ORDINARY LEVEL NOTES

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SAFETY, CAREERS AND BRANCHES IN BIOLOGY

Identify causes of accidents in the laboratory

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Causes of accidents in the laboratory are
1. Fires from use of Bunsen gas/ methylated spirit burners
2. Fumes such as chlorine and ammonia produced from chemical reactions
3. Skin burns from strong acids and bases
4. Handling of microorganism that can cause infection
5. Improper handling of apparatus such as glasses, razor blades and needles
6. Electricity
7. Handling hot liquids such water
During an experiment accidents may occur. Therefore a student is required to know safe
procedures and lab rules when carrying out an experiment.

Outline laboratory safety rules

 You should not be in the laboratory without the teacher
 You must always follow the teacher’s instructions
 You must not eat in the laboratory
 You should not run in the laboratory
 You must report any breakages or spills in the laboratory
 Know the safety procedures in case of accidents such as fires
 Never touch, smell or taste a chemicals without the permission of your teacher
 Never mix chemicals for fun as they could explode
 Dispose chemicals as instructed by your teacher
 Wash your hands after handling chemicals or microorganisms

Fire drills
A fire drill is a practice of what to do in case there is fire in the building. Fire drills must be
practiced several times a year. An alarm bell will ring first. When the alarm rings people must
stop whatever they are doing and in calm and orderly manner walk out of the building along a
predetermined route to a safe place. When at the safe place the teacher must take a roll call to
check if there if all student are out of the building. It is important that following be present in the
lab;
 A bucket of sand to douse the fire with sand
 A fire extinguisher to put out fire

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  A fire guard must be prepared around the laboratory
 Local emergency numbers of fire fighters and doctors must be displayed on the wall in
the laboratory
 Presence of a First Aid kit and know how to use it
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Safety and fumes

1. Experiments that produces poisonous fumes such as chlorine or acidic fumes must be
carried out in fume cupboard.
2. Keep the windows closed or carry the experiment out of the laboratory
3. Gas tapes must be closed when not in use and always close Bunsen gas burner after use.

Branches of Biology: identify various branches of Biology

Biology is the study of living organisms. Because Biology is so broad and diverse that no one
can study everything, it is therefore divided into various branches or fields.

Careers in Biology
 Medicine- doctor, laboratory scientist, clinicians, nurse

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  Research Scientist
 Ecologist
 Dieticians
 Conservationist
 Botanist Page | 4
Safety labels and symbols
Safety symbols are universally recognized. The enable you to understand the potential hazards
you face simply by looking at the posted symbols.

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 TOPIC 2: CHEMICALS OF LIFE

Water
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Water is one of the most important molecules of life. It makes up 70% of our bodies. It is
made up of 2 molecules of hydrogen and 1 atom of oxygen. Water is a polar molecule i.e. it
has both positively charged and negatively charged areas. Water is made up of two positively
charged hydrogen atoms and one negatively charged oxygen atom.

As a result of this polarity (the uneven distribution of charges), adjacent water molecules are
attracted to and become bonded to each other. The slight positive charge of a hydrogen atom
of one molecule is attracted to the slight negative charge of an adjacent oxygen atom. A
hydrogen bond forms between them.

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 Relate the properties of water to its uses in living organisms and as a habitat for living
organisms

1. It is transparent – This allows sunlight to penetrate and reach aquatic plants causing
photosynthesis. Aquatic animals such as fish can live in water as they can see in water. Page | 7
2. It is a solvent- Solutes such as food molecules can be dissolved and transported in
solution around the body. Enzymatic reactions occur in the medium of water.
3. It is a reagent- Water acts as reagent in the process of photosynthesis to make
carbohydrates. Water is a reactant in certain chemical reactions in the body, such as the
hydrolysis of food molecules during digestion.
4. It has a high specific heat capacity- It takes a lot of heat absorption from the
environment to raise a kilogram of water by 1oC. This means the body does not quickly
change in temperature with rising temperature in the environment allowing enzymes to
continue to operate. Water bodies such as oceans and rivers don’t change in temperature
suddenly with the increasing temperature of the environment allowing aquatic organisms
to adjust or adapt.
5. High latent heat of vaporization- Water absorbs a lot of heat for it to evaporate. When
it evaporates it goes away with a lot of heat. When water evaporates from body surfaces
as sweat it results in the cooling of the body as heat is lost in water vapor.

Carbohydrates

 Carbohydrates are organic molecules made up of carbon, hydrogen and oxygen.

Carbohydrates are classified into 3 main groups: monosaccharides, disaccharides and
polysaccharides depending on the number of basic sugar units they have.
 Monosaccharides are the most basic unit of carbohydrates and are the simplest form of
sugars. Common examples are glucose, fructose and galactose.
 Disaccharides are formed when two monosaccharides undergo a condensation reaction.
Common examples are maltose (formed by 2 glucose units), sucrose (1 glucose, 1
fructose) and lactose (1 galactose, 1 glucose).

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  A condensation reactionis a chemical reaction when two molecules combine together to
form a single molecule with the elimination of a water molecule.
 A disaccharide can be split into its component monosaccharides by undergoing hydrolys
is in which a water molecule is added to the disaccharide to break it down into its Page | 8
component monosaccharides. Enzymes are usually required for this process.
 Polysaccharides are long chains of glucose units joined together by glycosidic bonds

Functions of carbohydrates
 as a substrate for respiration; provide energy for cell activities
 to form supporting structures
 to be converted into other organic compounds
 for the formation of nucleic acids
 to synthesize lubricants

Test for non-reducing sugar

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A non-reducing sugar is a carbohydrate that is not oxidized by a weak oxidizing agent in an
aqueous solution. An example of non-reducing sugar is sucrose.

1. Add dilute HCL acid to the acid and heat in a water bath
2. Neutralize the solution with sodium hydrogen carbonate or sodium hydroxide. Use a red Page | 9
litmus paper to determine if the solution has been neutralized.
3. Carry out the Benedict’s test as normal; Add Benedict’s solution to the sample and heat
in a water bath that has been boiled. If a color change occurs a reducing sugar is present.
- The addition of acid will hydrolyze any disaccharide to a monosaccharide.

Test for reducing sugar (glucose)

Fats

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  Fats (lipids) are organic molecules made up of carbon, hydrogen and oxygen.
 Fats are made from two types of smaller molecules: glycerol and fatty acids. Each fat
molecule contains a glycerol molecule and 3 fatty acids. Each fatty acid is linked to the
glycerol backbone in a condensation reaction. Page | 10

When 3 water molecules are added to a fat molecule with the help of enzymes in a hydrolysis
reaction, the fat molecule breaks down into fatty acids and glycerol.

Functions of fats

 Fats are energy storage molecules that can store a large amount of energy.
 They are also an important component of cell membranes.
 Fats are used to make steroids and certain hormones
 Fats are also used as insulating material to prevent the loss of body heat
 Fat is also a solvent for fat-soluble vitamins.
 They are used as a source of water by some desert animals through respiration of fats
which produce water as a byproduct.

Test for fats

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Since fats do not dissolve in water, they precipitate out of the solution to give a cloudy white
emulsion. When ethanol is added and shaken the fats are emulsified (broken into small globules
or dissolved) and the emulsion disappears.

Proteins

-Proteins are polymers of many amino acids linked together by peptide bonds. They are made up
of carbon, hydrogen, oxygen and nitrogen. They may also contain sulfur.

-There are tens of thousands of different proteins, each serving a different function and having a
unique structure.

-Amino acids link up in a condensation reaction to form a polypeptide chain.

Functions of proteins

- growth and repair of cells and tissues

- formation of enzymes

- formation of hormones

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- can be respired to give energy when fats and glycogen reserves are used up

-Formation of antibodies

Test for proteins

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Nucleic acids

-They are polymers made of linked nucleotides. There are two types of nucleic acids i.e DNA
(deoxyribonucleic acid) and RNA (ribonucleic acid). They consists of oxygen, hydrogen, carbon
and phosphorous.

-Nucleic acids store and transmit hereditary information

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-Deoxyribonucleic acid (DNA) is a molecule that carries genetic information and a gene is a
small segment of DNA that contains information used to make a single protein.

-Nucleotides are building blocks of DNA and they can be joined together to form long chains
called polynucleotides. Page | 13

-DNA is found in the nucleus. RNA is made from DNA in the nucleus and then moves into the
cytoplasm where it is used to make proteins.

TOPIC 3: CELLS AND CELLULAR ACTIVITIES

A cell is the smallest structural and functional unit of all living organisms. All living things are
made up of cells. Cells are very tiny and need a microscope to view them.

Animal cell

Plant Cell

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The mitochondrion is the site of energy production through respiration of glucose.

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Cell Specialization

Cells specialize to perform a particular one job by changing certain physical and chemical
structures. The specialization of cells to carry out particular functions in an organism is
sometimes referred to as ‘division of labour’ within the organism. Page | 15

Palisade cell

These are found underneath the upper epidermis of plant leaves in the mesophyll layer. They are
columnar (quite long) and packed with chloroplasts to trap light energy. Their function is to
make food for the plant by photosynthesis using carbon dioxide, water and light energy.

Root hair cell

Responsible for absorption of water and salts from the soil. They are adapted for their functions
because;
- Have thin cell walls to allow water and nutrients to pass easily from the soil
- They are numerous to increase surface area for absorption of water and mineral salts
as they are in close contact with the soil.
-The root hair is long to increase surface area for absorption of water and minerals
- The hair like projection on each cell penetrates between the soil particles and offers a
large absorbing surface area.
- Large vacuole with concentrated solutes to make water move into the cell by osmosis.
- Thin cellulose cell wall, for quick diffusion of substances in and out.

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- Thin cytoplasm lining, for quick diffusion

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Neuron cell
These cells are specialised for conducting electrical impulses along the fibre, to and from the
brain and spinal cord. The fibres are often very long and connect distant parts of the body to the
central nervous system.

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Muscle cells

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-Muscle cells are specialized to contract and relax thereby changing the shape and length of the
cell.
- They contain actin and myosin proteins which slide past each other allowing the muscle to
contract and relax.
- They contract when stimulated by a nerve so that movement occurs.
- Have large numbers of mitochondria to provide energy for muscle contraction.
Sperm cells

Sperm cells are male sex cells. Sperm cells are specialized for fusing with the egg to form a
zygote.
-Sperm cells have a tail that they use for movement
-They a lot of mitochondria in the middle piece for production of energy for movement

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-The acrosome contain enzymes that break the membrane of the egg allowing the sperm to
penetrate the egg for fertilization.
-The nucleus contain the haploid genetic material to restore the diploid number at fertilization.

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Ovum cell

Ova are female sex cells. Egg cells are large with a large nucleus.
-The cytoplasm has a lot of nutrients to feed the growing zygote
-They have a specialized membrane that allow only on sperm to penetrate
-They have haploid genetic material to allow a diploid genetic state when fertilization occurs
with the haploid sperm
-The sperm and egg fuse to form a zygote
Red blood cells

Red blood cells deliver oxygen to the body tissues via the blood. Adaptations to this function
include;
- Red blood cells contain haemoglobin, an oxygen-carrying protein that allows it to reversibly
carry oxygen around the body.
- They have no nucleus to increase the oxygen carrying capacity of the cell.

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-They are flexible to allow it to squeeze through the narrow capillaries.
-They have a flattened biconcave to increase the diffusion rate and oxygen carrying capacity.
White blood cells
White blood cells have nuclei and mitochondria. Page | 19

-Macrophages have an ability to engulf pathogens and digest them.

-Lymphocytes have an ability to produce antibodies which destroys pathogens.

Cellular Transport
Diffusion is the net (overall) movement of molecules from a region of their higher concentration
to a region of their lower concentration down a concentration gradient. Concentration refers to
the number of particles per unit volume.

- A concentration gradient is the difference in concentration between a region of higher

concentration of a substance and a region of lower concentration of the substance.

- When the concentration gradient is steeper, the rate of diffusion will be faster. When a
concentration gradient exists, diffusion will take place until the particles are evenly distributed
throughout the region

Factors that affect the rate of diffusion

1. Surface area to volume ratio

Diffusion is faster when surface area is large and volume is small.

- As cells become bigger surface area to volume ratio decreases.

- Diffusion becomes less efficient. Cells divide to increase surface area to volume ratio.

- The rate of diffusion into a cell will depend on the cell’s surface area.

-The greater the surface area, the faster is the total diffusion

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2. Concentration gradient
-The bigger the difference in the concentration of a substance on either side of a membrane, the
faster it will tend to diffuse.
- The difference is called a concentration gradient or diffusion gradient.

Molecules move from high concentration to low concentration. If the concentration gradient is
steep (high) molecules move very fast.
3. Size of molecules or ions/Particle size
-The larger the molecules or ions, the slower they diffuse.
4. Temperature
-An increase in temperature causes an increase in the kinetic energy which molecules and ions
possess. This enables them to move faster, so the process of diffusion speeds up.
5. Thickness of the membrane
-The thicker the wall, the slower the rate of diffusion

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Osmosis
-Movement of water molecules from a region of their higher concentration to a region of their
lower concentration through a semi-permeable membrane. Net movement of molecules stops when
concentration on both sides become equal. Page | 21

-Water will diffuse from the dilute solution to the concentrated solution through the partially
permeable membrane. As a result, the liquid level will rise on the left and fall on the right.

- A partially permeable membrane is porous but allows water to pass through more rapidly than
dissolved substances.

Osmosis in plant cells

-Water potential is a measure of the tendency of water molecules to move from one region to
another

- A dilute solution has a higher water potential than a concentrated solution and pure water has the
highest water potential.

-In plants the cell wall is fully permeable while the cell membrane is partially permeable.

- When a plant cell is immersed in a solution of higher water potential relative to its cell sap, water
molecules enter the cell by osmosis

- The vacuole increases in size and the expanded cell contents exert pressure on the cell wall.

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- The cellulose cell wall of a plant cell is strong and rigid.

-The cell wall exerts an opposing pressure on the cell contents, preventing the entry of more water.
This prevents the cell from over-expanding and bursting.
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-The plant cell becomes very firm or turgid. Turgidity refers to the state of being turgid or swollen.
Turgor pressure provides mechanical support for the plant.

-When a plant cell is immersed in a solution with a lower water potential relative to its cell sap,
water diffuses out of the cell into the solution by osmosis.

-The vacuole shrinks and the cell stops exerting pressure on the cell wall. The cell becomes limp
or flaccid. If it is placed in a solution with a high water potential at this point, turgidity can be
restored.

-If more water leaves the cell, the vacuole and cytoplasm shrink to such an extent that the cell
surface membrane pulls away from the cell wall.

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-The phenomenon in which the cell surface membrane pulls away from the cell wall is called
plasmolysis. This can be lethal if the cell is not quickly transferred to a solution with a higher water
potential relative to its cell sap.

Osmosis in animal cells Page | 23

-When an animal cell is immersed in a solution with a higher water potential relative to its
cytoplasm, water diffuses into the cell by osmosis.

-The cell swells. As more water enters the cell, it swells to such an extent that it bursts. This is
because it does not have a cell wall. This process is called cytolysis.

-When an animal cell is immersed in a solution with a lower water potential, relative to its
cytoplasm, water diffuses out of the cell by osmosis.

-The cell shrinks and become dehydrated. In red blood cells, little spikes appear on the cell surface
membrane, and the cell is said to have undergone crenation/lysis. The animal cell will die if it is
not removed from the solution

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Active uptake
-Active transport is the process in which energy is used to transport substances across a biological
membrane against a concentration gradient.

-The energy used for active transport is obtained through cellular respiration
-Uptake of dissolved mineral salts by root hair cells and glucose uptake by cells in the villi of the
small intestine are examples of active transport.

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 TOPIC 4: ENZYMES
Enzymes are biological catalysts that speed up the rate of chemical reactions without being altered
in the reaction. They are made of proteins.
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-Enzymes work by lowering the activation energy of a chemical reaction. Activation energy is the
amount of energy needed for a reaction to take place

Properties of enzymes

- They are specific. →"Lock & Key" hypothesis (One enzyme act on one substrate)

- Enzymes are protein in nature.

- They are affected by temperature.

- They are affected by pH.

- They remain unchanged after a chemical reaction.

-They lower the activation energy needed to start a chemical reaction.

Enzymes are capable of working in two ways.

 By joining smaller molecules to form larger molecules( anabolic reactions)

 By splitting larger molecules into smaller molecules (catabolic reactions)

Enzymes are named after their substrate or the type of reaction they catalyse

 protease (enzyme) acts on proteins

 lipase (enzyme) acts on lipids
 sucrase (enzyme) acts on sucrose
 amylase (enzyme) acts on starch
 maltase (enzyme) acts on maltose

-Enzyme-catalysed reactions can be stopped or slowed down by inhibitors such as mercury, lead
and arsenide

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-They are substrate-specific. Substrates are the reactants that an enzyme acts on. Each enzyme can
only act on the particular substrate of the reaction they are supposed to catalyse

Mode of action (The lock and key hypothesis)

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-The lock and key hypothesis relates enzyme specificity to the presence of active sites. An active
site is the region on an enzyme molecule that the substrate binds to. It is usually a pocket or groove
on the surface of the enzyme that is part of the enzyme’s unique 3-dimensional structure.

- The enzyme is the lock and the substrate is the key

-The shape of the active site is complementary to the substrate. Only the correct substrate is able
to fit into the active site.

-The substrate molecule binds to the active site of the enzyme to form an enzyme-substrate
complex.

- The reaction is then catalysed at the active sites to convert the substrate into product molecules.

- The product molecules depart from the active site, leaving the enzyme free to catalyse another
reaction

Rate of enzyme - catalysed reaction is affected by

 Temperature

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  pH
 Substrate concentration
 Enzyme concentration
1. Effect of temperature Page | 28

- At low temperatures, enzymes are inactive and the rate of reaction is very low. Substrate and
enzyme molecules have little kinetic energy, hence the frequency of effective collision is low. In
addition, most substrate molecules do not contain sufficient energy to overcome the activation
energy required to start a reaction.

- As temperature increases, the rate of enzyme activity increases. Enzyme activity doubles with
every 10°C rise in temperature. This is because the reactants have higher levels of energy, and the
substrate molecules are able to collide with active sites more frequently.

- At the optimum temperature, enzyme activity is the highest. Most enzymes function at an
optimum temperature of 40°C

- As the temperature increases beyond the optimum temperature, enzyme activity drops sharply.
This is because enzymes are made of proteins, which are denatured at high temperatures. The
enzyme loses its 3-dimensional structure and active site conformation due to the breaking of the
weak bonds that hold the structure together.

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- At extremely high temperatures, the enzyme is completely denatured and the rate of reaction
drops to zero.

2. Effect of pH
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-Enzymes have a narrow pH range.

- Enzyme activity is the highest at the optimum pH of the enzyme

- As the pH increases or decreases from the optimum, enzyme activity sharply decreases. This is
because the hydrogen bonds and ionic bonds that hold the 3-dimensional structure are disrupted.
The shape of the active site is changed as the enzyme is denatured.

- At extreme pH levels, the enzyme is completely denatured and the rate of reaction drops to zero.

- The optimum pH for each enzyme differs. For example, pepsin works best under the acidic
conditions in the stomach, while intestinal enzymes work best under alkaline conditions.

