SENIOR SECONDARY BIOLOGY

FORM THREE NOTES

CHRISTOPHER Z.M. KANYIMBO

 TABLE OF CONTENTS

TOPIC ONE: PHOTOSYNTHESIS………………………………………………….. Page 3

TOPIC TWO: TRANSPORT IN PLANTS…………………………………………….. Page 22

TOPIC THREE: HUMAN DIGESTIVE SYSTEM…………………………………… Page 38

TOPIC FOUR: HUMAN BLOOD CIRCULATORY SYSYTEM ………………….. Page 58

TOPIC FIVE: RESPIRATORY SYSTEM……………………………………………. Page 75

TOPIC SIX: LOCOMOTION……………………………………………………... Page 89

TOPIC SEVEN: REPRODUCTION………………………………………………… Page 103

TOPIC EIGHT: HUMAN DISEASES……………………………………………… Page 123

TOPIC NINE: HUMAN POPULATION………………………………………....... Page 136

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TOPIC ONE: PHOTOSYNTHESIS (FOOD MAKINGIN GREEN PLANTS)

Photosynthesis is the process whereby green plants use water and carbon dioxide to make
organic food substances in presence of sunlight and chlorophyll. Photosynthesis occurs in green
parts of the plants especially leaves.

External parts of a leaf

Lamina-where most chloroplasts are located.

Petiole: attaches the leaf to the stem. It exposes the leaf to sunlight for photosynthesis. It also
contains vascular bundles

Veins: have phloems and xylems that transport food substances and water respectively.

Mid rib: holds the lamina in position. Have vascular bundles for transport of substances to and
from the leaf.

Cross section of a leaf

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Cuticle

- This is a thin transparent material covering the upper and lower epidermis
- It is thin and transparent to allow light to penetrate through

The functions of cuticle are the following:

a. It is waxy which protects the leaf from attacks by fungi and bacteria
b. It is water proof which prevents excessive water loss from the leaf surface by evaporation
c. Protects internal parts of the leaf from physical damage
d. Hairy cuticle protects the leaf from predators

Epidermis (both upper andlower epidermis)

- Consists of one layer of thin flattened cells that have no chloroplasts

- Outer walls are covered with cuticle a waxy and water proof substance produced by
epidermal cells
- Upper and lower epidermises contain small pores called stomata surrounded by pairs of
guard cells

The epidermis plays the following functions

a. They protect the inner parts of the leaf from damage

b. The cuticle prevents water loss as it is water proof; it also protects the leaf from attack by
disease causing organisms.
c. It contains stomata which are entry and exit for air into and out of the leaf.
d. They allow light to penetrate since they have no chlorophyll

Palisade mesophyll

- This is a layer of cells located below the upper epidermis

- The cells are elongated and column shaped
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 - Palisade mesophyll cells contains a lot of chloroplasts hence is the main site of
photosynthesis
- Palisade cells are closely packed with no air spaces
- Chloroplasts may move towards light

Functions of palisade mesophyll

- This is the main site of photosynthesis

Adaptations of Palisade mesophyll to capture more light

a. Contains a lot of chloroplasts

b. Cells are cylindrical in shape or column shaped hence more cells can be closely packed
together.
c. It is located near the top of the leaf
d. Chloroplasts can move towards light.

Spongy mesophyll

- A layer of cells located between the palisade mesophyll and lower epidermis
- The cells are irregular shaped which are fit loosely
- They have a lot of air spaces between them which allow air circulation and gaseous
exchange between the cells and air surrounding them..
- The spongy mesophyll cells are lined with moisture to aid gaseous exchange

Functions of spongymesophyll are as follows:

a. It is a site of photosynthesis but has fewer chloroplasts than palisade cells

b. It is a site of gaseous exchange in plants
c. The spongy mesophyll cells store starch produced during photosynthesis

Vascular Bundles

- Consist of xylems and phloem.

Functions of vascular bundles are:

a. The xylem vessel conducts water and mineral salts from the soil to the leaves.
b. The phloem transports food substances from the leaf to other parts of the plant.
c. Xylem walls are made of lignin and cellulose which provide support to the plant.

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 Stomata

These are pores located on both the upper and lower epidermis.

Adaptations of the Leaf for Photosynthesis

a. The leaf has chloroplasts which contain chlorophyll that absorbs sunlight for
photosynthesis
b. The leaf has thin lamina to allow light to penetrate to all cells and to allow faster diffusion
of oxygen and carbon dioxide
c. It has stomata which allow gases in and out of the leaf
d. It has branching network of veins which have vascular bundles to transport water to the
leaves and glucose to other parts of the plant.
e. The leaf has air spaces in the spongy mesophyll for exchange of oxygen and carbon
dioxide
f. It has transparent cuticle to allow light to pass through and reach cells for photosynthesis.
g. It has no chloroplasts in the epidermis-this is to allow sunlight to penetrate to mesophyll
layers.

Parts of a Mesophyll Cell

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A cell has the following parts:

Cell wall

- It is only present in plant cells. It is the outermost part of the plant cell.
- It is made of a carbohydrate called cellulose
- It is fully permeable. The cell wall has pores called plasmodesmata.

The cell wall performs the following functions:

- Cellulose is tough, hence supports the cell and gives the cell its shape
- It prevents bursting of the plant cell
- It is also one of the pathways of water and mineral salts

Cell membrane

- It is made of protein and lipids

- It is semi-permeable (selectively permeable)

The cell membrane performs the following functions:

- It regulates the movement of materials in and out of the cell

- It holds and encloses the contents of the cell

Cytoplasm

- Cytoplasm is composed of all cell contents except the cell nucleus. The fluid and semi-
fluid part of the cytoplasm is called cystol.

The following are the functions the cytoplasm:

- Cytoplasm contains many dissolved substances like food nutrients, mineral ions,
dissolved gases and acids.
- Many chemical processes take place in the cytoplasm.

Nucleus

- The nucleus is made of materials called nucleoplasm

- It is enclosed by a nuclear membrane
- Function of nucleus: the nucleus controls cellular activities and heredity

Mitochondrion

- It is an oval-shaped organelle
- Its inner membrane is highly folded. This increases the surface area for respiration.
- It contains enzymes and other special molecules required for respiration

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 - Function of mitochondrion: it is the site for respiration (to produce energy for the cell)

Vacuole

- It’s a sac surrounded by a single membrane called tonoplast.

- In plants they are large and centrally placed
- It is filled with cell sap solution of various solutes such as salts, sugars, amino acids and
waste products.

The following are the functions of the vacuole:

- It is a storage site of substances such sugars, salts and waste products

- It is responsible for elimination of excess water and waste products
- It is responsible for movement of water in and out of cells.

Chloroplasts

- These are ovoid organelles which are present in plant cells only.
- It contain green pigment called chlorophyll
- Cells that have chloroplasts are called photosynthetic cells
- Inside each chroloplast are small units called grana (granum: singular). The grana are
connected to each other by intergranal lamellae. The remaining part of chloroplast is
filled by a fluid called stroma: the stroma contains enzymes involved in photosynthesis.

The function of chloroplasts:

- It is the place where photosynthesis takes place.

Endoplasmic Reticulum

- It is a system of canals or channels within the cytoplasm.

- It can appear as rough or smooth
- The rough endoplasmic reticulum provides a surface for attachment of ribosomes.
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 - The smooth endoplasmic reticulum has no ribosomes

Functions of the endoplasmic reticulum:

- Rough endoplasmic reticulum: transports proteins made by ribosomes

- Smooth endoplasmic reticulum: it’s a site of lipid and protein synthesis

Ribosomes

- They are a site of protein synthesis

Golgi complex

- It is a stack of flattened membrane bound sacks

- It buds off from endoplasmic reticulum

Function of Golgi complex: it is responsible for internal processing and transport system within
or outside cells.

THE PROCESS OF PHOTOSYNTHESIS

Photosynthesis is the process whereby plants make organic food substances from water and
carbon dioxide in the presence of sunlight and chlorophyll.

Water and carbon dioxide are the raw materials for photosynthesis. Glucose is the main product
of photosynthesis while oxygen is the by-product.

Word Equation for Photosynthesis

Water + Carbon Dioxide Glucose + Oxygen

Chemical Equation for Photosynthesis

6H2O + 6CO2 C6H12O6 + 6O2

Photosynthesis takes place in two stages:

a. Light stage
b. Dark stage of photosynthesis

Light Stage

- It is the first stage of photosynthesis and depends on light. Light energy from the sun is
absorbed by chlorophyll and converted to chemical energy (adenosine triphosphate-ATP)
through a process called photophosphorylation. Light energy splits water molecules into
hydrogen and oxygen atoms, a process called photolysis.

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 E
2H2O 2H2 + O2 (Photolysis), E is energy from the sun.

- Oxygen molecules combine chemically to form oxygen molecules which are used in
respiration and excess oxygen molecules diffuse outside the leaf through stomata.
- Hydrogen molecules become the raw material for the second stage (dark stage)

Products of light stage: hydrogen, oxygen and adenosine triphosphate (ATP). ATP is an
energy rich molecule that stores energy for use in the dark stage of photosynthesis.

Dark Stage

- It is the second stage of photosynthesis and does not depend on light. It uses energy
provided by ATP molecules that are produced in
- In this stage hydrogen atoms react with carbon dioxide to produce glucose through a
process called reduction since oxygen is given out.
- Excess glucose molecules combine chemically with each other to produce starch a
process called condensation since water molecules are produced in the process.
ATP
6H2 + 6CO2 C6H12O6 + 3O2

The raw materials for the dark stage are hydrogen and carbon dioxide. The products are glucose
and oxygen.

NB: Glucose is the main product of photosynthesis. It is immediately changed to starch for
storage. Glucose cannot be stored by the plant because glucose is very reactive-can be involved
in reactions where it is not needed and is also soluble in water. Starch is insoluble hence easy to
store.

A. TEST FOR STARCH

 Pluck a leaf from a green plant
 Dip the leaf in boiling water for about 30 seconds. This stops further chemical
reactions by killing leaf cells and destroying enzymes. It also makes the leaf more
permeable to iodine.
 Boil the leaf in ethanol using a water bath. Ethanol dissolves chlorophyll and the
leaf looks white. Ethanol is not heated directly because it flammable.
 Ethanol makes the leaf hard and brittle. To soften the leaf, dip it in warm water.
This also removes ethanol from the leaf.
 Spread the leaf on a white tile. This makes any colour changes visible.
 Place few drops of iodine on the leaf to colour changes.

Results

- Blue-black colour forms or brown colour (colour of iodine)forms

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Conclusion

If blue-black colour forms then starch is present. If brown colour appears then there is no starch.

The Fate of Glucose after Photosynthesis

a. Glucose is used in respiration to produce energy

b. It is converted to starch for storage. Some glucose is combined with fructose to form
sucrose for storage in stems such as stems of sugarcane.
c. Used in formation of cellulose that is used to make cell walls of plants
d. Some glucose is converted to lipids especially oils and stored such in groundnuts
e. It reacts with nitrogen, phosphorous or sulphur to produce proteins.

Functions of Mineral Elements Involved in Photosynthesis

1. Formation of Chlorophyll

Magnesium and iron: magnesium and iron are essential in chlorophyll formation. Magnesium is
an essential component in chlorophyll formation. Iron is involved in activating chemical
reactions in the cell during chlorophyll formation.

2. Opening and Closing of Stomata

Potassium: potassium is essential for opening and closing of stomata. Accumulation of

potassium ions in the guard cells makes water to enter into the vacuole of guard cells. This
causes the guard cells to swell and become turgid. When guard cells become turgid they open the
stomates.

3. Formation of Glucose

Carbon, oxygen and hydrogen: these are used for formation of glucose as glucose is made of
the three minerals.

4. Energy Changes

Phosphorous and potassium: they are involved in energy changes. Potassium is involved in
activation of enzymes involved in the process of photosynthesis. Phosphorous is involved in the
formation energy carrier molecule ATP in the light stage of photosynthesis.

5. Protein Formation

Nitrogen, sulphur and phosphorous: the minerals combine with glucose to form proteins.
Nitrogen is the main mineral in protein formation.

6. Enzyme Formation

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Nitrogen and Sulphur: they are involved in formation of enzymes. Enzymes are organic
substances that speed up or slow down chemical reactions. Enzymes therefore are biological
catalysts. The process of photosynthesis requires enzymes.

Interdependence between Photosynthesis and Respiration

Photosynthesis uses water and carbon dioxide as raw materials and produces glucose as the main
product and oxygen as a by-product. Respiration uses glucose and oxygen as raw materials and
carbon dioxide, water and energy as products.

During the day when photosynthesis takes place, the products of photosynthesis are raw
materials for respiration and the products of respiration can be the raw materials for
photosynthesis.

During the day the process of photosynthesis is faster than respiration. This means:

- A lot of oxygen is produced than it is used by respiration hence excess oxygen is released
by the leaf into the atmosphere.
- More glucose is produced by photosynthesis than it is being used by respiration hence
some glucose is changed to starch for storage.
- Less carbon dioxide is produced by respiration than needed by photosynthesis hence
carbon dioxide diffuses into the leaf from the atmosphere.

During the night, there is no photosynthesis taking place. Respiration is the only process taking
place. This means during the night:

- More carbon dioxide is produced by the leaf through respiration hence the leaf releases
carbon dioxide to the atmosphere.
- More oxygen is required by the leaf cells to respire hence oxygen diffuses into the leaf
from the atmosphere.

During low light intensities such as at dusk and dawn, the rate of photosynthesis is equal to the
rate of respiration. The amount of oxygen and glucose produced by photosynthesis is just enough
to be used by respiration. At the same time, the amount of carbon dioxide produced by
respiration is just enough to be used by photosynthesis. The point at which the rate of
photosynthesis is equal to the rate of respiration is called compensation point.

Types of Pigments inLeaves

a. Chlorophyll
- This is the main pigment found in plant leaves. It is green in colour.
b. Carotene
- It’s a pigment that is usually yellow, orange or reddish in colour.
c. Xanthophyll

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 - It is a pigment that is light yellow in colour.

Carotene and xanthophylls are called carotenoids.

Functions of the pigments

- The pigments absorb light energy and convert it to chemical energy needed in the process
of photosynthesis. Carotenoids absorb light energy and transfer it to chlorophyll which
converts it to chemical energy.

ACTIVITY: TO INVESTIGATE TYPES OF PIGMENTS IN GREEN LEAVES

Materials:

 Green leaves
 Ethanol/alcohol
 Filter paper
 Tape
 Beakers (small and large)
 Mortar and pestle
 Glass rod
 Bunsen burner

Procedure

1. Collect fresh green leaves

2. Chop the leaves into small pieces or crush them using pestle or mortar.
3. Place the crushed leaves into a small glass beaker. Add ethanol to half fill the beaker.
4. Place the small beaker in the larger beaker with water (water bath). Heat the larger
beaker.
5. Heat the larger beaker until the alcohol turns green. This that shows the pigments in the
leaves have dissolved in ethanol.
6. Remove the alcohol mixture from the beaker. Filter the mixture it into another small
beaker.
7. Cut a small strip of filter paper 3cm wide and 10cm long. Stick it to a glass rod using
sello tape.
8. Suspend the filter paper strip into a container with the coloured ethanol such that the tip
of the paper touches the mixture.
9. Allow the strip to absorb the coloured ethanol for 30 minutes. Observe the colours
formed on the strip from the bottom.

Result

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The first colour to appear is green which is called chlorophyll, second colour is yellow/orange
which is called carotene and the final to appear is light yellow which is called xanthophylls.

Conclusion

Green leaves contain different types of pigments.

IMPORTANCE OF PHOTOSYNTHESIS

a. Food production: produces glucose which is a simple sugar that is used as a food
substance by living organisms. Glucose is also used to form proteins, lipids, starch which
are used by other organisms as food. Therefore photosynthesis is the main source of food
for the whole universe.
b. Oxygen production: the process of photosynthesis produces oxygen which is used for
respiration in organisms.
c. Reduction of carbon dioxide from the air: photosynthesis uses carbon dioxide as a raw
material. This prevents accumulation of carbon dioxide in the atmosphere hence prevents
global warming. This means photosynthesis purifies the air by removing carbon dioxide
in the air.
d. Humans depend on photosynthesis for energy containing fossil fuels
e. It is basis for drug industry
f. It is the basis for timber industry
g. It is the basis for textile industry

Factors Affecting the Rate of Photosynthesis

The rate of photosynthesis is how fast photosynthesis occurs. The factors that affect the rate of
photosynthesis are:

Light Intensity

In the dark, photosynthesis is impossible. If light intensity is slowly increased, the rate of
photosynthesis increases with increasing light intensity. The rate increases to a point at which it
can go no further. The point is called light saturation point.

Carbon dioxide concentration

An increase in carbon dioxide concentration increases the rate of photosynthesis. A decrease in

carbon dioxide concentration results in reduction in rate of photosynthesis. The rate of
photosynthesis increases up to a point where it does not increase even when carbon dioxide
concentration is increased. This point is called carbon dioxide saturation point.

Temperature

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The rate of photosynthesis increases with increasing temperature up to a point. If the temperature
is too high photosynthesis stops because the enzymes involved in photosynthesis are denatured
(destroyed). Enzymes become inactive in low temperatures. The optimum temperature is 35 .
Too high or too low temperatures lower the rate of photosynthesis since enzymes are affected
negatively.

Chlorophyll concentration

High chlorophyll concentration increases rate of photosynthesis. Low chlorophyll concentration

decreases rate of photosynthesis.

EXPERIMENTS ON PHOTOSYNTHESIS

Before doing experiments on photosynthesis a plant is destarched by placing it in the dark for at
least 24 hours. In the dark starch is changed to glucose and carried away from the leaf to other
parts of the plant, a process called translocation. Destarching is done to make sure that the
presence or absence of starch is due to set conditions.

EXPERIMENT 1: IS LIGHT NECESSARY FOR PHOTOSYNTHESIS?

Materials

 Destarched potted plant

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  Iodine solution and ethanol
 Test tube and beaker with water
 Piece of black paper or aluminium foil
 Dropper and white tile
 Bunsen burner

Procedure

 Take a potted plant and put it in the dark for 24 hours to destarch it.
 Pluck one leaf and test it for starch to make sure the plant has been destarched.
 Cover part of both sides of the leaf using black sello tape or aluminium foil.
 Leave the plant in the sun for about 5 hours.
 Pluck the leaf and remove the aluminium foil and test the leaf for starch.

Results

Areas which received light turn blue-black with iodine. The part which was covered is brown.

Conclusion

Light is necessary for photosynthesis.

EXPERIMENT 2: IS CHLOROPHYLL NECESSARY FOR PHOTOSYNTHESIS

- It is not possible to remove chlorophyll from a leaf without killing it, a variegated leaf is
used. A variegated leaf is a leaf that has chlorophyll in patches.

Materials

 Variegated potted plant

 Iodine solution
 Test tube and beaker with water
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  Dropper and white tile
 Bunsen burner

Procedure

 Destarch the plant by placing it in the dark for 24 hours

 Place the plant in the sun for at least 5 hours.
 Take the variegated leaf from the plant and test it for starch.

