By the end of the topic, the learner should be able to:

1. distinguish between excretion and egestion
2. explain the necessity for excretion in plants and animals
3. state the uses of excretory products of plants
4. describe the methods of excretion in a named unicellular organism
5. relate the structures of the human skin, lungs, liver and kidney to their functions name common kidney diseases
6. explain the concept of internal environment and homeostasis
7. compare responses to changes in temperature by behavioural and physiological methods in animals
8. relate heat loss to body size in
9. describe methods by which mammals gain and lose heat
10. explain how the functions of the following relate to homeostasis - skin, hypothalamus, liver and kidney
11. discuss the role of antidiuretic hormone, insulin and glucagons
12. describe simple symptoms of Diabetes mellitus and Diabetes insipidus.

Excretion in Plants
Methods of excretion in plants

• Useful and harmful excretory products of plants and their economic importance e.g. caffeine in tea and coffee, quinine, tannins, colchicines, cocaine, rubber, gum, papain (from pawpaw) and products of cannabis sativa (bhang) and khat (miraa)Excretion and homeostasis in Animals

Distinction between excretion, homeostasis and egestion
Excretion in a named uni-cellular organism (protozoa)
Structure and functions of skin and kidney
Neuro-endocrine system and homeostasis

• Water balance (blood osmotic pressure)
• Blood sugar level (control)
• Temperature regulation (mention the role of hypothalamus)

Common kidney diseases, their symptoms and possible methods of prevention and control
The role of the skin in thermoregulation, salt and water balance.
Major functions of the liver and their contributions to homeostasis.
Common diseases of the liver, their symptoms and possible methods of prevention and control
Practical Activities
Examine and draw the mammalian kidney
Make vertical sections of the kidney to identify cortex and medulla
Observe permanent slides of mammalian skin
Investigate effect of catalase enzyme on hydrogen peroxide

• Excretion is the process by which living organisms separate and eliminate waste products of metabolism from body cells.
• If these substances were left to accumulate, they would be toxic to the cells.
• Egestion is the removal of undigested materials from the alimentary canals of animals.
• Secretion is the production and release of certain useful substances such as hormones, sebum and mucus produced by glandular cells.
• Homeostasis is a self-adjusting  mechanism to maintain a steady state in the internal environment

• Plants have little accumulation of toxic waste especially nitrogenous wastes.
• This is because they synthesise proteins according to their requirements.
• In carbohydrate metabolism plants use carbon (IV) oxide released from respiration in photosynthesis while oxygen released from photosynthesis is used in respiration.
• Gases are removed from the plant by diffusion through stomata and lenticels.
• Certain organic products are stored in plant organs such as leaves, flowers, fruits and bark and are removed when these organs are shed.
• The products include tannins, resins, latex and oxalic acid crystals.
• Some of these substances are used illegally.
• Khat, cocaine and cannabis are used without a doctor's prescription and can be addictive.
• Use of these substances should be avoided.

1. Define the following terms
   1. Excretion
   2. Secretion
   3. Egestion
   4. Homeostasis
2. Explain why excretion is necessary in plants and animals
3. Describe how excretion takes place in green plants
4. Why do plants lack complex excretory structures like those of animals?
5. State the excretory products of plants and some of their uses to humans
6. Describe excretion in unicellular organisms
7. Draw and label a mammalian skin
8. Explain how the mammalian skin is adapted to its functions
9. What is the role of lungs in excretion?
10. State the functions of the liver
11. Draw a labeled diagram of mammalian nephrone
12. Describe how the human kidney functions
13. State the adaptations of proximal convoluted tubule to its function
14. Name the common kidney diseases
15. Why is homeostatic control necessary?
16. What is internal environment?
17. Why is constant body temperature maintained by mammals?
18. Explain the advantage gained by possessing a constant body temperature
19. How do mammals regulate body temperature?
20. Why does body temperature of a healthy person rise up to 37oC on a hot humid day?
21. Name the structures in the human body that detect external temperature changes 
22. State the advantages that organisms with small surface area to volume ratio experience over those with larger
23. Explain why individuals with smaller sizes require more energy per unit body weight than those with larger sizes.
24. What is the meaning of osmoregulation?
25. State the importance of osmoregulation
26. State the ways by which desert mammals conserve water
27. Explain why some desert animals excrete uric acid rather than water
28. Explain why eating a meal with too much salt leads to production of a small volume of concentrated urine
29. Explain how marine fish regulate their osmotic pressure
30. What is the biological significance of maintaining a relatively constant sugar level in a human body?
31. Discuss the role of the following hormones in blood sugar control Insulin
32. Explain the part played by antidiuretic hormone in homeostasis
33. What is the role of blood clotting in homeostasis?
34. Describe the role of the following hormones in homeostasis
35. Distinguish between diabetes mellitus and diabetes insipidus
36. How can high blood sugar level in a person be controlled?
37. Why does glucose not normally appear in urine even though it is filtered in the mammalian Bowman’s capsule?
38. When is glycogen which is stored in the liver converted into glucose and released into the blood?
39. How would one find out from a sample of urine whether a person is suffering from diabetes mellitus?

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TOPIC 9 - EXCRETION AND HOMEOSTASIS (42 LESSONS) [KCSE NOTES].pdf
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​All animals take in oxygen for oxidation of organic compounds to provide energy for cellular activities.
The carbon (IV) oxide produced as a by-product is harmful to cells and has to be constantly removed from the body.
Most animals have structures that are adapted for taking in oxygen and for removal of carbon (IV) oxide from the body.
These are called "respiratory organs".
The process of taking in oxygen into the body and carbon (IV) oxide out of the body is called breathing or ventilation.
Gaseous exchange involves passage of oxygen and carbon (IV) oxide through a respiratory surface by diffusion. 

Different animals have different respiratory surfaces.
The type depends mainly on the habitat of the animal, size, shape and whether body form is complex or simple.

• Cell Membrane: In unicellular organisms the cell membrane serves as a respiratory surface.
• Gills: Some aquatic animals have gills which may be external as in the tadpole or internal as in bony fish e.g. tilapia. They are adapted for gaseous exchange in water.
• Skin: Animals such as earthworm and tapeworm use the skin or body surface for gaseous exchange. The skin of the frog is adapted for gaseous exchange both in water and on land. The frog also uses epithelium lining of the mouth or buccal cavity for gaseous exchange.
• Lungs: Mammals, birds and reptiles have lungs which are adapted for gaseous exchange. 

• Gaseous exchange occurs across the cell membrane by diffusion.
• Oxygen diffuses in and carbon (IV) oxide diffuses out.
• Oxygen is used in the cell for respiration making its concentration lower than that in the surrounding water.
• Hence oxygen continually enters the cell along a concentration gradient.
• Carbon (IV) oxide concentration inside the cell is higher than that in the surrounding water thus it continually diffuses out of the cell along a concentration gradient. 

​Gaseous exchange in insects e.g., grasshopper takes place across a system of tubes penetrating into the body known as the tracheal system.
The main trachea communicate with atmosphere through tiny pores called spiracles.
Spiracles are located at the sides of body segments;
Two pairs on the thoracic segments and eight pairs on the sides of abdominal segments.
Each spiracle lies in a cavity from which the trachea arises.
Spiracles are guarded with valves that close and thus prevent excessive loss of water vapour.
A filtering apparatus i.e. hairs also traps dust and parasites which would clog the trachea if they gained entry.
The valves are operated by action of paired muscles.
Mechanism of Gaseous Exchange in Insects

• The main tracheae in the locust are located laterally along the length of the body on each side and they are interconnected across.
• Each main trachea divides to form smaller tracheae, each of which branches into tiny tubes called tracheoles.
• Each tracheole branches further to form a network that penetrates the tissues. Some tracheoles penetrate into cells in active tissue such as flight muscles.
• These are referred to as intracellular tracheoles.
• Tracheoles in between the cells are known as intercellular tracheoles.
• The main tracheae are strengthened with rings of cuticle.
• This helps them to remain open during expiration when air pressure is low.

Adaptation of Insect Tracheoles for Gaseous Exchange
The fine tracheoles are very thin about one micron in diameter in order to permeate tissue.
They are made up of a single epithelial layer and have no spiral thickening to allow diffusion of gases.
Terminal ends of the fine tracheoles are filled with a fluid in which gases dissolve to allow diffusion of oxygen into the cells.
Amount of fluid at the ends of fine tracheoles varies according to activity i.e. oxygen demand of the insect.
During flight, some of the fluid is withdrawn from the tracheoles such that oxygen reaches muscle cells faster and the rate of respiration is increased.
In some insects, tracheoles widen at certain places to form air sacs.
These are inflated or deflated to facilitate gaseous exchange as need arises.
Atmospheric air that dissolves in the fluid at the end of tracheoles has more oxygen than the surrounding cells of tracheole epithelium'.
Oxygen diffuses into these cells along a concentration gradient. '
Carbon (IV) oxide concentration inside the cells is higher than in the atmospheric.
Air and diffuses out of the cells along a concentration gradient.
It is then removed with expired air.
Ventilation in Insects
Ventilation in insects is brought about by the contraction and relaxation of the abdominal muscles.
In locusts, air is drawn into the body through the thoracic spiracles and expelled through the abdominal spiracles.
Air enters and leaves the tracheae as abdominal muscles contract and relax.
The muscles contract laterally so the abdomen becomes wider and when they relax it becomes narrow.
Relaxation of muscles results in low pressure hence inspiration occurs while contraction of muscles results in higher air pressure and expiration occurs.
In locusts, air enters through spiracles in the thorax during inspiration and leaves through the abdominal spiracles during expiration.
This results in efficient ventilation.
Maximum extraction of oxygen from the air occurs sometimes when all spiracles close and hence contraction of abdominal muscles results in air circulating within the tracheoles.
The valves in the spiracles regulate the opening and closing of spiracles.
Observation of Spiracle in Locust
Some fresh grass is placed in a gas jar.
A locust is introduced into the jar.
A wire mesh is placed on top or muslin cloth tied around the mouth of the beaker with rubber band.
The insect is left to settle.
Students can approach and observe in silence the spiracles and the abdominal movements during breathing.
Alternatively the locust is held by the legs and observation of spiracles is made by the aid of hand lens. 

​Gaseous exchange in fish takes place between the gills and the surrounding water.
The gills are located in an opercular cavity covered by a flap of skin called the operculum.
Each _gill consists of a number of thin leaf-like lamellae projecting from a skeletal base bronchial arch (gill bar) situated in the wall of the pharynx.
There are four gills within the opercular cavity on each side of the head.
Each gill is made up of a bony gill arch which has a concave surface facing the mouth cavity (anterior) and a convex posterior surface.
Gill rakers are bony projections on the concave side that trap food and other solid particles which are swallowed instead of going over and damaging the gill filaments.
Two rows of gill filaments subtend from the convex surface.
Adaptation of Gills for Gaseous Exchange
Gill filaments are thin walled.
Gill filaments are very many (about seventy pairs on each gill), to increase surface area.
Each gill filament has very many gill lamellae that further increase surface area.
The gill filaments are served by a dense network of blood vessels that ensure efficient transport of gases.
It also ensures that a favourable diffusion gradient is maintained.
The direction of flow of blood in the gill lamellae is in the opposite direction to that of the water (counter current flow) to ensure maximum diffusion of gases.
Ventilation
As the fish opens the mouth, the floor of the mouth is lowered.
This increases the volume of the buccal cavity.
Pressure inside the mouth is lowered causing water to be drawn into the buccal cavity.
Meanwhile, the operculum is closed, preventing water from entering or leaving through the opening.
As the mouth closes and the floor of the mouth is raised, the volume of buccal cavity decreases while pressure in the opercular cavity increases due to contraction of opercular muscles.
The operculum is forced to open and water escapes.
As water passes over the gills, oxygen is absorbed and carbon dioxide from the gills dissolves in the water.
As the water flows over the gill filaments oxygen in the water is at a higher concentration than that in the blood flowing, in the gill.
Oxygen diffuses through the thin walls of gill filaments/lamellae into the blood.
Carbon (IV) oxide is at a higher concentration in the blood than in the water.
It diffuses out of blood through walls of gill filaments into the water.
Counter Current Flow
In the bony fish direction of flow of water over the gills is opposite that of blood flow through the gill filaments.
This adaptation ensures that maximum amount of oxygen diffuses from the water into the blood in the gill filament.
This ensures efficient uptake of oxygen from the water.
Where the flow is along the same direction (parallel flow) less oxygen is extracted from the water.
Observation of Gills of a Bony Fish (Tilapia)
Gills of a fresh fish are removed and placed in a petri-dish with enough water to cover them.
A hand lens is used to view the gills.
Gill bar, gill rakers and two rows of gill filaments are observed. 

