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KCSE Biology Questions and Answers – KCSE Biology Revision

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6 years ago

April 13, 2019

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

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

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

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

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

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

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

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

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

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

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

c) Entomology– This is the study of insects.

d) Parasitology– This is the study of parasites.

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

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

Such cells include muscle cell, sperm cell, apical meristem cells, and kidney cell.

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

Figure 5. The Mitochondrion (Animal)

Figure 6, (generalize(lmage23 mitochondrion Structure)

d) Endoplasmic Reticulum

Endoplasmic reticulum appears as a series of interconnected channels, running
throughout the cytoplasm.

Their membranes are continuous with the outer membrane of the nuclear membrane.

Some endoplasmic reticula have granules called ribosomes on their surfaces and are
referred to as rough or granular endoplasmic reticula. Endoplasmic reticula that are
not associated with ribosomes are called smooth endoplasmic reticula.

The rough endoplasmic reticulum transports proteins while the smooth endoplasmic reticulum transports lipids.

Generally, endoplasmic reticula also act as storage areas for synthesized molecules such
as enzymes. They also contribute to mechanical support.

e) Ribosomes

These are spherical in shape. While some are bound to the endoplasmic reticula, some
ribosomes are scattered within the cytoplasm (free ribosomes). Their largest dimension is
25 nanometres.

They are synthesised in the nucleolus.

They form sites for protein synthesis.

f) Lysosomes

These are spherical sac-like organelles bound by a single membrane. They contain lytic
enzvmes which break down large molecules. destroy Worn out oraanelles or even the
entire cells.

Lysosomes also play crucial role in digestion in unicellular organisms.

The lysosomes are also vital in breakdown of bacteria and other harmful microbes
that might have been ingested in food. This explains their high relative abundance in
injured or infected cells.

The membrane of the lysosomes are intact. This is important because if the enzymes leak
out, they may destroy the whole cell.

g)Golgi bodies/Golgi apparatus

These are stacks of membrane bound tube like sacs. They are found close to the cell
membrane.

Golgi bodies perform the following functions:

1) They package and transport glycoproteins.

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

3) They manufacture lysosomes.

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

h)Centrioles

These are rod shaped structures located just outside the nuclear membrane.

They take part in cell division and also in the formation of cilia and ﬂagella in lower
organisms.

Plant cells lack centrioles.

i) Chloroplasts

Chloroplasts are egg-shaped structures surrounded by two membranes and contain a gel-
like stroma through which runs a system of membranes that are stacked together to form
grana.

The granum contains chlorophyll which traps light energy that is used during
photosynthesis.

It is in the chloroplasts that photosynthesis takes place.

j) Vacuoles

These are sacs that are filled with ﬂuid called cell sap. Vacuoles vary in size.

Animal cells contain small vacuoles which may be numerous in the cells while plant cells
contain one large centrally placed vacuole.

Sap vacuoles store sugars and salts thereby contributing to the osmotic properties of
the cell. This inﬂuences how materials move in and out of the cell.

In some unicellular organisms, food vacuole stores and digests food substances while
the contractile vacuole excretes unwanted materials from the cell.

k) Cell wall

This is the rigid outer cover of plant cells and some lower organisms.

In plants it is composed of cellulose fibres.

Cell wall is important in that:

1. It gives plant cells their definite shape

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

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

i) Nucleus

Nucleus is a double membrane bound structure made up of a viscous ﬂuid known as
nucleoplasm in which nucleolus and chromatin materials are suspended. The nuclear
membrane has minute pores, nuclear pores which allow materials to move in and out of
the nucleus.

Nucleus controls all the activities of the cell.

Nucleolus is responsible for manufacture of ribosomes while chromatin contains
hereditary materials.

Nucleus generally takes a sperical or oval shape.

Comparison between Plant Cells and Animal Cells

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

Plant cells

usually large

regular in shape

has a cell wall

usually has a large central vacuole

cytoplasm and nucleus are usually located towards the periphery of the cell

some have chloroplast

usually more store oil, starch and proteins

has no centriole

Animal cells

smaller in size

irregular in shape

has no cell wall

usually has no vacuole but when present,they are often temporary and small structures within the cytoplasm

cytoplasm occupies most space in the cell with the nucleus usually centrally placed

has no chloroplast

stores glycogen and fats

has centrioles

Estimation of Cell Size

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

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

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

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

Procedure in cell size estimation

One requires a microscope, transparent ruler marked in millimeters and a prepared slide
of cells.

With the low power objective lens in place, keep a transparent ruler on the stage of the
microscope.

Focus so that the millimeters marks on the ruler are seen as thick dark lines.

Estimate the diameter of the field of view by counting the one millimeter spaces between
the first mark and the last one across the field of view. Count only the spaces between
two thick dark lines.

Convert the diameter of the field of view from millimeters to micrometres.

Remove the ruler and place the prepared slide of cells.

Count the number of cells along the diameter of the field of view.

Calculate the diameter of one cell using the formula:

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

Cell Specialization. Tissues. Organs and Organ Systems

Cell Specialization/Cell Differentiation

This refers to the process by which a cell becomes structurally modiﬁed to perform
specific functions

While cells have a basic outline, they become differentiated to perform specific functions

In particular, the root hair cell has extended surface for absorption while the sperm cell
has a tail-like extension for swimming towards the ovum.

Tissues

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

a) Tissue types in animals

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

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

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

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

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

b)Tissue types in plants

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

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

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

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

Organs

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

Organs in animals include:

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

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

c) Brain– Composed of epithelial, connective tissues

d) Lungs– Composed of epithelial, connective tissues.

Organs in plants include:

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

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

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

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

Organ system

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

Organ systems are more pronounced in animals than in plants

Organ systems in animals include

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

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

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

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

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

Chapter Four: Cell Physiology

Introduction

Physiology refers to the branch of biology that deals with the study of functions and
activities of life or of living matter such as organs, tissues or cells. It aims at
understanding the mechanism of living.

In simpler terms, physiology refers to the processes and functions that take place inside
the body cells of organisms.

Cell physiology refers to the study of functions of the cell structures. The cell structures
perform various functions of life. In particular:

a) Chloroplasts play a vital role in carbohydrate synthesis.

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

c) Ribosomes manufacture of proteins.

These physiological processes require various raw materials for them to take place.

For photosynthesis to occur, carbon (IV) oxide, mineral salts and water have to be taken
into the chloroplasts.

For respiration (energy production) to take place, food substrate such as glucose and
oxygen have to be taken into the mitochondrion. Energy, carbon (IV) oxide, water and
alcohol (in plants) are some of the end products of respiration.

Some of the end products of the physiological processes such as carbon (IV) oxide can be
harmful when allowed to accumulate in the cells. They, thus, have to be eliminated from
the cells.

This implies that there is a constant ﬂow of materials in and out of the cells and the cell
organelles where these physiological processes are taking place. There is a constant
movement of materials across the cell membrane in the cells.

This chapter discusses the properties of the cell membrane and the processes through
which materials move in and out of the cells.

Structure of the membrane

A membrane is a surface structure that encloses the cell and cell organelles.

The membranes include the cell membrane, tonoplasts, nuclei membrane, mitochondrial
membrane and chloroplast membrane.

The membranes have a common basic structure which regulates the movement of
materials in and out of the cells.

The cell membrane is made up of a phospholipid layer sandwiched by two protein layer
(it is a lipoprotein layer) the overall thickness of the cell membrane is about 7.5 nm thick.

The membrane is perforated by small pores that allow the passage of substances in and
out of the cells.

Properties of the cell membrane

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

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

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

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

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

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

Physiological Processes of the Cell membrane

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

Materials move in and out of the cells through three main physiological processes:

a) Diffusion

b) Osmosis

c) Active transport

Diffusion

From kinetic theory, matter is made up of particles that are in continuous random motion.

In solids, the particles are at fixed positions and can only vibrate at these fixed positions.

In liquids and gases, the particles are loosely held and are free to move from one region
to another randomly. This movement of gas or liquid particles is observed to be from
regions of high concentration to a region of low concentration. The process by which
particles move from a region of high concentration to a region of low concentration
is known as diffusion.

In particular, the scent of a ﬂower or perfume experienced by an individual is as a result
of the flower scent particles or perfume particles move from a region of high
concentration.

Diffusion occurs until the regions have an even concentration of the liquid or gas
particles.

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

Demonstration of the process of diffusion using_potassium manganate (VII)

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

Procedure

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

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

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

d) Half fill the beaker with water.

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

f) Record your observations for the first 15 minutes.

g) Explain your observations.

Expected observations

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

Explanation

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

The Role of Diffusion in Living Organisms

a) In Plants

Diffusion plays an important role in plants in that:

It helps in absorption of mineral salts from the soil to the plant. Most salts dissolve in soil
water. For those salts whose concentration in soil water is higher that their concentration
in the cell sap of root hair cells, they move into the root hair cells through diffusion.
Plants require mineral salts for numerous life processes.

Diffusion plays a role in gaseous exchange in plants. The respiratory gases (oxygen and
carbon (IV) oxide) diffuse across the stomata and lenticels of plants.

Diffusion also contributes to the transportation of manufactured food materials from the
leaves to other parts of the plant.

b) In Animals

In animals diffusion plays the following important roles

It helps in the absorption of digested food materials in the alimentary canal. End products
of digestion such as amino acids and glucose diffuse across the wall of the ileum into the
blood for transport to other parts of the animal body.

Diffusion also plays a significant role in gaseous exchange in animals. In animals,
gaseous exchange occurs at certain structures known as respiratory surfaces.

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

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

Factors affecting the rate of Diffusion

a) Diffusion gradient

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

b) Surface area to volume ratio

Rate of diffusion directly depends on the surface area to volume ratio. The greater the
surface area to volume ratio, the greater the rate of diffusion will be. Conversely, low
surface area to volume ratio results in a low diffusion rate.

This implies that diffusion rate is greater in small organisms than the large organisms.
This is because the small organisms have a large surface area to volume ratio. As a result,
most of their body parts are closer to the external surrounding leading to faster diffusion.

Small organisms can, therefore, depend on diffusion alone as a means of transporting
foods, respiratory gases and waste products.

To large organisms, diffusion alone is inadequate as a means of transport of foods and
excretion. They have an additional transport system.

Organisms always lose heat to the surrounding through diffusion. This implies that small
animals lose a lot of heat to the surrounding compared to the large animals.

c) Thickness of membranes and tissues

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

The rate of diffusion is higher in thinner membranes.

d) Size of molecules

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

e)Temperature

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

Osmosis

Osmosis is a process by which solvent molecules move from a region of high
concentration (dilute solution) to a region of low concentration (concentrated solution)
through a semi permeable membrane.

Osmosis can be described as a special type of diffusion since it involves movement of
solvent (Water) particles from a region of high concentration to a region of low
concentration.

Demonstration of Osmosis Using a Visking Tubing

Requirements

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

Procedure

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

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

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

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

5. Leave the set up for about 30 minutes.

6. Record your observations.

7.Explain the observations made.

Observations

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

Explanation

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

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

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

Osmosis explained

When two separate solutions are separated by a semi permeable membrane, there will be
movement of water molecules from their region of high concentration (dilute solution) to
a region of low concentration (the highly concentrated solution) across the semi
permeable membrane. The semi permeable membrane does not allow movement of solute
particles across it.

The movement of the water molecules continues until the separate solutions have the
same concentrations.

Solutions with the same concentrations are referred to as isotonic solutions. The solutions
are said to be isotonic to each other.

A lowly concentrated solution (dilute solution) is referred to as a hypotonic solution. A
hypotonic solution has less of the solute molecules but more of the solvent molecules.

A highly concentrated solution with more of the solute particles but less of the solvent
particles is referred to as a hypertonic solution.

When isotonic solutions are separated with a semi permeable membrane, there will be no
net movement of solvent molecules to any of the solutions since they have the same
concentration of solvent molecules.

Osmotic pressure

When a concentrated solution is separated from distilled water by a semi permeable
membrane, the concentrated solution will develop a force with which it draws water
through the semi permeable membrane from the distilled water.

Osmotic pressure refers to the force with which a concentrated solution draws water to
itself.

An osmometer is an instrument used to measure the osmotic pressure.

Osmotic potential

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

Water Relations in Animals

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

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

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

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

b) Red blood cell in hypertonic solution

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

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

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

c) Red blood cell in isotonic solution

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

Note:

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

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

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

Water Relations in Plants

Water relations in plant cells differ with that in animal cells.

A plant cell has both a cellulose cell wall and cell membrane. The centre of the cell
contains vacuole with sap. The sap is a solution of salts and sugars and is bound by a
membrane, the tonoplast.

The cell membrane and tonoplast are semi permeable while the cellulose cell wall is fully
permeable.

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

If a plant cell is placed in water or hypotonic solution, the cell will draw water from the
hypotonic solution through osmosis causing the cell to distend.

The cellulose cell wall is rigid and does not allow plant cells to burst as in the case of
animal cells.

As the cell gains more water, the vacuole enlarges and exerts an outward an outward
pressure on the cell wall called turgor pressure.

The turgor pressure increases as more water is taken into the vacuole causing the cell to
stretch until the cell cannot stretch any more. The cell becomes firm and is said to be
turgid.

Turgor pressure is the outward pressure that the cell cytoplasm exerts on the cell wall as
it gains more water through osmosis.

When the cell wall is being stretched towards the outside, it will develop a resistant
pressure to stretching that is equal and opposite to turgor pressure called wall pressure.

b) A glam cell in a hygertonic solution

When placed in a hypertonic solution, the plant cell will lose water to the solution
through osmosis. As the water moves out of the cell, the cell starts to shrink, becomes
less rigid or ﬂabby and is said to be ﬂaccid.

It the cell loses more water, its contents reduce in size and the plasma membrane pulls
away from the cell wall towards the centre. The process through which plant cells lose
water, shrink and become ﬂaccid is called plasmolysis.

Plasmolysis can be reversed when a ﬂaccid cell is placed in distilled water in a process
called deplasmolysis.

Wilting

Plants always lose water to the atmosphere through transpiration and evaporation.

Simultaneously, the plant cells lose water and draw more from the soil.

Wilting is a phenomenon that occurs when plant cells lose more water than they draw
from the soil making the plant cells to lose their turgor pressure and droop.

At night, plants always recover from wilting since stomata are closed and water loss
through evapotranspiration is significantly reduced.

Where water supply from the soil is inadequate, the plants may fail to recover from
wilting and instead undergo permanent wilting.

Role of Osmosis in Organisms

Absorption of water from the soil-The root hair cell of plants absorbs water from the
soil through osmosis. Osmosis also helps in distribution and movement of water from the
roots to other parts of the plant.

Osmosis plays an important role in support in herbaceous plants and young seedlings.
When the cells of these plants take in water through osmosis, the cells become firm or
rigid and thus gain support.

Osmosis plays a role in opening and closing of stomata in plants– The guard cells
surrounding the stomata synthesize glucose through photosynthesis in the presence of
light.

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

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

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

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

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

Osmosis also plays a role in osmoregulation in animals

In kidney tubules of animals, water is withdrawn from the tubules into the body cells
through osmosis through the tubular walls. This enables animals to maintain the osmotic
pressure of the body ﬂuids.

Factors Affecting the Rate of Osmosis

Concentration of solutions and concentration gradient. Osmosis is greater when the
separated solutions have a greater difference in osmotic pressure. In summary, the greater
the concentration gradient, the greater the rate of osmosis and vice versa.

Temperature-An increase in temperature would increase the rate of osmosis as it
increases the energy content of the molecules.

Thickness of the membranes-The thicker the membrane the lower the rate of osmosis
while the rate of osmosis is greater through thinner membranes.

Active Transport

Active transport refers to the process through which substances are moved across the cell
membrane and against a concentration gradient.

Diffusion and osmosis alone do not account for movement of substances in and out of the
cells. In particular, there are some mineral salts that occur at low concentrations in the
soil water than in the cell sap.

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

Active transport requires energy. This is unlike diffusion and osmosis that only depend
on concentration gradient for them to take place.

It is postulated that there are protein carrier molecules on the cell membrane that aid in
the moving these substances across the membrane. These carrier molecules combine with
the substances being transported across the membrane and then move them from one side
of the membrane to the other side.

Cellular intake of solutes is largely through active transport.

Role of active transport in living organisms

Active transport is important in living things in that:

It helps in re-absorption of sugars and some salts by the kidney to the bloodstream.

It helps in absorption of some mineral salts from the soil by roots.

Absorption of digested food from alimentary canal of animals into the bloodstream.

It leads to accumulation of substances into the body to offset osmotic imbalance in arid
and saline environments

It plays a role in excretion of waste products from body cells.

Factors affecting the rate of Active Transport

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

These include:

a) Oxygen concentration

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

b) Change in pH

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

c) Glucose concentration

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

d ) Temperature

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

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

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

Nutrition Plants And Animals

Introduction

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

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

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

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

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

Modes of nutrition

There are two main nutrition modes:

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

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

Autotrophism

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

a)Chemosynthesis

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

b) Photosynthesis

This is the process by which organisms make their own food from simple substances in
the environment such as carbon (IV) oxide and water using sunlight energy.

Such organisms often have chlorophyll which traps the required sunlight energy.

This mode of nutrition is common in members of the kingdom Plantae. Some protoctists
and bacteria are also photosynthetic.

Importance of Photosynthesis

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

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

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

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

External leaf structure

Externally, the leaf has a petiole through which it attaches to the leaf branch or stem,
lamina- the broad ﬂat surface, margin- the outline and the leaf apex.

The leaf margin can be smooth, dentate, serrated or entire.

The size of a leaf depends on its environment. Plants in arid areas have small sized
leaves with some leaves reduced to needle like shape.

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

a) Cuticle

This is the outermost layer of the leaf.

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

Functions of the cuticle

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

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

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

b) Epidermis

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

Functions of the epidermis:

a) It protects the leaf from mechanical damage.

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

c) It secretes the cuticle.

There are many small pores on the epidennis known as stomata (singular-stoma) through
which exchange of materials occur. The opening and closing of the stomata is controlled
by the guard cells. Each stoma is controlled by two guard cells.

The guard cells have chloroplasts and are bean shaped. They have thicker inner cell wall
and thinner outer cell wall.

Adaptations of the guard cells

They have deferentially thicker walls to enable them bulge as they draw water through
osmosis from the neighboring cells making them to open the stomata.

They contain chloroplasts that manufacture sugars which increase osmotic pressure of the
guard cells. As they draw water through osmosis, they bulge making the stomata to open.

c) Palisade mesophyll

This is the chief photosynthetic tissue in plants. Its cells are regular in shape.

Its cells contain numerous chloroplasts for photosynthesis.

Their close packing and location just below the epidermis enables them to trap maximum
sunlight for photosynthesis.

Location of palisade layer on the upper surface explains why upper leaf surfaces are
greener than the lower surfaces.

d) Spongy mesophyll layer

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

e) Vascular bundle/tissue

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

Chloroplast

This is the organelle in which photosynthesis takes place. It is an oval shaped double
membrane bound organelle.

Internally, it is made up of membranes called lamellae suspended in a ﬂuid filled matrix
called stroma.

Lamellae forms stacks at intervals called grana (singular-granum). Chlorophyll molecules
are contained in the grana.

Within the stroma. fat droplets, lipid droplets and starch grains are found.

The strona contains enzymes and forms the site Where light independent reactions take
place.

Adaptations of the leaf to photosynthesis

The leaf has a ﬂat snd broad lamina to increase surface area for trapping sunlight energy
and for gaseous exchange.

The leaf has numerous stomata through which photosynthetic gases diffuse.

The leaf is thin to reduce the distance through which carbon (IV) oxide has to diffuse to the photosynthetic cells.

The palisade mesophyll cells contain numerous chloroplasts which contain chlorophyll
molecules which trap sunlight energy for photosynthesis.

The photosynthetic mesophyll is located towards the upper surface for maximum
absorption of sunlight energy.

The leaf has an extensive network of veins composed of xylem which conducts water to
the photosynthetic cells and phloem to translocate manufactured food materials to other
plant parts.

The epidermis and cuticle are transparent to allow light to penetrate to the photosynthetc cells.

Raw materials for photosynthesis

Water

Carbon (IV) oxide

Conditions for photosynthesis

Light energy

Chlorophyll

Photosynthesis Process

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

a)Light reaction/Light stage

This is the first stage of photosynthesis. It occurs in the presence of light. Without light it
cannot take place.

Light stage occurs in the grana of the chloroplasts.

During light stage, two fundamental processes occur:

i) Photolysis of water

This refers to the splitting of water molecules using sunlight energy to give hydrogen ions
and oxygen gas.

This is aided by the fact that the grana contain chlorophyll molecules that trap sunlight
energy for photolysis.

The oxygen gas produced can either be released into the atmosphere or be utilized by the
plant for respiration.

Water– Hydrogen atoms + Oxygen gas

ii) Formation of adenosine triphosphate (ATP)

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

ADP + P = ATP

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

b) Dark reaction/Dark stage

These reactions are light independent. The energy that propels these reactions are derived
from the ATP formed during light stage.

Also known as carbon (IV) oxide ﬁxation, dark stage involves combination of carbon
(IV) oxide molecule with hydrogen ions to form a simple carbohydrate and a water
molecule.

Dark reactions take place in the stroma.

Other food materials are then synthesized from the simple sugars through complex
synthesis reactions.

The simple sugar formed in dark stage is quickly converted to starch which is osmotically
inactive. When a lot of simple sugars accumulate in the chloroplasts, osmotic pressure of
the guard cells would increase causing the guard cells to draw a lot of water through
osmosis. This makes the guard cells to bulge and open the stomata. This can result into
excessive water loss.

To prevent, this, the simple sugars are quickly converted to starch. To test whether
photosynthesis has taken place in a leaf, therefore, a test for presence of starch and not
simple sugars is carried out.

Testing for starch in a leaf

Requirements

Iodine solution

Methylated spirit/alcohol

Boiling tube

Droppers

Water

White tile

Fresh leaf

Means of heating

Timer

Procedure

Detach a leaf that has been exposed to light for about six hours. This duration ensures
that the leaf has photosynthesized.

Put the leaf in boiling water for 10 minutes. This kills the protoplasm, denatures the
enzymes and stops any chemical reactions in the leaf.

Remove the leaf and put it in a boiling tube containing methylated spirit or alcohol and
boil in a water bath. Methylated spirit is highly ﬂammable hence should be boiled
indirectly. Boiling with methylated spirit or alcohol decolourises the leaf (removes the
chlorophyll). This ensures that the leaf becomes white so that colour changes can be
observed easily when iodine is added.

Remove the leaf and wash off in hot water to remove methylated spirit and to soften the
leaf.

Spread the leaf on a white tile and add drops of iodine solution onto the leaf and observe.

Observations

If there is formation of blue black patches on the leaf then starch is present

If the yellow/brown colour of iodine persists on the leaf then starch is absent in the leaf.

Factors affecting the rate of photosynthesis

a) Carbon (IV) oxide concentration

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

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

b)Light intensity

The rate at of photosynthesis increases with an increase in light intensity up to a certain
level. Beyond the optimum light intensity the rate of photosynthesis becomes constant.
To this effect, plants photosynthesize faster on bright and sunny days than on dull cloudy
days.

Light quality/wavelength also affects the rate of photosynthesis. Most plants require red
and blue wavelengths of light for photosynthesis. Light duration also affects
photosynthesis rate.

c)Temperature

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

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

d) Water

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

Experiment to investigate the gas produced during photosynthesis

Requirements

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

Procedure

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

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

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

d) Test the gas collected with a glowing splint.

e) Record your observations.

Note:

In this experiment, sodium hydrogen carbonate is added to the water to boost the amount
of carbon (IV) oxide in the water since water has a low concentration of carbon (IV)
oxide.

A water plant is also selected because Water plants are adapted to photosynthesis under
the low light intensity in water where terrestrial plants cannot easily photosynthesize.

This experiment can also be used to investigate the factors affecting the rate of
photosynthesis:

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

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

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

Experiments on factors necessary for photosynthesis

Light

Requirements

Methylated spirit, iodine solution, water, white tile, droppers, beaker, source of heat,
boiling tube, light proof material e.g. aluminium foil, potted plant and clips.
Procedure

Cover two or more leaves of a potted plant with a light proof material.

Place the plant in a dark place for 48 hours (keeping the plant in the dark for 48 hours is
to ensure that all the starch in it is used up. This makes the leaves ideal for investigating
whether starch would form in the experimental period. This is called destarching).

Transfer the potted plant to light for 5 hours.

Detach and uncover the leaves and immediately test for starch in one of the covered
leaves and one that was not covered.

Carbon (IV) oxide

Requirements

Sodium hydroxide pellets, ﬂask, jelly

Procedure

Destarch the plant for 48 hours

Place a few pellets of sodium hydroxide in the ﬂask

Bore a hole in the cork of the same size as the petiole of the leaf being used

Cut the cork lengthwise.

