Biology Form 2 Best Notes for all Topics

Transport in plants
This is the movement of water and mineral salts from the soil to other parts of the plant and food materials from the leaves to the rest of the plant.
Most single –celled organisms are very small hence have a very high S.A to volume ratio hence substance rapidly get in and out of the cell by simple diffusion.eg mosses and liverworts
Multicellular organisms are big hence have a small S.A to volume ratio thus they need a special transport system to efficiently move substances into and out of the cells.
In higher plants, the transport function is carried out by a specialized transport system known as the vascular bundle.
It comprises of ;
- (i)Xylem –transports water and mineral salts from the soil.
- (ii)Phloem –transports dissolved food substances such as sugars from the leaves.
- ROOTS
- Functions of roots
- (i)For anchorage-hold the plant firmly in the soil
- (ii)Absorption of water and mineral salts from the soil
- (iii)As storage organs of some plants e.g. carrots
- (iv)As breathing roots ( gaseous exchange) in some plants
- Internal structure of a root
- Piliferous layer
This is a special epidermis of young roots whose cells give rise to root hairs.
Its cells are thin walled to allow passage of water and mineral salts
As the root tissues mature a less permeable suberised epidermis replaces the piliferous layer
- Root cap
It covers the apex of the root.
It consists of simple parenchyma cells that protect the growing part ( apical meristem) of the root tip as it is pushed past soil particles.
Cells of root cap are relatively impermeable to water and solutes.
- NB Roots of aquatic plants lack root caps because they grow suspended in water.
- Epidermis
It’s the outermost layer of cells that protect the inner tissues.
The layer is one cell thick to reduce the distance over which water and mineral salts pass.
Some epidermal cells are modified to form root hairs.
- Cortex
Tissue found between epidermis and endodermis
Made up of loosely packed, thin walled parenchyma cells
- Endodermis
It’s a layer of surrounding the vascular bundles.
Its characterised by;
Rectangular shaped cells
Starch grains – hydrolysed to release energy
Many mitochondria
Root pressure is thought to develop within the endodermis.
Casparian strip – has an impervious deposit on the radial and cross walls.
Endodermis controls the amount of water and mineral salts entering into the vascular bundles.
- Pericycle
It’s a layer of cells found between endodermis and vascular bundles.
Gives rise to lateral roots
- Xylem
Comprises of vessel and tracheid elements.
It transports water and mineral salts from the soil.
Phloem –transports dissolved food substances such as sugars from the leaves to the rest of the plant.
Comparison between monocotyledonous root and dicotyledonous root
- Dicotyledonous root
xylem occupies the centre
Xylem forms a star shape
phloem is found between the two rays of the star
Pith absent
- Monocotyledonous root
Xylem and phloem are arranged to form a ring
Xylem tissue alternates with the phloem tissue
Pith present

Root hairs

they are modified outgrowth of epidermal cells
They are numerous, long and slender to provide a large surface area through which absorption of water and mineral salts take place
They have numerous mitochondria to supply energy for active transport
They have a thin cell wall which ensures rapid movement of materials
Cell vacuole has high solute concentration to maintain a high osmotic pressure to absorb water
Cell vacuole is large to store absorbed water and salts
Have short life span but are continuously replaced by new ones that develop nearer to the tip.
- Stem
- Functions
To support and expose the leaves and flowers to the environment
To conduct water and mineral salts from the roots to the rest of the plant
To conduct manufactured foods from the leaves to the rest of the plant
Other functions
Storage of food and water-in potato stem tubers
For gaseous exchange e.g. lenticels
Perennation –survival of perennial and biennial plants from one year to the next by vegetative means
Substance in the stem are transported within the vascular tissue
- Comparison between monocotyledonous stem and dicotyledonous stem
- Dicotyledonous stem
Vascular bundles arranged to form a ring
Have a central pith
Xylem located on the inside while the phloem on the outside
Cambium present between the xylem and phloem
Monocotyledonous stem
Vascular bundles arranged randomly/scattered
Cambium absent

NB most tissues in the root and stem are similar because these tissues are continuous from the root into the stem
Common tissues to both root and stem are;
- Epidermis
Cells are elongated
Outer walls are covered by a waxy cuticle that;
Prevents excessive loss of water through evaporation
Protects inner tissues from infection and mechanical injury
- Cortex
Made up of various types of cells i.e.
- (i)Collenchyma cells
They are angular
They have thick cellulose cell walls to provide support to the root
- (ii)Parenchyma cells
Spherical in shape
Have thin cell walls
Cells are loosely packed creating intercellular spaces filled with air
Cortex act as storage tissue for water and food
They may have chloroplasts to carry out photosynthesis hence called chlorenchyma
(iii) Sclerenchyma
Their walls are thickened by deposition of lignin in a process known as lignifications
It serves as a strengthening tissue
- Pith
It’s the central part of the stem. It consists of the parenchyma cells that store water and food substances. In some stems the pith may be hollow.
- Absorption of water
The soil particles are usually surrounded by a film of water
Root hair cells absorb water from the soil by osmosis. The cell sap in the vacuole of the root hair cell has high concentration of salts and sugars hence it’s hypertonic to the water found between the soil particles.
Due to this concentration gradient, water molecules move by osmosis from the soil through the semi-permeable membrane of the root hair cells into the cell sap.
The root hair cell sap becomes more dilute relative to the adjacent cortex cells. As a result water moves by osmosis into the adjacent cortex cells and their osmotic pressure is lowered relative to the inner cortex cells, which draw water by osmosis
Water passes through successive cortex cells and through the endodermis to the xylem by osmosis.
The endodermis actively pumps ions into the xylem vessels thus enhancing uptake of water into the xylem vessels by osmosis and creating root presure
The root hair cells will take up water as long as their concentration of salts is higher than that in the soil
- Active uptake of mineral salts
The soil water contains dissolved mineral salts which plants require for their growth and proper functioning.
The concentration of cell sap in root hairs is greater than that in the soil hence enter the root hairs against the concentration gradient. This process requires the use of energy therefore referred to as active transport.
Active transport involves substances known as carriers which combine with mineral ions and then carry them across the plasma membrane into the cell.
After absorption, the mineral salts move into the xylem vessels at the centre of the root then carried up the stem into the leaves.
- Factors that affect the absorption of mineral salts
(i) Metabolic inhibitors-these are chemical substances that prevent metabolic activities from taking place.
they prevent the release of energy thus active transport does not take place e.g. cyanide
(ii) Temperature-low temperature reduces the rate at which active transport takes place. Increase in temperature up to the optimum speeds up the rate of chemical reaction. High temperatures denature the enzymes.
(iii) Oxygen concentration- Oxygen is used in in oxidation of substrates that yield energy for use in the active uptake of mineral salts
- Transpiration
It’s the process by which plants lose water in the form of water vapour in the atmosphere.
Loss of droplets of water from the plant is called guttation.
Guttation occurs through special glands found mostly at points where the vein is in contact with the edge of the leaf. The glands are called hydathodes. They are located on the leaf margin or apex.
Guttation usually occurs in plants that grow in wet habitats.
- Role of leaf in transpiration
Water gets into the leaves through the xylem tissue. Water leaves the xylem and enters the cells of spongy mesophyll by osmosis.
Water diffuses into the sub-stomatal air spaces in the form of vapour.
The concentration of water molecules is higher in the air spaces than in the atmosphere. Water diffuses out through the stomata into the atmosphere
Movement of water through a leaf

Types of transpiration

(a) Stomatal transpiration
This is the loss of water in the form of water vapour through the stomata.
It accounts for 80-90% of the total transpiration in plants.
Most stomata occur on the leaves but may also occur on the epidermis of young herbaceous stems.
- (b) Cuticular transpiration
This is the loss of water in the form of water vapour through the cuticle.
In plants with thick cuticles the loss is negligible.
- (c) Lenticular transpiration
This is the loss of water in the form of water vapour through the lenticels.
Lenticels are areas with loosely fitted cells on woody stems.
The loss of water is negligible.
Forces involved in transportation of water and mineral salts
- Transpiration pull
Process by which water moves up the xylem due to evaporation of water in the leaf.
It enables a stream of water to move from the roots up the leaves
Energy from the sun causes evaporation of water increasing the diffusion gradient between the atmosphere and the mesophyll cells which leads to water vapour diffusing into the atmosphere.
The mesophyll cells draw water from the xylem. The water from the xylem is replaced by a continuous column of water known as transpiration stream moving up the roots.

Cohesion and adhesion forces

Water molecules attract one another in such a way that they always stick together. The forces that keep them together are referred to as cohesion force.
Also water molecules are attracted to the walls of the container in which the water is contained by a force referred to as adhesion force.
The cohesive and adhesive forces in very thin columns can be very high and not easily broken.
These forces maintain a continuous and an uninterrupted water column in the xylem vessels up the trees.
- Capillarity
It’s the tendency of water to rise in very narrow tubes.
The lumen of xylem tracheids and vessels is very narrow and this enables water to rise by capillarity.
- Root pressure
It’s the force that pushes water absorbed from the soil to move up the stem from the root.
The energy used to develop root pressure originates from the endodermal cells.
Cells of endodermis actively secrete mineral salts into the xylem. The osmotic pressure of the xylem content is increased thereby encouraging water movement.
When the stem of a plant is cut, water oozes out from the cut stem.
Root pressure can only raise water to a height of about 1 metre hence if a plant is growing in soil with little water the maximum height that the root pressure will raise water will be less than 1 metre.
- Importance of transpiration
Replace water lost through the leaves.
Aid in transportation of water and mineral salts
Cools the plant.
Helps in the removal of excess water especially in aquatic plants
Causes wilting- this is beneficial when a plant cannot obtain enough water to replace that lost by the plant through transpiration
Responsible for turgor in plants
- Factors affecting transpiration rate
- Structural factors
They are related to the morphology of the plant e.g.
Roots
Plants with extensive root system have a high rate of transpiration than those with few roots.
Extensive roots absorb more water hence more is available in the sub-stomatal spaces.
Leaf size
Large leaves have a large surface area over which transpiration takes place hence high rate of transpiration
Leaf structure
Cuticle
A thick cuticle reduces the rate of transpiration
The cuticle in most case is waxy-wax reflect away the sunlight hence lower temperatures in the leaf
Wax is also water proof hence reducing rate of transpiration
Stomata
- -Number of stomata-the fewer the number of stomata the lower the rate of transpiration
- -Position of stomata-the sun shines directly on the upper surface of leaves hence increasing the rate of vapourization thus high water loss
Stomata on the lower surface are sheltered from the suns rays hence lower water loss
-Sunken stomata-when the stomata are sunken water vapour accumulates in the sub-stomatal air spaces thus its not exposed to moving air hence reducing the rate of transpiration
Leaf fall
During periods of drought, some plants such as broad-leafed deciduous trees shed their leaves to reduce the surface area for water loss.
In some species of grass the aerial shoot dries up to ground level.
(e) Hairy leaves
In some plant, leaves are covered with hairs or scales. These trap a layer of still moist air on the surface of the leaves thus reducing transpiration
- Environmental factors
Temperature

High temperature increases the capacity of the atmospheric air to hold more water vapour.
High temperature increases the internal temperature of the leaf which in turn increases the latent heat of vapourization therefore enhancing evaporation from the leaf cells.
- Humidity
It’s the amount of water vapour in the atmosphere.
The humidity difference between the inside and the outside of the leaf is known as saturation deficit and it determines the rate of water loss from the leaf.
In dry weather, the saturation deficit if high hence increasing rate of transpiration
In high humidity, the saturation deficit if low hence decreasing rate of transpiration. Under such conditions some plants secrete droplets of water through specialized pores called hydathodes .
This process of water loss is called guttation and is common in hydrophytes ( plants growing in wet habitats)
- Wind
Wind carries water vapour as fast as it diffuses out of the leaves through the stomata.
This prevents the air around the leaves from being saturated with water vapour. This helps to maintain a high diffusion gradient between the inside and the outside of the leaf
When the air is still, the area around the leaf soon becomes saturated with water vapour. Diffusion of water vapour from the leaf surface is low leading to low rate of transpiration
- Light intensity
The stomata of most plants open fully during daylight hours when the light intensity is high
This brings the sub-stomatal air into direct contact with external environment.
The water vapour therefore diffuses out at a higher rate than in dim light when the stomata are partially closed.
- Atmospheric pressure
The lower the atmospheric pressure the higher the rate of evaporation
At high altitudes the atmospheric pressure is very low hence plants growing there lose a lot of water due to high rate of transpiration
Most of them have adaptations to prevent excessive water loss
- Availability of water
When there is adequate amount of water in the soil, water is absorbed and conducted to all the cells.
The mesophyll cells in the leaves become moist thus more water will diffuse into the inter-cellular spaces increasing the diffusion gradient. More water is lost to the atmosphere through transpiration
- Structure and function of xylem
Xylem comprises of
-xylem vessels
-tracheids
Xylem vessels
They are hollow tubes
They are made of dead cells placed end to end
Walls thickened with lignin to prevent them from collapsing as water is being transported up the plant.
Patterns of thickening
- The hollow part (lumen) provides passage for substances
- Xylem walls have perforations which form simple pits
- The pits on the xylem vessels permit the passage of water in and out of the lumen into the neighbouring cells
- Tracheid elements
- Have tapering or chisel-shaped ends
- Walls thickened with lignin
- Have tiny pores known as pits or perforations
- The pits on the side walls allow lateral water to the cells surrounding the xylem. This makes tracheids less efficient in conducting water than vessels
- NB Xylem vessels are more efficient in transport of water than tracheids because ;xylem vessels cross walls between their cells have dissolved forming a continuous hollow tube while tracheids have tapering ends whose cross walls remain perforated and this increases resistance
- Translocation
- It’s the movement of manufactured food substances from where they are manufactured in the leaves to the rest of the plant. It takes place in the phloem tissue in plants
  - Phloem tissue

Phloem tissue is made up of sieve tubes and companion cells.
Sieve tube – its long with perforated end walls which are called sieve plates
Cytoplasmic strands / Filaments run through sieve plates connecting adjacent cells.
At maturing sieve tube cells lack nuclei and ribosome
Mature sieve tube cells have few mitochondria
Companion cells – these cells have dense cytoplasm and a prominent nucleus and other cell organelles.
Companion cell generate the energy needed in the sieve elements because it has mitochondria
Plasmodesmata – these are passages found on the lateral walls. Substances move through them from the companion cells to the sieve tube cells.
Function of phloem
Materials move from one sieve tube element to another through the sieve pores in the sieve plates between adjacent elements. These materials are transported in solution form in the cytoplasm of the sieve elements
The organic products translocated are; sugar, amino acids and vitamins. They are translocated to;
(i) Growing and developing regions of the plants such as young shoots, leaves, flowers, fruits and roots
Storage organs or tissues such as tubers, corms, bulbs, rhizomes and seeds
Secretory organs such as nectar glands in some insect pollinated plants e.g. bananas
Experiment; Ringing experiment
Make a ring through the bark around the stem of a young tree using a sharp knife
Make a second ring 5cm above the first ring and peel off the bark between the two rings
X
Observe the experiment over the next two months
Discussion
When the ring of bark is removed, the phloem beneath it is also removed. After several weeks swelling above the ring is noted eg
X
This swelling is due to accumulation of food substances that were being transported from the leaves but could not get across the debarked part of the stem. As a result, there is no swelling on the lower part of the ring.