​An adult frog lives on land but goes back into the water during the breeding season.
A frog uses three different respiratory surfaces.
These are the skin, buccal cavity and lungs.
Skin
The skin is used both in water and on land.
It is quite efficient and accounts for 60% of the oxygen taken in while on land.
Adaptations of a Frog's Skin for Gaseous Exchange
The skin is a thin epithelium to allow fast diffusion.
The skin between the digits in the limbs (i.e. webbed feet) increase the surface area for gaseous exchange.
It is richly supplied with blood vessels for transport of respiratory gases.
The skin is kept moist by secretions from mucus glands.
This allows for respiratory gases to dissolve.
Oxygen dissolved in the film of moisture diffuses across the thin epithelium and into the blood which has a lower concentration of oxygen.
Carbon (IV) oxide diffuses from the blood across the skin to the atmosphere along the concentration gradient.
Buccal (Mouth) Cavity
Gaseous exchange takes place all the time across thin epithelium lining the mouth cavity.
Adaptations of Buccal Cavity for Gaseous Exchange
It has a thin epithelium lining the walls of the mouth cavity allowing fast diffusion of gases.
It is kept moist by secretions from the epithelium for dissolving respiratory gases.
It has a rich supply of blood vessels for efficient transport of respiratory gases.
The concentration of oxygen in the air within the mouth cavity is higher than that of the blood inside the blood vessels.
Oxygen, therefore dissolves in the moisture lining the mouth cavity and then diffuses into the blood through the thin epithelium.
On the other hand, carbon (IV) oxide diffuses in the opposite direction along a concentration gradient.
Lungs
There is a pair of small lungs used for gaseous exchange.
Adaptation of Lungs
The lungs are thin walled for fast diffusion of gases.
Have internal folding to increase surface area for gaseous exchange.
A rich supply of blood capillaries for efficient transport of gases.      
Moisture lining for gases to dissolve.
Ventilation
Inspiration
During inspiration, the floor of the mouth is lowered and air is drawn in through the nostrils.
When the nostrils are closed and the floor of the mouth is raised, air is forced into the lungs.
Gaseous exchange occurs in the lungs, oxygen dissolves in the moisture lining of the lung and diffuses into the blood through the thin walls.
Carbon (IV) oxide diffuses from blood into the lung lumen.
Expiration
When the nostrils are closed and the floor of mouth is lowered by contraction of its muscles, volume of mouth cavity increases.
Abdominal organs press against the lungs and force air out of the lungs into buccal cavity.
Nostrils open and floor of the mouth is raised as its muscles relax.
Air is forced out through the nostrils.              

​The breathing system of a mammal consists of a pair of lungs which are thin-walled elastic sacs lying in the thoracic cavity.
The thoracic cavity consists of vertebrae, sternum, ribs and intercostal muscles.
The thoracic cavity is separated from the abdominal cavity by the diaphragm.
The lungs lie within the thoracic cavity.
They are enclosed and protected by the ribs which are attached to the sternum and the thoracic vertebrae.
There are twelve pairs of ribs, the last two pairs are called 'floating ribs' because they are only attached to the vertebral column.
The ribs are attached to and covered by internal and external intercostal muscles.
The diaphragm at the floor of thoracic cavity consists of a muscle sheet at the periphery and a central circular fibrous tissue.
The muscles of the diaphragm are attached to the thorax wall.
The lungs communicate with the outside atmosphere through the bronchi, trachea, mouth and nasal cavities.
The trachea opens into the mouth cavity through the larynx.
A flap of muscles, the epiglottis, covers the opening into the trachea during swallowing.
This prevents entry of food into the trachea.
Nasal cavities are connected to the atmosphere through the external nares(or nostrils)which are lined with hairs and mucus that trap dust particles and bacteria, preventing them from entering into the lungs.
Nasal cavities are lined with cilia.
The mucus traps dust particles,
The cilia move the mucus up and out of the nasal cavities.
The mucus moistens air as it enters the nostrils.
Nasal cavities are winding and have many blood capillaries to increase surface area to ensure that the air is warmed as it passes along.
Each lung is surrounded by a space called the pleural cavity.
It allows for the changes in lung volume during breathing.
An internal pleural membrane covers the outside of each lung while an external pleural membrane lines the thoracic wall.
The pleural membranes secrete pleural fluid into the pleural cavity.
This fluid prevents friction between the lungs and the thoracic wall during breathing.
The trachea divides into two bronchi, each of which enters into each lung.
Trachea and bronchi are lined with rings of cartilage that prevent them from collapsing when air pressure is low.
Each bronchus divides into smaller tubes, the bronchioles.
Each bronchiole subdivides repeatedly into smaller tubes ending with fine bronchioles.
The fine bronchioles end in alveolar sacs, each of which gives rise to many alveoli.
Epithelium lining the inside of the trachea, bronchi and bronchioles has cilia and secretes mucus.
Adaptations of Alveolus to Gaseous Exchange
Each alveolus is surrounded by very many blood capillaries for efficient transport of respiratory gases.
There are very many alveoli that greatly increases the surface area for gaseous exchange.
The alveolus is thin walled for faster diffusion of respiratory gases.
The epithelium is moist for gases to dissolve.
Gaseous Exchange between the Alveoli and the Capillaries
The walls of the alveoli and the capillaries are very thin and very close to each other.
Blood from the tissues has a high concentration of carbon (IV) oxide and very  little oxygen compared to alveolar air.
The concentration gradient favours diffusion of carbon (IV) oxide into the alveolus and oxygen into the capillaries.
No gaseous exchange takes place in the trachea and bronchi.
These are referred to as dead space.
Ventilation
Exchange of air between the lungs and the outside is made possible by changes in the volumes of the thoracic cavity.
This volume is altered by the movement of the intercostal muscles and the diaphragm.
Inspiration
The ribs are raised upwards and outwards by the contraction of the external intercostal muscles, accompanied by the relaxation of internal intercostal muscles.
The diaphragm muscles contract and diaphragm moves downwards.
The volume of thoracic cavity increases, thus reducing the pressure.
Air rushes into the lungs from outside through the nostrils.
Expiration
The internal intercostal muscles contract while external ones relax and the ribs move downwards and inwards.
The diaphragm muscles relaxes and it is pushed upwards by the abdominal organs. It thus assumes a dome shape.
The volume of the thoracic cavity decreases, thus increasing the pressure.
Air is forced out of the lungs.
As a result of gaseous exchange in the alveolus, expired air has different volumes of atmospheric gases as compared to inspired air.

​Lung Capacity
The amount of air that human lungs can hold is known as lung capacity.
The lungs of an adult human are capable of holding 5,000 cm3 of air when fully inflated.
However, during normal breathing only about 500 cm3 of air is exchanged.
This is known as the tidal volume.
A small amount of air always remains in the lungs even after a forced expiration.
This is known as the residual volume.
The volume of air inspired or expired during forced breathing is called vital capacity.
Control of Rate of Breathing
The rate of breathing is controlled by the respiratory centre in the medulla of the brain.
This centre sends impulses to the diaphragm through the phrenic nerve.
Impulses are also sent to the intercostal muscles.
The respiratory centre responds to the amount of carbon (IV) oxide in the blood.
If the amount of carbon (IV) oxide rises, the respiratory centre sends impulses to the diaphragm and the intercostal muscles which respond by contracting in order to increase the ventilation rate.
Carbon (IV) oxide is therefore removed at a faster rate.
Factors Affecting Rate of Breathing in Humans

• Factors that cause a decrease or increase in energy demand directly affect rate of breathing.
• Exercise, any muscular activity like digging.
• Sickness
• Emotions like anger, flight
• Sleep.

Effects of Exercise on Rate of Breathing

• Students to work in pairs.
• One student stands still while the other counts (his/her) the number of breaths per minute.
• The student whose breath has been taken runs on the sport vigorously for 10 minutes.
• At the end of 10 minutes the number of breaths per minute is immediately counted and recorded.
• It is noticed that the rate of breathing is much higher after exercise than at rest.

Dissection of a Small Mammal (Rabbit) to Show Respiratory Organs
The rabbit is placed in a bucket containing cotton wool which has been  soaked in chloroform.
The bucket is covered tightly with a lid.
The dead rabbit is placed on the dissecting board ventral side upwards.
Pin the rabbit to the dissecting board by the legs.
Dissect the rabbit to expose the respiratory organs.
Ensure that you note the following features.
Ribs, intercostal muscles, diaphragm, lungs, bronchi, trachea, pleural   membranes, thoracic cavity.

Asthma is a chronic disease characterised by narrowing of air passages.
Causes:
1)Allergy
Due to pollen, dust, fur, animal hair, spores among others.
If these substances are inhaled, they trigger release of chemical substances and they may cause swelling of the bronchioles and bring about an asthma attack.
2)Heredity
Asthma is usually associated with certain disorders which tend to occur in more than one member of a given family, thus suggesting' a hereditary tendency.
3)Emotional or mental stress
Strains the body immune system hence predisposes to asthma attack.
Symptoms
Asthma is characterized by wheezing and difficulty in breathing accompanied by feeling of tightness in the chest as a result of contraction of the smooth muscles lining the air passages.
Treatment and Control

• There is no definite cure for asthma.
• The best way where applicable is to avoid whatever triggers an attack (allergen).
• Treatment is usually by administering drugs called bronchodilators.
• The drugs are inhaled, taken orally or injected intravenously depending on severity of attack to relief bronchial spasms. 

This is an inflammation of bronchial tubes.
Causes
This is due to an infection of bronchi and bronchioles by bacteria and viruses.
Symptoms

• Difficulty in breathing.
• Cough that produces mucus.

Treatment

• Antibiotics are administered. 

​Tuberculosis is a contagious disease that results in destruction of the lung tissue.
Causes

• Tuberculosis is caused by the bacterium Mycobacterium tuberculosis.
• Human tuberculosis is spread through droplet infection i.e., in saliva and sputum.
• Tuberculosis can also spread from cattle to man through contaminated milk.
• From a mother suffering from the disease to a baby through breast feeding.
• The disease is currently on the rise due to the lowered immunity in persons with HIV and AIDS (Human Immuno Deficiency Syndrome).
• Tuberculosis is common in areas where there is dirt, overcrowding and malnourishment.

Symptoms
It is characterised by a dry cough, lack of breath and body wasting.
Prevention

• Proper nutrition with a diet rich in proteins and vitamins to boost immunity.
• Isolation of sick persons reduces its spread.
• Utensils used by the sick should be sterilised by boiling.
• Avoidance of crowded places and living in well ventilated houses.
• Immunisation with B.C.G. vaccine gives protection against tuberculosis.
• This is done a few days after birth with subsequent boosters.

Treatment
Treatment is by use of antibiotics.

Pneumonia is infection resulting in inflammation of lungs.
The alveoli get filled with fluid and bacterial cells decreasing surface are for gaseous exchange.
Pneumonia is caused by bacteria and virus.
More infections occur during cold weather.
The old and the weak in health are most vulnerable.
Symptoms
Pain in the chest accompanied by a fever, high body temperatures (39-40°C) and general body weakness.  
Prevention

• Maintain good health through proper feeding.
• Avoid extreme cold.

Treatment

• If the condition is caused by pneumococcus bacteria, antibiotics are administered.
• If breathing is difficult, oxygen may be given using an oxygen mask. 

• Whooping cough is an acute infection of respiratory tract.
• The disease is more common in children under the age of five but adults may also be affected.

Causes
It is caused by Bordetella pertusis bacteria and is usually spread by droplets produced when a sick person coughs.
Symptoms:

• Severe coughing and frequent vomiting.
• Thick sticky mucus is produced.
• Severe broncho-pneumonia.
• Convulsions in some cases.

Prevention

• Children may be immunised against whooping cough by means of a vaccine which is usually combined with those against diphtheria and tetanus.
• It is called "Triple Vaccine" or Diphtheria, Pertusis and Tetanus (DPT).