Chlorophyll

For this experiment, a variegated leaf is required. This is a leaf in which some patches
lack chlorophyll.

These patches could be yellow. They lack chlorophyll hence photosynthesis does not take
place in them.

Procedure

Detarch or remove variegated leaf that has been exposed to light for at least three hours.

Draw a large diagram of the leaf to show the distribution of the chlorophyll

Test the leaf for starch and record observations.

Chemicals Of Life

These are chemical compounds that constitute the living organisms.

Biochemistry is the branch of biology that deals with the study of the chemicals of life
and their reactions.

Chemicals of life include carbohydrates, proteins and lipids.

Carbohydrates

Are compounds of carbon, hydrogen and oxygen in the ratio of 1:2: l.

They have a general formula (CH2O)n where n represents the number of carbon atoms.

Carbohydrates are grouped into three categories:

Monosaccharides

These are the simplest carbohydrates.

They include glucose, fructose, galactose.

Their general formula is C6H12O6.

Properties of Monosaccharides

They are sweet tasting

They readily dissolve in water

They are crystallisable

They are reducing sugars; monosaccharides reduce blue copper (II) sulphate in
Benedict’s solution to red brown copper (I) oxide when heated.

Note:

Most fruits are sweet tasting because they contain a lot of monosaccharides.

Monosaccharide units can be combined to form complex carbohydrate molecules through
a process known as condensation. Water molecules are produced in the process.
Functions

They are the chief respiratory substrate. They are broken down to release energy in the
body.

They are condensed to form complex important carbohydrates.

Disaccharides

These are complex sugars formeed by linking two monosaccharide units through
condensation.

They have a general formula CHHZZOH. The bond that holds two monosaccharide units
is called glycosidic bond.

Examples of disaccharides include:

Maltose-common in germinating seeds

Sucrose-fruits and sugar cane. Sucrose is the form in which carbohydrates are
transported in plants

Lactose- found in milk

Properties of Disaccharides

They are sweet tasting

They are crystallizable

They are water soluble

While they are non reducing sugars, some such as maltose is sugar reducing and is known
as a complex reducing sugar.

They can be broken down into their constituent monosaccharide units through hydrolysis.
Hydrolysis is the process through which complex molecules are broken down in the
presence of water molecules.

In living systems, hydrolysis is carried out by enzymes. However, in the laboratory,
hydrolysis can be carried out by boiling the disaccharide in dilute aid such as
hydrochloric acid.

Functions

They are hydrolyzed into monosaccharides and respired on to yield energy

They are the form in which carbohydrates are transported in plants due to their soluble
and inert nature.

Polysaccharides

These are formed through linking of numerous monosacchride units through
condensation.

Their general formula is (C6H10O5),, where n is a very large number.

Properties of polysaccharides

They are non sweet

They do not dissolve in water

They are non crystalline

They are non-reducing sugars

Examples of polysaccharides

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

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

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

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

Functions of polysaccharides

They are storage carbohydrates; their insolubility and inertness makes them ideal for
storing carbohydrates.

They are structural carbohydrates e. g. cellulose forms the plant cell walls

They can be hydrolyzed into monosacharides and be broken down to release energy

Lipids

These are compounds of carbon, hydrogen and oxygen. However, they contain lesser
oxygen but higher hydrogen compared to carbohydrates.

Building units for lipids are fatty acids and glycerol. To synthesize a molecule of lipid,
three fatty acids and a glycerol molecule are linked through a condensation reaction.

There is one type of glycerol but numerous fatty acids

There are different types of fatty acids. The property of a lipid therefore depends on the
type of fatty acids that link up with the glycerol.

There are complex lipids such as phospholipids, steroids, waxes and cholesterol. These
also form through condensation.

Properties of lipids

Fats easily change to oil when heated while oils easily solidify when cooled.

They are insoluble in water but readily dissolve in organic solvents such as chloroform to
form emulsions

They are inert hence can be stored in tissues of organisms.

Functions

They are a source of energy when oxidized. They yield more energy compared to
carbohydrates when oxidized per unit weight. However, they are less preferred as source
of energy because they require a lot of oxygen to oxidize. In addition, they are insoluble
hence not easy to transport to respiratory sites.

They are a source of metabolic water. When oxidized, they yield a lot of metabolic water.
This explains why some desert animals such as camels store large quantities of fat in their
bodies.

Lipids offer protection to internal organs as they are deposited around them to act as
shock absorbers.

Lipids provide heat insulation when stored underneath the skin as they are poor
conductors of heat hence do not conduct heat away from the body. Organisms in cold
areas tend to be short and plump as they have fatter fat adipose.

Lipids form structural compounds for instance phospholipids in cell membrane.

Complex lipids such as waxes in leaves help minimize water loss through transpiration.

Some lipids mediate communication between cells

Proteins

These are compounds of carbon, hydrogen and oxygen. In addition, they also contain
nitrogen and sometimes phosphorous or sulphur or both.
Some proteins molecules contain other elements. In particular, haemoglobin contains
iron.

Proteins are made up of amino acids. There are about twenty known amino acids. Amino
acids are of two kinds:

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

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

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

Proteins are of two kinds:

a) First class proteins– Contain all essential amino acids

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

Protein synthesis

Two amino acids combine through a condensation process to form a dipeptide molecule
Several amino acids link up to form a polypeptide chain. Proteins are made up of long
chain polypeptides.

Properties of a protein depend on the type of amino acids present in its chain and the
sequence in which the amino acids link up in the polypeptide chain.

Properties of Proteins

They dissolve in Water to form colloidal suspensions in which the particles remain
suspended in water.

They are denatured at temperatures beyond 40°C. Strong acids, bases, detergents and
organic solvents also denature proteins.

They are amphoten’c- possess both basic and basic properties.

This property enables them to combine with other non protein substances to form
conjugated proteins such as:

Mucus- Protein plus carbohydrate

Haemoglobin- Protein plus iron

Functions of proteins

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

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

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

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

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

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

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

Enzymes

What are enzymes?

Are organic catalysts that are protein in nature and regulate the rate of metabolic reactions.

They speed up or slow down the rate of metabolic reactions but to not get used up in the process.

Types of enzymes

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

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

Importance of Enzymes

They speed up the rate of chemical reactions that would otherwise be too slow to support
life.

Some enzymes take part in synthesis/building of useful complex substances such as
DNA.

Digestive enzymes breakdown complex food substances into simple foods that can be
utilized by the cells.

Some metabolic enzymes such as catalase play a vital role in detoxification (making
poisonous substances less harmful.

Enzyme nomenclature

Two systems of naming enzymes have been adopted.

a).Trivial naming

This is where an enzyme is named by the scientist who discovered it.

In trivial naming all enzyme names end in prefix —in.

Examples

Pepsin (Theodor Schwann, German physiologist -1836).

Ptyalin (Anselme Payen, a French chemist- 1833).

Trypsin.

b). Use of sufﬁx -ase

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

Substrates

Amylose (starch) ………… ..amylase.

Lipids …………………….. ..lipase.

Protein ………………….. .. protease.

Carbohydrate ……….. . . . . . . ..carbohydrase.

Lactose ……………………. ..lactase

Processes/Reactions

Hydrolysis ……………….. ..hydrolase

Reduction ………………… ..reductase

Oxidation …………………. ..oxidase

Mechanism of action of Enzymes

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

Properties of Enzymes

They are protein in nature; hence affected by temperature and pH.

They are substrate specific e. g. maltase cannot digest sucrose.

They are efﬁcient in small amounts since they are re-used in the reactions.

They mostly take part in reversible reactions.

They regulate the rate of metabolic activities but are not used up.

Factors affecting enzyme activity

Temperature.

pH.

Substrate Concentration.

Enzyme Concentration.

Enzyme co-factors and co-enzymes; Fe, Mg, Zn, Cu ions.

Specificity.

Enzyme inhibitors.

a)Temperature

At low temperatures, kinetic energy of enzymes and molecules are low. There are few
collisions leading to low enzyme activity.

As temperature increases, the kinetic energy of the enzyme and substrate molecules
increases leading to increased collisions hence increase in enzyme activity.

Enzyme activity is optimum at (35 -40)°C.

Beyond 40 °C the rate of enzyme activity decreases and eventually stops. This is because
enzymes get denatured and their active sites get destroyed.

b)pH

Enzymes work best under different pH conditions.

Some enzymes work best under alkaline conditions e. g amylase. Some also work better
under acidic conditions e. g. pepsin. However, most intracellular enzymes work better
under neutral conditions.

Altering the pH conditions would affect enzyme activity.

c)Enzyme Specificity

A particular enzyme will only act on a particular substrate or will only catalyze a
particular reaction.

For instance, sucrase enzymes can only breakdown sucrose.

d)Substrate Concentration

Assuming all other factors are constant, t low substrate concentration, the rate of enzyme
activity is low.

Increase in substrate concentration increases the rate of enzyme activity since more active
sites of the enzymes will be occupied and there will also be an increase in enzyme-
substrate collisions leading to increased reaction.

The reaction increases up to a point at which it becomes constant. At this point, all active
sites are utilized. The enzymes become the limiting factor of reaction. Increasing enzyme
concentration would increase the rate of enzyme activity.

e) Enzyme Concentration

An increase in enzyme concentration increases the rate of enzyme reaction up to a level
beyond which the rate of reaction becomes constant.

At low enzyme concentration, rate of enzyme activity is low because there are fewer sites
and also fewer enzyme-substrate collisions that would lead to reactions.

Increasing enzyme concentration increases rate of enzyme activity since there will be an
increase in number of active sites and enzyme-substrate collisions.

At optimum enzyme concentration, substrate concentration is the limiting factor.
Increasing substrate concentration increases the rate of reaction.

f) Enzyme co-factors

These are inorganic substances which activate enzymes.

Without them, most enzymes would not function properly.

Co- factors include mineral ions like iron, magnesium, copper, manganese, zinc as well
as vitamins.

They are used again and again since like enzymes, they do not get used up during the
reactions.

g) Co-enzymes

These are organic molecules that are required by some enzymes for their efficient
functioning. Some enzymes will not function without them.

Most co-enzymes are derivatives of vitamins.

Examples

NAD- Nicotine Adenine Dinucleotide.

FAD- Flavine Adenine Dinucleotide.

NADP- Nicotine Adenine Dinucleotide Phosphate.

h) Enzyme inhibitors

These are chemical substances which slow down or eventually stops enzyme activity.

They are of two types:

1. Competitive

2. Non- competitive

Competitive inhibitors

These are chemical substances which are structural analogs of the substrates i.e. they take
up the shape of the substrates and compete for the active sites of the enzymes.

They bind with the enzymes and do not disentangle easily (they stay in the enzyme active
site for a long time) thereby slowing down the rate of enzyme activity.

The reaction can be increased by increasing the substrate concentration.

Non competitive inhibitors

These are inhibitors that do not resemble the substrate molecules but they combine with
the enzyme at any site other the active site and alter the structure of the active site of the
enzyme. The normal substrate, therefore, fails to bind to the active site leading to
decreased rate of reaction.

Note that these substances do not compete for the active sites of the enzymes.

The enzymes are destroyed permanently hence the effect cannot be reversed.

Examples of non competitive inhibitors

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

Heterotrophism

This is a mode of nutrition in which organisms take in already manufactured complex
food substances such as carbohydrates, proteins and lipids.

Heterotrophs are organisms that feed on already manufactured food substances.

These substances are broken down in the bodies of the Heterotrophs into simple soluble
food substances that can be absorbed and be utilized by the cells.

Modes of Heterotrophism

There are four main heterotrophic modes on nutrition:

Holozoic- Where organisms ingest, digest and assimilate solid complex food
substances.

Saprophytism — Where organisms feed on dead decaying matter causing
decomposition.

Parasitism- a feeding association in which one organism (parasite) feeds on or obtain
nutrients on another organism, the host.

Symbiosis/Mutualism- An association where two organisms live together and
mutually benefit from each other.

a) Parasitism

There are two main types of parasites:

Endo parasites- Live inside the host

Ecto-parasites- Found on the external surface of the host.

The parasite benefits but the host does not. Some of the parasites cause diseases to the
hosts and damage their tissues thereby weakening them.

b) Symbiosis

In saprophytism, both organisms benefit:

Symbiotic relationships include

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

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

> Catalase digesting bacteria and ruminants.

Dentition

Large animals depend on complex manufactured food substances.

These food substances once ingested must be broken down to simpler forms that can be
utilized by the cells. The breakdown is both physical and chemical.

Most of the large animals have teeth to enhance physical breakdown of the complex food
substances.

Dentition refers to the description of types of teeth, their arrangement and specialization.

Types of Dentition

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

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

a) Incisors

Are flat and chisel shaped with sharp ridged edges for cutting and biting food.

They have one root.

a. Canines

Are conical teeth with sharp pointed edges modified for seizing and tearing prey among
carnivores.

They have one root

b. Premolar and molar

They have cusps on their surface to suit their grinding action.

Premolars have two roots.

Molars have either two or three roots.

Classes of Holozoic Heterotrophs

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

These are:

a) Herbivores: heterotrophs that exclusively feed on vegetation.

b) Carnivores: heterotrophs exclusively feed on ﬂesh.

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

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

Dental Formula

This is the of the number, type and position of teeth in the jaws of animals

Number of teeth recorded represents half the total teeth in the upper and lower jaws.

The teeth names are abbreviated as

a) i-incisors.

b) c-canines.

c) pm-premolars.

d) m-molars.

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

a) Write down its dental formula.

b) State its mode of feeding.

c) Give a reason.

Herbivores

Most do not have upper incisors. Instead they have a homy pad against which grass is
pressed and cut by the lower incisors.

They have a long tongue that assists in the cutting and moving food.

They have a gap in the lower jaw separating canines from premolars known as diastema
which allows the tongue to manipulate food.

Herbivore teeth have open enamel which allows for continuous growth to replace worn
out surfaces due to grinding.

Their incisors are wedge shaped to cut grass and vegetation together with the horny pad

The jaws have movable joints to allow the sideways movement of lower jaw to facilitate
grinding of grass.

Carnivores

Their incisors are chisel shaped and closely fitting to seize the prey.

Their canines are long, conical and curved to hold, kill and tear the prey.

Some of their premolars in the lower and upper jaw are modified into specialized
carnassial teeth which have smooth sides and sharp edges to slice through ﬂesh and crush
bones

Premolars and molars are broad with cusps for crushing bones.

Their jaws are attached to powerful muscles that move the jaws up and down

Carnivores are adapted to fast running by possessing well developed leg muscles.

Dental Diseases

a) Dental Carries

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

b) Periodontal Diseases

Caused by lack of vitamins A and C, lack of massage of the gums and imperfect cleaning
of gums.

The gums become ﬂabby and soft so they do not support the teeth. Common in adults
than children.

Are of two types:

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

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

Dental Hygiene

Proper teeth care requires:

Regular cleaning or brushing teeth after every meal

Avoid eating too much sugary foods.

Eating hard foods e. g. raw carrots, cassava, yams, sugar cane.

Eating diet rich in calcium, phosphate and vitamins A, C and D.

Teeth should be used for their correct purpose.

Regularly visit the dentist if necessary.

Digestion

The process through which complex food substances is broken down physically and
chemically into simpler food substances that can be absorbed by body cells.

However, small molecules like those of vitamins, mineral salts and water are directly
absorbed into the bloodstream without undergoing digestion.

Digestion occurs in the mouth, stomach, duodenum and ileum.

There are glands also associated to the digestive system. These include the pancreas, gall
bladder, salivary glands.

Digestion in the mouth

At the mouth both physical and chemical digestion takes place.

The food is mechanically broken down by the teeth through grinding and chewing. This
process is called mastication.

Mastication reduces the food into small size to increase the surface area for enzymatic
action.

The tongue helps in manipulation of the food as it mixes the food with the saliva secreted
from the salivary glands. The salivary glands are:

a) Sublingual salivary gland; beneath the tongue

b) Sub mandibular gland: under the jaw

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

All the glands have ducts through which saliva is directed to the mouth.

The tongue also rolls the food into small round masses called boluses. The boluses are
then pushed to the back of the mouth to initiate the swallowing process. The boluses are
then moved to the stomach via oesophagus. Movement is facilitated by a wave of
muscular contractions of longitudinal and circular muscles of the oesophagus known as
peristalsis.

There is a ﬂap of cartilage, epiglottis which closes the wind pipe (trachea) during
swallowing.

Digestion in the stomach

Upon swallowing, the boluses move down the gullet to the stomach. The boluses enter
the stomach via the cardiac sphincter (a muscular valve).

The stomach has thick circular and longitudinal muscle layers which contract and relax to
produce movements that mix the contents of the stomach. The mixing process is known
as churning and results in formation of a ﬂuid called chyme

Arrival of food in the stomach stimulates secretion of the hormone gastrin which
stimulates the gastric glands in the stomach walls to secrete gastric juice which contains:

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

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

e) Hydrochloric acid– This:

Activates pepsinogen to pepsin

Provides a favorable medium for action of the enzymes rennin and pepsin

Kills some bacteria ingested with food.

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

Duodenum

The chyme then passes down to the Duodenum through pyloric sphincter.

Duodenum is the first section of the small intestine. In humans it measures about 25-38 cm. the
chyme is let down into the duodenum in small quantities.

Secretions that contribute to digestion at the duodenum are received from:

a) Gall bladder in the liver- Secretes bile.

b) Pancreas- Secrete hormones and digestive enzymes.

Arrival of food in the duodenum stimulates secretion of

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

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

Pancreatic juice contains:

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

b) Trypsin– Digests proteins into peptides.

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

d) Sodium hydrogen carbonate– This:

Provides alkaline medium for activity of the duodenum enzymes.

It also neutralizes the acidic chyme.

The bile juice contains bile salts that include sodium glycocholate and sodium
taurocholate. These salts:

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

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

iii. In addition they neutralize the acidic chyme.

Digestion in the ileum

Ileum is the final part of the small intestine.

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

a) Maltase: speeds up breakdown of maltose to glucose

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

c) Peptidase: speeds breakdown of peptides to amino acids

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

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

f) Polypeptidase: speeds breakdown of plypeptides into amino acids

Note:

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

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

Absorption

This is the process through which the soluble end products of digestion diffuse into the
cellular lining of the villi.

Absorption of micronutrients such as water soluble vitamins, mineral salts and alcohol
are absorbed at the stomach. Alcohol is equally absorbed here without undergoing
digestion.

Most absorption of end products of digestion occurs in the ileum.

Molecules of amino acids and glucose pass through the epithelial lining and capillary
walls into the blood system by active transport.

The capillaries drain into the hepatic portal vein where the absorbed products are
transported to the liver before they are circulated to other body parts.

The fatty acids are absorbed into the lacteals of the villi which drain into the lymphatic
vessels. The lymphatic vessels later join the blood circulatory system which transports
them to other body parts.

The ileum is adapted to absorption in many ways

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

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

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

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

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

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

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

Egestion

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

Caecum and Appendix

While these have no roles in man, they play vital roles in the ruminant animals and other
herbivores.

They contain some bacteria which secrete cellulose enzyme. These enzymes
digest cellulose since most digestive systems cannot secrete cellulose digesting enzyme.
The bacteria and the herbivores are in a symbiotic relationship.

Assimilation

This is process of incorporation of the end products of digestion into the cell metabolism.

It involves utilization of the end products of digestion into various uses.

a) Glucose

Oxidized to release energy

Excess glucose is stored under the skin to provide heat insulation

Glucose is used to synthesize complex polysaccharide such as cellulose that is an
important structural compound in plants.

b) Fatty acids and glycerol

Oxidized to release energy

Combine to form neutral fats stored under the skin to provide heat insulation

Used to build structures

c) Amino acids

Used to synthesize proteins for general body growth

Oxidized during starvation to release energy.

Vitamins

These are organic chemical compounds that are essential for a healthy body.

Some are synthesized in the body through the action of some microorganisms while some
are also obtained in fresh fruits and vegetables.

Vitamins are destroyed when foods are excessively cooked. They are required in small
quantities.

They play vital roles in metabolic reactions. Some act as co-enzymes while some
inﬂuence the intake of certain substances. In particular, vitamin C inﬂuences uptake of
iron while vitamin D inﬂuences absorption of calcium ions in the gut.

Lack of vitamins in the body results into abnormities that manifest through various
deficiency diseases. These deficiency diseases can be corrected by inclusion of the
deficient vitamins in the diet or taking the vitamin supplements.

There are two classes of vitamins owing to their solubility:

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

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

Vitamin A (retinol)

main food source

liver, milk, eggs,cold liver oil, carrots, fresh green vegetables

uses in the body

for vision especially at night

protects skin and cornea from drying or becoming scaly

deficiency disease symptoms

poor night vision

sore eyes

dry scaly skin and cornea

reduced resistance to diseases

Vitamin B1 (thiamine)

main food source

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

uses in the body

cell respiration

proper growth in children

deficiency disease symptoms

general weakness

retarded growth in children

beriberi-wasting of muscles and swelling of feet and legs

Vitamine B2 (riboflavine and nicotinic acid)

main food source

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

uses in the body

cell respiration

normal skin health and function

deficiency disease symptoms

pellagra-skin disorders

sore and bleeding in mouth and gum

Vitamin B5 (pentathonic acid)

main food source

like B1 and B2 but more in eggs

uses in the body

cell respiration

proper function of nervous system and alimentary canal

deficiency disease symptoms

malfunctioning od nervous system and digestive system

Vitamin B12 (cobalamine)

main food source

liver, beef, kidney

uses in the body

formation of blood cells

deficiency disease symptoms

pernicious anaemia-low blood count

Vitamin C (absorbic acid)

main food source

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

uses in the body

protection against infections

deficiency disease symptoms

scurvy-bleeding of mouth and gum

anemia

swellings of skin

poor healing of wounds

reduced resistance to infection

Vitamin D (calciferol)

main food source

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

uses in the body

formation and hardening of bones and strong teeth

absorption of calcium and phosphorus

deficiency disease symptoms

rickets-an abnormal bone formation in children

soft and brittle bones in adults

Vitamin E (tosopherol)

main food source

egg-yolk, green vegetables and vegetable oil

uses in the body

necessary for normal fertility in some animals

cell metabolism

deficiency disease symptoms

sterility in some animals

Vitamin K (quinone)

main food source

liver, green veges, unpolished cereals, egg-yolk

uses in the body

necessary for blood clotting

deficiency disease symptoms

excessive bleeding

Mineral salts

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

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

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

Element: Nitrogen

source

meat, milk, egg, fish, other proteins

function in the body

synthesis of proteins

formation of cell, tissue and structures

deficiency symptoms

–

Element: Phosphorous

source

protein foods

function in the body

synthesis of proteins

bone and teeth formation

ATP formation

deficiency symptoms

rickets-poorly developed bones

Element: Calcium

source

green veges, milk, cheese

function in the body

blood clotting and muscle contraction

formation of bone and teeth

deficiency symptoms

muscle cramps

rickets

Element: Iodine

source

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

function in the body

formation of thyroxine hormone

regulate rate of energy production

deficiency symptoms

goiter- swelling of thyroid glands in the neck region

Element: Potassium

source

Liver, beef, veges, milk, egg

function in the body

transmission of nerve impulses

proper heart functioning

growth and maintenance

deficiency symptoms

mascular cramps

twitching and weakness

irregular heart beats

Element: Iron

source

liver, eggs, veges

function in the body

formation of hemoglobin in red blood cells

role in respiration

deficiency symptoms

anemia

Element: Sodium

source

table salt, green veges, milk, fish

function in the body

maintaining osmotic balance of the body fluids

transmission of nerve impulses

regulation of blood pressure

Element: Chlorine

source

table salt

function in the body

maintaining osmotic balance of the body fluids

transmission of nerve impulses

Element: Sulphur

source

Protein foods

function in the body

protein synthesis

formation of body tissues

Element: Magnesium

source

present in almost all foods

function in the body

bone and teeth formation

activates enzymatic activities in the body

proper functioning of the nerves and muscles

activating B vitamins

insulin secretion and functioning

energy production

making of new cells

deficiency symptoms

muscles tremors and convulsions

fatigue

nervousness

Roughage

This is the indigestible material in food. Mainly composed of cellulose from plant cell
walls.

They are found in full cereals, fresh fruit fibres like lemons, oranges, mangoes and
vegetables.

