State the importance of support in plants

  • exposing the surface area of leaf to sunlight for photosynthesis

  • ensure flowers are exposed to pollination agents

  • expose fruits and seeds to agents of dispersal

  • to resist breakages due to their own weight and that of other organisms

  • for proper transport and translocation of materials

    iii) Name the types of plant stems

  • herbaceous e.g. shrubs

  • woody e. g. trees

  • weak stems in creepers, twining plants and plants bearing tendrils

    iv) Name the tissues in plants that are strengthened with lignin

  • sclerenchyma

  • xylem vessels/tracheids/xylem

    v) What makes young herbaceous plants remain upright?

  • turgidity

  • presence of collenchyma

    vi) State the ways by which plants compensate for lack of ability to move from one place to another

  • ability to pollinate

  • response to nastic and tropic movement

  • ability to exploit localized nutrients

  • ability to disperse seed or fruit propagation

    c) i) Explain the Ways in which erect posture is maintained in a Weak herbaceous stem

    - This is the function of turgidity and presence of collencyma

    Cells take in water and become turgid

    ii) Explain how support in plants is achieved

  • Turgor pressure due to absorption of water keeps cells firm hence hold herbaceous plants upright

  • collenchyma and clerenchyma tissues are closely packed in stem and roots to provide support

  • inelastic cuticle on epidermis is covered by a waxy layer hence keeping shape of plant and setting inward pressure against turgid cells and this causes a force to hold plant upright

  • xylem vessels and tracheids are lignified to provide support to stems, roots and leaves

  • climbing plants obtain mechanical support from other plants and objects

  • they have climbing structures like tendrils which hold on to other objects

    d) i) Give the reasons why support is necessary in animals

  • for attachment of muscles

  • For attachment of other body organs

  • to protect delicate body organs

  • to maintain body shape/form

  • to enable movement/locomotion

    ii) Why is movement necessary in animals?

  • enables animals to search for food

  • enables animals to search for shelter

  • enables animals to escape predators/harmful conditions

  • enables animals to Search for water

  • enables animals to search for mates

  • enables animals to search for breeding sites

    e) i) Name the organ used for support by animals

    - Skeleton

    ii) Name the different types of skeletons in animals, giving an example of an animal for each type of skeleton named

  • exoskeleton e.g. arthropoda (crab, insect)

  • endoskeleton e. g. chordata (cat, fish)

    iii) State the difference between exoskeleton and endoskeleton

  • endoskeleton is a rigid framework covered by body tissues of an animal

  • exoskeleton is a rigid framework found on the surface of an animal

    iv) State the advantages of having an exoskeleton

  • supports/protects delicate inner parts

  • water proof/prevents drying up of body

  • provided surface for muscle attachment

    v) Explain the importance of having an endoskeleton

  • support the body

  • give body its shape

  • protect delicate organs e. g. skull, brain, ribs

  • used in locomotion e.g. bones serve as levers

  • red blood cells are formed in bone marrow

  • minerals are stored in bones e. g. calcium and phosphorus

    f) i) Explain how a fish is adapted to living in Water

  • streamlined body for easy movement in water

  • swim bladder controls depth of swimming

  • fins for movement, balance, direction and stability,

  • gills for gaseous exchange in water

  • presence of lateral line to sense vibrations

  • scales provide protection .

  • colour which offers camouflage against predators

    ii) Explain how a finned fish is adapted, to locomotion in Water

  • streamlined body to reduce resistance/friction )to swim smoothly)

  • the vertebral column consists of a series of vertebrae held together loosely so that it is flexible

  • myotomes/muscles associated with vertebral column produce movement

  • the sideways and backwards thrust of the tail and body against water results in resistance of water pushing the fish sideways and forwards in a direction opposed to thrust

  • heat not flexible so as to maintain forward thrust

  • presence of fins help in propulsion/balance/paired fins (pectoral and pelvic) for controlling pitch and slow down movement/unpaired fins (dorsal, ventral, anal) for yawing and rolling (caudal) for swimming/propulsion and steering/change of direction

  • presence of swim bladder to make fish buoyant

  • scales tip towards the back to provide smooth surface

  • body covered with mucus to reduce friction

  • flattened surface for easy floating

    g) i) Name the main parts of the vertebral column giving the types of bones found in each part

    Axial skeleton

  • forms the main axis of the body

  • formed by the skull, sternum, ribs and vertebrae

    Appendicular skeleton

  • composed of limbs and girdles

  • the forelimbs are connected to the trunk by the pectoral girdles (shoulder bones)

    hind limbs are connected to the pelvic girdle (hips)

  • bones are scapular, clavicle, humerus, ulna, femur, tibia, fibula, metacarpals, carpals, tarsals, metatarsals, phalanges, ilium, ischium and pubis

    ii) What are the vertebrae?