Results

- The part which was green turns blue-black in colour and white part is stained brown.

Conclusion

- Since starch is present only in parts which were green then we conclude that chlorophyll
is necessary for photosynthesis.

EXPERIMENT 3: IS OXYGEN PRODUCED DURING PHOTOSYNTHESIS

Materials

 A water plant (such as Elodea).

 Iodine solution
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  Glowing splint
 Test tube and beaker with water
 Dropper and white tile
 Bunsen burner

Procedure

 Place a funnel over the water plant in a beaker containing sodium hydrogen carbonated
water
 Invert the test tube over the funnel stem. The funnel should be raised to allow circulation
of water
 Place the set up in sunlight
 Bubbles of gas appear rising and collecting in the test tube.
 After sometime the test tube is removed and a glowing splint is inserted.

Result

- The glowing splint bursts into flames.

Conclusion

- Oxygen is produced during photosynthesis.

EXPERIMENT 4: IS CARBON DIOXIDE NEEDED FOR PHOTOSYNTHESIS?

Materials

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  Potted plant
 Potassium hydroxide
 Sodium bicarbonate
 Iodine solution
 Test tube and beaker with water
 Dropper and white tile
 Bunsen burner

Procedure

 Leave the plant in the dark for 24 hours.

 Choose two leaves on the plant.
 Put one leaf in a flask containing potassium hydroxide solution. Potassium hydroxide
solution absorbs or removes carbon dioxide. Leave the leaf attached to the plant.
 Put another leaf in a flask containing sodium bicarbonate solution. Sodium bicarbonate
produces extra carbon dioxide.
 Place the plant in sunlight for 5 hours.
 Pluck the chosen leaves and test them for starch.

Results

- The leaf from a flask containing potassium hydroxide remains brown hence no starch is
present. The leaf from flask containing sodium bicarbonate turns blue-black hence starch
is present.

Conclusion

- Carbon dioxide is necessary for photosynthesis.

PLANT PRODUCTS

These are substances produced by plants. They are used by human beings in various ways.

1. Human food
- These include starch stored in roots, stems, leaves, seeds and fruits, oils stored in
cotyledons, and sucrose stored in stems.
2. Medicine
- These are substances stored in plant materials for treatment of diseases. Examples of
medicines from plants are:
i. Quinine: quinine is used in treatment and control of malaria. It is found in the
bark of Cinchona tree.
ii. Codine: this is medicine for coughs. It contains caffeine which is a plant product.
iii. Eucalyptus: it is a tree which produces chemicals which are used to relieve colds.

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 3. Industrial Products
- These are substances found in plants that are used by humans to manufacture industrial
goods. Examples include:
i. Tannins: these are complex substances which are acidic. They occur widely in
plants and are dissolved in cell sap. They are used in conversion of cow hide into
leather, in dyeing clothes, printing fabrics and in the manufacture of ink.
ii. Rubber: rubber trees produce latex which is used to manufacture rubber products
such as tyres, shoes, etc.

REVISION EXERCISE

1. What is photosynthesis?
2. Write word and balanced chemical equations for photosynthesis.
3. Describe five adaptations of the leaf for photosynthesis.
4. Mention one function for each of the following parts of a leaf
a. Cuticle
b. Palisade cells
c. Stomata
d. Phloem
e. Mid rib
f. Lamina
5. What happens to glucose after photosynthesis? Give five points.
6. Glucose is produced during photosynthesis, why do you test for starch instead of glucose
to show that photosynthesis has taken place.
7. The figure below is a diagram of the cross section of a leaf. Use it to answer questions
that follow.

a. Name the parts marked R and S

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 b. Which tissue is the main site of photosynthesis in the leaf? Give a reason for your
answer.
c. Give two structural differences between T and U.
8. The figure below is a diagram showing gaseous exchange between the leaf and the
atmosphere. Use it to answer questions that follow.

a. During what time of the day is this gaseous exchange taking place?
b. What process leads to this gaseous exchange?
9. Give any two importance of photosynthesis
10. Mention any three plant products and their uses.
11. Describe an experiment that you can carry out to show that green leaves contain different
types of pigments.
12. Describe how plants make proteins
13. Name three products of the light stage of photosynthesis.
14. Give the role of the following minerals in photosynthesis
i. Nitrogen
ii. Potassium
iii. Magnesium
iv. Phosphorous

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 TOPIC TWO: TRANSPORT IN PLANTS
Meaning of Transport in plants

- Transport is a process whereby substances move from one part of the plant to another. It
is translocation of substances through vascular vessels.
- Substances transported include water, mineral salts and manufactured foods.
- Most of these substances are transported through structures called vascular bundles.
- The phloem and xylem form the vascular system in plants.

TISSUES USED FOR TRANSPORT IN PLANTS

- The tissues used for transport in plants are xylem and phloem tissues.

THE XYLEM VESSEL

The Xylem Vessel is made up of two types of cells which are tracheids and vessel elements.

Tracheids/Xylem Fibres

- These are empty dead cells. They are elongated and have tapering end walls.
- These are lignified which makes them strong. The walls have tiny pores called pits.
Water passes from one tracheid to another through pits.
- Tracheids are arranged side by side and end to end

Vessel Elements

- They are long tube-like structures which are continuous from roots to the leaves of the
plant.
- They are dead tissue without cell contents. This allows water to move through them
freely.
- Their walls also contain lignin which makes them strong and rigid to give support to the
plant.
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Structure of the Xylem Vessel

- The xylem vessel does not contain cytoplasm

- Does not have nucleus
- Their walls are made of cellulose and lignin
- They are made of dead cells
- They do not have cross-walls between adjacent cells.

Function of Xylem Vessels

- They transport water and mineral salts from the soil.

- They give support to the plant because they contain lignin which is a tough substance.

PHLOEM VESSELS

- The phloem tissue is made of sieve tubes and companion cells.

Structure of Phloem Vessels

- They have cytoplasm

- They do not have nuclei
- They are made of living cells called sieve elements
- Their end walls form sieve plates with small pores called sieve pores.
- Each sieve tube element has a companion cell next to it. The companion cell has nucleus
and other organelles. Companion cells produce energy for translocation in phloem
vessels.

Function of the Phloem

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 - Transport organic food substances especially glucose.

Evidence That Phloem Transports Sugars

1. Ring Barking or Girdling Experiments

This involves removal of a ring of a bark from a stem, a process called girdling. This removes
the phloem tubes and leaves xylem tubes unharmed. After some weeks, the tissues above the
ring/girdle swell due to accumulation of sugars which was supposed to go to the roots. Deprived
of food, roots die leading to death of the whole plant.

2. Use of Aphids

Aphids pierce their stylets into plants or fruits to suck cell sap. The stylets are cut while still
pierced to the plant. Cell sap starts oozing out of the stylet. The tests on the cell sap indicate
presence of sugars, this shows that phloem carry sugars.

A Vascular Bundle

DISTRIBUTION OF VASCULAR BUNDLES IN MONOCOTS AND DICOTS

Monocots: plants whose seeds have a single leaf/cotyledon.

Dicots: plants whose seeds have two leaves/cotyledons.

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Distribution of vascular Tissue in Monocot Root

In monocotyledonous plants the xylem and phloem are arranged to form a ring in which xylem
tissue alternates phloem tissue.

Cross-section of Dicotyledonous Root

In the dicotyledonous root the xylem occupies the centre where it forms a star shape. The phloem
is found in between the rays of the star.

Distribution of Vascular Bundles in Stems

Monocot Stem

The vascular bundles appear scattered in the stem. There is no cambium in the monocot stems.

Dicot Stem

In dicots the vascular bundles are arranged in form of a ring.

FORMS OF TRANSPORT IN PLANTS

- Diffusion

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 - Osmosis
- Active Transport
- Transpiration Stream

DIFFUSION

- Diffusion is the net movement of particles from a region of high particle concentration to
a region of low particle concentration.
- Particles diffuse to get equilibrium-a point at which there is equal concentration of
particles between two regions.

Importance of Diffusion

- Plants take up some salts from the soil through diffusion.

- Oxygen and carbon dioxide move in and out of the plant through diffusion.

FACTORS THAT AFFECT THE RATE OF DIFFUSION

Size of Particles

The smaller the particles the faster the rate of diffusion. Small particles diffuse faster than large
particles because small particles are light and pass through air and water easily.

Temperature

The higher the temperature the faster the rate of diffusion. The lower the temperature the slower
the rate of diffusion. Increase in temperature of particles increases their kinetic energy and
particles move faster.

Concentration Gradient

The difference in concentration of particles in two regions is called concentration or diffusion

gradient. The bigger the difference in concentration gradient between two regions, the faster the
rate of diffusion.

Thickness of Diffusion Membrane/Surface Area

The thinner the membrane the faster the rate of diffusion since the diffusion distance is short.

Activity: To Demonstrate Diffusion Using Visking Tubing

Materials:

 Visking tubing
 Starch solution
 Iodine solution

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  Beakers
 String

Procedure

1. Measure and cut a visking tubing 8cm in length.

2. Tie up one end tightly with a string about 1cm from the tip.
3. Fill the visking tubing with starch solution and tie the other end tightly with a string.
4. Immerse the visking tubing in a beaker filled with dilute iodine.
5. Leave it to stand for 15 minutes.
6. Make observations of colour changes.

Results

Inside the visking the colour of starch solution changes to blue-black as iodine diffuses into the
visking tubing. In the beaker the colour is brown as starch molecules fail to diffuse out of the
visking tubing because they are large molecules. Therefore the visking tubing is semi-permeable.

ACTIVE TRANSPORT

Active transport involves the movement of particles from an area of low concentration to that of
higher concentration.

Particles move against concentration gradient. In active transport the cell uses energy to move
molecules against concentration gradient.

In active transport protein molecules in cell surface membrane pick up and carry particles across
the membrane. The protein molecules that carry particles across cell membranes are called
carrier protein molecules. When carrier protein molecules work they use energy supplied by
the cell.

Examples of Active Transport

- Absorption of minerals from the soil to root cells.

- Translocation of glucose from leaves to storage organs

Facts about Active Transport

- It moves particles against diffusion gradient or concentration gradient.

- It requires energy.
- It involves protein carriers in membranes.

OSMOSIS

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Osmosis is a special type of diffusion that involves movement of water molecules from a region
of high water concentration to a region of low water concentration through semi-permeable
membrane.

Water is a solvent for many minerals and substances. The movement of water depends on the
concentration of water in the two regions.

A dilute solution has more water molecules compared to solute molecules. A concentrated
solution has more solute molecules than water molecules. A solution with many water
molecules has higher osmotic/water potential and a solution with few water molecules has low
osmotic/water potential. Water diffuses from high osmotic potential to low osmotic potential.

CELLS AND OSMOSIS

If a plant cell is in close contact with a solution of high solute concentration than its own, water
molecules leave the cell by osmosis. Water is lost from the cytoplasm and vacuole. The
protoplast shrinks and eventually pulls away from the cell wall, this is called plasmolysis.

The protoplast stops exerting pressure against the cell wall and the cell becomes very soft
(flaccid). This condition is called flaccidity.

When a cell is in contact with pure water or a solution of lower concentration than its own, water
diffuses into the cell by osmosis. The volume of the protoplast increases. Pressure begins to be
exerted against the cell wall. The pressure is called turgor pressure.

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The cell wall becomes strong and rigid and the cell is said to be turgid. The condition is called
turgidity. Turgidity helps plants to be firm and to maintain their shape.

When a cell is in contact with a solution that has the same concentration as the cell, there are no
changes in the cell as the cell neither gains nor loses water.

NB: plant cells are able to withstand extreme protoplast pressure because they have strong
cellulose cell walls. Animal cells burst due extreme protoplast pressure because the cells have no
cell walls.

Importance of Osmosis

- Helps plants to absorb water.

Activity: To Demonstrate Osmosis in Living Tissue

Materials:

 Irish potatoes ( 2 fresh and 2 boiled)

 Distilled water
 Scalpel
 Large beakers
 Strong salt solution

Procedure

1. Take two fresh potatoes and peel them.

2. Cut a piece from each potato so that they stand at 6cm high.
3. Cut and scoop out deep hollows in the peeled potatoes as well as the boiled one.
4. Place one fresh potato in a beaker with distilled water and put some strong salt solution in
the scooped hollow.
5. Place one fresh potato in strong salt solution and put distilled water in the scooped
hollow.
6. Note the level of water in both beakers and scooped hollows.
7. Let them stand for several hours and observe the levels of water and salt solution.
8. Repeat the experiment with boiled irish potatoes.

Results

In the beaker with distilled water and fresh potato the level of water increases in the cavity and
decreases in the beaker. This is because water diffuses from the potato cells into the cavity and in
turn the cells absorb water from beaker. In the beaker with salt solution and fresh potato, the
level of distilled water decreases in the cavity and increases in the beaker. This is because water
diffuses from the potato cells into the salt solution in the beaker, in turn, the cells draw absorb

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from the cavity. In boiled potatoes there no changes in level of water and salt solution as potato
cells are dead hence no osmosis.

MOVEMENT OF WATER AND MINERAL SALTS THROUGH A PLANT

Most water entering the plant is absorbed through root hairs.

It travels through the root cortex to the xylem. There are three pathways which water uses to
move from the soil to the root xylem. These pathways are:

Apoplast Pathway

- A system of adjacent cell walls which is continuous throughout the plant. Water move
between adjacent cell walls.

Symplast Pathway

- A system of interconnected protoplast in the plant. Water passes through cytoplasm.

Vacuolar Pathway

- Water moves from vacuole to vacuole.

Water Ascent in the Xylem

- Many factors cause water to rise in the xylem. Some of them are:

Cohesion and Adhesion

Cohesion: is the force of attraction between similar molecules. Adhesion: the force of attraction
between molecules which are not similar. Water molecules stick together as the molecules on top
move they pull those below them and next to them (cohesion). Water molecules also have strong
attraction to the walls of the xylem (adhesion). Due to these two forces water molecules next to

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the xylem walls creep up the wall due to adhesion and pull along water molecules that are not
near the wall by cohesion. Cohesion and adhesion prevent a column of water from breaking.

Capillarity

This is the tendency of water to rise inside a narrow tube. Xylems form narrow tubes through
which water moves. Water rises in the xylem because of strong forces of attraction between
water molecules and the cell walls of xylems.

Root Pressure

Water entering root xylem by osmosis causes build up of pressure. When water enters root cells
by osmosis, pressure builds up inside the cell, this forces water into the xylem vessels and up to
the leaves. Minerals dissolved in water enter together with water or are absorbed through active
transport.

Transpirational Pull

Evaporation of water in the spongy air spaces causes water to diffuse from spongy cells. In turn,
the cells draw water from the neighbouring cells which in turn draw water from the leaf xylem
which draw water from the stem and root xylem. Transpirational pull cause ascent of water in
xylems.

Activity: To Measure Rate of Transpiration

Materials:

 Freshly cut shoots

 Basin/beaker of water
 Potometer
 Stop watch

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Procedure

1. Cut a leafy shoot and fix it to the potometer

2. Allow the plant to equilibrate (5 minutes) before introducing an air bubble.
3. Measure the rate of bubble movement at least 3 times. Use the reservoir to return the
bubble to zero each time.
4. To measure transpiration rate, measure the distance covered by the air bubble divided
by time taken.

Result

When the air bubble moves long distance within a short time then it means transpiration rate is
high. When the air bubble moves slowly it means transpiration rate is slow.

NB: The potometer measures transpiration rate as well as water uptake since the water taken up
by the shoot is equal to amount of water lost by the plant through transpiration.

TRANSPIRATION STREAM

Transpirational stream is the continuous flow of water through a plant. Transpiration is the
evaporation of water from surfaces of plants especially leaves.The transpiration stream is onset
by evaporation of water from the leaf cells. This creates low water potential of mesophyll cell.
The mesophyll cells draw water from adjacent cells. The adjacent cells also draw water from the
xylem. The leaf xylem draws water from stem xylem and the stem xylem draws water from root
xylem. The roots absorb water from the soil. This is a continuous process.

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The loss of water in the mesophyll cells causes drawing of water from xylem. This creates a
sucking of water from the xylem which is known as suction. Suction is defined as the flow of
fluid from region of high pressure to low pressure.

IMPORTANCE OF TRANSPIRATION

Cooling of Plants

Transpiration cools plants as water evaporates. This prevents hot direct sunlight from damaging
delicate cells.

Absorption and Transport of Mineral Salts

As water enters plants, salts are also absorbed and transported in the plant.

Uptake of water by Plants

Evaporation of water from leaves draws water from xylems. This leads to absorption of water
from the soil.

Helps in gaseous exchange

Transpiration ensures that the walls of the spongy mesophyll are kept moist which is essential for
efficient absorption of gases (carbon dioxide for photosynthesis and oxygen for respiration)

FACTORS AFFECTING RATE OF TRANSPIRATION

Temperature

The higher the temperature the higher the rate of transpiration. The lower the temperature the
lower the rate of transpiration. High temperature leads to increase in evaporation of water from
plants. Low temperature reduces evaporation of water from plants.

Humidity

Humidity is the amount of water vapour in the air. The higher the humidity the lower the rate of
transpiration. The lower the humidity the higher the rate of transpiration.

Wind Speed

Wind blows away water vapour from leaves and this prevents air around leaves to be saturated
with water vapour. This increases the rate of transpiration. Calm conditions reduce transpiration
rate.

Light Intensity

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Light intensity affects the opening of the stomata. In high light intensity the stomata open more
and more water is lost which increases rate of transpiration. In low light intensities stomata open
less and the rate of transpiration is reduced.

ROOT HAIRS

Root hairs are fine structures of epidermal cells from the outer cells of plant roots that resemble
hairs. Root hairs increase the surface area for absorption of water and mineral salts.

Adaptations of Root Hairs for Absorption

a. They are long, narrow and numerous to increase surface area for absorption.
b. Their cytoplasm has more solute-this reduces the osmotic potential in root hairs hence
water moves from soil into root hairs.
c. Root hairs have vascular tissues which transport water and mineral salts.

Activity: To Measure Water Uptake in Plants

Materials:

 3 young plants (one dry)

 Cooking oil
 3 test tubes
 Vaseline

Procedure

1. Half fill each test tube with water and label your test tubes A, B and C.
2. Smear roots one plant with Vaseline and put it in test tube A. Put the second plant in test
tube B.
3. Put the young dry plant in test tube C.
4. Fill the test tubes with water of the same level.
5. Cover the surface of the water with cooking oil. Mark the level of water. Cooking oil
prevents evaporation of water.
6. Leave the set up to stand for 8-12 hours

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Result

The level of water in the dry plant does not change since the plant is dead and cannot absorb
water. The water level does also not fall in the plant smeared with Vaseline as Vaseline prevents
roots from absorbing water. In the plant with roots without Vaseline the water level in the test
tube falls meaning the roots have absorbed water which is lost through leaves.