Treatment

• Antibiotics are administered.
• To reduce the coughing, the patient should be given drugs.

Observation of permanent slides of terrestrial and aquatic leaves and stems
Leaves

• Observation of T.S. of bean and water lily are made under low and 'medium power objectives. Stomata and air space are seen.
• Labelled drawings of each are made.
• The number and distribution of stomata on the lower and upper leaf surface is noted.
• Also the size of air spaces and their distribution.

Stem

• Prepared slides (TS) of stems of terrestrial and aquatic plants such as croton and reeds are obtained.
• Observations under low power and medium power of a microscope are made.
• Labelled drawings are made and the following are noted:

1. Lenticels on terrestrial stems.
2. Large air spaces (aerenchyma) in aquatic stems.

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TOPIC 7 - GASEOUS EXCHANGE (36 LESSONS) [KCSE NOTES].pdf
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By the end of the topic, the learner should be able to:

1. Explain the need for gaseous exchange in living organisms
2. Explain the mechanism of gaseous exchange in plants
3. Compare the internal structures of aquatic and terrestrial roots, stems and leaves
4. Examine various types of respiratory structures in animals and relate them to their functions
5. State the characteristics of respiratory surfaces
6. Describe the mechanisms of gaseous exchange in protozoa, insects, fish, frog and mammal
7. Describe the factors which control the rate of breathing in humans
8. State the causes, symptoms and prevention of respiratory diseases.

​GASEOUS EXCHANGE (36 LESSONS)
Gaseous exchange in living organisms (necessity)
Gaseous Exchange in Plants

• Mechanisms of opening and closing of stomata
• The process of gaseous exchange in root, stem and leaves of both aquatic (floating) and terrestrial plants

Gaseous Exchange in Animals

• Types and Characteristics of Respiratory Surfaces - cell membrane, gills, buccal cavity, skin and lungs
• Mechanism of gaseous exchange in
  •    Protozoa - amoeba
  •    Insect – grasshopper
  •    Fish – bonyfish
  •    Amphibia – frog
  •    Mammal - human

Factors affecting rate of breathing in humans
Respiratory diseases: Asthma, Bronchitis, Pulmonary tuberculosis, Pneumonia and whooping cough
Practical Activities
Observe permanent slides of cross- sections of aerial and aquatic leaves and stems
Examine the distribution of spiracles on grasshopper or locust
Examine the gills of a bony fish
Dissect a small mammal and identify the structures of the respiratory system (demonstration) Construct and use models to demonstrate breathing mechanisms in a mammal (human) Demonstrate the effect of exercise on the rate of breathing

• Living organisms require energy to perform cellular activities.
• The energy comes from breakdown of food in respiration.
• Carbon (IV) oxide is a byproduct of respiration and its accumulation in cells is harmful which has to be removed.
• Most organisms use oxygen for respiration which is obtained from the environment.
• Photosynthetic cells of green plants use carbon (IV) oxide as a raw material for photosynthesis and produce oxygen as a byproduct.
• The movement of these gases between the cells of organisms and the environment comprises gaseous exchange.
• The process of moving oxygen into the body and carbon (Iv) oxide out of the body is called breathing or ventilation.
• Gaseous exchange involves the passage of oxygen and carbon (IV) oxide through a respiratory surface.
• Diffusion is the main process involved in gaseous exchange.

• Oxygen is required by plants for the production of energy for cellular activities.
• Carbon (IV) oxide is required as a raw material for the synthesis of complex organic substances.
• Oxygen and carbon (IV) oxide are obtained from the atmosphere in the case of terrestrial plants and from the surrounding water in the case of aquatic plants.
• Gaseous exchange takes place mainly through the stomata. 

• The stoma (stomata - plural) is surrounded by a pair of guard cells.
• The structure of the guard cells is such that changes in turgor inside the cell cause changes in their shape.
• They are joined at the ends and the cell walls facing the pore (inner walls) are thicker and less elastic than the cell walls farther from the pore (outer wall).
• Guard cells control the opening and closing of stomata.

• In general stomata open during daytime (in light) and close during the night (darkness).
• Stomata open when osmotic pressure in guard cells becomes higher than that in surrounding cells due to increase in solute concentration inside guard cells. Water is then drawn into guard cells by osmosis.
• Guard cells become turgid and extend.
• The thinner outer walls extend more than the thicker walls.
• This causes a bulge and stoma opens.
• Stomata close when the solute concentration inside guard cells become lower than that of surrounding epidermal cells.
• The water moves out by osmosis, and the guard cells shrink i.e. lose their turgidity and stoma closes.

Accumulation of sugar.

• Guard cells have chloroplasts while other epidermal cells do not.
• Photosynthesis takes place during daytime and sugar produced raises the solute concentration of guard cells.
• Water is drawn into guard cells by osmosis from surrounding cells.
• Guard cells become turgid and stoma opens.
• At night no photosynthesis occurs hence no sugar is produced.
• The solute concentration of guard cells falls and water moves out of the guard cells by osmosis.
• Guard cells lose turgidity and the stoma closes.

pH changes in guard cells occur due to photosynthesis.

• In day time carbon (IV) oxide is used for photosynthesis. This reduces acidity while the oxygen produced increases alkalinity.
• Alkaline pH favours conversion of starch to sugar.
• Solute concentration increases inside guard cells, water is drawn into the cells by osmosis. Guard cells become turgid and the stoma opens.
• At night when no photosynthesis, Respiration produces carbon (IV) oxide which raises acidity. This favours conversion of sugar to starch. Low sugar concentration lead to loss of turgidity in guard cells and stoma closes.

Ions

• In day time (light) adenosine triphosphate (ATP) is produced which causes potassium ions to move into guard cells by active transport.
• These ions cause an increase in solute concentration in guard cells that has been shown to cause movement of water into guard cells by osmosis.
• Guard cells become turgid and the stoma opens.
• At night potassium and chloride ions move out of the guard cells by diffusion and level of organic acid also decreases.
• This causes a drop in solute concentration that leads to movement of water out of guard cells by osmosis.
• Guard cells lose turgor and the stoma closes.

​Gaseous Exchange in leaves of Terrestrial Plants
Gaseous exchange takes place by diffusion.
The structure of the leaf is adapted for gaseous exchange by having intercellular spaces that are filled.
These are many and large in the spongy mesophyll.

• Aquatic plants such as water lily have stomata only on the upper leaf surface.
• The intercellular spaces in the leaf mesophyll are large.
• Gaseous exchange occurs by diffusion just as in terrestrial plants.

Observation of internal structure of leaves of aquatic plants
Transverse section of leaves of an aquatic plant such as Nymphaea differs from that of terrestrial plant.
The following are some of the features that can be observed in the leave of an aquatic plant;

• Absence of cuticle
• Palisade mesophyll cells are very close to each other i.e. compact.
• Air spaces (aerenchyma) in spongy mesophyll are very large.
• Sclereids (stone cells) are scattered in leaf surface and project into air spaces.
• They strengthen the leaf making it firm and assist it to float.

​Terrestrial Plants
Stems of woody plants have narrow openings or slits at intervals called lenticels.
They are surrounded by loosely arranged cells where the bark is broken.
They have many large air intercellular spaces through which gaseous exchange occurs.
Oxygen enters the cells by diffusion while carbon (IV) oxide leaves.
Unlike the rest of the bark, lenticels are permeable to gases and water. 

​The water lily, Salvia and Wolfia whose stems remain in water are permeable to air and water.
Oxygen dissolved in the water diffuses through the stem into the cells and carbon (IV) oxide diffuses out into the water. 

​Terrestrial Plants
Gaseous exchange occurs in the root hair of young terrestrial plants.
Oxygen in the air spaces in the soil dissolves in the film of moisture surrounding soil particles and diffuses into the root hair along a concentration gradient.
It diffuses from root hair cells into the cortex where it is used for respiration.
Carbon (IV) oxide diffuses in the opposite direction.
In older roots of woody plants, gaseous exchange takes place through lenticels.
Aquatic Plants
Roots of aquatic plants e.g. water lily are permeable to water and gases.
Oxygen from the water diffuses into roots along a concentration gradient.
Carbon (IV) oxide diffuses out of the roots and into the water.
The roots have many small lateral branches to increase the surface area for gaseous exchange.
They have air spaces that help the plants to float.
Mangroove plants grow in permanently waterlogged soils, muddy beaches and at estuaries.
They have roots that project above the ground level.
These are known as breathing roots or pneumatophores.
These have pores through which gaseous exchange takes place e.g. in Avicenia the tips of the roots have pores.
Others have respiratory roots with large air spaces.

Continue Reading ...

1. What is gaseous exchange?
2. Why is gaseous exchange important to organisms?
3. Name the structure used for gaseous exchange by plants
4. Briefly describe the structure of stomata
5. State the factors which affect stomatal opening
6. Name the theories suggesting the mechanism of opening and closing of stomata
7. Describe the mechanism of opening and closing of stomata
8. What is the advantage of having stomata open during daytime and having them closed at night?
9. State the ways in which leaves of plants are adapted to gaseous exchange
10. Describe how gaseous exchange takes place in terrestrial plants
11. State the ways in which floating leaves of aquatic plants are adapted to gaseous exchange
12. How is aerenchyma tissue adapted to its function?
13. Explain stomatal distribution in plants of different habitats
14. List the types of respiratory surfaces of animals
15. State the characteristics of respiratory surfaces in animals
16. Describe gaseous exchange in protozoa
17. Make a labeled drawing of a fish gill
18. How is a fish gill adapted to its function?
19. Discuss gaseous exchange in bony fish example is tilapia
20. What is counter-flow system?
21. What is the advantage of counter-flow system?
22. Describe the mechanism of gaseous exchange in terrestrial insects
23. State how traceholes are adapted to gaseous
24. What is breathing?
25. Name the structures in humans that are used in gaseous exchange
26. Describe the mechanism of gaseous exchange in a mammal
27. Explain how mammalian lungs are adapted to gaseous exchange
28. Name the features of alveoli that adapt them to their function
29. How is the trachea of a mammal suited to its function?
30. State the advantages of breathing through the nose rather than through the mouth
31. Give the conditions under which the carbon iv oxide level rises above normal in mammalian blood
32. Explain the physiological changes that occur in the body to lower the carbon iv oxide level back to normal when it rises
33. Describe the factors which control the rate of breathing in humans
34. Name the respirator diseases
35. Define respiration
36. Explain the significance of respiration in living organisms
37. Draw and label a mitochondrion
38. Explain the roles of enzymes in respiration
39. What is aerobic respiration?
40. Give a word equation for aerobic respiration
41. What are the end products of aerobic respiration?
42. What is anaerobic respiration?
43. What are obligate anaerobes?
44. What are facultative anaerobes?
45. State the word equation representing anaerobic respiration in plants
46. Name the end products of anaerobic respiration in plants alcohol/ethanol carbon iv oxide
47. Give a word equation of anaerobic respiration in animals
48. Name the end products of respiration in animals when there is insufficient oxygen supply
49. Why is there a high rate of lactic acid production during exercise?
50. Why does lactic acid level reduce after exercise?
51. State why accumulation of lactic acid during vigorous exercise lead to an increase in heartbeat
52. State the economic importance of anaerobic respiration
53. What is oxygen debt?
54. What is respiratory quotient(RQ)?
55. Why are respiratory quotient important?
56. Name the respiratory substrates 
57. Why does anaerobic respiration of a given substrate yield a smaller amount of energy than aerobic respiration?
58. Mention the types of experiments carried out for respiration

TOPIC 7 - GASEOUS EXCHANGE (36 LESSONS) [KCSE NOTES].pdf
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By the end of the topic, the learner should be able to:

1. define the cell
2. state the purpose of a light microscope
3. identify the parts of a light microscope and state their functions
4. use and care for the light microscope and state the magnification
5. identify the components of a cell as seen under the light and electron microscopes and relate their structure to functions
6. compare plant and animal
7. mount and stain temporary slides of plant cells
8. describe animal cells as observed from permanent
9. estimate cell size
10. state the differences between cells, tissues, organs and organ systems.