Transport in animals

Circulatory system
A circulatory system transports the substances and maintains a steep concentration gradient at the surfaces where diffusion takes place.
Its made up of a fluid, a pumping organ and vessels
There are two types of circulatory system: open and closed circulatory systems
- Open circulatory system
The transport fluid is contained in the general body cavity/ coelom/ sinuses. This type of system is common in invertebrates especially arthropods.
The transporting fluid in the body cavity is known as haemocoel
Cavities are free spaces between the body wall and organs. The fluid in the cavities is in contact with body tissues.
The fluid distributes oxygen, nutrients and hormones to tissues while removing CO₂ and nitrogenous wastes from the tissues.
- Closed circulatory system
The transporting fluid (blood) is conveyed in special tubes referred to as blood vessels.
- Differences between open and closed circulatory system

– Open	– Closed
– Blood flows under low pressure	– Blood flows under high pressure
– Blood circulates over a short distance at a slower rate	– Blood circulates over a long distance at a faster rate
– Fluid is not involved in the transport of O₂and CO₂	_–Blood transports O₂ and CO₂
– Is less efficient at supplying tissues and organs with nutrients and removing nitrogenous wastes	– More efficient at supplying O₂ and nutrients to the tissues
– Organisms with open circulatory systems are generally less active	– Animals with closed circulatory systems are more active

Transport in insects

In a cockroach there is a tubular heart just above the alimentary canal. The heart has 13 chambers, 3 in the thorax and 10 in the abdominal segments.
The anterior segment is joined to the aorta that empties the blood into sinuses of the head. Each chamber contains a pair of valves at the anterior part which prevent back flow of the blood.
Each chamber has a pair of lateral openings called Ostia which are closed by valves.
The valves allow blood to flow into the heart through the Ostia but not out of it.
- Mammalian circulatory system
Mammals have a closed circulatory system where a powerful muscular heart pumps blood into the arteries.
The arteries divide into even much smaller vessels called arterioles which in turn divide into even much smaller vessels called capillaries
Capillaries spread out in a network fashion in the tissues.
The capillaries eventually reunite to form venules that in turn form larger vessels called veins. Veins take blood back to the heart.
- Single circulatory system
This is where the blood flows only once through the heart for every complete circuit hence the heart has only one atrium a ventricle e.g. fish
- Double circulatory system
Blood flows into the heart twice for every complete circulation i.e. blood from the body tissues is pumped to the lungs and then back to the heart. This is called pulmonary circulation.
From the heart, blood is then pumped to the rest of the body organs. This is called systemic circulation.
The double circulatory system is found in birds, mammals and also crocodile (reptile). The other reptiles and amphibians have double circulatory system but the ventricle is not fully divided into the left and right ventricles.
Therefore efficiency of gaseous exchange is not fully realized due to mixing of oxygenated and deoxygenated blood.
- Structure and function of the heart
- External structure of the heart
The mammalian heart is broad at the anterior and narrower at the posterior end. Its made up of two auricles (left and right) and two ventricles (left and right)
The coronary artery which branches from the aorta supplies O₂ and nutrients to the heart tissues.
The two coronary veins transport CO₂ and the metabolic wastes away from the heart.
The heart is covered by a translucent membrane known as the
Pericardium prevents the heart from being overstretched as it pumps blood. It secretes pericardial fluid which reduces friction between the heart and the adjacent tissues when the heart beats.
At the anterior end of the heart are vessels i.e. aorta and pulmonary artery which take blood away from the heart and vena cava and pulmonary vein which return blood to the heart from the rest of the body.
- Internal structure of the heart
The heart is a muscular organ about the size of the fist.
It lies inside the chest cavity between two lungs.
Internally the heart is surrounded by a tough membrane called pericardium which covers and protects it.
It’s divided into two sides i.e. the left and the right sides which are completely separated by a wall called
Septum prevents the blood on the right side mixing with that on the left side. Each side consists of a small upper chamber called atrium (plural atria) and a larger lower chamber called ventricle. This makes the mammalian heart a 4 chambered organ
The atria are also called auricles and are thin walled and receive blood into the heart which they pump into the ventricles. Ventricles are thick walled and pump blood out of the heart.
The heart is made of special muscles called cardiac muscles. This muscle is special in 2 ways:
- -It can contract continuously without fatigue- the heart can beat for a life time without taking a rest.
- -Cardiac muscle is also myogenic e. its contractions are started by the muscle itself and not by nerves as the case with other muscle tissue in the body.
Four flap like valves control the direction of blood flow inside the heart. Two of these valves are called atrio- ventricular which allows the blood to flow only from the atria to the ventricles.
The one found in the right side of the heart is called tricuspid valve because it has three flaps.
In the left side of the heart is the bicuspid valve because it has two flaps. It is also called mitral valve.
The other two valves found in the heart are the semi – lunar valves. They are found at the base of the aorta and pulmonary artery. When open they allow blood to move from the ventricles into the arteries and away from the heart.
NB: –
Valves are attached to the walls of the ventricle by valve tendons or tendinous cords (cordae tendinae). The tendons allow the valves to open but prevent inversion of the flaps of the valves when blood attempts to flow back.
The wall of the left ventricle has thicker walls muscles than that of the right ventricle because the left ventricle pumps blood a further distance to all parts of the body while the right ventricle pumps the blood to the lungs.
Circulation of blood in the heart
The right atrium receives blood coming from the body tissues through the vena cava. This blood has very little oxygen dissolved in it hence it is described as deoxygenated blood. It is rich in CO₂ and appears dull red in colour.
The right atrium then pumps the blood into the right ventricle via the tricuspid valve. When full the right ventricle pumps blood into the pulmonary artery. Semi- lunar valves at the base of pulmonary artery prevent back flow into the right ventricle. At the same time tricuspid valve prevents any backflow into right Atrium.
Tendons (heart strings) hold the valve in a closed position preventing them from turning into the atrium.
The pulmonary artery carries the blood into the lungs where it picks up O₂ and gives up CO₂. It is now said to be oxygenated and appears bright red in colour. It goes to the left atrium of the heart via the pulmonary vein. This portion of the circulatory system that sends the blood to the lungs from the heart and back is called the pulmonary circulation.
X
The left atrium pumps blood into the left ventricle via the bicuspid valve. The left ventricle pumps blood to all parts of the body except the lungs. This blood leaves the left ventricle through the aorta. Semi- lunar valves that open into the aorta prevent back flow of blood.
The left ventricle walls are much thicker than the right ventricle walls in order to prevent develop a high enough pressure to pump blood to all parts of the body. The circulation of the blood from the heart to the tissues and back is called systemic circulation.
The mammalian heart therefore acts as a double pump. The left side sends blood rich in O₂ to the rest of the body and the right side sends blood poor in oxygen to the lungs.
The heart tissue itself receives food nutrients and O₂ via a vessel known as coronary artery which branches from the aorta and spreads through the heart muscle.
The function of the heart is to receive and pump blood. The heart receives blood when its muscle relax and it pumps the blood when the muscles contract. These two processes take place in a repeated sequence or cycle known as heart or cardiac cycle.
Adaptations of mammalian heart to its functions
It has valves which open to allow blood to flow in one direction and close when blood tries to flow back.
It has muscular walls which contract to pump blood and ensure its continuous flow.
It has a septum which separates oxygenated from deoxygenated blood.
It has an inbuilt system that controls contraction and relaxation of the muscles.
It has 4 chambers which store blood briefly before it is pumped to the rest of the body.
Its muscles contract and relax continuously without fatigue.
- The heart beat
The heartbeat can be felt as a pulse in various parts of the body where an artery is close to the skin surface such as wrist.
A pulse is a series of waves of dilation that pass along the arteries caused by the pressure of the blood pumped from the heart through contractions of the left ventricle.
A complete cycle of a heart beat takes less than one second. The human heartbeats at about 70-75 times/minute when one is at rest.
The heartbeat can increase up to 200times per minute during:
Exercise
Fever
Emotional disturbances (fear)
An increased heartbeat circulates blood with oxygen and glucose needed to produce energy for the vigorous activity in the muscle tissues faster and takes away Carbon iv oxide and other wastes away.
- Control of heartbeat
Heartbeat is started by collection of cells in the wall of the right atrium called pacemaker (Sino atrio node) SAN) it is controlled by nerve messages which come from a part of the brain called medulla oblongata.
The heart will continue to beat even if the nerves (vagus nerve) from the brain are cut but it will only beat at one rate.
Nerve impulses from the brain are needed to change the rate of heartbeat.
NB: Individuals who have a heartbeat which is too slow or faster can have it regulated by the fitting of an artificial pacemaker which takes over from normal pacemaker.
One heart beat consists of a systole and diastole phase i.e.
- Diastole (relaxation)
It refers to the phase when the ventricles relax in order to allow blood to flow in. During this phase, the ventricular volume increase and the pressure decreases.
When the right atrium contracts the tricuspid valve opens to allow deoxygenated blood to flow into the right ventricle.
At the same time the left atrium contracts and the bicuspid valve opens to allow oxygenated blood to flow into the left ventricle.
The semi-lunar valves close preventing blood from flowing back into the relaxed ventricles.
- Systole (contraction)
It refers to the phase when the ventricles contract to force the blood into the arteries while atria are relaxed.
When the left ventricle muscles contract the bicuspid valves close to prevent blood from flowing back into the relaxed atria.
The volume of the ventricles decreases while the pressure increases forcing blood to flow out of the heart.
Deoxygenated blood flows through the semi lunar valve through the pulmonary artery to the lungs while oxygenated blood flows through the semi lunar of the aorta and into the tissues of the body.
The sphygmomanometer is used for measuring blood pressure. Blood pressure is obtained by placing systolic pressure of the left ventricle over the diastolic pressure of the left ventricle i.e.

Average human blood pressure = 120mm Hg (systole)
- 80 mm Hg (Diastolic)
Blood vessels

The mammalian blood vessels are arteries, veins and capillaries.
The walls of veins and arteries consist of the following three layers
(i)inner lining of a single layer of epithelial cells called endothelium
(ii)middle layer of smooth muscles and elastic fibres. Its this layer that brings about dilation and constrictions of blood vessels
(iii)outer layer made up of fibrous connective tissue
Arteries
They take blood from the heart to the body tissues and organs. Due to the pumping action of the heart, blood from the heart enters the arteries at high pressure.
- Properties of arteries
Thick muscular walls to withstand and maintain higher pressure of blood.
An outer fibrous coat for strength and protection
A thick layer of muscle and elastic fibres which contract and relax to adjust their diameter as blood flows through them. Arteries have an inner lining of cells known as an
A narrow lumen to maintain the pressure of blood inside them.
Most arteries are located deep within our bodies for protection against injury. The size of the lumen in arteries can be adjusted by nerve control of muscles in their walls e.g. the amount of blood passing through the arteries can be adjusted during exercise so that more blood flows to the legs and less blood to small intestines. This ensures that blood is properly utilized by only the parts of the body that need it most.
Pumping of the blood can be felt on an artery if pressure is put on it with a finger. This pressure makes blood to flow in only one direction.
When the ventricles contract, the muscular layer of arteries stretch to reduce resistance to blood flow. When the ventricles relax the muscular layer of arteries contract compressing the blood and forcing it flow forward in one direction.
All arteries carry oxygenated blood except the pulmonary artery which carries deoxygenated blood.
Arteries branch out to form narrower vessels called arterioles, which branch further within the tissues into finer vessels called
Some arteries are specialized to perform certain functions e.g. arteries of the lungs have thin walls due to lower pressure in pulmonary circulation. Aorta and pulmonary arteries have cardiac muscles extending to their bases.
With age arteries change in structure. In old age elastic fibres have;
Irregular thickening
- -fat is deposited between the cells
- -calcification occurs between arterial walls thus making the walls brittle.
Veins
They carry blood under low pressure from the tissues towards the heart.
They have thin walls which are composed of a thin outer fibrous coat, a thin middle layer of muscle and elastic fibres and an inner layer of cells (endothelium)
They have pocket valves at intervals in their walls which allow blood to flow in one direction towards the heart. They carry deoxygenated blood except the pulmonary vein which carries oxygenated blood.
Portal veins have capillaries at both ends. They are unique veins that carry blood from one organ to another i.e. hepatic portal vein which carries blood from the small intestine to the liver.
Most veins are found between the skeletal muscles and may be visible. The skeletal muscles contract squeezing veins and forcing blood to flow towards the heart.
When breathing in the pressure in the chest cavity reduces. The volume of the heart increases and the blood in the veins is sucked up towards the heart.
Valves are found in the heart, at the junction of major arteries and the heart and also in the veins. The veins of the lower limbs have more valves.
Open valves allow blood to flow in one direction only. Closed valves prevent the back flow of blood.
Structural differences between arteries and veins
Arteries Veins VEINS

– Have thick muscular walls	– Have thin and less muscular walls
– Have no valves except pulmonary artery	– Valve present at intervals throughout their length
– have narrow lumen	– Have wide lumen

Functional differences

– Arteries	– Veins
– Transport blood away from the heart	– Carry blood towards the heart.
– Carry oxygenated blood except pulmonary artery	– Carry deoxygenated blood except pulmonary vein.
– Blood flows rapidly at high pressure	– Blood flows slowly at low pressure
– Blood flows in pulses	– Blood flows smoothly

Blood pressure in the arteries is greater than in veins for the following reasons
Arteries
Receive blood directly from the heart pumped under high pressure
Have relatively narrower lumen, which maintains high pressure
Have thick muscular wall, which resists and generates pressure
Veins
Receives blood whose pressure has been reduced by capillary resistance
Have relatively wider lumen, which reduces pressure
Have thin less muscular wall, which reduces pressure
Capillaries
They are narrow blood vessels whose walls are one cell thick
Capillaries have certain characteristics which make them a region suitable for exchange of substances between blood and the tissues.
- Characteristics of capillaries
They are numerous in number to increase their surface area for exchange of materials
Have thin walls(one cell thick) to allow rapid exchange of substances
They form a dense network in all the tissues in the body. This creates a large surface area over which the exchange takes place.
They are narrow t for high pressure build-up within them. This ensures faster movement of substances.
Have sphincter muscles at the arterioles end, which enables regulation of blood flow
The intensity of metabolism determines the density of Capillary network in the tissues and organs e.g. there is dense network of blood capillaries in the lungs, liver, kidney, skeletal muscles etc
The walls of the capillaries are said to be permeable i.e. allow the passage of molecules through them.
A fluid is formed which is referred to as tissue fluid. The cells obtain their requirements through diffusion from the tissue fluid e.g. water, glucose, mineral salts, and hormones. The cells are bathed by the tissue fluid and they release waste products into the tissue fluid e.g. nitrogenous waste, mineral salts, CO2 and heat.
Capillaries unite to form venules which unite further to form veins.
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Diseases and defects of the circulatory system
Arteriosclerosis(atheroma)
This is the hardening of the arteries. As the arteries age the body reacts by depositing cholesterol and calcium in their walls. This causes them to thicken and harden and to become less flexible or less elastic i.e. they become sclerotic. This forces the heart to work harder in order to pump blood efficiently throughout the body.
It also causes an increase in the blood pressure. High blood pressure can lead to a stroke or a heart attack.
- Prevention
Exercises
Avoid alcohol and smoking.
Avoid fatty foods
- Treatment
Take medication that lowers blood pressure.
Coronary thrombosis
Thrombosis is the formation of blood clots in the blood vessels. Coronary thrombosis refers to the clotting of blood in a coronary artery resulting in a heart attack.
Coronary arteries supply the heart muscles with oxygen and nutrients. When a clot blocks blood from reaching the tissues of the heart, the tissues experience shortage of oxygen and nutrients supply. CO₂ and nitrogenous wastes are not efficiently removed. This result in heart attack
Symptoms
Sharp pains especially on the left side of the chest.
Difficulty in breathing
Irregular heartbeats and swelling of the feet.oedema.
Cardiac cells die leading to heart failure and death.
Prevented in the same way as arteriosclerosis
- Treatment
Take medication to prevent blood clot formation.
Cerebral thrombosis /stroke
It occurs when a blood clot is formed in the vessels of the brain.
A stroke is caused by high blood pressure in the capillaries and arteries of the brain. Arteries supplying blood to the brain have thinner walls and the high blood pressure can burst the capillaries serving the brain tissues. The brain cells in the affected area die. Some parts of the body especially the left side maybe paralyzed.
Prevented same way as arteriosclerosis
Atherosclerosis
It’s a condition similar to arteriosclerosis but it is caused when cholesterol, fat and calcium are deposited along the inner walls of the arteries. This reduces the diameter of their lumen and causes high blood pressure as the heart is forced to pump harder.
Factors that increases risk of atherosclerosis
High level of blood cholesterol
Smoking
Obesity
Diabetes
Sedentary lifestyle which does not involve much physical activity
Varicose veins
It refers to the prominently swollen veins which may appear below the knees or at the back of the legs. This condition is brought about by failure of some valves in veins to function. Blood accumulates in the veins.
Some pregnant women develop this condition albeit temporarily. Also common in men soldiers who carry out parade drills.
Varicose veins can be caused by standing or sitting for a long time. To prevent varicose veins, shift your weight from one leg to another and stretch your limbs.
- Treatment
Wear special firm stockings every morning before getting out of bed.
Congenital heart defects
At birth, the blood circulatory systems of the mother and the foetus become independent. The pulmonary artery takes very little blood to the lungs of the foetus because they are not used for gaseous exchange
Blood flows between the right and left auricle through an opening in the wall between the two auricles called foramen ovale. The passage normally seals after birth.
When it fails to seal, lungs are denied adequate blood and gaseous exchange is not efficient. Blood transports less oxygen and removes less co₂ from the tissues .The baby turns dark and may die. This condition can be surgically corrected
Also when the valves within the heart fail to close adequately, the results a backflow of blood. The condition is said to be a murmur of the heart. It’s diagnosed by the sounds of the heart as the valves close. This condition can be corrected surgically.
Also the connecting vessel between the pulmonary artery and aorta (Ducts arteriosus) may not be sealed. The vessel normally seals at birth. Blood flow to the lungs is cut off and enters the aorta hence blood flow to the lungs is inadequate.
Gaseous exchange is impaired and tissues lack enough oxygen. The baby may turn dark. This condition can be corrected surgical.
Hypertension(High blood pressure)
Normal blood pressure varies between 90/60 and 140/90mmHg
It is caused by:
Heavy drinking
Smoking
Taking large quantities of salt in the food
General body stress
The heart of a hypertensive person is overworked and the person is prone to heart failure
Hypertension may lead to bursting of arteries and capillaries. If the blood vessels in the brain burst, a stroke results and brain cells die in the affected area. Paralysis for some parts of the body usually accompanies stroke
This disorder is more common in individuals aged over 40 years
- Control
Having regular exercises
Intake of less salt
Avoiding excessive drinking of alcohol.
Avoid smoking.
Avoiding general body stress
Structures and functions of blood
Blood is liquid which transports materials in mammals.
It has 3 major functions i.e.
A medium of transport of ,materials to and from other tissues
Regulation of body temperature
Protection against disease germs
Mammalian blood forms up to 10% of the body weight. An average human adult has 5-6 litres of blood in the body
- Composition of blood
Blood is composed of:
Cellular components which form 45% i.e.
Red blood cells(erythrocytes)
White blood cells(leucocytes)
Blood platelets(thrombocytes)
- Blood plasma
Plasma makes up about 55% of the total volume of blood
It’s a pale yellow fluid
90% of blood plasma is made up of water and the other remaining 10% consists of a variety of substances that are dissolved in the water. These substances are:
Food substances e.g. glucose, amino acids and fatty acids.
Waste substances like CO₂ and urea
Hormones like adrenaline and insulin
Enzymes and antibodies
Blood plasma without fibrinogen is called serum
- Functions of blood plasma
Transport red blood cells which contain oxyhaemoglobin to the tissues hence facilitate transport of O
Transports food nutrients from the alimentary canal to the liver and other tissues.
Transports metabolic wastes such as CO₂.
Transports hormones to target organs.
Transports small amounts of CO₂ in the form of carbonic acid or bicarbonate to the lungs.
Transports mineral ions or salts such as chlorides.
Transports antigens and antibodies to the site where they are required.
Regulation of body temperature by distributing heat generated in the liver to other parts of the body.
- Cellular components
- Red blood cells (erythrocytes)
They are biconcave in shape i.e. thinner in the centre than around the edge.
- Adaptations of red blood cells to their function
They have a biconcave shape to increase the surface area over which O₂ and CO₂ diffuse
Absence of nucleus increases the space in which hemoglobin is packed.
Has haemoglobin which has a high affinity for oxygen
They are small in size hence have a large surface area to volume ratio for the diffusion of oxygen.
The small size enables them to squeeze through the narrow capillaries.
They are pliable which enables them to move through capillaries
Have enzyme carbonic anhydrase which enables them to transport carbon iv oxide
Have thin plasma membrane, which allows rapid diffusion of gases
Red blood cells are produced in the bone marrow of ribs, sternum and vertebrae. In an embryo RBC are produced in the liver and the spleen.
Since the mature RBC lack a nucleus and other cell organelles such as mitochondria, they have a short life span. They survive for about 100-120 days.
Old blood cells are destroyed in the liver and spleen. The iron component of haemoglobin is released for the formation of new red blood cells
There are about 5 million red blood cells in every cubic millimeter (mm³) of human blood. However the number of red blood cells varies depending on any of the following factors :
Altitude- the higher the altitude the more there will be
State of health of a person –people with severe anaemia or malaria have much fewer red blood cells in their blood.
- Functions of red blood cells
Transport of oxygen-this is the main function of red blood cells. They transport O₂ from the lungs to the body tissues.
The haemoglobin found in these cells readily combines with O₂ when the blood passes through the lungs to form oxyhaemoglobin.
When blood reaches a region with low oxygen levels like in the tissues, the oxyhaemoglobin readily gives up the oxygen it was carrying, it then reverts back to haemoglobin. The cells take up the oxygen while hemoglobin is free to be used again to carry more oxygen i.e.
- Haemoglobin + Oxygen
- lungs
  - Oxyhaemoglobin
- Under low oxygen concentration e.g. in high altitude areas the bone marrow produces more RBC. When one moves from a low to a high altitude area, more RBC are manufactured to increase the oxygen carrying capacity of blood. In this way one becomes acclimatized to the high altitude. e.g. –Kenyan athletes train in high altitude areas like Nyahururu and Eldoret to increase the O₂ carrying capacity by increasing the number of their RBC.
- Foetal haemoglobin – it’s a pigment found in foetus.
- It has a high affinity for O₂ than the mother’s haemoglobin. This enables the foetus haemoglobin to obtain enough O₂ from the mother’s blood even at low O₂concentration
- After birth RBC containing foetal haemoglobin are destroyed in large numbers. The large number of RBC destroyed causes a lot of pigment in the blood hence the baby maybe slightly yellow, jaundiced due to the pigment – this occurs in the first two weeks of birth.
- Myoglobin – it is a pigment found in the muscles and it has high affinity for O₂ than haemoglobin. Thus oxyhaemoglobin readily release the o₂ to myoglobin which then releases o₂ to the cells in muscles.
- Haemoglobin can combine even more readily with (carbon ii oxide) gas than with O₂ to form carboxyhaemoglobin
- However carboxyhaemoglobin does not split to release haemoglobin. This prevents adequate O₂ from being supplied. This makes carbon ii Oxide a dangerous gas because a person who has inhaled even small quantity of it especially in a room with poor ventilation can die of suffocation
- Sources of carbon ii Oxide include:-
- Burning charcoal stoves(jikos)
- Exhaust fumes from vehicles
- Transport of carbon IV oxide (CO₂)
- About 95% of CO₂is transported by RBC. Most of the CO₂ from the tissues enter the RBC where an enzyme called carbonic anhydrase speeds up the dissolving of CO₂ to form carbonic acid This acid dissociates to form hydrogen ions(H⁺) and hydrogen carbonate (HCO₃) ions.