REVISION EXERCISE

1. What do you understand by the following terms?

a. Diffusion
b. Active transport
c. Osmosis
d. Osmotic potential
2. Figures 6A, 6B, 6C and 6D are diagrams showing an experiment that was done to
demonstrate osmosis using potatoes. The potatoes were cut in half. Part of each half was
peeled and a hollow was cut in the centre. The potatoes 6A and 6B were raw while those
in 6C and 6D were first boiled. Use them to answer questions that follow.

a. Describe the results in the set up above.

b. What conclusion do you make from the results?
c. Why do animal cells burst when placed in distilled or pure water?
3. The figure below shows a set up of an experiment done by some students. Use it to
answer questions that follow.

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 a. Describe the results in the set up.
b. Explain the results described above.
4. What is the difference diffusion and osmosis
5. Give structural differences between xylems and phloem.

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 TOPIC THREE: HUMAN DIGESTIVE SYSTEM
Digestion is the physical and chemical breakdown of large organic food molecules into smaller
and soluble molecules that can be used and absorbed in the body.

The Human Digestive Structure

FOOD SUBSTANCES

Food substances provide us with nutrients that provide energy and cell building materials.

FUNCTIONS AND CHEMICAL COMPOSITION OF DIFFERENT FOOD NUTRIENTS

There are six different food nutrients:

- Carbohydrates
- Proteins
- Vitamins
- Mineral salts
- Water
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 - Lipids

CARBOHYDRATES

Carbohydrates contain elements carbon, oxygen and hydrogen. Their general formula is CH2O.
Examples of carbohydrates are starch, glucose, cellulose, sucrose and galactose. Carbohydrates
are classified into three main groups:

i. Monosaccharides
ii. Disaccharides
iii. Polysaccharides

MONOSACCHARIDES

Monosaccharides are single sugar units. They are also called simple sugars. The general formula
of monosaccharides is (CH2O)n where n is from 3-6. They are classified according to number of
carbon atoms present e.g. trioses have 3 carbon atoms and pentose has five carbon atoms. The
digestion of carbohydrates produces monosaccharides. Monosaccharides are used in the
synthesis of disaccharides and polysaccharides.

Properties Monosaccharides

- They are soluble in water.

- They have a faint sweet taste.
- They react with oxygen to release energy hence are all reducing sugars.

DISACCHARIDES

Disaccharides are formed when two monosaccharides combine through a process called
condensation reaction and a water molecule is released as shown below.

C6H12O6 C12H22O11 + H2O

Examples of disaccharides are sucrose, maltose and lactose. The general formula for
disaccharides is C12H22O11.

Properties of Disaccharides

- They are soluble in water.

- They are sweet.
- Maltose and lactose are reducing sugars while sucrose is not.

POLYSACCHARIDES

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Polysaccharides are made by joining many monosaccharides, over seventy monosaccharides.
Polysaccharides are polymers of monosaccharides. Examples of polymers are starch, cellulose
and glycogen. Their general formula is CX(H2O)y where x and y are variables.

Properties of Polysaccharides

- They are insoluble in water.

- They are not sweet.
- They are non-reducing sugars

Functions of Carbohydrates

- They are a source of energy e.g. glucose is broken down to release energy through
respiration.
- They form part of plant cell structure, cellulose is part of the cell wall.
- They function as storage for energy e.g. starch in plants and glycogen in animals.
- They are a source of roughage in humans. Foods from plants are rich in fibre. The fibre
provides the bulk and resistance to muscles in the alimentary canal. This allows easy
movement of food in the gut and prevents constipation.

PROTEINS

Proteins contain elements carbon, oxygen, hydrogen and nitrogen. Apart from the elements
mentioned some proteins contain sulphur and phosphorous depending on their source. The basic
unit of a protein is the amino acid. The digestion of proteins produces amino acids.

Structure of an Amino Acid

The amino acid is made up of two parts: the amino part (which contains nitrogen) and the acid
part. R represents the functional group of the amino acid. There are twenty different types of
amino acids. These amino acids combine differently to form different proteins.

Properties of proteins
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 - Some are soluble in water such as haemoglobin and antibodies.
- They are affected by temperature-they are denatured by high temperatures.

Functions of Proteins

- Proteins are used for growth and repair of worn out cells.
- They are source of energy after deamination-the acid part of amino acid is changed to
carbohydrate which is a source of energy.
- Proteins are structural compounds of animal tissues such as keratin in hair, feathers and
horns, collagen in tendons and ligaments and myosin in muscles.
- Proteins are used to form functional proteins such as haemoglobin (helps blood to
transport oxygen), hormones (regulate life processes in animals), antibodies (provide
immunity against infection), fibrinogen (helps in blood clotting) and enzymes (speed
cellular chemical reactions)

LIPIDS

Lipids are fats and oils. Lipids contain elements carbon, hydrogen and oxygen. Lipids have less
oxygen atoms than hydrogen atoms compared with carbohydrates. For example in glucose there
are two hydrogen atoms for every oxygen atom (2:1). In a lipid there are twenty two hydrogen
atoms for every oxygen atom (22:1).

The basic units of lipids are fatty acids and glycerol. This means the digestion of lipids produces
fatty acids and glycerol.

Functions of Lipids

- Lipids are a source of energy. They store more energy than carbohydrates.
- They form part of cell membrane. Cell membrane is composed of a type of lipid called
phospholipid.
- Act as insulation under the skin. Prevents excessive heat loss in animals. This helps to
keep animals warm.
- Act as protective compounds. The fat around body organs such as the heart and the
kidney acts as a cushion against mechanical injury to organs. The fats also help to hold
the organs in place.
- They form components of hormones
- Help in storage of vitamins. Vitamins A, D, E and K are soluble in fat. These vitamins
are stored in the fat found in the liver.

MINERAL SALTS

A wide variety of salts is essential for chemical activities in the body.

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MINERAL SOURCES USE IN THE BODY DEFICIENCY SIGNS
Calcium  Milk, cheese  Formation of  Rickets
and vegetables strong teeth and  Osteomalacia (a
bones disease in which
 Needed for bones are painful and
clotting of blood fracture easily)
 Needed for
muscle
contraction
phosphorous  Milk and milk  Formation of  Weak bones and teeth
products such strong bones
as cheese and teeth
Iron  Liver, meat,  Formation of  anaemia
egg yolk, haemoglobin
green and myoglobin
vegetables in muscles
Sodium  common salt  keep nerves in  muscle cramps,
good working weaknesses and
order dullness
Potassium  meat,  proper  muscular weaknesses
vegetables, functioning of  paralysis and
fish, cereals, nerves, muscles drowsiness
vegetables and enzymes.
Magnesium  All food  Strong bones  Muscle tremors and
and teeth convulsions
 Proper
functioning of
muscles and
nerves
Iodine  Eggs, sea  Formation of  Goitre (the swelling of
foods, thyroxine. the thyroid gland)
vegetables,
iodised salt

VITAMINS

Vitamins are chemical compounds that are essential in small quantities for normal chemical
activities of the body. Most vitamins act as catalysts in essential chemical changes in the body.

Vitamins A, D, E and K are fat soluble vitamins. Vitamins B and C are water soluble vitamins.

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VITAMIN SOURCES USE IN THE BODY DEFICIENCY SIGNS
A (Retinol)  Liver, cheese,  It improves vision  Night blindness
butter, milk, eggs,  It promotes growth  Cornea of the eye
carrots, red palm  Maintains healthy becomes dry and opaque
oil. epithelial growth leading to keratomalacia
D (calciferol)  Egg yolk, cheese,  It strengthens bones  Osteomalacia (softness
fish liver oil, and teeth of bones)
butter, sunlight (calcification)  Rickets
 It enables absorption
of calcium and
phosphorous
C (ascorbic  Oranges, lemons,  It promotes  Bleeding and swollen
acid) mango, tomatoes, absorption of iron gums, bleeding under the
fresh green  Maintenance of skin (all these are signs
vegetables healthy cells, tissues of scurvy)
and blood vessels
 Formation of collagen
fibres in connective
tissues
 Promotes healing of
wounds
B1 (thiamine)  Whole grains of  Involved in cell  Wasting, partial
cereals, beans, respiration paralysis, accumulation
groundnuts, green  It promotes nerve of water in tissues, heart
vegetables, yeast activity failure (signs of beriberi)
B2 Milk products, cereals,  For cell respiration  pellagra
(Riboflavin) bread and milk  Keeps mucus
membranes and skin
healthy.
K  leafy vegetables  helps in blood clotting  slow blood clotting
and oil
 intestinal bacteria
E  sunflower oil,  involved in cell  Heart problems
(tocopherol) peanuts, avocado, metabolism
spinach  It strengthens muscles
B3 (niacin)  Fish, chicken,  Involved in  Pellagra characterized by
pork, liver, respiration diarrhoea and others.
peanuts, beef,  Processing fats in the
mushrooms, body and lowering
avocado, cholesterol levels
Function of Water

- Water is used to transport substances in the cell and in the blood.

- Oxygen is absorbed into the body after it dissolves in moisture lining of the lungs.
- It acts as a medium in which all chemical reactions take place in cells.
- Acts as a lubricant, for example in saliva or synovial fluid.

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 - Water gives organisms or their parts form such as eye ball or penis.

FOOD TESTS

A. TEST FOR STARCH

Materials:

 Food stuffs to be tested

 Test tubes
 Iodine solution
 Water

Procedure

 Crush the foodstuffs to form fine particles

 Put the crushed particles in test tube and add water to dissolve
 Add few drops of iodine

Result

 Dark blue colour indicates presence of starch and brown colour indicates absence of
starch in the foodstuff.
B. PROTEIN TEST (BIURET’S TEST)

Materials

 Foodstuffs to be tested
 Test tube
 Sodium hydroxide
 Copper sulphate solution

Procedure

 Put a 5ml of food solution in a test tube

 Add 5ml of sodium hydroxide to the food solution
 Then add 5ml of copper sulphate solution to the mixture

Result

A purple or violet colour shows that protein is present.

C. TEST FOR REDUCING SUGARS

Materials

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  Food solution
 Test tube
 Benedict’s solution
 Bunsen burner

Procedure

 Put 5ml of food solution in a test tube

 Add 2-3 drops of Benedict’s solution the food solution
 Heat the mixture for sometime

Result

Brick red colour indicates presence of reducing sugars

D. TEST FOR NON-REDUCING SUGARS

Materials:

 Food solution
 Benedict’s solution
 Test tube
 Hydrochloric acid
 Sodium hydroxide
 Bunsen burner

Procedure

 Put the food solution in a test tube

 Add 3ml of hydrochloric acid
 Add 3ml of sodium hydroxide
 Add 2-3 drops of Benedict’s solution
 Heat the mixture for sometime

Result

Brick red colour shows presence of non-reducing sugars

E. TEST FOR LIPIDS

Materials:

 Clean plain paper

 Food stuff

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Procedure

 Smear or rub the foodstuff on the piece of paper and wait.

Result

If translucent spot appears then lipids are present

DIGESTIVE ENZYMES

An enzyme is a protein substance which acts as a catalyst and controls the rate of reactions in
cells. Enzymes are involved in many body processes such as respiration and digestion.

A catalyst is a substance which speeds up a chemical reaction but remains unchanged itself.
Enzymes are biological catalysts. The substances on which enzymes work are called substrates.

GROUPS OF DIGESTIVE ENZYMES

1. Amylases: they digest carbohydrates to monosaccharides

2. Proteases: they digest proteins to amino acids
3. Lipases: digest lipids to fatty acids and glycerol

1. AMYLASES

Salivary amylase (ptyalin): converts cooked starch to maltose.

Pancreatic amylase: breaks down starch into maltose.

Maltase: changes maltose to glucose

Sucrase: converts sucrose to glucose and fructose

Lactase: converts lactose and glucose

2. PROTEASES

Pepsin: converts proteins to polypeptides.

Trypsin: converts polypeptides to peptides.

Peptidase: converts peptides to amino acids.

Rennin: causes coagulation (solidification) of milk by changing milk protein caseinogen into
insoluble casein. Pepsin can work on milk protein when it is changed to casein.

LIPASES

Lipases like pancreatic lipase convert fats or lipids into fatty acids and glycerol.
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PROPERTIES OF ENZYMES

a. They are Protein in Nature

Enzymes are made of proteins.

b. They are Specific in Their Action

Each enzyme speeds up a particular chemical reaction. For example lipases can only speed up
the breakdown of lipids not starch.

c. They Are Catalysts

Enzymes speed up chemical reactions.

d. They Are Affected by Temperature

Enzyme activity increases with temperature to a point where it starts to decline and eventually
stops. High temperatures denature enzymes and low temperature inactivates them.

e. They Are Affected by PH

Enzymes have a pH at which they work best. Some work best in acidic conditions, others work
best in alkaline or basic conditions while others work best in neutral conditions.
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INVESTIGATIONS ON ENZYMES

1. To Investigate the Effect of Temperature on Enzyme Activity

Materials:

 Starch solution
 1% ptyalin enzyme
 Iodine solution
 Test tubes
 Thermometer
 Bunsen burner

Procedure

 Place 2cm3 of starch solution into three different test tubes labeled A, B, and C.
 Add 1cm3 of ptyalin enzyme
 Immerse test tube A into a beaker of cold water/put in fridge
 Put test tube B in a water bath at 37
 Boil the contents of test tube C.
 Test the contents of each test tubes for starch

Results

Test tube A: dark blue colour appears as starch is present since ptyalin is inactivated by low
temperature. Therefore starch is undigested by ptyalin.

Test tube B: starch test is negative starch solution is brown. This means ptyalin has worked on
starch and converted it to maltose, a reducing sugar.

Test tube C: dark blue colour appears after starch test to show that starch is still present. This is
because ptyalin has been denatured by boiling.

2. To Investigate the Effect of pH on Enzyme Activity

Materials:

 Test tubes
 Sodium bicarbonate
 Starch solution
 Hydrochloric acid
 Saliva (with ptyalin)

Procedure

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  Collect six test tubes and label them A-F.
 Fill each test tube with 5ml 1 % starch solution.
 Put 10 drops of 0.1M sodium bicarbonate solution in A, 4 drops in B.
 Put 6 drops of the hydrochloric acid in D, 7 drops in E and 8 drops in F.
 Collect saliva and put 1ml in each test tube.
 After 5-10 minutes, test each test tube for starch

TEST TUBE STARCH TEST RESULTS

A
B
C
D
E
F
Expected results

The test tube where there is fastest negative result in starch test has the best pH for the enzyme.

Types/Forms of Digestion

a. Physical Digestion

This involves the breakdown of large food particles without changing their chemical properties.
Physical digestion changes size of food particles to smaller particles. Examples of physical
digestion include chewing and grinding by teeth and churning by stomach muscles.

b. Chemical Digestion

This involves the breakdown of large insoluble food molecules into small soluble molecules.
This involves action of enzymes.

MOVEMENT OF FOOD IN THE ALIMENTARY CANAL

Mouth

The food in the mouth is broken down physically by teeth through chewing. Chewing is
important because:

i. Small pieces of food are easy to swallow than larger pieces.

ii. Increases surface area on which enzymes act.
iii. It mixes food with saliva which lubricates food and mixes food with ptyalin.

The tongue rolls the food into a ball or bolus. Saliva contains an enzyme called salivary amylase
(ptyalin). Ptyalin converts cooked starch into maltose. This means digestion of starch begins in
the mouth. Saliva is produced by salivary glands.

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Oesophagus (swallowing and peristalsis)

During swallowing the soft palate is pulled upwards to block the passage leading to the nasal
cavity. The top of the trachea is pulled upwards and under the back of the tongue. The epiglottis
drops over the trachea and forms a bridge over which food passes as it goes into the oesophagus.
Once the food is in the oesophagus, it causes the muscles of the oesophagus to start contracting
and squeeze the food down the oesophagus. The wavelike ccontractions of muscles as food is
forced down the oesophagus is called peristalsis. The oesophagus leads the food to the stomach
through the cardiac sphincter.

Stomach

When food is in the stomach, gastric glands in stomach walls secrete gastric juice. Gastric juice
contains protein digesting enzymes (Pepsin and Rennin) and hydrochloric acid. This means
gastric juice causes acidic conditions in the stomach which are conducive for both pepsin and
rennin to work.

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Hydrochloric acid contained in gastric juice is significant because:

i. It creates acidic conditions which are conducive for pepsin and rennin to work in.
ii. Hydrochloric acid kills germs that may have been swallowed together with food.

The corrosive effects of hydrochloric acid are prevented by presence mucus in the linings of the
stomach walls.

The enzyme pepsin in the gastric juice converts proteins to polypeptides. Rennin causes
solidification of milk (coagulation) by changing soluble milk protein caseinogen to insoluble
casein. This means digestion of protein begins in the stomach.

Once the food is in the stomach muscles start contracting, a process called churning. Churning
is a form of physical digestion as the food is further broken down. Churning mixes the food with
gastric juice to form chyme which is semi-liquid. When chyme is formed, small quantities of
food are released at a time into the small intestines through the pyloric sphincter.

THE DUODENUM

The food from the stomach reaches the first part of the small intestine called the duodenum. Bile
and pancreatic juice are secreted into the duodenum. Bile is secreted by the gall bladder and is
released into duodenum through the bile duct. Pancreatic juice is released by the pancreas
through the pancreatic duct.

Bile is important because:

i. It aids digestion of lipids by breaking large fat globules into fat droplets, a process called
emulsification.
ii. It contains sodium bicarbonate which makes bile alkaline and neutralizes hydrochloric
acid from the stomach. This also creates an alkaline condition suitable for efficient
functioning of the pancreatic enzymes.

Pancreatic juice contains the following:

i. Trypsin: an enzyme that converts polypeptides to peptides.

ii. Pancreatic amylase: an enzyme that converts starch to maltose.
iii. Pancreatic lipase: an enzyme that converts lipids to fatty acids and glycerol.
iv. Sodium hydroxide: provides suitable alkaline conditions for the activation trypsin.

The food passes through the duodenum into the second part of the small intestines, the ileum.
The food moves through the alimentary canal by peristalsis.

ILEUM

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When food reaches the ileum, the glands in the walls of the ileum produce an intestinal juice
called succus entericus.

The succus entericus contains the following:

i. Peptidase: an enzyme that converts peptides to amino acids

ii. Lactase: converts lactose to glucose and galactose.
iii. Sucrase: an enzyme that converts sucrose to glucose and fructose.
iv. Maltase: an enzyme that converts maltose to glucose.
v. Lipase: an enzyme that converts lipids to fatty acids and glycerol.

End Products of Digestion

- End products of digestion of carbohydrates are monosaccharides ( glucose, galactose and

fructose)
- End products of digestion of proteins are amino acids.
- End products of digestion of lipids are fatty acids and glycerol

ABSORPTION

It is the process by which the final products of digestion are taken up into the blood.

Glucose, fructose, galactose, amino acids, water, vitamins, salts are absorbed into capillaries.

Fatty acids and glycerol are absorbed into the lacteal to the lymphatic system.

From the capillaries, the absorbed food substances move to the liver through the hepatic portal
vein. From the lacteals, fatty acids and glycerol go the lymphatic system and then to the liver.