Application of enzymes in the production of washing powders

- Biological washing powders contain protease and lipase to remove protein stains and fat/grease
from clothes. The enzymes break down proteins or fats on the fabric, forming water-soluble
substances that can be washed away.

- Many of the stains on clothes, like blood and sweat, are proteins.

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-For example blood contain the red protein Haemoglobin (Hb). The Proteases in biological
washing powder break Hb molecules into smaller molecules, which are not coloured and which
dissolve in water and can be washed away.

- This makes the washing powder more effective than detergent alone, especially at lower Page | 30
temperatures. This save energy (no need to boil water), but if the temperature is too high, the
enzyme will be denatured.

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 TOPIC 5: PLANT SCIENCE
NUTRITION

Photosythesis Page | 31

-Photosynthesis is the process by which plants convert carbon dioxide and water into sugars using
sunlight as energy in the presence of chlorophyll.

Conditions necessary for photosynthesis to occur are; chlorophyll, light, carbon dioxide

Is light necessary for photosynthesis?

As starch has not formed in the areas that received no light,

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-Light is needed for starch formation and thus for photosynthesis. You could argue that the
aluminium foil had stopped carbon dioxide from entering the leaf and that it was shortage of carbon
dioxide rather than absence of light which prevented photosynthesis taking place. A further control
could be designed, using transparent material instead of aluminium foil for the stencil.
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Is carbon dioxide necessary for photosynthesis?

-The leaf that had no carbon dioxide does not turn blue. The one from the polythene bag containing
carbon dioxide does turn blue

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- The fact that starch was made in the leaves that had carbon dioxide, but not in the leaves that had
no carbon dioxide, suggests that this gas must be necessary for photosynthesis

Is oxygen produced during photosynthesis?

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- The relighting of a glowing splint does not prove that the gas collected in the test-tube is pure
oxygen, but it does show that it contains extra oxygen and this must have come from the plant.
The oxygen is given off only in the light.

Is chlorophyll necessary for photosynthesis?

- It is not possible to remove chlorophyll from a leaf without killing it, and so a variegated leaf (fig
a), which has chlorophyll only in patches, is used.

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- The white part of the leaf serves as the experiment, because it lacks chlorophyll, while the green
part with chlorophyll is the control.

-After being destarched, the leaf – still on the plant – is exposed to daylight for a few hours.
Remove a leaf from the plant and test it for starch as described above. Page | 34

- Only the parts that were previously green turn blue with iodine. The parts that were white stain
brown

- Since starch is present only in the parts that originally contained chlorophyll, suggesting that
chlorophyll is needed for photosynthesis.

Testing a leaf for starch

- Dip leaf in hot water in a beaker to kill it. This stops enzyme action. Leaf becomes soft.

- Place leaf in boiling alcohol to remove/dissolve chlorophyll. Leaf becomes hard and white

- Note: alcohol is highly inflammable. Use a water bath to ensure that alcohol does not catch fire

- Dip leaf into boiling water to soften leaf

- Place leaf on a white tile and cover it with iodine solution

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- The parts containing starch will turn blue-black; parts without starch will stain brown with iodine.

Fate of end products of photosynthesis

Glucose

 Glucose is converted to starch in leaf cells for temporary storage to prevent osmotic effects
on leaf cells during the day.
 At night starch is converted to sucrose in leaves. Sucrose is translocated through phloem
vessels to storage organs e.g. roots, stem tubers or fruits.

Some carbohydrates are converted to;

 Together with nitrates and other mineral salts absorbed by the plant are used to make amino
acids which are used to make proteins to make enzymes and for structural purpose
 Cellulose for cell wall formation.
 Lipids for cell membranes

Oxygen

- Oxygen released into the atmosphere as a by-product and is used for respiration by plants and
animals.

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Importance of photosynthesis

- Makes light energy from the Sun available to animals and plants as chemical energy in the form
of glucose
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- In the day, the leaf produces more glucose than can be removed – excess glucose will then be
converted into starch and stored in the leaf

- Nitrates and other mineral salts absorbed by the plant are used to form amino acids and proteins
these will either be stored or used in making new protoplasm

- Fats can be formed from glucose and either stored, used to form protoplasm or in cellular
respiration

- Hence plants provide animals with food, either directly or indirectly

- Chemical energy present in fossil fuels is released when the fuel is burnt

- Photosynthesis ensures that living things have a constant supply of oxygen.

Leaf Structure

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Relate the structure of the leaf to its function in photosynthesis

- Their broad, flat shape offers a large surface area for absorption of sunlight and carbon
dioxide.
- Leaves are thin and the carbon dioxide and light energy has to diffuse across short Page | 37
distances to reach the inner cells
- There are many chloroplasts in the palisade cells to trap much sunlight for
photosynthesis
- The large spaces between spongy cells inside the leaf provide an easy passage through
which carbon dioxide and oxygen can diffuse
- There are many stomata to allow for the exchange of carbon dioxide and oxygen with
the air outside
- Palisade cells closely packed and elongated to increase surface area for absorption of
sunlight
- The branching network of veins provides a good water and mineral ions from the roots
to the leaves during photosynthesis.

Factors affecting the rate of photosynthesis

Light intensity

- Place a moveable light source at varying distances and count the number of bubbles of
oxygen produced per minute. These reflect the rate of photosynthesis.
- The rate of bubbling should decrease as the lamp is moved further away from the plant.
Assuming that the bubbles contain oxygen produced by photosynthesis, as the light
intensity is increased the rate of photosynthesis (as indicated by the rate of oxygen

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 bubble production) increases. This is because the plant uses the light energy to
photosynthesize and oxygen is produced as a waste product.
- As light intensity increases, so does the rate of photosynthesis.

Carbon dioxide concentration Page | 38

- Sodium hydrogencarbonate releases carbon dioxide when dissolved in water. Use the
apparatus shown in Figure 6.10
- Add varying amounts of sodium hydrogen carbonate, each time recording the number of
bubbles produced per minute at each level. More carbon dioxide becomes available to the
plant as more sodium hydrogen carbonate is added to the water.
- As the concentration of available carbon dioxide is increased, the number of bubbles
released also increases. So an increase in carbon dioxide increases the rate of
photosynthesis.

Effect of water on photosynthesis

- Water is necessary for the chemical reaction to take place. Plants need water to be turgid.
If a plant does not have enough water the stomata will close to prevent water loss by

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 transpiration. Hence the plant will not absorb carbon dioxide which is needed for
photosynthesis

Gaseous exchange in leaves

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- All stoma are capable of opening and closing where these movements are affected by the
intensity of light and the rate of evaporation of water
- Stoma usually open by day and close at night.
- When carbon dioxide within the leaf is used up by photosynthesis, the concentration of
carbon dioxide in the leaf becomes lower than that in atmospheric air.
- Carbon dioxide diffuses into the intercellular air spaces of the spongy mesophyll layer
through the stomatal openings
- The mesophyll cells exposed to the intercellular air spaces are covered by a thin film of
water. Carbon dioxide dissolves in it and diffuses into the cells.
- Oxygen molecules produced will then diffuse from the mesophyll cells into the
intercellular spaces and out through the stomata.

Mineral Nutrients

- Plants require nutrients require minerals for normal growth and for processes such as
photosynthesis
- Minerals that are needed in large amounts are called macronutrients
- Minerals that are needed in small amounts are called micronutrients
- There are three macronutrients required by plants; Nitrogen phosphorous and potassium
Nitrogen
- Nitrogen is found as nitrates or ammonium from soil or inorganic fertilizers
- It is used by the plant for the synthesis of proteins, nucleic acids and chlorophyll
- Deficiency of nitrogen leads to stunted growth due to lack of protein and yellowing of
leaves due to lack of chlorophyll

Phosphorous

- It is found from the soil and inorganic fertilizers.

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 - It is used to make cell membranes, energy carrying molecule (ATP), proteins and nucleic
acids.
- Deficiency of phosphorous leads to stunted growth of roots, purplish leaf and petioles.
Potassium
Page | 40
- It is used for maintaining sodium potassium pumps in cell membranes. It increase
resistance to diseases and frost and improves quality of fruits. It maintains ion and osmotic
balance
- Regulates the closing and opening of stomata
- Deficiency leads to yellowing and brown leaf margins, poor growth. Purple spots may
appear on leaf undersides. Poor flowering and fruit development.

Productivity

Biomass

-Is the total mass of living organisms in a given area in a given time for example a farm or an
ecosystem.

-Biomass can be expressed as an average mass per unit area

-Biomass is the organic content of a biological system

-Productivity is the rate at which biomass increases over time.

Factors affecting productivity

There are many factors which affect plant productivity. The most important are;

- Light
- Mineral salts
- Temperature
- Water availability
- Pests and disease

Light

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Light intensity and quality is the most important factor. The higher the light intensity and quality
the higher the rate of photosynthesis hence increase in biomass. The longer the light duration the
more time given to plants carrying photosynthesis.

Mineral salts Page | 41

The main minerals needed by plants are nitrogen, phosphorous and potassium. Lack of minerals
results in stunted growth, weak stems, yellow leaves and poor flower setting and fruiting.

Temperature

Increase in temperature results in increase in enzyme activity which are involved in

photosynthesis.

Water availability

Different plants need varying amounts of water. Water has many functions in plants such as solvent
for all nutrients, medium for all biochemical reactions and a reactant in photosynthesis

Pest and diseases

A pest is an organism that reduces plant productivity by either eating them or by spreading diseases
among them. All pests cause reduction in crop yield. Pests are divided into two main groups;

- Tissue eating pests and sap sucking pests

- Diseases such as bacterial wilt and fungal rust

Tissue eating and sap sucking pests

Examples of tissue eating pests are; grasshoppers, caterpillars and crickets

Examples of sap sucking pests are aphids and male mosquitoes.

Tissue eating pests eat parts of plant such as leaves, fruits and bucks. Eating of leaves reduces the
surface area for photosynthesis and makes the plant vulnerable to infection through the wounds.

Sap sucking pest suck the sugary sap in plant leant leaves. They transfer diseases such as tobacco
mosaic virus.

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Plant diseases

Bacterial diseases most common in Zimbabwe are bacterial soft rot and black rot.

Page | 42

Methods of controlling pests and diseases

There are three types of pest control namely cultural, biological and chemical method.

Cultural control method

Cultural control is the prevention of infestation of pests using non-chemical methods. They
involve;

- Removal of weeds
- Good cultivation practices
- Use crop rotation
- Cleaning pruning tools
- Intercropping
- Use disease free or resistant seed

Advantages of cultural control- the methods are relatively low in cost, accessible and safe

Disadvantages of cultural methods- they take time and need to be carried out often

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Biological method

It is the release of natural enemies of the pest to prey or destroy the pest.

Examples include;
Page | 43
-predatory mite against red spider

- birds against aphids and insect larvae and rates

Advantages- the method is natural and has no negative effect on the land or environment

Disadvantages- the process takes time and may lead to over multiplication of the natural enemy
being used

Chemical method

It involves the use of chemicals that kill or repel the pests. Pesticides includes fungicides,
insecticides and herbicides.

Advantages of chemical control- their effect is fast and specific and can be easily controlled
when applied correctly.

Disadvantages of chemical control – they are expensive, can kill other organisms or plants, can
stay in the soil or food chain for a long time, the pests can become resistant resulting in needing
higher doses of the chemical.

TRANSPORT IN PLANTS

Monocotyledonous and dicotyledonous plants

There are two types of plants namely monocotyledons and dicotyledons. A monocotyledon is a
plant with seeds that have one cotyledon or seed leaf. A dicotyledon is plant with seeds that have
two cotyledons or seed leaf.

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 Page | 44

Internal structure of a dicotyledonous stem

The stem is made up of the epidermis, cortex, vascular bundles and pith.

Food is stored in the cortex and pith.

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Internal structure of a dicotyledonous root

Page | 45

Root hair cells

- Root hairs are tubular outgrowths of root epidermal cells. Each root hair is usually an
outgrowth of a single epidermal cell, so they are one-cell thick.
- Being long and narrow, they have a large surface area to volume ratio for rapid absorption
of water and minerals
- The cell surface membrane controls the water potential of the cell sap. The cell sap has a
lower water potential than the soil solution, causing osmosis to take place.

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Absorption of water and minerals by root hair cells

- Soil particles are usually coated with water and dissolved mineral salts.2. The cell sap in
the root hair cells contains sugars and ions that cause it to be at a lower water potential than
soil solution. Page | 46
- Water moves across the partially permeable cell surface membrane from the soil solution
into the cell sap by osmosis.
- The cell sap now has a higher water potential than the cell sap in the adjoining cell.
- Water moves across the cell surface membranes into the adjoining cell by osmosis.
- This process continues until the water enters the xylem vessels and moves up the plant

Structure of the xylem tissue

- The xylem vessels are long hollow tubes made of dead lignified cells arranged end to end.
- The xylem vessel is specialized to transport water and dissolved minerals from the root up
to all the other parts of the plant, and also to help supporting the stem and strengthening it.

The xylem tissue is adapted to its functions in different ways:

- the cell wall are filled with lignin, which makes it stronger to support the stem,
- The cells are dead with no contents increase the volume of water being carried.
- It also makes all the water absorbed by the root hair cells get transported to the leaves
without being used by the cells of the vessel.
- The tube is also very narrow, to make it easier for the water to be transported upwards by
capillary effect.
- The vessel has pits to allow lateral flow of water to neighboring tissues
- They have no end walls to allow continuous flow of water without impediment

Structure of the phloem tissue

- This is a long tube that runs alongside the xylem tissue.

- They are made of long narrow tubes with perforated sieve plates along the thin length.
- The function of the phloem tissue is to transport food nutrients such as glucose and amino
acids from the leaves and to all other cells of the plant, this is called translocation.

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 - Unlike the xylem, the phloem tissue is made of living cells, because there are several forces
causing the transport of water in the xylem, but there are no forces causing the
translocation, so substances need to be moved along using active uptake, which needs
energy.
Page | 47
- The cells of the phloem vessels contains cytoplasm but no nucleus, and its activities are
controlled by a companion cell next to it which has a nucleus,
- Companion cells have no function in translocation

Transpiration

- Transpiration is the loss of water vapour from the internal tissues of living plants through
the lenticels and stomata
- Water evaporates from cells surrounding the intercellular spaces.
- Water vapour collects in the intercellular spaces before they escape into the atmosphere,
through the stomata and lenticels

Functions of transpiration

- Water evaporating from a leaf absorbs its latent heat and cools the leaf down
- Creates a transpiration pull that pulls water from the roots to the leaves where its needed
for photosythesis

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 - Creates a transpiration pull in the leaf that pulls water containing mineral salts from the
roots which are essential to the plant.

How water moves through the xylem

Page | 48
- In root hair cells, the mineral concentration is high, so more water is absorbed by osmosis.
This helps pushing the water towards the xylem and the stem.
- Capillarity- is a factor that helps in the movement of water in the xylem vessels. The water
molecules are attracted to each other by hydrogen bonds, as one moves upwards it pulls its
neighboring molecule with it. The xylem is narrow which enables water to be pulled as a
continuous stream.
- Transpiration pull- is the most effective force that causes water movement. In the leaf, the
water evaporates through the stomata, one molecule escapes pulling the other with it, and so
on, creating a suction force. You can think of it as using a straw to drink.

Factors affecting the transpiration rate

Humidity

- Humidity means more water vapour in the air, which means water vapour has a higher
concentration in the atmosphere than inside the leaf, so transpiration will be much slower
because the diffusion of water vapour outside the leaf will be slow. The higher the
humidity the slower the transpiration.

Temperature

- When the temperature is high, molecules move faster and evaporate faster, so transpiration
rate increases. The higher the temperature the faster the transpiration.

Wind speed

Wind removes the water vapour that accumulates outside the stomata due to transpiration. This
maintains the steep diffusion gradient of water vapour. The rate of transpiration will remain high
as long as water vapour is continually being removed by wind.

Light intensity

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 - When light intensity is high, the stomata will open to let carbon dioxide in for
photosynthesis, the water vapour has an easier chance to escape. In the dark the stomata
are closed, the transpiration rate is very slow.

Adaptations of leaves to minimize water loss Page | 49

Some leaves have special adaptive features to reduce the rate of water loss.

1. Reduction of surface area-Plants that grow in dry areas often have small leaves, rolled or
spines as leaves to reduce the surface area for transpiration.
2. Few or small/ sunken stomata which reduces water loss
3. Thick waxy cuticle- The thick cuticle reduces water loss by blocking it from escaping
from the leaf. The thicker the cuticle the more water is prevented from diffusing out
4. Presence of leaf hairs- They prevent water loss by trapping moist air between them on the
leaf which reduces the diffusion gradient hence reducing transpiration rate

How wilting occurs

- Wilting occurs when the transpiration rate is faster than the rate of water absorption.
- The amount of water in the plant keeps on decreasing.
- The water content of cells decreases and cells turn from turgid to flaccid.
- The leaves shrink and the plant will eventually die.

Translocation

- Translocation is the transport of sugars from the leaves to other parts of the plant. This is
done by the phloem tissues.
- The leaves, which supply sugar, are known as the source while other parts of the plant
which require sugar are known as the sink.
- Glucose, the product of photosynthesis is the most important food of the plant. Because
from it, it makes most of its other nutrients.
- Glucose is converted into other more complex sugar called sucrose.
- Sucrose in the leaves enter the phloem vessels. The phloem transports it to every other part
of the plant where it is made use of.

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 - Amino acids are also transported in the phloem. Sucrose and amino acids are transported
to every tissue of the plant, each cell use it in a different way.
- Root cells convert sucrose into glucose for respiration and store it. Growing cells make
cellulose for structure formation.
Page | 50
Ring barking

- Ring barking is the removal of the complete strip of bark consisting of cork cambium,
phloem, phloem and sometimes xylem from around the circumference of a branch or trunk.
- It causes death of the part of the plant that is above the bark over time. It makes the plant
prone to infection through the debarked area.

REPRODUCTION IN PLANTS

Reproduction is the process by which animals, plants and other living organism produce offsprings
of their kind. There are two types of reproduction namely; asexual and sexual reproduction.

ASEXUAL REPRODUCTION

Asexual reproduction is the production of offspring without involvement of gametes

Asexual reproduction involves;

- One parent which produces new individuals

- No formation of gametes ( sex cells)

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 - No production of seeds
- The offspring is identical to the parent

The offsprings produced are identical genetically and in appearance to the parent and among
themselves. Page | 51

Vegetative reproduction

- It is a form of asexual reproduction of a plant.

- It is a processes by which new organisms arise without production of seeds or spores.
- Plants produce new separate plants from their existing non-seed parts such as roots, leaves
and stems.
- Farmers use modified stems, roots, or leaves to increase the number of plants for example
in potatoes, grass and sugar cane (vegetative).
- Plant that are produced this way will give rise to identical copies of the parent plants.
- There are two main methods of vegetative reproduction that is;
- Natural vegetative reproduction
- Artificial vegetative reproduction.

Natural vegetative reproduction

TUBERS

- Tubers are a thickened part of a stem or root for example potatoes

- They have buds or ‘eyes’ from which a new shoot will develop.
- Stem tubers grow from a potato plant at the end of the growing season.
- Buds on the stem near the soil surface grow down into the soil.
- These growths from the stem then swell up with food reserves to form a tuber.
- Examples of tubers include Irish potatoes, sweet potatoes, cassava etc.