  • bones of the vertebral column

    iii) State the functions of the vertebral column

  • gives flexibility

  • absorbs shock

  • protects spinal cord

  • supports weight of body

  • provide surface for muscle attachment

  • between the vertebrae are soft discs which offer cushioning called interverterbral discs

    iv) State the general characteristics of vertebrae

  • have solid structure called centrum to support weight of body

  • has transverse process lateral to centrum for muscle attachment

  • neural spine is dorsal to centrum and provides surface area for muscle attachment

  • neural canal a passage for spinal cord and offers protection to it

  • has facets for articulation with other vertebrae

  • neural arch encloses neural canal

    v) Name the bones of the vertebral column

    - Cervical vertebra

    — Thoracic vertebra

    - Lumbar vertebra

    - Sacral vertebra

    - Caudal vertebra

    vi) Describe how the various vertebrae are adapted to their functions

    Bone:

    skull

    Structure:

  • cranium and jaw bones
  • made of several bones joined together
  • large box called cranium and smaller paired boxes for eyes, ears, nose, jaw
  • has large hole called foramen magnum for passage of spinal cord

    Function:

  • attachment of jaws
  • protect brain and other delicate parts

    Bone:

    cervical region Atlas (first cervical)

    Structure:

  • ring shaped
  • no centrum
  • broad flat transverse processes
  • vertebraterial canal for passage of vertebra artery
  • facet for articulation of condyles of skull

    Function:

  • protects the spinal cord
  • attachment of muscles
  • allow nodding of head

    Bone:

    axis (second cervical)

    Structure:

  • adontoid peg projects from centrum
  • large flattened neural spine
  • vertebraterial canal
  • small transverse process

    Function:

  • allows the head to rotate
  • protects the spinal cord
  • provides surface for muscle attachment

    Bone:

    cervical (others) Structure:

  • short neural spine
  • branched transverse process for neck muscles
  • vertebraterial canal
  • wide neural canal

    Function:

  • supports weight of the head
  • protects the spinal cord
  • neck muscle attachment

    Bone:

    Thoracid

    Structure:

  • long backwards pointing neural spine
  • transverse process that points sideways
  • facets for articulation of ribs
  • notch for spinal nerves to pass through

    Function:

  • forms ribcage
  • articulation with one end of rib
  • protects the spinal cord
  • muscle attachment

    Bone:

    lumbar

    Structure:

  • short neural spine
  • long transverse process towards abdomen
  • large centrum
  • extra processes e.g prezygapophysis, hypapophysis, anapophysis,metapophysis

    Function:

  • protects organs of the abdomen
  • supports the upper part of the body
  • protects the spinal cord
  • muscle attachment

    Bone:

    sacral

    Structure:

  • fused bones to form sacrum
  • well developed transverse processes of first vertebra
  • vertebraterial canal
  • short neural spine

    Function:

  • protects the alimentary canal
  • attachment of hip girdle
  • protects the spinal cord
  • muscle attachment

    Bone:

    Rib

    Structure:

  • long
  • flattened
  • attached to sternum from front

    Function:

  • protects internal organs
  • muscle attachment

    vii) Describe the bones that form the appendicular skeleton

    Bone:

    pectoral girdle (scapular shoulder bone)

    Structure:

  • broad i,e flattened blade
  • glenoid cavity to articulate with humerous
  • metacronium/acromion for muscle attachment
  • hard to provide support
  • socket with cartilage/smooth surface to reduce friction

    Function:

  • support muscle attachment
  • articulate with humerous

    Bone:

    Humerous

    Structure:

  • long shaft for muscle attachment
  • round head to articulate with glenoid cavity
  • trachlea for articulation with ulna
  • olecranon fosa to prevent arm bending the other way

    Function:

  • movement
  • muscle attachment

    Bone:

    Ulna and radius

    Structure:

  • ulna longer and on side of little finger
  • has sigmoid notch and olecranon process to form hinge joint with humerous
  • radius is smaller and lies along thumb side and does not join ulna
  • allows articulation with wrist bone

    Function:

  • movement
  • muscle attachment

    Bone:

    pelvic girdle (hip bone)

    Structure:

  • composed of three fused bones ilium, ischium, pubis
  • upper end fused to sacrum
  • lower end has acetabalum for articulation with femur
  • has abturator