1. Definition of the cell
2. Structure and functions of parts of a light microscope
3. Use and care of the light microscope
4. Cell structure and functions as seen under
   1. a light microscope
   2. an electron microscope
5. Preparation of temporary slides of plant cells
6. Estimation of cell size
7. Cell specialization, tissues, organs and organ systems
8. Observe, identify, draw and state the functions of parts of the light microscope
9. Prepare and observe temporary slides of plant cells
10. Observe permanent slides of animal cells
11. Comparison between plant and animal cells
12. Observe, estimate size and calculate magnification of plant cells

Introduction

• The cell is the basic unit of an organism.
• All living organisms are made up of cells.
• Some organisms are made up of one cell and others are said to be multicellular.
• Other organisms are made of many cells and are said to be multicellular.
• Cells are too little to see with the naked eye.
• They can only be seen with the aid of a microscope.

The microscope is used to magnify objects.
Magnification

• The magnifying power is usually inscribed on the lens.
• To find out how many times a specimen is magnified, the magnifying power of the objective lens is multiplied by that of the eye piece lens.
• If the eye piece magnification lens is x10 and the objective lens is x4, the total magnification is x40.
• Magnification has no units.
• It should always have the multiplication sign.e.g.x40

1. Eye piece - Has a lens which contributes to the magnification of the object under view.
2. Coarse adjustment knob - Moves the body tube up and down for long distances and it brings the image into focus.
3. Fine adjustment knob - Moves the body tube and brings the image into fine focus.
4. Body tube - Holds the eye piece and the revolving nose piece. It directs light from objective lenses to the eye piece lens.
5. Revolving nose piece - Holds and brings objective lenses into position.
6. Objective lens - Contributes to the magnification of the object.
7. Arm/limb - It is for handling the microscope and also tilting it.
8. Stage - Is the flat platform onto which the slide with the object is placed.
9. Clips - They hold the slide firmly onto the stage.
10. Condenser - Concentrates light onto the object.
11. Diaphragm - Regulates the amount of light passing through the object.
12. Mirror - Reflects light into the condenser.
13. Hinge screw - Fixes the arm to the base and allows for tilting of the arm. 
14. Base/stand - Provides support to the microscope

• Turn the low power objective lens until it clicks into position.
• Looking through the eye piece, ensure that enough light is passing through by adjusting the mirror.
• This is indicated by a bright circular area known as the field of view.
• Place the slide containing the specimen on stage and clip it into position.
• Make sure that the specimen is in the centre of the field of view.
• Using the coarse adjustment knob, bring the low power objective lens to the lowest point.
• Turn the knob gently until the specimen comes into focus.
• If finer details are required, use the fine adjustment knob.
• When using high power objective always move the fine adjustment knob upwards. 

• Great care should be taken when handling it.
• Keep it away from the edge of the bench when using it.
• Always hold it with both hands when moving it in the laboratory.
• Clean the lenses with special lens cleaning paper.
• Make sure that the low power objective clicks in position in line with eye piece lens before and after use.
• Store the microscope in a dust-proof place free of moisture. 

The cell as seen above has the following: 

• This is a thin membrane enclosing cell contents.
• It controls the movement of substances into and out of the cell. 

• This is a jelly-like substance in which chemical processes are carried out.
• Scattered all over the cytoplasm are small structures called organelles.
• Like an animal cell, the plant cell has a cell membrane, cytoplasm and a nucleus. 

• Plant cells have permanent, central vacuole. It contains cell sap where sugars and salts are stored. 

• This is the outermost boundary of a plant cell.
• It is made of cellulose.
• Between the cells is a middle lamella made of calcium precipitate. 

• With special staining techniques it is possible to observe chloroplasts.
• These are structures which contain chlorophyll, the green pigment responsible for trapping light for photosynthesis. 

• Capable of magnifying up to 500,000 times.
• The specimen is mounted in vacuum chamber through which an electron beam is directed.
• The image is projected on to a photographic plate.
• The major disadvantage of the electron microscope is that it cannot be used to observe living objects.
• However, it provides a higher magnification and resolution (ability to see close points as separate) than the light microscope so that specimen can be observed in more detail. 

• Under the electron microscope, the plasma membrane is seen as a double layer.
• This consists of a lipid layer sandwiched between two protein layers.
• This arrangement is known as the unit membrane and the shows two lipid layers with proteins within.
• Substances are transported across the membrane by active transport and diffusion. 

• This is a network of tubular structures extending throughout the cytoplasm of the cell.
• It serves as a network of pathways through which materials are transported from one part of the cell to the other.
• An ER encrusted with ribosomes it is referred to as rough endoplasmic reticulum.
• An ER that lacks ribosomes is referred to as smooth endoplasmic reticulum.
• The rough endoplasmic reticulum transports proteins while the smooth endoplasmic reticulum transports lipids. 

• These are small spherical structures attached to the ER.
• They consist of protein and ribonucleic acid (RNA).
• They act as sites for the synthesis of proteins. 

• Golgi bodies are thin, plate-like sacs arranged in stacks and distributed randomly in the cytoplasm.
• Their function is packaging and transportation of glycol-proteins.
• They also produce lysosomes. 

• Each mitochondrion is a rod-shaped organelle.
• Made up of a smooth outer membrane and a folded inner membrane.
• The folding of the inner membrane are called cristae.
• They increase the surface area for respiration.
• The inner compartments called the matrix.
• Mitochondria are the sites of cellular respiration, where energy is produced. 

• These are vesicles containing hydrolytic enzymes.
• They are involved in the breakdown of micro-organisms, foreign macromolecules and damaged or worn-out cells and organelles.

• The nucleus is surrounded by a nuclear membrane which is a unit membrane.
• The nuclear membrane has pores through which materials can move to the surrounding cytoplasm.
• The nucleus contains proteins and nucleic acid deoxyribonucleic acid (DNA) and RNA.
• The chromosomes are found in the nucleus.
• They are the carriers of the genetic information of the cell.
• The nucleolus is also located in the nucleus but it is only visible during the non-dividing phase of the cell. 

• These are found only in photosynthetic cells.
• Each chloroplast consists of an outer unit. Membrane enclosing a series of interconnected membranes called lamellae.
• At various points along their length the lamellae form stacks of disc like structures called grana.
• The lamellae are embedded in a granular material called the stroma.
• The chloroplasts are sites of photosynthesis.
• The light reaction takes place in the lamellae while the dark reactions take place in the stroma. 

Cells are specialized to perform different functions in both plants and animals.
Example;

• Palisade cells have many chloroplasts for photosynthesis.
• Root hair cells are long and thin to absorb water from the soil.
• Red blood cells have haemoglobin which transports oxygen.
• Sperm cells have a tail to swim to the egg.
• Multicellular organisms cells that perform the same function are grouped together to form a tissue.
• Each tissue is therefore made up of cells that are specialised to carry out a particular function. 

Examples of animal tissues; 

Example of plant tissues; 

• An organ is made up of different tissues e.g. the heart, lungs, kidneys and the brain in animals and roots, stems and leaves in plants. 

• Organs which work together form an organ system.
• Digestive, excretory, nervous and circulatory in animals and transport and support system in plants.

• Different organ systems form an organism. 

Observation and Identification of parts of a light microscope and their functions

• A light microscope is provided.
• Various parts are identified and observed.
• Drawing and labelling of the microscope is done.
• Functions of the parts of the microscope are stated.
• Calculations of total magnification done using the formula.
• Eye piece lens magnification objective lens magnification. 

• A piece of epidermis is made from the fleshy leaf of an onion bulb. It is placed on a microscope slide and a drop of water added.
• A drop of iodine is added and a cover slip placed on top.
• Observations are made, under low and medium power objective.
• The cell wall and nucleus stain darker than other parts.
• A labelled drawing is made.
• The following are noted: Nucleus, cell wall, cytoplasm and cell membrane. 

• Permanent slides of animal cells are obtained e.g, of cheek cells, nerve cells and muscle cells.
• The slide is mounted on the microscope and observations made under low power and medium power objectives.
• Labelled drawings of the cells are made.
• A comparison between plant and animal cell is made. 

• Using the low power objective, a transparent ruler is placed on the stage of the microscope.
• An estimation of the diameter of the field of view is made in millimeters.
• This is converted into micrometres (1mm=1000u)
• A prepared slide of onion epidermal cells is mounted.
• The cells across the centre of the field of view are counted from left and right and top to bottom.
• The diameter of field of view is divided by the number of cells lying lengthwise to give an estimate of the length and width of each cell.

the-cell.html

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These are fats and oils.
Fats are solid at room temperature while oils are liquid.
They are made up of carbon, oxygen and hydrogen atoms.
The structural units of lipids are fatty acids and glycerol.
Fatty acids are made up of hydrocarbon chain molecules with a carboxyl group (-COOH) at one end.
In the synthesis of a lipid, three fatty acid molecules combine with one glycerol molecule to form a triglyceride.
Three molecules of water are lost in the process.
This is a condensation reaction and water is given off.
Lipids are hydrolysed e.g. during digestion to fatty acids and glycerol, water is added.
Condensation = Glycerol + 3 Fatty hydrolysis Lipid + Water acids 

Properties of Lipids

• Fats are insoluble in water but dissolve in organic solvents e.g. in alcohols.
• They are chemically inactive, hence used as food storage compounds.

Functions of Lipids

• Structural materials - as structural material they make up the cell membrane.
• Source of energy - they are energy rich molecules. One molecule of lipid provides more energy than a carbohydrate molecule.
• Storage compound - They are stored as food reserves in plants. In animals e.g. mammals, all excess food taken is converted to fats which are stored in adipose tissue, and around internal organs such as the heart and kidneys.
• Insulation - They provide insulation in animals living in cold climates. A lot of fat is stored under the skin e.g. blubber in seals.
• Protection - Complex lipids e.g. wax on leaf surfaces protects the plant against water-loss and overheating. Fats stored around some internal organs acts as shock absorbers, thus protecting the organs.
• Source of Metabolic Water -:-lipids when oxidised produce metabolic water which supplements water requirements in the body. Desert animals e.g. the camel accumulate large quantities of fat in the hump which when oxidised releases metabolic water.

Proteins

• Proteins are the most abundant organic compounds in cells and constitute 50% of total dry weight.
• Proteins are compounds which are made up of carbon, hydrogen, nitrogen, oxygen and sometimes sulphur and phosphorus.
• The structural units of proteins are amino acids.
• The nature of a protein is determined by the types of amino acids it is made of.
• There are about 20 common amino acids that make up proteins. 

Essential and Non-Essential Amino Acids

• Essential amino acids are those which cannot be synthesised in the body of an organism and must therefore be provided in the diet.
• There are ten amino acids which are essential for humans.
• These are valine, leucine, phenylalanine, lysine, tryptophan, isoleucine, methionine, threonine, histidine and arginine.
• Non-essential amino acids are those which the body can synthesise and therefore need not be available in the diet.
• There are ten of them.
• These are glycine, alanine, glutamic acid, aspartic acid, serine, tyrosine, proline, glutamine, arginine and cysteine.
• Proteins are essential in the diet because they are not stored in the body.
• Excess amino acids are deaminated.

Formation of Proteins

• Proteins are made up of many amino acid units joined together through peptide bonds.
• When two amino acids are joined together a dipeptide is formed.
• The chemical process involved is called condensation and a molecule of water is eliminated .
• When many amino acids are joined together a polypeptide chain is formed.
• The nature of a particular protein depends on the types, number and sequence of amino acids from which it is made. 

Functions of Proteins
As structural materials proteins-

• These are the basic building structures of protoplasms
• Proteins in conjunction with lipid form the cell membrane.

Examples of structural proteins include:

• Keratin (in hair, nails, hoofs, feathers and wool)
• Silk in spider's web.
• Elastin forms ligaments that join bones to each other.

Protective proteins.

• Antibodies that protect the body against foreign antigens.
• Fribrogen and thrombin are involved in clot formation, preventing entry of micro-organisms when blood vessel is cut.

 
As functional chemical compounds.
Examples are hormones and enzymes that act as regulators in the body.
Respiratory pigments.
Examples are haemoglobin that transports oxygen in the blood and myoglobin that stores up oxygen in muscles.
Contractile proteins - make up muscles, i.e. myosin and actin.
Proteins combine with other chemical groups to form important substances e.g. mucin in saliva.
Source of energy.
Proteins are a source of energy in extreme conditions when carbohydrates and fats are not available e.g. in starvation.

