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BIOLOGY FORM ONE NOTES

October 5, 2025 Maverick John Leave a comment

BIOLOGY FORM ONE NOTES

INTRODUCTION TO BIOLOGY

What is Biology?

Biology is the branch of science that deals with the study of living things. In Greek, Bios means life while Logos means knowledge.

Branches of biology

There are two main branches:

Botany: Study of plants
Zoology: Study of animals

The others include:

Ecology: Study of living things in their surroundings.
Genetics: The study of inheritance and variation.
Entomology: Study of insects
Parasitology: Study of parasites
Taxonomy: Study of classification of organisms
Microbiology: Study of microscopic organisms
Anatomy: Study of structure of cells
Cytology: Study of cells
Biochemistry: Study of chemical changes inside living organisms

Name at least six other smaller branches of biology (6 marks).

Importance of Biology

Solving environmental problemsg. Food shortage, poor health services, pollution, misuse of environmental resources etc.
Choice of careers e.g. Medicine, Agriculture, public health, Veterinary, Animal husbandry, Horticulture, Dentistry etc.
Acquiring scientific skills g. observing, identifying, recording, classification, measuring, analyzing, evaluating etc.
International co-operation g. Development of HIV\AIDS vaccine, fight against severe Acute respiratory Syndrome (SARS), fight to save ozone layer from depletion, management of resources through international depletion.

Others

Help on study of other subjects
Learn what living things are made up of and their bodies work
Acquire knowledge about plant and animal diseases and their treatment.
Know the effects of our bodies on drug and substance abuse and can kill.
Learn about HIV\AIDS diseases and other viral diseases e.g. its treatment—balanced diets, proper hygiene, spreading, sexual behavior, cultural practices etc.

List five professional occupations that require the study of biology. (5 marks)

Characteristics of living things;

Nutrition: Process by which living things acquire and utilize nutrients: plants photosynthesize; animals feed on already manufactured foods.
Respiration: energy-producing process occurring in all the cells of living things.
Gaseous Exchange: where living things take in air (oxygen) and give out air(carbon iv oxide) across respiratory surfaces.
Excretion: Process by which waste or harmful materials resulting from chemical reactions within cells of living things are eliminated. Excess of such materials poison living things.
Growth and Development: Growth –is the irreversible increase in size and Mass.—Essential for body function. Development –Irreversible change in complexity of the structure of living things.
Reproduction: Process by which living things give rise to new individuals of the same kind.
Irritability: Is the ability of living things to perceive changes in their surroundings and respond to them appropriately. E.g. reaction to changes in temperature, humidity, light, pressure and to the presence of certain chemicals.
Movement: Change in position by either a part or the whole living thing. Locomotion – Progressive change in position by the whole living thing. In animals, movement include; swimming, walking, running, flying. In plants, closing of leaves, folding of leaves, closing of flowers, growing of shoots towards light etc.

Question

List four uses of energy obtained from the process of respiration. (4 marks).
List six characteristics of living things (6 marks).

Collection of specimens

Apparatus used

Sweep net: for catching flying insects.
Fish net: For trapping small fish and other small water animals.
Pooter:For sucking small animals from rock surfaces and tree barks.
Bait trap: For attracting and trapping small animals e.g. rats.
Pit fall trap: For catching crawling animals.
Pair of forceps: picking up small crawling animals e.g. stinging insects.
Specimen bottles: keeping collected specimen. Larger specimens require large bottles.
The magnifying lens: Instrument used to enlarge objects. Lenses are found in microscope and the hand lens (magnifier). Its frame is marked e.g. x8 or x10—indicating how much larger will be the image compared to object.

Precautions during Collection and Observation of specimens

Collect only the number of specimen you need.
Do not harm the specimens during the capture or collection exercise.
Handle dangerous or injurious specimens with care e.g. stinging plants or insects i.e. use forceps or hand gloves.
The teacher will immobilize highly mobile animals. (diethyl ether, formalin, chloroform)
Do not destroy the natural habitat of the specimens.

Practical activity 2

Practical activity 3

Comparison between plants and animals

Plants	Animals
1. Green in colour( have chlorophyll)	1. Lack chlorophyll thus feed on readymade food.
2. Their cells have cellulose cell walls.	2. Cells lack cellulose cell walls.
3. Respond slowly to changes in the environment.	3. Respond quickly.
4. Lack specialized excretory organs.	4. Have complex excretory organs.
5. Do not move about.	5. Move about in search of food and water.
6. Growth occurs in shoot and root tips.(apical growth)	6.Growth occurs in all body parts9intercalary growth).

Revision questions

CLASSIFICATION I

INTRODUCTION

Living things are also known as living organisms.

Organisms (forms of life) have distinguishing characteristics and therefore are grouped.

The Magnifying lens

-Is used for enlarging small objects.

(Diagram)

Procedure of its use

Place the object on the bench.
Move the hand lens from the object to the eye.
An enlarged image is seen.

Drawing magnification = Length of the drawing/ drawing Length

Length of the object/Actual Length

(Diagram)

External features of plants and animals

External features of plants

Rhizoids as in moss plant.
Fronds in ferns.

Roots, stems, leave, flowers, seeds, fruits, and cones in higher plants.

External features of animals

Tentacles in hydra
Feathers in birds

Shells in snails

Wings in birds
Fur and hair in mammals
Scales and fins in fish

Proglotids in tapeworms
Mammary glands in mammals

Locomotory Structures e.g. limbs in insects
Body pigmentation

Practical activity 1

To collect and observe animal specimens

To collect and observe plant specimens

What is classification?

-Is an area of biology that deals with the grouping of living organisms according to their structure. Organisms with similar structures are put under one group referred to as a taxon—taxa (plural).

The groupings also consider evolutionary relationships (phylogeny)—since all living organisms had a common origin at one time.

Taxonomy—Science of classification.

Taxonomist—Biologist who studies taxonomy.

Need for classification.

Reasons

To identify living organisms into their correct groups for reference and study
To bring together living organisms with similar characteristics but separate those with different features.
To arrange information of living organisms in an orderly manner. This avoids chaos and confusion.
To understand the evolutionary relationship between different organisms

Taxonomic Units

Are groups (taxa) into which organisms are placed as a matter of convenience.

Groups are based on observable characteristics common in the group.

In a classification scheme (taxonomic units or groups, a hierarchy of groups are recognized starting with the first largest and highest group; the Kingdom to the smallest and lowest unit; the species.

There are 7 major taxonomic units.

KINGDOM
	PHYLUM/ DIVISION
		CLASS
			ORDER
				FAMILY
					GENUS

SPECIES

The Kingdom

There are five Kingdoms of living organisms, namely:

Kingdom Monera: bacteria
Kingdom protoctista: algae, protozoa, amoeba, paramecium
Kingdom Fungi: Moulds, Yeast, Mushrooms
Kingdom Plantae: Moss plants, ferns, maize, garden pea, pine, meru oak, bean etc.
Kingdom Animalia: hydra, tapeworms, bees, human beings etc.

A kingdom is divided into Phyla in animals or divisions in plants and sorts out organisms based on body plan and form.

Plan is the adaptation to a special way of life.

The Class is further divided into small groups; Orders using structural features.

Orders are divided into families using structural features, then Families into Genera (singular genus) –based on recent common ancestral features that are less adaptive.

Genus is divided into species i.e. kind of plant, or animal.

Down the hierarchy, the number of organisms in each group decreases but their similarities increases.

The Species group members naturally interbreed to produce fertile off springs.

Minor differences are exhibited in the species groups e.g. on colour of the skin in human beings and varieties of plants.

The groups of the species are termed to as varieties, races or strains.