    Function:

  • movement
  • muscle attachment
  • support
  • absorbs pressure exerted by ground when animals move

    Bone:

    Femur

    Structure:

  • rounded head to fit in acetabalum of pelvis
  • projections called trochanter for attachment of thigh muscles
  • condyles at lower end for articulation with tibi
  • patella that covers knee and prevent leg from bending backwards

    Function:

  • movement
  • muscle attachment

    Bone:

    tibia and fibula

    Structure:

  • tibia is longer than fibula
  • tibia is outer bone and fibula is inner bone
  • tibia lies on the side of large toe
  • fibula is fussed to tibia on (outer side)

    Function:

  • movement
  • muscle attachment

    6. a) What is a joint?

  • the point where bones meet

    ii) State the functions of joints

  • provide a point of articulation between bones

    iii) Name the main types of joints

  • immovable joints e.g. skull, pelvic girdles and sacrum

  • slightly movable joints e. g. between vertebrae

  • Freely movable joints e. g. knee, elbow

    iv) Give the features of movable joints

  • ends of bones covered with articular cartilage

  • ends bound by capsules of ligaments

  • have joint cavity filled with lubricating fluid called synovial fluid secreted by synovial membrane

  • they are called synovial joints

    b) Describe the synovial joints

    iv) Ball and socket

  • allow movement in all planes /directions i.e. 360°

  • rounded end of bone fits into a rounded/cavity in another bone

  • e.g. shoulder joint and hip joint

    v) Hinge joint

  • convex surface of one bone fits into the concave surface of another bone

  • this allows movement in only one plane/direction 180°

  • e.g. elbow joint and knee joint

    vi) Pivot joint

  • allows rotation e. g. where atlas pivots on olecranon process of axis

    c) i) What is synovial fluid?

  • lubricating fluid produced by synovial membrane at movable joints

    ii) State the functions of synovial fluid

  • absorbs shock

  • reduces friction/ gives lubrication

  • nourishment

  • distributes pressure

    d) Explain the following terms

    v) Ligament

  • connective tissue joining one bone to another

    vi) Cartilage

  • supporting soft tissue found at joints

  • they cushion the bones and absorb shock

    vii) Tendon

  • tissue that connects muscle to bones

    7. Muscles

    e) i) What is a muscle?

  • fleshy part of body

  • composed of long cells enclosed in a sheath

  • specialized cells capable of contracting

    ii) State the functions of muscles

  • cover the skeleton

  • provide shape

  • contract and relax to enable body to move

    f) Describe the structure and function of various types of muscles

    i) skeletal muscles

  • also called voluntary/striated/stripped muscles

  • they are attached to skeleton

  • they consist of striated, multinucleated, ling fibers and are cylindrical shaped

  • found on legs, arms, eyes, neck where they cause movement

    ii) Involuntary muscles

  • also called smooth/visceral/unstriated/unstripped

  • their movement is not controlled by the will

  • they are unstriated, nucleated, short fibred and spindle shaped

  • are found in alimentary canal, blood vessels, secretory glands, other tubular visceral

    organs, bladder, uterus, urinary tract, reproductive system, respiratory tract, ciliary body iris

    iii) Cardiac muscles

  • also called myocardium

  • found in the Walls of the heart

  • are not under control of the will

  • composed of long cylindrical cells with special junctions

  • myogenic i.e. generate their own contraction

  • they are not fatigued

  • their function is contraction of the heart to pump blood

    g) Explain how muscles cause movement of the human arm

  • the muscles which bring about these movements are called biceps and triceps

  • biceps are attached to scapula and radius for bending

  • triceps are attached to scapula, humerus and ulna for stretching

  • when the biceps contracts, it pulls the radius (forearm) and the hand bends

  • the triceps relaxes at the same time

  • when the triceps contracts and biceps relaxes(extends) the arm is stretched

  • biceps flexes the arm (flexor) and triceps extend(extensor muscle) the arm

    h) i) State the structural differences between skeletal muscles e.g. biceps and smooth muscles e.g. gut muscle

    skeletal (biceps)

  • multi nucleated
  • striated/stripped
  • long muscle fibers
  • block/cylindrical

    smooth muscles

  • un nucleated
  • un striated
  • short muscle fibers
  • spindle shaped

    ii) Name the cartilage found between the bones of the vertebral column

  • intervebral disc

    iv) What are the functions of the cartilage named in (d) ii) above

  • acts as a cushion/absorbs shock

  • reduces friction

  • flexibility of vertebral column

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