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 Page | 52

RHIZOMES

- These are modified stems which remain underground and grow horizontally.
- New grass plants grow from buds along the stem.

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 - The horizontal stems can spread quickly and many grass plant become established over a
wide area.
- Such grass plants are used to grow lawn and playing fields.

SUCKERS Page | 53

A sucker is a structure similar to a small bulb or bud which grows from the roots, stem or
underground stem of the parent plant.

- Suckers develop to form a new plant

- In raspberries for example, the suckers develop from the root. In banana trees the suckers
develop from the underground stem of the parent plant. In covo vegetable plant suckers
develops from the stem.

RUNNERS

- Runners are long, thin stems that grow from the parent plant on the surface of the soil.
- These horizontal stems grow roots and shoots at every second node to form a new plant.
- Strawberries are examples of plants that reproduce by runners.

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 Page | 54

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BULBS

Page | 55

- A bulb is an underground stem with scales and fleshy leaves surrounding the central bulb
- An onion is an example of a bulb

Artificial vegetative reproduction

Artificial vegetative reproduction methods involve humans taking steps to propagate the plants.

CUTTINGS

- These are portions of stems, roots or leaves that are cut and planted in sand, loose soil or
even in water.
- A stem may be long with several nodes and lateral buds or leaves the lower end is buried
in sand or soil.
- The planted cut stem or roots develop sprouts and roots
- One parent can be used to produce many individuals over a large area.eg sugar plantation.

GRAFTING

- The bud or shoot from one plant is inserted under the bark on the stem of another, closely
related variety so that the cambium layers of both are in contact.
- The rooted portion is called the stock and the bud or shoot being grafted is the scion.
- A bud from a desired variety is grafted on the stem of a plant grown from seed.

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 - The bud grows using water and nutrients supplied by the stock, and later the stock is cut
off above the graft. Example of this is the grafting of rubber tree.

Page | 56

The advantages of grafting include combining the characteristics of two plants

Advantages of vegetative reproduction

- Plants can grow quickly.

- Plants have more chances of survival since they have more food and water than seed.
- There is no need for pollination, fertilization and dispersal of fruits and seeds
- Therefore it is an easy method to grow plants.
- The new plants establish over large areas very rapidly.
- The new plants are identical copies of their parents and good features of the plants will still
be found in the offspring

Disadvantages of vegetative reproduction

- Plants are crowded and usually they compete for light, water and nutrients.
- There is no genetic variation.
- Identical plants are liable to be attacked by the same pests and diseases.

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 - It is difficult to produce large numbers of plants as could be produced by seeds.

SEXUAL REPRODUCTION IN FLOWERING PLANTS

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Reproductive organ of a plant is the flower. It is adapted for pollination by both wind and insects

Structure of an insect-pollinated flower

Pedicel (flower stalk) – Modified stem that holds the flower

Receptacle – The end of the pedicel which holds the parts of the flower

Sepals – Modified leaves which are green in colour and are found on the outermost ring of floral
leaves. They make up the calyx and protect the flower when it is in bud stage.

Petals – Modified leaves which form the most conspicuous part of the flower; they make up the
corolla. They are brightly coloured in insect-pollinated plants and form a platform for insects to
land on.

Carpel– Female reproductive organ. It contains an ovary with one or more ovules and has a sticky
tip known as a stigma.

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Stigma– Receptor of pollen grains. Secretes a sugary fluid that stimulates germination of pollen
grains

Style– Stalk that connects the stigma to the ovary. Holds the stigma in position to trap pollen grains
Page | 58
Ovary– Each ovary contains one or more ovules

Ovule– Contains female gametes

Stamen – Male reproductive organ. It consists of an anther and a filament

Anther– Contains pollen grains. Pollen grains in insect-pollinated plants are heavy and sticky.

Filament– Stalk that holds the anther in a suitable position to disperse pollen

Structure of a wind-pollinated flower

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 Page | 59

Example of an insect pollinated flower is a grass flower.

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 Page | 60

Pollination

- It is the transfer of pollen grains from the anther to the stigma

- Pollen grains develop inside the anther
- When the anthers are matured, they split open and the pollen grains are released
- Pollen grains may be carried to the stigma by wind, insects or water

There are two kinds of pollination;

- self-pollination – transfer of pollen grains from the anther of a flower to the stigma of the
same flower or another flower of the same plant
- cross-pollination – transfer of pollen grains from the anther of a flower to the stigma of
another flower of a different plant of the same species

Advantages of self-pollination are:

- Not dependent on external agents of pollination such as insects or wind

- Less wastage of pollen and energy. During wind and insect pollination, a great number of
pollen grains are lost as only a few pollen grains come into contact with a stigma of a
flower of the same species.
- Only one parent plant is required.

A disadvantage of self-pollination is less genetic variation, hence the offspring is less adapted to
environmental changes.

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Advantages of cross-pollination are;

- Greater genetic variation, hence the offspring has a higher chance of surviving
environmental changes.
- Offspring may have inherited beneficial qualities from both parents Page | 61

Disadvantages of cross-pollination are;

- Energy-consuming – lots of energy is required to make large amounts of pollen grains.

- A great number of pollen grains are wasted due to the randomness of the dispersal methods.

How fertilisation occurs

- Pollen settles on a mature stigma. Stigma secretes a sugary fluid.

- Pollen grain produces a pollen tube. The pollen tube grows through the cells of the style
by secreting enzymes to digest them.
- Pollen tube carries two male nuclei down the style into ovary
- The two male nuclei enter ovule through micropyle. One nuclei fuses with the female
nucleus a zygote which then develops into an embryo of the seed.

- The other male gamete fuses with the definitive nucleus to form the endosperm. The
endosperm acts a food store for the germinating seed. The endosperm/cotyledon and
embryo together form a seed.

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 - Fusion of male nucleus and female nucleus to form a zygote is called fertilisation

Changes in the flower after fertilisation

-Petals dry up
Page | 62
- Ovules develop to form seeds

- Micropyle remains

- Ovary ripens to form a fruit

- Ovary and ovules develop special structures which enables them to be dispersed.

Seed dispersal

It is the movement or transport of a seed away from the parent plant.

Methods of seed dispersal

-Wind dispersal e.g. dandelion and spathodea

- Animal dispersal e.g. black jack and guava

- Self-dispersal e.g. msasa

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-Water dispersal

Animal dispersal

- Plants that produces fleshy and tasty fruits like guavas and berries have their seeds
Page | 63
transported by animals
- The animals are attracted to the fruits and eat them
- The seed is resistant to the digestive enzymes in the gut of animals therefore they are passed
out in feaces
- During the passing of the seeds in feaces the animal would have moved a great distance
away from the plant thereby dispersing the seed far away from the plant
- Some seeds like black jack seeds have spiked seeds that cling to clothes or hairs of animals.
- The later fall away in areas that are far away from the plant.

Wind dispersal

- Seeds that are dispersed by wind are generally small and light so that the wind can easily
carry them away to distant areas
- Some seeds have parachute hairs that enable the seed to be carried away by the wind for
example dendilions

Self-dispersal

- Self-dispersal occurs in seeds that develop in pods like beans. The pods dry out and split
shooting out the seeds away from the plant

Water dispersal

- Seeds dispersed by water are usually light and impervious to water to allow them to float
in water
- The seeds are carried by water to distant places where them may get discharged onto fertile
soil and germinate
- Example of a water dispersed seed in coconut seeds that grow on beaches or along rivers

Importance of seed dispersal

- Colonisation of new areas

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 - Reducing overcrowding of plants
- Increasing survival chances of plants
- It prevents or reduces the spread of disease from parent plant to seedlings

Seed structure Page | 64

A seed consists of;

Embryo-The embryo is the part that germinates and develops into a new plant. It consists of
radicle (embryonic root) and plumule (embryonic shoot)

Testa(seed coat)- protective covering. The helum the scar on the testa where the seed was attached
to the ovary wall. The micropyle is the small opening on the testa where water enters before
germination

Endosperm- It provides food for the developing embryo.

An example of a monocotyledon is maize seed and dicotyledon is bean seed

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 Page | 65

Germination

- Germination refers to the process by which a seed develops into a plant

- Seed germination involves enzymes breaking the materials stored in the seed down to be
used in growth, energy and building cells

The seed contains stored substances and enzymes such as:

1. Starch: Starch is broken down by amylase enzyme into maltose, maltose is then broken
down by maltase enzyme into glucose which is used in respiration.

2. Proteins: Proteins are broken down into amino acids by Protease enzyme, amino acids are
used in building up cells and growth.

3. Fats: Fats are broken down into fatty acids by lipase enzyme, they are used in making cell
membranes

In order for a seed to germinate, some conditions must be present:

1. Water:

- Makes the seed soft, causes it to swell and rapture. Water activates the enzymes.

2. Warm Temperature

- For providing the best conditions for enzymes to work. Enzymes work at optimum pH.

3. Oxygen

- To be used for aerobic respiration. Aerobic respiration releases energy.

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 Page | 66

The main difference between flasks A and B is that A lacks oxygen. Since the seeds in this
flask have not germinated, it shows that oxygen is needed for germination. Sodium hydroxide
absorbs carbon dioxide from the air. The mixture (sodium hydroxide + pyrogallic acid) in flask
A, therefore, absorbs both carbon dioxide and oxygen from the air in this flask. In the control
flask B, the sodium hydroxide absorbs carbon dioxide but not oxygen. If the seeds in B
germinate, it shows that lack of carbon dioxide did not affect them, whereas lack of oxygen
did.

Monocotyledonous seed and dicotyledonous seed

- The seed has the nutrients it needs in the food store.

- There are two type of seed, dicotyledonous (e.g. bean seed) and monocotyledonous (e.g. maize
seed).

- The food store in bean seed is formed in the two seed leaves or cotyledons.

- The cotyledons are the first leaves of the seedling.

- A maize grain has only one cotyledon which is very small.

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- The food is stored in a different part of the grain called endosperm

COORDINATION AND RESPONSE IN PLANTS

Page | 67

Phototropism

It is the growth of a plant in response to light. It ensures that a plant has enough light for
photosynthesis

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 Page | 68

Geotropism

It is the growth of a plant in response to gravity. It provides the anchorage of roots and ensures
that the roots can get adequate supply of nutrients and water. If a plant is placed horizontally in
the soil the roots grow vertically into the soil while the shoots grow vertically upwards. Roots are
positively geotropic, they grow towards gravity. Stems are negatively geotropic, they grow away
from the gravity.

Plant hormones

Plant hormones are also called plant growth regulators

There four types of plant hormones; Auxins, cytokinins, ethylene and gibberellins

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Auxin

- Plants release auxins in response to light and gravity

- It allows directional growth
- Auxin is mainly found in actively growing parts of plants such as new leaves, tips of roots Page | 69
and shoots
- It promotes cell elongation in the region behind the root and shoot tip
- It promotes fruit development since it delay fruit abscission
- It prevents leaf abscission

- Auxins are sensitive to light therefore they move arrears that are not exposed to light
- They then cause the cells in the region not exposed to light to multiply and elongate
resulting in the growth of the stem towards ight.
- In geotropism the auxin are concentrated at the root towards the gravitation pull. This
results in the growth of the roots downwards
Application of auxins
- Synthetic auxins are used as weed killers for example 2,4-D

Ethylene

It is the only plant hormone that is a gas. It diffuses through the plant tissue and around the plant
in air. Fruits such as apples, bananas and tomatoes produce ethylene gas.

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 - The ethylene produced by the green fruit will cause the fruit to ripen
- It is a ripening hormone because it causes the fruit to ripen
- It prevents leaf abscission

Application of ethylene gas Page | 70

It synthetically made in industries as a liquid form and used to ripen fruits such as bananas and
tomatoes.

Gibberellins

- The promotes cell growth through cell elongation in the stem

- They promote seed germination and breaks seed dormancy
- It promotes fruit development and growth

Application

- It can be applied by farmers to promote plant growth

Abscisic acid

- It is usually produced by plants in responds to stress such drought. It inhibits all other
hormones and promote dormancy of seeds and buds.
- It inhibits germination, root and shoot growths
- It triggers closing of stomata in response to lack of water
- It promotes dropping of fruits from trees ( abscission)
- It promotes leaf abscission and winter dormancy of plants

Application

It can be applied to plants to help them cope up with environmental stress by initiating dormancy

Cytokinins

They hormones that promotes cell division in plants. They are found in areas of active cell division
such as root and shoot tips

- It stimulates plant growth by promoting cell division

Application

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 - Cytokinins are usually used in combination with auxin in plant tissue culture to grow plant
from cut pieces of plant tissue such as young leaves

Page | 71

ANIMAL SCIENCE

TOPIC 6: NUTRITION

Balanced diet

- A balanced diet is a diet that contains all the essential nutrients in their correct proportions.

Components of a balanced diet

Carbohydrates

- Carbohydrates are energy rich foods that are largely made up of starch and sugars.
- They are easily broken down to glucose which helps the body generate energy through
cellular respiration.
- Supplies dietary fibre.
- Starch is abundant in potatoes, bread, maize, rice and other cereals. Sugar appears in our
diet mainly as sucrose (table sugar) which is added to drinks and many prepared foods such
as jam, biscuits and cakes.
- Glucose and fructose are sugars that occur naturally in many fruits and some

Lipids (fats and oils)

Supplies energy and heat. They contain higher energy values per gram than carbohydrates.

- Help the body to absorb certain vitamins

- Form structural components of cell membranes

- Help in blood clotting

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- Stored fats help to cushion internal organs and protect the body from extreme cold

- Animal fats are found in meat, milk, cheese, butter and egg-yolk. Plant fats occur as oils in fruits
(e.g. palm oil) and seeds (e.g. sunflower seed oil), and are used for cooking and making margarine.
Page | 72
Proteins

- Promotes growth and repair of body tissues

- Builds antibodies to fight infection

- Supplies energy in the absence of carbohydrates

- Speed up chemical reactions and serve as chemical messengers in the body

- Lean meat, fish, eggs, milk and cheese are important sources of animal protein. All plants contain
some protein, but soybeans, seeds such as pumpkin, and nuts are the best sources.

Vitamins

- Play important roles in metabolism, immunity i.e. they help to fight infections and
digestion and are required in minute quantities in order for metabolism to occur

Vitamin A (retinol) – Needed for growth and reproduction. Promote good sight and vision
especially in dim light. Maintain the health of skin and membranes.

- Helps develop bones and teeth. Helps fight infection. Sources include green vegetables,
spinach, liver, egg, palm oil

Vitamin C (ascorbic acid) – maintains healthy teeth and gums. Helps wound healing and helps
the body to use iron. It acts as an anti-oxidant that protects the body from harmful free radicals. It
forms part of an enzyme needed for protein digestion and maintaining healthy immune system.
Sources include oranges, lemons, tomatoes, guava, pawpaw, mango, green vegetables.

Vitamin D (calciferol) – for bone formation and maintain teeth. Helps the body to use calcium
and phosphorus. When exposed to sunlight, the skin produces vitamin D. Sources include liver,
milk, egg yolk, fish-liver oils.

Mineral salts

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 - Essential for the chemical activities (enzyme action) in the body and for construction of
certain tissues.
- Iodine – for the formation of hormone thyroxin in the thyroid gland which help to control
many processes in the body like growth and development.
Page | 73
- Calcium - for the formation of strong bones and teeth. It is also needed for proper muscle
contraction and relaxation. Promotes proper functioning of nerves, regulating blood
pressure and normal blood clotting. The richest sources of calcium are milk (liquid,
skimmed or dried) and cheese, but calcium is present in most foods in small quantities and
also in ‘hard’ water
- Iron – for the formation of haemoglobin in the red blood cells and transport oxygen in the
body. Red meat, especially liver and kidney, is the richest source of iron in the diet, but
eggs, groundnuts, whole grains such as brown rice, spinach and other.

Dietary Fibre

- It is made up of cellulose (plant fibre) and it aid digestion process by helping bowl
movement through the digestive tract.
- The fibre itself and the bacteria, which multiply from feeding on it, add bulk to the contents
of the colon and help it to retain water. This softens the faeces and reduces the time needed
for the undigested residues to pass out of the body. Both effects help to prevent
constipation and keep the colon healthy.
- Fibre binds with cholesterol to reduce cholesterol levels in the blood
- Good sources of dietary fibre are vegetables, fruits and whole wheat bread

Water

- About 70% of most tissue consists of water; it is an essential part of cytoplasm. The body
fluids, blood, lymph and tissue fluid are composed mainly of water.
- Water acts as a solvent and as a transport medium for digested foods, salts, vitamins and
urea.
- Digestion is a process that uses water in a chemical reaction to break down insoluble
substances to soluble ones. These products then pass, in solution, into the bloodstream.

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 - In all cells there are many reactions in which water plays an essential part as a reactant and
a solvent.
- Regulates body temperature through sweating and evaporation

Balanced meal for different groups of people Page | 74

The rate at which biochemical reactions occur in the body is called basal metabolic rate (BMR).
The amount of energy and nutrients required to maintain a normal BMR in an individual depends
on sex, age, health, body size and occupation.

Age- In growing children the BMR is higher than in adults. Growing children and teenagers are
active hence they need a balanced diet with increased protein, calcium, vitamin D and phosphates
for rapid growth, bone and teeth development. They also need high quality of body building foods
and starchy foods to provide energy and dietary fibre. With increasing age people become less
physically active and therefore there energy requirements is low.

Sex- Male are generally more physically active than females thus their bodies requires more energy
as compared to females. Females requires high amount of iron during the menstruation periods for
the synthesis of new blood.

Body size – The bigger the person the more energy and nutritional requirement of that body to
maintain the BMR.

Occupation- A person who does physical work for most of the day e.g. builder, road worker uses
a lot of energy and sweats a lot therefore need a balanced diet with higher energy giving foods,
more salts and water to replace lost energy, water and salts. Sedentary workers do need much
energy giving foods as manual workers

Health- People with certain diseases may require special nutrition requirements in order to heal or
manage the disease. For example people with high blood pressure eat foods with low amount of
salts. People with anemia eat more of fish, fruits, spinach and liver with high amounts of iron.

Food tests

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 Page | 75

Comparing energy content of carbohydrates and lipid

Experiment: Comparing the energy values of food

Materials: Burners, Small containers for heating water, Food holders, Thermometers, Balance

Variety of starchy and fatty foods

Method

1. Set up apparatus similar to the one shown above

2. Heat a small piece of food in a burner flame until it ignites on its own hold the burning
food under the container of water
3. Allow the food to burn until the flame dies outs
4. Measure the temperatures of the water again. Record the increase the increase in
temperature
5. Repeat with equal amounts of food
6. Plot some of the results on a bar graph

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 7. Make the following calculations to determine the energy of burning food;
 Temperature of water before heating ______ OC
 Highest temperature ______ OC
 Temperature rise of water ______ OC Page | 76
 Mass of food ______ g
 Mass of water ______ g

Therefore heat gained by water = mass of food x temperature rise/4.2

= _____________ Joules

Malnutrition

Malnutrition refers to lack or too much of nutrients in a diet

Overweight and obesity

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It is a condition that results when a person has diet that has too much of fat and carbohydrates. The
fats in the body are stored in the body as adipose tissue. This result in body mass increase. Obesity
is the excessive accumulation of fat in the body. Obesity can result in diseases such coronary heart
diseases and sugar diabetes.
Page | 77
Deficiency diseases

Marasmus

- Marasmus usually develops in children when they have prolonged lack of energy giving
foods mainly carbohydrates
- It results in body emaciation

Kwashiorkor

- It is a result of prolonged lack of proteins in the diet

- The symptoms of this condition are swollen belly, poor mental development, body
emaciation, poor hair growth or distribution.