Absorption of digested food happen through certain structures in the ileum called villi.

The Villus

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Adaptations of the Villus for Absorption

a. They have a network of capillaries. These capillaries absorb and transport glucose, amino
acids, salts and vitamins.
b. They have lacteal which absorbs and transports fatty acids and glycerol.
c. The epithelial walls of the villi are thin which makes absorption faster.
d. Epithelial cells have numerous mitochondria that produce energy for absorption.

ADAPTATIONS OF THE SMALL INTESTINE TO THEIR FUNCTION

Adaptations of small intestine for digestion

i. It produces enzymes that digest food substances

ii. It has optimum pH for different enzymes
iii. It is long which provides large surface area for digestion.

Adaptations of Small intestines for Absorption

i. It is long which increases surface area for absorption.

ii. It is rich in blood vessels that transport absorbed food substances.
iii. It has villi that that absorb digested food substances
iv. The epithelial walls of the small intestines are thin for faster absorption of digested food
substances.

The Large Intestine

The large intestine is also called the colon. The walls of the colon have no villi. It is about 1.5
metres in length. The functions of the colon are:

i. The main function is absorption of water and mineral salts. After water is absorbed the
undigested waste is called faeces.
ii. Bacteria in the large intestine promote the breakdown of undigested materials and make
vitamins especially vitamin K.

Assimilation of Digested Food

It is a process by which absorbed end products of digestion are taken up and used by the body
cells.

Glucose is used in respiration to produce energy. Excess glucose is converted to glycogen and
stored. Fatty acids and glycerol are used to form fats and some parts of the cell membrane.
Amino acids are used to form different types of proteins such as haemoglobin, enzymes,etc.

FUNCTIONS OF THE LIVER RELATED TO DIGESTION

1. Control of Proteins
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Deamination

Deamination is the breaking down of excess amino acids by the liver. The digestion of proteins
produces amino acids. Excess amino acids cannot be stored in cells hence they are broken down
by the liver. The amino acid is broken into the amino group (NH2) and the carboxyl group
(COOH). The amino part is changed to ammonia (NH3) which reacts with carbon dioxide to
form urea which is excreted together with urine. The acid part is converted to carbohydrates that
provide energy to cells.

Transamination

This is the process whereby the liver makes amino acids that are deficient in the diet.
Transamination means the transfer of an amino group from one amino acid to another substance
to form another amino acid. This enables the liver to provide an important amino acid that may
be lacking in the body.

2. Control of Lipids

The liver controls the amount lipids in the blood. Lipids are needed to form cell membranes. Too
much lipids like cholesterol may form deposits in arteries leading to the heart causing heart
attack. Excess insoluble cholesterol may accumulate in gall bladder and form gall stones that
may block the bile duct. The liver ensures that this does not happen by controlling the level of
lipids in the blood.

3. Control of Sugar

The liver controls sugar levels in the blood under influence of hormones produced by the
pancreas, insulin and glucagon. Under the influence of insulin, the liver converts excess glucose
in the blood to glycogen for storage in the liver and muscles. When glucose levels are low in the
blood, the liver converts glycogen back to glucose under the influence of glucagon.

4. Production of Bile

The liver produces bile. Bile is stored in the gall bladder. It contains sodium bicarbonate and bile
pigments. Bile is important for digestion of fats. Bile splits fat globules into fat droplets (a
process called emulsification). Bile also neutralizes acidic food from the stomach to create
conducive pH for enzymes in the small intestines.

5. Storage

The liver acts as a storage organ. It stores fat soluble vitamins such as vitamins A, D, E and K. It
also stores water soluble vitamins like B and C. The liver also stores minerals like iron and
potassium. It also stores glycogen.

PROBLEMS ASSOCIATED WITH THE DIGESTIVE SYSTEM

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 1. Constipation

This occurs when too much water is absorbed from food as food residues are moving slowly due
to reduced peristaltic movements in the alimentary canal. The faeces become hard and dry; there
are difficulties in passing out faeces, pain during defecation and swollen abdomen.

Constipation is caused by lack of fibre in diet, too little water in diet, stress and anxiety and
sickness and some medicines.

Constipation can be controlled by eating food in fibre such as vegetables, increased water intake
and increase exercise to induce movement of bowels.

2. Diarrhoea

This is a disorder in which an individual passes out watery stools. It is caused by food poisoning,
allergies to certain food substances; it can also be caused parasites like bacteria and protozoa.
The infections cause the food to move quickly such little water is absorbed. Diarrhoea can be
treated with necessary drugs and oral rehydration solutions.

3. Ulcers

This is a condition whereby the alimentary canal develops wounds. Ulcers can be found in the
gullet, the stomach and the small intestines. It is caused by gastric hydrochloric acid present in
the gastric juice which corrodes the walls of the gut and protein digesting enzymes start digesting
the intestinal muscles. Bacterial infections and eating spicy foods that increase acidity in the
stomach are other causes of ulcers. Ulcers can be controlled by using anti-acids to neutralize the
acidity, treat with antibiotics to eliminate the bacteria, etc.

4. Nausea

Nausea is an uncomfortable feeling that comes before vomiting. It can be caused by diseases
such as typhoid and cholera, reaction to bad smells, motion sickness, food poisoning, allergy to
some food products and early stages of pregnancy. It can be controlled by avoiding heavy meals
and take drinks between meals not after meals.

5. Indigestion

This is a condition when food eaten takes long to be digested. The symptoms of indigestion are
belching, bloating due to accumulation of gases, stomach cramps and a feeling of fullness.
Indigestion is caused mostly by poor eating habits such as eating too much or too quickly,
swallowing air while eating or not chewing food properly. It may also be caused by eating a lot
of fatty foods, improperly cooked foods etc. Indigestion can be controlled by eating food with
low fat content, doing exercise and use of antacids.

6. Heart Burn

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This is a burning feeling in the lower part of the chest followed by a sour or bitter taste on the
throat. It is a result of passage of acidic materials from the stomach to the gullet when the
sphincter muscle at the entrance of the stomach opens. Heart burn is caused by overeating,
eating too fast, eating spicy foods, stress and pregnancy, eating acidic foods like citrus fruits,
tomatoes and onions.

Heart burn can be controlled by avoiding eating spicy foods, avoid carbonated and acidic foods,
etc.

REVISION EXERCISE

1. Give any two functions of the following

i. Carbohydrates
ii. Proteins
iii. Vitamins
iv. Minerals
v. Water
vi. Lipids
2. Describe how you can test a food stuff for lipids
3. State two hormones that are involved in control of blood sugar levels.
4. Describe how nitrogen atoms eaten in beans find themselves excreted in urine.
5. Mention two places in the alimentary where physical digestion takes place.
6. Mention the end products of digestion and state how each product is used.
7. The figure below shows the optimum pH for enzymes G, H and I. Use it to answer
questions that follow.

a. Which enzyme is likely to be produced by the stomach?

b. What would happen to the activity of enzyme G at pH 8?
c. What conclusion can be drawn from the information shown by the graph?

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 8. Describe any four functions of the liver in relation to digestion.
9. The diagram below is longitudinal cross section of a villus. Use it to answer questions
that follow.

a. Name parts labeled X and Y

b. Mention two end products of digestion transported by part Y.
c. State three adaptations of the villus to its functions.
10. Give two differences between disaccharides and polysaccharides and an example for
each.
11. The figure below is a set up to investigate properties of enzymes. Use it to answer
questions that follow.

a. What property of enzymes is being investigated in the experiment?

b. If the test tubes were to be tested for starch after ten minutes, what would be the
results?
c. Apart from the factor being investigated above and pH, mention another factor that
affects enzyme activity.

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 TOPIC FOUR: THE HUMAN CIRCULATORY SYSTEM
In unicellular organisms, substances move to and from the body and distributed by the process of
diffusion. Large complex organisms need circulatory systems that transport useful substances to
cells and waste products from cells to excretory organs. Without circulatory system, diffusion
would be too slow for useful substances to reach cells where they are greatly needed. In all
vertebrates, the system is called blood vascular system or cardiovascular system. Human
blood is an example of a mass flow system. Mass flow system carries large volumes of fluid to
all parts of the organism. A mass flow system has four parts.

1. Medium. This is the fluid that flows in the system and carries materials around the body.
This medium is blood.
2. A system of tubes. This is a system which carries the fluid from place to place. These
tubes are arteries and veins
3. A pump. This pump supplies pressure to keep the fluid moving through the tubes. This
pump is the heart
4. Site of exchange. This site of exchange allows materials delivered by the blood to enter
the tissues that need them. These sites are the capillaries.

FUNCTIONS OF THE HUMAN CIRCULATORY SYSTEM

The following are functions of the human circulatory system.

a. Transport function
In the process of transport, the human circulatory system has different important functions.
These are:
i. Transport oxygen from lungs to tissues for cell respiration
ii. Transport carbon dioxide from tissues to the lungs
iii. Transport soluble or digested food from the small intestines to various parts of the
body
iv. Transport hormones from glands to target organs
v. Transport waste products of metabolism such as urea to excretory organs.
b. Defensive / protective function
The blood protects the body against diseases in the following ways:

i. Blood clotting which prevents loss of blood (prevents anaemia) and blocks entry of
disease causing organisms.
ii. Phagocytosis. White blood cells engulf germs and digest them
iii. Lymphocytes. These produce specific antibodies against disease causing organisms.
c. Homeostatic function
i. Controlling body temperature in distribution of heat
ii. The blood solute level regulates the movement of water between blood and tissues.
Blood solute solutes affect the water potential of blood. This affects water potential

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 gradient between the blood and the tissue fluid. The size of water potential gradient is
largely due to sodium ions plus plasma proteins.
d. Support function
i. The erection of the penis is achieved by filling large spongy spaces with blood. The
penis becomes flaccid when blood flows out quicker than it flows in.

PARTS OF THE HUMAN CIRCULATORY SYSTEM

The human circulatory system consists of the following parts.
1. Blood
2. Blood vessels
3. The heart
These parts are discussed below in details.

THE BLOOD
This is the liquid tissue consisting of several types of cells which are found bathed in fluid called
plasma. Blood contains plasma, red blood cells, white blood cells, and platelets. The components
of the blood are discussed below in detail.

A. Blood plasma
This is the liquid part of the blood. It is mostly water and many substances dissolved in it. Such
substances include hormones, glucose, amino acids, vitamins, blood proteins and mineral salts.
The following are functions of blood plasma:
i. Transport dissolved food such as glucose, amino acids and vitamins to body tissues
where they are needed
ii. Transport hormones from the endocrine glands to target organs
iii. Transport antibodies to tissues where they provide defense against disease causing
organisms.
iv. Transport waste products from tissues to excretory organs.

B. Red blood cells (Erythrocytes)

Red blood cells are very tiny circular biconcave discs. They are thinner in the center than the
edges. They contain a red iron that has a pigment called haemoglobin. The following are
functions of red blood cells

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 i. Transport oxygen in form of oxy-haemoglobin
ii. They prepare carbon dioxide for transport from all respiring tissues to lungs. Carbon
dioxide from tissues enters the red blood cells where an enzyme carbonic anhydrase
speeds up the dissolving of carbon dioxide to carbonic acid. The acid dissociates to
form hydrogen ions and hydrogen carbonate ions. The hydrogen carbonate ions leave
the red blood cells and enter the blood plasma and are transported to lungs. In the
lungs a reverse reaction takes place, the hydrogen carbonate ions are converted back
to carbon dioxide which is breathed out.

The red blood cells are adapted to their functions in the following ways

i. They contain haemoglobin which has high affinity for oxygen. Haemoglobin readily
combines with oxygen to form oxy-haemoglobin. Oxygen is transported in form of
oxy-haemoglobin.
ii. They have no nuclei which provide more space for haemoglobin thereby increasing
surface area for carrying oxygen
iii. They are numerous-to carry as much oxygen as possible.

Red blood cells are produced in the bone marrow of short bones. They have a life span of three
months.

C. The white blood cells (leukocytes)

White blood cells are fewer than red blood cells. They increase in number during an infection
but they are reduced by HIV virus. They have nuclei (singular; nucleus). They defend the
body against infections. There are two types of white blood cells.
a. Phagocytes or granulocytes
b. Lymphocytes or agranulocytes.
Phagocytes or granulocytes

Phagocyte means cell eater. They eat or engulf cells especially bacteria. They are called
granulocytes because they have tiny granules, like droplets, in their cytoplasm. These have lobed
nuclei. They are of two kinds which are:
i. Neutrophils

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These are the most abundant of white blood cells. They are first to arrive at the site of infection.
They defend the body by engulfing and digesting the germs. Some of these neutrophils are killed
and form part of the pus.
ii. Monocytes
These engulf and digest germs at the site of infection. They also engulf and digest dead cells and
dead neutrophils hence called the mop up crew. The monocytes circulate briefly in the blood
and migrate to tissues and change to macrophages. They protect tissues from pathogens.

Phagocytes are produced in bone marrow of long bones. The function of phagocytes is to engulf
and digest pathogens (disease causing organisms) thereby protecting the body against infections.
The phagocytes are adapted to their functions in the following ways.
i. They have irregular shaped nuclei which allow them to squeeze through gaps in walls
of capillaries to defend tissues against pathogens.
ii. They have enzymes in their cytoplasm which digest the pathogens once engulfed.

Lymphocytes or agranulocytes

They are called agranulocytes because their cytoplasm has no granules. They are called
lymphocytes because they are produced in the lymphatic system in lymph nodes or spleen.
Lymphocytes have a rounded nucleus. There are two types of lymphocytes.

a. The T-Lymphocytes
b. The B-Lymphocytes

The T-Lymphocytes or T-cells

They are called T-Cells or T-Lymphocytes because they are made and mature in the thymus.
They either attack pathogens directly or produce chemicals that coordinate cells in the immune
system. T-helper cells are invaded by HIV to cause AIDS. T-Lymphocytes burst membranes
around the pathogens thereby directly attacking the pathogens.

The B-Lymphocytes
B-lymphocytes (bone-marrow lymphocytes) are produced in the bone marrow. The bone
marrow is connected to the lymphatic system. They are the only lymphocytes that produce
antibodies (proteins produced by B-lymphocytes that help destroy pathogens). They are
adapted to their function by having large nucleus which contains many copies of genes for
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 control of antibody protein production. The function of lymphocytes is to produce antibodies-
proteins that help in the defence against diseases.

D. PLATELETS

These are cell pigments involved in blood clotting. They are formed in the bone marrow. They
are fragments which become detached from cells. They have no nucleus and they help in blood
clotting by releasing blood clotting enzymes. They also release a chemical (serotonin) which
causes blood vessels to constrict thereby reducing bleeding.

THE ROLE OF HAEMOGLOBIN IN OXYGEN TRANSPORT

The word haemo means ‘iron’ and globin means ‘protein’. Haemoglobin is made from the
mineral iron and protein. Haemoglobin has high affinity for oxygen because it readily combines
with oxygen to form oxy-haemoglobin.
Lungs
Haemoglobin + Oxygen Oxy-haemoglobin

Tissues

Oxygen is transported around the body in the form of oxy-haemoglobin. When the blood with
high oxygen levels reach tissues, the oxy-haemoglobin breaks into oxygen and haemoglobin.
Oxygen then is taken up by cells in tissues.

STRUCTURE AND FUNCTIONS OF ARTERIES, VEINS AND CAPILLARIES

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 Valves in veins

A. ARTERIES
The following are characteristics of arteries
 Carry blood away from the heart to tissues.
 They carry oxygenated blood except the pulmonary artery.
 Blood is at high pressure due to pumping of the heart
 They have narrow lumen and thick muscular walls
 They do not have valves.
 They have low blood volume.
 Blood flow is rapid and the blood is bright red due to richness in oxygen.

The following are adaptations of arteries for their functions

i. They have thick and muscular walls to withstand and maintain the high pressure
of blood
ii. They have an outer fibrous coat for strength and protection
iii. They have thick layer of muscles and elastic fibers which contact and relax to
change the diameter of blood flow through them
iv. They have narrow lumen to maintain pressure of blood inside them

The pumping of the blood can be felt on an artery if pressure is put on it with a finger. This is
called pulse. Arteries branch out to form narrow vessels called arterioles. The arterioles branch
further to form capillaries.

B. CAPILLARIES
The following are characteristics of capillaries

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  Capillaries are blood vessels that link arteries to veins.
 They contain both oxygenated and deoxygenated blood.
 Capillaries are one cell thick with very thin walls.
 They are numerous in number and form a dense network in all tissues in the body.
 They are sites of exchange of materials between blood and tissues.
 They have high blood pressure and lowest volume of blood
Capillaries have the following adaptations for their functions
i. They have thin walls. Substances diffuse faster into and out of them
ii. They are many which means they cover large surface area for diffusion to occur
iii. They are constantly supplied with blood keeping up the concentration gradient of
dissolved substances between blood and tissue fluid. Without concentration gradient
diffusion cannot take place.

Each tissue or body organ contains a dense network of capillaries. This dense network of
capillaries is called capillary bed.

Due to high pressure, plasma is squeezed out of capillaries to form tissue fluid.

TISSUE FLUID
Tissue fluid is formed when plasma is squeezed out of capillaries. Tissue fluid contains neither
red blood cells nor plasma proteins (prothrombin and fibrinogen). Tissue fluid contains water,
hormones, oxygen, antibodies, white blood cells, digested food, salts and vitamins. There is
exchange of substances between tissue fluid and cells /tissues. Useful substances like oxygen and
glucose will diffuse into cells and waste products like carbon dioxide and urea diffuse into tissue
fluid. Some of the fluid returns to blood at the venous end of a capillary. The remaining tissue

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 fluid drains into lymphatic vessels. Once the tissue fluid is in lymphatic vessels, it is called
lymph.
The importance of tissue fluid is the following:
a. It provides tissues cells with food nutrients and other important substances
b. It removes waste products away from cells to excretory organs

C. VEINS
The following are characteristics of veins
 They transport blood form tissues to the heart at low blood pressure
 They carry deoxygenated blood except the pulmonary vein
 They have valves at intervals that prevent back flow of blood
 Blood flow is slow and it is dark red in color
 Most veins are located between muscles. As muscles contract they squeeze the veins
and push blood forward
 They have a wide lumen
 They have high blood volume
Veins are adapted for their functions in the following ways:
 They have valves at intervals that prevent back flow of blood.
 They have large diameter/lumen and thin walls to reduce resistance to the flow of blood.
 They are located between muscles so that when muscles contract blood in veins is pushed
forward.
Blood circulation in the Body (Showing Main Vessels)

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 BLOOD CLOTTING PROCESS
When a blood vessel is damaged and blood is exposed to air, platelets release a chemical called
thromboplastin/thrombokinase. Thromboplastin changes blood protein called prothrombin to
an enzyme thrombin. Thrombin changes soluble blood protein fibrinogen into insoluble fibrin.
Fibrin forms a mesh of fibers which trap red blood cells. These dry out to form a scab which
seals or closes the wound.

Blood clotting on a wound/cut

Importance of Blood Clotting

 Blocks or prevents entry of pathogens into the body.
 Prevents further loss of blood hence prevents anaemia.