Classification of A human being and a maize plant

Taxonomic unit	Human being	maize	bean
kingdom	Animalia	plantae	plantae
Phylum or division	Chordata	Angiospermaphyta	Angiospermae
class	Mammalia	monocotyledonae	Dicotyledonae
order	Primates	Graminales	Rosales
family	Hominidae	Graminaceae	Leguminosae
genus	homo	zea	Phaseolus
species	sapiens	mays	Vulgaris

Scientific name Homo sapiens Zea mays phaseolus vulgaris

Scientific Naming Of Living Organisms

Present naming was developed by carolus Linnaeus 18^th c, where organisms were given 2 names in Latin language.

Living organisms have their scientific names and common names i.e. local or vernacular names.

Scientific naming uses the double naming system—Binomial system.

In binomial system, an organism is given both the genus and species name.

Binomial nomenclature (Double –naming system)-Is the assigning of scientific names to living organisms governed by a definite set of rules recognized internationally.

Principles of binomial nomenclature

The first, genus name, should begin with a capital letter and the second name, species, should begin or written in small letters e.g.

Lion—- Pantheraleo

Leopard—– Pantherapardus

Domestic dog—– Canisfarmiliaris

Human being— Homo sapiens

Maize plant—Zea mays

Lion and Leopard are closely related —Same genus but distantly related—different species.

The scientific names must be printed in italics in textbooks and where hand written to be underlined e.g.
The specific name (species) is frequently written with the name of the scientist who first adequately described and named the organism e.g.Phaseolus vulgaris i.e. Vulgaris is the scientist who described and named the bean plant.
Biologists should give a Latinized name for a newly described animal or plant species where Latin name is missing e.g.

Meladogynekikuyuensis – Is a scientific name of a nematode from kikuyu.

Aloe kilifiensis— A member of Aloeceae family from Kilifi discovery.

Garinsogaparviflorawaweruensis — a member of Macdonald eye family discovered by Waweru.

Study Question 1

Complete the table below

Taxon	Lion	Domestic dog	Garden pea	Napier grass
kingdom
Phylum/division
class
order
family
genus
species

Scientific name ——————— ———————— ———————– ————————

Revision Questions:

CLASSIFICATION 1

Review of the magnification lens
Calculating Magnification
External characteristics of plants and animals

Diversity of Living Organisms

Organisms with similar characteristics are placed under one group called taxon (taxa).
The science of classification is known as taxonomy.
Biologists who study taxonomy are called taxonomists.

Need For Classification

Help in identifying living organisms into their correct groups for reference.
It brings together organisms with similar characteristics and separates those with different features.
Help to organize information about living organisms in an orderly manner avoiding any confusion.
Help to understand the evolutionary relationship between different living organisms.

Historical Background of Classification

Long time ago classification was artificial where living things were classified as either plants or animals.
Plants were classified as herbs, shrubs and trees.
Animals were further divided into carnivores, herbivores and omnivores.
Today modern classification uses evolutionary relationships between living organisms.

Taxonomic Units of Classification

This refers to the groups into which living organisms are placed in classification.
These units start from the first largest and highest group (kingdom) to the smallest and lowest unit (species).
There are seven taxonomic units as shown below.

Kingdom

Carolus Linnaeus (1707-1778) initially introduced the two kingdom system of classification. However many new life forms have been discovered which are neither animals nor plants. This has led to a more accepted classification system that adopts five kingdoms. These are;

) Monera .eg bacteria
g algae and protozoa
Fungi e.g. mushrooms, moulds and yeast.
Plantae e.g. maize, ferns and all types of trees.
Animalia e.g. man, cow tapeworm, flies etc.

Kingdom is further divided into several phyla in animals or divisions in plants.

Phylum (phyla) or Division in plants.

It is the second largest and further divided into classes.

Class

Each class is divided into several orders.

Order

Orders are divided into smaller groups called families.

Family

Family is divided into several Genera.

Genus

Here members are closely related. It is further divided into the species.

Species

This is the smallest unit of classification.

Species is defined as a group of organisms whose members naturally interbreed to produce fertile offspring’s.

Members of a given species have small differences such as skin colour, height etc.

Classification of Man and Maize plant.( Table 2.1 Page 15 KLB Bk 1)

Scientific Naming of Living Organisms.

Today organisms are given two names in Latin language. This was developed by Carolus Linnaeus.
Latin language was used because it was widely spoken during his time.
In scientific naming, an organism is given the genus and the species name.
This double naming system is known as Binomial system (two name System)

Binomial Nomenclature.

This is the double naming system of organisms where organisms are assigned two names i.e. the generic name and the specific name.

In binomial nomenclature the following rules are observed.

Generic name is written first followed by the specific name. First letter in the generic name is in capital and the rest are in small letters. Specific name is written in small letters.
The two names are underlined separately when handwritten or italicised when printed.
Newly discovered species must be given Latinized names.
Specific name is frequently written with the name of the scientist who first adequately described and named the organism.

Examples

Revision Questions

CELL PHYSIOLOGY

This is the study of the functions of cell structures.

Membrane Structure and Properties

A membrane is a surface structure which encloses the cell and organelles. Membranes regulate the flow of materials into out of the cell or organelle.
Examples of membranes: cell membrane, tonoplast (membrane surrounding the vacuole), nuclear membrane, mitochondrial membrane, chloroplast membrane etc.

The Cell Membrane

It has three layers, two protein layers and a phos-pholipid layer sandwiched in between the two.

Diagram

Properties of Cell Membrane

Semi-permeability. – It has small pores allowing for the passage of molecules of small size into and out of the cell. Cell Wall however allows all materials to pass through it hence it is referred to as being Permeable.
Sensitivity to Changes in Temperature and pH – Extreme temperature and pH affects the cell membrane since it has some protein layers. Such changes alter the structure of the membrane affecting its normal functioning.
Possession of Electric Charges – it has both the negative and positive charges helping the cell to detect changes in the environment. These charges also affect the manner in which substances move in and out of the cell

Physiological Processes

The ability of the cell to control the movement of substances in and out of the cell is achieved through physiological processes such as Diffusion, Osmosis and Active Transport.

Diffusion

This is a process by which particles move from a region of high concentration to a region of low concentration.

Practical Activity 1

To demonstrate diffusion using potassium permanganate (VII)

The difference in concentration of particles between the region of high concentration and the region of low concentration is known as the diffusion gradient.

Role of Diffusion in Living Organisms

Absorption of Materials

Mineral salts in the soil enter the root by diffusion since their concentration in the soil is greater than in the root hair cells.
Digested food (glucose and amino acids) diffuse across the wall of the ileum into the blood for transport to rest of the body.

Gaseous Exchange in Plants and Animals

In both plants and animals, respiratory gases (oxygen and Carbon (IV) oxide) are exchanged through simple diffusion depending on their concentration gradient.

Excretion of Nitrogenous Wastes
Transport of Manufactured Food form Leaves to other Plant Parts.

Factors Affecting Diffusion

Diffusion Gradient

A greater diffusion gradient between two points increases the rate of diffusion.

Surface Area to Volume Ratio

The higher the ratio the greater the rate of diffusion and the lower the ratio the lower the rate.
This means that small organisms expose a large surface area to the surrounding compared to large organisms.
Small organisms therefore depend on diffusion as a means of transport of foods, respiratory gases and waste products.

Diagrams

Thickness of Membranes and Tissues

The thicker the membrane the lower the rate of diffusion because the distance covered by the diffusing molecules is greater. The thinner the membrane, the faster the rate.
Size of the Molecules
Small and light molecules diffuse faster than large and heavy molecules.

Temperature

Increase in temperature increases the energy content in molecules causing them to move faster.

Osmosis

This is the process where solvent molecules (water) move from a lowly concentrated solution (dilute) to a highly concentrated solution across a semi-permeable membrane.