Importance of roughage

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

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

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

Factors affecting energy requirements in humans

Discuss how the following factors affect energy requirements in humans:

Basal metabolic rate

Occupation

Health of an individual

Age

Sex

Body size

Environmental temperature

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

K.C.S.E ONLINE REVISION

BIOLOGY NOTES FORM 2

1. a) i) Define transport

Movement of substances from one pan of the body to another

ii) Explain the necessity of transport in plants and animals

make nutrients move from one point to another

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

elimination of metabolic wastes

movement of hormones

movement of water

movement of salts

movement of enzymes

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

root hairs are found near the root tip

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

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

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

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

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

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

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

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

Monocot root

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

Similarities

both used for anchorage and absorption of water and mineral salts

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

(xylem and phloem)

both may be used to store food/storage organs

Differences

Monocotyledonous

phloem and xylem are arranged in ring form alternately

pith present

Dicotyledonous

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

pith absent

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

Monocotyledonous stem

Dicotyledonous stem

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

Similarities

both are used for protection

both conduct water, salts and food

both have epidermis, cortex, pericycle and vascular bundles

Differences

Monocotyledonous

vascular bundles are many and scattered

some have hollow pith or pith is absent

no cambium layer therefore cannot

undergo secondary growth very

little cortex

Dicotyledonous

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

pith large and well developed

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

no cambium layer therefore cannot

undergo secondary growth

very little cortex

presence of cambium therefore

undergoes secondary growth

cortex has several layers of cells

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

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

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

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

lignified/thickened to prevent collapsing

narrow to facilitate capillary

no cross walls for continuous ﬂow/column of water

have bordered pits for lateral movement of water

a) i) Why do ﬂowering plants need water?

photosynthesis

transport

turgidity w h helps in plant support

solvent i.e. medium for chemical reactions

cooling effect during transpiration

seed germination

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

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

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

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

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

Stem

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

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

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

Leaves

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

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

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

active transport

diffusion

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

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

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

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

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

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

capillarity is due to narrowness of xylem vessels

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

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

ii) Explain the uptake of mineral salts by plants

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

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

transport which requires energy

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

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

b) i) What is transpiration?

loss of water from plant to the atmosphere

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

stomata (stomatal transpiration)

lenticels (lenticular transpiration)

cuticle(cuticular transpiration)

iii) State the importance of transpiration to plants

cooling the plant

transport of water

transport of mineral salts

excretion of excess Water from plants

excess transpiration causes wilting

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

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

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

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

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

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

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

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

humidity when high increases rate and when low reduces the rate

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

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

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

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

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

sieve tubes have cross wall while xylem vessels have none

xylem vessels are lignified while sieve tubes are not

Sieve tubes have cytoplasm elements while xylem vessels have none.

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

thick waxy cuticle

reduced leaf size/thorns/spines

shedding of leaves

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

rolling of leaves

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

increased light intensity

low relative humidity

temperature

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

reduces surface area exposed to sun reducing cuticular transpiration

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

a. Mesophytes

they grow in soils with enough water

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

no special adaptations

b. Xerophytes

they grow in dry conditions

root grow very deep to absorb water

succulent/ﬂeshy leaves to store water

few stomata which are sunken

thickened waxy cuticle

leaves are hairy and often folding

some leaves are needle-like/spines or scales

leaf surfaces are reduced i.e. small leaves

all these adaptations are to reduce water loss

c. Hydrophytes

plants that grow in water

presence of sclereids

leaves are broad

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

some leaves ﬂoat on water

absence or reduced leaf cuticle

large air spaces

some leaves are submerged

poorly developed or reduced vascular bundles

d) i) What is translocation

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

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

phloem tissue

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

active transport

Diffusion

Mass ﬂow

Cytoplasmic streaming

iv) Draw a labeled diagram to represent phloem tissue

ii) State the functions of the labbeled structures cytoplasmic strands

translocation

Companion cell

supply nutrients to sieve tube element

supply energy for translocation

regulates activities of tube cells/elements

Sieve tubes element

conduct food down the stem

iii) name the compounds that are translocated in phloem

sugars

amino acids

hormones e.g auxins

oils/lipids

resins

vitamins

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

a. Ringing experiment

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

phloem is found next to or just beneath the bark

observe daily for some time(more than three weeks)

a swelling of the bark appears above the ring

this is due to accumulation of food from leaves

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

a swelling does not appear

ii) Use the radio-active tracers

plant is exposed to carbon containing radio-active carbon C14

C14 is found in the end products of photosynthesis

It is finally detected in phloem

C14 is found to move in both directions

iii) Collecting exudate from stylets of aphids

aphids feed on certain plant phloem using their stylets

aphid mouth parts are dissected using a sharp razor

exudes from the mouth parts are collected and then analyzed

sucrose is found to be a major component of the exudates

this proves that phloem translocates manufactured food substances

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

i. Either

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

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

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

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

cut a thin section of stem or leaf

mount it on a slide and examine under a microscope

observe and note the distribution of the dye or ink

the dye appears only in the xylem vessels

ii. OR

use radio-active tracers, C14 in form of carbon

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

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

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

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

blood, a ﬂuid medium which contains dissolved substances and cells

the heart, a pumping mechanism which keeps blood in circulation

ii) Distinguish between closed and open circulatory systems

closed system has blood vessels through which blood moves eg vertebrates

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

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

Closed system has continuous vessels hence able to generate high pressure

Circulates blood over longer distance

Circulates blood at a faster rate

Efficient transport of nutrients and waste products

Animals are more active

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

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

Double circulation

blood enters the heart twice in a complete circulation

Pulmonary circulation from the heart to lungs and back

Systemic circulation from the heart to body systems and back

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

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

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

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

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

ii) Describe the structure and function of the mammalian heart

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

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

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

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

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

blood moves on to the capillaries

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

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

right ventricle pumps blood into the lungs through the pulmonary artery

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

left auricle pumps blood into left ventricle

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

both auricles contract simultaneously while both

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

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

nerve supply however, determine contraction strength and frequency

the heart is divided into four chambers

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

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

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

the tricuspid valve

The right ventricle pumps blood to the lungs

This is facilitated by the presence of pulmonary artery

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

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

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

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

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

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

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

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

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

under ventilation of the lungs

blockage of alveoli (air sacs)

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

e) Describe the structure and functions of the blood vessels

i. Arteries

carry away blood from the heart

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

have thick, muscular walls

are elastic

have narrow lumen

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

ii. Capillaries

link arterioles and venules to arteries and veins

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

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

thin walled to allow presence of intercellular spaces

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

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

lie close to the body for easy exchange of materials

iii. Veins

carry blood back to the heart

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

have thinner Walls than arteries

have valves to prevent back flow of blood

have wide lumen

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

pulmonary arterioles

deoxygenated

high carbon iv oxide

low oxygen

more nutrients

pulmonary venules

oxygenated

low carbon iv oxide

high oxygen

less nutrients

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

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

blood pressure in veins is reduced by capillary resistance

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

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

iii) Name the common heart diseases in humans

thrombosis

antheroma

arteriosclerosis

varicose veins

cerebral vascular thrombosis

c) i) State the functions of mammalian blood

transport of substances

defense against diseases

clotting

temperature regulation

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

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

transports hormones, enzymes from secretory glands to tissues when required

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

distributes heat

bathes the tissues allowing for exchange of materials

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

Red blood cells (Erythrocytes)

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

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

White blood cells (leucocytes)

engulf foreign bodies

produce antibodies for defense against disease

produce antitoxins which neutralize bacterial toxins

Blood platelets (thrombocytes)

produce an enzyme called thrombokinase/thromboplastin necessary for blood clotting

prevents loss of blood, water and mineral salts

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

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

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

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

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

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

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

Red blood cells

has hemoglobin

smaller size

lacks nucleus

White blood cells

not pigmented

larger size

nucleated

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

Red blood cell

Transports oxygen and carbon IV oxide

White blood cell

Protects body against harmful pathogens

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

stronger contractions

faster contractions/heartbeat

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

Oxygen

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

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

the oxygen combines with haemoglobin to form oxyhaemoglobin

blood then becomes oxygenated

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

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

respiration produces carbon IV oxide

Carbon IV oxide

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

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

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

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

from alveolar space carbon IV oxide is expelled during expiration

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

PH of blood is not altered/homeostasis is maintained

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

d) i) what is blood clotting?

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

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

Protein — fibrinogen/prothrombin

Vitamin – k/quinine

Enzyme — thrombokinase/thromboplatin/thrombin

Mineral element — calcium

iii) describe the blood clotting process

enzyme thromboplastin produced in the platelets of damaged tissues converts plasma

protein prothrombin into thrombin in the presence of calcium ions

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

fibrin is insoluble

fibrin forms fibres which form a meshwork that forms a clot

prothrombin thromboplastin thrombin

calcium ion

Fibrinogen thrombin fibrin clot

vitamin K

iv) State the role of blood clotting on wounds

prevents blood/body ﬂuids from being lost

conserves water and salts

prevents entry of microorganisms/pathogens

regulates body temperature

enables wound to heal faster

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

Presence of anticoagulant in blood

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

O, with neither B nor A antigen

AB, with both A and B antigens

A, with type A antigen

B, with type B antigen

iii. Explain the meaning of :

Universal donor

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

this is usually blood group O

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

Universal recipient

can receive blood from all blood groups without agglutination

this is usually blood group AB

however, can only donate blood to group AB

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

rhesus positive blood has the Rhesus (Rh) antigen

rhesus negative lacks the Rhesus antigen

vi) What is blood transfusion?

Introduction of blood from one person to another

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

during accidents

during surgery in hospitals

bleeding mothers when giving birth

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

transfusion

taking ﬂuids

eating iron rich food/taking iron tablets

How may excessive bleeding result in death?

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

State the precautions that must be taken before blood transfusion

blood must be disease free

sterilized equipment must be used

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

Fresh blood must be used.

j) i) What is immunity?

Resistance to disease by organisms

ii) Distinguish between natural and acquired immunity

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

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

iii) What are allergic reactions?

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

vi) How does an allergic reaction occur?

the substances act as antigens

an antigen-antibody reaction occurs on surface of cells

the cells release a substance called histamine

the histamine causes irritation, itching and may stimulate nasal discharge

ii) State the role of vaccination against certain diseases

protect body against infectious diseases

prevent spread/transmission of certain diseases

diseases for which vaccination is given include tuberculosis, poliomylitis,measles,

whooping cough, diphtheria

3. a) i) What is gaseous exchange?

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

ii) Why is gaseous exchange important to organisms?

to supply oxygen necessary for energy production

to remove carbon IV oxide produced during respiration

To remove Water vapour.

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

stomatal pores/stomata

lenticels

cuticle

pneumatophores

ii) Brieﬂy describe the structure of stomata

are minute pores found in leaf epidermis

each consists of a slit-like opening

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

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

Inner walls of guard cells are thicker than the outer cells

iii) State the factors which affect stomatal opening

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

light as stomata open in bright light and close in darkness

temperature

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

interconversion of starch and sugar

pH theory

mineral ion concentration

v) Describe the mechanism of opening and closing of stomata

stomata close at night and open during daytime

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

In the dark carbon Iv oxide accumulates in the intercellular spaces

This raises concentration of carbonic acid

The pH drops (pH lowered)

Enzymes convert sugar into starch in guard cells

Osmotic pressure in guard cells is lowered

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

The stomata close

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

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

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

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

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

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

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

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

presence of stomata for faster gaseous exchange

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

film of moisture around the surface of cells for easy diffusion

broad/ﬂattened shape to increase surface area

thin lamina to reduce distance of diffusion

exposed to air for easy diffusion

ii) Describe how gaseous exchange takes place in terrestrial plants

Gaseous exchange takes place in spongy mesophyll

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

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

Some of the oxygen diffuses out of the leaf through stomata

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

The air dissolves into film of moisture

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

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

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

Some gaseous exchange also takes place through cuticle

Gaseous exchange occurs through epidermis of young leaves and stems

The cork cells at lenticels are loosely packed

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

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

stomata found only on upper dermis to allow efficient gaseous exchange

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

absence of cuticle to enhance gaseous exchange

iv) How is aerenchyma tissue adapted to its function?

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

v) Explain stomatal distribution in plants of different habitats

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

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

in dry areas, plants have leaves with sunken stomata to reduce water loss by transpiration

Plants in wet areas have stomata equally distributed on both sides.

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

cell membrane in unicellular organisms e. g. amoeba

gills in fish

tracheal system

skin, buccal cavity and lungs in amphibians

lings in mammals

ii) State the characteristics of respiratory surfaces in animals

moist thin walled/thin membrane/thin surface

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

Large surface area

iii) Describe gaseous exchange in protozoa

example is amoeba

small and have large surface area

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

simple diffusion of gases is enough to meet its respiratory requirements

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

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

large surface area due to many filaments

extensive vascularisation due to capillaries, for gaseous exchange

thin filaments to facilitate diffusion of gases

presence of rakers to filter solid particles

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

iii) Discuss gaseous exchange in bony ﬁsh

example is tilapia

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

water then enters into the mouth cavity

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

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

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

iv) What is counter-flow system?

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

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

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

oxygen continues diffusing into blood and carbon iv oxide into Water

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

example is cockroach

air in the atmosphere contains oxygen

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

these movements cause the opening of spiracles

air moves through the trachea to tracheoles

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

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

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

ii) State how traceholes are adapted to gaseous exchange

thin walls of tracheoles

moist surface

large surface area due to numerous tracheoles

g) i) What is breathing?

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

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

nose

larynx

epiglottis

trachea

lungs

pleural membrane

pleural cavity

diaphragm muscles

iii) Describe the mechanism of gaseous exchange in a mammal

Breathing in

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

muscles of the diaphragm contract hence it ﬂattens

the volume of the thoracic cavity increases while pressure decreases

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

Breathing out

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

muscles of the diaphragm relax hence the diaphragm assumes dome shape

the volume of the thoracic cavity decreases while pressure increases

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

iv) Explain how mammalian lungs are adapted to gaseous exchange

large number of alveoli that increase surface area

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

through alveolar cavities and blood

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

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

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

have large surface area/spherical shaped

numerous/many to increase surface area

one cell thick

moist surface for air to diffuse

highly vascularised/numerous capillaries

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

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

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

mucus to trap dust, solid particles and microorganisms

hollow for passage of air

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

nose has hairs to filter solid particles

it has mucus lining to trap dust particles

the nose has cells sensitive to smell for survival

it warms the air before it reaches the lungs

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

vigorous exercise

emotions/stress

disease infection

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

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

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

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

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

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

breathing movements usually occur unconsciously

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

medullar oblongata is in the brain

respiratory centre transmits impulses to the diaphragm through phrenic nerves

carbon iv oxide concentration in the blood determines the breathing rate

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

cardiac frequency decreases and the arterioles constrict

therefore carbon iv oxide level is raised

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

the brain is triggered to increase breathing rate

cardiac frequency is increased

there is vasodilation of arterioles

carbon iv oxide level falls

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

ii) Name the respirator diseases

asthma

bronchitis

whooping cough

pneumonia

tuberculosis

4. a) i) Deﬁne respiration

the oxidation/breakdown of food within cells to release energy

ii) Explain the signiﬁcance of respiration in living organisms

it yields energy (ATP)

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

iii) Where does respiration take place?

in the mitochondria

b) i) Draw and label a mitochondrion

ii) State the most important function of mitochondria

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

iii) Give the functions of the labeled parts

Outer membrane

controls what enters and What leaves mitochondrion

Cristae

also called inner membrane

increase surface are for attachment of enzymes

this is Where cellular oxidation reactions occur

Matrix

enzymes are located here

other reactions occur here

c) Explain the roles of enzymes in respiration

they catalyse reactions i.e. speed up respiration

d) i) What is aerobic respiration

respiration in the presence of oxygen

ii) Give a word equation for aerobic respiration

glucose + oxygen – Water + carbon iv oxide + energy

iii) What are the end products of aerobic respiration?

energy

carbon iv oxide

water

e) i) What is anaerobic respiration

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

ii) What are obligate anaerobes?

are completely independent of oxygen

iii) What are facultative anaerobes?

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

iv) State the Word equation representing anaerobic respiration in plants

Glucose ethanol + carbon (iv) oxide + energy

v) Name the end products of anaerobic respiration in plants

alcohol/ethanol

carbon iv oxide

energy

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

Glucose —> lactic acid + energy

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

lactic acid

energy

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

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

iv) Why does lactic acid level reduce after exercise?

lactic acid is oxidized to form carbon iv oxide and water

some is converted to glucose

some is converted into glycogen

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

lactic acid is poisonous to tissues and must be removed

to increase supply of oxygen to tissues

State the economic importance of anaerobic respiration

brewing of alcohol

biogas production

compost manure formation

silage formation

baking bread

production of dairy products

fermentation of milk

sewage treatment

Fermentation of tea in industries.

What is oxygen debt?

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

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

ration of carbon IV oxide produced to oxygen consumed

RQ = volume of CO2 produced

volume of oxygen consumed

ii) Why are respiratory quotient important

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

iii) Name the respiratory substrates

carbohydrates

fats

proteins

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

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

substrate is completely oxidized in aerobic respiration

iv) Explain the disadvantages of anaerobic respiration

Less energy produced in anaerobic respiration since food is partially oxidized while in

aerobic respiration food is completely oxidized.

Some metabolic wastes accumulate in cells affecting cellular functions

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

causes muscle fatigue/muscle cramp and may stop muscle contraction

Such intermediate wastes are not produced in aerobic respiration

v) Mention the types of experiments carried out for respiration

germinating seeds which yield energy in form of heat

animals produced heat when they respire

yeast cells respire to produce heat

5. a) i) Define the following terms

Excretion

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

Secretion

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

Egestion

removal of indigestive materials from the body

Homeostasis

maintenance of constant internal environment

ii) Explain Why excretion is necessary in plants and animals

-products of excretion are usually harmful while some are toxic

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

– They are therefore removed through excretion

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

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

some toxic wastes are convened into non-toxic substances

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

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

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

plants have lower rates of metabolism

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

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

plants store waste products in roots, fruits and leaves

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

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

quinine used for treating malaria

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

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

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

Cannabis sative(bhang) is used to make drugs

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

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

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

Khat and miraa are used as stimulants

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

Papain used as meat tenderizer

c) i) Describe excretion in unicellular organisms

-examples are amoeba and paramecium

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

– These diffuse from the body surface into the surrounding Water

– Diffusion is due to large surface area

ii) List excretory organs and products of mammals

kidney excretes urea, water and salts

skin excretes Water, slats and urea

lungs excrete carbon IV oxide and water

liver excretes bile salts

d)i) Draw and label a mammalian skin

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

the skin is made up of dermis and epidermis

Epidermis

it is made up of three layers

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

granular layer made of living cells gives rise to corniﬁed layer

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

Dermis

has several components

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

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

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

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

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

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

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

e) What is the role of lungs in excretion?

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

carbon IV oxide is produced as a by-product

the carbon IV oxide must be eliminated from the body

elimination is through the lungs

also, water vapour is formed and must be removed

this removal is through the lungs

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

f) State the functions of the liver

i. Excretion

in this function the liver is aided by the kidney

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

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

breakdown of worn out blood cells and haemoglobin and the residue excreted through the

kidney to give urine a yellow tinge

Breakdown of sex hormones after they have performed their function and the wasted are

released through the kidney and bile.

ii) Homeostasis

regulation of blood glucose

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

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

insulin stimulates the liver to convert excess glucose to glycogen

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

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

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

fats, amino acids are converted to glucose

it also leads to reduced oxidation of glucose

Deamination

excess amino acids are deaminated by the removal of amino group

the amino group is converted to ammonia

ammonia combines with carbon IV oxide to form urea

urea is excreted in urine through the kidney

Detoxification

poisonous substances are converted to less harmful compounds

Thermal regulation

maintenance of body temperature

heat is generated in the liver by chemical activities

the heat is distributed

g) i) Draw a labeled diagram of mammalian nephrone

ii) Describe how the human kidney functions

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

the afferent arteriole has a wider diameter than the efferent arteriole

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

the walls of the blood capillaries are one cell thick hence glucose, amino acids, vitamins,

hormones, salts, cratinine, urea and water filter into Bowman’s capsule to form
glomerular filtrate

white blood cells, red blood cells, plasma proteins (such as globulin) and platelets are too
large to pass through the capillary walls hence remain in blood capillary

the filtrate flows into proximal convoluted tubule where amino acids, vitamins and all
glucose are selectively reabsorbed back into the blood stream

many mitochondria provide energy for reabsorption of these substances against a
concentration gradient by active transport

the glomerular filtrate ﬂows into the loop of Henle

water in the descending loop moves by osmosis into the blood capillaries

sodium chloride is actively pumped from the ascending arm of the loop of Henle into the
blood capillaries

the glomerular filatrate ﬂows into the distal convoluted tubule

water and salts are reabsorbed from distal convoluted tubule into blood capillaries

the glomerular filtrate ﬂows into collecting tubule (duct) from where more Water is
reabsorbed into blood stream

antiduretic hormone inﬂuences the amount of Water reabsorbed depending on osmotic
pressure of blood

the glomerular filtrate from collecting duct, now referred to as urine, is emptied into
pelvis and ureter into bladder and out of body through urethra

urine consists of excess water, slats and nitrogenous wastes

iii) State the adaptations of proximal convoluted tubule to its function

folded to increase surface area for absorption thin epithelium to reduce distance of diffusion micro-villi on inner

lining to increase surface area for absorption folded to reduce speed of ﬂow for efficient
absorption numerous mitochondira to provide energy for reabsorption dense capillary network to transport reabsorbed products

iv) Name the common kidney diseases

nephritis

kidney stones(renal calculi

cystitis

oedema

kidney failure

6. a) i) Why is homeostatic control necessary?

this provides a constant internal environment so that the cells of the body have the
optimum (best) condition for their survival

ii) What is internal environment?

immediate surrounding of body cells

refers to tissue ﬂuid within an organism

b) i) Why is constant body temperature maintained by mammals?

most enzymes in the body function within a narrow range of temperature

high temperature denatures enzymes

low temperature inactivates and inhibits enzymes

ii) Explain the advantage gained by possessing a constant body temperature

animals remain active despite ﬂuctuations in environmental temperature

higher chances of survival in various environments ie they colonize various environments

chemical processes in their body continues at an optimum rate

iii) How do mammals regulate body temperature?

the body temperature of a mammal is kept constant

to maintain this temperature the mammal must be able to balance its heat loss against the
heat gain

body temperature is controlled by the hypothalamus, a specialized part of the brain

changes in the temperature within the body and the surrounding are detected by the
hypothalamus it transmits impulses to the skin and the blood stream in response to
temperature changes hypothalamus acts as a thermostat for the body

a mammal loses heat by breathing out, urine, feaces, skin by radiation and by evaporation
of sweat.

A mammal generates heat by the activity of its muscles, by general metabolism in
respiration, or chemical activities

In hot conditions the hypothalamus stimulates responses that increase heat loss from the
body hence lowering the body temperature

Such responses include sweating, vasodilation, keeping its hair ﬂat on the surface of skin
and reduction of metabolic rate

In cold conditions the hypothalamus stimulates responses that generate heat gain in the
body and reduce heat loss to the environment

Such responses include shivering, vasoconstriction, raising its hair to trap a layer of air
around the skin because still air is a good insulator of heat and by generation of heat by
increasing metabolic rate.

iv) Why does body temperature of a healthy person rise up to 37 C on a hot humid day?

sweat evaporation is reduced hence cooling is less therefore more heat is retained in the
body causing temperature to rise

v) Name the structures in the human body that detect external temperature changes

temperature receptors (end bulb corpuscles e. g. bulb of Krause (warmth) and organ of
Ruffinni (cold)

heat (thermal) receptors

vi) State the advantages that organisms with small surface area to volume ratio experience
over those with larger

heat loss slow hence their body temperature can increase to intolerable levels

Heat gain from surrounding slower hence may remain inactive for a long time.