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Vitamins

Vitamin A

- They are found in dark green vegetables(e.g. pumpkin leaves and spinach), yellow
Page | 78
- vegetables (e.g. carrots), milk, eggs, liver, butter, Apples
- Improve eyesight and resistant to colds
- Lack of vitamin A results in;
- Respiratory tract infections, poor eye sight during the nigh

Vitamin C

- Strengthening teeth and bones

- Vitamin C is found in fresh fruits (especially citrus fruits) like oranges, lemons, grapes)
fresh vegetables
- Lack of vitamin C results in poor healing, scurvy (swelling of gums), bleeding under the
skin and around teeth and bruising

Vitamin D

- Vitamin D helps in the absorption of calcium and phosphorus through the gut wall
- Bone is made of the mineral calcium phosphate
- A lack of the vitamin therefore results in poor calcium and phosphorus deposition in bones,
leading to softening
- This results in rickets
- Sources of vitamin D are egg yolk, the sun, fats, liver, butter, milk, meat eggs, green
vegetables

Fibre

- Sources of fibre includes maize and fruits

- Helps food pass along the alimentary canal
- Facilitates peristalsis
- Lack of fibre causes abnormal bowel movements

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 Human digestive system

Page | 79

Mechanical digestion is the physical breaking down of large food substances to small substances
that can be easily digested by enzymes. Mechanical digestion is carried out by teeth and muscles
of the alimentary canal.

Digestion in the mouth

- Mechanical digestion occurs by teeth. Food is broken down with the aid of saliva into moist
substance
- Chemical digestion of starch by amylase. Salivary glands secretes saliva which contains
water and the enzyme amylase.

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 - The tongue roles food into bolus for easy swallowing
- The food moves down the oesophagus by peristalsis
- Peristalsis is the rhythmical contraction and relaxation of muscles of oesophagus thus
pushing the food to the stomach.
Page | 80
Stomach

- The walls of the stomach also secretes a liquid called gastric juice which contains
hydrochloric acid, mucus, and pepsin enzyme.
- The pepsin enzyme digests proteins into simpler peptides, while the
- Hydrochloric acid is to provide optimum pH (2) for the enzyme.
- Hydrochloric acid also kills germs and bacteria.
- The mucus is to lubricate the food and protect the walls of the stomach from the acid.
- After few hours, the sphincter which is a muscular valve opens allowing the food into the
small intestine.
- The walls of the stomach contain muscles that contract and relax together mixing the food
with the content of the stomach and turning it into liquid chyme, this process is called
churning.
Small intestines
- The small intestine is where most digestion and absorption takes place. It is divided into
two sections, duodenum and ileum.
- In the duodenum, chyme from the stomach mixes with digestive juices from the pancreas,
lgall bladder and intestinal glands.
- Bile Juice: it comes from the liver, stored in the gall bladder. It is squirted along the bile
duct in the duodenum. The bile works on fats only.
- Fats are very difficult to digest because they are very insoluble.
- The bile contains bile salts that breaks fats into tiny droplets that float in the content of the
small intestine.
- This makes it easier for the lipase to digest fats into fatty acids and glycerol. This process
is called emulsification.
- Pancreatic Juice: it comes from the pancreas and secreted along the pancreatic duct. It
contains enzymes and sodium hydrogen carbonate, which neutralizes the hydrochloric acid

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 that was added to the food in the stomach, creating better conditions for the enzymes to
work.
- The pancreatic juice contains the following enzymes:
• Amylase to digest starch into Maltose
Page | 81
• Trypsin to digest polypeptides or proteins into peptides
• Lipase to digest fats into fatty acids and glycerol
- Small intestine liquid: the small intestine its self also secrets a liquid that
- consists of lots of enzymes to make sure carbohydrates, fats and proteins
- are digested to their simplest form, these enzymes are:
For carbohydrates:
• Maltase to digest maltose into glucose + glucose
• Sucrase to digest sucrose into glucose + fructose
• Lactase to digest lactose into glucose + galactose
For fats;
• Lipase to digest fats into fatty acids and glycerol
For proteins;
Peptidase to digest polypeptides/peptones to amino acids
Absorption in small intestine

Absorption in the small intestine takes place in the second section, the ileum. Small intestines are
long and folded to increase surface area.

Adaptation of the small intestines for absorption

- They are long to increase the time for digestion and absorption of nutrients
- They have many folds to increase the surface area for absorption of nutrients
- They have many villi to increase the surface for absorption of nutrients
- Villi are made of single epithelium layer to increase the rate of diffusion
- A network of blood capillaries that carry blood away quickly to maintain a diffusion
gradient

The interior walls of the ileum is covered with a layer of villi, each villus is covered with another
layer of micro villi.

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 Page | 82

- Each villi has a branch of blood Capillaries in it as well as a lacteal which is a lymph vessel,
the Lacteal absorbs fats and lipids with vitamins dissolved in them into the lymphatic
system.
- Villi and microvilli are adapted to absorption by:
 They give a very large surface area for faster diffusion of food molecules
 Each villus contains a large network of blood capillaries transporting more blood, thus
faster diffusion
 Each villus is one cell thick, reducing the diffusion distance and making it faster
 Each villi contains a lacteal which absorbs fats

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 - By the time the food reaches the large intestine, there is not much left of it, only some
water, minerals, and fibres.

Diffusion and active transfer of nutrients into blood and lymphatic systems
Page | 83
- Nutrients diffuse into the blood of arterioles of the villi
- From there it moves into venules and eventually hepatic portal vein transport it to the liver.
- Energy is required for active absorption i.e. from low to higher concentration.
- Some substances move by diffusion
- Fatty acids combine with bile salts to form a soluble fatty acid which diffuses through the
epithelial cells of the villi
- Fatty acids separate from bile salts again and recombined with glycerol to form small fat
droplets, which pass into lacteals
Colon
The water, vitamin B formation and the minerals are absorbed into the blood, while the
fibres and dead cells of the alimentary canal are stored in the rectum then expelled through
the anus. This is called egestion
Assimilation of the absorbed food molecules
- After the food molecules are absorbed from the alimentary canal, it is transported to the
liver by a special blood vessel called the hepatic portal vein.
- The liver is a regulatory organ. It has many functions to deal with molecules it receives.
Each type of nutrient has its own fate in the liver.
Glucose
- When the absorbed glucose reaches the liver, the liver allows as much as needed by the
body to pass to the circulatory system to be used for respiration or other processes.
- The excess glucose is converted to glycogen and stored in the liver cells, when the blood
is short in glucose, glycogen will be converted back into glucose and secreted to the blood.
- Some glucose will also be converted to fats as an energy reserve. These functions are
controlled by the insulin and glucagon hormones which are made in the pancreas.

Amino Acids

- Some amino acids will be used by the liver cells to make proteins, the rest will be
allowed into the blood stream to be absorbed by the body cells.

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 - Body cells convert amino acids to proteins.
- Excess amino acids are deaminated (removal of amino group) in the liver to produce
urea as excretory product
- The amino group is removed and converted into urea. The remaining part of the protein
Page | 84
is converted into glucose. Urea is non-toxic and will be excreted in urine.

Functions of the liver

Formation of bile

- The liver changes dead red blood cells to iron and bile. Iron is stored in the liver, large
amounts of iron give it the red colour and used to build up new red blood cells. The
bile is stored in the gall bladder to be used in digesting food again

Detoxification

- The liver breaks down toxic materials such as alcohol which damages cells to fats.
Alcoholics are known to have liver diseases.

Helps in generating heat

- The liver contains a very large number of cells, which means a lot of metabolic
reactions take place in it producing lots of energy to warm the blood.

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Regulating blood sugar

- When there is too much glucose insulin is released which converts glucose to glycogen.
If blood sugar is low glucagon is released this causes glycogen to be converted back to
glucose. Page | 85

Making fibrinogen

- This is a plasma protein which helps in blood clotting when the skin is cut

Storage of glycogen, vitamin A and D

- The liver converts excess glucose into glycogen and stores it. It also stores vitamin A
and D.

Teeth

- Teeth are made of calcium salts.

- Their job is to cut, tear and grind food to give it more surface area for faster digestion,
they do mechanical digestion

Types of mammalian teeth

Incisors they are 4 in front of each jaw

They act like a blade to cut food (e.g. to cut a bite of a sandwich) they have a (chisel-like surface).

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 Page | 86

Canines

- They are two in each jaw.

- They are very pointed, in humans they are used for the same purpose as incisors.
- However in carnivores they are longer and sharper and used to kill the prey.

Premolars

- 4 on the sides of each jaw they are used to cut and grind food

Molars

- They are 6 at the back of each jaw, 2 of them are wisdom teeth. They have the same
use as Premolars.
- Note: remember that we have two jaws, so 4 incisors in each jaw means that we have
a total of 8 incisors in our mouth. We have 16 teeth in each jaw, 32 in the whole mouth.
- The tooth is divided into two parts, the crown and the root
Parts of the tooth:

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1. Enamel: made of calcium salts, it is very strong.

2. Dentine: it is covered by the enamel and surrounds the pulp cavity.

3. The pulp cavity: it contains the nerves and blood vessels.

Page | 87
The part of the tooth above the gum is called the crown, the part buried in the jawbone is called
the root. The enamel covers the crown, the root is covered by cement. And the tooth is held in
place by fibres.

Tooth Decay

- When we eat, some food particles stay in our mouth.

- Bacteria that lives in our mouth feed on these food particles, they respire anaerobically
producing lactic acid
- Like any acid, lactic acid reacts with the enamel (calcium salts) and dissolves it away
reaching the dentine.
- Dentine is softer than enamel and dissolves more quickly so cavities are formed.
- The cavities (tooth holes) reduce the distance between the outside of the tooth and the
nerve endings.
- The acids produced by the bacteria irritate the nerve endings and cause toothache.
- If the cavity is not cleaned and filled by a dentist, the bacteria will get into the pulp
cavity and cause a painful abscess at the root.
- Often, the only way to treat this is to have the tooth pulled out.

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Care of teeth

- Brushing teeth at least twice per day to remove food remains

- Visiting a dentist regularly
- Avoiding sugary foods between meals Page | 88
- Use a fluoride toothpaste to brush teeth

TOPIC 7: Gaseous exchange

- The human respiratory system begins in the nose and ends in the lungs.
- It is responsible for gaseous exchange of oxygen and carbon dioxide

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 Page | 89

Mechanisms of inhalation and exhalation

- The muscles involved in the diaphragm, intercostals muscles (external and internal)
and abdominal muscles.

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 Page | 90

Structure of an alveolus

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 Page | 91

Factors which increase the efficiency of gaseous exchange

- They numerous (millions of alveolus) to increase the surface area for absorption of
oxygen and excretion of carbon dioxide.
- Thin membrane for quick diffusion of gases oxygen and carbon dioxide.
- Moist for dissolving air quickly
- Capillary network around each alveoli to supply blood which carry oxygen to respiring
cells and carbon dioxide from cells.
- They are ventilated to maintain the concentration gradient which in turn allows quick
diffusion of gases

Differences between inhaled and exhaled air

- Exhaled air is the air that is breathed out inhaled air is the air breathed in.

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 Page | 92

Experiment: to compare the carbon dioxide content of inhaled and exhaled air

Method

- Prepare two large test-tubes, A and B, as shown in the Figure

- Put the mouthpiece in your mouth and breathe in and out gently through it for about 15
seconds. Notice which tube is bubbling when you breathe out and which one bubbles
when you breathe in.

Results

- The limewater in tube B goes milky. The limewater in tube A stays clear

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 - Carbon dioxide turns limewater milky. Exhaled air passes through tube B. Inhaled air
passes through tube A. Exhaled air must, therefore, contain more carbon dioxide than
inhaled air.
- Hydrogen carbonate indicator is an alternative to limewater. It changes from red to
Page | 93
yellow when carbon dioxide is bubbled through it.

Comparing oxygen concentration in inhaled and exhaled air

- Two candles are placed in two separate bell jars one with inhaled air and another in
exhaled air.
- The one in exhaled air goes out first and less water enters the bell jar.

Explanation of results

-Oxygen support burning / combustion, when oxygen is used up the candle stops burning.

- Candle in exhaled air takes less time to burn because it has less oxygen.

- Water moves up into bell jar to takes space left by used oxygen

Gases exchange in the alveolus

- Oxygen is more concentrated in alviolus than blood capillary. Oxygen diffuses from
alveolus into the blood capillary
- Carbon dioxide is more concentrated in blood and less in air sac. It diffuses down the
concentration gradient into the alveolus where it is breathed out.

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 - The concentration of carbon dioxide is high in the blood because it is the product of
cellular respiration

Effects of physical activity on breathing and blood circulation

Page | 94
- Physical activity increases depth and rate of breathing.
- Rate is the measure of how many breaths per minute.
- Depth – how much air is being taken in, normally ½ litre per breath.
- It is measured using a spirometer
- Deep breathing increases amount of air taken per breathe. This increases oxygen supply
to the body and removal of carbon dioxide from cells.
- Increased rate of breathing ensures that more oxygen is supplied and more carbon
dioxide is removed.

Effects of smoking on the respiratory system

- Cigarate smoke contains;

a. Nicotine
- Addictive stimulant that stimulates adrenaline release
- Adrenaline Increases heart rate and blood pressure
- Increases risk of stroke, heart attack and impotence
b. Carbon monoxide
- Poisonous gas that combines irreversibly with haemoglobin to form carboxy-
haemoglobin
- Reduces efficiency of blood to transport oxygen
- Increases risk of atherosclerosis and thrombosis
c. Tar
- It is carcinogenic and causes respiratory cancers such as lung cancer
- Paralyses cilia lining air passages, reducing effectiveness of dust and irritant
removal
d. Irritants
- Paralyse cilia lining air passages
- Increase risk of chronic bronchitis and emphysema

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 - Short term effects of cigarate smoking are; destruction of cilia, -increased mucus
production and constriction of the bronchioles
- Long term of effects are; lung cancer, bronchitis,emphysema, Reduced birth weight
of babies born to smoking mothers.
Page | 95
Passive smoking – is when non-smokers breathe in smoke when in the company of smokers. It has
similar effects as smoking

TOPIC 8: Respiration
Aerobic respiration

- It is the complete oxidation of food substance in the presence of oxygen to release energy
- Aerobic respiration takes place in mitochondria

Word equation

Glucose + oxygen → carbon dioxide + water + heat energy

Uses of energy released

- Muscle contraction
- Protein synthesis
- Growth
- Cell division
- Active transport
- Digestion
- Temperature maintenance

Anaerobic respiration

- Release of relatively small amount of energy by breakdown of food substances in the

absence of oxygen.
- It takes place in cytoplasm

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Word equation

- In plants

Glucose alcohol + carbon dioxide + energy

Page | 96
In animals

Glucose lactic acid + energy

- Lactic acid is produced when oxygen is in short supply.

- Lactic acid cause fatigue
- Lactic acid is broken down by the liver

During vigorous exercises lactic acid accumulates in the muscles. It is broken aerobically after
exercise to carbon dioxide, energy and water. The oxygen needed to get rid of lactic acid after the
exercise is called oxygen debt. A fit person with an efficient circulatory system gets rid of the
lactic acid quickly.

Experiment to show that a respiring organism release carbon dioxide

- At 1 carbon dioxide is removed from incoming air by potassium hydroxide / soda lime.
- At 2 the limewater is check to make sure there is no carbon dioxide in the air.
- At 3 the respiring organism is placed there. This organism could be cockroach, earth worm,
rate, frog etc.

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 - At 4 there is carbon dioxide indicator. When a plant specimen is used in 3 the jar must be
covered to prevent the plant from using up carbon dioxide, because photosynthesis uses
carbon dioxide. It easier to show respiration in animals than plants.

- The suction pump attached to a tap ensures that air flows in the apparatus continuously. Page | 97

Germinating seeds

- Germination is an energy consuming process.

- Germinating seeds respire and release heat energy.
- Energy released is used for growth.

Experiment to demonstrate that germinating seeds release heat energy

-Seeds are washed in mild disinfectant to kill bacteria and prevent rotting of seeds.

- Two flasks are set up one with dead seeds and the other one with living seeds.

- Flasks are used because they prevent heat loss or gain

- The temperature in the flask with the living seeds will be higher than that of the dead boiled
seeds.
- Flask is upside down to prevent loss of heat by rising warm air.
- Living seeds produce heat because they respire

TOPIC 9: Transport

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Main components of the circulatory system

- Heart
- Blood vessels
- Blood Page | 98

The human transport system is a system of tubes with a pump and valves to ensure one way blood
flow

- It is a double circulation because the blood passes through the heart twice before
completing a full circuit of the body

Functions of the Circulatory system

- Movement of food molecules

- Movement of oxygen
- Movement of carbon dioxide
- Distribution of heat
- Conveying the immune system which fights against diseases when foreign substances enter
the body

THE HEART

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 Page | 99

Adaptations of the heart to pump blood

-Thick heart muscle - to withstand high pressure of blood

- Valves – prevent backflow of blood

- Double pump – prevents oxygenated blood and deoxygenated blood mixing

The cardiac cycle

Deoxygenated blood is received from the vena cava. Tricuspid valve closes

- Right atrium fills with blood, right atrium wall contracts

- Tricuspid valve opens, Blood moves into right ventricle

- Right ventricle contracts, Tricuspid valve closes

- Right semi-lunar valve opens, Blood flows into the pulmonary artery

- Blood passes through lungs, where it collects oxygen and flows back through the pulmonary
vein

- Blood flows into the left atrium, Bicuspid valve closes

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- Left atrium fills with blood. When full, the left atrium contracts to push blood

- Bicuspid valve opens and blood flows into left ventricle

- Left ventricle wall contracts and blood pressure rises

Page | 100
- Left semi - lunar valve opens and blood flows into the aorta.

- The aorta sub divides to form arteries, arteries form arterioles and arterioles form capillaries,
capillaries form venules, venules form veins, and vein form vena cava

Pulmonary circulation is the circulation in which deoxygenated blood is pumped to the lungs
through the pulmonary artery. The blood is oxygenated in the lungs and returns to the heart by
pulmonary vein.

Systemic circulation involves the pumping of oxygenated blood to all parts of the body except the
lungs via the aorta, artery, arterioles and capillaries. The blood returns as deoxygenated blood via
veins which form the vena cava towards the heart

The systemic circulation system has high blood pressure because the blood needs to reach all body
parts. The left ventricle is thicker than the right ventricle because it has to pump blood to distant
parts of the body. The pulmonary circulation has low pressure because the blood is being pumped
to a closer organ, the lungs.