CO ₂ + H₂O ^Carbonic H₂CO₃
- _{Anhydrase (carbonic acid)}
The hydrogen carbonate ions leave the RBC and enter the plasma where they are eventually transported to lungs
In the lungs hydrogen carbonate ions are converted back to CO₂ which is released to the air when breathing out
White blood cells (leucocytes)
They are larger than RBC colourless and are fewer than in number. There are about 6000 per cm³of blood. This number increases during infections
They have a nucleus but reduce in the case of HIV infection.
They are formed in the bone marrow of long bones and lymph nodes. Their function is to protect the body against pathogenic micro-organisms such as bacteria, protozoa, viruses etc
Types of white blood cells
Granulocyte
They are also called phagocytes or polymorphs
They have a large lobed nucleus and cytoplasm containing granules hence the name granulocytes
They can change their shapes as they actively seek and engulf diseases causing germs in a process called phagocytosis hence the name phagocytes
Some white blood cells may die in the course of phagocytosis. The dead phagocytes, together with dead micro-organisms and damaged tissues form pus
They can squeeze through capillaries walls in order to reach infected tissues. They are made in the bone marrow
Agranulocytes
They have large rounded nuclei. Their cytoplasm is also non-granular
Types of agranulocytes
Monocytes
They are formed in the bone marrow. They
destroy micro-organism such as bacteria by engulfing them
Lymphocytes
They are formed in the lymph nodes and produce antibodies that protect the body from infections in the following ways:-
Antibodies which are anti-toxic neutralize the toxins (antigens)produced by the pathogenic organisms
Some antibodies such as agglutinins cause clumping together of micro-organism.
This stops the micro-organism from multiplying and eventually they die. They are then ingested by phagocytes.
Lysins destroy micro-organisms by digesting their cell membrane or walls
Opsonins are anti bodies which adhere to the outer surfaces of micro-organisms thus making it easy for phagocytes to ingest them Opsonins are only produced during infection
Platelets (thrombocytes)
They are very small and have no nucleus. They are fragments of RBC and they are made in the bone marrow.
They are approximately 250,000 platelets per mm³ of blood. They live for about 7 days.
Platelets produce an enzyme known as thromboplastin which plays a key role in blood clotting.
Blood clotting
Blood clot is a seal that forms to close blood vessels that are cut or damaged. This has 2 functions:
Stops further bleeding at the wound and therefore prevent excessive blood loss.
Prevents entry of harmful bacteria into the body through the damaged tissue.
Process of blood clotting
When the blood vessels are damaged, the damaged tissue and platelets release an enzyme called thromboplastin (thrombokinase).
Thromboplastin initiates the process of blood clotting by neutralizing the anticoagulants factor known as heparin which occurs naturally in blood.
Thromboplastin activates the conversion of prothrombin (blood protein) to thrombin in the presence of calcium ions. Vitamin K is required in the formation of prothrombin
Thrombin activates conversion of soluble fibrinogen which is an inactive protein to insoluble fibrin which forms a meshwork of fibres on the cut surface to trap RBC to form a clot.
Blood platelets

Thromboplastin/ Thrombokinase (Enzyme)

Prothrombin Vitamin K

Ca²⁺

Thrombin

Fibrinogen

Fibrin

BLOOD GROUPS

Human blood can be grouped using the ABC system and Rhesus factor.
- THE ABO SYSTEM
The ABC of humans has special types of protein called antigens. There are two types of antigens i.e. antigen A and antigen B
Antigens determine the blood type or blood group of a person.
A person with only antigen A on their RBC is said to belong to blood group A. people with antigen B
Sometimes both antigens A & B are found on the RBC of the individual. In such a case a person is said to belong to blood group AB.
In other people the blood has no antigens on the RBC such people have blood group O i.e.

Antigen present on RBC BLOOD GROUP
AA
BB
A&AB
NONO
In addition to the antigens on the RBC, blood plasma contains other types of proteins called antibodies. These are complementary to the antigens A & B
Antibodies are named a and b respectively. Antibodies and antigens do not correspond to each other e.g.
A person with antigen A will have antibody b in the plasma.
A person with antigen B will have antibody a in the plasma.
If both antigens are present as in blood type AB, then no antibodies will be present in the plasma.
If none of the antigens is present then both antibodies are present e.g. in blood group O e.g.

– Blood group	– Antigens	– Antibody
– A	– A	– B
– B	– B	– A
– AB	– A & B	– None
– O	– None	– A & b

NB The presence of an antigen and its corresponding antibody in the blood of an individual, would lead to clumping of RBC. This is referred to agglutination
BLOOD TRANSFUSION
It’s the process of putting donated blood into a receipt. A blood donor is someone who voluntarily goes to a hospital or heath centre to give blood. The donor should be a healthy individual between 18- 65 years.
Blood is taken from the donor through a vein in the arm and passed into a bag containing anti – clotting substances. The blood is kept I bank under suitable conditions to be given to a patient who needs it (within I month) because RBC will have died after I month.
A blood transfusion may be necessary in situations such as:
When a person loses too mush blood due to an injury that may result from motor accident, war e.t.c.
When a person becomes anaemic due to diseases such as malaria
When a woman loses too much blood after child birth.
When the blood of the donor and recipient mix freely without agglutination the blood from the two individuals is said to be compatible. The blood from two individuals is said to be incompatible if agglutination occurs when the two blood are mixed.
TABLE SHOWING BLOOD TRANSFUSION IN HUMANS
- DONOR

– RECIPIENT	–	– A	– B	– AB	– O
	– A	–	– X	– X	–
	– B	– X	–	– X	–
	– AB	–	–	–	–
	– O	– X	– X	– X	–

From the table above it shows that a person with blood group O can donate blood to receipts of all the 4 blood groups. This is because the type O blood lacks antigens on the RBC that could be agglutinated by the antibodies from the receipts plasma. Therefore referred to as universal donor.
Individual with blood group AB can receive blood from all the 4 blood groups because AB has no antibodies to agglutinate the receipts blood hence referred to as universal recipient
Precautions before transfusion
The recipient must be given compatible blood i.e. blood received by recipient, should not agglutinate. Compatibility of blood is determined by A & B antigens and rhesus antigens.
After somebody has donated blood, it’s first screened before it is kept in a blood bank or transfused into a recipient.
During screening doctors test blood for:
Presence of any infective micro- organisms e.g. HIV if blood is infected, it’s normally thrown away.
After somebody has donated blood he/she receives a blood donor card bearing the name of donor and hi/her blood type.
RHESUS FACTOR
The RBC may also have another antigen on their membrane known as Rhesus factor.
Individuals with Rhesus antigens on the membrane of RBC are said to be Rhesus positive (Rh+) while individuals without the Rhesus antigens are said to be Rhesus negative (Rh-)
When a Rh- woman marries a Rh + man the woman will conceive a Rh+ foetus. The Rh+ antigens of the foetus pass across the placenta into the mother’s bloodstream during the last month of pregnancy. The mother responds by producing Rh antibodies which cross the placenta into the foetal circulation. The Rhesus antibodies destroy some of the RBC of the foetus.
The first born child has a higher chance of survival because the destruction of RBC is minimal. But in subsequent pregnancies massive destruction of RBC occurs leading to the death of foetus. This condition of is referred to as erythroblastosis foetalis or haemolytic disease of the new born.
The mother can be treated with a Rhesus globulin which prevents her from producing antibodies against the foetal antigens. This will protect the RBC of the foetus in subsequent pregnancies.
Also the baby is transfused with Rh – blood after birth due to the extensive breakdown of RBC
LYMPHATIC SYSTEM
Animals particularly vertebrates have an additional transport system besides the blood system.
This is known as lymphatic system and it supplies all the regions of the body just like the blood system.
The lymphatic system is made of narrow, thin walled tubes known as lymph vessels which branch to form lymph capillaries in which a fluid known as lymph is transported.
LYMPH
This is a fluid similar to blood plasma except that it contains less protein.
It’s formed as a result of ultra- filtration of blood from the narrow blood capillaries.
As blood circulates it reaches the body tissues through the blood capillaries that form a network throughout the tissues. The pumping force from the heart together with the narrow lumens of the capillaries exert a high pressure that forces the fluid part of the blood to filter out of the capillary walls into the surrounding tissues.
This filtrate consists of all the constituents of blood plasma except the blood cells proteins. This is because the blood cells and proteins are too large to filter out of the capillary walls. The fluid is known as tissue fluid or intercellular fluid.
Once formed the tissue fluid bathes the cells of the tissues supplying them with O₂, food and other useful substances.
The cells absorb these substances and pass out CO₂ and other waste products in exchange.
Most of the tissue fluid then return to the blood system through the venule end of the blood at the capillary.
The excess tissue fluid drains into the lymph vessels where it is known as
Lymph vessels have a swelling along their length called lymph nodes. They contain lymphocytes which defend the body against infection by producing antibodies that kill bacteria.
Also in the lymph nodes there are phagocytes that engulf bacteria
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IMMUNE RESPONSES
The micro- organisms that cause diseases are called
The production of antibodies by special cells that inactivate foreign substances is called the immune response
The ability of the body to defend against infection by producing antibodies or cells that destroy pathogens is called immunity.
The immune system includes all the parts of the body that are involved in the recognition and destruction of foreign substances. Its made up of:
Bone marrow which produces white blood cells
White blood cells especially phagocytes and lymphocytes
Various tissues of the lymphatic system such as lymph nodes, tonsils, thymus and spleen which accommodate lymphocytes.
TYPES OF IMMUNITY
They are classified into 2 major groups’ i.e.
Innate(inborn)/inherited
Acquired
Innate immune responses
Refers to natural a natural body defense like the skin, sebum and mucus and sickle cell anaemia
This type of immunity is dependent on genetic constitution of an individual e.g. blacks are generally less susceptible to malaria than whites.
Acquired immunity
Natural acquired immunity
This occurs when the body naturally overcomes an nfection e.g.
(i) Natural active immunity – this is the type of resistance which is built- up in a person after suffering and then recovering from a disease. The person develops specific antibodies against future attack of these same pathogens. E.g. when a patient recovers from chicken pox, measles he develops immunity against these diseases. A patient can not suffer from re-infection
(ii) Natural passive immunity- it’s the resistance which is inherited i.e. passed on from parents to offspring via placenta or onto a new born baby through colostrum.
(b) Artificial acquired immunity
This is the immunity acquired when the antibodies are artificially introduced into the body or weakened pathogens are introduced in the body.
Its divided into:
(i) Artificial active immunity
its developed by introducing a weakened dose of a micro- organism into a healthy person to stimulate the immune system to produce antibodies and anti- toxins.
The process of weakening the disease causing micro- organism is known
The weakened micro–organisms such as bacteria and viruses are given in the form of a vaccine.
The immunity developed lasts for a certain period of time e.g. immunity against cholera last 6 months while that for small pox lasts several years.
- (ii) Artificial passive immunity
This is the immunity that comes from using antibodies produced in one organism to protect another organism from a specific disease.ie the immunity acquired when preformed antibodies are artificially introduced into the body of a patient. This antibodies are called antisera eg anti tetanus, antirabies and antivenom antisera
In this type of immunity antibodies are administered to the body when it cannot form its own antibodies this is common during a disease outbreak.
The immunization is provided in the form of anti- serum.
An anti- serum is a serum containing antibodies. It is administered in the case of tetanus, diphtheria, rabies and cholera. Immunity acquired this way lasts for a short time.
VACCINATION
ROLE
Protects individuals from infections e.g. small pox, tuberculosis (TB) e.t.c.
- Prevents the spread of diseases
A vaccine is a weakened or dead form of a disease causing micro- organisms vaccines are administered orally or by infection.
The immunization programme is carried out nation wide by the Kenya expanded programme of immunization (KEPI)

Name of disease	– Causative agent	– Age when administered	– Method of vaccination
– Tuberculosis (TB)	– Bacterium	– At birth	– injection
– Poliomyelitis (polio)	– Virus	– At birth, 6 10, 14 weeks	– Oral inoculation
– Diphtheria	– Bacterium	– 6,10, 14 weeks	– injection
– Whooping cough	– Bacterium	– 6 & 14 weeks	– injection
– Measles	– Virus	– 9 months	– injection

ALLERGIC REACTIONS

At times the body’s natural defense system may over- react against even harmless substances such as dust, pollen, certain food, insect stings and bites such substances are referred to as allergens and they provoke the cells to produce and release chemicals such as histamine which causes inflammation itchiness and pain.
Allergic reactions may cause skin rashes itching, sneezing, vomiting, coughing and swelling of the body.
A severe condition called anaphylaxis sometimes occurs in which the blood vessels get dilated and this lower the blood pressure to the extent of causing death. This is how the bee stings can cause death.
Doctor usually prescribe an anti- histamine treatment to counteract the effect of histamine.
ORGAN TRANSPLANT
Surgeons can replace damaged tissues of organs using similar organs from other persons or animals e.g. the pig in transplant operations.
It has also been possible to transplant kidneys, liver, spleen, reproduction organs or tissues transplanted onto larger parts of recipients are called
In some cases grafts may be reject by the receipt but in most cases grafts involving identical twins or those from the same individual are not rejected.
The grafts may be rejected because the body of the host recognizes the new tissues or organ as foreign to it.
Some transplant of the heart, kidney, cornea of the eye, lungs and bone marrow have been carried out by using drugs that suppress the immune response of the host.
A substance called interferon is also used to suppress rejection of grafts. In organ transplants sophisticated mechanic used to keep the organs to be transplanted and he patient alive.