Enzymes

• Enzymes are biological catalysts that increase the rate of chemical reaction in the body.
• They are all produced inside cells.
• Some are intracellular and they catalyse reactions within the cells.
• Others are extracellular and are secreted out of the cells where they work. E.g. digestive enzymes.

Properties of Enzymes

• Enzymes are protein in nature.
• Enzymes are specific to the type of reaction they catalyse.
• This is referred to as substrate specificity.
• Enzymes work in very small amounts.
• They remain unchanged after the reaction.
• They catalyse reversible reactions.
• They work very fast (high turnover numbers) e.g. the enzyme catalase works on 600 thousand molecules of hydrogen peroxide in one second. 

Naming of enzymes
Enzymes are named by adding the suffix -ase to:
Name of substrate that they work on e.g.

• Carbohydrates - carbohydrases e.g.sucrase.
• Starch (amylose) - amylase
• Protein - proteinase (protease)
• Lipids -lipases

Type of chemical reaction catalysed e.g.

• Oxidation - oxidase
• Reduction - reductase
• Hydrolysis - hydrolase

Temperature

• Enzymes are sensitive to temperature changes.
• Generally, the rate of an enzyme-controlled reaction doubles with every 10OC increase in temperature.
• However, temperatures above 40°C do not favour enzyme reaction.
• This is because enzymes are denatured by high temperatures.

pH

• Every enzyme has a particular pH range over which it works best.
• Some enzymes work best in acidic media while others function better in alkaline media.
• Many enzymes function well under neutral conditions.

Enzyme Concentration

• Under conditions where the substrate is in excess, the rate of an enzyme-controlled reaction increases as the enzyme concentration is increased.

Substrate Concentration

• If the concentration of the substrate is increased while that of the enzyme remains constant, the rate of the reaction will increase for some time and then become constant.
• Any further increase in substrate concentration will not result in corresponding increase in the rate of the reaction.

Enzyme Inhibitors

• These are substances that either compete with substrates for enzyme active sites or combine with enzymes and hence they inhibit the enzyme reaction; e.g. certain drugs, cyanide and nerve gas.

Co-factors

• Most enzymes require the presence of other compounds known as co-factors which are non-proteins.
• There are three groups of co-factors.
• Inorganic ions - e.g. iron, magnesium, copper and zinc.
• Complex organic molecules known as prosthetic groups are attached to the enzyme e.g. flavin adenine dinucleotide (FAD) derived from vitamin B2 (riboflavin).
• Co-enzymes e.g. coenzyme A is involved in respiration.
• All co-enzymes are derived from vitamins.

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​TOPIC 5 - NUTRITION IN PLANTS AND ANIMALS [KCSE NOTES].pdf
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1. Meaning of cell physiology
2. Structure and properties of cell membrane (Theories of membrane structure not required)
3. Physiological processes - diffusion, osmosis and active transport
4. Factors affecting diffusion, osmosis and active transport
5. Role of diffusion, osmosis and active transport in living organisms
6. Water relations in plant and animal cells: turgor, plasmolysis, wilting and haemolysis
7. Practical Activities
8. Diffusion as demonstrated with Potassium permanganate or potassium iodide/flower dyes/coloured plant extracts/smoke
9. Experiments with visking tubing and living tissues: fresh arrow roots/cassava/sweet potatoes/leaf petioles/Irish potatoes/carrots
10. Plasmolysis can be demonstrated by using any of the following: spirogyra,  epidermal cells of onion or raw egg that has been put in dilute hydrochloric acid overnight

By the end of the topic, the learner should be able to:

1. Define cell physiology
2. Correlate the membrane structure with cell physiology in relation to permeability
3. Differentiate between diffusion, osmosis and active transport
4. State and describe factors affecting diffusion, osmosis and active transport
5. Carry out experiments on diffusion and osmosis
6. Explain the roles of diffusion, osmosis and active transport in living organisms
7. Explain turgor and plasmolysis in terms of osmotic pressure.

​The term physiology refers to the functions that occur in living organisms.
Cell physiology refers to the process through which substances move across the cell membrane.
Several physiological processes take place inside the cell e.g. respiration.
Oxygen and glucose required enter the cell while carbon (IV) oxide and water produced leave the cell through the cell membrane.

• The cell membrane is the protective barrier that shelter cellular contents.
• Movement of all substances into and out of the cells takes place across the cell membrane.
• It is made up of protein and lipid molecules.
• Lipid molecules have phosphate group attached to it on one end.
• They are then referred to phospholipids.
• The phospholipids are arranged to form a double layer.
• The ends with phosphate group face outwards.
• The proteins are scattered throughout the lipid double layer.
• Some of these proteins act as carrier molecules that channel some material in and outside the cells.
• The cell membrane allows certain molecules to pass through freely while others move through with difficulty and still others do not pass through at all.
• This is selective permeability and the cell membrane is described as semi-permeable.

Permeability

• The cell membrane is semi-permeable.
• It allows small molecules that are soluble in lipid to pass through with more ease than water soluble molecules.
• This is due to the presence of the phospholipids double layer.

Polarity

• The cell membrane has electrical charges across its surface.it has positive charged ions on the outside and negatively charged ions on the inside. This property contributes to electrical impulses sent along nerve cells.
• Sensitivity to changes in temperature and pH
• Very high temperatures destroy the semi-permeability nature of the cell membrane because the proteins are denatured by extreme pH values have the same effect on the membrane permeability.
• Physiological processes
• Some of the physiological processes include diffusion, osmosis and active transport.

Diffusion

• Diffusion is the movement of molecules or ions from a region of high concentration to a region of low concentration aided by a concentration gradient.
• Diffusion continues to occur as long as there is a difference in concentration between two regions (concentration gradient).
• Stops when an equilibrium is reached i.e., when the concentration of molecules is the same in both regions.
• Diffusion is a process that occurs inside living organisms as well as the external environment..
• Does not require energy.

Concentration Gradient
An increase in the concentration of molecules at one region results in a steeper concentration gradient which in turn increases the rate of diffusion.
Temperature
High temperature increases kinetic energy of molecules. They move faster hence resulting in an increase in rate of diffusion, and vice versa.
Size of Molecules or Ions
The smaller the size of molecules or ions, the faster their movement hence higher rate of diffusion.
Density
The denser the molecules or ions diffusing, the slower the rate of diffusion, and vice versa.
Medium
The medium through which diffusion occurs also affects diffusion of molecules or ions. For example, diffusion of molecules through gas and liquid media is faster than through a solid medium.
Distance
This refers to the thickness or thinness of surface across which diffusion occurs. Rate of diffusion is faster when the distance is small i.e., thin surface.
Surface Area to Volume Ratio
The larger the surface area to volume ratio, the faster the rate of diffusion.
For example, in small organisms such as Amoeba the surface area to volume ratio, is greater hence faster diffusion than in larger organisms.

Some processes that depend on diffusion include the following:

• Gaseous exchange: Movement of gases through respiratory surfaces is by diffusion.
• Absorption of materials into cells: cells obtain raw materials and nutrients from the surrounding tissue fluid and blood through diffusion, e.g., glucose needed for respiration diffuses from blood and tissue fluid into cells.
• Excretion: Removal of metabolic waste products like carbon (IV) oxide, and ammonia out of cells is by diffusion.
• Absorption of the end-products of digestion from the intestines is by diffusion.

• Osmosis is the movement of water molecules from a region of high water concentration to a region of low water concentration through a semi-permeable membrane.
• Osmosis is a special type of diffusion that involves the movement of water molecules only and not solute molecules.
• Osmosis takes place in cells across the cell membrane as well as across non-living membranes e.g. cellophane or visking tubing which are also semi-permeable,
• It is purely a physical process.

Size of solute molecules-
Osmosis' occurs only when solute molecules are too large to pass through a semi-permeable membrane.
Concentration Gradient.
Osmosis occurs when two solutions of unequal solute concentration are separated by a semi-permeable membrane.
Temperature.
High temperatures increase movement of water molecules hence influence osmosis. However, too high temperatures denature proteins in cell membrane and osmosis stops.
Pressure
Increase in pressure affects movement of water molecules.
As pressure increases inside a plant cell, osmosis decreases.

The following processes depend on osmosis in living organisms:

• Movement of water into cells from the surrounding tissue fluid and also from cell to cell.
• Absorption of water from the soil and into the roots of plants.
• Support in plants especially herbaceous ones, is provided by turgor pressure, which results from intake of water by osmosis.
• Absorption of water from the alimentary canal in mammals.
• Re-absorption of water in the kidney tubules.
• Opening and closing stomata. 

• The medium (solution) surrounding cells or organisms is described by the terms hypotonic, hypertonic and isotonic.
• A solution whose solute concentration is more than that of the cell sap is said to be hypertonic. A cell placed in such a solution loses water to the surroundings by osmosis.
• A solution whose solute concentration is less than that of the cell sap is said to be hypotonic. A cell placed in such a solution gains water from the surroundings by osmosis.
• A solution which has the same solute concentration as the cell sap is said to be isotonic. When a cell is placed in such a solution there will be no net movement of water either into or out of the cell.

• The term osmotic pressure describes the tendency of the solution with a high solute concentration to draw water into itself when it is separated from distilled water or dilute solution by a semi-permeable membrane.
• Osmotic pressure is measured by an osmometer.
• When plant cells are placed in distilled water or in a hypotonic solution, the osmotic pressure in the cells is higher than the osmotic pressure of the medium.
• This causes the water to enter the cells by osmosis.
• The water collects in the vacuole which increases in size.
• As a result the cytoplasm is pushed outwards and it in turn presses the cell membrane next to the cell wall.
• This builds up water pressure (hydrostatic pressure) inside the cell.
• When the cell is stretched to the maximum, the cell wall prevents further entry of water into the cell.
• Then the cell is said to be fully turgid.
• The hydrostatic pressure developed is known as turgor pressure.

• When a plant cell is placed in a hypertonic medium, it loses water by osmosis.
• The osmotic pressure of the cell is lower than that of the medium.
• The vacuole decreases in size and the cytoplasm shrinks as a result of which the cell membrane loses contact with the cell wall.
• The cell becomes flaccid. The whole process is described as plasmolysis.
• Incipient plasmolysis is when a cell membrane just begins to lose contact with the cell wall.
• Plasmolysis can be reversed by placing the cell in distilled water or hypotonic solution.
• However, full plasmolysis may not be reversed if cell stays in that state for long. 

• The term wilting describes the drooping of leaves and stems of herbaceous plants after considerable amounts of water have been lost through transpiration.
• It is observed in hot dry afternoons or in dry weather.
• This is when the amount of water lost through transpiration exceeds the amount absorbed through the roots.
• Individual cells lose turgor and become plasmolysed and the leaves and stems droop.
• The condition is corrected at night when absorption of water by the roots continue while transpiration is absent.
• Eventually, wilting plants may die if the soil water is not increased through rainfall or watering. 

• Haemolysis is the bursting of cell membrane of red blood cells releasing their haemoglobin.
• It occurs when red blood cells are placed in distilled water or hypotonic solution.
• This is because the cell membrane does not resist further entry of water by osmosis after maximum water intake. 

• Takes place when red blood cells are placed in hypertonic solution.
• They lose water by osmosis, shrink and their shape gets distorted.
• Animal cells have mechanisms that regulate their salt water balance (osmoregulation) to prevent above processes that lead to death of cells.
• An Amoeba placed in distilled water, i.e. hypotonic solution, removes excess water using a contractile vacuole.
• The rate of formation of contractile vacuoles increases.

• Active transport is the movement of solutes such as .glucose, amino acids and mineral ions;
• From an area of their low concentration to an area of high concentration.
• It is movement against a concentration gradient and therefore energy is required.
• As such it only takes place in living organisms.
• The energy needed comes from respiration.
• Certain proteins in the cell surface membrane responsible for this movement are referred to as carrier proteins or channel proteins.
• The shape of each type of carrier protein is specific to the type of substances conveyed through it.
• It has been shown that the substance fits into a particular slot on the protein molecule,
• As the protein changes from one form of shape to another the substance is moved across and energy is expended. 

• Energy needed for active transport is provided through respiration.
• An increase in the amount of oxygen results in a higher rate of respiration.
• If a cell is deprived of oxygen active transport stops. 