Diagram fig 4.6

The highly concentrated solution is known as Hypertonic Solution.
The lowly concentrated solution is called Hypotonic solution.
Solution of the same concentration are said to be Isotonic.
Osmosis is a special type of diffusion because it involves the movement of solvent (water) molecules from their region of high concentration to region of low concentration across a semi permeable membrane.

Practical activity 2

Practical activity 3

Osmotic Pressure

This is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semi permeable membrane. This is the pressure needed to nullify osmosis.
Osmotic pressure is measured using the

Osmotic Potential

This is the 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

Cell membrane of the animal cell is semi permeable just like the dialysis/visking tubing.
Cytoplasm contains dissolved sugars and salts in solution form.
If an animal cell e.g. a red blood cell is placed in distilled water (hypotonic solution), water flows in by osmosis.
The cell would swell up and eventually burst because the cell membrane is weak. The bursting of the red blood cell when placed in hypotonic solution is called Haemolysis.
If a similar red blood cell is placed in a hypertonic solution, water is drawn out of the cell by osmosis. The cell will shrink by a process called Crenation.
Body fluids surrounding the cells must therefore have same concentration as to that which is found inside the cell.

Diagrams

Water Relations in Plants

When a plant cell is placed in a hypotonic solution it gains water by osmosis and distends outwards.
As the cell gains more water, its vacuole enlarges and exerts an outward pressure called turgor pressure. As more water is drawn in, the cell becomes firm and rigid and is said to be turgid.
The cell wall in plant cell is rigid and prevents the cell from bursting unlike the case in animal cells.
The cell wall develops a resistant pressure that pushes towards the inside. This pressure is equal and opposite the turgor pressure and is called wall pressure.

Diagrams

When a plant cell is placed in hypertonic solution, water molecules move out of the cell into the solution by osmosis. The cell shrinks and becomes flaccid.
If the cell continues to lose more water, plasma membrane pulls away from the cell wall towards the center.
The process through which plant cells lose water, shrink and become flaccid is called
Plasmolysis can be reversed by placing a flaccid cell in distilled water and this process is called

Study Question 5

Practical Activity 4

Wilting

When plants lose water through evaporation and transpiration, cells lose turgidity, shrink and the plant droops. This is called
If water supply from the soil is inadequate, plants do not recover hence permanent wilting.

Study Question 6

Role of Osmosis in Organisms

Absorption of water from the soil

Root hair cells of plants absorb water from the soil by osmosis.

Support

Cells of herbaceous plants, which are less woody, absorb water, become turgid hence support.

Opening and closing of the stomata

During the day, guard cells synthesize glucose, draw in water, become turgid hence open the stomata.
During the night, they lose turgidity since there is no photosynthesis. As a result, they shrink thus closing the stomata.

Feeding in insectivorous plants

These plants are able to change their turgor pressure on the leaves which close trapping insects which are digested to provide the plant with nitrogen.

Osmoregulation

In the kidney tubules, water is reabsorbed back to the body by osmosis.

Factors Affecting Osmosis

Concentration of Solutions and Concentration Gradient. The greater the concentration gradient between two points, the faster the rate of osmosis.
Optimum Temperature as long as it does not destroy the semi-permeability of the membrane.

Active Transport

This is the process that moves substances across cell membranes against a concentrationgradient.
This process requires energy to move these substances across cell membranes and involves
Substances such as amino acids, sugar and many ions are taken in by living organisms through active transport.

Role of Active Transport

Re-absorption of sugars and useful substances by the kidney
Absorption of some mineral salts by plant roots
Absorption of digested food from the alimentary canal into the blood stream
Accumulation of substances in the body to offset osmotic imbalance in arid and saline environment
Excretion of waste products from body cells

Factors Affecting Active Transport.

Oxygen concentration.
Change in pH.
Glucose concentration.
Enzyme inhibitors.

NB/ Any factor affecting energy production affect the rate of active transport.

Revision Questions.

Cell Specialization, Tissues, Organs and Organ Systems

Cell specialization

This is where cells are modified to perform specific functions. Such cells are said to be specialized.
Examples include the sperm cell which has tail for swimming and the root hair cell which is extended creating large surface area for water absorption.

These are cells of a particular type that are grouped together to perform the same function.

Animal tissues include;

Epithelial tissue – which is a thin continuous layer of cells for lining and protection of internal and external surfaces.
Skeletal – it is a bundle of elongated cells with fibres that can contract. Its contraction and relaxation brings about movement.
Blood tissue – this is a fluid containing red blood cells, white blood cells and platelets. It transports many substances and protects the body against infections.

Connective tissue – made up of strong fibres that connect other tissues and organs holding them together.

Plant tissues include:

Epidermal tissue of a plant – this is a single layer of cells protecting the inner tissues of the plant.
Palisade tissue – this is a group of cells rich in chloroplasts containing chlorophyll. They absorb light energy during photosynthesis.
Parenchyma tissue – it is made thin walled irregularly shaped cells. They store water and food.
Vascular bundle – consists of the xylem and phloem. Xylem conducts water and mineral salts while phloem conducts food substances.

Organs

Many tissues become specialized and grouped together to perform a functional unit called the organ.
Examples of organs in plants include; roots, leaves, flowers and stem.
In animals they include heart, lungs, kidney, brain, stomach and the liver.

Organ systems.

This is made of several organs whose functions are coordinated and synchronized to realize an effective action is called an organ system. Examples include; digestive, circulatory, excretory, respiratory, reproductive and nervous system.

Revision Questions

MICROSCOPE

Microscope Parts & Function

Parts of the Microscope

	1. Eyepiece	Contains a magnifying lens that focuses the image from the objective into your eye.
	2. Course Adjust	For focusing under low magnification
	3. Fine Adjust	For focusing under high magnification or low
	4. Low Power Objective	For large specimens or overview
	5. High Power Objective	For detailed viewing or small specimens
	6. Specimen on glass slide	What you want to look at
	7. Stage	Supports specimen in correct location to lens
	8. Condenser	Focuses the light on specimen
	9. Diaphragm (iris or disc)	Regulates amount of light and contrast
	10. Light Source	Illuminates the specimen for viewing

Handling and Care of the Microscope

The following rule should be observed:

Use both hand when carrying the microscope. One hand should hold the base and the other holds the limb.
Never place the microscope too close to the edge of the bench.
Do not touch the mirror and the lenses with the fingers.
Clean dirty lenses using soft tissue.
Clean other parts using a soft cloth.
Do not wet any part of the microscope.
Make sure the low power clicks into position in line with the eye piece before and after use.
Always store the microscope in a safe place free from dust and moisture.

Using the Microscope

Place microscope on the bench with the stage facing away from you.
Turn the low power objective lens until it clicks into position.
Ensure the diaphragm is fully open.
Look through the eyepiece with one eye. Adjust the mirror to ensure maximum light can pass through.
Place the slide containing the specimen on the stage and clip it into position. Make sure the slide is at the centre of the field of view.
Again look through the eyepiece while adjusting the mirror to ensure maximum light reach the specimen.
Use the coarse adjustment knob to bring the low power objective lens to the lowest point. While viewing through the eyepiece, 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 see.
For higher magnification, turn the medium power into position and adjust the focus using the coarse knob. Use the fine adjustment knob for sharper focus.
For even large magnifications, turn the high power objective lens into position. In this case use only the fine adjustment knob to bring details into sharper focus.

Magnification

Magnification of the object viewed under the microscope is calculated by;

Magnification = Eye Piece Lens Magnification X Objective Lens Magnification.

If the eyepiece lens has the magnification of x5 and the low power objective lens has a magnification of x10, the total magnification is 5×10=50.

Study Question 1

Fill the table below.