Blood Circulation in Mammals

Blood in mammals circulates through two systems which are described as double circulation.
There is pulmonary circulation which conveys blood to and from the heart and lungs. The
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second system is called systemic circulation which conveys blood to and from the heart and
other parts of the body.

STRUCTURE OF THE HEART

The heart is the muscular pumping organ of the blood circulatory system. The muscles of the
heart are called Cardiac muscles. The heart is surrounded by a tough membrane called
Pericardium which covers it and protects it. The pericardium fluid reduces friction when the
heart is pumping

The heart is divided into four chambers. These are the two upper thin-walled atria and two
ventricles. The left side of the heart is completely separated from the right side by a wall called
Septum. The right side deals with deoxygenated blood and the left side deals with oxygenated
blood.

The Right Side of the Heart

a. Vena cava: It is the main vein of the body. It returns deoxygenated blood from tissues to
the right atrium

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 b. Right atrium: It receives blood from the vena cava. Its muscular walls pump blood into
the right ventricle.
c. Tricuspid valve: This prevents flow back of blood to the atrium when the right ventricle
contracts
d. Tendons: These tighten in order to make sure the valves does not turn inside out when
ventricles contract
e. Right ventricle: This receives deoxygenated blood from the right atrium. Its walls are
thinner or less muscular than that of the left ventricle because it pumps blood to lungs
with less force and pumps blood a short distance.

The Left Side of the Heart

a. Pulmonary vein: Returns oxygenated blood from the lungs to the left atrium.
b. Left atrium: Receives oxygenated blood from the lungs. Atria have thin walls because
they need to pump blood to the ventricles which is a short distance.
c. Bicuspid valve: It prevents blood flowing back to the left atrium when the left ventricle
contracts
d. Left ventricle: It receives oxygenated blood from the left atrium. It pumps blood to all
tissues of the body. It has thick muscles because they need to pump blood to all tissues of
the body and with more force.
e. Semi-lunar valves: Prevent blood flowing back into the ventricles when pressure falls
during relaxation.
f. Aorta: It is the main artery of the body. It carries oxygenated blood to the tissues. Blood
pressure is highest in the aorta.

BLOOD FLOW IN THE HEART

Blood from the body tissues and lungs goes to the atria through the vena cava and pulmonary
vein. The atria muscles contract and force blood to the right and left ventricles through the
bicuspid valve and tricuspid valves. The ventricle muscles walls contract and the bicuspid
and tricuspid valves close to prevent backflow of blood. When ventricles contract, blood is
forced to the lungs through the pulmonary artery and to the rest of the body through aorta.
This is called cardiac cycle or one heartbeat.

Blood Pressure
Blood pressure is the force developed by the push of blood against the walls of the vessels
measured by a sphygmomanometer. When heart muscles contract (systole), the pressure
created is called systolic pressure. When heart muscles relax (diastole), the pressure is called
diastolic pressure. Pressure is calculated as: systolic pressure/diastolic pressure.

When the ventricles contract, pressure rises to 120/130mm Hg. When the ventricles relax
pressure falls to 80/90mm Hg.

Therefore one’s blood pressure is normally:

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 or

The figures above the normal ones are described as high blood pressure or hypertension
while the lower figures are described as hypotension or low blood pressure.

Pulse Rate

Pulse rate is the number of heart beats per minute. A pulse is felt when the artery passes near
a bone. At rest an adult’s pulse rate is 72 heart beats per minute. During exercise, the
muscles need an increased supply of oxygen and glucose for respiration and carbon dioxide
and heat to be removed. The pulse rate increases during vigorous activity. The increase in
pulse rate results in increased supply of blood rich in oxygen and glucose to tissues and faster
removal of carbon dioxide from tissues. The pulse rate also increases during fear or
excitement.

Problems of the Circulatory System

a. High Blood Pressure

This is a condition whereby the pressure of the blood flowing in the blood vessel is higher than
normal. This is caused by accumulation of yellow fats inside arteries called cholesterol.
Cholesterol causes narrowing of arteries which increases blood pressure. Smoking also causes
narrowing of blood vessels leading to high blood pressure.

b. Heart Attack

This is also known as coronary heart attack. It’s a condition in which the heart tissue becomes
damaged and stops functioning. It is caused by blockage of coronary artery due to blood clots.
The heart muscles fail to contract due lack of energy as there is no supply of oxygen and glucose
to the heart tissues. Eventually the tissues die, if the whole heart is affected the person dies.

c. Stroke

A Stroke is also referred to as cerebral thrombosis. It is a blood clot in the brain. The clot
blocks an artery inside the brain causing the part supplied by the artery to stop working and die.
A stroke may result in loss of speech, paralysis or loss of memory.

d. Anaemia

Anaemia is a condition in which there are few red blood cells or when red blood cells have little
haemoglobin in the body. This affects the way blood transports oxygen as little oxygen is carried
and supplied by blood to tissues. The result is fatigue, dizziness and paleness.

e. Thrombosis

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This is the formation of a blood clot within a blood vessel. This may block or partially block a
blood vessel. It may be a result of long periods of immobility such as in old people or sick
people.

f. Haemophilia

It is a condition in which the blood of a person clots slowly or not at all. It is an inherited blood
disorder. People with haemophilia either have few platelets or their platelets cannot produce
thromboplastin, a chemical that helps in blood clotting.

Ways of Preventing Problems Associated with the Circulatory System

a. Avoid smoking. Cigarettes contain nicotine which makes arteries to constrict and cause
high blood pressure.
b. Reduce taking food which is rich in lipids especially cholesterol such as fatty and red
meat. Instead one should eat white meat such as fish.
c. Exercise regularly to strengthen the heart and improve circulation of blood.
d. Learn to be organized to avoid stress.
e. Avoid obesity as it causes the heart to overwork and causes high blood pressure.

THE LYMPHATIC SYSTEM

The lymphatic system is a special system of vessels connected to the tissues to transport excess
tissue fluid back to the blood after exchange of substances between cells and tissue fluid.

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The lymphatic system is a system of tiny, thin walled vessels called lymphatic vessels.
Lymphatic vessels are also called lymphatics.

The lymphatic system consists of lymph, lymph vessels, lymph nodes or lymph glands and
spleen.

Lymph

- Lymph is excess tissue fluid that drains into lymphatic vessels. The lymph is drained
back into the blood at the subclavian vein near the heart.

Lymph vessels

- They transport lymph

- They have valves at intervals to prevent backflow of lymph.

Lymph nodes

- Lymph nodes are located along lymph vessels. Examples include tonsils at the back of
the mouth.
- They produce lymphocytes and phagocytes. Large phagocytes are attached to the walls of
the lymph nodes to engulf bacteria and dead cells from the lymph.

Spleen

- The spleen removes iron from haemoglobin of red blood cells for use in the body.
- It also removes waste materials such as bile pigments for excretion by the liver.
- It produces antibodies against various diseases.
- It produces red blood cells in an unborn child, a function taken over by bone marrow
after birth.

Movement of Lymph in the Lymph Vessels

a. By muscular contractions. When muscles contract they squeeze the lymph vessels in
between hence squeeze lymph inside lymph vessels to move forward.
b. By force of gravity especially from the upper parts of the body.
c. By action of valves just like in veins.
d. Inspirational movements of the chest wall.

Importance of the Lymphatic System

a. It transports lipids in form of fatty acids and glycerol from intestine to blood stream
through lacteal.
b. Lymphocytes in lymph nodes produce antibodies that protect the body against germs.
Phagocytes also engulf and digest germs in lymph nodes.

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 c. Transports excess tissue fluid back to the blood.

Problems Associated With Lymphatic System

Oedema: the accumulation of tissue fluid in the tissues. It is corrected by movement of the body
part affected.

Elephantiasis: is the swelling of body parts as lymph accumulated due to blockage of lymph
vessels by filarial worm. It can be treated in hospitals.

Other problems include inflammation and tuberculosis of lymph nodes.

Lymphoma which is cancer of the lymphatic system.

REVISION EXERCISE

1. The figure below shows cross-section of blood vessels M and N. Use it to answer
questions that follow.

a. Name the parts marked R and T.

b. State the structural differences between M and N.
c. Mention one way in which blood is transported in N.
2. The figure below shows blood pressure in different blood vessels. Use it to answer
questions that follow.

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 a. Find diastolic and systolic pressure.
b. Why blood pressure is lowest in veins?
c. Why does blood pressure in arteries repeatedly rise and fall?
3. Name two vessels in the body that have valves and explain what could happen if the
valves are damaged.
4. Describe five components of blood and state the function of each component of blood.
5. Describe the following blood circulation systems in mammals:
i. Pulmonary circulation
ii. Systemic circulation
6. Describe the blood clotting process and give two importance of blood clotting.
7. Explain the following problems of the blood circulatory system:
i. Heart attack
ii. Haemophilia
iii. Stroke
iv. Thrombosis
v. High blood pressure.
8. The figure below is a cross section of the human heart. Use it to answer questions that
follow.

a. Name the parts marked A and B

b. State the difference in structure between C and D and explain the difference.
c. Mention any two substances contained in blood conducted by A and B.
9. Describe an investigation you can carry out to find out the effect of exercise on pulse
rate.
10. State three ways preventing problems associated with the human circulatory system.
11. The diagram below represents blood as seen under a microscope. Use it to answer
questions that follow.

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 a. Using letters name the component of blood that produces antibodies, that engulfs germs,
that transports oxygen and that helps in blood clotting.
b. State the adaptation of the cell that transports oxygen.
c. State the functional difference between C and D.

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 TOPIC FIVE: THE RESPIRATORY SYSTEM

Respiration is the breakdown of organic food substances to release energy. Respiration takes
place in cell organelles called mitochondria.

The mitochondrion is adapted for respiration because:

a. It is highly folded which creates large surface area for respiration.

b. It contains enzymes and other special molecules required for respiration

Mitochondria are found in almost all cells but they are abundant in cells that need a lot of energy
such as sperms and muscle cells.

Breathing: the taking in of oxygen and release of carbon dioxide by animals.

Gaseous exchange: the exchange of oxygen and carbon dioxide across a membrane.

Importance of Breathing

a. Allows organisms to get oxygen for respiration in cells

b. Enables organisms to get rid of carbon dioxide produced by respiration

There are two types of respiration

a. Aerobic respiration
b. Anaerobic respiration

AEROBIC RESPIRATION

This type of respiration takes place in the presence of oxygen. Glucose reacts with oxygen and
produces carbon dioxide, water and energy. Energy is the main product; water and carbon
dioxide are by-products.

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Glucose + Oxygen Carbon dioxide + Water + Energy

C6H12O6 + 6O2 6CO2 + 6H2O + 2898Kj

60% of the energy is in form of heat energy which is lost or used to warm up the body. Some
energy is immediately used by the cell.

The remainder is converted to storable form of energy molecule called Adenosine

Triphosphate (ATP). ATP is a combination of a complex organic molecule called Adenosine
and three phosphate groups.

When the third phosphate group is removed the stored energy is released. Adenosine is left with
two phosphate groups called Adenosine diphosphate (ADP).

In aerobic respiration glucose is completely broken down hence the release of energy in large
quantities.

ANAEROBIC RESPIRATION

The release of energy from organic food substances in the absence of oxygen. In plants and fungi
it is called alcoholic fermentation. Because alcohol or ethanol is produced.

Glucose ethanol + Carbon dioxide+ Energy

C6H12O6 2CH3CH2OH + 2CO2 + 210kJ

Energy is the main product, and Carbon dioxide and ethanol are by-products of anaerobic
respiration in plants.

In animals like human muscles anaerobic respiration is called lactic fermentation because acid
is produced.

Glucose Lactic acid + energy

C6H12O6 2CH3CHOHCOOH + 150Kj

In animals, anaerobic respiration produces energy as a main product and lactic acid as a by-
product.

Lactic acid is toxic when it accumulates in animal cells. It causes muscle fatigue. It is usually
broken down to water and carbon dioxide.

This happens when oxygen becomes available. The amount of oxygen needed to break down
lactic acid is called oxygen debt.

Uses of Energy Produced by Respiration

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 a. Energy is used for growth e.g. in protein synthesis.
b. Heat energy is used to warm up the body- to maintain body temperature.
c. Is used in active transport to move molecules against concentration gradient.
d. Movement-contraction of muscles requires energy.

GASEOUS EXCHANGE IN LIVING THINGS

Gaseous exchange is the diffusion of oxygen and carbon dioxide across a gaseous exchange
structure.

Importance of gaseous exchange

a. Organisms are able to obtain useful gases from their environment

b. Organisms are able to get rid of waste gases into their environment

Properties of Efficient Gaseous Exchange Structures

a. They are permeable to oxygen and carbon dioxide

b. They are moist-to dissolve the gases so that they are transported by blood in animals with
transport systems
c. They are thin for faster diffusion due to short distance
d. They are rich in blood capillaries in animals with transport systems to transport gases.
e. They have large surface area for maximum gaseous exchange

GASEOUS EXCHANGE IN HUMANS

Gaseous exchange in humans takes place in the alveolus located in the lungs.

Structure of the Human Respiratory System

Twelve pairs of ribs surround and protect the lungs and the heart. Intercoastal muscles are
attached to the ribs.

A large sheet of muscle (diaphragm) separates the thorax from the abdomen.

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The nostrils/nasal cavity: have hairs that filter the air. It also warms and moistens the air.

The pharynx: it is located behind the nasal cavity and above the larynx. It is a food and air
passage.

Trachea: made of rings of cartilage that keeps the trachea open. Rings of cartilage prevent the
collapse of the trachea during inhalation.

Larynx/Voice box: it is a passage of air. It has two membranes called vocal cords. The vocal
cords can be made to vibrate to produce speech.

Bronchi: these are branches of the trachea. They branch into bronchial tubes which further
divide into bronchioles that lead to the alveoli.

Alveoli: they are a site of gaseous exchange in lungs.

Diaphragm: a dome shaped sheet of muscles located at the bottom of the rib cage. During
inhalation it contracts and moves downwards and increases volume of chest cavity and air rushes
into lungs. During exhalation it relaxes and air is expelled.

Intercoastal muscles: during inhalation the external intercoastal muscles contract and pull the
chest cavity upwards and outwards. This increases volume of the chest cavity and air rushes into
the lungs. During exhalation internal intercoastal muscles contract pulling the chest cavity
inwards and downwards and air rushes out.

The alveolus

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This is the site of gaseous exchange in lungs.

Oxygen diffuses through a thin epithelium of the alveolus and the endothelium of the capillaries.
It combines with haemoglobin to form oxyhaemoglobin. Carbon dioxide diffuses in reverse
direction.

ADAPTATION OF THE ALVEOLUS FOR GASEOUS EXCHANGE.

a. It has a network of blood capillaries that carry the gases being exchanged.
b. Thin walls in between capillaries and alveolus –gases diffuse faster.
c. It is lined with a thin film of moisture to dissolve the diffusing gases.
d. Diffusion gradient: There are differences in concentrations of gases in the blood and
alveolus, more oxygen in alveolus than the blood hence oxygen diffuses into capillaries,
and more carbon dioxide in blood capillaries hence oxygen diffuses into the alveolus.
e. They are numerous: increase surface area for gaseous exchange.

The lung is surrounded by a pleural cavity. It is a space lined by pleural membranes,

membranes protect the lungs, stop them leaking air into the thoracic cavity. In between the
membranes there is pleural fluid that reduces friction between lungs and thorax.

Breathing mechanism

Breathing is the taking of air into and outside the lungs.

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The following structures help in breathing:

i. Ribs
ii. Diaphragm
iii. Intercostals muscle (both external and internal)

Breathing takes place in two phases:

i. Breathing in (inspiration)
ii. Breathing out (expiration)

BREATHING IN (INHALATION)

Diaphragm contracts and moves downwards (flattens). External intercoastal muscles contract
and pull the rib cage upwards and outwards. This increases the volume of the chest cavity. Air
pressure inside the chest cavity and that of the lungs decreases compared to atmospheric air
pressure. Air rushes into the lungs from the atmosphere.

BREATHING OUT (EXHALATION)

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Diaphragm relaxes and returns to its dome shape. External intercoastal muscles relax but internal
contract and pull rib cage downwards and inwards. Lung volume decreases and pressure
increases. Air rushes out.

Regulation/control of Breathing.

Breathing is controlled by the Medulla oblongata. Medulla oblongata monitors the levels of
carbon dioxide and oxygen in the blood stream and adjusts the breathing rate to maintain balance
of the gases. In case of high carbon dioxide concentration receptors in the Aorta and carotid
arteries detect this. Receptors send an impulse to the oblongata which sends messages to the
breathing structures such as lungs to increase air intake and transport organs such the heart to
speed transport of gases.

GASEOUS EXCHANGE IN TISSUES

Gaseous exchange in lungs is between the air and blood cells. In the tissues it is between tissue
fluid and cells. The fluid surrounding cells is called tissue fluid. Tissue fluid has higher
concentration of oxygen than cells and oxygen diffuses from tissue fluid into the cells. On the
other hand carbon dioxide is highly concentrated in cells than in surrounding tissue fluid. Carbon
dioxide diffuses out of cells into tissue fluid.

Activity: Investigating the Effect of Exercise on Breathing Rate

Materials

 Stop watch
 Students
 Rope

Procedure

1. Count the number of breaths for 5 minutes of a student while he or she is standing.
2. Calculate the breathing rate per minute and record.
3. Let the student skip twenty times with the rope.
4. Count the number of breaths for 5 minutes of the student after skipping.
5. Calculate the breathing rate per minute and record the breathing rate.

Result

Exercise increases breathing rate.

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Effects of exercise on breathing

a. Increases the rate of breathing (number of breaths per minute) to expel carbon dioxide
and get oxygen
b. Increases depth of breathing.
c. Increased concentration of carbon dioxide in the blood due to increased respiration
d. Decrease of amount of oxygen in the blood.

Complete breath= one inhalation + one exhalation. During normal breathing the rate is 12-18
breaths per minute. During an exercise breathing rate may go up to 27 breaths per minute.

Lung Volumes and capacities

The average female has lung capacity of 4 litres and adult male 5 litres.

Lung capacity: is the total amount of air held by lungs when they are fully inflated (4L for
females and 5L for males)

Tidal volume: the volume of air breathed in and out during one normal resting breath (0.5L)

Complementary air: when breathing deeply 2 litres of air is forced in and out of the lungs. The
extra 1.5 litres on top of tidal air is called complementary air.

During exercise a person takes in and expels an additional 3 litres to tidal air. 3 litres of air is
exchanged during exercise. This air is called vital lung capacity-the maximum volume of air
breathed in and out from deepest inhalation and deepest exhalation.

Residual air: the amount of air that cannot be expelled during breathing. It is about 1.5 litres.

Residual air = lung capacity vital capacity.

The Spirometer is the device that is used to measure the volume of air going in and out of lungs.