GASEOUS EXCHANGE

This is the process by which respiratory gases (oxygen and carbon IV Oxide) and water vapor are passed across the respiratory system
Importance gaseous exchange
It promotes oxygen intake for respiration in living organism
It facilitates carbon IV oxide removal from the body. Accumulation of large amounts of carbon IV oxide in the tissues is toxic to cells.
Enables green plants to obtain carbon IV Oxide for photosynthesis
Excess water is expelled from the plants through transpiration. Higher animals expel it partly in its gaseous form i.e. water vapor in the exhaled air.
Gaseous exchange in plants
It involves two main respiratory gases i.e. CO₂ and O₂
CO₂ taken in is used for photosynthesis and O₂ produced as a by-product of photosynthesis is released into the atmosphere.
However some of O₂ produced is used in the same plant for respiration. But since the rate of photosynthesis proceeds faster than respiration at daytime, excess O₂ produced is removed.
At night respiration proceeds in the absence of photosynthesis in green plants hence plants take in O₂ for respiration but give out CO₂.
In flowering plants stomata in the woody stems and roots provide surfaces for gaseous exchange
- Structure and function of stomata
Stomata are tiny pores scattered on the surface of the leaf.
Stoma comprise of a stomatal pore and two specialized guard cells -curved sausage-shaped (bean shaped).
The guard cells are structurally adapted to their function by;
(i) Having chloroplasts
(ii) The uneven thickness of their cell walls i.e. the outer walls of the guard cells is thin and stretches easily. The inner wall is thicker and does not easily stretch.
Two guard cells join at the end walls to leave apore in the middle
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Mechanism of opening and closing stomata
In the presence of light, stomatal pores open. They close during darkness.
The opening and closing of the stomatal pores is due to a change in turgidity of guard cells surrounding the pores combined with the uneven thickness of their cell walls. When guard cells are turgid the stomatal pores opens, when they are flaccid the pore closes.
- Theories supporting opening and closing of stomata
Photosynthetic theory
In the presence of light the guard cells carry out photosynthesis using the chloroplast. The accumulation of sugar in their cytoplasm raises the osmotic potential and so water enters the guard cells by osmosis.
This leads to an increase in turgidity of guard cells which then curve more due to their uneven thickness and cause the stomatal pore to open.
During darkness the guard cells cease to photosynthesize. Their osmotic potential is lowered as their sugars are transported out and so water leaves the guard cells which then become flaccid causing pore to close.
Starch –sugar interconversion theory
It has been observed that in the presence of light the guard calls take up potassium ions (K+). This causes water to enter the guard cells making them more turgid and so cause the stoma to open.
In darkness K+ ions move out of the guard cells, and also water moves out of guard cells leaving them flaccid hence their pore closes.
The starch- sugar conversion theory is under the influence of PH through enzyme action e.g. during the day photosynthesis take place in guard cells using CO The PH in the guard cells tends to rise hence becomes less acidic. This less acidic condition favours the conversion of starch into glucose. The glucose being more osmotically active brings about an osmotic effect that result in water being drawn into the guard cells. Consequently the guars cells become turgid and bulge outwards making the stomata to open.
At night CO₂ is not used up because photosynthesis doesn’t take place hence PH decreases thus favouring the conversion of glucose into starch. Starch is osmotically inactive and therefore the guard cells do not gain water. Due to the resulting flaccid state of guard cells the stomata close.
The potassium ions theory/K+theory
Guard cells have chloroplasts hence in the presence of light ATP is produced
ATP drives a K+ pump on guard cell membrane which actively transports K+ from adjacent epidermal cells into guard cells
The accumulation of potassium ions raises osmotic pressure of guard cells
Guard cells absorb water from the adjacent epidermal cells becoming turgid
The inner walls are thicker than the outer walls so the outer walls stretch more than the inner walls causing the guard cells to stretch outwards and stomata open
In absence of light (at night) ATP rapidly decreases so that there is no energy to sustain the potassium ions pump
Potassium ions migrate by diffusion from the guard cells to the adjacent epidermal cells
This lowers the osmotic pressure of guard cells which lose water to the adjacent epidermal cells becoming flaccid
The thinner outer walls of the guard cells shrink and the curvature of the thicker inner walls reduces thus closing the stomata
Mechanism of gaseous exchange in plants
Terrestrial plants
They are those growing on land under ordinary soil conditions.
Gaseous exchange occurs in the following:
Spongy mesophyll
CO₂and O₂ diffuse in and out of the leaf through
the stomata. Most of the gaseous exchange occurs through the spongy mesophyll
The rapid gaseous exchange through the leaves is due to:
Numerous stomata that increase the volume of diffusing gases.
The large air spaces within the mesophyll which increase the surface area for gaseous exchange.
Epidermis is the outer layer of the pant. The epidermal layer is one cell thick. This reduces the distance over which the gases diffuse.
Oxygen which is at higher concentration in the atmosphere or soil diffuses into the plant tissues through the epidermis of the older stems and roots peel off thus gaseous exchange only occurs through the epidermis in young stems and roots.
Gaseous exchange through lenticels
Stems of woody terrestrial trees and shrubs have areas of loosely arranged cells with large areas of loosely arranged cells with large air spaces between them. These cells together form a structure called
Lenticels are formed when the epidermis is replaced by the bark. Lenticels appear scattered on the surface of the stem as well as raised openings.
They allow gaseous exchange of O₂ and CO₂ between the atmosphere and internal tissues of the stem.
Gaseous exchange through the roots
The roots of plants such as ficus are modified to carry out gaseous exchange.
The epidermal layer of the ficus roots is thin. O₂ diffuses from the atmosphere where it is at a lower concentration.
Gaseous exchange in aquatic plants
CO₂ and O₂ gases are dissolved in water in which aquatic plants grow. Aquatic plants may either be submerged, emergent or floating.
Submerged plants
They obtain carbon dioxide and oxygen from water by diffusion through the epidermis. They don’t have stomata.
Their leaves are generally thin with large air spaces and lack cuticle e.g. Elodea spp and ceratopyllum and spirogyra
They are able to carry out photosynthesis under low carbon dioxide concentration.
Emergent plants
These are plants whose roots are firmly anchored on substratum such as a rock. The rest of the plant emerges from the water e.g. potomageton and nymphae, reeds, sedges
These plants have most of their stomata on the upper surface of their leaves. In some cases e.g. Nymphae the stomata are on the upper side only.
The plant tissues are made up of cells with thin walls of large air spaces called aerenchyma tissue which is found in stems and leaves. A lot of air is stored in the aerenchyma tissue making the stem and leaves of the plant buoyant.
Gaseous exchange occurs through the stomata. The aerenchyma tissue provides a large surface area over which gaseous exchange takes place.
Floating plants
They are those plants whose roots hang freely in water while the leaves float.
They have most of their stomata on the upper surface of leaves, gaseous exchange occurs through the stomata e.g. water hyacinth, salvia molesta, water fern, water lily, water lettuce, duck weed.
- NB The roots of these plants have aerenchyma tissue that enables plants to float.
Gaseous exchange in plants found in marine water and estuaries
Some plants growing in waterlogged soil develop breathing roots. The roots emerge from the soil. The roots are called pneumatophores
Gaseous exchange occurs through the epidermis e.g. white mangrove (Avicania spp)
PRACTICAL ACTIVITIES
- Activity 1: To investigate presence of stomata on leaves
- Materials
Water in a beaker
Leaves of various plants
Bunsen burner
Procedure
Heat the water to boiling point. Turn off the burner and wait for the water to stop boiling.
Immerse a leaf into the hot water and notice the air bubbles emerging from the leaf.
Repeat the procedure using other leaves
Compare the average numbers of air bubbles from the upper and lower epidermis of different leaves.
- Leaf of bubbles
- Activity 2: To investigate the shape of guard cells and distribution of stomata on leaves
- Materials
Clear nail varnish
Microscope
Cover slip
Forceps
Microscope slide
Leaves of various plants (maize)
Beans, hibiscus, zebrine, water lily
Procedure
Apply a thin coat of clear nail varnish on the upper and lower epidermis of a leaf, let it dry
Peel off the varnish off the leaf using a pair of forceps.
Place the varnish with the imprint of stomata on a microscope slide.
Add a drop of water and gently lower a cover slip on the specimen
Observe the specimen under the microscope starting with the low power objective lens and then shift to the medium power objective lens.
Note the arrangement of the guard cells
Count the number of stomata in the field of view under the medium power objective lens.

– Plant	– Number of stomata		– Likely habitat
–	– Upper epidermis	– Lower epidermis	–
– Water lily	–	–	–
– Maize	–	–	–
– Zebrina	–	–	–
– Tradescantia	–	–	–
– Hibiscus	–	–	–

Activity 3: To investigate internal structures of stems or leaf stalks in aerial and aquatic plants
Materials
Water lily leaf stalks
Bougainvillea twig
Beaker containing water
Scalpel
- Procedure
Cut off the apex of the bougainvillea twig and pluck the leaves
Insert one end of the stem into the water and try to blow into or suck water from the beaker
Repeat the above procedure using water lily leaf stalk
Account for the difference
GASEOUS EXCHANGE IN ANIMAlS
Types of respiratory surfaces in animals

– Type Of Respiratory Surface	– Environment	– Example
– Cell membrane	– Water	– Amoeba
– Gill filaments	– Water	– Fish
– Tracheoles	– Air	– insects
– Alveoli/ lungs	– Air	– Mammals, birds, frogs, reptiles
– Skin	– Water, – air	– Frog – earthworm
– Buccal cavity	– air	– frog

Respiratory surface is the basic unit of any breathing system upon which gaseous exchange takes place by diffusion.
- Characteristics of respiratory surfaces
Covered with a thin epithelium for faster diffusion of gases across it.
It’s moist to dissolve gases as they diffuse across it.
It has a large surface area for maximum gaseous exchange
It should posses a rich capillary network to quickly transport gases to and from cells
Mechanism of gaseous exchange
Protozoa
These are single- celled organisms e.g. Amoeba, plasmodium
Trypanasoma, these are microscopic organisms
They are mainly found in water or in the body fluids of other organisms. The respiratory surface of protozoa is the cell membrane. Gaseous exchange occurs across the cell membrane directly by diffusion.
Due to the respiration the concentration of carbon dioxide inside the unicellular organisms is higher than that in the surrounding water therefore carbon dioxide diffuses out of organisms into the surrounding. The concentration of oxygen is higher in the surrounding water than inside the organism. Oxygen therefore diffuses from the surrounding water into the organism.
- X
- Gaseous exchange in insects
The respiratory system in insects is called the tracheal system; it consists of spiracles, trachea and Tracheoles.
- X
The spiracles are found only on the sides of the thorax and abdomen. There are no spiracles on the head.

The spiracles have a muscular valve which can be opened or closed to regulate the flow of air.
There are also hairs in the spiracle which prevent excessive loss of water by evaporation from the tissues.
The spiracles open into large tracheal tubes called tracheae (singular trachea). These tubes are strengthened with spiral bands of chitin to keep them open at all times.
There are several large air sacs which are connected to tracheal tubes, which act as reservoirs.
The tracheae are subdivided into microscopic tubes called Tracheoles. Tracheoles penetrate the body tissues and are in direct contact with all the living cells. They lack the spiral bands of chitin and their ends are filled with a fluid. Those ends act as respiratory surfaces between the cells and the Tracheoles.
Inspiration (breathing in) in a grasshopper
During inspiration (breathing in) air enters the body of the insect. Inspiration takes place when the internal muscles in the abdomen of the grasshopper relax. This makes the abdomen and the tracheal system to expand and increase in volume.
The pressure of the tracheal system decreases compared to that of the atmosphere. This causes air to be sucked into the tracheal tubes via the spiracles in the thorax which are open at the time. This air travels through to the Tracheoles.
Oxygen from the air dissolves in the fluid in the Tracheoles and diffuses directly into the cells. Carbon dioxide which is at a higher concentration in the cells than in the Tracheoles.
Expiration (breathing out) in a grasshopper
In order to expel the used air, internal muscles in the abdomen of the grasshopper contract and compress the abdomen. This causes a compression of the tracheal system. The reduce volume and increased pressure in the tracheal system forces air (CO₂) out of the system through the spiracles.
In the grasshopper the 4 anterior (front) spiracles close while 6 pairs of posterior spiracles open so that air flows from the front to the rear end and then out of the insect
Insects which live in water also carry out gaseous exchange in water. Insects such as the dragonfly or may fly larvae (nymphs) use tracheal gills that are seen as paired plates on either side of the abdomen e.g.
X
However most of the aquatic insects have an elaborate tracheal system and are not truly aquatic because they need to come to the surface to breathe e.g. mosquito larvae have the spiracles near the rectum carried on a tube called respiratory siphon.
The siphon is opened when the larva comes to the surface of the water to take in air and closed by valves when the larva submerges. Larvae come to the surface of water periodically to breathe and position themselves.
X
In the pupa stage, a pair of siphons open just behind the head, pierce through the water surface to allow for gaseous exchange.
X
Some adult insect like water beetles and water bugs use bubbles of air trapped by hairs. The air bubbles give these insects a silvery appearance.
Some insects use the respiratory device, plastron for gaseous exchange. A plastron is a pile of very fine non- washable hairs which cover the cuticle for some distance around the spiracle to hold off water and also maintain a film of air over the body surface.
Gaseous exchange in a fish (bony fish)
In a bony fish the respiratory structures are the gills.
The bony fish ahs 4 gills on each side of the body
The gills are located inside a cavity in the head region known as operculum cavity
Each side of the fish has an operculum cavity which has an opening to the outside of the fish called operculum opening.
The gills are protected by a thick gill cover or operculum on both sides of the body near the head.
X
The gills of a fish consist of a long curved bony structure called gill bar/ gill rakers. It provides attachment to the gill filaments and gill rakers.
Gill rakers- they are teeth like structures. They prevent food and other solid materials in water from reaching the delicate filaments.
Gill filaments – they are membranous protection on gill bar. The filaments are richly supplied with blood due to the presence of many capillaries.
Each gill filament sub divides into gill lamellae
The two rows of gill filaments provide a large surface area for gaseous exchange.
Mechanism of gaseous exchange in the gills of a bony fish.
Inspiration: flow of water into the mouth cavity
The process below brings water into the mouth cavity
The mouth opens
Muscular contractions in the mouth lower the floor of the mouth. This increases volume in the mouth cavity and decreases the pressure inside it.
The water outside is at a higher pressure and it rushes in through the open mouth.
Each operculum on the side of the fish bulges outwards by muscular action. This increases the volume in the operculum cavity and lowers the pressure there. Water from the mouth is sucked into the opercular cavity. Meanalbile body wall of he fish. This prevents water outside the fish from entering through the operculum cavity.
X
Expiration 🙁 flow of water over the gills during expiration)
The mouth closes
The floor of the mouth is raised. This (space) in the mouth cavity and increases the pressure.
The operculum presses inwards by muscular action decreasing.
The volume in the operculum cavity but increasing its pressure.
The free edge of the operculum moves away from the body wall of the fish to open the operculum cavity.
Water rushes from the operculum cavity and flows out of the fish via the operculum opening.
X
Exchange of gases between the water and gill filaments
Gaseous exchange in fish takes place on the gill filament as water passes over the gills.
Blood in the capillaries in the gill filaments has a lower concentration of o₂than the water entering the mouth. Therefore O₂diffuses from the water flowing over the gill filaments into the blood through the thin walls of the capillaries.
On the other hand blood in the capillary has no higher concentration of CO₂than the water entering the mouth cavity. Therefore co₂diffuses from the blood through the walls of the capillaries into the water flowing over the gill filaments.
In order to have maximum gaseous exchange between the blood in the gill filaments and the flowing water a steep concentration gradient must be maintained across the respiratory surfaces. This is achieved by the flow of water and blood in opposite directions. This is called counter current flow system.
As the movement of blood and water continues in opposite directions within the respiratory surface, o₂diffuses out of the water into the blood and co₂ from the blood leaves the respiratory surface into the water. By the time the blood leaves the respiratory surface, it has as much o₂as the water. This is so because water moves along, less and less o₂diffuses out of it as blood becomes more and more concentrated with o
X
NB reasons why fish cannot live in air
When out of water, the gill filaments stick together. This reduces the surface area compared to when its in the water hence gaseous exchange is more efficient in water….
In air, the moisture evaporates fast from the gill filaments. Since gaseous exchange requires moist surfaces, the diffusion of o2 and co2 cannot take place.
- Gaseous exchange in amphibians
Amphibians by nature they both live in land and in water. This double habitation calls for special adaptation in gaseous exchange. The respiratory structures are:
Buccal cavity
Lungs
Skin
Buccal (mouth) cavity
Air is taken or expelled from the mouth cavity by raising and lowering the floor of the mouth.
The lining of the mouth cavity is moist and O₂ from the air dissolves in it.
Under the lining of the mouth, there is a rich supply of blood capillaries and O₂ diffuses into the blood and is carried by haemoglobin to all parts of the body.
CO₂ from the tissues is brought by the blood to the mouth cavity where it diffuses out.
- Lungs
When the nostrils are closed the air can be forced into the lungs by the pumping action of the floor of the mouth.
The air reaches the alveoli sacs of the lungs that are well supplied with blood through a large network of blood capillaries.
The o₂in the air dissolve into the moist inner lining of the alveoli. It then diffuses into the blood across the wall of the capillaries, combines with haemoglobin in the RBC and is transported to all parts of the body.
The co₂from the tissues is carried by the blood and diffuses into the alveoli then pumped out by the pumping action of the mouth cavity.
- Skin
Frogs have thinner and moist skin than the toads. Beneath the skin there is a large network of blood capillaries. O₂ from the air and from the water diffuses through the skin into the bloodstream.
CO₂in the blood diffuses out of the blood capillaries through the moist skin into the surrounding water and air.
Toads do not use the skin surface for gaseous exchange normally except when they are hibernating.
Mechanism of gaseous exchange in mammals
Nose
The nose has two openings called nostrils which let in air into the air passages (nasal cavity).
Function of nasal cavity
Nasal cavity is lined with mucus secreting cells and hairs. The mucus and hair filter and trap dust and micro-organisms from the air. So particles are prevented from entering the lungs.
Air is warmed and moistened in the nasal cavity.
The lining of the nasal cavity also houses sense organs for smell which can detect and distinguish different types of smell.
Pharynx /Throat
It’s that part where the mouth cavity and the nasal cavity meet.
Larynx /Voice box
It’s a hollow box- like structure. It’s noticeable externally by the sight projection at the front of the throat (Adams apple).
The pharynx connects with the larynx through a slit-like opening called the glottis.
The glottis has a gap known as epiglottis which closes when a person is swallowing to prevent food from entering the trachea.
Choking and coughing are reflex actions which remove any foreign particles which accidentally enter the trachea.
X
Just below the glottis there are two membranous cords called vocal cords. The vibrations of these cords caused by the movement of air out of the lungs during exhalation, results in the production of sound.
Trachea /wind pipe
It’s made up of rings of cartilage to ensure it does not collapse during breathing. Also they enable the tubes to be stretched e.g. during coughing.
The incomplete rings (c-shaped) have gaps on the side facing the oesophagus which allow smooth swallowing.
The inner lining of the trachea has mucus to trap and filter micro-organisms and dust particles preventing them from entering the lungs.
X
The trachea is lined with cilia which move mucus upwards into the pharynx. From the pharynx the foreign matter is expelled from the air passages by spitting or swallowing.
X
NB: cigarette smoke is known to inhibit the action of cilia in the respiratory tract. The result is accumulation of dust particles, bacteria and mucus.
The bacteria may invade the cells of the mucous membrane causing diseases. As a result smokers get frequent respiratory tract infection.
Also smokers cough frequently as the body tries to get rid of the accumulated mucus and other material
Bronchi
The trachea branches in to the tubes called bronchus. They are similar to trachea except that they are narrower and have other materials.
Bronchioles
Each bronchus enters a lung and extensively branches into narrow tubes called bronchioles.
Bronchioles have no rings of cartilage and each bronchiole end up into a tiny sac called alveolus (plural alveoli) hence the spongy nature of lungs.
Alveoli
The walls of epithelium are composed of thin and flat epithelium
Structural adaptation of alveoli
They provide a very large surface area. There are approximately 300million alveoli in the lungs of a human adult
NB: total area is 90m²(nearly as large as a basketball pitch)
The internal surface is moist being lined up with mucus to help in the rapid diffusion of gases
Have a rich supply of blood capillaries which allows rapid gaseous exchange between the air in the alveoli and the blood in the adjacent capillaries.
The walls of the alveoli are made up of a layer of thin epithelial cells. This thin barrier permits rapid diffusion of gases.
Lungs
Each lung is enclosed by two membranes (double membrane) known as plural membrane.
One part of the membrane adheres tightly to the lungs and the other covers the inside of the thoracic cavity. The space between these membranes is known as pleural cavity.
It’s filled with pleural fluid which reduces friction and therefore makes the lungs move freely in the chest cavity during breathing.
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Thoracic cavity
The lungs and pleural membranes are contained in the thoracic cavity.
Thoracic cavity is surrounded by ribs, sternum and vertebrae which are all held together by muscles at the lower end known as the diaphragm.
Ribs are curved bones which project from the vertebral column dorsally and ventrally with sternum
However the lower most ribs are not attached to the sternum .the ribs protect the lungs and heart.
Between the ribs are internal and external tissue referred to as interrcostal muscles. These muscles work antagonistic to each other i.e. when one set of muscles contract each other set relaxes.
Thorax
It’s an airtight cavity enclosed by the ribs and the diaphragm.
Mechanism of breathing in humans
It involves two processes: inspiration / inhalation/ breathing in and expiration/exhalation/ breathing out. These two processes are brought about by movement of the ribs and diaphragm.
Inspiration/ inhalation/ breathing in
This process occurs when the thoracic cavity increases in volume and thereafter decreases in pressure.
During inspiration the external intercostal muscles contract while the internal intercostal muscles relax. This movement pulls the ribs upwards and outwards.
The diaphragm which is dome shaped flattens by the contraction of its muscles. The flattening of the diaphragm together with the outward movement of the ribs increases the volume of the thoracic cavity and decreases the pressure inside it.
Atmospheric pressure being higher than pressure inside the thoracic cavity forces air to rush into the lungs through the nose and trachea hence inflating the lungs.
Expiration/ exhalation
This process occurs when the volume of the thoracic cavity decreases and the pressure inside it increases.
This is brought about by the following:
The external intercostal muscles relax while the internal intercostal muscles contract bringing the ribs down to their original position. At the same time the muscles of the diaphragm relax and regain its original dome shape.
These movements decrease the volume of the thoracic cavity and increase the pressure inside it. Thus air is forced out of the lungs through the air passages into the atmosphere thus deflating the lungs.
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The alveoli and blood capillaries are made of very thin walls.
The walls of the alveolus are covered by a film of moisture which dissolves O₂ in the inhaled air.
Since O₂ concentration in the blood is lower than in the alveolus it diffuses through the epithelium, the capillary wall, the plasma and into the RBC where it combines with haemoglobin.
CO₂ in the capillaries surrounding the alveoli is at a higher concentration than inside the alveoli hence it diffuses into the alveoli.
Changes during inhalation and exhalation