Need specialized and complex transport system and also gaseous exchange system

Explain why individuals with smaller sizes require more energy per unit body weight than
those with larger sizes.

surface area to volume ratio is higher in smaller individuals than larger ones, therefore
smaller heat is lost faster by smaller ones than larger ones

they therefore require more energy per unit body weight to maintain body temperature

c) i) What is the meaning of osmoregulation?

mechanism which regulates osmotic pressure of internal environment of an organism

the regulation/maintenance of salt/solute-water balance of an internal environment

ii) State the importance of osmoregulation

Maintenance of constant level of water and slats (osmotic pressure) for optimum/suitable
conditions for metabolism suitable for cellular functions

iii) State the ways by which desert mammals conserve water fewer glomeruli longer loop of
Henle

excretion of dry feaces or concentrated urine

hump for fat to be metabolized to give metabolic water for use

nocturnal, burrowing, aestivate or hibernate

sweat glands few or absent

more ADH (vasopressin)

iv) Explain why some desert animals excrete uric acid rather than Water

uric acid is less toxic than ammonia, hence elimination of uric acid requires less water

than ammonia therefore more water conserved

uric acid being less toxic is safer to excrete where there is less water/desert

v) Explain why eating a meal with too much salt leads to production of a small volume of
concentrated urine

the concentration of salts in the blood rises leading to production of more ADH hence
higher rate of water reabsorption by kidney tubules

vi) Explain how marine ﬁsh regulate their osmotic pressure

swallow plenty of sea water to increase amount of water in the body

have chloride excretory cells in their gills to remove excess salts

eliminate nitrogenous wastes in form of trimethalamine oxide which requires little water
for elimination

few/small glomeruli thus slow filtration rate in the kidneys

retain nitrogenous wastes in form of urea to raise osmotic pressure of body ﬂuids

d) i) What is the biological signiﬁcance of maintaining a relatively constant sugar level in a
human body?

body cells are surrounded by tissue ﬂuids that are isotonic/same osmotic pressure as
cytoplasm

if sugar level is high/hypertonic, cell will lose water by osmosis to the surrounding, thus
increasing the concentration of the contents

this changes the physiology of the cell

if the blood sugar is lower than the normal, the cytoplasm gains water by osmosis,

diluting the cell contents, thus altering the physiology of the cell

ii) Discuss the role of the following hormones in blood sugar control

Insulin

insulin is produced when there is increase in blood sugar concentration

it converts glucose to glycogen which is in the liver or muscle thus lowering sugar level

Glucagon

when glucose level decreases glucagon is produced, which causes the breakdown of
glycogen to glucose thus raising blood sugar level

e) Explain the part played by antidiuretic hormone in homeostasis

Produced when there is less water (high osmotic pressure above normal level of salt
concentration) in the blood.

It acts on kidney tubules (nephron) thus increasing water reabsorption from tubules to the
blood stream, thus restoring osmotic pressure

When there is more water(lower osmotic pressure) or decreased salt concentration in
blood, little or no ADH is produced, less water reabsorbed hence water loss in urine
(more dilute urine) hence raising the osmotic pressure in body ﬂuids/blood

f) What is the role of blood clotting in homeostasis?

when a blood vessel is cut, there is exposure of blood platelets to the air

this triggers fibrinogen to be converted to fibrin

the fibrin forms a clot that prevents body ﬂuids e. g. blood from being lost

therefore the clot conserves water and salts in the body

g) Describe the role of the following hormones in homeostasis

i. Aldosterone

concerned with regulation of ionic balance

secreted by the cortex of adrenal glands

it increases sodium ion uptake by the gut and promotes the reabsorption of sodium ions
(and therefore water) in the kidneys)

this is accompanied by elimination of potassium ions

this raises the overall level of sodium and lowers the overall level of potassium in the
blood

as sodium ions are absorbed in the blood, chlorine ions follow so as to neutralize the
effect of sodium ions

the production of aldosterone is regulated by the concentration of sodium ions which has
an inhibiting effect, and a fall in sodium ions has a stimulating effect on the adrenal
cortex

the ﬂow of aldosterone is stimulated by the adreno-cortic-tropic hormone (ACTH)
produced in the anterior of the pituitary gland however, the main method of control is
dependent on the fact that adrenal cortex itself is somehow sensitive to the relative
concentration of potassium and sodium in the blood

ii. Adrenaline

produced by adrenal glands

in high concentrations, it increases hydrolysis of glycogen and increases blood sugar

it is usually released in emergency cases to increase glucose level for respiration

this releases energy for the emergency

h) i) Distinguish between diabetes mellitus and diabetes insipidus

diabetes mellitus is a condition resulting from insufficient production of insulin causing
hyperglucaemia and presence of glucose in urine

diabetes insipidus is a condition whereby less or no antidiuretic hormone is secreted
hence a high volume of water is passed out in urine in a condition called diuresis

ii) How can high blood sugar level in a person be controlled?

administer insulin

iii) Why does glucose not normally appear in urine even though it is filtered in the
mammalian Bowman’s capsule?

glucose molecules are actively reabsorbed in the proximal convoluted tubules

iv) When is glycogen which is stored in the liver converted into glucose and released into
the blood?

after activity/when blood sugar (glucose) falls below normal

when glucagon

stimulates the liver/when glucagon is produced

after strenuous/vigorous activity

during starvation

v) How would one ﬁnd out from a sample of urine whether a person is suffering from
diabetes mellitus?

test or react urine in Benedict’s solution

positive result i.e. orange or red precipitate

Positive result is an indication of diabetes mellitus

KCSE Biology Questions and Answers Form 3 – Biology Form Three Notes

Biology Questions and Answers Form 3

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

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

ii) State brieﬂy the general principles of classiﬁcation of living organisms

scientific names must be in Latin or should be latinised

family names are formed by adding the suffix “idea” to the stem of the genus e.g the
genus Rana become Ranaidea

generic names should be a single unique name

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

i. Monera

e.g. bacteria

unicellular (single celled)

prokaryotic (genetic material not surrounded by membrane)

cell Wall without cellulose

lack most organelles

small in size (microscopic)

ii. Protista(protoctista)

single celled(unicellular)

eukaryotic (most cell organelles present)

when cell Walls are present have no cellulose

e.g. protozoa and algae

usually microscopic

iii. Fungi

have hyphae (which form mycelia)

absence of chlorophyll

have rhizoids (lackroots, leaves, stem)

have spore forming structures (sporangia)

e.g. mucor, rhizopus

iv. Plantae

most are green/contain chlorophyll

autotrophic/feed by photosynthesis

cells have cellulose cell walls

respond slowly to stimuli (tropism)

lack locomotion (are stationary)

indefinite growth (at meristems)

lack specialized excretory structures

v. Animalia

cells do not have cell walls

most carry out locomotion

heterotrophic

fast response to stimuli (tactic)

have specialized excretory structures

c) Describe the economic importance of:

i. Fungi

some cause decay to our food

some cause diseases to humans and animals e. g. ringworms

may be used as food e. g. mushrooms, yeast

some are used in production of antibiotics e. g. penicillin, chloromycin, streptomycin

yeast is used in brewing industry, baking and source of vitamin B

many cause diseases to our crops e. g. late blight

important in recycling nutrients in soil since they cause decay of organic matter

mycorrhizal association in forest development may help in Water intake/absorption

help in nitrogen fixation

ii. Bacteria

are useful in the manufacture of antibiotics

silage formation,

fermentation of cheese, butter, milk yoghurt

curing of tea, tobacco and retting ﬂax

formation of vitamin B12 and K

enzymes such as amylase and invertase

hormones such as insulin ‘

vinegar, acetic acid, lactic acid, citric acid

in septic tanks and modern sewage Works make use of bacteria

biogas production

saprophytic bacteria are used in compost decomposition or cause decay

symbiotic bacteria are used in compost decomposition or cause decay

symbiotic bacteria in herbivores/ruminants help in digestion

some diseases in animals/humans and plants are caused by bacteria

many bacteria cause‘ food spoilage/decay

nitrifying and nitrogen fixing bacteria increase soil fertility/make nitrates available

denitrifying bacteria reduce soil fertility/convert nitrates into nitrogen/reduce nitrates

d) State the main characteristics of the following division of kingdom plantae

i. Bryophyte

e.g. mosses and liverworts

presence of rhizoids

lack of vascular tissues (lack phloem and xylem)

body pans not differentiated into root, stem, leaves

capsule or seta

gametophyte generation dominant.

ii. Pteridophyta

e.g. ferns

has true roots, stems and leaves

fond with sori on under-surface

vascular tissues present

sporophyte generation is dominant

iii. Spermatophyte

photosynthetic

well differentiated into roots, stems and leaves

well developed vascular system

seed bearing plants

e) Name sub-divisions of spermatophyte and state the characteristics of each class

i. Gymnospermae (cornifers)

naked seeds (exposed

are all woody trees

reproduce by means of cones

show xerophytic characteristics

xylem have tracheids but lack vessels

phloem lacks companion cells ~

single fertilization

pollen lands directly on ovules

ii. Angiospermae (ﬂowering plants)

reproduce by ﬂowers

seeds enclosed (in fruits)

flowers bisexual hence double fertilization

herbaceous

pollen grains land on stigma of pistil

xylem contains vessels

phloem contains companion cells

ovules contained in ovary

iii. Name the classes and state characteristics of angiospermae

Dicotyledonae

two seed leaves

network venation of leaves

regularly arranged vascular bundles

tap root system

broad leaves

secondary growth occurs

Monocotyledonae

one seed leaf

parallel venation of leaves

irregularly arranged vascular bundles

fibrous root system

narrow leaves

sheath like leaf stalk (petiole)

no secondary growth

iv)State the importance of plants

balancing carbon IV oxide and oxygen in the atmosphere during photosynthesis and
respiration
inﬂuence water cycle

reduce soil erosion by bind soil particles together

useful products e. g. food, medicine, timber, paper and clothing

habitat ( e. g. forests and grassland) for animals which may also be tourist attraction
earn money from sales of products

aesthetic value/beauty e. g. flowers, shade/shelter, live fences, windbreaks

Some are harmful e. g. poisons, weeds, injurious (stinging nettles, thorns), water hyacinth

f) i) Give the general characteristics of phylum arthropoda

jointed appendages

presence of exoskeleton

triploblastic and coelomate

segmented body

bilateral symmetry (similar halves)

ii. State the characteristics of the following classes of arthropoda

Diplopoda

the millipedes

two pairs of legs per segment

many segments

terrestrial habitat

body cylindrical and long

herbivorous

one pair of antennae

Chilopoda

the centipedes

one pair of legs per segment

many segments

terrestrial habitat

body long and ventro-dorsally ﬂattened

carnivorous

last pair of legs pointing backwards with poison claws called maxillipedes

one pair of antennae

Insecta

three body pans i.e. head thorax, abdomen

six legs/three pairs of legs

a pair of compound eyes

presence of wings

a pair of antennae

Crustacean

two body parts

segmented body

have pincers (modified legs) to catch prey

have hard exoskeleton

a pair of compound eyes

Arachnida

body divided into two parts( abdomen and cephalothorax)

simple eyes

eight legs (four pairs of legs)

iii) State the economic importance of insects

Beneficial effects

food supply

important in food chains

pollinators

biological control of pests and other organisms

aesthetic value

contribute to decomposition e. g. litter feeders like beetles

Harmful effects

pests

vectors

dirt and disease carriers

injurious e.g. stings and bites

g) i) State the general characteristics of chordate

notochord

dorsal slits (pharyngeal cleft during development)

bilateral symmetry

triploblastic (three layer body-ectoderm, mesoderm and endoderm)

clear cut head formation

multilayered epidermis

post anal tail

closed circulatory system

segmented muscle blocks(myotomes)

single pair of gonads

Give the characteristics of the following classes of chordate

Pisces

presence of fins for locomotion

two chambered heart *

presence of overlapping scales ~

presence of gills or operculum for gaseous exchange

presence of lateral line for protection

streamlined body

poikilothermic (body temperature varies with that of environment)

Amphibian

partially live in fresh Water and partially on land

poikilothermic

pentadactylous with two pairs of limbs

webbed feet for locomotion in water

body streamlined

heart is three chambered

moist skin for gaseous exchange

Reptilia

scales on body

poikilothermic

homodont teeth except tortoise and turtle

all have limbs except snakes

skin is dry

oviparous (lay eggs)

no pinna (external ear)

three chambered heart 9crocodile has four chambers)

skin not glandular

no mammary glands

Aves

the birds

homoeothermic (constant body temperature)

four chambered heart

streamlined body for locomotion in air

skin dry and covered by feathers

scales on legs

hollow bones

oviparous (lay eggs)

mouths modified into beaks

Mammalian

hair on the body

homoeothermic

viviparous (give birth to live young) eXcept a few

have mammary glands

glandular skin e.g. sweat glands, sebaceous glands

four chambered heart

pinna (external ear)

two pairs of pentadactyl limbs

presence of diaphragm

have salivary glands

a) i) What is a dichotomous key?

A biological device (tool) which enables one to identify an organism by progressively
opting between two alternative observable characteristics

i. State the necessity of using a dichotomous key

used to identify organisms quickly and accurately

by following the statements in the key we are able to identify each organism on the basis
of a characteristic which is not to be found in other specimens

ii. List the rules followed in constructing a dichotomous key

use observable characteristics only

start with major characteristics, placing organisms into two groups at each stage

use a single characteristics at a time

use contrasting characteristics at each stage e.g 1(a) short, 1(b) tall

avoid repeating the same characteristics

iv) Describe the procedure of using a dichotomous key. Make a list of major features of the
characteristics to be identiﬁed

look at the features of similarities

look at the features of differences between the organisms

we can then be able to identify the organisms by distinguishing one from another

the key uses a method of elimination by following statements that are correct only for the organism

iv You are provided with a specimen kale leaf. Use the dichotomous key below to identify
the taxonomic group to which the specimen belongs. Show the steps (number and letter) in
the key that you followed to arrive at the identify of the specimen

1 a) Leaf broad……. Go to 2

b) Leaf narrow……. Araicaria

2 a) Leaf parallel vein……. Cynodon

b) Leaf net veined……. Go to 3

3 a) Leaf with one lobe (simple Leaf)……. Go to 4

b) Leaf with many lobes (compound Leaf)……. Grevellea

4 a) Leaf Fleshy……. Kalanchoa

b) Leaf not fleshy……. Go to 5

5 a) Leaf petiole modified to form sheath……. Go to 6

b) Leaf petiole not modified to form sheath……. Brassica

6 a) Leaf purple……. Tradescantia

b) Leaf green……. commelina

Steps 1a, 2b, 3a, 4b, 5b

Identify- Brassica

v) You have been provided with four animals labeled K (mature adult houseﬂy), L (mature
adult grasshopper, M(maize flour beetle) and N(Worker termite) use the dichotomous key
below to identify the specimens. Write down in the correct order, the steps (number and
letter) in the key that you followed to arrive at your answer.

Dichotomous key

1 a) Animal with wings……. Go to 2

b) Animal without wings……. Go to 7

2 a) With two pairs of wings……. Go to 3

b) With one pair of wings……. Diptera

3 a) With membranous wings……. Go to 4

b) Hind pair of membranous wings……. Go to 6

4 a) With long abdomen ……. Odontata

b) Medium sized abdomen……. Go to 5

5 a) Wings with colored scales……. Lepidoptera

b) Wings without scales……. Hymenoptera

6 a) Forewings hard and shell-like……. Coleoptera

b) Forewings hard but not shell-like……. Orthoptera

7 a) Body horizontally flattened……. Isoptera

b) Body laterally flattened……. Symphonopteria

Identify the orders of the various specimen as per the table below

Specimen Order Step followed

K- housefly Diptera 1a, 2b

L- grasshopper Orthoptera 1a, 2a, 3b, 6b

M- beetle Coleoptera 1a, 2a, 3b, 6a

M- termite Isoptera 1b, 7a

2 a) Deﬁne the following ecological terms

i. Ecology

study of the interrelationships between organisms and their environment

ii. Environment

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

iii. Habitat

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

iv. Ecological niche

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

v. Population

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

vi. Community

Refers to different species of (plants and animals) organisms in a given habitat (area) co-
existing or interacting (living) with each other and the environment in which they live

vii. Ecosystem

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

vm. Biosphere

The earth and its atmosphere where living organisms are found

ix. Autecology

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

x. Synecology

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

xi. Carrying capacity

maximum number of organisms an area can support without being depleted

xii. Biome

geographical area with particular climatic conditions and ﬂora and fauna

it constitutes many ecosystems

xiii. Biomass

dry weight (mass) of a living organism in a given area

units of measurement are kg/m2/year

b) i) What are abiotic factors?

non-living components of the ecosystem

ii) Explain how abiotic factors affect living organisms

Wind

this inﬂuences rate of water evaporation from organisms

therefore it affects distribution of organisms e. g. wind increases rate of transpiration and
evaporation of water from the soil

wind is an agent of soil erosion, may break and uproot trees

may aid in the formation of sand dunes which can form habitats for some desert plants

wind disperses fruits, seeds, spores

wind forms waves in lakes and oceans which enhances aeration of water which
replenishes oxygen concentration necessary for life

wind is an agent of pollination

Temperature

inﬂuences rate of enzyme action in photosynthesis and other metabolic reactions in plants
and animals

organisms function within a narrow range of temperature

it affects distribution of organisms

changes in temperature affect rate of photosynthesis and biochemical reactions e.g.
metabolism and enzyme reaction

temperature increases rate of transpiration

Light

needed by green plants and photosynthetic bacteria which are primary producers

animals depend on plants directly or indirectly for food

main source of light is the sun

light is necessary for synthesis of vitamin D in certain animals

some plants need light for ﬂowering

seeds like lettuce need light for germination

Humidity

amount of water vapour held by the air

affects the rate at which water is lost from organisms body by evaporation and stomatal
transpiration

when humidity is low the rate of transpiration increases

humidity inﬂuences distribution of organisms

each plant requires a specific PH in which to grow (acidic, neutral or alkalinic)

pH affects enzyme reaction in metabolism

Salinity

some ions are needed for plant and animal nutrition

osmoregulation implants and animals is affected by salinity

Topography

altitude affects light, atmospheric pressure and light

Slope influences surface runoff, wind erosion, etc.

mountains affect distribution of organisms which differs in leeward side and windward
side

mountains affect distribution of organisms which differ on lowlands and on highlands

mountains also form physical barriers to migration of organism and may cause isolation
of species

background may offer camouflage to some organisms hence protection from enemies

Rainfall (Water) or precipitation

amount and distribution of rainfall affect vegetation type

this consequently affects distribution of animals e. g. polar region water frozen hence only

well adapted organisms survive

fewer organisms found in deserts where rainfall is less

Water is required for seed germination, raw material for photosynthesis, solvent for
mineral salts. Provides turgidity for plant support, medium for transport, disperses fruits,
seeds and spores

Pressure

the weight atmosphere exerts upon the earth

varies with altitude the higher the altitude the less the pressure

this variation implies change in density which directly means less oxygen for respiration
and less carbon iv oxide for photosynthesis and this affects distribution of organisms

Mineral salts (trace elements)

these affect distribution of plants in the soil

plants thrive best where elements are available

Plants living in soil deficient in a particular element must have special methods of
obtaining it.

They harbor nitrogen fixing bacteria and others have carnivorous habit

Plant distribution inﬂuences animal distribution

c) i) What are biotic factors?

refers to living organisms in an area

biotic environment of an organism constitutes all organisms around it, which it relates or
interacts with in various ways

ii) Give examples of biotic factors affecting ecosystems

feeding relationships

predation

competition

diseases and pests

human activities

d) Discuss how the various biotic factors affect living organisms

i. Competition

organisms compete with one another for food, light, water, mates and shelter

organisms must live together for competition for available resources

those which cannot cope either structurally or behaviorally will migrate or die

those remaining, due to better adaptations will increase in population

competition between members of the same species is called intra-specific competition
e.g. for mates

Competition between members of different species is inter specific competition e. g. for
food and space.

ii. Predation

this is predator-prey relationship

predator feeds on prey hence both control the other’s population

Distribution of predator and prey is important as predator cannot survive without prey

It there is no predator the prey will increase in population beyond carrying capacity hence
die due to environment depletion

iii. Parasitism

an association where an organism lives in or on another living organism obtaining
food(and other benefits) from it, causing harm to it (without necessary killing it)

parasites may kill host

they deprive host of food

make host weak by introducing diseases

make reproductive ability of host low hence host becomes susceptible to predation

iv. Diseases and parasites

make organisms weak and susceptible to predation

kill organisms and reduce their population

v. Symbiotic

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

vi. Human activities

these are human factors which have an inﬂuence on the biosphere

examples are road construction, industrialization, deforestation, agriculture, pollution,
poaching, ﬁshing conservation, population control

affect ecosystem and balance of nature

Saprophytism

saprophytes are organisms which obtain organic matter in solution from dead and
decaying tissues of plants and animals

they include saprophytic bacteria and fungi

they make available carbon, nitrogen and other elements form dead to living organisms

they are useful in recycling nutrients in nature

e)i) What is nitrogen cycle?

The process by which nitrogen in the air is made available plants and animals and
eventually returns to the air.

ii) Draw a simpliﬁed diagram representing the nitrogen cycle

iii) Describe the nitrogen cycle

during thunderstorms/lightning nitrogen gas combines with oxygen to form nitrogen
oxides

nitrogen oxides dissolve in water to form nitric acid

acid is deposited in the soil by rain

nitric acid combines with chemical substances to form nitrates or nitric acid dissociates to
form nitrates which are absorbed by plants

symbiotic bacteria (Rhizobium) which are found in root nodules of leguminous plants fix
free nitrogen to nitrates

free living bacteria (clostridium and Azotobacter) fix nitrogen to nitrates

nostoc algae (Anabaema chlorella) fix nitrogen to nitrates

plants use nitrates to form plant proteins

animals feed on plants and convert plant proteins into animal proteins

plants and animals die and are decomposed by putrefying bacteria, fungi(saprophytes)

decomposing plants, animals and nitrogenous wastes release ammonia which is converted
to nitrites by Nitrosomonas and nitrococcus bacteria

nitrites are converted to nitrates by nitrobacter bacteria

nitrates in the soil can be converted to free nitrogen (denitrification) by some fungi,
pseudomonas and theobaccilus bacteria generally called denitrifying bacteria

iii. Nitrogen in the atmosphere cannot be directly utilized by plants. State two ways
by which this nitrogen is made available for plant use

fixation by microorganisms (Rhixobium, Axotobacter)

fixation by electrical discharge in atmosphere i.e. conversion by thunderstorm or
lightning

f) i) Describe how energy ﬂows from the sun through the various trophic levels in an
ecosystem

energy from the sun is trapped by green plants during photosynthesis, producing
chemical energy9food or carbohydrates

green plants are producers and occupy the first trophic level

green plants are eaten by herbivores called primary producers as they occupy the second
trophic level

herbivores are eaten by carnivores, secondary consumers, which occupy the third trophic
level

when organisms – plant and animals) die, fungi and bacteria which are saprophytic
organisms feed on them thus causing them to decompose into simple substances e. g.
mineral salts

these organisms are called decomposers and detrivores

decomposer feed on dead organic matter hence cause decomposition and decay which
releases nutrients for plants, linking biotic and a biotic components

at all levels energy is lost through respiration

Give the reasons for loss of energy from one trophic level to another in a food chain

insufficient utilization of food resources(wastage) e.g by defalcation

through respiration

through excretion e.g. urination and sweating

Why are green plants referred to as primary producers in an ecosystem?