Eye piece lens maginification	Objective lens magnification	Total magnification
X5	X4
X10	X5
X10		X100
	X40	X600
X10	X100

Practical Activity 1

Cell Structures as Seen Under the Light Microscope

The following cell organelles can be seen under the light microscope.
Cell wall.
Cell membrane
Cytoplasm
Nucleus

Diagrams- plant and animal cells

The Electron Microscope.

It is more powerful than the light microscope.
It can magnify up to 500,000 times and has high resolving power.
The high resolving power of the electron microscope enables it to separate objects which lie close to one another.
Electron microscope uses a beam of electrons instead of light to illuminate the object.

Study Question 2

Practical Activity 2

Cell Structures as Seen Under the Electron Microscope

Diagrams – Plant and Animal Cells

The Cell Organelles

Cell membrane (Plasma Membrane).

It has three layers i.e. one layer of phospho-lipid layer sandwiched between two protein layers.
It is flexible with pores and ahs the following main functions.

Encloses all the cell contents.
It allows selective movement of substances into and out of the cell since it is semi-permeable.

Diagram

Cytoplasm

It is s fluid medium in which chemical reactions take place.
It has some movement called cytoplasmic streaming.
It contains organelles, starch, glycogen, fat droplets and other dissolved substances.
Nucleus
It has double membrane called the nuclear membrane.
The membrane has pores allowing passage of materials into and out of the cell.
Nucleus has a fluid called nucleoplasm in which the nucleolus and chromatin are suspended.
Nucleolus manufactures ribosomes while chromatin contains the hereditary material.

Mitochondria(Mitochondrion)

They are sausage shaped and are the respiratory sites.
Mitochondrion has two membranes. Inner membrane is greatly folded into cristae to increase the surface area for respiration.
Cells that require a lot of energy have large number of mitochondria e.g. muscle cell, sperm cell, kidney cell etc.

Diagram

Endoplasmic Reticulum (ER)

Some endoplasmic reticulums have granules called Ribosomes on their surfaces hence referred to as rough endoplasmic reticulum.
Others do not contain ribosomes hence the name smooth endoplasmic reticulum.
Rough endoplasmic reticulum transport proteins while the smooth endoplasmic reticulum transports lipids.

Diagrams

Ribosomes

They are spherical in shape and form the site for protein synthesis.
Lysosomes
They contain lytic enzymes which break down large molecules, destroy worn out organelles or even the entire cell.
Golgi Bodies (Golgi apparatus)
Their function is to package and transport glyco-proteins.
They are also associated with secretion of synthesized proteins and carbohydrates.

Diagram

Centrioles

They are rod shaped structures that are used in cell division and in the formation of cilia and flagella.
Plant cells lack the Centrioles.

Chloroplasts

They are egg shaped and contain two membranes.
Chloroplast has chlorophyll which traps light energy to be used during photosynthesis.

Vacuoles

This are sacs filled with a fluid called cell sap.
Animal cells contain small vacuoles while plant cells have large vacuoles.
Sap vacuoles store sugars and salts.
Food vacuole store and digest food while contractile vacuoles excrete unwanted materials from the cell.
Cell wall
It is a rigid outer cover of the plant cells made of cellulose.
It gives the plant cell a definite shape while providing mechanical support and protection.
Cell wall also allows water, gases and other materials to pass through it.

Study Question 3

Differences between Plant and Animal Cells

Preparation of Temporary Slides

Practical Activity 3

Estimation of Cell Sizes.

NUTRITION IN PLANTS AND ANIMALS

Nutrition

This is the process by which organisms obtain and Assimilate
There are two modes of nutrition; Autotrophism and Heterotrophism.

Autotrophism

This is where living organism manufacture its own complex food substances from simple substances such as carbon (iv) oxide, water, light or chemical energy.
Where sunlight is used as a source of energy, the process is referred to as photosynthesis.
Photo means light while synthesis means to make.
Some nonegreen plants make their own food using energy obtained from certain chemicals through a process called
Organisms that make their own food are referred to as autotrophs.

Heterotrophism

This is where organisms take in complex food materials such as carbohydrates, proteins and fats obtained from bodies of plants and animals.
Organisms that feed on already manufactured foods are called Heterotrophs.

Autotrophism

External Structure of a Leaf

A leaf is a flattened organ which is attached to the stem or a branch of a plant.

Diagrams

Parts of a leaf

Lamina: This is the flat surface. It is green in colour and contain the photosynthetic tissue.

Midrib: This is a thick structure running through the middle of the leaf

Veins: They arise from the midrib to forming an extensive network of veins.

Leaf Apex: This is the tip of the leaf and usually it is pointed.

Petiole: It attaches the leaf to the stem or branch.

In some monocotyledonous plants the leaves are attached to the stem by the leaf sheath.

Practical Activity 1: To examine the External Features of a Dicotyledonous and Monocotyledonous leaf

Study Question 1

InternalStructure of a Leaf

Internal structure of the leaf is composed of the following parts.
It is a thin waterproof and transparent layer that coats the upper and lower surfaces of the leaf.
It reduces excess water loss and protects the inner tissue of the plant against mechanical injury.
It also prevents entry of disease causing micro organisms.
Since it is transparent, it allows penetration of light for photosynthesis.
It is a one cell thick tissue on both the upper and lower leaf surfaces.
It secretes the cuticle and also protects the inner tissues from mechanical damage and prevents entry of pathogens.
Epidermal cells have no chloroplast except the guard cells.
Guard cells are special bean shaped cells. They have chloroplast and are able to carry out photosynthesis hence controlling the opening and closing of the stomata.
Air moves into and out of the leaf through the stomata.
Palisade layer.
This is layer of cells located beneath the upper epidermis.
It is made of cylindrical shaped cells closely packed They have numerous chloroplasts containing chlorophyll.
Their position and arrangement enables them to receive maximum light.
Spongy Mesophyll Layer.
This is below the palisade layer. The cells are irregularly shaped and loosely packed creating large air spaces in between them.
The air spaces allow gases to diffuse in between the cells. They contain fewer chloroplasts as compared to the palisade cells.
Leaf Veins.
Each vein is a vascular bundle consisting of xylem and phloem.
Xylem conducts water and mineral salts from the roots to the leaves while the phloem translocates manufactured food from the leaves to the rest of the plant.

Study Question 2

Adaptations of Leaves to Photosynthesis.

Broad and flat lamina to increase surface area of Carbon (IV) oxide and sunlight absorption.
Thin transparent cuticle and upper epidermis; to allow easier penetration of light to photosynthetic cells;
Thin; for faster diffusion of gases;
Palisade cells placed next to the upper surface; to trap maximum light for photosynthesis;
Palisade cells with numerous chloroplasts; to trap maximum amount of light for photosynthesis;
Large/ intercellular air spaces in the spongy mesophyll layer; for storage of Carbon (IV) oxide for easier gaseous exchange;
Waxy water proof cuticle; to reduce water loss sand reflect excess light;
Leaf mosaic/ non-overlapping leaves; for maximum exposure to light;
Guard cells, modified cells to open and close stomata; to control amount of water loss from the leaf and allows gaseous exchange;
Leaves have leaf veins; xylem to conduct water to photosynthetic cells, Phloem to translocate products of photosynthesis to other parts of plant;

The Chloroplast

They are disc shaped organelles found in the cytoplasm of plant cells.
Each chloroplast has a double membrane; the inner and outer membrane.
Chloroplasts are made of layers of membranes called lamellae contained in a fluid matrix called stroma.
Several lamellae come together to form the granum (grana).
Granum contains chlorophyll molecules and other photosynthetic pigments.
The stroma contains enzymes that speed up the rate of photosynthesis.

Practical Activity 2: To Observe Distribution of Stomata

Study Question 3.

The Process of Photosynthesis

The raw materials for photosynthesis are; water and carbon (IV) oxide. The process however requires the presence of sunlight energy and chlorophyll pigment.
The products of photosynthesis are glucose and oxygen. The process can be summarized using an equation as shown below.