X
Percentage composition of gases inhaled and exhaled air

– Gas	– % in inhaled air	– % in exhaled air
– Oxygen	– 20	– 16.9
– Co₂	– 0.03	– 4.0
– Nitrogen & other gases	– 79.97	– 79.97

Regulation of breathing
The average breathing rate in human beings is 16 to 18 times per minute.
Breathing movements normally take place unconsciously
In the brain there is a region called medulla oblongata which controls the breathing movements.
As CO₂ in the blood reaches this region it triggers this part of the brain to send impulses to the rib muscles and the diaphragm which in turn respond appropriately. This makes breathing to continue on and on.
During vigorous activity the concentration of CO₂ increases into the body tissues hence more CO₂ diffuses into the blood and reaches the medulla oblongata.
The high concentration of CO₂ in blood triggers the medulla oblongata to increase the rate of breathing.
Increased rate of breathing helps to increase the amount of O₂ in the blood thereby meeting the demands of the increased tissue respiration.

– inhalation	– Exhalation
– External intercostal muscles relax	– External intercostal muscles relax
–	–
– Internal intercostal muscles relax	– Internal intercostal muscles contract
– Ribcage is lifted up outwards	– Ribcage moves downwards and inwards
– Diaphragm muscles contract	– Diaphragm muscles relax
– Diaphragm flattens	– Diaphragm archs upwards and becomes dome – shaped
– Volume of thoracic cavity increases	– Volume of thoracic cavity decreases
– Air pressure decreases	– Air pressure increase
– Air moves into the lung through the nostrils, pharynx, glottis, the trachea and into the alveoli	– Air is forced out of the alveoli into the trachea, glottis, pharynx, nostrils and into the atmosphere
– Lungs inflate	– Lungs deflate

Factors affecting the rate of breathing
Exercise
During vigorous physical activity the rate of breathing increases so as to meet the increased demand of O₂
Faster breathing also eliminates the extra CO₂ produced by the increased respiration.
Age
Young people have a higher demand of O₂. They therefore have faster breathing rate. This is because young people are actively growing hence the faster rate of breathing is to supply tissues with O₂
Emotions
Generally the body emotions affect the production of hormone adrenaline which increases the general metabolism and hence increased rate of breathing e.g. fear anxiety and fright
Temperature
When the temperature is high there is a tendency in the rate of gashouse exchange to increase. However if temperature is too high the breathing rate will reduce
Health
During sickness the rate of breathing increases. The faster rate of breathing enables the liver to remove toxins in drugs those released by diseases causing micro-organism
The faster rate of breathing also enables the kidneys to excrete waste products of body metabolism through urine
Altitude
At high altitude the rate of breathing is faster than at low altitude. At high altitude O₂ concentration is low thus faster rate of breathing helps supply tissues with sufficient oxygen.
LUNG VOLUMES
Lungs of an adult can hold approximately 5500cm³ of air when completely filled. The volume is known as lung capacity
During normal breathing a small volume of air 500cm³is taken in and out of the lungs. This volume of air is referred as to as the tidal volume.
In addition to tidal volume a person can have a forced inhalation. this additional volume is called inspiratory reserve volume (200cm³)
Tidal volume +inspiratory reserve volume =inspiratory capacity
After normal exhalation it is possible to force out extra volume of air. This volume is called expiratory reserve volume (1300cm³)
It is possible to have deepest possible exhalation. Such volume of air which can only be forcibly pushed out of lungs is called vital capacity.
After the deepest possible exhalation some air normally remains in the lungs. His volume of air is called residual volume (1500cm³)
- Respiratory diseases
These are the diseases that affect the breathing structures and make gaseous exchange in animals difficult.
Asthma
This is a disease which mainly affects the air passages
- Causes
Allergy which can be due to pollen grains dust, spores, flowers, fur of animal e.t.c.
Constant lung infection caused by viruses and bacteria.
Emotional and mental stress such as anxiety, anger and fear
Mild or extreme cold weather
Certain hereditary diseases especially those affecting respiratory organs increase the chances of infection.
- Treatment and control
The spraying of a muscle- relaxant directly into the bronchial tubes.
Injection of drugs or oral application pills prescribed by a health physician.
Avoiding the causative agents.
Bronchitis
This is the inflammation of the bronchial tubes. There are two types of bronchitis .i.e.
Acute bronchitis
This is widespread illness in children and frail adults. It is caused by.
A complication of the common cold. It results into the chilling of the body giving way to bacterial infection.
A complication resulting from a previous disease attack e.g. measles, whooping cough, influenza and dengue fever.
Coughing
Head aches
Fever
Pain beneath the sternum
Breathing fast
- Control
Keep warm
Seek prompt treatment for infections
Chronic bronchitis
Result from heavy cigarette smoking and constant attacks by acute bronchitis.
- Symptoms
Production of thick sputum (phlegm) that is green or yellow in colour due to pus from respiratory surface.
Difficulties in breathing
- Control
Avoid smoking or smoking places and continuous exposure to dusty places.
Keep warm and live in well ventilated places.
Seek medical attention immediately the symptoms are observed.
- (iv) Whooping cough
Results from an acute infection of the respiratory tract by a bacterium called Bordetella pertussis.
The disease is endemic in Kenya .i.e. it’s regularly found in a specific group of people.
- Symptoms
Prolonged coughing and vomiting
Bleeding of the eyes (conjunctival haemorrhage)
Convulsions and coma
Ulcers and cardiac failure
Malnutrition especially protein and calory deficiency due to repeated vomiting and difficulty in eating.
Treatment
Patients with complications should be admitted to the hospital for special care and treatment.
Patients should be fed well during the time of sickness.
Immunization should be given soon after birth.
Pneumonia
It’s a disease caused by the bacterium Streptocococcus The chances of attack are increased by other chest infections e.g. bronchitis, whooping cough e.t.c.
- Symptoms
Shallow and difficult breathing.
Coughing with production of sputum
Fevers and chest pains
Lungs become inflamed and alveoli are filled with fluid.
- Control and treatment
Avoid overcrowded and poorly ventilated places
Use antibiotics eg penicillin and sulphonamides prescribed by a doctor.
- (v) Pulmonary Tuberculosis
It is caused by the bacterium Mycobacterium tuberculosis
This disease affects any part of the body.
Its an air borne disease and its spread through saliva droplets, sputum and infected milk.
Symptoms
Fevers and fatigue
Deep coughing sometimes with sputum containing blood
Loss of body weight.
Slight afternoon fever
The bacterium destroys lung tissues making it hard for the patient to breathe. It may eventually result into death.
Control
Suspected sufferers should have a medical check up and can be detected in its early stages by radiographical method
Avoid overcrowded and dirty places.
Vaccination of the population using BCG(Bacille calmette Guerin)
- (vi) Common cold
It’s a mild disease of the upper respiratory tract caused by a large variety of viruses.
Each year about ¾ of human population suffer one or more colds hence the name common cold.
Symptoms
Stuffy nose
Watery eyes
Sneezing, coughing and fever. In severe cases there may be a headache, backache and muscle ache.
Transmission
It’s through close contact with infected people especially through coughing and sneezing. It can also be transmitted through contaminated eating utensils.
Treatment
So far there is no cure for common cold.
The disease normally cares itself within a few days.
The patient should however lie in bed and have plenty of fluids.
Painkillers like aspirin may be taken to relieve various aches and to relieve fever.
If the disease does not cure within few days or if there are persistent aches, then it is advisable tosee the doctor.

RESPIRATION
It is the process by which food substances are chemically broken down in all living cells to release energy, CO₂, water or alcohol.
It takes place in all living cells and involves a series of complex enzyme catalyzed reactions.
NB– Respiration is a chemical process taking place inside tissue cells while gaseous exchange is a purely physical process which takes place at respiratory surfaces
Respiration is also called tissue respiration or internal respiration
SIGNIFICANCE OF RESPIRATION
It provides energy which is obtained due to the break down of food. Foods which can provide lots of energy are carbohydrates (starch and glucose) and fats.
The energy derived from these food substances is used for activities such as muscular contraction, conduction of nerve impulses, secretion of enzymes, growth etc.
Tissue respiration takes place mainly in cell organelles called
Structure of Mitochondria
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Mitochondria are small round or rod shaped cell organelles found in cells and provide sites for respiratory activity.
Living cells such as the kidney cells, the flight muscles of insects and birds, the sperm cells and muscle cells have high energy requirements and consequently posses’ large number of mitochondria.
Mitochondrion has two membranes, the outer and inner membrane that are separated by fluid filled spaces.
The inner membrane folds into projections inside the area for respiratory activities. Enzymes are bound to the cristae.
TYPES OF RESPIRATION
There are two types:
- -Aerobic respiration
- -Anaerobic respiration
Aerobic respiration
It is the process in which food substances such as glucose are broken down in the presence of oxygen in tissue cells to release energy water and carbon iv oxide.
The total energy released at the end of respiration (oxidation) is very high.
If all the energy were released at once in the form of heat it would burn the body cells. To protect the cells from burning, the heat energy is released in small quantities in stages.
This energy is used to bring about a chemical reaction in which a compound in the cell called adenosine diphosphate (ADP) combines with an inorganic phosphate molecule to form another compound called Adenosine Triphosphate (ATP)
ADP +(PO₄)^3- +Energy ATP (High Energymolecule)
- _(Adenosine _Triphosphate
_{(Adenosine Diphosphate)}
Aerobic respiration can be summarized by the following equation
C₆H₁₂O₆+6O₂6CO₂+6H₂O +Energy (ATP)
Molecules of ATP store the energy released in respiration in their bonds and avails it to cells readily when required.
Activity 1: To investigate what gas is given off when food is burnt
Materials
Food sample (starch powder)
Source of heat
Boiling tubes
One holed rubber stopper
Delivery tube
Calcium hydroxide
Solution (lime water)
Procedure
Place some food sample in a dry boiling tube and insert a one-holed rubber stopper into the mouth of the tube.
Hold the boiling tube containing the food sample horizontally.
Pour a little calcium hydroxide solution into another boiling tube and support it. Using a delivery tube connect the two boiling tube into the lime water is as illustrated in the figure below:-
Heat the boiling tube containing the food substance strongly.
Observe and record what happens to the food sample, lime water and the upper sides of the test tube with the food sample
Disconnect the apparatus and rub anhydrous cobalt II Chloride paper on the inner upper side of the boiling tube containing the food sample.
Record the colour change observed on the cobalt II Chloride
Discussion
When the starch was heated at the beginning, some drops of water were deposited on the walls of the test tube. This water comes from starch
When the food sample was heated strongly, it turned into a black substance. This substance is
When carbon was heated with the delivery tube dipped in the boiling tube containing lime water, the lime water turned to a white precipitate/ became cloudy/turbid. This is due to the presence of carbon iv oxide in the gas that was produced.
The results indicate that the food sample contains Carbon, Hydrogen and Oxygen (CHO)
Respiration takes place in two major phases i.e.
- First phase (Glycolysis)
The earliest stages of respiration takes place without using oxygen. These stages involve a series of chemical reactions which occur in the cytoplasm of the cell.
A compound with a 3-carbon molecule called pyruvic acid is formed from glucose.
After pyruvic acid has been formed and oxygen is not supplied to the cell, pyruvic acid is partially broken down to lactic acid in animals or ethyl alcohol (ethanol) and CO₂ in plants e.g.

NB- In Glycolysis one molecule of glucose yields 8 molecules of ATP
C₆ H₁₂O₆ ^enzyme CH₃COCOOH + 6O₂ 6CO₃ +6H₂O + ATP _{(Pyruvic acid) controlled reactions in cytoplasm}

Second phase (Kreb’s cycle) citric acid cycle
This phase takes place in the matrix of the mitochondria.
It involves a series of enzyme controlled reactions that require oxygen
The pyruvic acid formed in first phase is further oxidized by oxygen in a series of enzymatic reactions into CO2, Energy and water as end products i.e.
CH₃COCOOH + 6O₂ ^enzyme 6CO₂ + 6H₂O + ATP
_{(Pyruvic acid) Oxygen controlled reactions carbon iv oxide water30 molecules}

At the end of this cycle, 30 molecules of ATP are produces thus at the end of aerobic respiration, 38 ATP molecules are produced i.e. 8 ATPS – Glycolysis

For the above process to be maintained in the living cells, the following conditions are necessary: –
Cells must be provided with glucose/food
Oxygen must be taken in and react with glucose
There must be respiratory enzymes to catalyze the reaction
Favorable temperature should be maintained for efficient enzyme functioning
The end products of the reaction i.e. CO₂, water and energy must constantly be removed from the mitochondrion.
Expt: To show that heat is produced during respiration
Soak seeds for 24 hours and then divide them into 2 equal portions
Boil one portion of the seeds for 10 minutes, let them cool and wash them in 10% formalin
Place a thermometer in each flask such that the bulb is surrounded by seed
Hold each thermometer with cotton wool and record the initial temperature
Record the temperature every morning and evening for a week.
Germinating seeds break down stored carbohydrates in the process of respiration in order to get energy which they require for growth.
Some of the energy is released as heat; hence there will be temperature rise in the flask containing germinating seeds.
The boiled seeds did not produce any heat because they didn’t carry out any respiration.
Before the experiment the seeds were disinfected with 10% formalin to kill bacteria that would cause decay of seeds
The flasks were inverted in order to prevent loss of heat. Warm air rises up and if the flasks are not upside down, warm air in the flask would rise and lead to heat loss from the germinating seeds
Anaerobic respiration
It occurs in the absence of oxygen. In the plants glucose is oxidized in the absence of O₂ to give ethanol, CO₂and energy e.g.
C₆H₁₂O₆2C₂H₅OH +2CO+ energy(Glucose) (Ethanol) (Carbon IV oxide)
Anaerobic respiration in plants is also referred to as Fermentation Fermentation occurs when bacteria or fungi breakdown glucose to form alcohol, CO₂and energy.
In animals anaerobic respiration leads to the formation of lactic acids and energy e.g.