Blood Vessels

Arteries

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 - They are vessels that carry blood away from the heart to body organs. Arteries branch into
arterioles and then into capillaries
- They have small lumen, Thick muscle layer and no valves
- The thick muscle layer is for withstanding the high blood pressure
Page | 101
Vein

- They are vessels that return blood to the heart

- They have a wider lumen, Thin muscle layer and valves
- The valves prevent the backflow of blood
- Blood in the veins towards the heart is mainly caused by muscular contraction

Capillaries

- Microscopic vessels that connect between the arteries and veins. They converge into
venules which converge into veins. They form networks called capillary beds that are
present in most body tissues.
- They are permeable wall, one cell thick and no muscle or elastic tissue
- The lumen is approximately one red blood cell wide
- They have no valves
Causes of high blood pressure
- Genetic predisposition,
- Stress
- lack of exercise
- Diet rich in fats

Coronary heart disease

- Coronary heart disease occurs when the coronary arteries become blocked or narrowed
- The heart muscles will no longer be able to receive sufficient oxygen and nutrients
- This can cause a heart attack. During a heart attack, blood supply to part of the heart muscle
is completely cut off due to blockage in the coronary arteries. The affected part dies, which
can affect the heart’s ability to pump and lead to heart failure.

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 - A cause of coronary heart disease is atherosclerosis, in which an artery wall thickens and
hardens due to the deposition of plaque, which causes the lumen of the artery to become
narrower.
- The narrowing of the lumen of the arteries causes an increase in blood pressure. This causes
Page | 102
arteries to develop rough linings, which increases the likelihood of formation of blood clots
inside the arteries. This is known as thrombosis.
- This obstructs blood flow in the afflicted artery. If itoccurs in a coronary artery, a heart
attack takes place.

Factors that contribute to atherosclerosis (or coronary heart disease) include;

- Diet rich in saturated fats and processed carbohydrates

- Stress
- smoking,
- obesity
- genetic predisposition

Preventive measures include;

- Healthy diet – low in cholesterol and saturated fats

- Not smoking – nicotine increases blood pressure
- Exercising – lowers stress and strengthens the heart

Functions of the blood

- Transports oxygen from the lungs to the body cells

- Transports nutrients from the digestive system to all body cells
- Transports wastes and carbon dioxide to be removed from the body to the excretory organs
- Distribute heat around the body
- Form clots at wounds to prevent excessive loss of blood
- Transports white cells that fight off pathogens or toxins
- Transports hormones from glands to all parts of the body

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Components of mammalian blood

- Blood is a connective tissue consisting of 45% cells suspended in 55% plasma.

- Plasma is a clear yellowish liquid consisting mostly of water. It contains soluble proteins
such as albumin and fibrinogen, as well as dissolved substances such as nutrients, waste Page | 103
products and ions

Cellular elements in blood include:

- Red blood cells (erythrocytes) which function to transport oxygen.

- White blood cells (leukocytes) are responsible for fighting infections in the body.
There are two main types of white blood cells:
 Phagocytes have lobed (bi-lobed, tri-lobed, multi-lobed) nuclei and granular
cytoplasm. They engulf and digest foreign particles such as bacteria
 Lymphocyte shave a large rounded nucleus and a small amount of cytoplasm.
They produce antibodies to protect the body from pathogens

- Platelets (thrombocytes) are small cell fragments which have no nuclei. They play
a role in blood clotting

Movement of materials between capillaries and tissue fluid

- Capillaries are found between tissue cells. As blood enters the capillaries, the
narrow lumen of the capillaries forces red blood cells to travel in a single line.
- Rate of blood flow decreases, allowing more time for the exchange of materials
between tissue cells and red blood cells.

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 - At the arterial end of capillaries, the blood pressure is high, forcing plasma through
capillary walls into tissues. Plasma proteins are unable to pass through capillary
walls.
- The solution bathing tissue cells becomes known as tissue fluid, or interstitial
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fluid.
- There is a higher concentration of nutrients and oxygen in blood than in the
interstitial fluid. They diffuse across the endothelium of the capillary into the
interstitial fluid, and from there, across the plasma membranes of tissue cells.
- Waste materials from the tissue cells diffuse into the interstitial fluid, where they
are present in higher concentrations than within the blood. They diffuse across the
endothelium of the capillary into blood and are transported to excretory organs for
removal.

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 Page | 105

TOPIC 10: IMMUNITY

- Immunity is the body’s ability to fight infection and pathogens at cellular level.
- Pathogens can enter the body’s through the mouth, the skin, blood etc
- There natural defense mechanisms are the skin, tears and white blood cells
- Skin-acts as a physical barrier against pathogens
- Tears – cleans the eye and have an enzyme called lysozyme which digest cell walls of
pathogens and so destroys them
- Mucus – traps microorganisms: spores and bacteria
- Clotting of blood – closes wounds and prevents loss of blood and entry of microorganisms
- White blood cells:
- There are two types of white blood cells
- Phagocytes engulf pathogens
- Lymphocytes produce antibodies which destroys pathogens

Active immunity

- When a pathogen or toxin enters the body, the body gradually responds by producing B
and T lymphocytes that can fight the pathogens. B-lymphocytes produce antibodies that
can specifically destroy the antigen (foreign substance).

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 - T lymphocytes bind to the antigen and destroys it. T lymphocytes divide and differentiate
to form T-killer lymphocytes that bind to pathogens and kill them
- The immunity is considered to be active because it is able to produce immune cells that
can destroy the antigens.
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There two types of active immunity; natural active immunity and artificial active immunity
(vaccination).

- Natural active immunity involves natural infection of the body by pathogens and the body
responding by producing immunity cells and antibodies to destroy the pathogen
- Artificial active immunity is also called vaccination. It involves introduction of an
attenuated antigen such a virus or bacteria into the body. The body in turn responds by
producing specific immunity cells and antibodies to destroy the pathogens.
- Artificially passive immunity involves the introduction of antibodies into the body to
fight a particular antigen. The immunity system is not activated to produce its own
antibodies. The antibodies are synthetically made in the laboratory or harvested as serum
from other humans or animals that have naturally produced the antibodies.
- Natural passive immunity is transfer of antibodies from the mother to child during
pregnancy or breastfeeding.

Effects of the human immunodeficiency virus (HIV) on the body

- The virus attacks CD4 lymphocytes, the specialized white cells that activate the body’s
immune system.
- The virus destroys the cells resulting in the failure to activate the immunity to fight an
infection. The body becomes vulnerable to opportunistic infections such as TB.

The importance of immunization or vaccination

- Introducing an antigen into the body triggers an active immunity. A vaccine is a half
dead/attenuated antigen that is introduced into the body orally or by injection.
- Vaccination programs can successfully control diseases. In order for vaccination to be
successful they should be affordable, easy to store and transport and have no or little side
effects.

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 - Zimbabwe has an Extended Immunization program to protect infants and children from
diseases such measles, polio, whooping cough, tetanus, diphtheria and diarrhea caused by
rotavirus.

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TOPIC 11: REPRODUCTION IN HUMANS

Male Reproductive System

- Testes – The male reproductive organs (gonads). Produces sperms (male gametes) and
male sex hormone, testosterone. Male sex hormones are responsible for development and
maintenance of secondary sexual characteristics. Leading from the end of each testis is a
narrow tightly-coiled tube called the epididymis in which sperms are stored.
- Scrotum– The two testes are held in a pouch-like sac outside the body called the scrotum.
The lower temperature in the scrotum is essential for sperm production.
- Sperm ducts– The sperm ducts (vas deferens) lead from the epididymis. During
ejaculation, they transport sperm from the epididymis to the urethra
- Prostate gland– The prostate gland is a large gland which secretes directly into the urethra
through several small ducts. The fluid contributes to semen. Semen is a composition of
sperm and fluids from the sex glands containing nutrients and enzymes which nourish and
activate the sperm, allowing them to swim actively.

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 - Seminal vesicles– Ducts from the seminal vesicles join the vas deferens. The seminal
vesicles are a pair of glands that secrete a fluid that makes up a proportion of semen
- Cowper’s glands– The Cowper’s glands, also known as bulbourethral glands, are a pair
of pea-sized glands located beneath the prostate. The fluid produced by the gland
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contributes to semen.
- Urethra– The urethra is a common passage for urine and semen to pass out of the body.
The sphincter muscle at the base of the bladder prevents urine from passing out of the
bladder during ejaculation of semen.
- Penis– The penis consists of cylinders of spongy erectile tissue around the urethra. The
tissue contains numerous spaces that allow it to fill up with blood. When that happens,
the penis becomes erect and hard, allowing it to enter the vagina of a woman during sexual
intercourse to deposit semen.

Gamete formation

- Inside each testis are thousands of narrow, coiled tubules called seminiferous tubules.
- They are packed into sections called lobules. Sperms are produced inside these tubules.
The sperms are stored inside the epididymis. Around these tubules are the cells that produce
testosterone.

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Female Reproductive System

Page | 109

- Ovaries– The female reproductive organs (gonads). Produces ova (singular: ovum) and
female sex hormones e.g. estrogen and progesterone. Female sex hormones are responsible
for development and maintenance of secondary sexual characteristics. Mature eggs are
released from the ovaries into the oviducts.
- Oviducts– The oviduct (fallopian tube) is a narrow muscular tube leading from the ovary
to the uterus. The oviduct has a funnel-like opening to make it easier for ova to enter the
oviduct. Cilia on the inner lining help move the ovum to the uterus. The ovum is usually
fertilised in the oviduct.
- Uterus– The uterus is a thick muscular organ that can stretch as the fetus increases in size
during pregnancy. The smooth muscles in the uterine wall contract to expel the fetus during
birth. The uterus is lined by a lining called the endometrium (uterine lining). The
endometrium is richly supplied with blood vessels and is the site of implantation of the
embryo post-fertilisation. It is broken down every month and flows out of the body in the
process called menstruation.
- Cervix– The cervix is a circular ring of muscle at the neck of the uterus. It opens into the
vagina. It enlarges during birth to allow the passage of the fetus.
- Vagina– The vagina is a thin-walled chamber where sperm is deposited during sexual
intercourse. It forms the birth canal through which the baby is born.

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The female gametes are called the ova or eggs. Ova are much larger than the sperm. A female is
born with about 450-500 immature ova. She produces usually one mature egg every month from
the onset of her puberty.

Structure of male and female gametes Page | 110

Ovum

- They have an oval/ circular shape

- They are much larger than the sperm cell ( about 0.1mm in diameter)
- They a dense cytoplasm containing food reserves in form of yolk
- They are usually the largest cells in the animal body
- One mature ovum is produced by the ovary per month

Sperm

- The male gamete, the sperm (singular: spermatozoon, plural: spermatozoa), consists of a
head, middle piece and tail
- The head contains:
- (a) An acrosome, an enzyme-containing sac. The acrosome contains digestive enzymes
which break down the outer membrane of the ovum, allowing for fertilisation
- (b) A small amount of cytoplasm and a large haploid nucleus

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 Page | 111

- The middle piece contains numerous mitochondria arranged spirally to provide energy for
the sperm to swim to the egg.
- The tail (flagellum) beats to propel the sperm towards the egg
- They are very small in size as compared to the ovum (10 000 smaller than the ovum)
- Sperms are continuously produced in the testis. One ejaculation contains about 300 million
sperms

The menstrual cycle

- It is a monthly cycle experienced by all woman and girls of age between 11-45 years.
- The menstrual cycle normally spans over 28 days
- Day 1 to 5: Menstruation lasts for 5 days. The first day of menstruation is day 1 of the
menstrual cycle. The endometrium breaks down and flows out of the body.
- Day 6 to 13: The ovaries secrete estrogen which causes the repair and growth of the
endometrium. The endometrium becomes thicker.
- Day 14: A mature ovum is released from the ovaries. Secretion of progesterone is
stimulated. The ovum dies after about 1 to 2 days if it is not fertilised.
- Day 15 to 28: Progesterone and estrogen are continually being secreted for continued
development and maintenance of the endometrium. Progesterone maintains the
endometrium by causing it to become thicker. The endometrium readies for implantation.

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 Towards the end of the cycle, secretion of progesterone and estrogen decline sharply. The
endometrium is no longer maintained and disintegrates. It flows out from the uterus
together with some blood through the vagina. This marks the beginning of another cycle.
- The fertile phase of the cycle is from day 11 to 17. This is because sperms can survive for
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2 to 3 days in the female reproductive system. Sperms deposited in the vagina from day 11
onwards can fertilise the ovum which is released from the ovaries on day 14. The ovum
can survive for 1 to 2 days after ovulation; hence fertilisation is possible up till day 17.
- The rest of the days make up the infertile phase of the menstrual cycle. Sexual intercourse
during this period is unlikely to result in fertilisation since no ovum is present.

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 Page | 113

Pathway of sperm from testes to ovum

- During sexual intercourse, semen containing sperms is deposited into the vagina of a
woman.
- The fluids from the male sex glands that make up semen provide nutrients and protection
for the sperms, as well as a medium for them to swim in.
- The sperms swim up the oviducts and encounter the ovum.
- The acrosome of the sperms release enzymes to disperse the layer of cells surrounding the
ovum and break down the outer membrane of the ovum.
- Only 1 sperm will enter the ovum. The plasma membranes of the sperm and the ovum fuse
and the sperm nucleus enters the ovum.
- The plasma membrane of the egg undergoes a change as soon as a single sperm has entered,
preventing other sperms from entering.
- The sperm nucleus fuses with the egg nucleus, forming a fertilised ovum known as a
zygote.
- Fusion of male and female nuclei to form a zygote is called fertilisation
- `The remaining sperms eventually die.

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 The development of a zygote
- The cilia on the oviduct lining help move the zygote towards the uterus.
- In the meantime, the zygote divides many times to form a hollow ball of cells called the
embryo.
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- 5 to 7 days after fertilisation, the embryo comes into contact with the endometrium and
becomes embedded. This process is known as implantation.
- Tissues growing out from the embryo invade the endometrium, forming the placenta. The
placenta is an organ that contains both maternal and embryonic blood vessels.
- It allows for diffusion between the maternal blood circulation and embryonic blood
circulation.

The placenta:

(a) Provides nutrients (glucose, amino acids and mineral salts) and oxygen for the embryo

(b) Removes waste materials such as urea and carbon dioxide

(c) Allows protective antibodies to diffuse from maternal blood into embryonic blood

(d) Provides a barrier preventing maternal blood and embryonic blood from mixing. Reasons for
this include:

 Maternal blood pressure is much higher than embryonic blood pressure and would damage
vital tissues.
 The embryo might have a different blood group, resulting in agglutination if mixing of
blood occurs.
 Produces progesterone which maintains the endometrium during pregnancy

The placenta cannot prevent the passage of certain chemicals like drugs and viruses for example
HIV

The embryo eventually becomes connected to the placenta by the umbilical cord. Embryonic blood
travels to the placenta via the arteries of the umbilical cord and returns with oxygen and dissolved
food substances via the umbilical vein.

- A membrane called the amniotic sac begins development at the same time as the placenta,
and encloses the embryo in a fluid-filled space. The fluid is known as amniotic fluid.

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 - The amniotic fluid functions to:
- (a) Absorb shock, support and protect the embryo from physical injury
- (b) Lubricate the vagina during birth to reduce friction
- (c) Allow the fetus to move freely during development
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- (d) Prevents sudden temperature fluctuations
- About 9 weeks after fertilisation, the embryo has developed into a fetus.

Dangers of taking drugs during pregnancy

Some things taken into the body whilst pregnant can harm the developing baby.

- Smoking, drinking alcohol, abusing prescription drugs or using illicit drugs such as
cocaine and cannabis can all pass through the placenta and have a negative effect on
the baby.
- Illicit drug use during pregnancy may cause; miscarriage, preterm labour, birth defects,
still birth, withdrawal symptoms in the baby after birth, poor fetal growth rate,
cognitive and behavioral problems
- Nicotine in the cigarate smoke constricts blood vessels in the placenta resulting in low
supply of nutrient and oxygen rich blood to the developing fetus. This ultimately results
in poor development of the baby, underweight and addiction to nicotine.
Causes of infertility

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 - Infertility means being unable to become pregnant. There several reasons why couples
fail to have a baby.
- Causes of infertility in woman include;
 Problems with ovulation due to thyroid problem or failure to ovulate
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 Blocked oviducts due to fibroids or growths preventing passage of ovum
 Damaged uterus which prevents implantation
 Age; the older the woman the less likely she is to conceive
 Alcohol abuse reduces the production of health ova
 Growth of structures such as cancer, fibroids in the uterus preventing
implantation
 Physical damage of the male reproduction system by STIs
 Hormonal imbalance
- Causes of infertility in men includes;
 Low sperm count in the semen
 Abnormal sperm structure resulting in poor mobility
 Some drugs or medication can damage sperms
 Cancer of the prostate

Methods of contraception

Natural methods;

 Abstinence
 Rhythm method
 Withdrawal

Chemical methods;

 Spermicide- the come as a cream or gel and they are placed high in the vagina before sexual
intercourse. They kill sperms

Hormonal methods’

 Oral contraceptive pill- contains hormones that prevent the ovary from releasing the ovum

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  Norplant- a small device planted under the skin of a woman. Prevents pregnancy for upto
5 years by releasing hormones into the blood stream that prevents ovulation

Barrier methods;
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 Condom
 Femidom
 Intra Uterine device
 Diaphragm- a small thin rubber disc placed in the vagina at the cervix before sex. It covers
the cervix and prevents passage of the sperms

Sterilization methods;

 Vasectomy- the sperm ducts are cut and tied. This prevents the passage of the sperms into
the urethra.
 Tubal ligation- the fallopian tubes are tied, blocked or cut. This prevents the passage of
ovum to the uterus thus preventing fertilization with the sperm

Sexual transmitted Infections (STIs)

Sexually transmitted diseases are diseases that are passed from an infected person to a healthy
person during sexual intercourse. Sexually transmitted infections are caused by bacteria, viruses
and fungi.

Gonorrhea

- It is caused by a bacteria Neisseria gonorrhoeae. The signs include;

 burning sensation during urinating due to the inflammation of the urethra
 thick creamy yellowish discharge from the tip of the penis or the vagina joints are
swollen and painful
 Swelling and abnormal vaginal discharge
 If untreated it spreads to other body parts including heart valves, and joints
 joints are swollen and painful
 Can result in sterility
 newborn baby may be infected as it passes through the vagina

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Gonorrhea is treated using antibiotics such as kanamycin.

Syphilis

Syphilis is caused by a bacteria.

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- painless sore appears on or near the genital organs usually just inside the vagina or on the
end of the penis
- mild fever occurs when the bacteria infect other parts of the body
- lymph nodes swell
- non-itchy rash appears on the body
- blindness, insanity and paralysis may occur when the bacteria attack the brain

Syphilis can be treated with antibiotics such as penicillin

Chancroid (ulcers)

It is a bacterial disease. It causes open sores on or around the penis and vagina 3-5 days after sexual
intercourse. The ulcers can be treated with antibiotics.

HIV/AIDS

Acquired Immune Deficiency Syndrome (AIDS) is a disease cause by Human Immunodeficiency

virus.