They utilize the energy from the sun to manufacture food for themselves and for subsequent
trophic level (consumers) and other organisms

vi. Explain the following terms giving suitable examples

Food chain

a nutritional sequence between producers and consumers through which energy ﬂows in a
straight line i.e. linear representation of feeding relationship between different organisms
in an ecosystem

if one consumer or the producer is removed the food chain is broken

arrow points to the direction of energy ﬂow e. g. green plant herbivore carnivore decomposer

Food web

complex feeding relationship Where a on more than one type of food
while several herbivores feed on one type of plant

it is an interrelationship of many
consumers are usually fewer to ensure survival of both

Pyramid of numbers

this is a diagrammatic representation of numbers of organisms at each trophic level in a
food chain

usually there are more producers than consumers

hence producers herbivores carnivore

the reason for the pyramid is because herbivores feed on many plants (producers) as
camivores feed on many herbivores

sometimes this may not be true e. g. when many caterpillars feed on one tree or parasites
on a herbivore

this gives an inverted pyramid of numbers

Pyramid of biomass

refers to diagrammatic representation total dry weight of organisms at different trophic
levels in a food chain

producers have greater biomass than any level of consumers progressively

size of organisms in successive e trophic levels increases

amount of individuals decreases in successive levels

Account for the decrease of biomass in the successive trophic levels

fixed energy which supports living matter decreases at each successive trophic level since
energy is lost by respiration and indigested (unconverted) materials hence less biomass
supported at each level

h) i) Describe the three characteristics of a population growth

increase in numbers

decrease in numbers growth rate

change in numbers

Dispersion

spread or distribution of organisms in a habitat

Density

the number of individuals per unit area

ii) Explain how the following methods are used to estimate population of organisms

quadrat method

identify the study area

throw or mark out the quadrat in the area of study at random

identify or label the various species of plants in the quadrat

count plants of each species

record the numbers

repeat the process

work out the average per quadrat for each species

calculate the total number of different species in the area or calculate the population for
the total area of habitat Q

Line transect

a string is stretched along an identified area

all plants touching the string are counted

Belt transect

preliminary study of the study area to estimate siie or make a sketch map

two parallel lines (strings or ropes) running for a determined distance and width

count the number of organisms in the transect

calculate the area covered by the transect

calculate the number of organisms being investigated per unit area

repeat this process at least three times in other parts of the study area

find the mean number of organisms per unit area from all the belt transects

from this figure calculate the total population of the desired organisms in the study area

Capture-recapture method

e.g. grasshoppers or fish

capture the grasshoppers

count and mark using permanent ink

record

release and allow time

recapture and count the marked and unmarked

total population is equal to the number of marked and unmarked grasshoppers in the
second sample multiplied by the number of marked grasshoppers in the first sample
divided by number of grasshoppers marked in the second sample that were recaptured

2. a) Describe the adaptations of plants to various habitats

i. Xerophytes

grow in areas with scarcity of water

roots grow deeply and extensively (widely spread) to ensure access to water

thick succulent stems, roots and leaves for water storage

photosynthetic stems take place of leaves which would lose a lot of water

Leaves are needle-like (reduced to spines), scaly, have sunken stomata. Some have curled
(rolled) leaves. Some have thick waxy cuticle, reduced number of stomata to reduce
water loss by transpiration

some shed leaves during dry season to reduce water loss

presence of thorns for protection

short life cycle to ensure survival

reversed stomatal rhythm

ii. Hyrophytes

grow in places with plenty of water(waterlogged)

aerenchyma a tissue (airspaces) and large intercellular spaces and long fibrous roots for
buoyancy (ﬂoating in water)

poorly developed support tissues (sclerenchyma) because water provides the necessary
support

upper epidermis of leaves have more stomata than lower epidermis for gaseous exchange
or for increased rate of transpiration

poorly developed conducting tissues (xylem and phloem) because plants obtain water by
diffusion

iii. Mesophytes

grow in well watered soils ‘(common plants)

no special adaptations, but depending on particular habitat, may have some adaptations

in forests they grow fast; tall to capture light. Have climbers while some are adapted to
carry out photosynthesis in low light intensities (those that form undergrowth)

in places with adequate water they form broad leaves, thin cuticle and many stomata on
both leaf surfaces

in direr regions they possess more stomata on the lower leaf surface and are deep rooted

some are shallow rooted and develop buttress and prop roots for support

some have waxy or glossy surface to reﬂect sun rays and drip off rain water

iv. Halophytes

plants that grow in very salty soil where the salt concentration is higher than that in the
plant

have root cells which concentrate a lot of salts in them and enable then to take in water by
osmosis

succulent roots to store water

have pneumatophores (breathing roots) to take in oxygen

some have buttress roots for support

secrete excess salt by use of salt glands

have large airspaces in leaves and stems for buoyancy and to store air

capable of photosynthesis at low light intensities
e.g. mangrove

b) 1) What is pollution?

any process which leads to adverse or harmful changes in the environment

ii) Explain the various human activities that have caused pollution

Causes and effects of air pollution

sulphur iv oxide, hydrogen sulphide, chlorine, oxides of nitrogen produced by industries,
sewage, decomposing organic matter and fumes affect gaseous exchange, makes acid rain
and damage plant leaves

aerosols, herbicides, insecticides (agrochemicals), paint spays, acaricides and CFC’s
sprayed to control diseases, pests and weeds affect respiratory organs of animals. The
chemicals are residual and persistent (not easily broken down) and bring depletion of the
ozone layer

smoke and fumes produced in areas withheavy industries, motor vehicles, fires which
bum fuel, oil, wood and coal cause carbon ii oxide, poisoning affect respiratory systems
and affect visibility

particles in smoke and fumes settle on leaves and stop photosynthesis

carbon iv oxide causes green house effect which causes temperature inversion as a result
of heating the lower layers of atmosphere

sound and noise produced incessantly by machines, aeroplanes and heavy vehicles affect
hearing in animals

dust from cement factories, quarries, dust roads settles on leaves limiting photosynthesis

removal of vegetation interferes with carbon cycle
radio-active emissions from nuclear reactors, mines and bombs cause cancer, mutations
and death.

Control of air pollution

use of lead free petrol in motor vehicles, air craft, aeroplanes and petroleum engines

uses of smokeless fuels and electricity

filtration, dissolution and use of chemicals to remove harmful gases

factories should be erected far away from residential areas

use of tall chimneys

reduce volume or intensity of sound e. g. by use of ear muffs

concords should ﬂy at higher altitudes and aeroplanes to ﬂy high up

State the causes, effects and methods of controlling and prop roots for support water
pollution

Causes and effects

agrochemicals e.g. fertilizers cause eutrophication leading to increase in animal
population

Silting makes water surfaces shallow and silt clogs stomata and gills of fish reducing
rates of photosynthesis and gaseous exchange. It also leads to reduction of algae which
causes reduction of consumers i.e. animal population

industrial and domestic wastes contain toxic materials which kill producers and other
organism while oily substances in wastes may clog gills of fish and may change pH of
water oxygen solubility is also reduced by oily surfaces

Untreated sewage and effluents where decomposition or organic matter in sewage
reduces oxygen supply and sewage provides food for bacteria increasing their population
and demand for oxygen thus depriving fish of oxygen.

Human feaces causes eutrophication, carbon IV oxide produced by decomposition of
faecal matter changes pH of water interferes with photosynthesis and may clog fish gills
or block light penetration which interferes with producers thereby decreasing
productivity.

Dumping of chemicals from industries with toxic pollutants which kill organisms

Spillage of oil and chemicals block oxygen and kill organisms

Discharge of water from industries into water body where high temperatures reduce
amount of oxygen in the water causing organism to suffocate and die

Untreated sewage may lead to outbreak of epidemics

Control of water pollution

pollution caused by domestic efﬂuents may be controlled by treating domestic waste, using
biotechnology, banning the use ofphosphate-based detergents, using plastic pipes instead of
those made from lead, recycling gabbage, using biodegradable detergents.

Pollution caused by industrial waste may be controlled by treating/cooling industrial waste,
carrying out environmental impact assessment before establishing industries

Oil spillage may be controlled by cleaning spilled oil biotechnology and penalizing the industry

individual or companies which cause oil spills/water pollution

Pollution caused by agrochemicals may be controlled by using mechanical control of weeds,
biological control of weeds and pests, biodegradable organic fertilizer herbicides, insecticides
pesticides, organic farming educate farmers on the use of correct amount of agrochemicals

silting may be controlled by appropriate farming practices, contour farming,
reafforestation, building gabions and terracing

iv) State the causes /effects and control methods of soil pollution

Causes and effects

Air pollutants e. g. sulphur IV oxide fumes form sulphuric acid with rain water. The acid
rain alters soil pH therefore affecting plants that cannot tolerate acidic soil

most aerosols sprayed to control pests and diseases precipitate in the soil and are taken up
by plants which make its concentration many times higher, increasing the toxicity in the
plants which absorb them

petroleum products due to spillage by oil tankers making it impossible for plant roots to
obtain oxygen in oil saturated soils, therefore plants are killed

agrochemicals and inorganic fertilizers contain heavy metals that are not used up by
plants and eventually soil microorganisms cannot inhabit the soils

organic matter slows down, life ceases and soil becomes exhausted

community, household wastes and industrial wastes disposal is a major problem in big
towns and cities. commodities packaged in metal tins, rubber, plastic containers, scrap
metal, glass bottles, different types of paper are nuisance to the environment, rendering it
useless for agricultural purposes

Control of soil pollution

use of organic farming techniques _

biological control of pests, diseases, parasites

recycling of non-degradable containers or burying them safely after use

controlled burning of garbage

treatment of human and industrial waste for safe disposal

avoid spilling chemicals and oil when used

v) Define biological control give suitable examples

using a living organism to regulate, control or reduce the population of another organism
e.g beetles to feed on water hyacinth, fish to feed on mosquito larvae.

vi) What is eutrophication?

enrichment of water bodies with nutrients due to discharge of sewage leading to rapid
growth of surface plants

i) What are the effects of eutrophication?

enrichment of water bodies with nutrients due to discharge of sewage leading to rapid
growth of surface plants

vii) What are the effects of eutrophication?

The plants block light from reaching plants underneath hence no photosynthesis
The plants die and decompose leading to lack of oxygen hence animals also die

c) Describe the symptoms, mode of transmission and control of cholera, typhoid, malaria and amoebic dysentery in humans

Cholera

causative agent

Vibrio cholerae (bacterium)

Transmission

Contaminated food or water

Spread by flies from faeces

Symptoms

Intestinal pain

Diarrhea

Vomiting

Dehydration

Control

Proper hygiene e.g boiling drinking water

vaccination

Typhoid

Causative agent

salmonella typhi (bacterium)

Transmission

Contaminated food or water

Spread by flies from faeces

Symptoms

Fever

Rashes

diarrhea plus blood from bowels

Control

Proper hygiene e.g boiling drinking water

vaccination

Malaria

Causative agent

Plasmodium (protozoa)

Transmission

Bite by infected anopheles female mosquito

Symptoms

Fever

Joint pains

Vomiting

Headache

Anaemia

Control

Killing the mosquito

Killing the mosquito larvae

Draining stagnant water

Clearing bushes

Treatment

Sleep under mosquito nets

Amoebic dysentery (amoebiasis)

Causative agent

Entamoeba hystolytica (bacterium)

Transmission

Contaminated food or water due to improper faeces disposal

Symptoms

Intestinal pain

Diarrhea

Vomiting

Dehydration

Control

Sanitation

Personal hygiene

Cook food well

Treatment using drugs

d) Discuss Ascaris lumbricoides under the following sub-headings

i. Mode of transmission

through ingestion of contaminated food

live in intestines

ii. Effects of parasite on the host

inﬂammation of lungs

pneumonia

produce toxic substances

intestinal obstruction

iii. Adaptations

thick cuticle which protects it against digestion

lays many eggs to ensure survival

mouthparts for sucking partly digested food

lack of elaborate alimentary canal

tolerant to low oxygen concentration

two hosts to ensure survival

eggs have protective cover to ensure survival in adverse environments

iv. Control and prevention

proper sanitation

wash hand after defaecation and before eating

e) Discuss schistosoma under the following sub-headings

i. Mode of transmission

through contaminated water in swamps, etc

ii. Effects on host

bleeding in lungs

blood stained urine

unthriftiness

iii. Adaptations

has two hosts to increase chances of survival

eggs have a hook like structure which raptures the walls of intestine or bladder

lay large number of eggs to ensure survival

larvae have a sucker for attachment on human skin which it digests

larva has a tail which it swims with in search of host in water

prolonged association between male and female to ensure that fertilization takes place

adults can tolerate low oxygen concentration (in the animal tissues)

adult worm secretes chemicals against antibodies

larvae and eggs (have glands that) secrete lytic enzymes to soften the tissues that ease
penetration

larvae are encysted so as to survive adverse conditions

Control and prevention

proper use of toilet facilities

boiling water before use

avoid bathing/washing in infected water

Use of molluscicides (chemicals that kill snails/biological control/clearing water weeds
on which snails feed.

Drainage of stagnant water

Wearing gum/rubber boots

3. a) i) What is reproduction?

process by which living organisms give rise to new members of their own species which
resemble the parents

ii) Why is reproduction important?

for continuity of speciesl to ensure survival of species

maintaining life of species

replace dead individuals

iii) Name the types of reproduction

sexual which involves fusion of male and female gametes

asexual in which no gametes are involved but parts of a mature organism develops into
new individuals

b) i) What is cell division?

process by which cells are formed from pre-existing cells

ii) What are chromosomes?

Threadlike structures found in nucleus of a cell.

The units called genes

Genes are factors that cause inheritance or determine characteristics of offspring

c) i) What is mitosis?

A type of cell division that occurs during growth leading to increase in number of cells

all cells maintain the same chromosome constitution i.e. the diploid state

ii) Describe the five stages of mitosis

Interphase

replication of organelles

duplication of DNA

production of energy (ATP) for cell division

Prophase

stage of dehydration

chromosomes shorten and thicken

chromosome replicates into two chromatids

chromatids joined at centromere

formation of spindle fibers

Metaphase

chromosomes move to equator (early metaphase)

chromosomes line up at the equator

homologous chromosomes do not associate

Anaphase

Chromatids separate

move to opposite ends (poles) of the cells

Telophase

chromatids reach the poles

formation of two daughter cells occurs i.e. cytoplasmic division

ii) State the signiﬁcance of mitosis

ensures each daughter cell has same number and kinds of chromosomes as daughter cells

gives rise to new cells (responsible for growth)

d) i) What is meiosis?

division of diploid cells to form gametes which are haploid

ii) State the signiﬁcance of meiosis

gives rise to gametes

source of variation

iii) Give a summary of the stages of meioeis

First meiotic division

Interphase I

cell is in non-dividing condition

chromosomes appear threadlike

Prophase I

chromatic material shorten and thicken

double stranded chromosomes appear (bivalent)

double stranded chromosomes pair and twist round each other (synapsis)

point of contact of chromosomes is called chiasma

Metaphase I

paired homologous chromosomes line up at the equator

Anaphase I

paired homologous chromosomes move to the poles

Telophase I

paired homologous chromosomes reach the pores

two new nuclei are formed

Second meiotic division

Prophase II

chromosomes shorten, thicken and become visible,

stage of dehydration

Metaphase II

movement of chromosomes to equator

Anaphase II

chromatids of each chromosome separate to the poles

Telophase II

reach the poles

four haploid daughter cells are formed

iv) Give the similarities between mitosis and meiosis

both take part in cells

both involve division (cell multiplication)

v) What are the differences between mitosis and meiosis?

Mitosis

maintenance of chromosome number (diploid)

take place in somatic cells/growth

no crossing over/no variation

results in to two daughter cells

no pairing/no synapsis/no bivalent formed

a one division process of four stages

meiosis

reduction halving of chromosomes (haploid)

occurs in reproductive cells/gonads/produces gametes

crossing over takes place/variation occurs

results in to 4 daughter cells

there is pairing/synapsis/bivalent

a two dicision process of four stages each

d) i) What is asexual reproduction

formation of new individuals as a result of the fusion of two gametes

fusion is called fertilization

ii) What is the signiﬁcance of sexual reproduction in living organisms?

leads to genetic variation e. g. cross breeding which gives rise to hybrids

iii) State the advantages of sexual reproduction

genetic variation

greater adaptability to environment by offspring

few bad or good traits inherited/retained

greater amount of dispersal is possible

may result in stronger offspring

iv) Give the disadvantages of sexual reproduction

less certainty in egg and sperm meeting

low rate of survival

sex-linked diseases easily transmitted

e) i) What is asexual reproduction?

formation of new organisms without fusion of gametes

occurs with only one parent

parts of organism develop into new individual

ii) State the advantages of asexual reproduction

retention of useful characteristics/genes/traits

offspring establish faster/shorter life cycle

better chances of survival because of suitable environment

iii) Give the disadvantages of asexual reproduction

lack of genetic variation

lowered resistance to disease ~

loss of hybrid vigor

competition for resources due to overcrowding

iv) Explain how reproduction occurs by the following methods of asexual reproduction

Sporulation

formation of spores

spores are small haploid cells produced by plants

Spores give rise to new haploid organisms

includes moulds, ferns, bryophytes, pteridophytes

Budding

where an outgrowth arises from a parent and drops off to develop into a new organisms

hereditary material in the daughter cell and parent are exactly the same

occurs in organisms such as hydra, jelly fish, sea anemones, yeast and some fungi

Binary fission

a cell splits into two new cells of equal size

each daughter cell grows into anew organism

Occurs in organisms such as amoeba, euglena, paramecium, some fungi and bacteria.

f) i) What is a ﬂower?

this is the reproductive structure which bears the reproductive pans of a plant

it produces seeds and fruits

ii) Draw a longitudinal section of a labeled diagram of a ﬂower

iii) Give the functions of the parts of a flower

Receptacle

expanded end of stalk which bears ﬂoral parts

Calyx

consists of sepals

usually green

protect ﬂower in bud

Corolla

consist of petals

often colored or scented to attract insects

Androecium

male part of ﬂower

consist of stamens

each stamen consists of an anther containing pollen sacs

anther produces pollen grains which contain male gametes

Gynaecium

female part of ﬂower

consists of one or more carpels

each carpel contains one or more ovules in an ovary

style bearing a stigma extends from ovary

ovary contains female gametes which when fertilized become seeds

iv) What is inﬂorescence?

a group of ﬂowers borne on the same branch (main stalk)

v) Explain the meaning of the following terms which describe ﬂowers

Hermaphrodite

one with both stamen and carpel

most ﬂowers are hermaphrodite/bisexual

Unisexual

have only one of carpel or stamen i.e. either male or female

Carpelate

also called pistilate

contains only carpels hence a female ﬂower

Staminate

also called male ﬂower

contains only stamens

Dioecious plants

have pistilate and staminate ﬂowers on different plants e.g. pawpaw

Monoecius plants

have pistilate and staminate on one plant

however, pistilate and staminate occur at different plants e. g. maize

Complete ﬂower

Has all four parts i.e. Calyx, corolla, androecium and gynoecium

Incomplete ﬂower

does not have all four parts

at least one is missing

vi) Explain the meaning of the following types of ovary

Superior
Q ovary occurs above other ﬂoral parts on the receptacle
Inferior (epigynous)
Q other ﬂoral parts arise above ovary on the receptacle

g) i) What is pollination?

transfer of pollen grains from anther of a stamen to stigma of a ﬂower

ii) Explain the types of pollination

self pollination takes place when mature pollen grains of a flower fall on the stigma of the
same ﬂower

cross pollination takes place when pollen grains of a ﬂower fall on the stigma of another
ﬂower of the same species

iii) State the advantages of pollination

healthy offspring

leads to variation

greater chances of dispersal

iv) List the agents of pollination

wind

water

insects

v) How are ﬂowers adapted to wind and insect pollination?

Insect pollinated ﬂowers (entomophilus)

are scented to attract insects

have stick stigma for pollen grains to stick on

are brightly coloured to attract insects ,

presence of nectar to attract insects

have nectar guides to guide insects to the nectarines

have nectarines to secrete nectar

stigmal anthers located inside the ﬂower/tubal/funnel shaped corolla to increase chances
of contact by insects

sticky/spiny/spiky pollen grains which stick on the body of insects and on stigma

large/conspicuous ﬂowers easily seen by/attract insects

anthers firmly attached to the filament for insects to brush against them

landing platform to ensure contact with anthers and stigma

mimicry to attract (male) insects

Wind pollinated ﬂower (anemophilus)

anthers/stigma hang outside the ﬂower to increase chances of pollination

the style/filament is long to expose stigma/anthers

stigma is hairy/feathery/branched to increase surface area over which pollen grains
land/to trap pollen grains

pollen grains are smooth/dry/light/small to be easily carried by wind

large amount of pollen grains to increase chances of pollination

anthers loosely attached to filaments to enable them to sway to release pollen grains

pollen grains may have structures which contain air to increase buoyancy

ﬂowers have long stalks holding them out in the wind

vi) State the Ways in which plants prevent self-pollination

protandry(anthers/stamens mature first)

protagyny (pistils mature first)

monoecism (where male and female parts are on same plant but different parts)

dioecism(where male and female parts are on different plants)

incompatibility (self sterility)

heterostyly (styles at different heights)

vii) Give the characteristics that ensure cross pollination takes place in flowering plants

presence of special structures that attract agents of pollination

protandry/dichogamy

protagyny/dichogamy

monoecism

self sterility

heterostyly

viii) State the advantages of cross pollination

hybrid vigour

less prone to diseases

promotes genetic variation

greater evolutionary potential

h) i) What is fertilization?

Fusion of male and female gametes to form a zygote

ii) Describe how fertilization takes place in a flower

this follows pollination

pollen grain is deposited on the stigma

pollen grain sticks to the surface of the stigma

the surface of the stigma produces a chemical substance which stimulates the pollen grain
to produce a pollen tube/to germinate

the pollen tube grows through the style tissues on which it feeds until it enters the ovary

the generative nucleus divides into two giving two male nuclei

embryo sac contains eight nuclei i.e. two synergids, egg cell, two polar nuclei and three
antipodal cells

the pollen tube enters the embryo sac through the micropyle and one of the male nucleus
fuses with the egg cell/ovum to form a zygote

the other male nucleus fuses with the two polar nuclei to form the triploid
nuclei/endosperm)food storage used by developing embryo)

the pollen tube nucleus in the pollen tube disintergrates soon afterwards

this process is referred to as double fertilization

zygote grows into an embryo containing plumule, radicle and cotyledons

iii) What is double fertilization?

there are two male nuclei entering embryo sac

one fuses with the ovum to form a zygote, while the other fuses with the polar nuclei to
form a triploid primary endosperm nucleus

therefore there are two fusions at fertilization

iv) Name the changes that Occur in a ﬂower after fertilization

petals, stamen, calyx and style wither

ovary wall changes into pericarp

intergument changes in to seed coat/testa

zygote changes into embryo ‘(by mitosis)

primary endosperm nucleus changes into endosperm

whole ovule changes in to seed

ovary develops and grows into fruit(under the inﬂuence of gibberrellic hormone)

b) i) Distinguish between a fruit and a seed

a fruit is a fertilized ovary and has two scars

a seed is a fertilized ovule and has one scar

ii) How is a seed formed?

after fertilization, zygote grows into an embryo, primary endosperm nucleus developed
into endosperm, interguments harden to form testa, hence the whole ovule becomes the
seed

the seed loses water to become drier

the seed has plumule, radicle, seed leaves called cotyledons, a microphyle and a scar

iii) Draw a labeled diagram of a seed

iv) Describe the main parts of a seed

Testa

also called seed coat

a tough outer covering which protects the seed from insects, bacteria etc

segment is the membrane inside the testa

Hilum

a scar

spot where the seed was attached to the fruit or pod

Micropyle

small hole through which water and air enter the seed

Radicle

embryonic root

grows into the shoot system

Cotyledons

embryonic leaves

store food for the germinating seed i.e. for plumule and radicle

when plumule and radicle grow, they use food stored in the cotyledon

in some seeds food is stored in the endosperm

v) Draw a labeled diagram of a fruit

vi) How is a fruit formed?

one of the organs that remains on the plant after pollination and fertilization is the ovary

within the ovary, the developing embryo produces special chemical substances that
stimulate the young ovary

these substances also signal the start of the formation of the fruit, which is a mature ovary

the fruit may contain one or more seeds

during fruit formation the ovary increases in size while ripening or maturing

a true fruit is formed from the ovary of a ﬂower after fertilization

it has two scars(style scar and stalk scar) and contains seeds

some seeds are not formed from the ovary of a ﬂower

some other parts of a ﬂower develop to form a fruit

such fruits are called false fruits

vii) Explain the importance of fruits in the survival of plants

protect the seed against dessication, predators and adverse conditions

aid in seed dispersal by attracting agents of dispersal

stores food for the plant

vii. Distinguish between parthenogenesis and parthenocarpy

parthenogenesis is development of new animals from unfertilized eggs

paithenocarpy is development of a fruit without fertilization

iv) state the differences between a seed and a fruit

A Seed

fertilized ovule

attached to the placenta through funicle

one scar called hilium

has seed coat/testa

seed wall undifferentiated

fruit

fertilized ovary

attached to branch through a stalk

two scars (style scar and stalk scar)

has fruit wall/pericap

fruit wall is differentiated

j. i) What is placentation?

arrangement of ovules within the plant ovary

ii) Explain the following types of placentation

Marginal

placenta appears as one ridge on ovary wall

ovules are attached to placenta in rows e. g. peas in a pod

Basal

placenta formed at the base of the ovary With numerous ovules attached to it

Parietal

edges of carpels fuse together

dividing Walls disappear, leaving one

have numerous seeds e. g. passion fruit

placenta of each carpel appears as ridge on ovary Wall

Axile

edges of carpels fuse together to form a single central placenta

numerous ovules arranged on placenta

ovary divided into a number of loculi by walls of the carpel e. g.

Free central placentation

edges of carpels fuse together

dividing was disappears leaving one loculus

placenta appears at base of ovary

has numerous ovules

c) i) How are fruits grouped?