• Optimum temperature is required for respiration, hence for active transport.
• Very high temperatures denature respiratory enzymes.
• Very low temperatures inactivate enzymes too and active transport stops. 

• Carbohydrates are the main substrates for respiration.
• Increase in amount of carbohydrate results in more energy production during respiration and hence more active transport.
• Lack of carbohydrates causes active transport to stop. 

• Metabolic poisons e.g. cyanide inhibit respiration and stops active transport due to lack of energy. 

Processes requiring active transport:

• Absorption of mineral salts from the soil into plant roots.
• Absorption of end products of digestion e.g. glucose and amino acids from the digestive tract into blood stream.
• Excretion of metabolic products e.g. Urea from the cells.
• Re-absorption of useful substances and mineral salts back into blood capillaries from the kidney tubules.
• Sodium-pump mechanism in nerve cells.
• Re-absorption of useful materials from tissue fluid into the blood stream. 

1. Experiment to Demonstrate Diffusion

• Various coloured substances such as: dyes, plant extracts and chemicals like potassium permanganate are used.
• Potassium manganate (VII) crystals are introduced to the bottom of a beaker filled with water using a glass tubing or drinking straw which is then removed.
• Observations are made and the disappearance of the crystals and subsequent uniform colouring of water noted.

2. Experiment to Demonstrate Osmosis Using a Visking Tubing

• A strip of visking tubing 8-10 cm is cut and tied at one end using strong thread.
• About 2 ml of 25% sucrose solution is put inside and the other end tied with thread.
• The tubing is washed under running water and then blotted to dry.
• It is immersed in a beaker containing distilled water and left for at least one hour or overnight.
• It will then be observed that the visking tubing has greatly increased in size and has become firm.
• A control experiment can be set up using distilled water inside the visking tubing in place of sucrose solution.

3. Experiment to Show Osmosis using Living Tissue

• Irish potato tubers are peeled and scooped out to make hollow space at the centre.
• Sucrose solution is placed inside the hollow, and the potato tuber placed in a beaker or petri-dish with distilled water. A control is set using a boiled potato.
• Another one using distilled water inside hollow in place of sugar solution.
• The experiment is left for 3 hours to 24 hours.

 
4. Experiment to Demonstrate Turgor and Plasmolysis in Onion Epidermal Cells

• Two strips of onion epidermis are obtained.
• One is placed on a slide with distilled water while the other is placed on a slide with 25% sucrose solution and a coverslip placed on top of each.
• The mounted epidermis is observed under low power microscope and then left for 30 minutes.
• After 30 minutes, observations are made again.
• The cells in distilled water have greatly enlarged. Cells in 25% sucrose have shrunk.

1. 1994 Q6 P1
Give a reason for each of the following
a) A mature plant cell does not lose its shape even after losing water.
b) Xylem vessels do not collapse even when they do not contain water.
2.   1995 Q4 P1
Explain what would happen to red blood cells if they are placed in a concentrated salt solution ( 2 marks)
3. 1995 Q10 P1
An experiment was carried out to investigate the rate of reaction shown below
 Sucrose →Fructose + Glucose
For the products fructose and glucose to be formed, it was found that substance K was to be added and the temperature maintained at 370C. When another substance L was added, the reaction slowed down and eventually stopped.
(a) Suggest the identify of substances K and L (2 marks)
(b) Other than temperature state three ways by which the rate of reaction could be increased (3 marks)
(c) Explain how substance L slowed down the reaction (2 marks)
4. 2000 Q8 P1
Why is oxygen important in the process of active transport in cells?
5. 2004 Q16 P1
a) What is diffusion (2 marks)
b) How do the following factors affect the rate of diffusion?
i) Diffusion gradient (1 mark)
ii) Surface area volume ratio (1mark)
iii) Temperature (1mark)
c) Outline three roles of active transport in the human body (3 marks)
6. 2005 Q7 P1
State the importance of osmosis in plants. (3 marks)
7. 2009 Q13 P1
(a) Distinguish between diffusion and active transport (2 marks)
(b) State one role that is played by osmosis in (1 mark)
  (i) Plants
  (ii) Animals
8. 2010 Q7 P1
 Distinguish between haemolysis and plasmolysis. (2 marks)

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By the end of the topic, the learner should be able to:

1. Define biology
2. List branches of biology
3. Explain the importance of biology
4. State the characteristics of living organisms
5. State the main differences between plants and animals.

INTRODUCTION (5 LESSONS)

1. Definition of biology
2. Branches of biology
3. Importance of biology
4. Characteristics of living organisms
5. Cornparison between plants and animals
6. Practical Activities
7. Collecting, observing and recording external features of plants and animals

Biology derived from Greek words

1. BIOS meaning LIFE and
2. LOGOS meaning STUDY or KNOWLEDGE.

Biology means "life knowledge".
Biology is therefore the study of living things/organisms. 

1. Botany - study of plants.
2. Zoology - study of animals.
3. Microbiology - study' of microscopic organisms.
4. Morphology - study of external structure of organisms.
5. Anatomy - study of internal structure of organisms.
6. Physiology - study of the functioning or working of the cells or body.
7. Biochemistry - study of the chemistry of materials in living organisms.
8. Cytology - study of cells.
9. Genetics - study of inheritance.
10. Ecology- study of the relationship between organisms and their environment.
11. Taxonomy - sorting out of organisms into groups.
12. Histology - study of fine structure of tissues.
13. Virology - study of viruses.
14. Bacteriology - study of bacteria.
15. Entomology - study of insects.
16. Ichthyology - study of fish. 

1. One learns about the functioning of the human body.
2. One understands the developmental changes that take place in the body.
3. It contributes immensely to improved life. 
4. It enables one to enter careers such as:
   1. Medicine,
   2. Nutrition,
   3. Public Health,
   4. Dentistry,
   5. Agriculture
   6. Environmental Studies.
   7. Teaching

Life defined through observations of activities carried out by living things;
Nutrition
Nutrition is the processes by which food/nutrients are acquired/made and utilized by living organisms.
Green plants and certain bacteria make their own food.
All other organisms feed on complex organic materials.
Respiration
This is the breakdown of food to provide energy.
The energy released is used for various activities in the organism.
Gaseous Exchange
Process through which respiratory gases (CO2 & O2) are taken in and out through a respiratory surface.
Excretion
Excretion is the removal of metabolic wastes from the body.
Substances like urea, carbon dioxide (Carbon (IV) oxide).
These substances are poisonous if allowed to accumulate in the body.
Growth and Development
Growth means irreversible change in size.
All organisms increase in size that is, they grow.
Development is irreversible change in complexity.
As they do so, they also become differentiated in form. 
Reproduction
Reproduction is the formation of new individuals of a species to ensure continued existence of a species and growth of its population.
Irritability
The ability of organisms to detect and respond to changes in the environment. This is of great survival value to the organism.
Movement
This the progressive change in position from one place to another.
Some organisms are sessile (i.e. fixed to the substratum).
The majority of plants move only certain parts. 

Biology as a practical subject is learnt through humane handling of organisms.
Materials needed for collection of organisms include:-

• Knives to cut portions of plant stem/root or uproot.
• Polythene bags to put the collected plant or specimens.
• Insect collecting jars.
• Insect killing jars.
• Hand gloves.
• Sweep nets
• Pooters
• Traps 

• Observe the plant/animal in its natural habitat before collecting.
• Identify the exact place -on surface, under rock, on tree trunk, on branches.
• What does it feed on?
• How does it interact with other animals and the environment?
• How many of that kind of plant or animal are in a particular place?
• Plant specimens placed on the bench and sorted out into;- seeds/stems/roots/leaves/fruits.
• Animal specimens may be left inside polythene bags if transparent.
• Others (killed ones) are put in petri­ dishes.
• Use hand lens to observe the external features of small animals.

Organisms are observed and important features noted down: colour, texture ­hard or soft; if hairy or not. Size is measured or estimated.
Biological DrawingsIt is necessary to draw some of the organisms.
In making a biological drawing, magnification (enlargement) is noted.
Indicate the magnification of your drawing, i.e. how many times the drawing is larger/smaller than the actual specimen MG=length of drawing/length specimen
How to Draw

• Several drawings of one organism may be necessary to represent all features observed, e.g.
• Anterior view of grasshopper shows all mouth parts properly, but not all limbs.
• Lateral (side) view shows all the legs. 

​Collection
Plants and animals collected from the environment, near school or within school compound using nets, bottles and gloves.
Animals collected include:-
arthropods, earthworms and small vertebrates like lizards/chameleons/ rodents.
Place in polythene bags and take to the laboratory.
Stinging/poisonous insects killed using ether.
Other animals are observed live and returned to their natural habitat.
Plant specimen collected include: -
leaves, flowers and whole plants.
Observations are made to show the following:-

• Plants have roots, stems, leaves and flowers.
• Animals have legs, hair, hard outer covering, feathers, eyes, mouth, limbs and other appendages, 

COMPARISON BETWEEN PLANTS AND ANIMALS ​

INTRODUCTION TO BIOLOGY

Previous Topic

​​Large and complex animals have circulatory systems that consist of tubes, a transport fluid and a means of pumping the fluid.
Blood is the transport fluid which contains dissolved substances and cells.
The tubes are blood vessels through which dissolved substances are circulated around the body.
The heart is the pumping organ which keeps the blood in circulation.
The types of circulatory system exist in animals: open and closed. 

In an open circulatory system;
The heart pumps blood into vessels which open into body spaces known as haemocoel.
Blood comes into contact with tissues.
A closed circulatory system;
Found in vertebrates and annelids where the blood is confined within blood vessels and does not come into direct contact with tissues. 

• In an insect, there is a tubular heart just above the alimentary canal.
• This heart is suspended in a pericardial cavity by ligaments.
• The heart has five chambers and extends along the thorax and abdomen.
• Blood is pumped forwards into the aorta by waves of contractions in the heart.
• It enters the haemocoel and flows towards the posterior.
• The blood flows back into the heart through openings in each chamber called Ostia.
• The Ostia have valves which prevent the backflow of blood.
• Blood is not used as a medium for transport of oxygen in insects.
• This is because oxygen is supplied directly to the tissues by the tracheal system.
• The main functions of blood in an insect are to transport nutrients, excretory products and hormones. 

• Mammals have a closed circulatory system where a powerful heart pumps blood into arteries.
• The arteries divide into smaller vessels called arterioles.
• Each arteriole divides to form a network of capillaries inside the tissues.
• The capillaries eventually re-unite to form venules, which form larger vessels called veins.
• The veins take the blood back to the heart.
• Blood from the heart goes through the pulmonary artery to the lungs and then back to the heart through pulmonary vein.
• This circulation is called pulmonary circulation.
• Oxygenated blood leaves the heart through the aorta and goes to all the tissues of the body.
• From the tissues, deoxygenated blood flows back to the heart through the vena cava.
• This circulation is called systemic circulation.
• In each complete circulation, the blood flows into the heart twice.
• This is called double circulation.
• Some other animals like fish have a single circulation.
• Blood flows only once through the heart for every complete circuit.

Structure and Function of the Heart

• The heart has four chambers:
• Two artria (auricles) and two ventricles.
• The left and right side of the heart are separated by a muscle wall (septum) so that oxygenated and deoxygenated blood does not mix.
• Deoxygenated blood from the rest of the body enters the heart through the vena cava .
• Blood enters the right atrium, then through tricuspid valve into right ventricle.
• Then via semi-lunar valve to the pulmonary artery to the lungs.
• Oxygenated blood from the lungs enters the heart through pulmonary vein.
• It enters the left atrium of the heart, then through bicuspid valve into left ventricle.
• Then via semi-lunar valves to aorta which takes oxygenated blood round the body.
• A branch of the aorta called coronary artery supplies blood to the heart muscle.
• The coronary vein carries blood from the heart muscle to the pulmonary artery which then takes it to the lungs for oxygenation.

Pumping Mechanism of the heart
The heart undergoes contraction (systole) and relaxation (diastole).
Systole
When the ventricular muscles contract, the cuspid valves (tricuspid and bicuspid) close preventing backflow of blood into auricles.
The volume of the ventricles decreases while pressure increases.
This forces blood out of the heart to the lungs through semi-lunar valves and pulmonary artery, and to the body tissues via semi-lunar valve and aorta respectively.
At the same time the atria are filled with blood.
The left ventricle has thicker muscles than the right ventricle, and pumps blood for a longer distance to the tissues. 