6H₂O + 6CO₂ ———-> C₆H₁₂O₆+ 6O₂

Water + Carbon (IV) oxide Glucose + Oxygen.

The above chemical equation translates as:

Six molecules of water plus six molecules of carbon (IV) Oxide produce one molecule of sugar plus six molecules of oxygen

The process of photosynthesis is however more complex than shown in the above equation and can be divided into two stage; the light and dark

Light stage (Light Dependent Stage)

– Occurs in the grana containing chlorophyll which traps / absorbs sun light energy.

– This Energy is used to split water molecules into hydrogen ion and oxygen gas.

– This process is called photolysis of water and is shown below.

2H₂O 4H + O₂

(Water) Hydrogen atom Oxygen

– Hydrogen atoms produced here enter into the dark stage.

– Oxygen gas removed through stomata or is used for respiration within the plant;

– Some Light energy is used in Adenosine Triphosphate (ATP) formation; ATP an energy rich compound.

– ATP is later used in the dark stage.

Dark stage. (Light Independent Stage)

– Carbon (IV) oxide combines with hydrogen atoms to form glucose/simple carbohydrate.

– This is called Carbon (IV) Oxide fixation.

Carbon (IV) oxide + Hydrogen Atom Simple Carbohydrate

CO₂ + 4H C₆H₁₂O₆

– This stage takes place in the stroma and proceeds whether light is present or not.

– ATP Energy from light stage is used to provide the required energy in this reaction;

– Simple sugars formed are used for respiration to provide energy or are converted to storable forms e.g lipids, proteins, starch, cellulose, etc.

Study Question 4

Practical Activity 3: To Investigate the Presence of Starch in a Leaf.

Study Question 5

Factors Affecting the Rate of Photosynthesis

Light Intensity.
Increase in light intensity increase the rate of photosynthesis up to a certain level where it slows down and finally levels off.
Very bright sunshine may damage the plant tissues due to high amount of ultra violet light.
Light quality or light wavelength also affects the rate of photosynthesis.
Red and blue wavelengths of light are required by most plants for photosynthesis.

Range of optimum light intensity

Light intensity

Carbon (IV) oxide concentration
Increase in Carbon (IV) oxide concentration increases the rate of photosynthesis linearly up to a certain level after which it slows down and levels off.

Range of optimum CO₂ concentration

Carbon (IV) oxide concentration

Temperature
Photosynthesis is an enzyme controlled process, therefore increase in temperature increase the rate of photosynthesis up to the optimum temperature.
Increase in temperature beyond the optimum decreases the rate sharply as the enzymes become denatured.
Water
Plants need water for photosynthesis. Hydrogen atoms required in the dark stage during Carbon (IV) oxide fixation are derived from water during photolysis.

Study Question 6

Practical Activity 4: To Investigate Factors Necessary for Photosynthesis.

Light

Study Question 7

Carbon (IV) oxide.

Study Question 8

Study Question 9

Study Question 10

Practical Activity 5: To Investigate the Gas Produced During Photosynthesis.

Study Question 11

Chemical Compounds Which Constitute Living Organisms

Cells, tissues and organs are made of chemicals which are referred to as chemicals of life.
The study of chemical compounds found in living organisms and reactions in which they take part is called Biochemistry.
Chemicals of life include carbohydrates, lipids and proteins.

Carbohydrates

They are compounds of carbon, hydrogen and oxygen in the ratio of 1:2:1 respectively.
Carbohydrates have a general formula of (CH₂O)_nwhere n represents the number of carbon atoms in a molecule of carbohydrate.
Carbohydrates are divided into three groups; Monosaccharide’s, Disaccharides and Polysaccharides.

Monosaccharides

They are the simplest carbohydrates and have a general chemical formula of (CH₂O)_n where n = 6.
Their chemical formular is therefore C₆H₁₂O₆. They include; glucose, fructose, galactose etc.

Properties of Monosaccharides

They are soluble in water to form sweet tasting solutions.
They are crystalissable.

They have the reducing property where they reduce copper sulphate in Benedicts solution to red copper (I) oxide.

Functions

They are oxidized to release energy during respiration.
When condensed together, they form polysaccharides such as starch, cellulose or glycogen.
ii) Disaccharides

They are formed by linking two Monosaccharide molecules through the process of condensation where a molecule of water is liberated.

Condensation

Monosaccharide + Monosaccharide Disaccharide + Water.

C₆H₁₂O₆+ C₆H₁₂O₆ C₆H₂₂O₁₁+ H₂O

Examples

Glucose + Glucose Maltose + Water.

Glucose + Fructose Sucrose + Water

Glucose + Galactose Lactose + Water.

The type of disaccharide formed depends on the monosaccharide units that condense together.

Properties of Disaccharides

i) Soluble in water to form sweet tasting solutions
ii) They are non reducing sugars. Some such as the maltose can reduce copper sulphate in Benedict’s solution when heated together and are therefore referred to as complex reducing sugars.

iii) They are readily broken into their constituent monosaccharide molecules in a process known as Hydrolysis in the presence of water.

Hydrolysis

Disaccharide + Water Monosaccharide + Monosaccharide

C₆H₂₂O₁₁+ H₂O Hydrolysis C₆H₁₂O₆+ C₆H₁₂O₆

Sucrose + Water Hydrolysis Glucose + Fructose

Lactose + Water Hydrolysis Glucose + Galactose

Maltose + Water Hydrolysis. Glucose + Glucose.

Naturally disaccharides are hydrolyzed by enzymes. In the laboratory, hydrolysis is achieved by boiling them in dilute Hydrochloric acid.

Functions

They are hydrolyzed by enzymes into monosaccharide’s which are then oxidized to produce energy.

iii) Polysaccharides.Theyare made of many monosaccharide molecules hence are long and more complex.

They have a general formula of (C₆H₁₀O₅)_n; where the value of n is a very large number.

Examples of polysaccharides

Starch

It is present as stored food in plant tissues e.g. maize, wheat, potatoes, rice etc.

Cellulose

This is the component of the cell wall in plants. Cellulose gives the plant cells their definite shape.
Glycogen
This is the form in which carbohydrates are stored in animal tissues. Excess glucose is converted into glycogen for storage in the liver.

Properties of Polysaccharides

All are insoluble in water.
Do not have a sweet taste hence are referred to as non-sugars.

Study Question 12

Practical Activity 6: To Carry out Food Tests for Carbohydrates

i) Starch
ii) Reducing sugars

iii) Non Reducing Sugars

Lipids

These are the fats and oils. Fats are found in animals while oils are found in plants.
Oils are liquid while the fats are solid at room temperature.
They contain carbon, hydrogen and oxygen just like the carbohydrates. However they contain fewer number of oxygen atoms than in carbohydrates.
Lipids are made up of three fatty acid molecules and one molecule of
The nature of a lipid formed, depends on the fatty acids it contains. Glycerol remains the same in all lipids.

Diagram

Complex lipids are formed through condensation of many lipid molecules just like in carbohydrates.
Examples of complex lipids include; phospholipids, waxes, steroids and cholesterol.
Presence of lipids in a food sample is detected using the grease spot test or emulsion test.

Properties of Lipids

When fats are heated they change into liquid while oils solidify under low temperature.
Both fats and oils are insoluble in water. They however dissolve in organic solvents such as alcohol to form emulsions and suspensions.
Lipids are inert hence can be stored in the tissues of organisms.

Functions of Lipids

Source of energy

They give almost twice as much energy as the Monosaccharides.

Source of metabolic water

When oxidized, lipids release more water than Monosaccharides. Such water is referred to as metabolic water.
Structural compounds
Lipids are constituents of plasma membrane and protoplasm.