Carbon Monoxide Poisoning

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Carbon monoxide poisoning occurs after inhalation of a lot of carbon monoxide. Carbon
monoxide is a toxic gas. Carbon Monoxide (CO) is a product of incomplete combustion
(burning) of organic materials in insufficient oxygen.

Causes of Carbon Monoxide Poisoning

a. Running generators or small engines inside buildings.

b. Burning charcoal in poorly ventilated rooms
c. Chimneys that are not working properly or are blocked

How Carbon Monoxide Occurs

The poisoning occurs after inhalation of carbon monoxide. Carbon monoxide has higher affinity
for haemoglobin than oxygen in that it readily combines with haemoglobin to form
carboxyhaemoglobin. Unlike oxyhaemoglobin, which splits readily in cells to release oxygen,
carboxyhaemoglobin is very stable and does not easily split. In this case it does not release
oxygen for use by cells.

Since cells are denied oxygen, they cannot respire to produce energy. This results in fatigue (lack
of energy), headache and unconsciousness or death. Due to lack of energy body processes stop
taking place and a person may die due to suffocation. This is called carbon monoxide
poisoning.

First Aid for Carbon Monoxide Poisoning

Take the person out of the room and make them lay comfortably in an open space. If air
circulation is not sufficient fan the patient. If the person is having difficulties in breathing then
use mouth to mouth resuscitation (kiss of life).

Ways of Preventing Carbon Monoxide Poisoning

a. Do not run generators or small engines inside houses or buildings.

b. Ensure that chimneys are working
c. Avoid burning charcoal in poorly ventilated rooms

Smoking

Tobacco contains about 300 chemical compounds. Most of these are harmful to lungs.

Effects of Smoking

a. Respiratory Infections

Cigarette smoke contains substances that irritate the respiratory tract hence increasing mucus
production. The cilia on the respiratory tract are destroyed and bacteria and other harmful

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substances are not removed. This may result in lung infections such as bronchitis and
emphysema.

b. Addiction

Nicotine in tobacco is addictive leading to the person to depend on the smoking habit.

c. Cancer

Smoke from cigarettes contains tar which is a carcinogen. The carcinogen encourages cancerous
cells to develop in the lungs by damaging DNA of the cells.

d. Harm to foetus

Tobacco smoke contains carbon monoxide and nicotine. Carbon monoxide may combine with
foetal haemoglobin leading to retarded foetal growth, may also result into still-borns or
miscarriages.

RESPIRATION IN FISH

Gaseous Exchange in Fish

Gills are the gaseous exchange structures in fish. The gills are located in the opercular cavity.
Gills are protected by a thick gill cover or operculum.

Gill rakers: they sieve out plankton (food) from water.

Gill bar: holds filaments and gill rakers in position.

Gill filaments: contains numerous capillaries and this is where gaseous exchange takes place.

Gill filaments are richly supplied with blood due to presence of many capillaries. The barrier
between blood capillaries and water is thin. The thin surface allows rapid diffusion of carbon
dioxide and oxygen between fish blood and water. Gaseous exchange in fish occurs between gill
filaments and water. This means there is need for contact between water and the gill filaments.
Such contact is brought by ventilation process of inspiration and expiration.

Breathing Mechanism in Fish

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Inspiration/Flow of Water into the Mouth Cavity

The mouth opens. Muscular contractions in the mouth lower the floor of the mouth. This
increases the volume of the buccal cavity and decreases the pressure inside it. Water rushes into
the mouth. Each operculum bulges outwards to increase volume of the opercular cavity and
reduce pressure. Water from the mouth is sucked into the opercular cavity. The operculum is
closed to prevent water from outside the fish to enter through the operculum.

Expiration/Flow of water over the Gills

The mouth closes. The floor of the mouth is raised. This reduces the volume of the buccal cavity
and increases the pressure. The operculum presses inwards by muscular action. The free edges of
the operculum move away from the body wall to open the operculum cavity. Water flows out of
the operculum cavity and out of the fish.

Gaseous Exchange in Between Water and Gill Filaments.

Gaseous exchange in fish takes place in the gill filament as water passes over the gills. Blood
capillaries in the gill filaments have lower oxygen concentration than the water entering the
mouth. Oxygen diffuses from the water into the blood capillaries. Blood in the capillaries has
high concentration of carbon dioxide than the water. Carbon dioxide diffuses from the blood into
the water. The water flowing over the gill filaments and blood in the capillaries flow in opposite
directions. This is called counter current system. This ensures maximum uptake of oxygen by
the blood and maximum uptake of carbon dioxide by the water.

Apart from carrying oxygen, the water entering the mouth of the fish performs the following
functions:

i. It contains plankton which is food for fish.

ii. As the water is expelled by the fish it propels the fish forward hence helps in locomotion
iii. It is also used for drinking by fish.

RESPIRATORY SYSTEM IN INSECTS

The respiratory system in insects is called the tracheal system. It consists of the spiracles,
trachea and tracheoles.

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Spiracles: openings or holes on the sides of the body of an insect. Spiracles are found on the
sides of the abdomen and thorax. They are the entrance and exit for air.

Trachea: the spiracles open into the large tracheal tubes called trachea. The tubes are
strengthened with spiral bands of chitin to keep them open at all times. A lot of air sacs are
connected to the tracheal system.

Tracheoles: the tracheae are subdivided into microscopic tubes called tracheoles. Tracheoles
penetrate the body tissues and are in direct contact with all living cells. They lack chitin. Their
ends are filled with a fluid. The ends act as respiratory surfaces between cells and the tracheoles.

Gaseous Exchange in Insects

Oxygen from the air dissolves in the fluid in the tracheoles and diffuses directly into the cells.
Carbon dioxide which is at higher concentration in the cells than tracheoles diffuses from the
cells into the fluid and then expelled through spiracles during expiration.

Adaptations of the Gills, Tracheal System and Lungs

Gills

a. Gill filaments are thin for faster diffusion of gases

b. Gill filaments are numerous and contain gill lamellae which increases surface area for
gaseous exchange
c. They are rich in blood capillaries for gas transport
d. They are held in position by gill bars

Lungs

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 a. Presence of numerous alveoli-increases surface area for gaseous exchange
b. Trachea has rings of cartilage to hold the trachea open.
c. Alveoli have thin walls for fast diffusion of gases.
d. Alveoli have dense network of blood capillaries for gas transport
e. The trachea has cilia and goblet cells that produce mucus-cilia and mucus help to clean
the respiratory system

The Tracheal System

a. Made of chitin that keeps it open at all times

b. Has spiracles for gaseous exchange
c. Tracheoles connect with each cell-makes gaseous exchange very efficient
d. Tracheoles are very small and numerous-increases surface are for gaseous exchange
e. Tracheoles are thin for faster diffusion of gases

REVISION EXERCISE

1. Describe how carbon monoxide poisoning occurs.

2. What are the products of anaerobic respiration in plants?
3. Describe an experiment you can carry out to see the effect of exercise on breathing rate.
4. Describe the breathing mechanism in fish.
5. How does the counter current system between water and blood in fish gills ensure
maximum gaseous exchange?
6. Briefly describe gaseous exchange in insects.
7. How are the following adapted for their functions
a. Alveolus
b. Gills
c. Tracheal system
8. The diagram below shows a summary of respiration. Use it to answer questions that
follow.

a. Name the product represented by letter L?

b. What type of respiration is shown in the figure above?
c. State two ways in which stored energy is used.

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 9. The diagram below shows a structure found in mammals. Use it to answer questions that follow.

a. Identify the structure.

b. From which chamber of the heart does blood flow at point T?
c. Explain the difference in concentration between point T and point S.
d. What is the role of the thin layer of moisture in the structure?

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 TOPIC SIX: LOCOMOTION

Locomotion is the movement of the whole organism from one place to another.

Reasons for locomotion

 To Search for food

 To run away from danger
 To search for mates

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  To search for new and favourable habitats

SKELETON

A skeleton is a supportive framework in an animal’s body.

Types of skeletons

i. Endoskeletons

This is the skeleton found inside the body of an organism. Hard material is inside soft material. It
is jointed hence enabling movement. It is found in vertebrates such as fish, dogs, birds,etc. The
advantage of endoskeletons is that it does not hinder growth/permits growth. The disadvantage
is that it does not offer maximum protection to soft tissues.

ii. Exoskeleton

A skeleton found on the outside of the body of an organism. The hard covering is outside the soft
tissues. The skeleton is made of chitin which prevents water loss and protects tissues inside.
Animals with exoskeletons include millipedes, crabs, etc. The advantage of exoskeleton is that it
offers maximum protection to tissues inside and prevents water loss since its water proof. The
disadvantages are that it limits growth (to increase in size they have to moult-shed skin) and it
restricts movement.

iii. Hydrostatic skeleton

Type of skeleton by which support is provided by a fluid enclosed in a cavity under pressure.
Examples of animals with hydrostatic skeleton are earthworms and caterpillars.

Functions of the skeleton

a. Support: the skeleton holds the rest of the body in position and helps in maintaining its
shape.
b. Protection: the skeleton protects delicate organs. For example the spine protects the
spinal cord and the skull protects the brain.
c. Storage: stores minerals such as calcium and phosphorous
d. Locomotion: bones meet at joints which form levers. Muscles pull on these levers to
move the body
e. Manufacture of blood cells: the marrow inside some of the bones makes blood cells.

Structure and functions of parts of a bone

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 Cartilage

a. Acts as a shock absorber and prevents friction

b. Connects ribs to the sternum

Bone marrow and spongy bone

a. Manufacture blood cells

Compact bone

Made of collagen fibres and minerals (calcium and phosphorous)

a. Strong and rigid for support

b. Used for muscle attachment

THE HUMAN SKELETON

a. Axial Skeleton

Consists of the skull, vertebral column, ribs and sternum.

b. Appendicular Skeleton

Consists of the two girdles attached to the limbs.

The axial Skeleton

i. The Skull

Consists of the cranium and jaws. The cranium protects the brain.

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 ii. Vertebral Column

The main axis of the body. It consists of a series of bones called vertebrae separated by inter
vertebral discs made of cartilage.

The neural spine and transverse process are for muscle attachments. The centrum forms a central
rigid body to the vertebral column. The neural arc encloses the spinal cord.

Structure, divisions and functions of vertebrae

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 a. Cervical Division

This is the neck region. Has small and short neural spine. First of the two cervices is called atlas
which supports the head and permits up and down movements of the head. The second part is
called the axis which enables the head to rotate.

b. Thoracic division

Its vertebrae of the ribs region.Has long backward pointing neural spines and small transverse
processes. Provides support to the ribs.

c. Lumbar division

The abdomen region. Has big centrum and neural spine for attachment of large muscles of the
back. It also has long and wide transverse processes. These bones permit bending, sideways and
rotation movement of the body.

d. Sacral Division

These are hip vertebrae. They have reduced neural arc and transverse processes.

e. Coccyx Division

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Tail bones. Has well-developed transverse processes fused to the pelvic girdle.

The ribs, sternum and rib cage

Each rib is a flattened curved bone. Ribs join the sternum through coastal cartilage for the first
seven ribs. The remaining five are floating ribs-they are not attached to the sternum. The space
inside the ribs where lungs and the heart are located is the rib cage.

Appendicular Skeleton

Consists of the limbs and limb girdles. The limbs are of two types that is the fore limbs and hind
limbs. The limb girdles are of two types, the pectoral girdle and pelvic girdle. Fore limbs are
attached to the pectoral girdles. Hind limbs are attached to the pelvic girdles.

Function of the Appendicular Skeleton

a. For locomotion and movement

b. Holding and grasping objects

JOINTS

A joint is a point where bones meet.

General structure of a joint

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Synovial membrane- secretes synovial fluid

Synovial fluid-acts as lubricant and contains nutrients

Articular cartilage-acts as a shock absorber

Ligament-holds the bones firmly together

Types of Joints

a. Immovable joints

These do not allow any movement. They are called sutures. Examples include bones of the skull
and of the girdles (pelvic and pectoral)

b. partially immovable joints

These show partial movements. Such joints include:

a. gliding joints- these allow movement by sliding over each other such as between bones
of the vertebrae, wrist and ankles
b. swivel joints-joints between the atlas and axis vertebrae

Movable Joints/Synovial joints

They are associated with synovial fluid and membrane. These include:

i. Hinge joints- movement is in one plane/direction (180 degrees). Examples are knee
and elbow joints. Able to bear heavy loads

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 ii. Ball and socket-a rounded head of one bone fits into a cup-shaped socket of another.
Allow movement in all planes. Unable to bear heavy loads.

Problems associated with joints

a. Rheumatoid arthritis: inflammation of joints due to trauma, infection, or age

accompanied by pain. This may lead to loss of mobility.
b. Gout: a red tender and swollen joint normally on the big toe. It is caused by high levels
of uric acid in the blood deposited at the joint.

The Muscle System

Muscles are made of elongated cells called muscle fibres that are able to contract and relax.
There are three types:

a. Skeletal muscles/Voluntary Muscles

These are also called voluntary/striated/striped muscles. They are attached to bones and are
associated with locomotion. Contract quickly and tire easily. They are also controlled by the
voluntary nervous system.

b. Smooth Muscles/Involuntary Muscles

They are also called involuntary/unstriped/unstriated muscles. They are found in the walls of
internal organs such as the gut and bladder. They are controlled by the autonomic nervous
system. They contract and tire slowly.

c. Cardiac muscles

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These are muscles of the heart. They are specialised striated muscles. They do not fatigue or tire.
They are also controlled by autonomic system.

How muscles and bones bring about movement

Muscles cause movement by contracting (shortening) and pulling at bones. Skeletal muscles are
attached to bones in pairs. When one skeletal muscle contracts, the other relaxes. The muscle that
contracts is called agonistic muscle while the muscle that relaxes is called antagonistic muscle.

Muscles that contract and bend or flex limbs are called flexor muscles e.g. biceps. Muscles that
contract and extend a limb are called extensor muscles e.g. triceps.

LOCOMOTION IN BIRDS

Locomotion in birds occurs in three ways: walking, swimming and flying

Flying

A bird overcomes force of gravity and remains afloat in the air. Birds fly by flapping wings and
gliding.

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Flapping wings

The flapping of wings is brought about by a pair of antagonistic muscles called pectoralis
muscles. Pectoralis minor is attached to the keel and top of the humerus. Pectoralis major is
attached to the keel and bottom of the humerus. When flying the wings are flapped. When the
wings are flapped up, the movement is called upstroke.

An upstroke

During upstroke the pectoralis minor contracts and pulls on the humerus, the pectoralis major
relaxes and the wings are pulled up.

When the wings are flapped down, the movement is called downstroke.

Pectoralis major contracts and pulls the humerus down and the wings are pulled down.

Gliding flight

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The wings are spread and used as aerofoils. The stream-lined shape of the wing is called an
aerofoil shape. The aerofoil allows air being faster on the upper surface hence low pressure and
slower on the lower surface hence high pressure. This results in high upward pressure (lift) and
lower downward pressure and gravity is overcome making the bird afloat.

Soaring flight

The bird spreads out its wings in soaring movements to allow upward air currents to lift the bird,
allowing it to gain height without moving its wings.

Bird Feathers

A feather consists of two principal parts, the axis or spine and the barb or side branch of the
stem. The axis consists of two principal parts the quill and the shaft. The barbs which form the
vane or fringe are linked to each other by pointed barbules or smaller barbs which are interlocked
by minute hooks.

Types of Feathers

i. Flight feathers

They are broad and flat feathers with strong and large shaft and quill. They are attached to the
wings-they help in flight. They prevent air from passing through them.

ii. Down feathers

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These are small fluffy feathers covering the body of the bird. They have small and weak shaft.
They keep the bird warm.

Feathers play an important role in a bird’s flight. Flight feathers overlap during down stroke to
prevent air flowing through them and create lift. During upstroke feathers open to allow air to
pass between them and less effort is needed to lift the wings. Contour feathers cover angular
parts of the body help to reduce drag by giving the bird a smooth aerodynamic form.

Bird tails help in stability and changing direction. When soaring, birds spread their tail feathers
to gain more lift. When landing birds turn their tails downward so that tails act as brakes.

Adaptations of birds for Locomotion

i. They are light in weight: they have light hollow skeletons, are toothless which
reduces their weight and have light feathers.
ii. Their skeleton is firm and rigid for attachment of flight muscles.
iii. They have efficient respiratory and transport systems. Birds breathe faster than other
organisms. This provides more oxygen for respiration hence more energy when the
bird is flying.
iv. The aerofoil shape of the wing help to create lift (an upward force) that counters
gravity in order to fly.
v. Birds have a stream lined body. This makes it possible for them to move in air with
less resistance to air currents.
vi. The bird has fore limbs called wings. Wings have feathers which create large surface
area to create lift.

LOCOMOTION IN FISH

Locomotion of a fish in water is by swimming. The structures used for swimming are fins,
scales, tail muscles (myotomes) and swim bladder.

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Caudal fin (tail fin)-causes propulsion (forward movement of fish). The tail has a pair of
muscles on either side called myotomes that contract to move the fish. When the muscles on the
left contract, the muscles on the right relax, the body then bend on the left side and vice versa.

Dorsal and ventral fins-control rolling of fish and yawing (the tendency to move from side to
side). They help the fish to be stable.

Pectoral and pelvic fins-control pitching (the movement of fish up and down)

Swim bladder-helps in buoyancy of the fish. When filled with air the fish becomes lighter and
floats. When emptied the fish becomes denser and sinks downwards.

Scales-reduce drag by producing a slimy substance and overlapping backwards.

Adaptation of fish for Locomotion

a. Fish are streamlined in shape to reduce drag or water resistance

b. They have fins that maintain stability and propel fish through water
c. They have tail muscles (myotomes) that contract to bring about movement
d. They have swim bladders which help fish to be very light (to control vertical movements)
e. They have scales which overlap backwards and produce slimy substance which reduce
drag or friction with water.

REVISION EXCERCISE

1. Name one locomotory structures each in fish and birds

2. Mention two adaptations for locomotion common in both fish and birds.
3. What is the advantage of the following in locomotion?
a. Scales that overlap backwards in fish.
b. Hollow bones in birds.

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 4. The figure below shows a cross section of the thorax. Use it to answer questions that
follow.

a. Mention the labelled X and Y.

b. Mention two vital organs located in cavity marked Z.
c. Give one region within region Z where lymph is found.
5. The diagram below shows a bird in flight. Use it to answer questions that follow.

a. Identify the type of stroke shown in the flight.

b. Explain how the stroke above occurs.
c. Explain how the shape of the wing helps to generate lift in the bird.
6. Describe the following types of joints
a. Gliding joints
b. Hinge joints
c. Sutures
d. Ball and socket joints
7. Give the role of the following fins in locomotion in fish.
a. Dorsal fin
b. Pectoral fins
c. Caudal fins

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 TOPIC SEVEN: REPRODUCTION
This is the process of producing new young organisms.

Types of Reproduction

a. Asexual reproduction

Producing new organisms from a single parent without male and female gametes.

b. Sexual reproduction

Producing new organisms through combination of male and female gametes.

Structure of the Chromosome

A chromosome is a thread-like structure located in the nucleus of the cell containing hereditary
information of the cell.