Diastole
When ventricular muscles relax, the volume of each ventricle increases while pressure decreases.
Contractions of atria force the bicuspid and tricuspid valves to open allowing deoxygenated blood from right atrium into right ventricle which oxygenated blood flows from left atrium into the left ventricle.
Semi-lunar valves close preventing the backflow of blood into ventricles.
The slight contractions of atria force the, blood flow into ventricles.
The Heartbeat
The heart is capable of contracting and relaxing rhythmically without fatigue due to its special muscles called cardiac muscles.
The rhythmic contraction of the heart arise from within the heart muscles without nervous stimulation.
The contraction is said to be myogenic.
The heartbeat is initiated by the pacemaker or sino-artrio-node (SAN) which is located in the right atrium.
The wave of excitation spreads over the walls of atria.
It is picked by the artrio-ventricular node which is located at the junction:
Of the atria and ventricles, from where the purkinje tissue spreads the wave to the walls of the ventricles.
The heart contracts and relaxes rhythmically at an average rate of 72 times per minute.
The rate of the heartbeat is increased by the sympathetic nerve, while it is slowed down by the vagus nerve.
Heartbeat is also affected by hormones e.g. adrenaline raises the heartbeat.

​Arteries
Arteries carry blood away from the heart.
They carry oxygenated blood except pulmonary artery which carries deoxygenated blood to the lungs.
Arteries have a thick, muscular wall, which has elastic and collagen fibres that resist the pressure of the blood flowing in them.
The high pressure is due to the pumping action of the heart.
The pressure in the arteries originate from the pumping action of the heart.
The pulse or number of times the heart beats per minute can be detected by applying pressure on an artery next to the bone e.g. by placing the finger/thumb on the wrist.
The innermost layer of the artery is called endothelium which is smooth.
It offers least possible resistance to blood flow.
Have a narrow lumen.
The aorta forms branches which supply blood to all parts of the body.
These arteries divide into arterioles which further divide to form capillaries.
Capillaries
Capillaries are small vessels whose walls are made of endothelium which is one cell thick.
This provides a short distance for exchange of substances.
Capillaries penetrate tissues,
The lumen is narrow therefore blood flowing in capillaries is under high pressure.
Pressure forces water and dissolved substances out of the blood to form tissue fluid.
Exchange of substances occurs between cells and tissue fluid.
Part of the tissue fluid pass back into capillaries at the venule end.
Excess fluid drains into small channels called lymph capillaries which empty their contents into lymphatic vessels.
Capillaries join to form larger vessels called venules which in turn join to form veins which transport blood back to the heart.
Veins
Veins carry deoxygenated blood from the tissues to the heart (except pulmonary vein which carries oxygenated blood from the lungs to the heart).
Veins have a wider lumen than arteries.
Their walls are thinner than those of arteries.
Blood pressure in the veins is low.
Forward flow of blood in veins is assisted by contraction of skeletal muscles, hence the need for exercise.
Veins have valves along their length to prevent backflow of blood.
This ensures that blood flows towards the heart.
The way the valves work can be demonstrated on the arm.
By pressing on one vein with two fingers, leaving one and pushing blood toward the heart then releasing the latter finger, it can be observed that the part in between is left with the vein not being visible.
This is because bleed does not flow back towards the first finger.

​Thrombosis
Formation of a clot in the blood vessels is called thrombosis.
Coronary thrombosis is the most common.
It is caused by blockage of coronary artery which supplies blood to the heart.
Blockage may be due to artery becoming fibrous or accumulation of fatty material on the artery walls.
Narrow coronary artery results in less blood reaching the heart muscles.
A serious blockage can result in heart attack which can be fatal.
Heavy intake of fat, alcohol, being overweight and emotional stress can cause coronary thrombosis.
A blockage in the brain can lead to a stroke causing paralysis of part of the body, coma or even death.
A healthy lifestyle, avoiding a lot of fat in meals and avoiding alcohol can control the disease.
Arteriosclerosis
This condition results from the inner walls having materials being deposited there or growth of fibrous connective tissue.       
This leads to thickening of the wall of the artery and loss of elasticity.
Normal blood flow is hindered.
Arteriosclerosis can lead to thrombosis or hypertension.
A person with hypertension which is also called high blood pressure has his/her blood being pumped more forcefully through the narrow vessels.
This puts stress on the walls of the heart and arteries.
Regular exercise, healthy diet and avoiding smoking can help maintain normal blood pressure.
Varicose Veins
Superficial veins especially at the back of the legs become swollen and flabby due to some valves failing to function properly.
This results to retention of tissue fluid.
Regular physical exercise will prevent this condition.
Repair of valves through surgery can also be done.
Wearing surgical stockings may ease a mild occurrence. 

Composition of Blood
The mammalian blood is made up of a fluid medium called plasma with substances dissolved in it.
Cellular components suspended in plasma include;

• Erythrocytes (red blood cells),
• Leucocytes (white blood cells)
• Thrombocytes (platelets)
• Blood proteins.

Plasma
This is a pale yellow fluid consisting of 90% water.
There are dissolved substances which include;

• Glucose, amino acids, lipids, salts,
• Hormones, urea, fibrinogen, albumen,
• Antibodies, some enzymes suspended cells.

Serum is blood from which fibrinogen and cells have been removed.
The functions of plasma include:
Transport of red blood cells which carry oxygen.
Transport dissolved food substances round the body.
Transport metabolic wastes like nitrogenous wastes and carbon (IV) oxide in solution about 85% of the carbon (IV) oxide is carried in form of hydrogen carbonates.
Transport hormones from sites of production to target organs.
Regulation of pH of body fluids.
Distributes heat round the body hence regulate body temperature.
Erythrocytes (Red Blood Cells)
In humans these cells are circular biconcave discs without nuclei.
Absence of nucleus leaves room for more haemoglobin to be packed in the cell to enable it to carry more oxygen.
Haemoglobin contained in red blood cells is responsible for the transport of oxygen. 

​Oxygen is carried in form of oxyhaemoglobin.
Haemoglobin readily picks up oxygen in the lungs where concentration of oxygen is high.
In the tissues, the oxyhaemoglobin breaks down (dissociates) easily into haemoglobin and oxygen.
Oxygen diffuses out of the red blood cells into the tissues.
Haemoglobin is then free to pick up more oxygen molecules.
The biconcave shape increases their surface area over which gaseous exchange takes place.
Due to their ability, they are able to change their shape to enable themselves squeeze inside the narrow capillaries.
There are about five million red blood cells per cubic millimetre of blood.
They are made in the bone marrow of the short bones like sternum, ribs and vertebrae.
In the embryo they are made in the liver and spleen.
Erythrocytes have a life span of about three to four months after which they are destroyed in the liver and spleen.
Also in the red blood cells is carbonic anhydrase which assists in the transport of carbon (IV) oxide.
Leucocytes (White Blood Cells)
These white blood cells have a nucleus.
They are divided into two:

1. Granulocytes (also phagocytes or polymorphs)
2. Agranulocytes.

White blood cells defend the body against disease.
Neutrophils form 70% of the granulocytes.
Others are eosinophils and basophils.
About 24% agronulocytes are called lymphocytes, while 4% agranulocytes are monocytes.
The leucocytes are capable of amoebic movement.
They squeeze between the cells of the capillary wall to enter the intercellular spaces.
They engulf and digest disease causing organisms (pathogens) by phagocytosis.
Some white blood cells may die in the process of phagocytosis.
The dead phagocytes, dead organisms and damaged tissues form pus.
Lymphocytes produce antibodies which inactivate antigens.
Antibodies include:
Antitoxins which neutralise toxins.
Agglutinins cause bacteria to clump together and they die.
Lysins digest cell membranes of microorganisms.
Opsonins adhere to outer walls of microorganisms making it easier for phagocytes to ingest them.
Lymphocytes' are made in the thymus gland and lymph nodes.
There are about 7,000 leucocytes per cubic millimetre of blood.
Platelets (Thrombocytes)
Platelets are small irregularly shaped cells formed from large bone marrow cells called megakaryocytes.
There are about 250,000 platelets per cubic millimetre of blood.
They initiate the process of blood clotting.
The process of clotting involves a series of complex reactions whereby fibrinogen is converted into a fibrin clot.
When blood vessels are injured platelets are exposed to air and they release thromboplastin which initiates the blood clotting process.
Thromboplastin neutralises heparin the anti-clotting factor in blood and activates prothrombin to thrombin.
The process requires calcium ions and vitamin K.
Thrombin activates the conversion of fibrinogen to fibrin which forms a meshwork of fibres on the cut surface to trap red blood cells to form a clot.
The clot forms a scab that stops bleeding and protects the damaged tissues from entry of micro-organisms.
Blood clotting reduces loss of blood when blood vessels are injured.
Excessive loss of blood leads to anaemia and dehydration.
Mineral salts lost in blood leads to osmotic imbalance in the body.
This can be corrected through blood transfusion and intravenous fluid.
ABO Blood Groups
There are four types of blood groups in human beings: A, B, AB and O.
These are based on types of proteins on the cell membrane of red blood cells.
There are two types of proteins denoted by the letters A and B which are antigens.
In the plasma are antibodies specific to these antigens denoted as a and b.
A person of blood group A has A antigens on the red blood cells and b antibodies in plasma.
A person of blood group B has B antigens on red blood cells and a antibodies in plasma.
A person of blood group AB has A and B antigens on red blood cells and no antibodies in plasma.
A person of blood group a has no antigens on red blood cells and a and b antibodies in plasma. 

​Blood transfusion is the transfer of blood from a donor to the circulatory system of the recipient.
A recipient will receive blood from a donor if the recipient has no corresponding antibodies to the donor's antigens.
If the donor's blood and the recipient's blood are not compatible, agglutination occurs whereby red blood cells clump together.
Blood typing
A person of blood group 0 can donate blood to a person of any other blood group.
A person of blood group 0 is called a universal donor.
A person of blood group AB can receive blood from any other group.
A person with blood group AB is called a universal recipient.
A person of blood group A can only donate blood to another person with blood group A or a person with blood group AB.
A person of blood group B can only donate blood to somebody with blood group B or a person with blood group AB.
A person with blood group AB can only donate blood to a person with blood groupAB.
Blood screening has become a very important step in controlling HIV/AIDS.
It is therefore important to properly screen blood before any transfusion is done.
Rhesus factor
The Rhesus factor is present in individuals with the Rhesus antigen in their red blood cells.
Such individuals are said to be Rhesus positive (Rh+), while those without the antigen are Rhesus negative (Rh-).
If blood from an Rh+ individual is introduced into a person who is Rh- , the latter develops antibodies against the Rhesus factor.
There may not be any reaction after this transfusion.
However a subsequent transfusion with Rh+ blood causes a severe reaction, and agglutination occurs i.e. clumping of red blood cells.
The clump can block the flow of blood, and cause death.
Erythroblastosis foetalis (haemolytic disease of the newborn) results when an Rh- mother carries an Rh+ foetus.
This arises when the father is Rh+.
During the latter stage of pregnancy, fragments of Rhesus positive red blood cells of the foetus may enter mother's circulation.
These cause the mother to produce Rhesus antibodies which can pass across the placenta to the foetus and destroy foetal red blood cells.
During the first pregnancy, enough antibodies are not formed to affect the foetus.
Subsequent pregnancies result in rapid production of Rhesus antibodies by the mother.
These destroy the red blood cells of the foetus, the condition called haemolytic disease of the newborn.
The baby is born anaemic and with yellow eyes (jaundiced).
The condition can be corrected by a complete replacement of baby's blood with safe healthy blood.
Lymphatic System
The lymphatic system consists of lymph vessels.
Lymph vessels have valves to ensure unidirectional movement of lymph.
Lymph is excess tissue fluid i.e. blood minus blood cells and plasma proteins.
Flow of lymph is assisted by breathing and muscular contractions.
Swellings called lymph glands occur at certain points along the lymph vessels.
Lymph glands are oval bodies consisting of connective tissues and lymph spaces.
The lymph spaces contain lymphocytes which are phagocytic.
Lymph has the same composition as blood except that it does not contain red blood cells and plasma proteins.
Lymph is excess tissue fluid.
Excess tissue fluid is drained into lymph vessels by hydrostatic pressure.
The lymph vessels unite to form major lymphatic system.
The main lymph vessels empty the contents into sub-clavian veins which take it to the heart.
Immune Responses
Immune response is the production of antibodies in response to antigens.
An antigen is any foreign material or organism that is introduced into the body and causes the production of antibodies.
Antigens are protein in nature.
An antibody is a protein whose structure is complementary to the antigen.
This means that a specific antibody deals with a specific antigen to make it harmless.
When harmful organisms or proteins invade the body, lymphocytes produce complementary antibodies, while bone marrow and thymus gland produce more phagocytes and lymphocytes respectively.
Types of Immunity
There are two types of immunity; natural and artificial.
Natural Immunity is also called innate immunity.
It is inherited from parent to offspring.
Artificial Immunity can be natural or induced.
When attacked by diseases like chicken pox, measles and mumps, those who recover from these diseases develop resistance to any subsequent infections of the same diseases.
This is natural acquired immunity.
Artificial Acquired Immunity:
When attenuated (weakened) or dead microorganisms are introduced into a healthy person.
The lymphocytes synthesis the antibodies which are released into the lymph and eventually reach the blood.
The antibodies destroy the invading organisms.
The body retains 'memory' of the structure of antigen.
Rapid response is ensured in subsequent infections.
Vaccines generally contain attenuated disease causing organisms. 