Heat insulation

Fats are deposited under the skin of animals forming the adipose tissue which acts as a heat insulator.
Mammals in the temperate regions have thick adipose tissue to greatly reduced heat loss.
Thick adipose tissue in aquatic animals helps them to be buoyant in water.

Protection

Fat is deposited around the major organs such as kidney, heart etc where they act as shock absorber.
Wax in plant cuticles reduces excessive water loss.

Study Question 13

Practical Activity 7: testing for the Presence of Lipids

i) The Grease Spot
ii) The Emulsion Test
Proteins

Like carbohydrates and lipids, proteins are compounds of carbon, hydrogen and oxygen.
In addition they contain nitrogen and sometimes phosphorous and sulphur.
Some proteins such as haemoglobin contain other elements such as iron.
Proteins are made up of small units called amino acids. There are about 20 different types of amino acids.
All amino acids contain the amino group (-NH₂) which consists of hydrogen and nitrogen.
Two amino acids combine to form a dipeptide molecule through the process of condensation.
The bond between two amino acids is called peptide Bond. Many amino acids join together to form a long protein chain called polypeptide chain.
The type and sequence of amino acids contained in such a chain determine the uniqueness of the protein being formed.

Properties of Proteins

They dissolve in water to form colloidal suspensions (not true solutions) where particles remain suspended in water.
They are denatured by temperatures above 40 ⁰ Heat alters the structure of the protein molecule. Chemicals such as detergents, acids, bases and organic solvents also denature proteins.
They are amphoteric whereby they have both acidic and basic properties. This property enables them to combine with non-protein compounds to form conjugated proteins such as mucus, and haemoglobin. In mucus the non protein compound is a carbohydrate while in haemoglobin, iron is a non protein.

Functions of Proteins

Structural Functions
Proteins make the framework of living systems e.g. plasma membrane, connective tissues, muscle fibres, hair, nails, hooves, skeletal materials etc.
Metabolic Regulators
These are divided into two

a) Enzymes

Enzymes are organic catalysts which speed up the rate of metabolic reactions such as respiration, photosynthesis, digestion etc.

b) Hormones

They are chemical messengers which regulate many body processes such as growth, reproduction, amount of sugars, salts and water in the blood etc.
Source of Energy
Under extreme starvation, proteins are broken down to release energy.

Study question 14

Practical Activity 8

To Test for Proteins

Enzymes

They are organic catalysts which are protein in nature. They speed up or slow down the rate of chemical reactions in the body without themselves being used up.
They are divided into two;

a) Extracellular Enzymes

Extracellular enzymes are produced within the cells but are used outside the cells which produce them e.g. the digestive enzymes.

b) Intracellular Enzymes

They are secreted and used within the cells which produce them e.g. the respiratory enzymes.

Naming of the Enzyme

There are two methods on naming enzymes;

i) Trivial Naming

Enzymes are given names of persons who discovered them.
The names end in -in such as pepsin, trypsin ptyalin etc.

ii) Use of suffix –ase

This is the modern method of naming. The suffix –ase is added to the substrate (type of food) or the reaction the enzyme catalyzes.

Example 1

Substrate	Enzyme
Carbohydrate	Carbohydrase
Starch e.g. amylose	Amylase
Sucrose	Sucrase
Maltose	Maltase
Protein	Protease
Lipid	Lipase

Example 2

Reaction	Enzyme
Hydrolysis	Hydrolase
Oxidation	Oxidase
Reduction	Reductase

Properties of Enzymes

They are protein in nature hence are affected by changes in temperature and pH.
They are substrate specific.
They are efficient in small amounts as they are not affected by the reactions they catalyze. They can be used again and again.
They are catalysts that speed up the rate cellular reactions and are not used up in the reactions they catalyses.
Most of the enzyme controlled reactions are reversible.

Factors Affecting the Rate of Enzyme Controlled Reactions

Temperature
Enzymes are sensitive to changes in temperature and pH since they are protein in nature.
Enzymes work best within a narrow range of temperature called the optimum temperature.
Above the optimum temperature, reaction decreases sharply as the enzymes are denatured.
Most enzymes have optimum temperature between 35-40^o
Very low temperature inactivates the enzymes hence decrease rate of reaction.

Diagrams

pH
Most enzymes have a pH of close to 7.
Some however work best in acidic pH e.g. pepsin while others work best in alkaline conditions.
As pH changes from the optimum, enzyme activity decreases.
Extreme acidity or alkalinity denatures most enzymes.

Diagrams

Specificity
Enzymes are specific in nature where a particular enzyme acts on a particular specific substrate.
For example, sucrose works on sucrose and not any other substrate.
Substrate Concentration and Enzyme Concentration.
When substrate concentration increases, the rate of enzyme reaction also increases upto a certain level.
Further increase does not increase the rate of reaction as all the active sites of an enzyme are occupied.
When enzyme molecules are increased, the rate of reaction increases proportionally.

Diagrams

Enzyme Co-factors and Co-enzymes
Co-factors are non protein substances which activates enzymes. They are required in small quantities and they include metallic ions such as those of iron, magnesium, zinc, copper etc. Some are vitamins.
Co-enzymes are non protein molecules that work in association with particular enzymes. Most co-enzymes are derived from vitamins.
Enzyme Inhibitors
Inhibitors compete with the normal substrate for the active sites and they take up the active site of the enzyme permanently.
There are two types of inhibitors;

a) Competitive Inhibitors

These are chemicals closely related to normal substrate and they compete for active sites with the normal substrate. They slow down the rate of reaction.

b) Non Competitive Inhibitors

They do not compete with the substrate. They combine permanently with enzyme molecules thus blocking the active sites. They include poisons such as cyanides, mercury and silver-arsenic compounds.

Importance of Enzymes

Enzymes speed up the rate of cellular reactions and also control them. This way, they help prevent violent reactions in the cells.

Study Question 15

Practical Activity 9

Study Question 16

Study Question 17

Practical Activity 10

Teachers' Resources

BIOLOGY REVISION NOTES FORM 1 TO 4 IN PDF

October 5, 2025 Maverick John Leave a comment

BIOLOGY FORM 4 REVISION 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

iii) List some characteristics which are inherited

size
height/length
colour/type
shape
yield

HERE ARE THE NOTES IN PDF;

BIOLOGY FORM FOUR SUMMARIZED NOTES

Biology notes form 1-4 pdf download free

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

F1 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

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 F1 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 1red:2pink:1white

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

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

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

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

State the importance of sex linkage

possible to determine sex of day old chicks

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 X^hX

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

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

Name the disorders in humans caused by gene mutation

albinism
sickle cell anaemia
achondroplasia/chondordystorphic dwarfism
haemophilia
colour blindness
phenylketonuria

State the practical applications of genetics
1. Breeding programmes (research)

high yielding/hybrid vigour/heterosis
resistance to diseases
resistance to drought/salinity
early maturing

Genetic engineering

genetic manipulation to produce desired characteristics

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.

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

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

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.