- HIV progressively reduces the effectiveness of the infected person’s immune system in
protecting it from infection.
- Symptoms of AIDS include:
 Persistent fever, sweat, swollen glands, chills, weakness and weight loss
 Pneumonia
 Tuberculosis
 Chronic diarrhea
 Brain infection

HIV is transmitted:

 By sexual intercourse with an infected person

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  By sharing and reusing contaminated needles during intravenous drug use, tattoos and
piercing
 By receiving a blood transfusion from an infected donor
 During pregnancy and childbirth. An infected mother could pass on the disease to her child Page | 119

Spread of HIV can be prevented by:

 Having protected sexual intercourse. A condom reduces the risk of infection.

 Abstinence from sex or having sex with only one partner
 Not sharing objects that could be contaminated with blood or bodily fluids such as
hypodermic syringes, razors and toothbrushes
 Screening of blood in a blood bank for HIV infection to reduce chances of transmission
during blood transfusions
 Infected mothers should undergo antiretroviral therapies and give birth by caesarean
section to minimise risk of transmission to the foetus. Breastfeeding should be avoided
after birth.
 Visiting reliable operators for tattoos, piercings or acupuncture where needles are
sterilized or disposable

Genital warts

They are caused by human papilloma virus (HPV). Symptoms include;

 Skin colored or whitish bumps on the vulva, vagina, cervix, scrotum, anus, penis, and groin.

They can be treated by surgical removal or prevented by vaccination or antiviral drugs

Genital herpes

It caused by simplex virus. Symptoms includes sores, itching on genitals. Antiviral drugs are used

MICROBIOLOGY AND BIOTECHNOLOGY

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Characteristics of microorganisms

- Microorganisms are organisms that are too small to be seen with a naked eye.
- A light microscope or electron microscope is used to view microorganisms.
- They are usually unicellular Page | 120
- They are able to carry out functions of life; reproduction, respiration, growth, excretion,
sensitivity to the environment, nutrition and movement
- Contain genetic material usually in DNA form
- They reproduce quickly.
- They have no sex (male and female)

Types of microorganisms

Virus

- These are very small structures, from 0.02 – 0.3um in diameter

- Viruses can be seen only by using an electron microscope using a magnification of about
x30,000
- When a virus is not invading a cell, it does not grow or reproduce.
- It does not feed, respire or excrete

Bacteria

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 Page | 121

- They are unicellular microorganisms

- They usually feed on dead animal and plant material
- Some live as parasites causing harm on their host
- Most reproduce by binary fission

Fungi

- They feed on dead organic matter

- Some live as parasites causing diseases
- They have thread-like filaments called hyphae

Roles or economic application of microorganisms

1. decomposition (economic application)

- Bacteria and fungi breakdown dead organic matter, releasing nutrients into the soil. The
nutrients are absorbed by plants.
- Microorganisms can be genetically engineered to breakdown complex chemicals or
substances such as plastics, crude oil, uranium heavy metals and utilize it as food source.
- This helps to remove environmental contaminants that would destroy organisms. This
process of contaminants removal by microorganisms is called bioremediation.

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 2. Yeast is used in the production of bread by fermentation
3. Yeast is used in fermentation of starch to produce alcohol
4. Certain bacteria is used to produce yoghurt, milk, cheese etc
5. Fungi is used in the production of penicilin drug
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6. Genetically engineered bacteria is used to produce insulin hormone

Recombinant Gene Technology

- Biotechnology is the use of plants, animals and microorganisms to produce useful products
such as drugs and food (eg cheese, milk and yoghurt).
- Recombinant DNA is a DNA made of genetic material from two or more sources. The
process involves artificially joining pieces of DNA from different species.
- An allele of one organism for example a bacteria coding for a characteristic of interest for
example Bt toxin can be cut from the DNA of the bacteria.
- The cut allele or gene can be joined or spliced into the DNA of another organism that lacks
that allele.
- The organism that has received the new gene can now express the new characteristic, in
this case the Bt protein toxin.
- This process is called recombinant DNA technology. It makes it possible to transfer genes
from one organism to another without sexual reproduction process.

Production of insulin using recombinant DNA technology

- Insulin gene is cut out from the DNA of beta cells of islets of Langerhans of the pancreas
using restriction enzymes
- The insulin gene is the gene of interest.
- A plasmid is removed from a bacteria. The plasmid is cut open using the same restriction
enzyme to produce sticky ends that are complementary to the cut insulin gene.
- The insulin gene is joined to the plasmid using ligase enzyme making it a recombinant/
modified plasmid.
- The recombinant plasmid is placed into a bacteria.
- The bacteria multiplies together with the plasmid

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 - The insulin gene is used by the bacteria to produce insulin hormone
- The insulin is harvested, purified and packaged for use

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Benefits of recombinant DNA technology

- Production of insulin for treating diabetes

- Production of human growth hormone for treating people who are abnormally short
- Production of bovine growth hormones which are injected into dairy cows to produce
more milk
- Production of vaccines for example COVID-19 vaccines, hepatitis B and HIV vaccines
- Production of transgenic plants that are drought resistant, salt tolerant, higher nutrition
content.
- Production of modified bacteria that can make better yoghurt and cheese
- Higher yield since fewer crops are lost to disease or poor environmental conditions.

Potential risks for recombinant DNA technology

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 - Loss in genetic diversity in crops due to monoculture
- Pest resistant crops may kill untargeted insects for example Bt maize may kill butterflies
instead of fall armyworm.
- May introduce allergens in crops
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- Its long term effects to the environment is not yet fully established
- Herbicide resistant genes can be transferred to other wild related plants through pollination
resulting in super weeds
- World food production would be controlled by a few biotechnology companies.

GENETICS
- Chromosome– A chromosome is an organised structure of deoxyribonucleic acid (DNA)
and protein that is found in the nuclei of cells. DNA contains genetic information used in
the development and functioning of all organisms
- A gene is a DNA segment located in a chromosome, which codes for a single unit of
inheritance. The place on the chromosome where the gene is located is called the gene
locus.
- Allele– It is a different version of the same gene. They are located on the same gene locus
in homologous chromosomes
- Phenotype– An observable characteristic of an organism. It can be physical (appearance),
behavioral or physiological. It depends on the genotype of the organism.
- Genotype– The genetic make-up of an organism. The genotype of an organism cannot be
easily predicted from the phenotype (appearance) because of the existence of dominant and
recessive alleles.
- Homozygous– Each organism inherits two alleles for a given characteristic, one from the
mother and one from the father. An organism is said to be homozygous for a given trait
when it contains two identical alleles for that trait.
- Heterozygous– An organism is said to be heterozygous for a given trait when it contains
two different alleles for the characteristic.

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 - Dominant allele– A dominant allele is the allele that is fully expressed in the phenotype
under both homozygous and heterozygous conditions.
- Recessive allele– A recessive allele is the allele that is only expressed in the phenotype
under the homozygous condition. It is masked in the phenotype under heterozygous
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conditions.

Monohybrid cross

Pure purple flowers were crossed with pure white flowers. The resulting offspring were all purple.
Draw a monohybrid cross that gave the results. Let P represent the dominant allele for purple
flowers, and p, the recessive allele for white flowers.

- A homozygous dominant plant (PP) will only produce gametes containing a single copy of
the P allele.
- A homozygous recessive plant (pp) will only produce gametes containing a single copy of
the p allele
- It is accomplished by crossing the organism with an organism that is homozygous
recessive.

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 Page | 126

- A PP x pp cross produces only Pp offspring. Hence, if all the offspring have purple flowers,
then the unknown parent must be homozygous dominant for the trait.
- A Pp x pp cross produces a 1: 1 phenotypic ratio. Hence if both purple and white
phenotypes appear among the offspring, then the unknown parent must be heterozygous
for the trait.

Dominance

Complete dominance is when the heterozygote has the same phenotype as the dominant
homozygote. The recessive allele present in the heterozygote is masked by the dominant allele.

Co-dominance is when both alleles contribute equally to the phenotype.

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 -
An example would be the ABO blood typing system in humans. Human blood groups are
determined by 3 alleles for 1 gene: IA, IB and IO
-
IO is recessive to both IA and IB, while IA and IB are codominant when paired together.
- The various combinations of the alleles and the resultant phenotypes are shown in the table
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below:

- The gene for blood group codes for a protein present on the surface of red blood cells,
called an antigen.
- The allele IA codes for antigen A, IB codes for antigen B, and no antigen is expressed for
allele IO
- .For IA IB genotype, both antigen A and antigen B are expressed since each of the alleles
produces its own antigen. Both alleles contribute to the phenotype, which is blood group
AB.
- The gene for human blood groups is said to have multiple alleles since it exists in more
than two alleles.

Sex determination

- A karyotype is a picture of a set of chromosomes in a cell. During the preparation of a

karyotype, chromosomes are stained and examined under a microscope. A picture is taken
and edited to arrange the chromosomes by size.
- A normal karyotype will show 22 pairs of homologous chromosomes called autosomes,
and 1 pair of sex chromosomes.

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 Page | 128

- In humans, sex is determined by sex chromosomes. Human sex chromosomes are the X
chromosome and the Y chromosome.
- From the karyotype, it can be seen that the X chromosome is much larger than the Y
chromosome.
- Human males have one X chromosome and one Y chromosome. They have the XY
genotype.
- Human females have two X chromosomes. They have the XX genotype.
- Genetic diagram for sex determination:

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Mutations

- Mutation is a change in gene or chromosomal structure. Mutations that occur in gamete

DNA can be passed down to the next generation.
- Mutations that occur in normal body cells (somatic mutations) are not passed on to the next Page | 129
generation. However, they are responsible for certain types of cancer.
Factors that increase rate of mutation
- Mutations can also be caused by exposure to mutagens. Mutagens are physical or chemical
agents that increase the rate of mutation. Examples of mutagens are ultraviolet radiation,
X-rays, radioactive particles such as gamma rays, certain chemicals such as benzene,
ethidium bromide and nitrous acid. Genetic disposition also increases the risk of
developing cancer.

Gene mutation increases the amount of genetic variation in the gene pool as it introduces
new alleles. Some mutations can be favourable.
- Examples of a disease caused by gene mutation is sickle-cell anaemia and albinism
- Example of chromosomal mutation is Down syndrome (a condition in which each body
cell of the afflicted individual contains 47 chromosomes instead of the usual 46.

Variation

- Genetic variations are differences in phenotypes between individuals of the same species.
- In discontinuous variation of a characteristic, individuals possess distinct and separate
phenotypes with no intermediates.
- Examples of discontinuous variation are the flower colour in pea plants (either purple or
white), ABO blood types and sex (either male or female)

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 Page | 130

- Discontinuous variation is controlled by alleles of a single gene or a small number of genes

and is seldom affected by the environment.
- In continuous variation of a characteristic, an unbroken range of phenotypes exist in the
population.
- Examples include height, skin colour, intelligence and weight, in which many intermediate
phenotypes exist.
- Continuous variation is caused by the effect of many genes and is often affected by
environmental factors.

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 Page | 131

- Intermediate phenotypes are usually more common than extreme phenotypes (i.e. very tall
or very short, very dark skin or very pale skin, etc), and when plotted on a graph, a bell-
shaped curve is obtained.
Causes of variation
- Genes- genes determine how an organisms will look. Organisms with different alleles will
look differently
- Environment- It determines the extent of the expression of genes in the phenotype. For
example if a plant has genes for high yield, it will give low yields if grown on soil lacking
nutrients

Selection

- Evolution is the change in genetic material of a population from one generation to the next.
Over time, it can produce major changes in a population that could give rise to a new
species.
- Natural selection is a major mechanism by which evolution takes place because it causes
helpful genes to become more common and deleterious genes to become rarer.
Natural selection as a possible mechanism for evolution

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 - In a given population there is variation among the organisms. The variations are a result of
genes, environmental factors and mutations
- There is completion for food, shelter and mating. The environment also apply selection
pressure such as weather and climate. The organisms that have the most favorable
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characteristics survive while the ones with unfavorable traits do not survive to reproduction
stage.
- The organisms with favorable traits would have adapted to the environment. They grow
and reach the reproduction stage. They mate and produce off-springs.
- A high number of the off-springs will be possessing the favorable traits and a few off-
springs will have unfavorable traits.
- Over many years of repetition of selection and reproduction, the unfavorable traits
disappear from the gene pool and the favorable traits increases. Eventually a population
emerges that is different from the original population.

Artificial selection

- Artificial selection, also known as selective breeding, is the intentional breeding for
particular genetic traits.
- It is used to produce several economically important crops and animals.
- Traits such as disease-resistance or high quality and yield of crop, tolerance to
environmental pressures such as pH, salinity, drought, temperature, tolerance to insects,
and tolerance to herbicides are selected for by plant breeders.
- In animals, traits such as fast-growing, muscular, reproductively-efficient (fertile), good
fat marbling (in cattle bred for meat), good milk production (in cows), and good egg
production (chickens) are selected.
- Artificial selection involves the following stages;
 Choosing the off-springs with desirable features
 Crossing these individual to produce the next generating of off-springs
 Selecting the off-springs that have the most desirable features.

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 BIODIVERSITY
Five kingdoms of living organisms Page | 133

- Prokaryotae/Monera
- Protoctista/Protista
- Fungi
- Plantae
- Animalia
Characteristic features of the five kingdoms
Prokaryotae/Monera
- Simple, single celled prokaryotes
- Some use chemicals, sunlight to make food
- Others live as parasites
- Reproduce by simple cell division
- Examples include bacteria and cyanobacteria

Protoctista/Protista

- Simple, single celled eukaryotes and sometimes single joined

- Some make their own food
- Some feed on other organisms
- Most reproduce by asexual reproduction
- Examples include amoebas and diatoms

Fungi

- They are multicellular eukaryotes

- There chitin is made up of chitin
- They feed on dead plant and animal remains
- Some are parasites
- They reproduce sexually and asexually by spores
- Examples include mushrooms, yeasts and molds

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 Plantae
- Complex multicellular eukaryotes with cellulose cell walls
- They make their own food by photosynthesis
- Their cells contain chlorophyll Page | 134
- They reproduce sexually by gametes or asexually
- Examples include trees, grasses, and ferns

Animal

- Complex multicellular eukaryotes with no cell walls

- They feed on other organisms
- They reproduce sexually by gametes and asexually
- Fish, snakes, birds, Animalia

Threats and Conservation measures

Threats to biodiversity
- Ecosystems are destroyed as a result of human activities
- As ecosystems are lost species become extinct

Deforestation

- It is the permanent clearing of forest land for firewood, agriculture, timber and
industrialization.
- Forests are habitats for organisms such as birds and animals.
- They provide food and shelter to animals.
- Clearing forests results in loss of habitat and food resulting in death of animals and loss of
biodiversity
- Forests are carbon sinks removing a lot of carbon dioxide from the atmosphere.
Deforestation therefore results in buildup of carbon dioxide in the atmosphere resulting in
global warming

Invasive species

- These are plants or animals that were not naturally in an area and were introduced in
that area artificially or naturally

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 - They have a rapid growth rate thus they quickly colonize the area and push the
indigenous plants
- This reduces biodiversity in that area
- Examples of alien plants are hyacinth
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Habitat destruction

- Animal habitat is mainly lost through urbanization, mining and agriculture

- This results in loss of biodiversity

Climate change

- Climatic changes are being caused by global warming. Global warming is the result of
release of greenhouse gases in the atmosphere. They trap heat radiation from the earth
resulting in gradual increase in the earth atmosphere
- Climatic changes results in adverse weather patterns such as drought and floods
- Floods and drought destroys forests, rivers and the ground resulting in destruction of
animal habitat and animals. There is loss of habitat

Pollution

- Pollution is the introduction of substances into the environment has has harmful effect
- Pollutants are spread through the air, water, soil and food chains
- Examples of pollutants include heavy metals such as uranium, plastics, oil spills,
sulphur dioxide, soot and sewage.
- Pollution kills plants, aquatic organism and reduces biodiversity

Conservation measures

- Afforestation
- Uses of alternative sources of energy
- Preservation of endangered species and agents

ECOSYSTEMS

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 - It is a self-contained system of interdependent organisms and their physical environment

Components of an ecosystem

- Physical components are soil, water, air and rocks

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- Biological components are the living organisms

The role of soil in an ecosystem

-Soil is where trees grow on, animals walk and live on

- It acts as a habitat for many organisms.

Biological components of soil

- The biological components of the soil are all the living organisms found in the soil.
- This includes earthworms, litter, humus, microorganisms (fungi and bacteria), termites and
nematodes

The role of the biological components

- The humus and litter improve the crumb structure of the soil when decomposed.
- Microorganisms such as fungi and bacteria decompose dead plant and animal material and
release nutrients into the soil. This improves soil fertility
- Nitrogen fixing bacteria improves soil fertility by converting atmospheric nitrogen to
nitrates in the soil. The nitrates are used by plants.
- Worms such as earthworms and nematodes aerate the soil by burrowing the soil
- Microorganism also moderate the soil pH by decomposition of humus.
- The soil with high humus content have good crumb stricter and high nutrient content which
is good for plant growth

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 Page | 137

Properties of clay, loam and sandy soils

The size of soil particles in a soil sample is known as soil texture. Soil texture can be classified as
loam, clay and sand. Loam is a mixture of clay and sand

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 Page | 138

Air content of soil

- The spaces between soil particles are called pores.

- These pores contain air, water and minerals. Air is important in soils as plant roots need
oxygen for healthy growth
- The humus content in the soil increases the air content found in the soil

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 Page | 139

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 Page | 140

Soil pH
- It is a measure of how acidic or alkaline is the soil water.
- Soil pH can be tested using a universal indicator, pH meter. Most plants grow best in neutral
Ph

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 Page | 141

Natural ecosystem
- A natural ecosystem is an ecosystem that has not been affected by human influence
- Natural ecosystems consists of organisms that interact with each other through feeding
relationships and with abiotic components of the ecosystem.
- The organisms are divided into trophic levels which are; producers, consumers and
decomposers
Producers
- Producers are organisms that can make their own food for example plants
- Plants make their own food through the process of photosynthesis

Consumers

- Consumers cannot make their own food, they feed on other organisms to get energy and
nutrients
- All animals are consumers they depend on plants and other animals for food
- There different classes of consumers;
- Primary consumers- are animals that feed on plants to obtain their food. They are also
called herbivores

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 - Secondary consumers- They are animals that feed on primary consumers to get their food.
They are also called carnivores. Some secondary consumers feed on both animals and
plants. They are called omnivores
- Tertiary consumers- they are animals that feed on primary and tertiary consumers
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- Decomposers- these are organisms that break down dead animal and plant remains to get
nutrients. The process of decomposition releases nutrients into the soil. Decomposers
includes bacteria and fungi
Food chains
- A food chain is a linear flow of energy or nutrient in an ecosystem
- Food chains always start with a producer

Food webs

- A food web is the interconnections of all food chains in an ecosystem

Energy flows in food chains and food webs

- The ultimate source of energy for all organisms is the Sun

- Producers converts sunlight energy into carbohydrates.
- Primary consumers feed on plants to obtain energy stored in carbohydrates
- The energy is stored in the body of primary consumers as glycogen and fat

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 - Some of the energy consumed from plants is used for movement, reproduction, growth and
warming the body
- Some of the is lost as heat in urine and respiration
- When primary consumers are eaten by secondary consumers, the energy is transferred to
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the secondary consumers from primary consumers.
- When tertiary consumers feed on secondary producers the energy is transferred to them.
- At every trophic level most of the energy is used for growth, reproduction and movement
- Energy passes from organism to another in a food web or food chain through feeding
- Decomposers are the last to receive the energy when the organism dies

Trophic means feed. Producers are in the first trophic level, primary consumers are in the second
trophic level, secondary consumers are in third trophic level and the fourth trophic level is the
tertiary level.