Simple fruits

formed from a single ﬂower or one ovary e. g. mango

Aggregate fruits

consists a group of ovaries that appear on a common receptacle e. g. strawberry

Multiple (compound) fruits

formed from several ﬂowers whose ovaries fuse together after fertilization

form a bunch e. g. pineapple, figs

are always false fruits

ii) What are succulent fruits?

also called ﬂeshy fruits

all or part of pericarp (fruit wall) becomes juicy

iii) Give types of juicy fruits

Berry

has many seeds

whole pericarp is succulent e. g. orange, tomato, pawpaw

Drupe

only one seed

pericarp divided into three layers i.e. epicarp, mesocarp(juicy) and endocarp(hard) eg mango and coconut

Pome

juicy part is swollen receptacle

is usually a false fruit

example is a pear

iv) What are dry fruits?

have a pericarp that is dry, hard and Woody

either dehiscent or indehiscent

called dry because they are not succulent

v) What are dehiscent fruits?

split open when ripe to release seeds

contain many seeds

vi) Give types of dehiscent fruits

Legumes

split along two edges

are usually pods e.g. beans, peas, crotolaria

Follicle

split on one side only e. g. Sodom apple

Capsule

has several lines of Weakness/sutures

open in many places e.g. castor oil, cotton

vii) What are indehiscent fruits?

non-splitting fruits

usually one seeded only

ii) Give main types of indehiscent fruits

Nut

pericarp woody, hard and thick e.g. cashew

Achene

has thin, tough pericarp e.g. sunﬂower

d) i) What is seed and fruit dispersal?

spreading of seeds and fruits away from parents so as to settle where conditions are
suitable for their germination

ii) Why is dispersal of seeds and fruits necessary?

prevent overcrowding

reduces competition for space, nutrients and light

colonization of new areas is made possible

to increase chances of survival

to prevent inbreeding

to avoid extinction due to over competition for the necessities

iii) Explain how seeds and fruits are adapted to various methods of dispersal

Adaptations for wind dispersal

they have wings, feathers or hair-like structures to increase surface area for wind to carry
them easily/buoyancy

seeds/fruits are loosely attached on the stalks so that they can easily be released and
carried away by wing

seeds/fruits are generally light and small sized to be easily carried by wind

some seeds/fruits have parachute-like structures to be easily carried b wind

some have censor mechanism where seeds and fruits are borne on long stalks that are
loosely attached which allows swaying so that movements of capsule by wind releases
the seeds

Water dispersal seeds

seed mesocarp has air spaces thus light/buoyant to ﬂoat hence carried by water

they have waterproof cover and tough pericarp protects seeds from getting soaked

fibrous and spongy mesocarp to easily ﬂoat

Animal dispersal seeds

presence of hooks for attachment to animals thus carried to other parts

fruits are brightly coloured, succulent and scented to attract animals

seed coats are hard and resistant to digestive enzymes hence seeds are dropped away
from mother plant

large in size or borne on clusters to be easily seen

Self dispersal/explosive

self opening seeds

they have lines of weakness called sutures for violent opening thus scattering seeds away
from parent plant

5. a) i) Distinguish between external and internal fertilization in animals

in external fertilization fusion of the male and female gametes takes place outside the
body of the female e. g. amphibians and fish

in internal fertilization union of gametes occurs inside the body of the female

ii) State the advantages and disadvantages of external fertilization

Advantages

large numbers produced therefore many offspring per breeding season

female does not suffer gestation stress

mother does not need to care for the young except in a few species

the surviving individuals are highly selected for better survival

Disadvantages

many predators surround the eggs before and after fertilization

fewer chances of fertilization/a lot of gametes wasted

embryo development at mercy of environment

large numbers of female gametes are required therefore female gets much exhausted

iii) State the advantages and disadvantages of internal fertilization

Disadvantages

number of gametes fewer hence less number of offspring

less adapted for sudden change of environment after birth

in mammals females suffer gestation stress

Advantages

more chances of fertilization

fewer predators of oval/fertilized egg protected in females body

Stable internal environment

fewer gametes required

iii) Give a reason why it is necessary for frogs to lay many eggs

to increase chances of survival/fertilization

iv) Compare external and internal fertilization

b) i) Draw and label the human male reproductive system

ii) Describe how the mammalian male reproductive system is adapted to perform its
functions

Penis

is highly vascularised/spongy

has a sensitive glands

becomes erect to allow entry into the vagina

Scrotum

contains the testes outside the body on whose walls the process of spermatogenesis takes
place

the process is favored by lower temperature

it contains sertoli cells which nourish sperms until they are mature

Epididymis

long and coiled for the purpose of sperm storage

Vas deferens

muscular

upon contraction pushes sperms out and allows ejaculation

Gametes

produced in large numbers to increase chances of fertilization

the sperms have a tail for swimming/large number of mitochondria to provide
energy/allow swimming to reach the egg

Accessory glands

are seminal vesicle, Cowper’s gland and prostate gland

they produce seminal ﬂuid to provide a medium/nutrients for sperms to swim

iii) How is the sperm adapted to perform its function?

acrosomes contain enzymes to digest egg membrane

nucleus contains genetic material

mitochondria produce energy to move the tail back and forth
the lashing movement of the tail enables the sperm to move/propulsion in ﬂuid medium
towards the egg

it is streamlined for faster/easier movement/swimming to meet the egg

c) i) Draw and label the human female reproductive system

ii) Describe how the various structures of the human female reproductive system are
adapted to their function

Ovaries

have several graafian follicles that develop and burst open to release/produce mature ova

secretes sex hormones(oestrogen) which initiate/control development of secondary sexual
characteristics

produce hormones oestrogen and progesterone which prepare the uterus for implantation
and subsequent nourishment of the embryo

Oviducts (Fallopian tube)

are thin narrow and tubular to increase ﬂowing speed of semen containing sperms

are funnel shaped on the end next to ovary which enables them to receive the ovum

their lining contains cilia which propel the ovum towards the uterus

has peristaltic muscles that enable movement of zygote/ovum to the uterus for
implantation

is fairly long to increase surface area for fertilization

Uterus

is muscular for protection of developing embryo

has elastic wall that allows growth and development of foetus/embryo

has a highly vascularised endometrium that provides nutrients/gaseous exchange to
developing embryo

Cervix

has valves that close the lower end of the uterus to ensure continued pregnancy during
gestation period

is capable of dilating ~

has narrow entrance/neck-like entrance to uterus that enables quick swimming of sperms
to uterus

has suction mechanism that draws up/pulls sperms into uterus

has a “W” shape that ﬁts well with the glands of the penis to ensure sperms are deposited
at the right point

Vagina

is elastic and muscular to enable good accommodation or penetration of the penis thus
proper deposition of sperms and for easy parturition

allows menstrual ﬂow

has sensitive labial walls which secrete/produce lubricating substances that

ensure/enable/facilitate good coition

capable of considerable enlargement, due to elastic muscles, to accommodate baby
during parturition

Clitoris

has sensitive cells for orgasm

iii) Explain how the ovum is adapted to its function

nucleus contains genetic material

ventelline membrane encloses plasma membrane which encloses yolky cytoplasm

yolky cytoplasm provides nourishment

jelly coat protects ovum against dehydration

iv) Explain the differences between sperm and ovum

d) i) Explain the process of fertilization

a process whereby the egg and sperm are brought together and fuse to form a zygote

occurs in the fallopian tube after copulation

sperm head penetrates the outer coat of the ovum While the tail remains outside

penetration is due to reaction of acrosome

acrosome digests the vitelline membrane

thereafter a zygote is formed

zygote which is diploid undergoes rapid cell division to form a mass of cells called
blastocyst

after fertilization a membrane forms around the ovum to prevent further entry of sperms

blastocyst eventually develops into an embryo

i) Explain the process of implantation

this is the embedding and attaching of the embryo in the uterine wall/endometiium

implantation marks the beginning of pregnancy

sometimes implantation occurs in the oviduct Wall which is abnormal and results in
ectopic pregnancy which is fatal

the outer wall of the blastocyst develops ﬁnger like projections which project into the
uterine wall for attachment

the projections are called villi

the villi and endometrium develop into an organ that is called the placenta

the embryo is attached to the placenta through a cord called the umbilical cord

State the functions of umbilical cord

it contains blood vessels umbilical artery, iliac arteries and umbilical veins)

it joins the placenta to the embryo

passage for nutrients other

passage of excretory substancess from foetus to mother for final discharge

gaseous exchange

passage of antibodies from mother to foetus, for protection of foetus against diseases

State the role of placenta

exchange of gases between mother and foetus

exchange of nutrients and nitrogenous wastes

anchorage/attachment of foetus

produces hormones (oestrogen and progesterone)

e) i) What is gestation period?

time taken from fertilization to birth/pregnancy

ii) Explain the functions of the membranes associated with placenta

Chorion

surrounds the embryo

has fingerlike projections that attach embryo to the uterus

Amnion

contains amniotic ﬂuid

ﬂuid surrounds embryo

protects embryo from mechanical injury by acting as shock absorbers

ﬂuid also protects embryo from dehydration

distributes pressure equally over embryo

Yolk sac

surround the yolk

produces blood cells for embryo until its own liver is able to perform the task

Allantois

present only for a short time

removes and store waste material

it eventually becomes the umbilical cord

iii) Explain the events that take place to facilitate parturition

near birth the placenta produces less progesterone

oxytocin hormone is produced by posterior lobe of pituitary gland

because progesterone level has decreased the uterus becomes sensitive to oxytocin

oxytocin causes the contraction of the uterus (myometrium)

these contractions are called labour pains

just before parturition the head turns downwards

the contractions eventually push the baby through the vagina

amnion breaks and amniotic ﬂuid is released

oxytocin dilates the cervix

foetus is expelled through cervix with head coming out first

finally the whole infant comes out

the umbilical cord is cut and the placenta is expelled as afterbirth

iv) State the reasons why later in pregnancy the ovary will b e removed without disturbing
the pregnancy

corpus luteum in the ovary secretes progesterone which maintains pregnancy and
development of foetus after conception

after four months pregnancy is maintained by progesterone from the placenta

f) i) What are secondary sexual characteristics

Characteristics (physiological and anatomical) that start developing at puberty due to the
inﬂuence of male and female hormones

ii) State the main secondary changes in

Boys

deepening of the voice

growth of hair on face, pubic part, chest, legs

penis and testes become bigger

muscular development

sperm production begins at puberty and may continue throughout life

Girls

growth of hair on pubic part and armpits

widening/enlargement of hips

development of breasts

menstrual cycle starts as ovaries mature

body acquires extra fat

iii) Describe the role of hormones in secondary sexual characteristics in

Boys

Follicle stimulation hormone (FSH)

from pituitary

stimulates production of androgens(male hormones) mainly testosterone by testis

Testosterone

secondary sexual characteristics

Girls

FHS

from pituitary

development of follicles

stimulates oestrogen production by ovary

from pituitary

ovulation

stimulates release of progesterone by ovary

Oestrogen

stimulates release of LH

secondary sexual characteristics

Progesterone

also from placenta

sustains pregnancy as it inhibits prolactin and oxytocin during pregnancy

Prolactin

milk formation

Oxytocin

parturition

milk ejection

g) i) What is menstruation?

vaginal discharge due to disintegration of endometrium

ii) Describe the role of hormones in the human menstrual cycle

it is controlled by sex hormones which are responsible for the onset of secondary sexual
characteristics and also control of the menstrual cycle

the onset is signaled by discharge of blood/menses 14 days following the start of
menstruation

anterior lobe of pituitary gland secretes follicle stimulating honnone(FSH)

Follicle stimulating hormone causes graafian follicle to develop in the ovary. It also
stimulates tissues of the ovary/wall (theca) to secrete oestrogen

oestrogen causes repair/healing of uterine wall

oestrogen stimulates anterior lobe of pituitary to produce luteinising hormonge (LH)

LH causes ovulation. It also causes graafian follicle to change into corpus luteum. LH
stimulates corpus luteum to secrete progesterone

Progesterone causes proliferation/thickening of uterine wall

Oesterogen/progesterone inhibits, the production of FSH by anterior lobe of pituitary, thus
no more follicles develop and oestrogen production reduces

In the next two weeks progesterone level rises and inhibits production of LH from
anterior lobe of pituitary“

The corpus lutetium stopssecreting progesterone and menstruation occurs when the level
of progesterone drops

Anterior lobe of pituitary starts secreting FSH again.

iii) What is menopause?

end of ovulation in women

occurs after age of 45 years

does not occur in males

h) Explain the symptoms, methods of transmitting and prevention (control) of the following
sexually transmitted diseases

i) Gonorrhea

caused by a bacterium called neisseria gonorrhea

transmitted through sexual intercourse,

infects urethra and vaginal tract (epithelia)

Symptoms include pain, discharge of mucus and bad smell (females)

Effects include sterility, heart diseases, blindness of foetus and arthritis

Treatment by antibiotics

Control and prevention by proper sexual conduct

ii) Herpes

notably Herpes simplex and H. genitalis

caused by virus which attacks genitalia

symptoms are painful sores in genitalia, skin lesions

transmitted in saliva, sexual intercourse and injection by drug addicts

no treatment

iii) Syphilis

caused by bacterium called Treponema palladium

symptoms are painless wounds in genitalia

attack genitalia, nervous system, lips

treated by antibiotics

iv) Trichomoniasis

caused by plasmodium called trichomonas

attacks reproductive tract

symptoms are itching and discharge of pus from the genitals

treated by antibiotics

v) Hepatitis

Viral disease

Affects the liver

Transmitted through sexual intercourse

No known treatment

vi) Candidiasis

caused by fungus called candida albicans

transmitted through sexual intercourse

symptoms include itching urethra, and vaginal discharge (odourless)

controlled by personal hygiene, early treatment and responsible sexual behavior

vii) HIV/AIDS

caused by HIV virus

transmitted by sexual intercourse, blood transfusion, sharing piercing instruments from
infected mother to foetus, infant and baby

symptoms include fever, swollen lymph nodes, night sweating, cough, weight loss,
fatigue, loss of appetite, diarrhea, headache, a opportunistic infections and tumors

Control by responsible sexual behaviour, education, screening blood for transfusion and
using sterile piercing instruments.

6. a) Deﬁne the terms

i) Growth

an irreversible change in size of a cell, organ or whole organism

growth is due to synthesis of protoplasm or extracellular substances

ii) Development

refers to a series of changes which an organism goes through in its lie cycle

during development both qualitative and quantitative changes take place(involves
differentiation)

iii) Differentiation

refers to changes in which the cells of the body undergo and become specialised to
perform specific functions

b) i) Differentiate growth in plants and animals

More differences between Plant Growth and Animal Growth

Plant Growth:

1. Growth continues throughout the life of the plant.
2. Here the growth involves increases in the number of parts.
3. Growth take place during definite seasons.
4. Growing pattern is distinct each species.
5. Plant possess well-defined growing regions.
6. A seedling does not resemble an adult plant.
7. A juvenile stage with distinct may be present in the life-history of a plant.
8. Growth is by addition of new parts ahead or around the older ones.

Animal Growth:

1. Growth takes place for definite periods before maturity.
2. Here it does not involve increase in the number of parts.
3. Each species has a distinct season for growth.
4. Growing pattern is absent.
5. They have no such defined growing regions.
6. The young one are identical to adults except in the body size and sexual maturity.
7. A juvenile stage with different morphology does not occur in higher animal.
8. Growth is diffused by all round increases in different organs of the body.

ii) List the processes involved in growth

assimilation

cell enlargement

cell division(by mitosis)

iv) List the parameters used to measure growth

height/length

dry Weight

number of individuals

volume

leaf area of plant

iv) Name the patterns of growth in organisms

allometric and isometric

limited and unlimited

discontinuous growth

c) i) Name the different types of growth curves

sigmoid curve(normal growth curve)

intermittent growth curve

ii) Draw a sigmoid growth curve and explain its different phases/stages

A-lag phase

– Slow growth rate at first

Organism adapting to the environment

B-exponential phase

– organisms already adapted

– first growth due to birth rate that is higher than death rate

C- Stationery phase (plateau)

– Birth rate equals death rate (equilibrium)

Lack of nutrients, accumulation of toxic waste products

D-phase of decline

– due to depletion of nutrients, accumulation of toxic wastes, lack of space

– some individuals old hence not reproducing

– death rate higher than birth rate

iii) Draw an intermittent curve and explain the various stages

A-growth

B-no growth

C- moulting/ecdysis

– seen in arthropods

– growth in in arthropods is intermittent(takes place during some time only because their
hard cuticles (exoskeleton) does not expand to cause growth

– the cuticle must be shed off first to allow further growth

– the shedding is called ecdysis or moulting

– when moulting has taken place animal grows but growth stops when the exoskeleton
hardens again

d) i) What is seed dormancy?

– A state where a viable seed is incapable of germinating when all conditions are
favorable.

ii) State the biological importance of seed dormancy

– gives embryo time to reach maturity

– gives time for dispersal

– allows plant to survive adverse conditions

iii) State the factors which cause seed dormancy

Internal factors

– presence of abscisic acid/ABA/ presence of germination inhibitors

– embryo not fully developed

– absence of hormones/enzymes/inactivity of hormones/enzymes/gibberellins/cytokinins

– impermeability of seed coat

External factors

– unsuitable temperature

– absence of light

– lack of oxygen

– lack of water

iv) Give the conditions necessary to break seed dormancy

– scariﬁcation/scratching to make seed coat impermeable

– vernalisation/cold treatment in some seeds like wheat

– burning/nicking/expose to heat e.g. wattle seeds

– destruction of germination inhibitors

e) i) What is seed germination?

– process by which a seed develops in a seedling

ii) What is viability

– ability of a seed to germinate

iii) Discuss the various conditions necessary for the germination of seeds

Water

– medium for enzymatic activity

– hydrolysis of food into simpler substances

– medium of transport

– softens the seed

– acts as a solvent

Air

– in form of oxygen

– oxygen is used for respiration/oxidation of food to release energy

Suitable (optimum) temperature

– activates enzymes involved in mobilization of food reserves

Enzymes

-breakdown and subsequent oxidation of food

– conservation of hydrolyzed food products in to new plant tissues

Viability

– only viable seed are able to germinate and grow

iv) Name and describe the types of germination

Epigeal

cotyledons are brought above the ground level during germination due to elongation of
the bean seed that elongates to bring about epigeal germination

Hypogeal

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

vi) Account for the loss in dry weight of cotyledons in a germinating bean seed

food stored is mobilized/used up for respiration and growth

vii) Describe the physiological changes that occur in a seed during germination

in presence of oxygen, optimum temperature and water, food reserves in the seed are
hydrolysed or broken down into soluble diffusible form by enzymes

soluble food diffuses to the growing embryo

oils and carbohydrates provide energy

simple sugars converted to cellulose to form cell wall

amino acids make protoplasm

seed develops plumule and radicle hence germinates

viii) Explain the biological signiﬁcance of cotyledons being brought above the ground in
epigeal germination

cotyledons have inadequate food

they are brought above the ground to acquire chloroplasts to carry out photosynthesis

before the formation of foliage leaves to supplement food supply required for growth
during germination

f) i) Distinguish between primary and secondary growth

Primary growth

occurs at the apical (shoot and tip) apices regions where meristematic cells occur

causes plant elongation since cells divide by mitosis

Secondary growth

occurs at the cambium meristems

Increases width (girth) of the stem

ii) What are meristems

dividing cells

meristem means they are dividing

iii) State the characteristics of meristematic cells

dense cytoplasm

thin cell walls

absence of vacuoles/cell sap

iv) State the location and function of the following meristematic tissues

Apical meristem

located at tips of roots and shoots

increase length of stem and roots/primary growth

Intercalary meristem

found at bases of internodes

responsible for elongation of internodes and increase in leaf sheath in grasses

Lateral meristems

found near the periphery of stem and root

responsible for secondary growth/growth in girth of stem and root/lateral growth

called cambium and constitute vascular and cork cambium

v) Describe primary growth

occurs at tips of shoots and roots in the meristematic tissues of apical meristem

at the apex there is a zone of cell division/mitosis

cells elongate at elongation zone

the elongated cells differentiate at the region of differentiation resulting in increase in size

in the stems meristems give rise to leaf premodia which envelop the apex to form a bud

the bud protects the delicate inner cells

in roots the meristem is protected by root cap

after cells differentiate the form permanent tissues

vi) Describe secondary growth in plants

also called secondary thickening ‘

only occurs in dicotyledonous plants that have cambium

monocotyledonous plants do not undergo secondary growth because they lack
intervascular cambium

cambium cells divide to produce more cells on either side of the cambium

cells produced to the inside become secondary cambium

cells produced to the outside become secondary phloem

division of cambium cells occurs yearly producing new rings of secondary phloem and
secondary xylem each year

intervascular cambium(cambium between vascular bundles) divide to form secondary
parenchyma, thereby increasing growth of medullary rays

much more xylem is formed than phloem, thus pushing phloem and cambium ring
outward

the rate of secondary growth is depended on seasons(rains) resulting in annual rings

cork cambium is located beneath epidermis ad is responsible for secondary thickening of
the bark of perennial plants

cork cambium divides to form new cork(bark) tissues to accommodate increased growth
on outside and secondary cortex on the inside

Cork cells (cells of the bark) are loosely parked at some points to form lenticels for
gaseous exchange.

vii) State the signiﬁcance of secondary growth

increase girth or circumference of trees

annual rings which show seasonal growth can be used to tell the age of trees

g) i) Describe one method which can be used to measure the average growth rate of a single
leaf of a plant

Either

– chose/identify a young leaf (just unfolded)

– use the same leaf throughout

– measure (total) length of (whole) leaf

– record

– repeat at regular intervals until no more change occurs/constant length

– average rate of growth is equal to total increase in length divided by the period taken to
achieve full length

Average rate of growth = total increase in length divide by
period taken to achieve full length

– choose/identify a young leaf(just unfolded)

– use the same leaf throughout

– trace the outline on a graph paper and work out the area

– record

– repeat at regular intervals until regular area

– average rate of growth equals to total increase in area divided by the period of time taken
to achieve full area

Average rate of growth = total increase in area divide by
period of time taken to achieve final area

i) Describe how the growth of a root can be determined

Materials

– fine thread, marking ink, germinating bean seedlings, blotting paper, ruler marked in
millimeters, pins, cork, a boiling tube and moist cotton wool

Procedure

– dry seedlings using blotting paper

– place inside against the ruler marked in mm

– dip the fine thread in waterproof ink

– mark the radicle at equal intervals

– pin the seedling to the cork

– suspend the seedling into the boiling tube containing moist cotton wool

– allow the seedling to grow for two days/some
time observe the intervals with the marks

– record your observations the Widest intervals are found in the region just behind the tip
indicating/showing region of greatest growth

iii) A boy hammered a nail in the bark of a tree at a height of 1.5 metres above the ground
Four years later, the nail was found at the same height although the tree had grown 3
meters taller. Explain the above observation

The nail was hammered at a point where vertical growth had stopped/further growth was
confined to increase in width/diameter.

Vertical growth is confined to tips/apex/vertical apical meristem

h) i) Describe the role of hormones in growth and development of plants

indole acetic acid/IAA/ auxins

Cell division/increase in cell division

Tropic responses

Cell elongation/increases in ell elongation

Development of abscision layer

Growth of ovaries into fruits/parthenocarpy/initiates ﬂowers

Inhibits growth of lateral buds/produces apical dominance

Stimulates adventitious/lateral roots ‘

Gibberellins (Gibberellic acid/GA3

Promote cell elongation/rapid cell division/increase in length of the internodes

Promote fruit formation without fertilization/parthenocarpy

Reduces root growth

Breaks seed dormancy/promotes germination

Cytokinnins (Kinnins/Kinnetin/Zeatin)

– breaks dormancy

– promotes flowering

– promotes cell division

– stabilizes protein and chlorophyll

– promotes root formation on a shoot

– low concentration encourages leaf senses

– normal concentration increases cell enlargement in leaves

– stimulates lateral bud development

Ethylene (ethynel C2H4)

– accelerates ripening in fruits

– encourages fruit fall/leaf fall

– induces thickening in stern/inhibits stem elongation

– promotes ﬂowering (in pineapples)

– promotes germination in certain seeds

Abscisic acid (ABA) abscisin hormone/dormin)

– causes bud dormancy

– encourages fruit/leaf fall

– high concentration causes closing of stomata

– causes seed dormancy

– inhibits cell elongation

Traumatin

– heals wounds by callous formation

Florigen

– promotes ﬂowering

ii) State the applications of plant hormones in agriculture

– induce root growth in stem cuttings

– selective weed killers

– encourage sprouting of lateral buds

– breaking seed dormancy

– induce parthenocarpy

– accelerate ripening of fruits

– promote ﬂowering

– cause dormancy

iii) Explain apical dominance

– a phenomenon whereby production of auxins by a growing apical bud of a shoot inhibits
growth of lateral buds

– this inhibition is due to high concentration of auxins (indoleacetic acid/IAA) in apical
bud

– removal of terminal/apical bud causes development and sprouting of several buds which
later develop into branches

– applied in pruning coffee, tea and hedges

– this leads to more yield

iv) Describe the role of hormones in the growth and development of animal

somatotrophin (growth hormones)

– from anterior pituitary

– promotes cell division

– overproduction causes gigantism

– underproduction causes dwarfism

Thyroxine

– promotes growth and metamorphosis

– underproduction leads to a child becoming a cretin (mentally retarted)

Androgens

– in males

– growth of male reproductive organs

Oestrogen

– in females

– growth of female reproductive organs

Ecdysone

– in arthropods

– moulting (ecdysis)

t) i) What is metamorphosis?

– change in form during which there are changes in structure and function in body of
organism

– prepares organism for life in a different habitat

ii) Explain complete metamorphosis

radical changes in the body during the life cycle of an organism

called holometabolous development

example is egg larva pupa adult (imago)

occurs in animals such as butterfly and bee

iii) What is the significance of each of the four stages in complete metamorphosis?