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)

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

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
illama, jaguar, panther in S. America
lion, camel in Africa
tiger in Asia

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

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

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

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
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

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

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/parts 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

Tropisms

Taxes

– growth curvature in response

– slow

– influenced by hormones

– locomotory response

– fast

– external influence

d) The diagram below represents growing seedlings which were subjected to unilateral light at the beginning of an experiment

State the results of P, Q and R after 5 days

P will bend/grow towards light
Q will remain straight/have little or no growth
R will remain/grow straight/grow upwards

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

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

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

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

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

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 right 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

Describe the structure and function of a motor neurone

motor neurone relays impulses from CNS (brain/spinal cord) to effectors ( muscles/glands)

Describe the structure and function of sensory neurone

sensory neurone relays impulses from receptors (sense organs) to CNS

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)

Describe the structure and function of a relay neurone

also called intermediate/internuncial/associate/connector/interneurone
locate inside central nervous system and spinal cord
usually lack myelin sheath

c) State the functions 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

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

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. Are stimulated
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

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

What are the functions of a synapse?

allows transmission of nerve impulses from neurone to neurone
ensures nerve impulses travel in only one direction
in the brain they store information/memory

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

Simple reflex	Conditioned reflex
independent of experience one stimulus to evoke response some sensory and motor neurons used reflex is simple	dependent on experience both substitute and original reflex evoke response sensory component replaced but motor remains unchanged reflex is modified

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	Hormone	Functions
Thyroid	Thyroxine	Increases rate of metabolism
Parathyroid	Parathyroid hormone	Regulates calcium and phosphate levels
Pituitary	Hormone growth	Regulate growth of body
	Gonadotrophic hormone	Stimulates the development of male and female sex organs
	Lactogenic hormone (prolactin)	Stimulates secretion of milk after child birth
	Thyrotropic hormone(TSH)	– proper functioning of thyroid gland/thyroxine production
	Adrenocorthicotropic hormone (ACTH)	– stimulates release of adrenal cortex hormone
	Oxytocin	regulates blood pressure stimulates smooth muscles stimulates contraction of uterus during childbirth aids in flow of milk from mammary glands
	Follicle stimulating hormone(FSH)	causes maturation of egg in females stimulates sperm production in males
	Vasopressin (ADH) Antiduretic hormone	– regulates water balance by kidneys
Adrenal	Adrenaline (epinephrine)	for emergency prepares body to cope up with stress
	Aldosterone	– maintains balance of salt and water in blood
	Cortisone	breaks down stored proteins to amino acids aids in breakdown of adipose tissue regulates sugar level in blood prevents inflammation
	Sex hormones	supplements sex hormones produced by gonads promotes development of sexual characteristics
Pancrease	Insulin	regulates level of sugar in blood enables liver to store sugar
Pancrease	Glucagons	regulates level of sugar in blood
Ovaries	Oestrogen	causes sexual secondary characteristics in females prepares uterus for pregnancy
Ovaries	Progesterone	growth of mucus lining of uterus maintains uterus during pregnancy
Testes	Androgens(testosterone)	causes secondary sexual characteristics in males
Stomach cells	Gastrin	stimulates release of gastric juice
Intestinal cells	Secretin	stimulate release of pancreatic juice

iv) Give the differences between nervous and endocrine (hormonal) communication

Nervous	Hormonal (endocrine)
Response confined to effector organs (localized targets)	Response more widespread (various targets)
Speed of response is rapid	Response less rapid
Nervous impulse thro\\ugh nerves/nerve cell/neurons	Hormones transferred through blood
Duration of response is short	Persist for long
Speed of transmission is rapid	Speed of transmission is slower
Transmission is electrical	Transmission is chemical

v) State the effects of over secretion and under secretion of adrenaline and thyroxine in humans

Hormone	Over secretion	Under secretion
Adrenaline	thin toneless muscles high blood pressure weak bones obesity early onset of sexual development	low blood pressure inability to withstand stress fatigue muscular weakness muscle wasting increased dark pigmentation of skin
Thyroxine	increased metabolism increased heartbeat physical restlessness mental restlessness protruding eyeballs enlarged thyroid gland	cretinism(retarded growth and low mental development lowered metabolism low ventilation rate of lungs low body temperature lowered mental activity coarse hair puffy eyes enlarged thyroid gland

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

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 cornea/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/relax/ slackens

– Lens bulges/thickens/increases curvature

– Radial muscles contract

– Circular muscles relax

– Size of pupil becomes large to allow in more light.

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

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 inverted and smaller than object, back to front/reversed
Retina forms a fine image when light rays reach it.

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

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 i) What are the functions of the human ear?

hearing
maintaining body balance and posture

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

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	Structure	Function
Skull	cranium and jaw bones made of several bones joined together large box called cranium and smaller paired boxes for eyes, ears, nose, jaws has large hole called foramen magnum for the passage of spinal cord	attachment of jaws protect brain and other delicate parts
Cervical region Atlas (first cervical)	ring shaped no Centrum broad, flat transverse processes vertebraterial canal for passage of vertebral artery facet for articulation of condyles of skull	protect spinal cord attachment of muscles allow nodding of head
Axis (second cervical)	adontoid peg projects from Centrum large flattened neural spine vertebrasterial canal small transverse process	allows head to rotate protects spinal cord provides surface for muscle attachment
Cervical (others)	short neural spine branched transverse process for neck muscles vertebraterial canals wide neural canal	support weight of head protect spinal cord neck muscle attachment
Thoracid	long backward pointing neural spine transverse process that points sideways facets for articulation of ribs notch for spinal nerves to pass through	forms rib cage articulation with one end of a rib protects, spinal cord muscle attachment
Lumbar	short neural spine long transverse process pointing towards abdomen large Centrum extra processes e.g. prezygapophysis, hypapophysis, anapophysis, metapophysis	protect organs of abdomen support upper part of body protect spinal cord muscle attachment
Sacral	fused bones to form sacrum well developed transverse process of first vertebra vertebraterial canals short neural spine	protects alimentary canal attachment of hip girdles protect spinal cord muscle attachment
Rib	long flattened attached to sternum from front	protect internal organs muscle attachment

vii) Describe the bones that form the appendicular skeleton

Bone	Structure	Function
Pectoral girdle scapular (shoulder bone)	Broad i.e. Flattened blade glenoid cavity to articulate with humerus metacromion/acromion for muscle attachment hard to provide support socket with cartilage/smooth surface to reduce friction	Support Muscle attachment Articulates with humerus
Humerus	long shaft for muscle attachment round head to articulate with glenoid cavity trochlea for articulation with ulna olecranon fosa to prevent arm bending the other way	movement muscle attachment
Ulna and radius	ulna longer and on side of little finger has sigmoid notch and olecranon process to form hinge joint with humerus radius is smaller and lies along thumb side and does not join ulna allows articulation with wrist bones	movement muscle attachments
Pelvic girdle(hip bone)	composed of three fused bones (ilium, ischium, pubis) upper end fused to sacrum lower end has acetabalum for articulation with femur has abturator foramen for passage of nerves and blood vessels	movement muscle attachment support absorbs pressure exerted by ground when animal moves
Femur	rounded head to fit in acetabulum of pelvis projections called trochanter for attachment of thigh muscles condyles at lower end for articulation with tibi patella that covers knee and prevents leg from bending backwards	movement muscle attachment
Tibia and fibula	tibia is longer than fibula tibia is outer bone and fibula is inner bone tibia lies on side of large toe fibula is fused to tibia (on outer side)	movement muscle attachment

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

Ball and socket

allow movement in all planes /directions i.e. 360^o
rounded end of bone fits into a rounded cavity in another bone
e.g. shoulder joint and hip joint

Hinge joint

convex surface of one bone fits into the concave surface of another bone
this allows movement in only one plane/direction 180o
e.g. elbow joint and knee joint

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

Explain the following terms
Ligament

connective tissue joining one bone to another

Cartilage

supporting soft tissue found at joints
they cushion the bones and absorb shock

Tendon

tissue that connects muscle to bones

Muscles

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

Describe the structure and function of various types of muscles
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

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

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

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

i) State the structural differences between skeletal muscles e.g. biceps and smooth muscles e.g. gut muscle

Skeletal (biceps)	Smooth (gut) muscle
multinucleated striated/stripped long muscle fibers block/cylindrical	uninucleated unstriated short muscle fibers spindle shaped

ii) Name the cartilage found between the bones of the vertebral column

intervertebral disc

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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BIOLOGY NOTES FORM 1-4 IN PDF FREE

October 5, 2025 Maverick John Leave a comment

BIOLOGY FORM 3 REVISION NOTES

a) i) What is meant by the term binomial nomenclature?

scientific system of naming organisms using the generic(genus) and specific (species) names

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

DOWNLOAD ALL THE FREE PDF NOTES HERE; Biology notes form 1-4; Free KCSE downloads

b) State the main characteristics of the five kingdoms of organisms
1. 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)

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

Fungi

have hyphae (which form mycelia)
absence of chlorophyll
have rhizoids (lack roots, leaves, stem)
have spore forming structures (sporangia)
e.g. mucor, rhizopus

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

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:

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

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

Bryophyte

e.g. mosses and liverworts
presence of rhizoids
lack of vascular tissues (lack phloem and xylem)
body parts not differentiated into root, stem, leaves
capsule or seta
gametophyte generation dominant.