The chromosome is made up of proteins and DNA (deoxyribonucleic acid).

The DNA is made up of chemical compounds called nucleotides. The nucleotides are linked to
form a chain arranged like a twisted ladder called double helix.

Composition of Nucleotides

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 a. Sugar molecule called deoxyribose
b. A phosphate group
c. Bases – adenine (A), thymine (T), guanine (G) and cytosine (C). The bases control the
production of genes. The genes occupy a location on the chromosome called a locus.

Function of Chromosomes

a. They store hereditary information in form of genes.

b. They permit DNA to replicate or reproduce itself so that as the cell divide, each of the
new cells will contain all the necessary genetic information or code.
c. They contain genes that are responsible for production of proteins responsible for
directing life processes.

CELL DIVISION

This is the process whereby a cell divides to form two or more new cells.

Forms of Cell division

a. Mitosis
b. Meiosis

MITOSIS

It is a process by which a cell nucleus divides into two daughter cells containing sets of
chromosomes identical to the parent cell.

This type of cell division occurs in somatic cells or general body cells such muscle, blood and
hair cells.

Mitosis is called copying cell division because the daughter cells are identical to the parent cell.

STAGES IN MEIOSIS

Interphase

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This is a period of synthesis and growth i.e. DNA, mitochondria and centriole replicate.
Chromosomes exist as pairs of chromatids. Alot of energy is produced.

Prophase

Chromosomes shorten and thicken to become visible. Centrioles move to the opposite poles of
the cell. Nuclear membrane disappears. Spindle fibres start to form.

Metaphase

Chromosomes line up at the equator (mid-line). Spindle fibres attach to the centromeres of
chromatids.

Anaphase

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Spindle fibres shorten and separate chromatids into opposite poles. The cell starts to constrict.

Telophase

The chromatids reach the poles of the cell. The spindle fibres disintegrate. Nucleoli reappear.
Nuclear membrane reappears. Cytoplasm divides to form two daughter cells.

Importance of Mitosis

a. It ensures genetic stability-same number of chromosomes as in parent cells

b. Growth-increase in size due to increase in number of cells in an organism
c. Cell replacement and regeneration
d. Asexual reproduction such as in amoeba

MEIOSIS

The type of cell division which reduces number of chromosomes in a cell by half to form
gametes or sex cells. Meiosis is also called reduction cell division because it halves the number
of chromosomes in cells.

The number of chromosomes in normal body cell is diploid (2n) and in gametes is haploid (n).
Meiosis produces four daughter cells and occurs in two phases.

MEIOSIS PHASE 1

Prophase 1

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Chromosomes shorten and thicken to become visible. Homologous chromosomes pair up to form
bivalents. Bivalents are joined at several points called chiasmata where genetic material is
exchanged between chromosomes. The exchange of genetic material between chromosomes is
called crossing over. Crossing over creates genetic variation. Centrioles move to opposite poles.
Nucleoli and nuclear membrane disappear. Fibre spindle forms

Metaphase 1

Bivalents line up at the equator. Fibre spindles attach to the chromosomes.

Anaphase 1

Bivalents are separated by spindle fibres towards opposite poles.

Telophase 1

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Nuclear membrane reforms around the two sets of chromosomes. Cleavage start to form.
Nucleoli reappear. Two daughter cells with half number of chromosomes of parent cell are
formed.

MEOSIS 2

Meiosis 2 is similar to mitosis.

Importance of Meiosis

a. Sexual reproduction-produces gametes such as sperms and ova.

b. Causes genetic variation due to crossing over

Comparison of Mitosis and Meiosis

MITOSIS MEIOSIS
 Two daughter cells formed  Four daughter cells formed
 Daughter cells are identical to parent  Daughter cells not identical to parent
cell cell
 The number of chromosomes is  Number of chromosomes is halved
retained
 Chiasmata does not form hence no  Chiasmata forms and crossing over
crossing over may occur

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PARTS AND FUNCTIONS OF THE REPRODUCTIVE SYSTEM

Male reproductive system

Testes: these are the male gonads where sperms are produced. They are located in a sac called
scrotum. They produce sperms. They also produce a sex hormone called testosterone which
stimulates sperm production and controls male secondary characteristics.

Scrotum: it is a muscular sac in which testes are located. It hangs outside the abdominal cavity
where temperatures are lower to avoid damage of the sperms. It also protects the testes.

Seminiferous tubules: these are small tubules in the testes where sperms are produced.

Epididymis: it stores the sperms. Sperms mature in the epididymis.

Vas deferens/sperm duct: leads the sperms to the urethra.

Urethra: conduct urine and sperms through the penis

Penis: contain erectile tissue which has spaces that fill with blood during sexual excitement. The
penis deposits sperms into the vagina.

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Seminal vesicles, prostate glands and Cowper’s glands

Secretions from these glands contain

a. Mucus: which lubricates the vagina during sexual intercourse

b. Fructose: energy source for sperm
c. Alkaline solution: neutralises the acidity of nature of the urethra and vagina and making
sperms more mobile.

Female Reproductive System

Ovaries: female gonads-produce ova or eggs. They also produce hormones Oestrogen and
Progesterone.

Oviduct/Fallopian tube: leads ova from the ovaries to the uterus. It also site of fertilisation. Has
cilia that help to propel eggs to the uterus.

Uterus/womb: place for embryo implantation and development.

Cervix: is the narrow entrance to the uterus. It is normally closed by a plug of mucus and a ring
of muscles. During pregnancy the muscles of the uterus remain contracted to keep the baby in
the womb.

Vagina: it receives semen during intercourse. It is also a birth canal.

Vulva: the outside part of the female reproductive system. It contains the clitoris, labia majora
and labia minora.

Reproductive Cells (Sperms and Eggs)

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The sperm

The sperm is made of the head, middle piece and tail. The head contains the nucleus containing
haploid number of chromosomes. It also has an acrosome –a sac containing an enzyme called
acrosin that break part of the egg’s wall during fertilisation. The middle piece has mitochondria
that provide energy for sperm movement. It has a tail for swimming towards eggs. It is smaller
than an egg.

The egg

It does not have a tail. The cytoplasm contains food reserve. The ovum is unable to move or
swim on its own. It is propelled by cilia in the fallopian tube.

Fertilisation and Conception

Fertilisation is the fusion of the male and female gametes (ovum and sperm nuclei) to form a
zygote. For fertilisation to take place the ovum must meet the sperm. Sperms are deposited in
the vagina of a female in a process called copulation, coitus or sexual intercourse. During
sexual intercourse the erect penis is inserted into a vagina moved back and forth reaching an
orgasm and release semen containing sperms into the vagina. The release of semen containing
sperms is called ejaculation. Once the sperms are ejaculated into the vagina, they swim and are
propelled through the cervix and into the oviducts where they meet an egg. Only one sperm fuses
with an ovum.

When an egg has been fertilized the egg membrane hardens to prevent other sperms from
entering the ovum. The zygote starts to divide mitotically to form a hollow mass of cells called

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blastocyst. The outer layer of cells develops into two membranes called the chorion and amnion.
These membranes surround and protect the embryo till birth. The chorion is the outer membrane.
Continued cell division forms a mass of cells called a morulla. It develops finger-like
projections called villi with which it attaches to the endometrium 6-9 days after fertilisation. It is
then referred to as an embryo. The villi is used for absorbing nutrients from the endometrium.
The whole process from from fertilisation to implantation is called conception. The woman is
described as pregnant.

The Role of Hormones in Oogenesis (egg development) and the Menstrual Cycle

Menstruation is the shedding of the uterine lining and blood through the vagina. These events
are cyclic which means the whole sequence repeats itself once every month in what is called
menstrual cycle. It occurs every 28 days of the month.

The cycle begins with the production of the follicle stimulating hormone (FSH) by the pituitary
gland. The FSH travels in the blood to the ovaries. The FSH stimulates the growth of follicles in
the ovary. One of the follicles develops into a Graafian follicle. To form the Graafian follicle, the
follicle forms a space, accumulates some fluids and increases in size. The fluid-filled sac and the
developing ovum inside it is called a Graafian follicle.

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The follicles secrete a hormone called oestrogen. The oestrogen has two targets, the uterus and
the pituitary gland. In the uterus oestrogen stimulates the growth and repair of the lining of the
uterus shed during the previous menstruation.

In the pituitary gland Oestrogen inhibits FSH production and stimulates production of
luteinising hormone (LH). Luteinising hormone stimulates ovulation (egg release) and
formation of the corpus luteum. The Graafian follicle changes into a yellowish body called a
corpus luteum.

The corpus luteum produces a hormone called progesterone. Progesterone targets the uterus
and pituitary gland. In the uterus progesterone maintains the thickening of the endometrium.

The pituitary glands it inhibits FSH and LH production. When the egg is not fertilized, the
corpus luteum starts to degenerate about 28 days into the cycle.

The levels of progesterone and oestrogen decline so there is no inhibition of FSH production.
The endometrium of the uterus starts to break up leading to accumulation of blood in the uterus.
The blood flows out of the uterus through the vagina for about 5 days. This is called
menstruation.

Ovulation

This is the release of ovum from the ovary. The LH triggers ovulation. For ovulation to take
place a mature Graafian follicle moves to the surface of the ovary.

It forms a bulge on the ovary surface. It then ruptures (bursts) to release the ovum.

Pregnancy

It is also called gestation period. In humans it lasts for about 38-40 weeks. During this time two
major structures are formed (the placenta and the amnion). Placenta is an organ found only in the
category of mammals called placentals. At the time of fertilisation, the ovum is the size of a full
stop. The first organ to form is the heart followed by the brain during the first five weeks. After

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2 months the embryo develops limbs with fingers and toes, other organs and a well formed face.
At six months the embryo develops hair, finger and toe nails and milk teeth develop in the jaws.

The structure and Function of the Placenta

The placenta begins to develop at implantation. It is a thick disc-like structure with finger like
projections called villi that extend deep into the wall of the uterus. The uterus increases in size
as the embryo grows and it weighs 500g at the time of birth. The foetus is attached to the
placenta by the umbilical cord. It is surrounded by the amniotic sac which is filled with amniotic
fluid. The blood of the foetus and the mother do not mix.

Why the Blood of the Mother and Foetus Do not Mix

a. Male children would be damaged by the level of female hormones in the mother’s blood
b. The higher blood pressure of the mother can damage the foetus
c. To prevent transmission of infections from the mother to the foetus.
d. To prevent agglutination of blood of the mother and foetus due to different blood groups.

Functions of the Placenta

a. It allows exchange of substances between mother and foetus. Water, nutrients, antibodies
diffuse from the mother to foetus through umbilical vein and excretory products (such as
CO2 and urea) diffuse from the foetus to the mother through the umbilical artery.
b. It helps physical attachment of the foetus to the walls of the uterus
c. Protects the foetus from the mother’s immune system and dangerous fluctuations in the
mother’s blood.
d. It acts as an endocrine gland by producing progesterone, oestrogen and Human
chorionic gonadotropin (HCG-which is the basis for pregnancy test)

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The umbilical cord

It is a tube or cord that connects the foetus to the placenta. The umbilical cord enables the
exchange of substances between the mother and her foetus. The umbilical cord contains one
large vein which delivers oxygen and nutrients to the foetus from the mother and two large
arteries which carry wastes from the foetus to the mother.

BLOOD IN THE UMBILICAL ARTERY BLOOD IN THE UMBILICAL VEIN

High concentration of urea Low concentration of urea
Low concentration of glucose High concentration of glucose
High concentration of carbon dioxide Low concentration in carbon dioxide
Low concentration of amino acids, fatty High concentration of amino products, fatty
acids and glycerol acids and glycerol
Low concentration of oxygen High concentration of oxygen
Dark red in colour Bright red in colour

The Amnion

The amnion is the membrane that surrounds the foetus. It secretes a fluid called amniotic fluid.
The amnion holds the baby in position. The amniotic fluid performs the following functions:

a. Controls/regulates the body temperature of the foetus by acting as an insulator between

the foetus and its mother. Prevents temperature fluctuations.
b. It protects the foetus from external mechanical/physical forces and acts as a shock
absorber.
c. It lubricates the birth canal (vagina) during birth by making it slippery so that the baby
comes out quickly.

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The Process of Birth

In the last stages of pregnancy progesterone hormone levels drop in the blood. The pituary gland
produces a hormone called oxytocin. Oxytocin causes contractions of muscles of the walls of
the uterus.

The level of oestrogen increases, oestrogen makes the uterus more sensitive to oxytocin. The
waves of contraction of these muscles create pain commonly called labour pain. The
contractions provides a force that starts to push the foetus from the uterus to the cervix. Birth
occurs in three stages:

First Stage: the cervix dilates to about 10cm wide. The plug of mucus that blocks the cervix
comes away and passes out of the vagina. This is called show and consists of sticky pinkish
mucus. The chorion and amnion burst and release amniotic fluid through the vagina and makes it
slippery.

Second stage: the baby is pushed downwards through the cervix into the birth canal. The birth
canal is elastic and it widens allowing the baby to be born. The baby is born head first, if its
bottom first then its abnormal and the birth is called breech birth. The placenta is cut to separate
the baby from the placenta. The baby takes its first breath and the lungs become functional.

Third stage: the placenta comes out. It is also known as after birth.

TWINS

There are conditions where two children are born at a single birth. There are three types of twins:

i. Identical twins
ii. Fraternal twins
iii. Siamese twins

Identical Twins

They are also called monozygotic twins. A single ovum is released from the ovary. The ovum is
fertilised by one sperm to form a zygote.

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 The zygote divides by mitosis to form two zygotes. The zygotes develop into two identical
embryos. Each embryo develops into a baby. Twins are identical because both of them have the
same set of genes and are of the same sex.

Fraternal/Non-identical twins

These are produced when a woman has released two eggs and both eggs are fertilized to form
zygotes. Two ova are released from the ovary at the same time. Each ovum is fertilised by a
different sperm to form zygotes. Each zygote forms an embryo which develops into a baby. The
twins are non-identical because they contain different sets of genes. They may be of the same sex
or not.

Conjoined or Siamese twins

They are produced from one fertilized egg. In the course of dividing to form identical twins, the
zygote fails to completely divide hence results into closely connected children. They usually
share vital organs such as the heart, lungs, the liver, etc.

Lactation/Breast Feeding

Lactation is the process of milk production for feeding young babies. Milk is produced by
mammary glands under the influence of proclactin. The first milk produced by the mammary is
colostrum. The colostrum is rich in proteins, lactose, antibodies, fats, calcium and vitamins.

Importance of Breast Feeding

a. Breast milk contains all nutrients needed for growth and development of the baby
b. Colostrum contins antibodies that provide natural passive immunity to the infant against
diseases.
c. Breast milk is perfectly marched to human child at the right temperature.
d. Breast milk is generally sterile and safe to the baby
e. Improves emotional and psychological condition between mother and baby
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CONTRACEPTION

This is the prevention of conception. It can be achieved by natural or artificial means. Some of
contraceptive methods include:

Condoms/sheath

Sheaths made of thin rubber. There are both male and female condoms which prevent sperms
being released into the vagina.

Spermicides-chemicals applied as a cream, gel or foam which kills sperms

Diaphragm or Cap

This is a thin rubber barrier with a springy outer ring to ensure a close fit onto the cervix.
Prevents sperms from entering uterus.

Intra-uterine device (IUD)

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Small copper/plastic/steel devices are put into the uterus through the vagina. They prevent
implantation. The device may come out and may cause bleeding or discomfort. It is highly
effective.

Contraceptive pill

The pill contains hormones oestrogen and progesterone. It prevents the development of egg and
ovulation from taking place stopping production of FSH during menstrual cycle.

Vasectomy

The vas deferens (sperm ducts) of the male is cut so that sperms cannot reach the vagina. It has
no side effects and is difficult to reverse.

Tubal litigation

This involves the cutting of the oviduct in females.

This hinders the movement of the ova through the oviduct. It is a permanent method hence it is
effective.

Norplant

This is the placement of a contraceptive pill just beneath the skin on the upper side of the arm of
the woman. The contraceptives are released continuously for a period of up to five years. It can
be removed by a medical person when the woman wants to bear children. It is reliable and very
effective.

Abstinence

Sexual intercourse is avoided. Its failure rate is zero. It’s very effective.

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PROBLEMS ASSOCIATED WITH REPRODUCTION

a. Sterility

This is the permanent inability of an individual to reproduce. It may be caused by STIs or

accidents. It may involve poorly developed organs or failure of reproductive organs to produce
gametes.

b. Sexually Transmitted Infections

These infections include HIV & AIDS, Gonorrhoea, Syphilis, Chancroid, Genital warts, etc.
They may lead to sterility, blindness and death.

c. Maternal mortality

This is also called maternal death. It refers to all deaths of women that are related to child
bearing. The deaths occur either during the period of pregnancy or at the time of giving birth.

REVISION EXERCISE

1. Give any three differences between mitosis and meiosis.

2. Describe any four adaptation of the placenta to its functions.
3. Give two importance of the amniotic fluid to the baby in the womb
4. Mention any three importance of breast feeding
5. Suggest why the temperature of the foetus is above that of its mother?
6. Why is it important that the blood of the mother and foetus do not mix?
7. Give three problems associated with reproduction.
8. The figure below is a diagram of a male reproductive organ showing a contraceptive
method.

a. Name the parts A and B and state one function for each.
b. State the method of conception shown in the diagram above and explain how the method
works.

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 c. Is it possible for a man who is using this method of contraception to transmit HIV to
another person? Explain your answer.
9. The graph below shows the levels of the hormones oestrogen and progesterone in a
woman during a month. Use it to answer questions that follow.

a. When are the levels of oestrogen and progesterone equal?

b. Give one function for each of these hormones (oestrogen and progesterone).
c. What evidence from the graph shows that an ovum was fertilised?
d. Which process occurred between day 0 and day 5?
10. Mrs. Phiri claims that Peter her son and Joyce, her daughter are identical twins. Briefly describe
how Mrs. Phiri’s claims are wrong.
11. Give any two functions of the placenta.

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 TOPIC EIGHT: HUMAN DISEASES
A disease is a disordered state of the body of an organism.

Non-Infectious Diseases

- Nutritional diseases
- Genetic diseases
- Mental diseases
- Ageing diseases
- Human induced diseases (due to alcohol or drugs)

Infectious diseases

They are also known as parasitic diseases. They are caused by other living organisms such as
viruses, bacteria, fungi, protozoa and worms. The diseases are often communicable because they
can be transmitted from one person to another.

Diseases are transmitted by organisms called vectors. A vector is an organism that carries
disease causing organisms. A person who carries pathogens but he or she is not sick is called a
carrier.

Incubation period of a disease is the time between catching a disease and the appearance of its
symptoms.

Modes of transmission of Diseases

a. Air-diseases spread through the air and are called airborne diseases such as T.B. and
common cold.
b. Water-diseases spread by contaminated water and they are called water-borne diseases
such as cholera and typhoid.
c. Food – spread by contaminated food such as cholera and dysentery.
d. Vectors-spread by living organisms such malaria and trypanosomiasis
e. Direct contact-diseases spread by direct contact with an infected person or their clothing.
These are called contagious diseases.