Ecological pyramids

- They are constructed to show numbers of organisms, biomass or energy stored at each
trophic level

Pyramids of numbers

- Pyramids of numbers give the number of organisms at each trophic level

- It is a bar chart plotted horizontally with the area of each bar being proportional to the
number of organisms in that trophic level

- The number of organisms decreases at each level as we go up the pyramid

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 - However the case is the different in a baobab tree because producer is one and there are
many consumers. The baobab tree is big enough to support the whole ecosystem with
energy

Pyramid of biomass Page | 144

- Pyramids of biomass are a measure of mass of living organisms at each trophic level
- The total mass of all living tissue at each trophic level is called biomass
- Biomass is expressed as kilograms of organic matter per unit area (kg/m2)

Pyramid of energy

- A pyramid of energy shows the amount of energy that can be transferred from one trophic
level to the next
- The amount of the energy at each trophic level decreases as we go up the pyramid because
much energy is utilized in movement, reproduction and lost as heat during resperiation

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 Page | 145

Nutrient cycles
- Organisms recycles all nutrients that organisms need for survival and reproduction
Carbon cycle
- Carbon is found in animals and plants in the form of carbohydrates, fats and proteins
- Carbon is found in atmosphere, sea, in organisms, oil, coal and calcium carbonate
- Photosynthesis and respiration are the main processes that drive the carbon cycle

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 1. Carbon dioxide is removed from the atmosphere by plants by plants during
photosynthesis. They convert it into carbohydrates mainly starch
2. Animals obtain carbon when they eat plants and other animals. They use the carbon to
make other compounds such as fats, glycogen and proteins
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3. Carbon returns into the atmosphere in form of carbon dioxide during cellular
respiration
4. Carbon also enters the atmosphere when fossil fuels such as coal and petrol are burned
5. Carbon is also released in the form of carbon dioxide through the decomposition of
dead animal and plant material

Nitrogen cycle

- Organisms need nitrogen to make proteins. Nitrogen is found in the atmosphere in the form
that cannot be utilized by plants
- It must firstly be changes to nitrates that can be absorbed by plants
- Animals get their protein from plants and animals they feed on

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 - Nitrogen fixing bacteria convert nitrogen in the soil into nitrates. The nitrates are inturn
absorbed by plants which uses the nitrogen to make proteins
- Animals excrete nitrogen in the form of ammonia or urea. Decomposers in the soil such as
nitrifying bacteria converts ammonia into nitrites while other bacteria converts nitrites to
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nitrates which can be absorbed by plants
- Atmospheric nitrogen can be converted into nitrogen dioxide during lightning. The
nitrogen dioxide dissolves in rain. In the soil the nitrogen dioxide is converted to nitrates
by bacteria
- Denitrifying bacteria converts nitrates to atmospheric nitrogen

Artificial ecosystem
- Artificial ecosystems are ecosystems that have experienced changes because of human
activities such as agricultural systems
Biodiversity in natural and artificial ecosystems
- Biodiversity is a measure of variety of organisms in any given ecosystem
- Natural ecosystems have a greater variety of organisms than artificial ecosystems
- Artificial ecosystem have only animals or plants are beneficial to humans
Problems caused by limited species diversity
- Low soil fertility due to lack of plants, animals and microorganisms that add nutrients to
the soil
- Upset weather patterns due to clearing of forests
- Pests and disease problems. Having only one or few types plants in the field means the
pests or diseases of that plant will increase

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 Page | 148

Management of ecosystems

Advantages of ground cover

Ground cover is the vegetation that covers the top soil

- Top soil preservation –the roots of the plants hold and trap topsoil thus preventing its loss
by soil erosion. The leaves and branches prevent topsoil loss by wind or water
- Water retention – the roots of plants hold the soil making the soil to contain water easily.
They also reduce surface runoff of water allowing water to infiltrate the soil
- reduced evaporation- ground cover reduces the heat of the sun reaching the sun thus
reducing the evaporation of water

Harmful human activities on the ecosystems

Agricultural activities

- Agricultural activities include crop farming and livestock farming

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 - Poor farming practices have negative impacts to the environment for example riverbank
farming
- Farming results in leaching of fertilizers and animal wastes into the water bodies resulting
in eutrophication which kills aquatic organisms
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- Pesticides kill microorganisms in the soil that are useful in the nutrient cycle. It also leach
into water bodies and kill aquatic organisms

Mining

- Mining results in clearing of trees which disrupts the ecosystem structure

- Mineral harvesting processes uses chemicals that may be released into the environment
and harm the environment.
- For example mercury used in gold purification usually is discharged into the environment
in waste water

Industries

- Industries to deferent factories that produce products such as vehicles, food, metals, clothes
and chemicals
- Factories usually uses fuels that generates air pollution
- Industrial water wastes usually contains toxins which if poor managed can escape into the
environment and kill organisms
- Sulphur dioxide and nitrogen dioxide from some industries causes acid rain that destroys
vegetation and aquatic organisms

Social activities

- Social activities refers to things humans do to the environment because of their daily lives
- It includes release of litter, household refuse, sewage into the environment
- These wastes destroys the environment for example sewage causes eutrophication in water
bodies

Corrective measures to harmful human activity

- Application of proper farming methods and techniques that does not harm the environment
- Prevention of industrial discharge into the environment

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 - Rehabilitation of the ground after mining for example afforestation
- Construction of proper sewage disposal systems
- Collection of refuse by city councils or municipalities
- Recycle of material such as plastics, paper, bottles and metals to reduce their discharge of
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these into the environment
- Use of better technologies in industries and vehicles that do not produce toxic wastes for
use of electric vehicles that don’t produce carbon dioxide, use of solar power instead of
fossils which release greenhouse gases
- Rural electrification to reduce forests clearing for firewood
- Educating people about environmental awareness
- Governments should establish policies that bans and fines the release of wastes into the
environment
- gully reclamation

Carrying capacity

- It is the maximum number of animals or plants a given area can carry

- The area can be a farm or a natural ecosystem such as a forest
- Limiting factors are factors that determines whether a population of organisms will
increase, decrease or remains static
- The limiting factors of carrying capacity are;
 Water
 Food
 Oxygen
 Space- animals need space to move and search for food. Lack of space leads to
overcrowding. Overcrowding leads to disease outbreak
 Shelter- need shelter from harsh environments factors such as heat, cold and rain

Effects of exceeding the carrying capacity

- Degradation of
- ecosystem
- overgrazing

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 - diseases
- pollution

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HEALTH AND DISEASE

Health is a state of physical, mental and social wellbeing of the body and not just the absence of a
disease

Levels of hygiene

Personal hygiene

- A person may reduce the chances of contracting a disease and infection by improving his
or her personal hygiene
- Personal hygiene includes;
 Eating balanced diet
 Do regular exercise to strengthen the body
 Avoiding drugs such smoking, alcohol and marijuana
 Washing teeth at least twice per day
 Bathing daily
 Washing hands after using toilet etc

Domestic hygiene

- Domestic hygiene is the hygiene we do in the places we live or work

- This includes;
 Washing of cutlery and kitchen ware before use
 Provision of proper refuse disposal
 Provision of clean toilets
 Sweeping and moping the house
 Consumption of clean and safe food and water
 Good storage of food for example storage of meat in refrigerators

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Community hygiene

 The community must have proper waste disposal systems

 Provision of proper and functional community toilets
 Provision of clean and safe water such boreholes and treated tape water Page | 152

 Provision of health facilities such as clinics

Sanitation- using safe methods to collect, store, dispose human waste such as urine and feces

Diseases
- Disease is a disorder or malfunctioning of the body that leads to the loss of a good health
- causes of diseases;
 infection,
 Genetic defects
 Chemicals
 Radiation
 malnutrition
 degenerative causes

Classification of diseases

Infectious diseases

- Cholera

- Malaria

- Tuberculosis (TB)

- Typhoid

- Bilharzia

Non-infectious diseases

- Deficiency diseases

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- Genetic diseases

- Cancer

Infectious diseases
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Cholera

- Is caused by bacterium
- Is transmitted through contaminated food and water

Signs and symptoms are:

- Diarrhoea

- Fever

- Body weakness

- Severe dehydration

Cholera is prevented by:

- Proper sewage disposal

- Water treatment

- Practising good personal and domestic hygiene

- Proper siting of wells

Treatment

- Can be treated using

- Oral rehydration solution/ salt sugar solution

- Antibiotics which kill the bacterium.

Malaria

- Is caused by a protozoa called plasmodium

- Plasmodium is transmitted by the female anopheles mosquito

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Symptoms and signs of malaria

- Fever every 48 hours

- Weak joints
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- Headache

- Vomiting

- diarrhoea

Prevention of malaria

- Use of mosquito coils;

- Mosquito repellents;

- Spraying using insecticides;

- sleeping under a mosquito net;

-Putting oil on stagnant water;

- Wearing long clothes at night;

- Use of prophylactic drugs;

- Cutting grass around the home yards

- Methods can be classified under the following headings: reducing population of mosquitoes,
prevent mosquito bites,

Treatment

- Use of quinine, coartem tablets and chloroquine

Tuberculosis (TB)

- It is a bacterial disease that is common in developing nations

- It is mainly spread by air droplets released when an infected person coughs or sneezes
Symptoms
- Inflammation of lungs

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 - Persistent dry coughing and coughing up blood
- Wight loss
- Chest pain and fever
- Shortness of breath
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Treatment and prevention
- Can be prevented by vaccination of babies with BCG vaccines
- Isolation of patients to prevent spreading of the disease
- Health education
- Cured with a cocktail of antibiotics for 6 months

Bilharzia

- It is caused by a flatworm (blood fluke)

- The flatworms are able to penetrate the skin
Signs and symptoms
- Fever
- Vomiting
- Liver and spleen enlargement
- Blood in urine and faeces
- Weight loss
- Abdominal pains

Treatment and prevention

- Provision of treated water

- Preventing swimming in stagnant rivers
- Destroying water snails which are carrier of the parasite
- Drugs such praziquantel (anti- parasite drugs
- Vaccination of kids

Typhoid

- It is caused by a bacteria that live in the intestines

- It is a water borne disease
- The disease is spread by contaminated water and food

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Signs and symptoms

-fever

-Rash on chest and abdomen

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-stomach pains

Headache

Loss of appetite

Diarrhea

Treatment and prevention

- Can be cured with antibiotics

- It can be prevent by thorough washing and cooking of food
- Drinking of treated water

Drug use and abuse

- A drug is a chemical that alters the biochemical reactions of the body resulting in some
physiological, psychological and behavioral effect
- Some drugs are medicinal drugs, they are useful and used to treat diseases for example
amoxylin and penicillin antibiotic
- Some drugs are recreational and addictive such as marijuana and cocaine
- The drug may be one taken legally to reduce a symptom such as a headache or to treat a
bacterial infection (medicinal drugs), but it could also be one taken – often illegally – to
provide stimulation or induce sleep or create hallucinations (recreational drugs)

Medicinal uses of drugs

- Medicinal drugs are used to treat or cure an illness or infection

- They interact with the metabolism of the body or of a pathogen

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 Page | 157

Antibiotics – they are used to kill pathogenic bacteria in the body. Examples include
penicillin, amoxylin, ciproflxin
Analgesics – they are also called painkillers. They are used to stop to stop pain in the body
for example paracetamol, asprin
Anti-malaria – they are used to kill malaria parasite (plasmodium) in the body. Examples
include chloroquine and coartem tablets

Physical, mental and social ill-effects of;

Alcohol
- The alcohol in wines, beer and spirits is a depressant of the central nervous system.
- Small amounts give a sense of wellbeing, with a relief from anxiety.
Effects of alcohol
- Slows down impulse transmission hence decreasing reaction time
- Slurred speech by affecting the cerebrum
- Increases acidity in the stomach and can cause stomach ulcers
- Can cause liver cirrhosis (shrinkage and wasting away of the liver)
- Reduces sperm count, so may lead to male infertility
- Causes vasodilation, giving a sensation of warmth but in fact leading to a greater loss of
body heat (hypothermia)

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 - Too much alcohol in the blood may lead to coma and death
Social effects includes; aggressive behavior, neglect of good diet, lack of responsibility to
family, domestic violence
Effects of tobacco smoke on human health
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- Excessive smoking can cause chronic obstructive pulmonary disease (COPD), lung
cancer and coronary heart disease
- The term, chronic obstructive pulmonary disease (COPD) covers a number of lung
diseases, which include chronic bronchitis, emphysema and chronic obstructive airways
disease.
- A person suffering from COPD will experience difficulties with breathing, mainly because
of narrowing of the airways (bronchi and bronchioles)
Cannabis/Marijuana (mbanje)
- It is usually taken as a recreational drug because of its psychological effects to the body
- It gives a sense of euphoria to the body making the person lose touch with reality
- Increases the risk of developing bronchitis
- Weakens the immune system

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 - It relieves pain
- Interferes with the development of the fetus during pregnancy
- Interferes with brain development in teenagers
- It leads to aggressive and wayward behavior
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- It gives hallucinations and sometimes madness in high doses

Solvents

- Solvents include substances such as glue, petrol, and aerosols.

- Peoples sniff or inhale solvents in order to get high
- The chemicals in the solvents such as alcohol affects the mental state of the brain, giving a
sense of euphoria
- High doses of solvents leads to intoxication and hallucinations
- It destroys the nervous system, liver, kidneys and brain
- Some aerosols can cause death or coma

Productivity in animals
- Productivity refers to yield in farm animals in terms of milk, meat, eggs and litter.
- The goal of every farmer is to have high yields
Feed conversion efficiency
- It is a simple measure to rate the ability of farm animals to turn feed nutrients into mass
gain or milk production.
- A good farm animal must be able to convert little into higher gains in mass or milk
- Growth curves are constructed to show the relationship between feed intake and mass gain
in animals.
- The growth curve is used by the farmer to determine the amount of feed needed to fatten a
cow in a given period.

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 Page | 160

- The graph shows that as the feed intake increased per kg, there is a relative increase in mass
gain over time.

Animal pests and related diseases

Anthrax

- It is a fatal diseases common in cattle. It is caused by a bacteria.

- Symptoms include;
 Swollen head, neck and chest
 Fever
 Difficulty in breathing

Control and treatment

 All livestock should be vaccinated against anthrax

 Infected animals are treated with penicillin
 Quarantine all infected animals to prevent spread of the disease
 Burn all dead infected animals

Foot and mouth disease

- It affects all hooved animals such as cattle, goats, horses and sheep
- It is caused by a virus. Foot and mouth disease is a very fatal infection
- Symptoms include;

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  Fever
 Excessive production of saliva or drooling
 Loss of appetite
 Difficulty in walking Page | 161
 Blisters and ulcers on gums, tongues, nose, hooves, toes and skin
 Decreased milk production

Control and treatment

 Vaccination of animals to prevent infection animals

 Quarantine of infected animals
 All infected animals are slaughtered and burned
 It is a notifiable disease, it must be reported to the authority.

Liver fluke

- Liver flukes affect goats, sheep and cattle

- They are internal parasites that feed on blood in the liver
- Liver flukes are flat worms that live in their mammalian host
- They damage the liver and eventually kill the liver
- Symptoms include;
 Slow growth
 Weight loss
 Decrease in milk production
 Poor quality meat

Control and treatment

 Do not allow animals to graze in swampy and wet areas

 Rotating grazing
 Dosing livestock with appropriate drugs

Red water

- It is a tick borne disease caused by a protozoa

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 - The protozoa infects and destroys red blood cells
- The ticks are the vectors of the pathogen
- Symptoms of red water;
 Fever
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 Lack of appetite
 Red urine
 Pale, yellowish gums and eyes
 Difficult in walking

Appropriate drugs should be used. Vaccination and dipping to remove ticks should be practiced.

How animal pests and diseases affect productivity

- Pests and disease results in reduced feed conversion ratio hence there is reduced yields

Ways of preventing plant pests and diseases

-Dosing- application of the drug through the mouth. It mainly targets pathogens in the animal gut
or liver

-Vaccination- application of vaccines through injection

-Dipping- animals walk immersed or swim through water with chemicals that kills ticks

-Quarantine- separation of infected animals from the health ones to prevent spreading of the
disease to health animals

Homeostasis
- Is the maintenance of a constant internal environment despite changes in the external
environment
- Keeps internal parameters at a constant level such as temperature, blood glucose, blood pH
and water level
Skin structure and functions of its parts

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 Page | 163

- Epidermis – upper/outer part of the skin

- Dermis – found below the epidermis
- Adipose tissue – fat acts as an insulator.
- Receptors – detect changes temperature.
Relate the functions of parts of the skin to temperature regulation
- When it is hot, thermo receptors in the skin detects the stimulus and sends the information
(electrical impulses) to the brain (hypothalamus) via the sensory neurons
- The hypothalamus sends information to the relevant parts of the body via the motor neuron
and the following occurs:
Vasodilation
- The blood capillaries in the skin widen and more blood flows near the surface of the skin
and heat is radiated to the environment
Hair erector muscle
- Relaxes and the hair on the skin flattens so that les heat is trapped
Shivering
- stops to generate no heat

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 - Excessively low temperature;
- When it is cold, thermo receptors in the skin detects the stimulus and sends the information
(electrical impulses) to the brain (hypothalamus) via the sensory neurons
- The hypothalamus sends information to the relevant parts of the body via the motor neuron
Page | 164
and the following occurs:
- Vasoconstriction
- The blood capillaries in the skin contract and less blood flows near the surface of the skin
and little heat is radiated to the environment
- Hair erector muscle
- Contracts and the hair on the skin erects so that more air is trapped which acts as an
insulator of heat
Shivering
- Involuntary shaking of muscles to increase the metabolic rate. This increases heat
production due to increase in respiration of cells.
Metabolic processes
- increases to generate heat
Sweat glands
-Produce sweat. Sweat takes heat away. Temperature falls. When temperature is high;
sweat glands stop producing sweat.
Function of the brain in homeostasis
- The hypothalamus in the brain regulates body temperature by receiving information about
temperature changes from thermo-receptors located in the skin and within the
hypothalamus itself, and activating mechanisms that promote heat gain or loss.
- The hypothalamus acts a thermostat for the body. The hypothalamus regulates our
temperature 35.6 – 37.8 degrees by promoting heat loss or gain through shivering or
sweating.
When the temperature is high or above normal level;
- When the external temperature rises above normal levels, thermoreceptors within the skin
send signals to the hypothalamus in the brain. Any corresponding rise in blood temperature
is also detected by thermoreceptors located within the hypothalamus itself. The
hypothalamus is stimulated to send out nerve

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 - impulses to:
 Arterioles in the skin, stimulating vasodilation. Increased blood flow in superficial
capillaries causes more heat loss through conduction, convection and radiation.
 Sweat glands, stimulating sweat production. Heat is lost through evaporation of Page | 165
sweat from the skin.
 Hair erector muscles, which relax so that hair follicles lie flat. This ensures that
no air is trapped by the hairs as air is a good insulator. This is more evident in
animals.
 Lungs, stimulating rapid breathing or panting. Heat is lost through exhaled air. This
is also more evident in animals.
- Body temperature returns to normal

When the temperature is low;

- When the external temperature falls below normal levels, thermoreceptors in the
skin send signals to the hypothalamus. A decrease in blood temperature is also
detected by thermoreceptors in the hypothalamus. The hypothalamus is
stimulated to send out nerve impulses to:
- Arterioles in the skin, stimulating vasoconstriction. Decreased blood flow in
superficial capillaries causes less heat loss through conduction, convection and
radiation.
- Sweat glands, stopping sweat production
- Hair erector muscles, which constrict so that hair follicles are raised. This traps
a layer of air between the hairs which acts as an insulating layer.
- Muscles, causing involuntary and increased contraction of muscles, known as
shivering. This increases cellular respiration in muscle cells, producing heat.
- Body temperature returns to normal.
- In humans, the always-present layer of adipose tissue beneath the skin acts as
insulation.
Negative feedback
- When there is a change of parameter within the internal environment, a self-
regulatory mechanism is stimulated or triggered to bring back the original

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 conditions for example when the glucose level increases the pancreas secretes
(releases) insulin which is transported to the liver by the blood. This triggers the
liver to convert the glucose to glycogen for storage. This also increases the use of
glucose in respiring tissues thus bringing the glucose level back to normal
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Excretion
- Excretion is the process by which the body removes metabolic waste products and
toxic materials.
- Metabolic processes consist of anabolic processes and catabolic processes.
- Anabolic processes are ‘building-up’ processes where larger molecules are
synthesized from smaller molecules. Examples include:
(a) Synthesis of proteins from amino acids
(b) Synthesis of glycogen from glucose
(c) Photosynthesis with oxygen as waste material
- Catabolic processes are ‘breaking-down’ processes where larger molecules are
broken down to form smaller molecules. Examples include:
(a) Cellular respiration with carbon dioxide and water as by-products
(b) Deamination of amino acids in the liver with urea as a by-product
(c) Breakdown of haemoglobin in the liver with bile pigments as by-products
- Waste products have to be removed because they can be harmful if they accumulate
in the body.