C₆H₁₂O₆2C₃H₆O₃+2O₂ + energy
(Glucose) (lactic acid)
NB the incomplete breakdown of glucose in anaerobic respiration result in the production of less energy than in case of aerobic respiration.
In the absence of O₂, most plant and animal tissues can respire anaerobically for a limited period.
It is essential that they get rid of the end products (lactic acid in animals and ethanol in plants) immediately. This is because these end products become toxic to the organism if left to accumulate within the cells.
Oxygen debt
This is the O₂ required to get rid of the lactic acid that accumulates in the body tissues when the supply of O₂ is less than the demand.
Under these conditions the animal’s tissues respire through anaerobic respiration and this causes lactic acid to accumulate in the tissues.
The lactic acid might cause fatigue and result in muscular cramps e.g. When a short distance runner or driver holds his/her breathe while running or diving. The O₂debt incurred here is “paid” back by the person breathing more quickly and more deeply in order to increase the supply of O₂ during the recovery period after the race.
During the process of paying back the O₂ debt, lactic acid is oxidized to CO₂, water and energy when O₂is available.
Anaerobic organisms
The organisms that carry out anaerobic respiration are called anaerobes. There are 2 types of anaerobes.
Obligate anaerobes.
Respire in the absence of O₂ and die in the presence of O₂. They lack the enzyme catalysis which breaks down hydrogen peroxide. (H₂O₂) e.g.
Escherichia coli
Bacillus subtilis
Clostridium botulinum
Clostridium tetan.
Facultative anaerobes
Respire in the presence or absence of O₂g. yeast, most bacteria, parasites or fungi.
- Comparison between aerobic and anaerobic

– Aerobic respiration	– Anaerobic respiration
– O₂ is necessary for the process to take place hence a complete oxidation of the substrate	– O₂ is not required hence substrate is not broken down completely
– More energy released ( 38 ATP molecules) from one glucose molecule	– Less energy released (2 ATP molecules) from one glucose molecule.
– Substrate is completely broken down to CO₂ and water	– Substrate is not completely broken down producing lactic acid and alcohol
– The end products are water and CO₂	– End products are alcohol in plants. Lactic acid in animals.
– Occurs in cytoplasm. Mitochondria	– Occurs in cytoplasm

Application of anaerobic respiration
Commercial production of alcohol

In the brewing industry, barley is fermented with yeast to produce beer.
In the wine industry, sugar from grapes is the source of germination. Different strains of yeast are used during the anaerobic process to produce wines of different flavours.
Distillation of some of the products of fermentation gives rise to stronger alcoholic drinks called spirits e.g. Distilling wine makes brandy.
- In the dairy industry
Milk contains lactic acid bacteria which anaerobiccaly breaks down milk sugar called lactose to form lactic acid which makes the milk sour. The dairy products include: cheese, butter, yoghurt and cream.
- Sewage treatment plants
Certain bacteria are introduced into the sewage to break it down by anaerobic respiration. These reduce the bulk of the sewage which on further treatment is purified and is safe for release into rivers or water bodies.
- In agriculture
The making of silage is an anaerobic fermentation process which is carried out on farms.
Silage is prepared by allowing bacteria to ferment vegetation giving it a good flavour and scent. The silage is used as animals feed.
- Production of biogas and gasohol
Manures from cows or other waste plant materials can be used as a substrate for fermentation, producing biogas which contains 70% methane. The gas can be used for cooking and lighting.
Cane sugar is used to produce gasohol in the presence of yeast. Gasohol can also be pressed from ethanol. Gasohol can be used on its own to run engines.
- In the home.
In bread production for domestic and commercial use. During fermentation using yeast, CO₂ produced in the dough mixtures causes the dough to rise as bubbles of the gas are produced. Thus the bread becomes porous.
- Commercial production of oxalic acid, citric acid and vinegar.
These are produced through anaerobic respiration. Those products are used in food processing.
- Fossil fuel formation.
As the organic remains take many years to decay. Fossil fuel such as natural oil, gas, coal and peat are formed.
- Expt: to investigate the gas produced during fermentation
Boil about 20 cm³ of glucose in a tube, cool to 40 O^c and add some yeast.
Pour onto the glucose and yeast suspension some kerosene oil. Leave for about one hour. ( several minutes)
Put some lime water (calcium hydroxide) in a test tube and connect this test tube to the boiling tube using the delivery tube. Rubber
stopper as shown in the diagram below
- Discussion
The water was first boiled to expel any dissolved oxygen to prevent any aerobic respiration form taking place.
Yeast being a living organism would be killed or its enzymes denatured with hot water. This is the reason for first cooling the water before the yeast is added to it.
As the yeast respires in the absence of O₂, it uses up some of the sugar and produces a gas and ethanol.
The gas causes a lot of frothing in the conical flask and some of it goes up the delivery tube and makes the lime water appears turbid (white precipitate is formed). This is carbon iv oxide
- Respiratory substrates
They are substances that are oxidized to release energy. They are:
- Carbohydrates
They are the common oxidized substrates. Excess carbohydrates are stored in plants in the form of starch and in animals in the form of glycogen.
Carbohydrates are broken down into simple forms of glucose and fructose before being oxidized
19% carbohydrates release 17kj when oxidized.
- Fats
They are oxidized when carbohydrates resources are depleted. Fats are broken down by enzymes called lipases into glycerol and fatty acids before being oxidized.
Ig of fat yields 38kj when oxidized. Most food stored in plants and animals is in the form of fats and lipids.
Fats are not the main substrates of respiration because:
They are not very soluble and therefore not easily transported to the sites of respiration.
It will also require more O₂to oxidize one gram of fat than one gram of glucose
- Proteins
They are oxidized when both carbohydrates and fat reserves are exhausted especially during prolonged starvation. Proteins are hydrolyzed by enzyme protease into amino acids. The amino acids are denominated to urea and a carboxyl group.
One gram of protein produces 22kj when oxidized.
- Respiratory quotient (R.Q)
It’s a ratio showing the relationship between the amount of carbon IV oxide produced against the amount of oxygen used in respiration i.e.
Q= volume of CO₂ produced
Volume of O₂consumed
During aerobic respiration of carbohydrates the RQ=I i.e.

Q of fat= 0.7
Q of proteins= 0.9
Q of Carbohydratest= 1.0
- Factors affecting Respiratory quotient (R.Q)
Type of respiration– Aerobic respiration gives an R.Q of 1.0 or less while anaerobic respiration gives an R.Q greater than 1.0.
Type of substrate– Oxidation of carbohydrates gives an R, Q of 1.0, proteins 0.9, lipids 0.7.
Metabolic processes
Synthesis of fats, carbohydrates and organic acids use a lot of oxygen to produce low volumes of CO2.
During seed dormancy the R.Q is more than 1.0.During germination the value of R.Q reduces to 0.7.
Hibernation-It’s the state of inactivity during winter when animals burrow underground to escape the low temperatures.
During this time the animals are less active. The major substrate respired are fats.
Aestivation- It’s the state of inactivity during which some animals burrow to escape hot weather.
(g) Age–R.Q increases when one becomes
Temperature of the surrounding-R.Q will be lower in low temperatures and higher during higher temperatures.
Health status of organism-During sickness R.Q increases due to the effect of the infection such as the presence of toxins.
Factors affecting the rate of respiration
Age
Young people are more active than old people. The rate of respiration or metabolism is faster in young people than in old people.
Young plants have a faster rate of respiration than old plants.
State of health
The rate of metabolism increases during illness so as to remove toxic substances released by pathogens.
Size
Small animals have a large surface area to volume ratio compared to bigger animals. Small animals lose heat at a faster rate thus they respire at a faster rate to replace the lost heat.
Temperature
Respiration is an enzyme controlled reaction. At low temperatures, the rate of respiration is low. An increase in temperature increases the rate of respiration.
Above the optimal temperature, enzymes become denatured and the reaction stops.
Activity
An organism at rest mainly requires energy for sustaining of life processes e.g. breathing and circulation of blood. This energy is referred to as Basal Metabolic Rate (BMR)
BMR increases in active organisms. In humans, males have a higher BMR than females.
Hormones
Certain hormones in the body such as adrenaline and Thyroxine increase respiratory activities.
Substrate concentration
The primary respiratory substrate in the tissues is sugar. When sugar concentration increases, the rate of respiration also increases. The reverse is also true.
Oxygen concentration
Respiration is affected by the amount of oxygen available in the tissues. When the amount of oxygen is low the rate of respiration slows down. When the amount of oxygen is high the rate of respiration increases.
In diving animals the oxygen concentration in their environment is low hence as soon as they dive, cardiac frequency drastically decreases (bradycardia) and the arterioles of all the vital body organs constrict so that oxygen can be delivered to the vital organs that cannot endure oxygen deprivation e.g. the brain and the heart.
As a result of this, less oxygen reaches other body tissues and organs hence their respiration rate reduces.
Expt; To demonstrate that respiration takes place in plants
Procedure
Set up the apparatus as shown below

The delivery tubes should be arranged so that one arm forms the inlet and the other outlet.
Use petroleum jelly or wax to seal off any gaps in the tubes to stop air entering into the apparatus.
The potted plant is placed under the bell jar and the bell jar is covered with the impermeable materials to exclude any carbon iv oxide from the soil.
When the filter pump is switched on, air flows through the whole set up.
NB Soda lime is used to remove any carbon iv oxide in the air entering conical flask A hence lime water in A remains clear.
After 30 minutes, a white precipitate forms in the lime water in conical flask B. this shows that the potted plant is respiring producing carbon iv oxide which reacts with lime water to produce the white precipitate.
The black cotton prevents the green plant from carrying out photosynthesis.
- Expt; To show aerobic respiration in animals
Put some 2cm³ of bicarbonate indicator solution in 2 conical flasks and label them A and B.
Put 2 grasshoppers on a muslin cloth or wire net and place them in conical flask A. Cover the conical flask immediately with the rubber bung.

In conical flask B place only a muslin cloth or wire net. Cover the conical flask immediately with the rubber bung and leave the set-up for 30 minutes.

After 30 minutes the bicarbonate indicator solution in A turns from red to yellow. This shows that grasshoppers are releasing carbon iv oxide through respiration.
The bicarbonate indicator solution in B remains red. Set-up B acts as a control experimen

EXCRETION AND HOMEOSTASIS
Excretion- It’s the process by which living organisms get rid of metabolic waste products. In plants some waste products are removed while others are reused or stored as harmless substances.
In animals, waste products resulting from the metabolic processes are generally removed from the body.
- Homeostasis– It’s the control and maintenance of a constant internal environment around the cells in body despite the fluctuations in the external environment.
Egestion- It’s the removal of indigestible and undigested food substances from the body.
Secretion- It’s the release of substances from the cells into the body fluids such as blood and the tissue fluid or to the outside of the body. Examples of secretions; hormones, enzymes, mucus, sebum etc
Ecretion in Plants
Metabolic processes in plants occur at a slower rate than in animals. Some of the waste products prodused in one procces are used in another process eg CO₂ released during respiration is utilised in photosynthesis.
Most of the substances that are broken down in plants are carbohydtrates in nature. Waste products from carbohydrates are not harmful to the plants.
Some of the waste products eg resins, gums are stored in dead tissues of plants such as xylem.
Methods of Excretion
Diffusion– Eliminate waste products that are in gaseous form eg CO₂, Oxygen and water vapour.
(ii) Transpiration– water vapour.
Guttation– water and dissolved mineral salts.
Exudation– It’s the release of a fluid from a plant at a slow rate eg gums, latex, mucilage, rubber, resins and Caicium pectate and oxalates.
Deposition– Resins, tannins, caffeine, nicotine, quinine etc are deposited in the Xylem, bark, seeds, fruits, flowers and leaves of plants.
Storage of excretory substances in plant parts
Some plant waste substances that may be toxic to the plant are converted to less harmful substances which are then stored in different parts of the plant such as petals, leaves, fruits and seeds. Some of these plant parts are eventually shed by the plant.
Some plant waste substances are stored in the vacuoles of plant cells. Some are stored in in dead permanent tissues such as the wood or barks or leaves which are shed seasonally. In this state they have no harmful effects on the activities of living tissues.
Most perennial plants store excretory materials in dead tissues.
Aquatic plants lose most of their waste substances by diffusion directly into the surrounding water.
Useful Excretory Products
Anthocyanin
Gives colour to petals and leaves in plants. The dominant colours are red, purple and blue.
These colours are of great aesthetic value and are extracted to make dyes.
Tannins
They are deposited in the dead tissues of trees such as wood and bark. They are common in conifers and mangroves.
Tannins are used in the treatment of leather and manufacture of ink.
They are also used in cosmetics eg henna which is a plant extract used to colour the nails, feet and hair.
Latex
It’s a milky substance that is produced by some plants. Latex from the rubber tree is used to make rubber.
Gums
They are produced by different plants such as arabic, ghath and carob. These gums are edible and are used to thicken food and creams.
Sapodilla gum is used in the manufacture of chewing gum.
Alkaloids
They are produced in many forms and are stored in different organs of plants eg
- Quinine
It’s obtained from the bark of cinchona tree
It’s used in the treatment of malaria.
Also its added in drinks as a stimulant.
- Cannabis
It’s stored in flowers, fruits and also leaves of Cannabis sativa.
It’s normally extracted and used in the manufacture of drugs such as painkillers.
Cannabis sativa induces hallucinations ie seeing or hearing unreal things.
- Cocaine
It’s obtained from the leaves of a south American plant called coca plant.
It’s used as a local anaesthetic . when taken in large quatities it causes great physical or mental effects such as convulsions or hallucinations.
It’s addictive when taken in large amounts and can lead to ailments of the heart.
- Nicotine
Occurs in the leaves of the tobacco plant. Its used to manufacture insecticides and narcotic drugs.
- NB Narcotic drugs are substances that cause one to sleep or become very relaxed and feel no pain.
The tar from the tobacco is poisonous and cause lung cancer in human beings.
- Caffeine
It’s stored in coffee beans and tea leaves.
It’s a mild stimulant which is refreshing. It increases mental activity and reduces fatigue.
Excessive intake of caffeine can cause sleeplessness and so may cause mental illness.
It can cause changes in cells of the foetus.
It increases the activity of adrenaline.
- Morphine
It’s extracted from the poppy plant and is used to make narcotic drugs.
It’s also a painkiller and muscle relaxant.
- Papain
Its extracted from pawpaw trees and used as a meat tenderiser.
- Colchicine
Its obtained from the roots of crocus plant. Its used to bring about mutation in genetic materials thus useful in plant breeding.
Its carcinogenic ie it can cause cancer.
- Khat
Also reffered to as miraa (Khat edulis). Its extracted by chewing the leaves and the twigs of the tree.
Its used as a stimulant.
- Pyrithrin
Its extracted from pyrethrum flowers. Its used to make insecticides.
- Alkaloids
Produced in irish potatoes when exposed to sunlight turn the tubers green. They are bitter and can be poisonous if ingested in large quantities. Naturally, the alkaloids protect tubers exposed on the groundfrom being fed on.
Excretion in animals
Unlike plants, animals have more problems of getting rid of waste substances for several reasons;
-Animals are more active than the plants threfore their metabolic processes takesplace at a higher rate producing large quantities of waste products.
-Animals do not put most of their waste products to other uses the way the plants do.
-Animals take in certain substances in their food in excess of their needs. These extra substances eg proteins are broken down with the formation of toxic substances such as ammonia.
Excretion in unicellular organisms
Most simple organisms such as protozoa live in aquatic environments. Their waste products include CO₂and nitrogenous wastes.
Protozoa such as amoeba and paramecium depend on diffusion as a means of excretion.
Their bodies have high surface Area to volume ratio that provide a large surface area for gaseous exchange and excretion to take place by simple diffusion. These waste products diffuse from the cytoplasm where they are at a higher concentration across the cell membrane into the surrounding water where their concentration is low.
Another method of excretion is by use of contractile vacuole.
Amoeba and paramecium live in an aquatic environment that is hypotonic to their body fluid hence there is excess inflow of water by osmosis. Excess water and dissolved chemicals accumlate in the contractile vacuole.
On reaching the maximum size, contractile vacuole moves to the cell surface and bursts releasing the contents to the surrounding.
Soon afterwards other contractile vacuoles form in the cytoplasm, accumlate more waste contents and the process continues eg