Larval stage

– feeding takes place

– larva is quite different from adult

– larva sheds its cuticle (exoskeleton) several times to emerge as pupa

– dispersal stage avoids overcrowding

Pupa

– enclosed in a case called puparium (cocoon)

– no feeding

– organ formation takes place

Adult

– emerges from puparium

– reproductive stage of the life cycle

iv) Describe incomplete metamorphosis

– called hemimetabolous development

– changes are gradual

– eggs develop into nymphs which develop into adults

– nymph resembles adult but are sexually immature

– a nymph moults several times as some parts develop before it becomes an adult

– stage of development between one moult and another is called instar

– occurs in insects such as locust and cockroach

v) Name the hormones that control metamorphosis in insects

– brain hormone responsible for moulting because it simulates production of ecdyson
(moulting hormone)

– ecdysone(moulting hormone) causes moulting

– juvenile hormone causes moulting in larvae

vi) State the advantages of metamorphosis in the life of insects

– the adult and larvae exploit different niches

– do not compete for food

– pupa cam survive adverse pupa can survive adverse conditions eg-feeding stage

– dispersal prevents overcrowding

KCSE Biology Questions and Answers Form 4 – Biology Form Four Notes

Biology Questions and Answers Form 4

Biology Form 4 Notes

a) i) Define the term genetics

the study of heredity(inheritance) and variation or study of mechanisms by which
characteristics are passed from parents to offspring

ii) List some characteristics which are inherited

size

height/length

colour/type

shape

yield

iii)State the importance of genetics

helps to explain differences between organisms of the same species

helps to explain the transmission of characters from generation‘ to generation

improvement in livestock

improvement in crops

can be used to treat some difficult diseases

b) i) Explain the meaning of the following terms

Heredity

the resemblance among individuals related by descent

transmission of traits from parents to offspring

Trait

also called character

A character of the organism e.g. type of ear, colour of eyes, height, yield etc.

Gene

unit of inheritance

it is the heredity factor which transmits traits from parents to offspring

genes are located at ‘fixed points on chromosomes

each point is called a locus (loci)

Allele

genes can exist in a series of alternative forms at a particular locus

allele refers to alternative forms of genes controlling a particular characteristic

Chromosomes

threadlike structures found in nuclei of all plants and animals

they carry genes which are hereditary materials

they consist of substances called DNA and proteins called histosones

DNA

deoxyribonucleic acid

substances that make up chromosomes

double helix(strand) molecule that contains genes

DNA consists of nucleotides

A nucleotide consists of an inorganic phosphate, ribose sugar and a base

There are four bases in a DNA molecule i.e. Adenine(A), guanine(G), thymine(T) and
cystosine (C)

Ribose sugar has four bases attached to it i.e. adenine, cystosine, guanine and thymine

Adenine pairs with thymine while guanine pairs with cystosine

Nucleotide initiates and controls protein synthesis

ii) List the types of chromosomes

somatic (body) chromosomes also called autosomes

sex chromosomes (related to reproduction)

c) i) What is variation?

sequence of differences occurring among individuals of the same species

ii) State the causes of variation in organisms

random assortment of genes during meiosis

crossing over

fertilization

doubling of chromosome numbers(mutation)

environmental conditions

iii) Name the types of variation

Continuous variation (differences not clear cut) e. g. height, length, weight, skin colour,
intelligence etc. They are quantitative and show intermediates

discontinuous variation(differences are clear cut) e. g. ability to roll tongue, ABO blood
grouping system, RH factor, patterns of ﬁngerprints, and ability to taste PTC. They are
qualitative and have no intermediates

iv) Explain the following terms

Acquired characteristics

they are as a result of adaptations due to the environment and are not inherited
Inherited characteristics

are passed down to offspring during sexual reproduction

Genotype

genetic constitution of an individual/genetic makeup

Phenotype

characteristics of an individual observed or discernible by other means i.e. observable
character

Dominant gene (character)

expressed in the phenotype when homozygous or heterozygous

Recessive gene

only expressed in homozygous state

Homozygous

when two alleles are identical e.g. LL,ll

Heterozygous

when two alleles are different at a particular locus e.g. Ll

F1 and F2

Fl means first filial generation i.e. the first generation produced when two varieties can
be crossed

F2 means second generation i.e. product of offspring or from F1 generation

d) i) Explain Mendels ﬁrst law of inheritance

also called law of segregation

it states that genes are responsible for the development of individual characters

these characters are transmitted individually without any alterations

Only one character from a contrasting pair can be carried in a gamete, hence only one
character can be inherited.

ii) Give an example of this law

In an experiment, Drosophila (fruit ﬂy) with long wings were crossed with those having
short wings. Assume letter L denotes gene for wing size. The gene for long wings is
dominant to that for short wings

the genes for dominant are LL and for recessive ll.

State the expected results for the first cross

iii) What is monohybrid inheritance?

when inheritance of one character is studied one at a time e.g. wing size only

the F2 generation (when selfed) always gives a phenotypic ratio of 3:1 and a genotypic
ratio of 1:2:1 in a complete dominance

i) What is complete dominance?

refers to where only one dominant character is expressed while the other character which
is recessive is not expressed in the heterozygous state e. g. the case of wing size above

e) i) What is meant by co dominance?

When genes produce independent effects when heterozygous/none of the genes is
dominant over the other/where two or more alleles does not show complete
dominance/recessiveness due to the failure of any allele to be dominate in a heterozygous
condition.

ii) Give an example of co dominance

In a certain plant species, some individual plants may have only white, red or pink ﬂowers.
In an experiment a plant with white ﬂowers was crossed with a parent with red ﬂowers. Show results
of Fl generation. Use letter R for red gene and W for white gene.

If the plants form F1 were selfed, work out the phenotype ratio for the F2 generation
Phenotypic ratio 1 red:2 pink: 1 white

Genotypic ratio 1:2:1

f) i) What is a test cross?

A cross between an individual showing a character for a dominant gene(that is homozygous or
heterozygous) with a homozygous recessive individual

a cross between individual(organism) of unknown genotype with a homozygous recessive
individual

ii) State the importance of a test cross in genetics

helps in determining the genetic constitution/genotype of an organism

iii) What are multiple alleles?

a set of more than two alleles that may determine a character

example is blood group which can be determined by any two of three alleles i.e. A,B and
O

iv) Explain the inheritance of ABO blood groups

in humans blood groups are determined by three alleles i.e. A,B and O

it is only possible to have two genes at a time

genes A and B are co-dominant while gene O is recessive to genes A and B

Give a worked example using parents with heterozygous blood groups Ao and BO

ii) Explain the inheritance of Rhesus factor (Rh) in human beings

in humans blood is either Rh positive or Rh negative

people who have Rh antigen are Rh(+ve) while those without Rh antigen in their blood
are Rh(-ve)

Rh(+ve) is due to a dominant gene while the recessive gene causes lack of Rh factor.

When a person who is homozygous dominant marries a person who is homozygous

recessive the result is as shown below

Let the gene for dominant Rh factor be R while gene for recessive be r

iii) How is sex determined in human beings .

there are two sex chromosomes in humans, x and y

males are xy and females are xx

in females all ova have x chromosome

in males 50% of sperms contain x chromosomes While 50% of sperms contain y

chromosome

when a sperm containing x chromosome fuses with an ovum this results into a girl

when a sperm containing y chromosome fuses with an ovum the result is a boy

an example is given below

g) i) What does the term linkage mean?

– These are genes which occur together on a chromosome and are passed to offspring without
being separated

ii) Deﬁne the term sex-linked genes

genes carried in the sex chromosome that are transmitted along with genes that determine
sex

iii) What is meant by the term sex linkage?

genes are located on the sex chromosome

they are transmitted along with those that determine sex

iv) Name the sex-linked traits in humans

colour blindness

haemophilia

Hairy ears. pinna, nose

Baldness

Duchene muscular dystrophy (DMD) muscular wasting

v) Give an example of a sex linked trait in humans on:

Y Chromosome

tuft of hair sprouting from pinna/baldness

X Chromosome

colour blindness/haemophilia

vi) In humans red-green colour blindness is caused by a recessive gene C, which is sex-
linked. A normal man married to a carrier Woman transmits the trait to his children. Show
the possible genotypes of the children.

Let C represent the gene for normal colour vision (dominant)

Let c represent the gene for colour blindness

Parental phenotype Norman man x carrier woman

iv) State the importance of sex linkage

possible to determine sex of day old chicks

v) Haemophilia is due to a recessive gene. The gene is sex-linked and located on the
x chromosome. The ﬁgure below shows sworn offspring from phenotypically
normal parents

What are the parental genotypes?

XY and XhX

Work out the genotypes of the offspring

h) i) What is mutation?

sudden change in the structure of DNA at a particular locus/chromosome/ gene

ii) Describe how mutations arise

mutations arise due to alterations in normal number of chromosomes

change in a portion of a chromosome affecting one or more genes

by chromosomal aberration e.g.
dleltion/duplication/substitution/inversion/translocation/crossing over

caused by mutagenic agents e. g. radiation (x-rays, ultra violet light, gamma rays) and
chemicals e. g. mustard gas/colchicines

iii)State the factors that may cause mutation

these are chemicals and radiations

Radiations Effects

X-rays gene/chromosome alteration

Ultra violet rays structural distortion of DNA

Chemicals Effect

colchicines prevents spindle formation

Cyclamate chromosome aberrations

Mustard gas chromosomes aberrations

Nitrous acid adenine in DNA is deaminated so behaves like guanine

Acridone orange addition and removal of bases of DNA

Formaldehyde

iv) State the characteristics of mutations

arise suddenly

are unpredictable

random

generally rare

may breed true

some are desirable while others are lethal

v) Explain chromosomal mutation

– Change in nature, structure or number of chromosomes

vi) Explain how the following types of chromosomal mutations occur

Duplication

a section of a chromosome is repeated/replicates

therefore genes are repeated

Inversion

occurs when chromatids break at 2 places and when rejoining the middle piece rotates
and joins in an inverted position

Deletion

portion of a chromosome is left out after it breaks off

alters number and sequence of genes

Translocation

occurs when a section of a chromatid breaks off and becomes attached to another
chromatid of another chromosome

Non-disjuntion

Failure of homologous chromosomes/sister chromatids to separate/segregate during meiosis

Polyploidy

where number of chromosomes double or triple

beneficial in plants due to the following

increased yields/hybrid vigour//heterosis

resistance to pests

early maturity

resistance to drought

resistance to diseases

vii) What are gene mutations?

an alteration in the structure of a gene

i) Explain how the following occur during gene mutation

Deletion

some bases/nucleotides of a gene are removed

Inversion

the order of some bases/nucleotides of a gene is reversed

Insertion

addition of a base between two existing bases

Substitution

a portion of a gene is replaced by a new portion

ii) Name the disorders in humans caused by gene mutation

albinism

sickle cell anaemia

achondroplasia/chondordystorphic dwarfism

haemophilia

colour blindness

phenylketonuria

I. State the practical applications of genetics

i. Breeding programmes (research)

high yielding/hybrid vigour/heterosis

resistance to diseases

resistance to drought/salinity

early maturing

ii. Genetic engineering

genetic manipulation to produce desired characteristics

iii. Law

– legal questions of paternity knowledge of blood groups or blood transfusion

iv) Genetic counseling

aimed at reducing harmful traits e.g. albinism, congenital idiots, colour blindness e.t.c

v) Others

– Pre-sex determination

Understanding human evolution and origin of other species.

2. a) i) Explain the meaning of evolution

a gradual change in living organisms from simple life forms to more complex forms over
a long period of time.

ii) Differentiate organic evolution from chemical evolution as theories of origin of life

organic evolution refers to the emergence of present forms of organisms gradually from
pre-existing forms (some of which no longer exist)

chemical evolution explains the origin of life as having occurred when simple chemical
compounds reacted to form the simplest life forms

iii) What is special creation?

maintains that the whole universe and all living organisms came into being due to the act
of a supernatural being

b) Discuss the various kinds of evidence for evolution

i) Fossils

fossils are remains of organisms preserved in naturally occurring materials for many
years

they give evidence of types of plants/animals that existed at certain geological age/long
ago/millions of years ago

gives evidence of morphological/anatomical/structural changes that have taken place over
a long period of time e. g. human skull, leg of horse

ii) Comparative anatomy

gives evidence of relationship among organisms/gives evidence of a common ancestry of
a group of organisms

organisms have similar structures/organs performing the same function e. g. digestive
system] urinary system/nervous system/vestigial structures and vertebrate heart

Divergence where the basic structural form is modified to serve different functions e.g.
vertebrate forelimb/beak structure in birds/birds feet/parts of a ﬂower. These are called
homologous structures

homologous structures have a common embryonic origin but are modified to perform
different functions e.g. the pentadactyl limb

adaptive radiation is a situation where organism have a homologous structure with
common embryonic origin which is modified to perform different functions to adapt
organisms to different ecological niches/habitats e.g. beaks of Darwinian finches(birds)

Convergence is where different structures are modified to perform a similar function e.g.
wings of birds and insects/eyes of humans and octopuses. These are called analogous
structures

Vestigial structures are greatly reduced in size and have ceased to function e.g. human
appendix/caecium/coccix in humans, wings of kiwi (ﬂightless bird), presence of hind
limb pad in python, halters in insects, human hair nictitating membrane in human eye,
human ear muscle, pelvic girdle in whale and third digit of wing of bird.

iii) Comparative embryology

some embryos of different animals appear very similar thus showing relationship and
possibility of a common ancestry

e.g. different classes of vertebrates larvae of annelida and mollusca are similar
(tocophere)

iii) Comparative serology/physiology

these show biochemical and immunological comparisons of blood groups/components to
show immunological similarities of tissues therefore showing relatedness of different
organisms

e.g. antigen antibody reactions, human blood groups/Rh factor reveal some phylogenic
relationship among organisms/common ancestry

iv) Geographical distribution

organisms differ in various geographical regions

present continents are thought to have been a large land mass joined

together/pangea/Eurasia/Gondwanaland

present continents drifted apart from one land mass/continental drift

as a result of continental drift isolation of organisms occurred bring about different
patterns of evolution

organisms in each continent evolved along different lines hence emergence of new
species/divergence/convergence

Examples

marsupials in Australia

llama, jaguar, panther in S. America

lion, camel in Africa

I tiger in Asia

vi) Cell biology (cytology)

structures and functioning of cells are similar

occurrence of organelles e.g. mitochondria in all cells/both plant and animal cells

these point at a common ancestry

c) i) State the evolutionary characteristics that adopt human beings to the environment

– Brain

– Eyes

– Upright posture/bipedal locomotion

– prehensible arm/hand

– Speech

ii) State the ways in which Homo sapiens differs from Homo habilis

standing upright/erect posture

intellectual capacity/higher thinking capacity/bigger brain/higher brain capacity

communication through language/speech

d) i) Explain Larmarck’s theory of evolution

– Inheritance of acquired characteristics/environment induces production of a favorable
trait which is then inherited

ii) Explain why Lamarck’s theory of evolution is not accepted by biologists today

– evidence does not support Lamarck’s theory

– acquired characteristics are not inherited/inherited characteristics are found in
reproductive cells only

iii) Explain Darwin’s theory of evolution

– inheritance of genetically acquired characteristics

– a character happens to appear spontaneously which gives advantage to an organism
therefore adapted then inherited through natural selection

e) i) What is natural selection?

– Organisms with certain characteristics are favoured by the environment

Such organisms tend to survive and produce viable offspring

Others not favored are eliminated from subsequent generations

ii) With examples, explain how natural selection takes place

– organism with certain characteristics are favored by their environment

– such organisms tend to survive and produce viable offspring

– others not favored are eliminated from subsequent generations

– as the environmental conditions change the survival value of a character may alter with
time so that characteristics which were favored may no longer have advantage and other
characters may then become favorable

– if a favorable character is inherited, then offspring produce generations which are better
adapted to survive in a population

– more offspring are produced than can survive which results in struggle for survival
– the fittest survive

iii) State the advantages of natural selection to organisms

– assist to eliminate disadvantageous characteristics/perpetuates advantageous
characteristics

– allows better adapted organisms to survive adverse changes in the environment/less
adapted organisms are eliminated

iv) State the ways in which sexual reproduction is important in the evolution of plants and
animals

– brings about useful variations/desirable characters

– variations make offspring better adapted for survival/more resistant to diseases

– may lead to origin of new species

v) Explain the signiﬁcance of mutation in evolution

– Mutation bring about variation which can be inherited

– Some of these variations are advantageous to the organism

– Others are disadvantageous

– The advantageous variations favour the organism to compete better in the struggle for survival

– This results into a more adapted organism to its environment or new species/varieties

– Those with disadvantageous characters will be discriminated against therefore eliminated from
the population/death/perish

vi) Plain why it is only mutations in genes of gametes that inﬂuence evolution

– gametes form the new offspring

vii) How would you prove that evolution is still taking place?

– resistance of organism to antibiotics, pesticides and drugs

– new varieties of bacteria are resistant to certain antibiotics such as penicillin

– houseﬂies and mosquitoes are resistant to DDT

vii) Explain why some bacteria develop resistance to a drug after they have bee
subjected to it for some time

– bacteria mutates/develops a new strain/chemical composition is altered hence is able to
produce enzymes/chemicals which degrade the drug rendering it non-susceptible to the
drug

– the new strain is favoured by selection pressure natural selection

f) How has industrial melaninism i.e. peppered moth contributed towards the mechanism
of evolution

– This is an example of natural selection

– The peppered moth exists in two distinct forms, the speckled white form (normal form) and a
melanic form (the black/dark)

– They usually rest on leaves and barks of trees that offer camouﬂage for protection

– Originally the “speckled white” form predominated the unpolluted area of England

– This colouration offered protection against predatory birds

– Due to industrial pollution tree barks have blackened with soot

– The white form underwent mutation

– A black variety/mutant emerged suddenly by mutation

– It had selective advantage over the white forms that were predated upon in the industrial areas

– The speckled white form is abundant in areas without soot/smoke

3. a) i) Deﬁne irritability, stimulus and response irritability

-also called sensitivity

– Responsiveness to change in environment

Stimulus

A change in the environment of organism which causes change in organism’s activity

Response

– change in activity of an organism caused by a stimulus

ii) State importance of irritability to living organisms

– Adjusting to environmental conditions. Sensitive/defect/responding

iii) List the examples of external stimuli to organisms

– air/oxygen (aero)

– light(photo)

– osmotic pressure (osmo)

– current (Rheo)

– chemical concentration (chemo)

– water/moisture (hydro)

– Touch/contact (hapto/thigmo)

– Gravity/soil (geo)

– Temperature (thermo)

b) i) What are tactic responses?

– response in which whole organism or its motile parts move e. g. gamete

ii) What causes tactic responses?

– caused by unidirectional stimulus

– usually doesn’t involve growth

– response is either positive or negative

– named according to source of stimulus

– e.g phototaxis, aerotaxis, chemotaxis

iii) State the importance of tactic response to:

Members of kingdom protista

– move towards favorable environment/move away from unfavorable environment

– move towards their prey/food

Microscopic plants

– escape injurious stimuli/seek favorable habitats

iv) Name the type of response exhibited by:

Euglena when they swim towards the source of light

– phototaxis

– sperms when they swim towards the ovum

– chemotaxis

v) State the advantages of tactic responses to organisms

– to avoid unfavorable environment/injurious stimuli

– escape from predators

– to seek favorable environment

– to seek for food/prey

c) i) Define the term tropism

– growth movement of plants in response to external unilateral/unidirectional stimuli

ii) Explain the various types of tropism in plants

Phototropism

– growth movements of plant shoots in response to unilateral sources of light

– the tip of the shoots produce auxins down the shoot

– light causes auxins to migrate to outer side/darker side causing growth on the side away
from light hence growth curvature towards source of light roots are negatively
phototrophic

Geotropism

– response of roots/pans of a plant to the direction of force of gravity

– auxins grow towards the direction of force of gravity causing positive geotropism in roots
while shoot grows away from force of gravity (negatively geotrophic)

Thimotropism/Haptotropism

– growth response of plant when in contact with an object

– contact with support causes migration of auxins to outer side causing faster growth on the
side away from contact surface

– this causes tendrils/stem to twin around a support

Hydrotropism

– growth movement of roots in response to unilateral source of water/moisture

– the root grows towards the source of water/ positively hydrotropic while leaves are
negatively hydrotropic

chemostropism

– growth movement of parts of plant to unilateral source of chemicals

– the chemicals form a gradient between two regions e.g. pollen tube growing towards the
ovary through the style

iii) State the ways in which tropisms are important to plants

– expose leaves/shoots in positions for maximum absorption of sunlight for photosynthesis

– enables roots of plants to seek/look/search for water

– enables plant stems/tendrils to obtain mechanical support especially those that lack
woody stems.

– enables roots to grow deep into the soil for anchorage

– enables pollen tube grow to embryo sac to facilitate fertilization

iv) Explain the differences between tropic and tactic responses

Tropism

-growth curvature in response

-slow

-influenced by hormones

Taxes

-locomotory response

-fast

-external influence

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

i) State the results of P, Q and R after S days

– P will bend/grow towards light

– Q will remain straight/have little or no growth

– R will remain/grow straight/grow upwards

ii) Account for your results in (i) above

P- Growth substance/growth hormone/IAA/auxin are produced by the stem tip

– they move (downwards and get distributed) to the side away from light where they cause
rapid/more growth/cell division/elongation that results in bending

Q- Source of auxin has been removed

R- The auxins cannot be affected by light because the tip has been covered

iii) If the tin foil were removed from the tip of seedling R, what results would be
observed after two days

– it will bend/grow towards light

iv) State the expected results after 3 day is if the box were removed

– all seedlings will grow straight/upwards

e) In an experiment to investigate a certain aspect of plant response, a seedling was placed
horizontally as shown in diagram I below. After seven days the appearance of the seedling
was as shown in diagram 2

Account for the curvature of the shoot and root after the seven days

i) Shoot

– auxins accumulate on the lower side of the seedling due to gravity

– high concentration of auxins in shoot stimulates faster growth causing more elongation
on the lower side than the upper side hence curvature occurs upwards

ii) Root

– the high concentration of auxins inhibits growth hence the upper side with less auxins
grows faster than the lower side therefore the curvature occurs downwards

f) What is etiolation?

– phenomenon exhibited by plants when grown in darkness

– such plants are pale yellow due to absence of chlorophyll, have small leaves, long
stems/hypocotyle and slender stems

– plants exhibit etiolation to reach light/obtain light

– this is a survival response

4. a) i) What is coordination in animals

– The linking together of all physiological activities that occur in the body so that they take place
at the night time and in the correct place

ii) Name the main systems for coordination in animals

– Nervous system/sensory system

– Endocrine (hormonal system)

iii) List the components of the mammalian sensory system

– Central nervous system (CNS), brain & spinal cord

– Peripheral nervous system (PNS) cranial and spinal nerves

– Sense organs

– Autonomic nervous system (ANS) nerve fibers and ganglia

iv).Explain the terms receptors, conductors and effectors

– Receptors are structures that detect stimuli i.e. sense organs

– Conductors transmit impulses from receptors to effectors e. g. neurons

– Effectors are the responding parts e.g. muscles, glands

v) What are the functions of the central nervous system?

– provides a fast means of communication between receptors and effectors

– coordinates the activities of the body

vi) State the differences between somatic and autonomic systems of peripheral nervous
system

– Somatic is concerned with controlling the conscious or voluntary actions of the body i.e. skin,
bones, joints and skeletal muscles

– the autonomic (automatic) nervous system controls involuntary actions of internal organs,
digestive system, blood vessels, cardiac muscles and glandular products.

b) i) What is a neurone?

the basic unit of the nervous system

also called nerve cell

conducts impulses

include monitor sensory and relay neurons

ii) Name the parts of a typical neurone and state the functions of each part

cell body/centron contains nucleus and cytoplasm

axon transmits impulses away from cell body

dendrites relays impulses across adjacent neurons

myelin sheath insulates axon and speeds up transmission of impulses

schwan cells forms myelin sheath and aid in nutrition and regeneration of axon

node of ranvier occur between schwan cells, where axon is not covered, speeds up
impulse transmission

nissils granules contain mitochondria that provide cell body with energy for metabolic
process

i) Describe the structure and function of a motor neurone

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

ii) Describe the structure and of sensory neurone

sensory neurone relays receptors (sense organs) to CNS

iii) State structural differences between motor and sensory neurons

Cell body in motor neurone is terminal (at the end) and inside central nervous system.