Pteridophyta

e.g. ferns
has true roots, stems and leaves
fond with sori on under-surface
vascular tissues present
sporophyte generation is dominant

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
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

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

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)

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 parts 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

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

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

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 veined Cynodon

b) leaf net-veined go to 3

3 a) leaf with one lobe (simple) go to 4

b) leaf with many lobes (compound) 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 coloured scales Lepidoptera

b) wings without scales hymenoptera

6 a) forewings hard and shell-like coleopteran

b) forewings hard but not shell-like Orthoptera

7 a) body horizontally flattened Isoptera

b) body laterally flattened Symphonoptera

Identify the orders o the various specimens as per the table below

Specimen

Order

Steps followed

K-housefly

L- grasshopper

M- beetle

M-termite

Diptera

Orthoptera

Coleoptera

Isoptera

1a,2b

1a, 2a, 3b, 6b

1a, 2a, 3b, 6a

1b, 7a

2 a) Define the following ecological terms

Ecology

study of the interrelationships between organisms and their environment

Environment

surrounding of the organism i.e. biotic or a biotic factors

Habitat

A specific locality (home) of a living organism with a set of factors (conditions) in which an organism lives.

Ecological niche

Role of an organism in its habitat e.g. feeding relationship

Population

Number (group) of organisms of a species occupying a given habitat

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

Ecosystem

A community of organisms interacting with one another and the environment in which they live

Biosphere

The earth and its atmosphere where living organisms are found

Autecology

Study of a single (individual) species of plants or animals within a community, ecosystem, habitat or environment.

Synecology

Study of natural communities (plants and animals) or populations interacting within an ecosystem.

Carrying capacity

maximum number of organisms an area can support without being depleted

Biome

geographical area with particular climatic conditions and flora and fauna
it constitutes many ecosystems

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

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 9the 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

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.

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

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

Diseases and parasites

make organisms weak and susceptible to predation
kill organisms and reduce their population

Symbiotic

and association of organisms of different species where both benefit from the association i.e. there is mutual benefit

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

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 9plant 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 consumer feeds on more than one type of food while several herbivores feed on one type of plant
it is an interrelationship of many food chains
consumers are usually fewer than producers 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 carnivores 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

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 size 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

a) Describe the adaptations of plants to various habitats

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

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

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

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) i) 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 with heavy industries, motor vehicles, fires which burn 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 of phosphate-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

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

Disease	Causative agent	Transmission	Symptoms	Control
Cholera	Vibrio cholerae(bacterium)	Contaminated food or water Spread by flies form faeces	Intestinal pain Diarrhea Vomiting Dehydration	Proper hygiene e.g. boiling drinking water Vaccination
Typhoid	Salmonella typhi (bacterium)	contaminated food or water spread by flies from faeces	fever rashes diarrhea + blood from bowels	proper sanitation vaccination
Malaria	Plasmodium (protozoa)	– bite by infected female anopheles mosquito	– fever Joint pains Vomiting Headache Anaemia	killing mosquito killing the mosquito larvae draining stagnant water clearing bushes treatment sleep under mosquito net
Amoebic dysentery (amoebiasis)	Entamoeba hystolytica (bacterium)	– contaminated food or water due to improper disposal of faeces	– intestinal pain Diarrhea Vomiting Dehydration	sanitation personal hygiene cook food well treatment using drugs

d) Discuss Ascaris lumbricoides under the following sub-headings

Mode of transmission

through ingestion of contaminated food
live in intestines

Effects of parasite on the host

inflammation of lungs
pneumonia
produce toxic substances
intestinal obstruction

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

Control and prevention

proper sanitation
wash hand after defaecation and before eating

e) Discuss schistosoma under the following sub-headings
Mode of transmission

through contaminated water in swamps, etc

Effects on host

bleeding in lungs
blood stained urine
unthriftiness

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

iv) 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

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 species/ 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 cell

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 meiosis

First meiotic division

Interphase

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 poles
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

Meiosis

maintenance of chromosome number (diploid)
takes place in somatic cells/growth
no crossing over/no variations
results into 2 daughter cells
no pairing/no synapsis/no bivalent formed
a one division process of four stages

reduction/halving of chromosomes (haploid
occurs in reproductive cells/gonads/produces gametes
crossing over takes place/variation occurs
results into 4 daughter cells
there is paring/synapsis/bivalent
a two division 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 parts 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

ovary occurs above other floral parts on the receptacle

Inferior (epigynous)

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
stigma/ 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 into seed coat/testa
zygote changes into embryo (by mitosis)
primary endosperm nucleus changes into endosperm
whole ovule changes into seed
ovary develops and grows into fruit(under the influence of gibberrellic hormone)

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

Distinguish between parthenogenesis and parthenocarpy

parthenogenesis is development of new animals from unfertilized eggs
parthenocarpy is development of a fruit without fertilization

iv) State the differences between a seed and fruit

Seed	Fruit
fertilized ovule attached to placenta through funicle one scar called hilum has seed coat/testa seed wall undifferentiated	fertilized ovary attached to branch through a stalk two scars (style scar and stalk scar) has fruit wall/pericarp fruit wall is differentiated

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 loculus
have numerous seeds e.g. passion fruit
placenta of each carpel appears as ridges 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

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)
e.g. 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

Give main types of indehiscent fruits

Nut

pericarp woody, hard and thick e.g. cashew

Achene

has thin, tough pericarp e.g. sunflower

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

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

External	Internal
occurs in water outside the bodies of animals many eggs are laid usually less contact between male and female both fertilized eggs exposed to danger	occurs inside the body of the female animal fewer eggs released from ovary very close contact in form of copulation between male and female Fertilized eggs are enclosed hence highly protected inside females’ body.

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

Sperm	Ovum
long with a tail and head small locomotory stores little food has acrosome (tip with lytic enzymes) nucleus prominent but cytoplasm negligible	spherical large stationary a lot of food stored in yolky cytoplasm lacks acrosome a lot of cytoplasm

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/endometrium
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 fingerlike 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

iii)

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 from the mother
passage of excretory substances from foetus to mother for final discharge
gaseous exchange
passage of antibodies from mother to foetus, for protection of foetus against diseases

iv) 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

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 hormone(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 stops secreting 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.

a) Define the terms

Growth

an irreversible change in size of a cell, organ or whole organism
growth is due to synthesis of protoplasm or extracellular substances

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)

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

Plants	Animals
confined to shoots/root tips (apical) have definite growth regions(meristems) often indefinite/continuous growth results in branching affected by light, auxins, hormones and temperature	occurs all over the body(intercalary) different parts grow at different rates(allometric) maximum growth on maturity(definite) no branching affected by nutrients

ii) List the processes involved in growth

assimilation
cell enlargement
cell division(by mitosis)

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 favourable.

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 into 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 hypocotyls

Hypogeal

the cotyledons remain below the surface during germination due to elongation of epicotyl e.g. maize

v) Name the part of the bean seed that elongates to bring about epigeal germination

hypocotyl

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

period taken to achieve full length

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

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 1.5metres 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 (ethynelC₂H₄)

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

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