Excretion in animals
Excretion in animals is carried out by elaborate systems made up of specialized tissues and organs. This is because their bodies are complex and have greater number of cells.
The excretory tissues and organs include;
-Flame cells-Platyhelminthes
-Nephridia-Annelida
-Malphigian tubules-Insects
- -Gills, lungs, liver and kidney- Vertebrates
These organs are specialized to function in different environments such as aquatic (marine and fresh) and terrestrial.
Excretion in mammals
The main excretory organs in mammals are;
(a) Skin
This is the largest body organ as it covers the whole body surface and even continues into many body openings like nostrils, mouth and ears.
Functions
- Protection of the uderlying tissues from entry of micro-organisms, physical damage and ultra-vilet rays from the sun.
-Since the outermost layer is waterproof, the skin preventsthe body from drying up.
- Regulation of body temperature.
- Excretion of salts, excess water and traces of urea.
- Reception of stimuli of heat, cold, pain, touch and pressure.
- Synthesis of vitamin D.
- Storage of fat.
The skin consists of two main layers; outer epidermis and inner dermis.
The Epidermis
It’s the upper layer of the skin and its made up of 3 layers of cells i.e.
The cornified layer
It’s the outermost layer and it’s made up of flattened dead cells that become filled with a tough flexible substance called keratin. This layer provides protection against mechanical damage and invasion of bacteria.
It also reduces the loss of water by evaporation. Cells of this layer are continuously lost through friction and replaced from beneath by granular layer.
Its thickness varies in the body e.g. its thickest in areas of high friction like palms of hands and soles of feet, but thinnest on lips and eyeballs.
Granular layer
It’s the middle layer of epidermis and consists of living cells that have granules. It gives rise to the cornified layer.
Malphigian layer
It’s the innermost layer of cells and is made up of actively dividing cells that give rise to new epidermis.
The cells have pigment granules called melanin that gives colour to the skin. The more it is, the darker the skin colour. It also gives protection against harmful ultra-violet rays from the sun.
Dermis
This is thicker than the epidermis and is located below it. It contains the following;
Sweat glands
These are tiny coiled tubes which secrete and release sweat through the pores on the surface of the skin.
Sweat consists of water and mineral salts such as sodium chloride and traces of urea and lactic acid. The liquid that forms sweat is absorbed by the sweat glands from the blood capillaries supplied to each gland.
It reaches the surface of the skin through the pore and water in it evaporates into the air. This cools the body.
Sweat glands function when the body temperature rises above the normal by between 0.2 ºC-0.5 °C.
Blood vessels and Lymphatic vessels
Blood vessels contain blood that supplies nutrients and O₂ to the skin tissues and remove waste products and CO
Blood also helps in temperature regulation.
Lymphatic vessels drain excess tissue fluid.
Nerve endings
The nerve cells that detect changes from the external environment thus creating awareness within the body of the changes in temperature (cold and heat), pressure and touch.
Hair
Originates from a deep infolding of the epidermis that forms the hair follicle. The hair follicle is lined with granular and malphigian layers of epidermis.
At the base of the hair is a dermal or hair papilla from which the hair root develops.
The hair follicle is supplied with sensory nerve to increase sensitivity of the skin and blood vessels, for the supply of nutrients and removal of waste products.
Each hair is made up of a base called hair root and hair shaft which protrudes outwards.
‘Growth of hair’ is due to continuous addition of new dead cells at the base of the hair.
Erector pili muscles are attached to the follicle at one end and on the other end to the epidermis. These muscles undergo contraction and relaxation to alter the angle between the hair shaft and the skin and therefore vary the amount of air trapped between the hair and the skin.
NB Certain hairs have become specially specialized adapted e.g.
-Eye lashes and the hairs inside the human nose which help to keep out dust particles.
-Cats, dogs, cats etc have long whiskers which help with the sense of touch.
-The long stiff spines of porcupines, the horns of rhinoceros and the pangolin’s scales are examples of modified hairs.
Sebaceous glands
They are attached to the follicle and the gland opens into the follicle. They secrete sebum which keeps the hair and epidermis flexible and waterproof (water repelling property).
Also sebum contains antiseptic substances for protection against bacteria.
Also keeps epidermis supple and reduces the tendency for it to become dry due to evaporation.
Subcutaneous layer
This is a layer of fat beneath the dermis and binds the skin to the muscles and other organs deep in the body.
It acts as a storage region for fats and an insulation layer against heat loss.
NB Skin lightening creams contain among other chemicals, mercury. They destroy;
Malphigian layer- this leads to the destruction of melanin producing cells making skin appear lighter, but this exposes the skin to harmful U.V rays which cause cancer.
Cornified layer- its destruction gives the impression of a softer skin but this exposes the skin to mechanical injury and microbial attack.

Lungs
In mammals , birds, reptiles and amphibians, CO2 formed during tissue respiration is removed from the body by the lungs.
The Kidney
The functions of kidney are;
-Excretion
-Osmoregulation
-Ionic balance
-Regulation of PH
The kidney is an organ found in vertebrates and each organism has two kidneys.
Kidneys are bean-shaped and are red in colour. They lie near the back of the abdominal cavity about the level of the waistline.
Each kidney weighs approximately 142.5g, ie about the size of a clenched fist. The right kidney is generally slightly lower than the left. The kidney is surrounded by a layer of fat which helps to cushion it from mechanical or physical injury.
The kidney is supplied with blood from the general circulatory system via the renal artery which branches off the aorta.
Blood from the kidneys goes back to the general circulation through the renal vein which joins the vena cava.
A tube called the ureter connects each kidney to the bladder located in the lower abdomen. From the bladder another tube called the urethra opens to the exterior of the organism.
In males, the urethra is long and is joined to the reproductive system unlike in females hence refered to as urinogenital system.
Two rings of sphincter muscles encircle the urethra and they control the emtying of the bladder. The two kidneys, two ureters, the bladder and the urethra make up the urinary system.
Structure ot the kidney
The kidney has two main functions;
Excretion-They remove excess salts, water and nitrogenous wastes from the blood.
Osmoregulation-They regulate the concentration of water and salts found in the body fluids.
A longitudinal section of mammalian kidney shows 3 distinct regions i.e.
-Cortex– Its dark red in colour and found to the outside.
-Medulla– Its red in colour and lies to the center of the kidney and extends to form conical structures called pyramids. These pyramids open into swollen cavity called pelvis.
-Pelvis– Its white in colour and narrows to form ureter.

Nephron
It’s the basic functional unit of the kidney. Each kidney has about 1.25 million nephrons.
Each nephron is made up of two main parts namely;
- Renal tubule
-Glomerulus
Renal tubule
It has 5 main parts i.e.
Bowmans capsule-It’s a thin double-walled and cup-shaped structure.

Proximal convoluted tubule-Its coiled and extends into a U-shaped part.
Loop of henle-It’s the U-shaped part.
Distal convoluted tubule– Its coiled and extends into a collecting tubule.
Collecting tubule– Drains into a collecting duct into which Collecting tubules from several nephrons drain thus forming an outlet of urine through a pyramid into the pelvis.
Glomerulus
It’s a fine network of blood capillaries enclosed by the Bowman’s capsule. Glomerulus is formed from the;
-Afferent arteriole– It’s a branch from renal artery.
-Efferent arteriole– It collects blood from the glomerulus and extends to the renal tubule where it divides into capillaries that ramify the tubule.
It channels blood away from the glomerulus.
Functions of the glomerulus
Excretion in the nephron is carried out in two stages i.e.
-Ultra-filtration
lumen-Reabsorption
Ultra-filtration
This is the process by which the useful substances enter the nephron.
Reabsorption
This is the process by which the useful substances are taken back into the blood so that they are not lost.
Kidneys receive blood from the renal artery and branch off the dorsal aorta. This blood is rich in nitrogenous wastes e.g urea. It also contains dissolved food substances, plasma, proteins, mineral ions, hormones and oxygen.
The Afferent arteriole entering the Glomerulus has a wider lumen than the Efferent arteriole leaving it.
The narrowness of the Efferent arteriole produces both resistance to blood flow and back pressure which create extremely high pressure in the glomerulus.
Also the renal artery branches directly from the dorsal aorta whose blood flow is at a high pressure.
This pressure forces water, mineral ions and small molecules like glucose, amino acids and urea out of the the glomerulus. These pass through the tiny pores in the walls of the glomerular capillaries into the Bowman’s capsule. This process is known as ultra-filtration and the liquid collected in Bowman’s capsule is called glomerular filtrate.
The larger molecules in the blood eg blood proteins, white blood cells, red blood cells and platelets cannot pass through the capillary walls of the glomerulus hence the blood which remains is rich in plasma proteins and little water.
The glomerular filtrate then flows from the capsular space into the Proximal convoluted tubule of the nephron. As the glomerular filtrate flows along, most of the filtered substances which are useful to the body are selectively reabsorbed back into the blood.
In the Proximal convoluted tubule, all glucose , amino acids, some water (80%) and mineral salts are actively reabsorbed against the concentration gradient, a process that requires energy (active transport).
NB The substances reabsorbed are those which are useful to the body hence refered to as selective Reabsorption
Adaptations of Proximal convoluted tubule for efficient Reabsorption
-Cells lining the tubules have numerous mitochondria which provides the necessary energy in the form of ATP.
- -Cells of the tubules have micro-villiwhich increases the surface area.
-The tube is long and highly coiled to provide a large surface area for Reabsorption.
- -The coiling of the tubule reduces the speed of flow of the filtrate thereby giving more time for efficient Reabsorption.
-The tubule is well supplied with blood capillaries.
The glomerular filtrate flows into the loop of henle, which has a unique U –shape feature with a descending and an ascending limb.Salts especially sodium chloride are reabsorbed into the blood.
The U-shape loop is generally longer and has a counter-current flow established between the flow of the filtrate and the blood supply in vessels.
Active transport is involved in the reabsorption of sodium salts.To regulate the intake of sodium salt, a hormone called aldosterone is secreted by the adrenal glands.
Low content of salt in the blood stimulates adrenal glands to secrete more aldosterone hormone and therefore more salt is reabsorbed from the filtrate and vice versa.
The glomerular filtrate flows into the distal convoluted tubule where controlled amount of water is reasorbed into the blood by osmosis .This process is enhanced in 2 ways:
(i) Due to the active intake of sodium salt into the blood at the loop of henle which increases the osmotic potential of the blood.
(ii) A hormone known as antidiuretic hormone (ADH)/vasopressin. This hormone is secreted by the pituitary gland.
ADH increases the permeability of the tubule and blood capillaries to water. When there is excess water in the body eg as a result of excessive intake of fluids, osmotic potential of the blood falls causing the pituitary gland to reduce its secretion of ADH into the blood. Water reabsorption in the tubule is thereby reduced and results in the production of large amounts of dilute urine.
If the body loses a lot of water through sweating, the blood pressure is raised hence the pituitary gland release more ADH which results in increased water reabsorption from the tubule into the blood. This results in the production of little amounts of concentrated urine.
NB Adaptations of distal convoluted tubule are similar to those of proximal convoluted tubule.
The glomerular filtrate flows into the collecting tubule from where more water is reabsorbed. The glomerular filtrate now becomes urine and trickles down into the collecting duct where it joins urine from the collecting tubules of other nephrons.
The urine then flows into the pelvis via the pyramid and is finally emptied into the urinary bladder through the ureter.
About 1-2 litres of urine trickles into the urinary bladder in a day. In the urinary bladder, about 250ml of urine will initiate the urge to urinate. The sphincter muscles relax and the urine is passed out.
The resultant urine composition of a healthy person maybe as follows;
Water——————-95%
Urea———————2%
Uric acid—————-0.03%
Creatinine————–0.1%
Salts (Na+, K+, cl-)—1.4%
Ammonia—————0.04%
Proteins—————–0.0%
Glucose—————–0.0%
The quatinty and concentration of urine in animals is affected by terrestrial, aquatic, desert conditions, the physiological and structural adaptations of the animals eg in a desert rat, water reabsorption is maximised by the development of a long loop of henle.
Kidney Diseases and Disorders
- Nephritis
This is a condition which affects the glomerulus. It is due to the poisons released during infection by certain bacteria called streptococci in various parts of the body.
It can also be caused by small pox, measles, typhoid and sore throat.
The glomeruli become so swollen that they are unable to carry out fitration of the blood.
Symptoms
Headaches, fever, vomiting and weakness.
Swelling of the body called oedema.
Urine is highly coloured and cloudy due to the presence of albumen.
Treatment and Control
Dietary restrictions especially salts and proteins.
Administration of drugs.
- Kidney Stones
There are various causes;
Improper balance of diet, lacking certain vitamin and inadequate intake of water.
Chemical salts in urine eg oxalates, phosphates, urates and uric acid. These may undergo precipitation and form hard deposits or stones in pelvis, ureter hence causing blockage of urine.
Symptoms
Increased frequency in passing out urine.
Pain and soreness in the upper back side.
Pain, chills and fever.
Difficulty in passing out urine.
Treatment and Control
Consult a physician.
Take balanced diet with plenty of water.
Take hot baths and massage the back with hot soft material.
Dialysis or artificial washing out of wastes.
Use of laser beams to disintegrate the stones.
In severe cases, surgical treatment which may involve kidney transplant.
- Albuminuria (Protein in urine)
This disorder is also called proteinuria. It’s a condition in which protein, mainly albumen, is found in urine.
This is due to increased permeability of glomerular capillaries which may be caused by bacterial infections.
Symptoms
Fluid accumulation in tissues (oedema). Its fatal if not treated.
- Kidney failure/Renal failure
The failure of the kidneys to function may occur as a result of a drop in blood pressure due to heart failure, haemorrhage or shock. Haemorrhage means excessive bleeding.
Due to the drop in blood pressure, the filtration rate in each glomerulus is reduced. In some cases the blood pressure is so low that no urine is formed and the kidneys stop working.
If one kidney fails, a person can still lead a normal life using the other kidney. However, if both kidneys malfunction, the individual will still survive if treated promptly. Such treatment can be administered in two forms i.e.
-Kidney dialysis
-Kidney transplant
- Pyelonephritis
This is a bacterial infection of the renal pelvis. The infection may spread to the urethra and bladder.
The kidney becomes swollen and filled with pus. It can be treated with antibiotics.
- Uremia (Uraemia)
It’s a condition in which there is excess urea in the blood.
It occurs when the kidneys are not working properly and the poisonous nitrogen-containing waste products accumulate in blood.
Symptoms
-Convulsions
-Coma
-Vomiting
-Diarrhoea
-Lethargy
-Mental disorientation and confusion.
-Difficulty in breathing
- Gout
This is a disorder caused by the absorption of uric acid salts into the blood.
In high concentrations, uric acid salts form crystals in joints in the toes, fingers and even the kidney itself. Its very painful for the patient to make any movements including walking.
Gout is caused by a diet that has too much organ meat eg kidneys or red meat.
Treatment and Control
Patients are put on medications that break up uric acid into harmless compounds.
They are advised to have a diet low in protein.
Avoid red meat.
Drink plenty of water.

The liver
It’s the 2^nd largest organ after the skin (Adult 2-3% of body weight-1.5kg) and it’s a special organ of excretion because many excretory products are produced by it.
It lies immediately beneath the diaphragm and is made up of several lobes.
It receives blood from the blood vessels i.e hepatic portal vein and hepatic artery. Blood flows out of the liver through the hepatic vein.
The liver consists of a large number of lobules. Each lobule is made up of many liver cells. The blood supply to each lobule is from two sources e. hepatic portal vein and hepatic artery. These vessels branch between the liver lobules.
Between the plates of liver cells are channels called canaliculi which receive blood. The bile moves outwards to the periphery of the lobules where it collects into bile salts.
Functions of the liver
- Deamination
It’s the removal of the amino group from an amino acid. Proteins which are taken in by the body are digested producing amino acids. Excess amino acids are are not stored in the body but are deaminated.
The amino group deaminated enters the ornithine cycle where it combines with CO₂ to form urea, which is excreted from the body through the kidney e.g

2NH₃ +CO_{2 ornithine cycle} → CO(NH₂)_{2 (Urea)} +H₂O

NB Reptiles and birds need to conserve their water. Their ammonia is converted to uric acid that does not need water to eliminate. They are refered to as uricotellic organisns and they produce white droppings instead of urine.
Animals that excrete mainly ammonia live in aquatic environments. CO₂and the toxic ammonia can be diluted to harmless concentrations with plenty of water hence refered to as ammonotelic eg fresh water fish.