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 Page | 167

Structure of the urinary system

- The kidneys, which are two bean-shaped organs located in the abdominal cavity.
- The ureters, which are narrow tubes that emerge from a depression in the concave
surface of the kidney called a hilum. The ureters connect to the urinary bladder.
- The urinary bladder is an elastic and muscular organ that collects and stores urine
excreted by the kidneys. The sphincter muscle at the base of the bladder controls
the flow of urine into the urethra. It is controlled by nervous impulses from the
brain.

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 - The urethra is a duct that connects the urinary bladder to the outside of the body. Urine
passes through this tube to the outside.

Structure of the kidney

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The kidney is made up of two distinct regions: an outer cortex and the inner medulla.
The cortex is covered by a protective fibrous capsule called the renal capsule.
The medulla consists of 8 to 18 conical pyramids.
Across the cortex and medulla are numerous excretory tubules called nephrons, as well
as collecting ducts and their associated blood vessels?
Nephrons are the urine-producing units of the kidney.
The tips of the pyramids empty urine into an area called the renal pelvis.
The renal pelvis functions as a funnel collecting urine from all the pyramids to deliver to
the ureter.
Blood enters each kidney from the renal artery and leaves via the renal vein, both connected
to the kidney at the hilum.
Functions of the kidney
- Kidneys excrete waste products, eg urea, uric acid, creatinine and drugs.

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 - They perform an osmoregulatory function and regulate the water content of the body fluids.
- They play a role in maintaining the osmotic pressure of body fluids by excreting excess
salts and by retaining water and glucose
- They regulate the pH of blood plasma, ie they control the acids-base equilibrium in blood
Page | 169
Kidney dialysis

The kidney can malfunction due to injury or disease. This is called kidney failure.

In the case of kidney disease, the patient can survive with only one kidney, but if both fail, the
patient’s blood composition has to be regulated by a dialysis machine

- A dialysis machine consists of a long cellulose tube coiled up in a water bath.

- The patient’s blood is led from a vein in the arm and pumped through the cellulose
(dialysis) tubing
- The tiny pores in the dialysis tubing allow small molecules, such as those of salts, glucose
and urea, to diffuse out into the water bath.
- Blood cells and protein molecules are too large to get through the pores
- This stage is similar to the filtration process in the glomerulus.

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 - To prevent a loss of glucose and essential salts from the blood, the dialysis fluid consists
of a solution of salts and sugar of the correct composition, so that only the substances above
this concentration can diffuse out of the blood into the bathing solution.
- Thus, urea, uric acid and excess salts are removed.
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- The bathing solution is also kept at body temperature and is constantly changed as the
unwanted blood solutes accumulate in it.
- The blood is then returned to the patient’s arm vein.
- A patient with total kidney failure has to spend 2 or 3 nights each week connected to the
machine.
- With this treatment and a carefully controlled diet, the patient can lead a fairly normal life
- A kidney transplant, however, is a better solution because the patient is not obliged to return
to the dialysis machine.

Coordination and Response

- The human nervous system consists of:
(a) Central nervous system (CNS) consisting of the brain and spinal cord
(b) Peripheral nervous system (PNS) consisting of nerves connecting the central nervous
system and the rest of the body. The function of the PNS is to conduct sensory and motor
signals between the CNS and the limbs and organs (receptors and effectors).
- A stimulus is a change in the environment that causes an organism to react. Stimuli are
detected by sensory receptors.
- A response is a change in the body as a result of the stimulus. Effector cells are muscle
cells or gland cells, which carry out the response to stimuli.
- Bodily functions are classified into voluntary actions and involuntary actions.
- Involuntary actions are actions that cannot be consciously controlled, such as heartbeat,
peristalsis, vasoconstriction and reflex actions.
- Voluntary actions are actions that are consciously controlled

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Structure of a neurone

- Nerve impulses are transmitted by nerves, which are bundles of neurones wrapped in
Page | 171
connective tissue.
- A neurone is a nerve cell.
Sensory neurone

- Sensory neurones carry impulses from the sense organs to the central nervous system.

Motor neurones

- Motor neurones carry impulses from the central nervous system to muscles and glands

Relay neurones

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 Page | 172

- Relay neurones (also called multi-polar or connector neurones) are neither sensory nor
motor but make connections to other neurones inside the central nervous system.

Spinal reflex arc

- Reflex arc is the path by which an impulses is transmitted from a receptor to an effector to
bring about a response to the stimulus
- Reflex arcs provide the basis for reflex actions
- A reflex action is a rapid, automatic response to stimulus
- It is an instinctive action and it does not involve the brain
- Examples are blinking, yawning, coughing, sneezing, heartbeat, peristalsis, dilation and
constriction of the pupil
It consists of:
(a) Receptor
(b) Sensory neurone
(c) Intermediate neurone / relay neurone (located in CNS)
(d) Motor neurone
(e) Effector
- Involuntary (in biology) is not under the control of the will of an individual.

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 - Involuntary responses by muscles, glands, etc. Occur automatically when required

Page | 173

- The sequence of events in a simple reflex arc of a knee jack is shown below.

Functions of the main parts of the brain

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 Page | 174

- The brain receives, interprets and give specific responses.

- It is covered by layers of connective tissue. It is enclosed by the skull / cranium.
The cerebrum/ cerebral hemisphere
- Receives sensory impulse from all parts of the brain; which is concerned with movement
of voluntary organs, memory, thinking, intelligence, problem solving.
- Deals with speech, expression of thoughts, behavior and reasoning

Hypothalamus

- Regulation of body temperature, heart rate, hunger, thirst, aggression, sleep etc.
- Controls (stimulates) the pituitary gland
- Monitors the level of hormones and other chemicals passing through it.

Medulla oblongata

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 - Has three important centres namely cardiac centre, the respiratory centre and vasomotor
centre.
- Also has centre which control sneezing, cough, vomiting and swallowing
- Controls involuntary (reflex) actions like heart rate, respiratory cycle, constriction and
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dilation of blood vessels resulting in control of blood pressure.

Cerebellum

- Coordinates movement of skeletal muscles.

- Maintains body equilibrium and posture. (balance)

Structure of the eye

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 Page | 176

1. Iris– Pigmented circular sheet of muscles that control the contraction and dilation of the
iris through the contraction and relaxation of the circular muscles and radial muscles
2. Pupil– A hole in the middle of the iris which allows light to enter the eye
3. Sclera– Tough white outer layer of connective tissue
4. Conjunctiva– Thin, transparent mucous membrane that helps to lubricate the eye
5. Cornea– Transparent refractive layer covering the iris and pupil. It causes the most of the
refraction of light entering the eye. The cornea is continuous with the sclera.
6. Tear gland– Gland lying at the upper corner of the eyelid. Secretes tears which lubricate
the eye, nourish the cornea and keeps it free from dust.
7. Choroid– Black middle layer of the eyeball, between the sclera and retina. Contains blood
vessels that supply oxygen and nutrients, and remove metabolic waste products. It is
pigmented black to prevent an internal reflection of light.
8. Retina– Innermost layer of the eyeball which contains photoreceptors. Photoreceptors are
connected to nerve endings from the optic nerve.
9. Lens– Transparent biconvex structure that refracts light onto the retina. The lens is
flexible and its curvature can be changed. It is responsible for the process of
accommodation, a reflex action where the lens is able to change its curvature to focus
sharp images on the retina.
10. Ciliary body– Contains ciliary muscles which control the curvature of the lens. It is also
responsible for producing aqueous humour.
11. Suspensory ligament– Connects the ciliary body to the lens

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 12. Aqueous humour – A transparent, water substance filling the space between the
cornea and the lens. It keeps the front of the eye firm and helps refract light into the eye.
13. Vitreous humour– Clear gel filling the space between the lens and the retina. It
keeps the eyeball firm and helps refract light onto the retina.
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14. Fovea– Yellow pit in the retina where images are usually focused
15. Optic nerve– Transmits visual information from the retina to the brain. There are no
photoreceptors in the area of the retina where the optic nerve leaves the eye. This area is
called the blind spot.

How does the eye focus?

- As light rays travel through the cornea, aqueous humour, lens and vitreous humour, they
are bent so that they can focus on the retina
- Image formed on the retina is inverted, smaller than the actual size of the object
- Various photoreceptor cells are stimulated
- Nerve impulses produced are relayed to the visual area of the brain
- Messages are interpreted by the brain and the person becomes aware of the object

Focusing on a near object

- Is the viewing of an object at a distance less than 6 metres

- Light rays from a near object enter the eye as diverging rays to fall on the retina.

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 - The retina sends impulses to the brain, which sends impulses to the ciliary muscles.
- The ciliary muscles contract, causing the suspensory ligaments to become slack.
- The suspensory ligaments relax their pull on the lens. The elastic lens becomes more
convex (thicker and rounder), causing more refraction of the rays of light.
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- The light rays from the nearby object are brought to focus onto the fovea of the retina,
forming sharp image on the retina
- For near vision, special adjustment is necessary and accommodation takes place

Focusing on a distant object

- Is the viewing of an object 6 metres or more away

- Light rays from a distant object enter the eye as almost parallel rays to fall on the retina.
- The retina sends impulses to the brain, which sends impulses to the ciliary muscles.
- The ciliary muscles relax, causing the suspensory ligaments to become taut.
- The suspensory ligaments pull on the lens more. The elastic lens becomes thinner and less
curved/less convex, causing less refraction of the rays of light, enabling a sharp image to
be focused on the retina.
Accommodation- is the adjustments made in the eye in order to focus the image of distant
or near object onto the retina
Pupil reflex

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 - The pupil reflex is an involuntary action where the pupils contract or dilate in response to
changing light intensities.
- The pupils dilate to allow more light to enter the eye for better vision when light intensity
is low, and contract to restrict light entry when light intensity is high as excessive light can
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damage the retina.
- The size of the pupil is controlled by two sets of involuntary muscles in the iris called the
circular muscles and the radial muscles.
- The reflex arc involves these components:
- (a) Light entering the eye falls on the retina.
- (b) Photoreceptors on the retina sends impulse via optic nerve to the brain. The brain is
the organ of the CNS that is nearest to the eye.
- (c) The brain sends impulse to the iris muscles.
- (d)The circular and radial muscles respond to change the size of the pupil, to adjust to the
light conditions

When light intensity is high:

(a) Circular muscles in the iris contract.
(b) Radial muscles in the iris relax.
(c) The pupil constricts.
When light intensity is low:
(a) Circular muscles in the iris relax.

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 (b) Radial muscles in the iris contract.
(c) The pupil dilates.

Eye defects and correction

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- There are three eye defects; short sightedness, long sightedness and cataracts.
Short sightedness
- A person who is shortsightedness can focus nearby objects but cannot focus distant objects
- The condition is called myopia
- This caused by the lens bending too much of light rays or the eye ball is too long
- The result is that the light rays meet in the front of the retina, causing the image on the
retina to be blurred
- Shortsightedness can be corrected by wearing glasses with concave lenses to bend the light
rays outward before they reach the eye

Long sightedness
-Long sighted people can focus objects that are far away but cannot focus near objects.
- This is caused by the lenses not able to bend the light rays enough to focus them on the
retina or the eye ball is too short
- This result in the light rays meeting at the point beyond the retina, causing the image to be
blurred
- Long sightedness can also be caused by lens being too hard that it cannot adjust normally
- Long sightedness can be corrected by wearing glasses with convex lenses that bend the
rays inward before they reaches the eye.

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 Page | 181

Cataracts
- Cataracts are caused when the lens becomes cloudy, the cloudiness is caused by
precipitation of protein molecules which will block light rays
- The lens can be replaced surgically with artificial lens

Structure of the ear

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 Page | 182

- The inner part of the ear has parts that have different functions
- One part (semicircular canals) gives us balance and the cochlea enables us to hear
Sound conduction
- A vibration from a sound source sets off sound waves that travel through the air. The sound
waves reaches the ear and are caught by the pinna
- The pinna directs the waves into the auditory canal
- They pass along the auditory canal to the eardrum
- When they hit the eardrum they cause it to vibrate
- The ossicles act as a lever system to amplify the sound vibrations
- Inside the cochlea, there are two membranes. The lower membrane has receptor cells.
Vibrations of the cochlea fluid makes the cochlea membrane vibrate
- When the lower membrane vibrates it stimulates the receptor cells. These cells then sends
electrical impulses along the auditory canal.
- The impulses are send to the auditory cortex of the brain where it is interpreted as sound

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 ENDOCRINE SYSTEM
- A hormone is a chemical substance produced by a gland and carried by the blood, which
alters the activity of one or more specific target organs
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- Endocrine glands are ductless glands which produce and release hormones directly into the
blood.

Effects of adrenaline

- Adrenaline is a hormone produced by the adrenal glands located above the kidneys. It is
responsible for the ‘fight-or-flight response’ triggered by stress (emotional or physical
threats to the organism).
- The adrenaline travels to target organs, causing:
(a) Increased conversion of glycogen to glucose in the liver and skeletal muscles
(b) Increased glucose release into blood by liver cells
(c) Increased metabolic rate, causing more energy to be released in cellular respiration
(d) Increased heart rate and volume of blood pumped per unit time, increasing oxygen and
glucose supply to muscle cells
(e) Dilated bronchioles and increased breathing rate and depth, allowing more oxygen to
be taken in for cellular respiration
(f) Decreased blood supply to the digestive system, the kidneys and the skin as
vasoconstriction occurs in several body parts, diverting blood supply to the heart, brain and
skeletal muscles
(g) Vasodilation occurring in other body parts, increasing blood supply to these organs
(h) Dilated pupils, enhancing vision
(i) Contracted hair erector muscles, producing ‘goose pimples

The role of insulin and glucagon

The islets of Langerhans in the pancreas are areas in the pancreas that contain groups of
endocrine cells.These cells produce the hormones insulin and glucagon.
- Insulin and glucagon are antagonistic hormones that participate in homeostatic control of
blood glucose level by negative feedback mechanism.

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 - When blood glucose level exceeds the normal level, more insulin is released and acts to
lower the glucose level.
- When blood glucose level falls below the normal level, more glucagon is released and acts
to increase the glucose level.
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Insulin decreases blood glucose concentration by:
(a) Stimulating body cells to increase glucose uptake by increasing permeability of plasma
membranes to glucose
(b) Stimulating the liver and muscle cells to store glucose in the form of glycogen
(c) Decreasing production of glucose from glycogen breakdown in the liver
(d) Decreasing the conversion of fatty acids and amino acids to glucose in the liver
Glucagon increases blood glucose concentration by stimulating liver cells to:
(a) Convert glycogen to glucose
(b) Convert amino acids and fatty acids to glucose
(c) Convert lactic acid into glucose

Diabetes mellitus
- Diabetes mellitus is a condition in which the body does not produce sufficient insulin or
does not respond to insulin.
- The excess glucose cannot be completely reabsorbed by the kidneys and are excreted in
the urine.
Symptoms include:
- (a) A persistent high blood glucose concentration
- (b) Presence of glucose in the urine
- (c) Excessive urination, excessive thirst and weight loss
- (d) tiredness
- Diabetes mellitus can be managed by injecting insulin into the body according to doctor’s
prescription
- Foods that are rich in sugars should be avoided

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 Skeletal system
Functions of the skeleton

- Support and structure- skeleton holds the soft tissues and organs in place. It als gives Page | 185
shape to the body
- Movement- It gives place of attachment for the muscles. When muscles contract the
skeleton moves at the joints allowing the animal to move from one place to the other
- Protection- Certain parts of the skeleton gives protection to vital organs for example the
skull protects the brain, the ribs protect the heart and lungs
- Production of white blood cells
- Storage of minerals such as calcium and phosphorous

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 Page | 186

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Types of joints

Synovial joint

- A synovial joint is the type of joint found between bones that move against each other, Page | 187
such as the joints of the limbs. It has a joint cavity filled with fluid. The synovial fluid is a
stick fluid that nourishes, lubricates the cartilage surfaces as they move again each other.
The lubrication prevents injury. Other types of joints allow little or no movement, including
fibrous joints (e.g between the bones of the skull) and cartilaginous joints (e.g between the
ribs and the breastbone). Example of synovial joints are hinge joint, gliding joint, ball
and socket joint.

Hinge joint

- This joint allows movement in one plane

- It is characterised by the movement of an opening door
- The elbow and knees joints are examples of this joint

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 Page | 188

Ball and socket joint

- These allow considerable movement in all directions

- The joints in the hip and shoulder are examples
- This joint allows movement in three planes or universal movement

Gliding joints

- These joints have restricted movement although they have a smooth continuous
movement
- Examples are the ankle and wrist bones
- They allow bones to glide past one another in any direction along the plane of the joint

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 Antagonistic muscles (extensor and flexor muscles)
- The biceps muscle lies above the humerus and the triceps is under the humerus
- The forearm is raised when the biceps contracts and the triceps relaxes
- The forearm is extended when the triceps contracts and the biceps relaxes
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