DISEASES CAUSED BY BACTERIA

A. TUBERCLOSIS (T.B.)

T.B. of the lungs is caused by bacterium called mycobacterium tuberculosis. T.B. of the bones
is caused by bacterium called mycobacterium called mycobacterium bovis.

Mode of Transmission

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 - droplets from breathing or sneezing (airborne)
- dry infected sputum in particles of dust
- T.B. of the bones is transmitted through drinking contaminated milk.

Signs and Symptoms of T.B.

- General weight loss and fatigue

- Fever
- Persistent coughing
- Chest pains
- Sweating at night
- Sputum may contain blood

Prevention of T.B.

- Drink clean boiled milk.

- Always stay in well ventilated homes.
- Avoid overcrowding.
- Immunization of children with BCG vaccine (BCG: Bacillus Calmate Guerin).
- Isolate the patient.

Treatment of T.B.

- Use drugs such ethambutal, isoniazid streptomycin and rifampicin.

B. PNEUMONIA

It is caused by pneumonococcus streptococcus bacteria. It affects the respiratory tract. It causes

production of fluid which collects in the alveolus. The lungs become filled and have no air hence
prevents exchange of gases in lungs.

Mode of Transmission

- It is spread by inhaling contaminated air. It is an airborne disease.

Signs and symptoms

- Fever
- Headache
- Coughing
- Chest pains
- Difficulties in breathing

Prevention of Pneumonia

- Avoid overcrowding

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 - Live in well-ventilated homes.
- Vaccination.

Treatment of Pneumonia

- Use antibiotics such as erythromycin, penicillin, and tetracycline.

C. CHOLERA

It is caused by bacterium called vibrio cholerae. The bacteria can survive in areas of low oxygen
like in small intestine.

Mode of transmission

- Fecal contamination
- Food contamination
- Handling of contaminated objects and putting dirty fingers in the mouth.
- Vectors like flies from human faeces to food.
- Through contaminated water

Signs and Symptoms of Cholera

- Severe diarrhoea due to toxins produced by bacteria

- Abdominal pains
- Watery rice-like stools
- Severe vomiting
- Dehydration and loss of mineral salts

Prevention of Cholera

- Correct disposal of faeces

- Wash hands after using the toilet
- Wash hands before eating
- Treating water before drinking such as boiling or chlorination.
- Education awareness campaigns on hygiene
- Covering food to prevent contact with flies
- Wash raw food with clean water before eating

Treatment of Cholera

- Use of antibiotics
- Administering of ORS to the patient
D. TYPHOID

It is caused by bacteria called salmonella typhi. It affects the alimentary canal, spreading to the
lymph and blood, lungs, bone marrow and spleen.
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Mode of Transmission

- Contaminated food and water

- Contaminated objects
- Vectors-flies or carriers

Signs and Symptoms

- Mild fever
- Slight abdominal pain
- Ulceration and rupture of the intestine
- Diarrhoea
- Constipation

Prevention of Typhoid

- Vaccination
- Proper disposal of faeces
- Treatment of water
- Thorough cooking of food to kill bacteria
- Wash fruits and vegetables before eating them

Treatment of Typhoid

- Use of antibiotics

DISEASES CAUSED BY VIRUSES

A. COMMON COLD

It is caused by a variety of viruses.

Mode of Transmission

- Transmitted by droplets through coughing, sneezing, from infected people.

Signs and Symptoms of Common Cold

- Running nose
- Sneezing
- Fever
- Sore throat

Prevention of Common Cold

- Avoid overcrowded areas

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 - Keeping rooms well-ventilated

Treatment

- Taking prophylactic drugs

- Taking a lot of fluids
B. INFLUEZA OR FLU

It is caused by the influenza virus

Mode of transmission

- It is spread by droplet infection through the air

- It can also be spread by touching items with the virus and touching the mouth

Signs and Symptoms

- Sudden fever and headache

- Sore throat and muscle pains
- Nausea and vomiting
- Dizziness

Prevention

- Use back of hand or cloth when sneezing

- Vaccination

Treatment of Influenza

- Use antiviral drugs in severe cases

- Drinking hot drinks
- Use cough drops
- Use drugs that lower the fever
 There are no drugs for most of influenza.
C. MEASLES

It is caused by two viruses:

1. Rubella virus: causes German measles

2. Rubeola virus: causes ordinary or red measles

It occurs mainly in children.

Means of transmission

- By droplets

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 - Through contaminated eating utensils and clothes

Signs and Symptoms of Measles

- Sore throat
- Running nose
- Coughing and fever
- Small white spots in mouth called koplik spots
- Skin rash, swollen glands, and swollen eyes.
 Complications that may happen include blindness and deafness. It may also result in
sterility when it affects the testes and the ovaries.

Treatment

- There is no specific treatment for the disease

Prevention

- Immunization or vaccination.

NB: Survivors of measles get natural active immunity. They can never be affected by the disease
again.

D. AIDS

Meaning of AIDS

A: Acquired-means passed from one person to another

I: Immune-means the body’s defence or protection against infections

D: Deficiency-means weakening of the body’s defence against diseases

S: Syndrome-a group of diseases that come when the immunity is weak

AIDS is caused by Human Immunodeficiency Virus (HIV). The body destroys the body’s
immune system. The virus infects and destroys certain types of white blood cells called T-helper
Lymphocytes. The T-helper cells cannot stimulate killer cells to fight infection. This breaks
down the immunity of the body.

Mode of Transmission of AIDS

- Through sexual intercourse with an infected person

- From infected mother to child during birth
- Sharing of piercing objects such as needles, syringes and razor blades
- Blood transfusion with infected blood

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 - Through close contact between infected and non-infected person through cuts or open
wounds

Signs and Symptoms of AIDS

- Sudden loss of weight

- Lymphoma (cancer of the lymphatic system)
- Chronic diarrhoea for more than a month
- Persistent cough
- Shingles
- Fever
- Swollen lymph glands or lymph nodes
- Loss of appetite

Prevention of the Disease

- Abstinence from sex before marriage

- Practicing protected sex
- Being faithful to one partner
- Screening blood for HIV before blood transfusion
- Avoid sharing piercing objects such as blades, needles and syringes.

Treatment

- Use antiretroviral drugs (ARVs) which slow down the spread of the virus in the body.
AIDS has no cure.
E. CHICKEN POX

This is a skin disease caused by a virus called varicella zosta.

Mode of Transmission

- Through air droplets

- Contact with infected person and their clothes

Signs and Symptoms

- Rashes on the skin

- A lot of itching on the skin rashes
- Mild fever

Treatment

There is no specific treatment.

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Prevention of Chicken Pox

- Through vaccination or immunization

A person who recovers from the disease gets natural active immunity. They can never be
affected by the disease again.

DISEASES CAUSED BY PROTOZOA

A. MALARIA

Malaria means bad air as it was believed that it was caused by contaminated air.

Malaria is caused by a parasite called plasmodium.

Mode of Transmission

The malaria parasite is transmitted by a female anopheles mosquito.

When the female anopheles mosquito bites an infected person, it passes saliva down the
proboscis to prevent blood clotting before it sucks up the blood. The plasmodium remains in its
salivary glands. When the mosquito bites a healthy person it injects the plasmodia present in its
saliva into the blood stream of a healthy person and the person becomes infected.

Effects of Plasmodia on the Host

The plasmodia multiply in the liver. Then invade red blood cells. They reproduce in red blood
cells and cause the cells to burst releasing more plasmodia. The bursting of red blood cells by
plasmodia may cause anaemia. When red blood cells burst toxins from plasmodia are also
released. The toxins and damaged red blood cells cause symptoms of malaria.

Signs and Symptoms of Malaria

- High fever
- Headache
- Sweating
- Convulsions and coma if the parasite attacks the brain
- Nausea
- Anaemia
- Little deeply coloured urine

Prevention of Malaria

- Sleeping under mosquito nets

- Draining stagnant water-where mosquitoes breed
- Spraying oil on stagnant water which suffocates larvae and pupa of mosquitoes

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 - Clearing bushes near and around residential areas
- Introducing ducks and fish in ponds or lakes to eat mosquito larvae
- Using insecticides to kill mosquitoes
- Wearing long sleeved clothes especially at night
- Using mosquito repellants

Treatment of malaria

- Using drugs such as artemesinin, chloroquine, fansidar, lumefantrine artemether.

B. SLEEPING SICKNESS/TRYPANOSOMIASIS
- It is caused by protozoon called trypanosome rhodesience.

Mode of Transmission

It is transmitted by tsetse flies when they bite infected people or cattle and later bite healthy
people.

Trypanosome releases chemicals which go to the brain causing a person to become

unconscious hence sleeping sickness.

Signs and Symptoms

- Fever and headaches

- Enlargement of lymph nodes, spleen and liver
- Muscular spasms and frequent sleeping
- Emaciation: thinness of the body
- Fever

Treatment

- Use drugs such as pentamidine

Prevention

- clearing bushes
- spraying insecticides
- releasing sterile males

C. AMOEBIASIS (AMOEBIC DYSENTRY)

It is caused by protozoon Entamoeba histolytica.

Mode of Transmission

- It is transmitted by houseflies, uncooked food and unhygienic food preparation.

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Signs and Symptoms

- Fever
- Nausea and vomiting
- Diarrhoea and blood in stools

Treatment

- Use drugs such as metronidazole.

Prevention

- Hygienic food handling and preparation

- Control of flies
D. ELEPHANTIASIS

Elephantiasis is not caused by protozoa but a type of round filarial worm wuchereria bancrofti.

The worm lives in the circulatory and lymphatic system. It is transmitted by a bite from the culex
mosquito. The worm enters the lymphatic vessels and blocks them. This causes the lymph to
accumulate in that part of the body. This causes the affected part to swell to large proportions.

Signs and Symptoms

- Massive swelling on legs and arms

- It may also lead to swellings of the scrotum and breasts

Control and prevention

a. Mosquito control
b. Treatment using appropriate drugs

DISEASES CAUSED BY FUNGI

A. RINGWORM

It is caused by a fungus called Tinea. It is a contagious disease.

Mode of Transmission

- Direct contact with infected heads

- Using infected combs or shaving equipment
- Sharing head brushes and hats

Signs and Symptoms

- Round grey patches on the head and face

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 - Itching on the grey patches
- Hair loss on the patches

Treatment

- Use fungicide creams and tablets

- Drugs such as griseofulvin

Prevention of Ringworm

- Hygiene in care of hair

- Avoid sharing of combs, brushes and hats
B. THRUSH/CANDIDIASIS

It is caused by a fungus called candida albicans. It can occur in the mouth, vagina and
intestines. It may arise due to changes in acidity in the vagina in females during pregnancy or
diabetes. Newborn babies can be infected in the mouth during birth.

Mode of transmission

- It is transmitted mainly through sexual intercourse

- From mother to child during birth

Signs and Symptoms

- Fluffy white patches on infected area

- Red inflamed skin under the patches
- Severe irritation

Control and prevention

- Drugs used as lotions, creams or pessaries (for vaginal infections)

- Use drugs such clotrimazole
C. ATHLETE’S FOOT

It is a fungal disease that affects feet in human beings. It occurs due to:

- Wearing closed shoes for a long time

- Keeping the feet wet for a long time
- Excessive sweating in the feet.

It common in areas with warm wet weather.

Mode of transmission

- Contact with infected feet, floors, mats on which people walk barefoot.

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 - Contact with shoes of infected people

Signs and Symptoms

- Itching feet
- Pain between toes
- Swollen, peeling and craved skin between toes

Prevention

- Proper drying of feet after bathing

- Use sandals in public showers
- Change socks frequently

Control

- Treatment with antifungal drugs such griseofulvin in form of powders and creams.

PREVENTION AND CONTROL OF DISEASES

a. Water treatment: this is the process of removing undesirable properties of raw water to
make it safe for human consumption. Water treatment kills pathogens such as bacteria
and flukes hence preventing spread of diseases. There are many methods of water
treatment such as filtration, boiling and using chemicals such chlorination.
b. Proper disposal of human and domestic wastes: this includes using latrines, toilets and
sewage treatment and rubbish pits. This helps in prevention of diseases such as cholera,
typhoid and amoebiasis.
c. Personal hygiene: this involves observing personal cleanliness such as washing hands
before eating food and after using toilet, washing the body daily, covering food and
brushing teeth. Personal hygiene reduces risk of infection.
d. Vector control: control of vectors such as tsetse flies, mosquitoes and worms prevents
the spread of diseases.
e. Food treatment and preservation: this is the practice of processing food to prevent
spoilage and food poisoning. Microbes decompose unprocessed food and when microbes
are consumed together with food they can cause serious illness or death. Preserved and
treated food has less risk of ill-health as microbes are unable to grow and multiply on
preserved food. Some ways of food preservation and treatment include smoking, salting,
drying, freezing, canning, pasteurization and radioactive preservation.
f. Health services: they provide treatment of diseases to prevent spread of diseases,
provision of safe water and sanitary services, health education and maternity services.
Health services help to prevent spread of diseases.

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REVISION EXERCISE

1. Explain the following

a. Vector
b. Incubation period of a disease
c. Two ways by which parasitic bacteria cause disease.
2. The figure below shows the head of a child with an infection. Use it to answer questions
that follow.

a. Name the infection.

b. Name the causative agent of the infection.
c. Give one way of preventing the infection.
3. Describe how plasmodia reproduce inside an infected person.
4. Explain the relationship between anemia and malarial infection.
5. Describe how HIV infection affects the immunity of a person.
6. Describe the symptoms of the following diseases
a. Typhoid
b. Malaria
c. Tuberculosis
d. Pneumonia
7. Describe any five ways of disease prevention and control.
8. Mention diseases whose mode of transmission is
i. Air
ii. Water
iii. Food
iv. Vectors
v. Direct contact

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 TOPIC NINE: HUMAN POPULATION
Population refers to the total number of organisms of one species living in a given place.

Population Growth

This refers to the increase in the number of individuals in a given area over time.

Population Growth Curves

These are graphs that show the relationship between population and time. They show how a
population of a given place grows over time. There are two types of population growth curves:

i. J-curve
ii. S-curve

The J-Curve

This is a curve that assumes the shape of the letter J when population of a given place is plotted
against time. The J-curve shows that in earlier years population increased slowly and in later
years population increased rapidly. The rapid increase in population is called exponential
growth.

Reasons for the Increase in Human Population as Shown by the J-Curve

i. Medical revolution: advances in medicine and sanitation have improved control of

infectious diseases hence less people are dying of diseases.

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 ii. Agricultural revolution: this has improved food production through introduction of
better methods of farming. Less people are now dying of hunger.
iii. Industrial revolution: the development of machinery increased agricultural efficiency
and improved housing. More people earned enough money to afford larger families.

The S-Shape

This is a curve that assumes the shape of letter S when population of a given place is plotted
against time. In a new environment, the population density of an organism increases slowly
initially as it adapts to the new environment, then it increases rapidly approaching an exponential
growth rate until it reaches zero. At the rate of zero the rate of reproduction equals the rate of
death. Then growth rate start declining due to overpopulation as organisms compete for
resources. The S-shape is related with populations of micro-organisms.

Factors Affecting Human Population Growth

a. Birth rates and fertility Rates

Birth rate refers to the number of children born alive per year per thousand people in a
population. Fertility rate is the number of children born alive per 1000 women in a year in
women within the child bearing age. More births than deaths lead to rise in existing
population. Birth rates and fertility rates are affected by the level of education of parents,
value given to children, cost of living, infant mortality rates, average age of marriages,
availability of birth control methods and religious beliefs.

b. Death rates

This is number of deaths per thousands of a population. When death rates are greater it leads to
decrease of existing population. When deaths equal births the population remains the same.
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 c. Population age structure

This refers to the age-sex composition of a population. This structure may be shown in form of a
population pyramid. The pyramid shows:

i. Age-sex composition divided into 5 year ages.

ii. Percentages of males and females in each group.
iii. Changes in birth and death rates.
iv. Population of young and old people.

Pyramid of England above has a narrow base widened middle and a tapering off top. It indicates:

- Low birth rates

- Low death rates
- Long life expectancy
- An ageing population as there are more elderly than young people.

Pyramid of Malawi has a wider base with a tapering top. It indicates:

- High birth rates.

- High death rates.
- Short life expectancy.
- Decreasing number of people as you go up the pyramid.
- A youthful population as there are more youths than older people.

Youthful population indicates that more people are giving birth hence greater increase in
population.

d. Urbanisation

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This is the shift of population from rural areas to cities in search for greener pastures. This leads
to an increase to urban population because people move from rural areas to urban areas to work
in industries, companies and shops for a living.

e. Migration

It is the movement of people from one place to another .If it is into country, it is called
Immigration and Emigration is outside movement from the country –immigration increases
population and emigration decreases population.

WAYS OF CONTROLLING RAPID POPULATION GROWTH (HUMAN)

a. Awareness campaign on disadvantage of large families.

b. Provision of health and contraceptives services.
c. Enacting and enforcing minimum age child labour laws.
d. Conservation of resources

PROBLEMS ASSOCIATED WITH RAPID POPULATION GROWTH.

a. Depletion of resources

Rapid population results to depletion of available resources such as land, water, forests
and food. The remaining resources become limited and expensive.

b. Pressure on social services.

Social service like police, hospitals would not cater for all the people hence very long
queues in hospitals and inability of the police to provide adequate security and
overcrowding in public hospitals. The social services facilities are available but are not
adequate for the large number of people living in a given place.

c. Spread of diseases

Infectious diseases spread rapidly where people live in overcrowded areas. Diseases like
T.B. and AIDS spread easily in highly populated areas due high rate of interaction
between individuals.

d. Pollution

The higher the population the greater the volume of waste produced hence the greater the
rate of environmental pollution. High population growths result in increase in pollution of
water, air and land.

e. High unemployment levels

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 High population growth results in increase in people looking for jobs and jobs become
scarce. This results in increase in crime as those who are unemployed engage in crime to
make ends meet.

CONTROLLING PROBLEMS ASSOCIATED WITH RAPID POPULATION GROWTH

a. Reducing Birth Rates

This can be done by using birth control measures and information on contraceptive on all women
at reproductive age.

b. Conservation of Resources

This ensures availability of resources to sustain the population. This helps to control depletion of
resources. Conservation of resources ensures continued availability of fish, water, etc.

c. Improving Sanitation

Sanitation can be improved by developing proper housing systems, efficient sewage system and
waste recycling or disposal projects.

d. Reducing Over Consumption

Avoid over consumption of resources such as food by avoiding waste and over-preparation of
food.

REVISION EXERCISE

1. Explain the factors that affect human population growth in Malawi.

2. Discuss five problems associated with high population growth and provide a solution to each
problem.
3. The figure below is a diagram of a population graph. Use it to answer questions that follow.

a. Describe the shape of the graph from 1400 to 2000.

b. Explain the shape of the graph from 1400 to 2000.
4. Describe factors that affect human birth rates and fertility rates.

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