Cell body in sensory neurone is terminal but has axon at both ends (bipolar)

iv) Describe the structure and function of a relay neurone

also called intermediate/internucial/associate/connector/interneurone

locate inside central nervous system and spinal code

usually lack myelin sheath

c) State the function of the major parts of the human brain

i) Cerebrum

called forebrain

occupies most of the brain

consists of four lobes each with specific function

temporal lobe controls taste smell hearing learning and memory

partial lobe controls sensory output and touch

occipital lobe controls vision, motor output and speech

frontal lobe controls personality, learning thought and speech

also has parts called thalamus and hypothalamus

thalamus helps to sort sensory information

hypothalamus controls hunger, heartbeat body temperature and aggression

ii) Mid brain

quite small in humans

relay centre for audio and visual information

also involves in some sight, hearing and orientation responses

i) Hind brain

consists of cellebral and medulla oblongata

cerebellum is responsible for coordinating impulses, posture and balance, motor
coordination and muscle tone

medulla oblongata controls heartbeat, blood pressure breathing rate, coughing and
sneezing

a) i) What is reﬂex action?

an automatic response to an external stimulus e. g. sneezing or Withdrawing hand from a
hot object

ii) Describe a reﬂex action that will lead to the Withdrawal of a hand from a hot object

Receptors in the skin respond to stimuli. Arestimulated

an impulse is transmitted through the sensory neurone, across a synapse to the central
nervous system (White matter), through the relay neurone into grey matter, then to the
motor neurone and finally to the effect muscle which contracts

the hand is then withdrawn

iii) Explain how an impulse is transmitted across the synapse (gap)

impulse initiates release of transmitter substance acetylcholine at the end of the sensory
neurone

acetylcholine diffuses across the synapse and generates an impulse in the next neurone

ii) Brieﬂy describe the transmission of a nervous impulse across a neuro-muscular
junction

impulse arrives at synoptic knob and causes vesicle to move to the pre-synaptic
membrane

vesicle discharges transmitter substance into synaptic cleft

transmitter substance/acetylcholine diffuses across the cleft and attaches to post-synaptic
membrane

the membrane is depolarized, generating the action potential

iii) What are the functions of a synapse?

allows transmission of nerve impulses from neurone to neurone

ensures nerve impulses travel in only one direction W

in the brain they store information/memory

b) i) What is a conditioned reﬂex?

A response caused by a unilateral stimulus (associated stimulus) which substitutes the
normal stimulus

ii) Explain a conditioned reﬂex

it is automatic

it involves the spinal cord

it is usually learned e. g. writing, cycling, dancing

it involves the interaction of highly specialized centers of the brain with a large number
of neurone necessary to bring about conditioning

example is experiments carried out by Pavlov using dogs

iii) Compare a simple reflex action with a conditioned reﬂex

c) i) What are endocrine glands?

ductless glands that produce hormones in animals

hormones are chemical substances which help to coordinate the functions of the body

ii) State the functions of hormones in animals

regulate growth and development

control behavior during breeding

proper functioning of cells

regulate metabolic activities

iii) Name the main endocrine glands, their secretions and functions in the human body

Gland: Thyroid

Hormone:

Thyroxine

Function:

increases the rate of metabolism

Gland: Parathyroid

Hormone:

Parathyroid hormone

Function:

regulates calcium and phosphate levels

Gland: Pituitary

Hormone:

growth hormone

Function:

regulates growth of the body

gonadotrophic hormone

Function:

stimulates the growth of male and female organs

lactogenic hormone (prolactine)

Function:

stimulates secretion of milk after child birth

thyrotropic hormone( TSH)

Function:

proper functioning of thyroid glands/thyroxine production

adrenocorthicotropic hormone (ACTH)

Function:

stimulate release of adrenal cortex hormone

oxytocine hormone

Function:

regulates blood pressure

stimulates smooth muscles

stimulates contraction of uterus during child birth

aids flow of milk from mammary glands

follicle stimulating hormone (FSH)

Function:

causes maturition of egg in females

stimulates sperm production in male

Vasopressin (ADH) antidiuretic hormone

Function:

regulates water balance by kidney

Gland: adrenal

adrenaline (epinephrine hormone)

Function:

for emergency

prepares body to cope up with stress

aldosterone hormone

Function:

maintain balance of salt and water in blood

cortisone hormone

Function:

break down the stored proteins to amino acids

aids in the break down of adipose tissue

regulates sugar levels in the blood

prevents inflammation

sex hormone

Function:

supplements sex hormones produced by gonads

promotes development of sexual characteristics

Gland: Pancreas

Hormone:

insulin

Function:

regulates levels of sugar in blood

enables liver to store sugars

glucagon

Function:

regulates levels of sugar in blood

Gland: ovaries

Hormone:

oestrogen
Function:

causes secondary sexual characteristics in female

prepares the uterus for pregnancy

progesterone
Function:

growth of mucus lining of uterus

maintains the uterus during pregnancy

Gland:testes

Hormone:

androgen testosterone

Function:

causes secondary sexual characteristics in male

Gland: stomach cells

Hormone:

gastrin

Function:

stimulates release of gastric juice

Gland:intestinal cells

Hormone:

secretin

Function:

stimulates secretion of pancreatic juice

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

nervous

response confined to effector organs( localized target)

speed of response is rapid

nervous impulse through nerve/nerve cells/neurons

duration of response is short

speed of transmission is rapid

transmission is electrical

hormonal(endocrine)

response more widespread (various targets)

response less rapid

hormones transferred through blood

persistent for long

speed of transmission is slower

transmission is chemical

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

g) i) Define the following terms

Drug

a substance that causes a change in body function

Drug abuse

indiscriminate use of drugs without minding their side effects

misuse or wrong use of drugs

ii) State the types of drugs, examples and side effects

Sedatives

also called depressant

a drug that decreases the action of the central nervous system

reduce anxiety, and tension, induce sleep and act as muscle relaxants

when abused they cause withdrawal effects such as anxiety, delirium and death

includes barbiturates, other sedatives, tranquilizers and alcohol

Pain-killers

suppress centers of pain in the brain

Hallucinogens

given to people with hallucination or mentally ill patients to calm then down

when abused they lead to a feeling of confusion, agitation, depression and violent
behavior that can lead to murder or suicide

examples include valium, LSD, bhang, narcotics and cannabis

Stimulants

drugs that temporarily increase the action of the central nervous system

they create a feeling of alertness, wakefulness, a sense of self confidence and well being

used to decrease fatigue and mild depression

when abused they cause feelings of persecution, hallucination and addiction

include amphetamines, cocaine, caffeine, miraa and nicotine

iii) State the general effects of drug abuse on human health

damage to body organs e. g. liver cirrhosis

drug addiction

impaired judgment resulting in clumsiness

socio-economic problems e. g. crime, loss of jobs, divorce, prostitution, HIV/AIDS

may cause poor health

h) i) List the special sense organs in mammals and the major function of each

– Eye for sight

– Ear for hearing and balance

– Nose for smell

– Skin for touch, temperature detection, pain detection

iii) How is the human eye adapted to its function?

conjunctiva is thin/transparent/tough to allow light to pass through/to protect the eye
Sclerotic layer is made up of (collagen) fibers/fibrous. It maintains shape of the
eyeball/protects the eye

cornea is transparent/curved thus refracts light rays/allows light to pass through

Choroid is a layer of tissue with black pigment/dark pigment. Prevents internal reﬂection
of light in the eye/contains blood vessels that supply oxygen/nutrients/remove
(metabolic) wastes from the eye

retina has cones/rods for bright colour vision/low light vision

yellow spot has a high concentration of cones for accurate vision/visual acuity

Blind spot has no cones and rods. Place where optic nerve leaves/enters the eye

optic nerve has (sensory) nerve fibers for transmission of impulses to the brain (for
interpretation)

Lens is biconvex/made up of elastic material/transparent. Adjust focus on far or near
objects allow light to pass through/for refraction of light rays

ciliary body is made up of muscle fibers glandular which contract/relax to change shape

suspensory ligaments are inelastic to hold lens in position/attach it to ciliary body

iris(is the coloured part of the eye it) has radial and circular muscles which control size of
pupil

pupil is the small hole at the centre of iris through which light passes into the eye

aqueous humor is a ﬂuid through which oxygen/nutrients pass to the
comea/lens/maintains shape of the eyeball/refracts light rays

vitreous humor is a ﬂuid which maintains shape of eye/refracts light rays

iii) What is accommodation of the eye?

ability of the eye to adjust to bring an image from a near or far object into sharp focus on
the retina

iv) Explain how an eye viewing a near object adjusts to viewing a far object

ciliary muscles relax

suspensory ligaments become taut/tight

lens decreases curvature/becomes thinner

radial muscles relax

circular muscles contract

size of pupil decreases to reduce amount of light

v) What changes occur in the eye if it changes from observing an object at a distance to one
at a closer range?

– ciliary muscles contract

– Tension in suspensory ligaments reduces/relaxes slackens

– Lens bulges/thickens/increases curvature

– Radial muscles contract

– Circular muscles relax

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

viii) State the changes which would take place in the eye if a person in a dark room
had lights switched on

circular muscles contract and radial muscles relax

pupil becomes small to allow less light into the eye

ix) Explain how the eye forms an image

the mammalian eye works like a camera

light rays enter the cornea pass through the pupil, aqueous humor, lens and vireous humor

light rays are refracted by the aqueous and humor and lenses

finally light falls on the retina to form an image

the image is real and invened and smaller than object, back to front/reversed

Retina forms a fine image when light rays reach it.

x) Name the defects of the eye and state how they can be corrected

Short sight (Myopia)

eye cannot focus on far objects

image is formed in front of the retina because light rays converge in front of retina

the lens is too thick, curve and eyeball too long

corrected by wearing concave/biconcave/lenses

these lenses diverge light rays onto retina

Long sight (Hypermetropia)

eye lenses are unable to focus because they are flat, thin and weak hence unable to focus
image on the retina

they are unable to accommodate/change the focal length

near image is formed behind the retina but a distant one is correctly focused on the retina

corrected by wearing convex/biconvex/converging lenses

Presbyopia

occurs in old age hence called old sight

caused due to loss of elasticity of lenses, weakness of ciliary muscles hence lack of focus
of light rays

this causes long sight

corrected by wearing biconvex/convex/converging lenses

Squinting

eyeballs are uncoordinated/do not turn at the same time

eye muscles move in different directions

this makes accommodation and focusing difficult

corrected through surgery

Astigmatism

surface of cornea is uneven

leads to weak focus of light raise on retina

corrected by using cylindrical lenses/lenses with combined curvature

xi) State the advantages of having two eyes in human beings

stereoscopic vision

gives a wider angle of binocular vision

if one is damaged human is not blinded

i) What are the functions of the human ear?

hearing

maintaining body balance and posture

iv) How are the structures of the human ear suited to perform the function of
hearing?

Pinna is funnel shaped allows collection of sound waves and channels them down the
auditory canal/auditory mateus

auditory canal is a tube that concentrates and directs sound waves to tympanic
membrane/tympanum/eardrum

Eardrum is thin and tight. It sets into vibration/vibrates/converts sound waves into
vibrations

the vibrations are transmitted to the ear ossicles/malleus, incus and stapes that amplify the
sound vibrations

the vibrations are then transmitted to the fennestra ovalis/oval window

Oval window is a membrane which amplifies/transmits vibrations to the ﬂuids
(perilymph and endolymph) then to cochlea.

The cochlea is coiled to occupy a small space and accommodate a large number of
sensory cells

The sensory cells/hairs (in the cochlea) are set into vibrations/stimulated producing nerve

impulses in the auditory nerve

Impulses in the auditory nerve are transmitted to the brain for interpretation for hearing

Eustachian tube connects the inner ear to the throat. It equalizes air pressure in the middle
ear with the atmospheric air pressure (in outer ear)

Fennestra rotundus/round window dissipates/discharges/discards vibrations from inner
ear to middle ear

iii) Explain how the structure of the human ear performs the function of balancing

there are three semi-circular canals/utriculus/succulus/vestibular apparatus arranged in
planes at right angles to each other

at the end of each canal is a swelling called ampulla which contains receptors

the movement of the head causes movement of the ﬂuid/endolymph in at least one canal

the ﬂuid movement causes stimulation of the receptors/sensory hairs

sensory impulses are generated

the auditory nerve transmits the impulses to the brain for interpretation for the position of
body/posture/balance

iv) State what would happen if the auditory nerve was completely damaged

deafness

loss of body balance

impulse not transmitted to the brain

5. a) i) What is support?

to support is to carry part of the weight/mass of an organism

ii) What is locomotion?

progressive change in the position of an organism

iii) State the importance of support systems in living organisms

they provide a framework for the body of organisms and help to determine their shape

provide land animals with means for support to their weights against gravity

organs are attached to the skeleton for support and stability to avoid entanglement and
crushing each other

they protect very important and delicate organs whether inside or outside the body e. g.
eyes, heart

in large plants the rigid trunks of trees support the greater mass of leaves and fruits

iv) State the importance of locomotion in animals

in search of food

Search for mates

escaping predators

b) i) Name the tissues in higher plants that provide mechanical support

Sclerenchyma

collenchyma (not ligniﬁed)

xylem/tracheids and vessels

ii) State the importance of support in plants

exposing the surface area of leaf to sunlight for photosynthesis

ensure ﬂowers are exposed to pollination agents

expose fruits and seeds to agents of dispersal

to resist breakages due to their own weight and that of other organisms

for proper transport and translocation of materials

iii) Name the types of plant stems

herbaceous e.g. shrubs

woody e. g. trees

weak stems in creepers, twining plants and plants bearing tendrils

iv) Name the tissues in plants that are strengthened with lignin

sclerenchyma

xylem vessels/tracheids/xylem

v) What makes young herbaceous plants remain upright?

turgidity

presence of collenchyma

vi) State the ways by which plants compensate for lack of ability to move from one place to
another

ability to pollinate

response to nastic and tropic movement

ability to exploit localized nutrients

ability to disperse seed or fruit propagation

c) i) Explain the Ways in which erect posture is maintained in a Weak herbaceous stem

– This is the function of turgidity and presence of collencyma

Cells take in water and become turgid

ii) Explain how support in plants is achieved

Turgor pressure due to absorption of water keeps cells firm hence hold herbaceous plants
upright

collenchyma and clerenchyma tissues are closely packed in stem and roots to provide
support

inelastic cuticle on epidermis is covered by a waxy layer hence keeping shape of plant
and setting inward pressure against turgid cells and this causes a force to hold plant
upright

xylem vessels and tracheids are lignified to provide support to stems, roots and leaves

climbing plants obtain mechanical support from other plants and objects

they have climbing structures like tendrils which hold on to other objects

d) i) Give the reasons why support is necessary in animals

for attachment of muscles

For attachment of other body organs

to protect delicate body organs

to maintain body shape/form

to enable movement/locomotion

ii) Why is movement necessary in animals?

enables animals to search for food

enables animals to search for shelter

enables animals to escape predators/harmful conditions

enables animals to Search for water

enables animals to search for mates

enables animals to search for breeding sites

e) i) Name the organ used for support by animals

– Skeleton

ii) Name the different types of skeletons in animals, giving an example of an animal for
each type of skeleton named

exoskeleton e.g. arthropoda (crab, insect)

endoskeleton e. g. chordata (cat, fish)

iii) State the difference between exoskeleton and endoskeleton

endoskeleton is a rigid framework covered by body tissues of an animal

exoskeleton is a rigid framework found on the surface of an animal

iv) State the advantages of having an exoskeleton

supports/protects delicate inner parts

water proof/prevents drying up of body

provided surface for muscle attachment

v) Explain the importance of having an endoskeleton

support the body

give body its shape

protect delicate organs e. g. skull, brain, ribs

used in locomotion e.g. bones serve as levers

red blood cells are formed in bone marrow

minerals are stored in bones e. g. calcium and phosphorus

f) i) Explain how a fish is adapted to living in Water

streamlined body for easy movement in water

swim bladder controls depth of swimming

fins for movement, balance, direction and stability,

gills for gaseous exchange in water

presence of lateral line to sense vibrations

scales provide protection .

colour which offers camouﬂage against predators

ii) Explain how a finned fish is adapted, to locomotion in Water

streamlined body to reduce resistance/friction )to swim smoothly)

the vertebral column consists of a series of vertebrae held together loosely so that it is
ﬂexible

myotomes/muscles associated with vertebral column produce movement

the sideways and backwards thrust of the tail and body against water results in resistance
of water pushing the fish sideways and forwards in a direction opposed to thrust

heat not ﬂexible so as to maintain forward thrust

presence of fins help in propulsion/balance/paired fins (pectoral and pelvic) for
controlling pitch and slow down movement/unpaired ﬁns (dorsal, ventral, anal) for
yawing and rolling (caudal) for swimming/propulsion and steering/change of direction

presence of swim bladder to make fish buoyant

scales tip towards the back to provide smooth surface

body covered with mucus to reduce friction

ﬂattened surface for easy ﬂoating

g) i) Name the main parts of the vertebral column giving the types of bones found in each
part

Axial skeleton

forms the main axis of the body

formed by the skull, sternum, ribs and vertebrae

Appendicular skeleton

composed of limbs and girdles

the forelimbs are connected to the trunk by the pectoral girdles (shoulder bones)

hind limbs are connected to the pelvic girdle (hips)

bones are scapular, clavicle, humerus, ulna, femur, tibia, fibula, metacarpals, carpals,
tarsals, metatarsals, phalanges, ilium, ischium and pubis

ii) What are the vertebrae?

bones of the vertebral column

iii) State the functions of the vertebral column

gives ﬂexibility

absorbs shock

protects spinal cord

supports weight of body

provide surface for muscle attachment

between the vertebrae are soft discs which offer cushioning called interverterbral discs

iv) State the general characteristics of vertebrae

have solid structure called centrum to support weight of body

has transverse process lateral to centrum for muscle attachment

neural spine is dorsal to centrum and provides surface area for muscle attachment

neural canal a passage for spinal cord and offers protection to it

has facets for articulation with other vertebrae

neural arch encloses neural canal

v) Name the bones of the vertebral column

– Cervical vertebra

— Thoracic vertebra

– Lumbar vertebra

– Sacral vertebra

– Caudal vertebra

vi) Describe how the various vertebrae are adapted to their functions

Bone:

skull

Structure:

cranium and jaw bones

made of several bones joined together

large box called cranium and smaller paired boxes for eyes, ears, nose, jaw

has large hole called foramen magnum for passage of spinal cord

Function:

attachment of jaws

protect brain and other delicate parts

Bone:

cervical region Atlas (first cervical)

Structure:

ring shaped

no centrum

broad flat transverse processes

vertebraterial canal for passage of vertebra artery

facet for articulation of condyles of skull

Function:

protects the spinal cord

attachment of muscles

allow nodding of head

Bone:

axis (second cervical)

Structure:

adontoid peg projects from centrum

large flattened neural spine

vertebraterial canal

small transverse process

Function:

allows the head to rotate

protects the spinal cord

provides surface for muscle attachment

Bone:

cervical (others)

Structure:

short neural spine

branched transverse process for neck muscles

vertebraterial canal

wide neural canal

Function:

supports weight of the head

protects the spinal cord

neck muscle attachment

Bone:

Thoracid

Structure:

long backwards pointing neural spine

transverse process that points sideways

facets for articulation of ribs

notch for spinal nerves to pass through

Function:

forms ribcage

articulation with one end of rib

protects the spinal cord

muscle attachment

Bone:

lumbar

Structure:

short neural spine

long transverse process towards abdomen

large centrum

extra processes e.g prezygapophysis, hypapophysis,
anapophysis,metapophysis

Function:

protects organs of the abdomen

supports the upper part of the body

protects the spinal cord

muscle attachment

Bone:

sacral

Structure:

fused bones to form sacrum

well developed transverse processes of first vertebra

vertebraterial canal

short neural spine

Function:

protects the alimentary canal

attachment of hip girdle

protects the spinal cord

muscle attachment

Bone:

Rib

Structure:

long

flattened

attached to sternum from front

Function:

protects internal organs

muscle attachment

vii) Describe the bones that form the appendicular skeleton

Bone:

pectoral girdle (scapular shoulder bone)

Structure:

broad i,e flattened blade

glenoid cavity to articulate with humerous

metacronium/acromion for muscle attachment

hard to provide support

socket with cartilage/smooth surface to reduce friction

Function:

support muscle attachment

articulate with humerous

Bone:

Humerous

Structure:

long shaft for muscle attachment

round head to articulate with glenoid cavity

trachlea for articulation with ulna

olecranon fosa to prevent arm bending the other way

Function:

movement

muscle attachment

Bone:

Ulna and radius

Structure:

ulna longer and on side of little finger

has sigmoid notch and olecranon process to form hinge joint with humerous

radius is smaller and lies along thumb side and does not join ulna

allows articulation with wrist bone

Function:

movement

muscle attachment

Bone:

pelvic girdle (hip bone)

Structure:

composed of three fused bones ilium, ischium, pubis

upper end fused to sacrum

lower end has acetabalum for articulation with femur

has abturator

Function:

movement

muscle attachment

support

absorbs pressure exerted by ground when animals move

Bone:

Femur

Structure:

rounded head to fit in acetabalum of pelvis

projections called trochanter for attachment of thigh muscles

condyles at lower end for articulation with tibi

patella that covers knee and prevent leg from bending backwards

Function:

movement

muscle attachment

Bone:

tibia and fibula

Structure:

tibia is longer than fibula

tibia is outer bone and fibula is inner bone

tibia lies on the side of large toe

fibula is fussed to tibia on (outer side)

Function:

movement

muscle attachment

6. a) What is a joint?

the point where bones meet

ii) State the functions of joints

provide a point of articulation between bones

iii) Name the main types of joints

immovable joints e.g. skull, pelvic girdles and sacrum

slightly movable joints e. g. between vertebrae

Freely movable joints e. g. knee, elbow

iv) Give the features of movable joints

ends of bones covered with articular cartilage

ends bound by capsules of ligaments

have joint cavity filled with lubricating ﬂuid called synovial ﬂuid secreted by synovial
membrane

they are called synovial joints

b) Describe the synovial joints

iv) Ball and socket

allow movement in all planes /directions i.e. 360°

rounded end of bone fits into a rounded/cavity in another bone

e.g. shoulder joint and hip joint

v) Hinge joint

convex surface of one bone fits into the concave surface of another bone

this allows movement in only one plane/direction 180°

e.g. elbow joint and knee joint

vi) Pivot joint

allows rotation e. g. where atlas pivots on olecranon process of axis

c) i) What is synovial ﬂuid?

lubricating ﬂuid produced by synovial membrane at movable joints

ii) State the functions of synovial ﬂuid

absorbs shock

reduces friction/ gives lubrication

nourishment

distributes pressure

d) Explain the following terms

v) Ligament

connective tissue joining one bone to another

vi) Cartilage

supporting soft tissue found at joints

they cushion the bones and absorb shock

vii) Tendon

tissue that connects muscle to bones

7. Muscles

e) i) What is a muscle?

ﬂeshy part of body

composed of long cells enclosed in a sheath

specialized cells capable of contracting

ii) State the functions of muscles

cover the skeleton

provide shape

contract and relax to enable body to move

f) Describe the structure and function of various types of muscles

i) skeletal muscles

also called voluntary/striated/stripped muscles

they are attached to skeleton

they consist of striated, multinucleated, ling fibers and are cylindrical shaped

found on legs, arms, eyes, neck where they cause movement

ii) Involuntary muscles

also called smooth/visceral/unstriated/unstripped

their movement is not controlled by the will

they are unstriated, nucleated, short fibred and spindle shaped

are found in alimentary canal, blood vessels, secretory glands, other tubular visceral

organs, bladder, uterus, urinary tract, reproductive system, respiratory tract, ciliary body
iris

iii) Cardiac muscles

also called myocardium

found in the Walls of the heart

are not under control of the will

composed of long cylindrical cells with special junctions

myogenic i.e. generate their own contraction

they are not fatigued

their function is contraction of the heart to pump blood

g) Explain how muscles cause movement of the human arm

the muscles which bring about these movements are called biceps and triceps

biceps are attached to scapula and radius for bending

triceps are attached to scapula, humerus and ulna for stretching

when the biceps contracts, it pulls the radius (forearm) and the hand bends

the triceps relaxes at the same time

when the triceps contracts and biceps relaxes(extends) the arm is stretched

biceps ﬂexes the arm (ﬂexor) and triceps extend(extensor muscle) the arm

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

skeletal (biceps)

multi nucleated

striated/stripped

long muscle fibers

block/cylindrical

smooth muscles

un nucleated

un striated

short muscle fibers

spindle shaped

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

intervebral disc

iv) What are the functions of the cartilage named in (d) ii) above

acts as a cushion/absorbs shock

reduces friction

ﬂexibility of vertebral column

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Rayvanny officially leaves Diamond’s WCB Wasafi after 6 years

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