_{Enzyme orginase}

Terrestrial animals produce more urea since it does not need to much water for dilution hence refered to as ureotelic eg mammals.
- Detoxification
It’s the process by which harmful compounds such as drugs or poisons are converted to less toxic compounds in the liver.
The toxic substances are subjected to biochemical reactions. The toxins are rendered harmless through oxidation and reduction.
Detoxification can also involve combining the toxin with another compound. The toxic substances are then excreted in the urine.
Toxic compounds in the body may arise from medication, drugs and micro-organisms.
(c ) Heat production
Many metabolic activities take place in the liver. These metabolic activities release heat energy which is distributed by the blood to the other parts of the body.
Haemoglobin elimination
Haemoglobin from the worn-out red blood cells is broken down in the liver and the residual pigments, urochrome which gives urine a yellow tinge, is eliminated by the kidney.
- (e) Regulation of plasma proteins
Plasma proteins are synthesised from amino acids in the liver eg prothrombin and fibrinogen which are involved in blood clotting.
Other plasma proteins eg serum, albumen contribute to the maintenance of osmotic pressure in the body. Also non-essential amino acids are synthesised in the liver.
Haemoglobin is broken down into haem and globin. Globin is digested into amino acids and enters the amino acid pool while the haem group is changed into biliverdin and bilirubin and taken to the gall bladder. These are later released into the gut as bile and then passed out through the faeces. These two substances give faeces its characteristic brown colour.
- (f) Storage of vitamins and mineral
The liver stores vitamins A, B, D, E and K. The liver of cod fish is a rich source of vitamin A and D. When the RBC are broken down, iron is released and stored in the liver in the form of a compound called ferritin.
Regulation of blood sugar level
Excess glucose is converted into glycogen and fat under the influence of insulin. If the blood reaching the liver has less glucose, the stored glycogen is converted to glucose.
- (h) Storage of blood
The liver is highly vascularised and therefore able to hold a large volume of blood. This is achieved through the dilation of blood vessels to accommodate more blood.
Formation of erythrocytes
Erythrocytes are formed in the liver of the foetus. As the foetus develops, the role of the liver in the formation of erythrocytes declines. The liver breaks down old erythrocytes.
Diseases of the liver
- Liver cirrhosis
This disease is also called liver rot.
Its caused by alcoholism i.e. taking too much alcohol over a long period causes the liver cells to die and they are replaced by fibrous scar tissue. The normal functions of the liver are greatly reduced.
- Signs and Symptoms
Loss of appetite and indigestion.
Abdominal pain around the location of the liver.
Haemorrhage evident in the blood stained vomit.
Treatment and Control
There are no drugs for curing cirrhosis. Most peopple with severe cirrhosis die from it.
If the feet are swollen, the patient should stop taking salt in the food.
Strict diet containing easily digestible foods.
- Hepatitis
It’s caused by viruses. There are 3 types i.e.
-Hepatitis A
-Hepatitis B
-Hepatitis C
Hepatitis A is common among children and young adults.
It’s infectious and transmitted through contact, food and water contaminated with faeces of infected peopple.
Hepatitis B
It’s common among adults and transmitted through body fluids eg saliva, blood and semen. Also transmitted through dry blood.
Hepatitis C
Transmitted in blood causing chronic liver disease.
Symptoms of Hepatitis B
Inflammation of the liver.
Loss of appetite, nausea and fatigue.
Abdominal discomfort.
Jaundice of mucous membranes especially in the eyes.
Treatment and Control
Hygienic processing of food.
Proper disposal of sewage.
Treatment of water.
Vaccination against the disease
Proper handling of the blood products.
Screening of all blood and blood products to be transfused .
Use properly sterilised needles and syringes.
- Jaundice
Its caused by an increase in bile pigment called bilirubin in the blood. This may be due to;
-Damage of the liver cells by toxic or infectious materials. This blocks the bile canals in the liver and can not be transported to the gall bladder. As a result, bile pigments are reabsorbed into the blood.
-Excessive destruction of red blood cells.
-Obstruction of bile flow between the liver and duodenum. This occurs when gall stones block the bile duct. Gall stones are formed as a result of accumulation of excess insoluble cholesterol in the gall bladder.
Symptoms
Patient may have itching caused by retention of bile salt in the blood.
The presence of bile pigment in the blood makes the eyes look yellow.
Activity; To investigate effect of catalase on Hydrogen peroxide
Requirements
Test tubes
Labels
Measuring cylinder
Hydrogen peroxide
Liver
Muscle tissue
Potato
Water bath
Source of heat
Procedure
- Label 4 test tubes A, B, C and D.
Measure 2cm³of Hydrogen peroxide and put in test tube A. Repeat the same procedure for test tube B and C.
Cut a small piece of liver and place in test tube A. Immediately introduce a glowing splint into the mouth of the test tube.
Repeat step III using muscle tissue (in test tube B) and a potato (in test tube C).
Repeat step III using boiled liver (in test tube D) and make sure that the liver is thoroughly boiled for about 5 mins. Tabulate your results e.g.

– Test tube	– Observation	– Conclusion
– A-Hydrogen peroxide+ raw liver	– -Relights glowing splint – -Vigorous production of bubbles	– A lot of catalase enzyme present
– B-Hydrogen peroxide+ muscle tissue	– -Relights glowing splint – -A lot of bubbles produced	– Medium amount of catalase enzyme present
– C-Hydrogen peroxide+ potato	– -Relights glowing splint – – Production of bubbles	– Little amount of catalase enzyme present
– D- Hydrogen peroxide+ boiled liver	– -No bubbles	– Enzymes denatured

Discussion
Living things contain an enzyme called catalase which breaks down hydrogen peroxide to water and oxygen. The oxygen produced relights a glowing splint i.e.
2H₂O₂→ 2H₂O + O₂
_{Hydrogen peroxide catalase water oxygen}

Homeostasis
It’s a process that adjusts changes in the body of an organism to optimum standards or levels and threfore brings about a steady state.
- External environment-It’s the immediate surrounding of the organism. It may be aquatic or terrestrial.
- Internal environment– It’s the immediate surrounding of the body cells.
Neuro-endocrine system and homeostasis
Neuro-endocrine system comprises of the nervous and endocrine system.
Nervous system comprises of the receptors and nerve fibres that make up the nervous tissue.
Receptors detect the changes in the internal or external environment. An impulse passes through fibres to the Central Nervous System (CNS). The CNS in turn initiates the correct response. The CNS sends an impulse to the organ which responds appropriately.
Receptors also send nerve impulses up the endocrine glands which comprises of the glands that secrete hormones. Endocrine system is also known as hormonal system. The hormones secreted are transported in the bloodstream to the target organs.
Principles of homeostasis
Inorder to maintain a state of balance in the internal environment, the various systems in the body work on a feedback mechanism eg
- Negative feedback
When a factor in the body such as temperature drops below or shoots above the normal, it is detected and corrective action is taken. Such an action is either;
-An increase in the level if it was dropping or
-A decrease in the level if it was increasing. This feedback restores the condition to normal.
- Positive feedback
In Positive feedback, a change below or above the normal is not corrected, instead, what is meant to be corrective action leads to further undesirable change from the normal e.g

Role of hypothalamus in thermoregulation

Hypothalamus is a small region between the cerebrum and cerebellum part of the brain. It acts as a thermoregulatory centre.
It has numerous temperature receptor cells which detect the slightest changes in the body temperature. The external temperature affecting the body is determined by the thermoreceptors in the skin.
Thermoreceptors relay the impulse to the hypothalamus through the sensory nerves.
The internal temperatures are detected by the hypothalamus as the blood flows in the brain.

Role of the liver in homeostasis

Regulation of blood glucose

The normal amount of glucose in blood is about 90-100mg /100cm³of
The liver carries out the control of the blood sugar level through two hormones produced by the pancreas i.e insulin and glucagon which are produced by the interstitial cells of the pancreas in the islets of langerhans and released into the bloodstream. The functions of insulin are antagonistic to those of glucagon eg
After a meal, carbohydrates are digested forming glucose, thereby increasing glucose level in the liver. The high glucose level in the liver is detected by the brain which sends impulses to the pancreas to secrete insulin, which carries out corrective measures as follows;
-Converts glucose into glycogen which is then stored in the liver and muscles.
-Changes glucose into fats which is then stored under the skin.
- -Breaks down glucose into CO₂and water in a process of tissue respiration.
When there is decreased glucose concentration in the blood eg during fasting, the pancreas is stimulated to release a hormone called glucagon which affects the liver ie
-Converts glycogen to glucose.
-Converts fats to glucose.
- -Reduces respiration i.e. reduces rate at which glucose is being broken down to form water and CO
Also another hormone called adrenaline produced by the adrenal gland causes increased hydrolysis of glycogen and this results in increase in blood sugar. This hormone is produced during emergencies to increase available glucose for respiration and release of energy for the emergencies.
Diabetes mellitus (sugar disease)
_{From Greek –meaning sweet urine.}
This is a condition in which the pancreas fails to produce insulin or produces inadequate amounts. This may be due to hereditary reasons or disease affecting the islets of langerhans.
A person with Diabetes mellitus has an abnormally high level of glucose in the blood (hyperglycaemia). The kidney eliminates some glucose in the urine, a condition called glycosuria (sweet urine).
Symptoms
Passing large amounts of urine.
Excessive excretion of glucose in the urine.
Loss of body weight due to the breakdown of proteins and fats.
Chronic starvation.
Feeling of thirst.
Treatment and Control
Eating foods with less carbohydrate.
Taking tablets that activate islets of langerhans in the pancreas to produce sufficient insulin.
Administering injections of insulin everyday.
NB insulin cannot be taken by mouth because it is a protein and hence will be digested in the alimentary canal before reaching the liver.
Avoid excessive intake of alcohol.
NB when a higher than normal amount of insulin is introduced in the blood, the patient;
-Feels hungry
-Sweats
-Becomes irritable
-Has double vision

Deamination;

The liver breaks down excess amino acids; The amino group is removed as ammonia; and the remaining carbon skeleton oxidized to carbon IV oxide and water; This process leads to release of energy. The carbon skeleton may be converted to glucose to be used during respiration;

Detoxification;

Ammonia from the process of deamination is converted in the liver into urea; which is less toxic. Bacterial toxins are converted to less toxic substances by liver cells;

Regulation of plasma proteins;

The liver produces most of the proteins found in blood; fibrinogen and prothrombin which play a role in blood clotting. Albumin and globulins are also produced by the liver. Globulins act as antibodies;. Albumin contributes to the maintenance of osmotic pressure in the body; Non essential amino acids are synthesized by the liver;

Heat production;

The various metabolic activities of the liver lead to release of heat energy; This energy is distributed by the blood to other parts of the body hence contributing to maintenance of constant body temperature;

Regulation of fat metabolism;

When carbohydrates are in short supply in the body, fats in different parts of the body are mobilized and taken to the liver; The fats are oxidized to carbon (IV) oxide and water with the production of energy or modified and sent to tissues for oxidation;

Role of kidney in homeostasis
- Osmoregulation
It’s the mechanism of regulating water in the body. It attempts to maintain an optimum osmotic pressure in the body tissues and fluids that is favourable to normal functioning of cells.
When the osmotic pressure of the body rises as a result of dehydration, the hypothalamus is stimulated and sends impulses to the pituitary gland which releases a hormone called Antidiuretic hormone (ADH)/vasopressin into the blood.on reaching the kidney, the diastal convoluted tubule and the collecting tubules become more permeable to water which is then reabsorbed into the bloodstream thus lowering the osmotic pressure of the blood. This leads to the production of concentrated urine.
When the osmotic pressure of the blood falls due to large intake of water, pituitary gland is less stimulated. This leads to reduced release of ADH into the bloodstream. The kidney tubules become less permeable to water and less reabsorption of water into the bloodstream takes place. The osmotic pressure of the blood rises and dilute urine is produced.
Diabetes Insipidus
When pituitary glandreleases very little ADH or fails to release it completely, the kidney nephrons are unable to reabsorb the required amounts of water. This leads to the production of excessively large volumes of dilute urine. This is known as diuresis. Patients may excrete upto 20 litres of urine per day.
The urine can also be described as ‘tasteless’ or insipid thus the name Diabetes Insipidus.
Symptoms
Frequent urination .
Secretion of a lot of urine.
Production of dilute urine.
Frequent thirst sensation.
Treatment
Administration of synthetic or natural ADH.
Regulation of ionic content
A hormone called aldosterone which is produced by the adrenal glands regulates the level of sodium ions.
When the level of the sodium ions is low in the blood, adrenal glands are stimulated to release aldosterone into the blood which then stimulates loop of henle of the kidney and the gut to reabsorb Na+ into the blood.
If the sodium concentration in the blood rises above the optimum level, adrenal glands produce less aldosterone into the blood and less amount of Na+ are reabsorbed.
Role of the skin in homeostasis
- Salt and water balance
Skin has sweat glands which secrete waste products of metabolism such as water, mineral salts especially sodium chloride. These waste products are lost in the form of sweat through the pores in the skin.
About 99% of the sweat is water while the remaining 1% is mainly mineral salts. The water and mineral salts lost in the sweat contribute to osmotic changes of the body cells and fluids.
On a hot day, the body loses a lot of water and mineral salts resulting in a sensation of thirst being felt due to tissue dehydration. The osmotic balance is however restored by drinking large volumes of water and intake of mineral salts in the diet.
- Temperature regulation
- Homeotherms/Endotherms– They are organisms whose body temperature is maintained at a constant despite the wide fluctuations in the temperature of the external environment.
Poikilotherms/Ectotherms- Their body temperatures fluctuates with that of the external environment.
Thermoregulation in humans
Heat loss
The body loses heat to the environment when it’s in a cold environment. The heat is lost by;
-Radiation
-Conduction
-Convection
-Evaporation
Radiation– It’s the transfer of heat by diffusion through the air between a warmer body and a colder one.
Conduction– It’s the transfer of heat from a hot body to a colder one when the two are in contact.
Evaporation– It’s the change of liquid to vapour.
Convection– It’s the movement of air in which warm air in one place rises and cooler air replaces it.
Heat loss occurs through;
-Sweating and breathing
-Passing out of urine and faeces.
- -Mammals such as cats lose heat by licking fur on their limbs and bellies.
Heat gain
The body gains heat from metabolic activities such as respiration and by muscle contraction.
The body uses physiological and behavioural means to regulate the temperature.
When cold
- Physiological mechanisms
Decrease in sweat production-This leads to less heat lost through the latent heat of vapourisation.
Shivering- It involves the rapid contraction of skeletal muscles to generate heat.
Increased metabolism yields heat to raise the body temperature. Increase in secretion of the hormone Thyroxine raises metabolism and heat production.
Arterioles beneath the skin constricts which decreases the blood flow to the skin hence less heat is brought close to the skin surface and this reduces heat loss. This is called vasoconstriction. White people appear pale/white
The liver and spleen store some of the blood which should be in the general body circulation. Thus heat is retained in the body.
Erector pili muscle contract and pull the hair follicles. This way, the hair is raised to trap a layer of air which is a good insulator against heat loss.
- Behavioural mechanisms
Dressing in warm heavy clothing enables the body to conserve heat.
Basking in the sun or warming of the body using a source of heat.
Increased muscular activity such as rubbing hands and stamping feet
- NB Some animals hibernate i.e. go into deep sleep due to cold conditions.
- When hot
- Physiological mechanisms
Increase in sweat production– It leads to heat loss through latent heat of vapourisation.
Arterioles beneath the skin dilate and this increases the blood flow to the skin hence more heat is brought close to the skin surface. This increases heat loss to the atmosphere. This is called White people appear pink.
Erector pili muscles relax and this makes the hair to lie flat on the skin. This way, air is not trapped beneath the hair and a lot of heat is lost to the environment
- Behavioural mechanisms
Dressing in light clothes which do not retain much heat.
Moving to a shade to avoid exposure to direct sunshine.
Some homeotherms such as elephants have large ears which are flapped vigorously to create air currents which take heat away from the body of the animal.
Some animals aestivate i.e. a state of inactivity by some animals that occur during prolonged period of heat e.g. Bats and lungfish. Some animals are only active around sunrise, sunset and at night.
Decreased muscular activity.
Parts of the skin concerned with thermoregulation
Sweat glands
They are coiled tubular glands in the dermis. When the body temperature increases, the sweat glands increase the rate of sweat production. Water in the sweat evaporates by absorbing heat (latent heat of vapourisation) from the body and a cooling effect results.
- NB (i) Birds do not have sweat glands.
Dogs only have them on the pads of the feet.
Hair and Erector pili muscles
When the body temperature lowers, Erector pili muscle contract and pull the hair follicles. This way, the hair is raised to trap a layer of air which is a good insulator against heat loss.
When its hot, the Erector pili muscles relax thus trapping little air hence heat can be lost from the body surface.
Blood vessels
When the body temperature lowers, the blood vessels in the skin constrict (vasoconstriction) and blood is diverted to a shunt system. This reduces the blood flow to the skin and more blood is stored in the spleen as an adaptation to lose less heat.
Dilation of blood vessels (vasodilation) increases blood flow to the skin encouraging heat loss when the body temperature is too high.
Subcutaneous fat
It’s a good insulator against heat loss. Animals in cold areas have thick cutaneous fatty layer for this purpose.
Organisms in warm areas have thin fatty layer to encourage more heat loss to the environment.
Once the temperature changes have been detected by the hypothalamus, the hypothalamus sends impulses to the appropriate responding tissues of the skin.
When the hypothalamus fails to register an increase in the body temperature above normal level, a further rise in body temperature occurs. This causes fever in humans.
If this condition is not corrected, abnormally high body temperature occurs (Hyperthermia). This leads to death if body temperature goes above 43ºC.
If a decrease in body temperature below normal continues, without correction due to the failure of homeostatic mechanisms, abnormally low body temperature occurs (Hypothermia). Death occurs if body temperature falls below 26°C.
Temperature regulation in other animals
- Camels
The camel is able to withstand high environmental temperatures without sweating and will only start to sweat when its body temperature goes beyond 40ºC.
Its hump stores fat which can be metabolized to provide water in times of shortage.
The camel goes for a long time without drinking water and survives as much as 30% reduction in body weight due to dehydration. Under such conditions, a man would die in 2 days.
When a dehydrated camel finds water, it drinks very fast and can drink water equivalent of 30% of its body weight in about 10 minutes.
A camel has a long loop of henle and collecting ducts. These enable it to secrete scanty but highly concentrated urine.
- Kangaroo rat
It has fewer and smaller glomeruli and Long loops of henle. This reduces ultra filtration while increasing the reabsorption of water
It releases insoluble uric acid thus conserving water in the body.
It metabolizes fats and retains the water resulting from the oxidation of fats.
- Birds
They are homeotherms and use physiological and behavioural mechanisms to regulate body temperature
- Reptiles
They are ectotherms and its body is cooled when water evaporates from its skin surface.
.when the temperature is high; the reptiles open their mouths and pant. Panting leads to heat loss through evaporation of water from its mouth.
- Amphibians
They have moist skin and lose heat through evaporation of water. They lose heat rapidly to the dry atmosphere.
- Fish
They are aquatic ectotherms. The body temperature is in equilibrium with the temperature of the water.
Size of animal and body size
Small animals such as rats have a large surface area to volume ratio hence they tend to lose heat at faster rate than the large animals.
Large animals e.g. elephants have a small surface area to volume ratio hence they tend to retain most of their body heat. Hence small animals eat a lot of food to increase their metabolism. This produces heat which replaces the lost heat.