​Artificial Passive Acquired Immunity:
Serum containing antibodies is obtained from another organism, and confers immunity for a short duration.
Such immunity is said to be passive because the body is not activated to produce the antibodies.
Importance of Vaccination
A vaccine is made of attenuated, dead or non-virulent micro-organism that stimulate cells in the immune system to recognise and attack disease causing agent through production of antibodies.
Vaccination protects individuals from infections of many diseases like smallpox, tuberculosis and poliomyelitis.
Diseases like smallpox, tuberculosis and tetanus were killer diseases but this is no longer the case.
Diphtheria Pertussis Tetanus (DPT) vaccine protects children against diphtheria, whooping cough and tetanus.
Bacille Calmette Guerin (BCG) vaccine is injected at birth to children to protect them against tuberculosis.
Measles used to be a killer disease but today, a vaccine injected into children at the age of rune months prevents it.
At birth children are given an inoculation through the mouth of the poliomyelitis vaccine.
Allergic Reactions
An allergy is a hypersensitive reaction to an antigen by the body.
The antibody reacts with the antigen violently.
People with allergies are oversensitive to foreign materials like dust, pollen grains, some foods, some drugs and some air pollutants.
Allergic reactions lead to production of histamine by the body.
Histamine causes swelling and pain.
Allergic reactions can be controlled by avoiding the allergen and administration of anti-histamine drugs. 

Previous Topic

TOPIC 6 - TRANSPORT IN PLANTS AND ANIMALS [KCSE NOTES].pdf
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Meaning, importance and types of nutrition
Nutrition in plants (autotrophism)
Definition of photosynthesis and its importance in nature

1. Adaptations of leaf to photosynthesis
2. Structure and function of chloroplast
3. Process of photosynthesis - light and dark stages (omit details of electron transport system and chemical details of carbon dioxide fixation)
4. Factors influencing photosynthesis
   1. Light intensity
   2. Carbon dioxide concentration
   3. Water
   4. Temperature
   5. Chemical compounds which constitute living organisms
   6. Chemical composition and functions of carbohydrates, proteins and lipids (omit details of chemical structure of these compounds and mineral salts in plant nutrition).
5. Properties and functions of enzymes (omit lock and key hypothesis)
6. Nutrition in Animals (heterotrophism)
7. Meaning and types of heterotrophism
8. Modes of feeding in animals
9. Dentition of a named carnivorous, herbivorous and omnivorous mammal
10. Adaptation of the three types of dentition to feeding
11. Internal structure of mammalian teeth
12. Common dental diseases, their causes and treatment
13. Digestive system and digestion in a mammal (human)
14. Digestive system, regions, glands and organs associated with digestion
15. Ingestion, digestion, absorption, assimilation and egestion
16. Importance of vitamins, mineral salts, roughage and water in human nutrition
17. Factors determining energy requirements in humans

Practical activities

1. Carry out experiments on factors affecting photosynthesis
2. Observe stomata distribution
3. Carry out food test experiments
4. Carry out experiments on factors affecting enzymatic activities
5. Investigate presence of enzymes in living tissues (plants and animals)
6. Observe, identify, draw and label different types of mammalian teeth
7. Carry out dissection of a small mammal to observe digestive system and associated organs (demonstration)

By the end of the topic, the learner should be able to:

1. Define nutrition and state its importance in living organisms
2. Differentiate various modes of feeding
3. Describe photosynthesis and show its importance in nature
4. Explain how the leaf is adapted to photosynthesis
5. Explain the factors affecting photosynthesis
6. Distinguish between carbohydrates proteins and lipids
7. State the importance of various chemical compounds in plants and animals
8. Explain the properties and functions of enzymes
9. Relate various types of teeth in mammals to their feeding habits
10. Differentiate between omnivorous, carnivorous and herbivorous modes of feeding
11. Relate the structures of the mammalian (human) alimentary canal to their functions
12. Explain the role of enzymes in digestion in a mammal (human)
13. Explain the factors that determine energy requirements in humans.

​External Structure 
The external structure of the leaf consists of a leaf stalk or petiole and a broad leaf blade or lamina.
The lamina has a main vein midrib from which smaller veins originate.
The outline of the leaf is the margin and the tip forms the apex.

​Epidermis
This is the outer layer of cells, normally one cell thick.
It is found in both the upper and lower leaf surfaces.
The cells are arranged end to end.
The epidermis offers protection and maintains the shape of the leaf.
It is covered by a layer of cuticle which reduces evaporation.

Leaf Mesophyll
Consists of the palisade layer, next to upper epidermis, and the spongy layer next to the lower epidermis. 

Palisade Mesophyll Layer
The cells are elongated and arranged close to each other leaving narrow air spaces.
These contain numerous chloroplasts and are the main photosynthetic cells.
In most plants, the chloroplast are distributed fairly uniformly throughout the cytoplasm.
In certain plants growing in shaded habitats in dim light, most chloroplasts migrate to the upper region of the palisade cells in order to maximize absorption of the limited light available.

Spongy Mesophyll Layer
The cells are spherical in shape.
They are loosely arranged, with large intercellular spaces between them.
The spaces are air-filled and are linked to the stomatal pores.
The spongy mesophyll cells have fewer chloroplasts than the palisade mesophyll cells.

Vascular Bundles
These are made up of the xylem and the phloem tissues.
The xylem transports water and mineral salts to the leaves.
The phloem transports food manufactured in the leaf to the other parts of the plant and from storage organs to other parts.

Adaptations of Leaf for Photosynthesis
Presence of veins with vascular bundles.
Xylem vessels transport water for photosynthesis.
Phloem transports manufactured food from leaves to other parts of the plant.
Leaf lamina is thin to allow for penetration of light over short distance to reach photosynthetic cells.
Broad lamina provides a large surface area for absorption of light and carbon (IV) oxide.
Transparent cuticle and epidermal layer allow light to penetrate to mesophyll cells.
Palisade cells are close to the upper epidermis for maximum light absorption.
Presence of numerous chloroplasts in palisade mesophyll traps maximum light.
Chloroplast contain chlorophyll that traps light energy.
Spongy mesophyll layer has large intercellular air spaces allowing for gaseous exchange.
Presence of stomata for efficient gaseous exchange (entry of carbon (IV) oxide into leaf and exit of oxygen).
Mosaic arrangement of leaves to ensure no overlapping of leaves hence every leaf is exposed to light.

Structure and Function of Chloroplasts
Chloroplasts are large organelles (5 um in diameter) found in the cytoplasm of green plant cells.
They are visible under the light microscope.
They contain chlorophyll, a green pigment and other carotenoids which are yellow, orange and red in colour.
Certain plants have red or purple leaves due to abundance of these other pigments.
Chlorophyll absorbs light energy and transforms it into chemical energy.
The other pigments absorb light but only to pass it onto chlorophyll.

​The wall of chloroplast consists of an outer and an inner membrane.
The two make up the chloroplast envelop.
Inner membrane encloses a system of membranes called lamellae.
At intervals, the membranes form stacks of fluid filed sacs known as grana (singular granum).
Chloroplast and other pigments are attached to the grana.
In between the lamellae is a gel-like stroma that contains starch grains and lipid droplets.
Enzymes for the dark stage reaction (light independent stage) are embedded in the stroma.
Enzymes for the light dependent stage occur in the grana.

Functions of Chloroplast
Absorption of light by chlorophyll and other pigments.
Light stage of photosynthesis occurs on the grana. (Transformation of light energy to chemical energy.)
Carbon fixation to form carbohydrate takes place in the stroma which has enzymes for dark stage of photosynthesis.

​The reaction occurs in two main phases or stages.
The initial state requires light and it is called the light dependent stage or simply light stage.
It takes place on the lamellae surfaces.
Its products are used in the dark stage.
The dark stage does not require light although it occurs in the light and is called light independent stage.

Light-Stage
Two reactions take place that produce raw materials for the dark stage:
Light energy splits the water molecules into hydrogen and oxygen.
This process is called photolysis.
The hydrogen is taken up by a hydrogen acceptor called Nicotinamide adenine dinucleotide phosphate (NADP) while oxygen is released as a by-product.

​Light energy strikes the chlorophyll molecules and sets in motion a series of reactions resulting in the production of a high energy molecule called adenosine triphosphate (ATP).

​Dark Stage
This stage involves the fixation of carbon i.e. the reduction of carbon (IV) oxide by addition of hydrogen to form carbohydrate.
It uses the products formed during the light stage. Carbon (IV) oxide + Hydrogen = Carbohydrates
The synthesis of carbohydrates does not take place in a simple straight line reaction as shown in the equation above.
It involves a series of steps that constitute what is known as the Calvin cycle.
Carbon (IV) oxide is taken up by a compound described as a carbon (IV) oxide acceptor.
This is a 5-carbon compound known as ribulose biphosphate and a six carbon compound is formed which is unstable and splits into two three-carbon compounds.
Hydrogen from the light reaction is added to the three carbon compound using energy (ATP) from the light reaction.
The result is a three carbon (triose) sugar, (phosphoglycerate or PGA).
This is the first product of photosynthesis.
Glucose, other sugars as well as starch are made from condensation of the triose sugar molecules.
The first product is a 3-carbon sugar which condenses to form glucose (6-C sugar).
From glucose, sucrose and eventually starch is made.
Sucrose is the form in which carbohydrate is transported from the leaves to other parts of the plant. 
Starch is the storage product.
Other substances like oils and proteins are made from sugars.
This involves incorporation of other elements e.g. nitrogen, phosphorus and sulphur.

​Certain factors must be provided for before photosynthesis can take place.
The rate or amount of photosynthesis is also influenced by the quantity or quality of these same factors. 

Carbon (IV) Oxide Concentration
Carbon (IV) oxide is one of the raw materials for photosynthesis.
No starch is formed when leaves are enclosed in an atmosphere without carbon (IV) oxide.
The concentration of carbon (IV) oxide in the atmosphere remains fairly constant at about 0.03% by volume.
However, it is possible to vary the carbon (IV) oxide concentration under experimental conditions.
Increasing the carbon (IV) oxide concentration up to 0.1 % increases the rate of photosynthesis.
Further increase reduces the rate.

Light Intensity
Light supplies the energy for photosynthesis.
Plants kept in the dark do not form starch.
Generally, increase in light intensity up to a certain optimum, increases the rate of photosynthesis.
The optimum depends on the habitat of the plant.
Plants that grow in shady places have a lower optimum than those that grow in sunny places.
Water
Water is necessary as a raw material for photosynthesis.
The amount of water available greatly affects the rate of photosynthesis.
The more water available, the more the photosynthetic rate, hence amount of food made.
Effect of water on photosynthesis can only be inferred from the yield of crops.
It is the main determinant of yield (limiting factor in the tropics).
Temperature
The reactions involved in photosynthesis are catalysed by a series of enzymes.
A suitable temperature is therefore necessary.
The optimum temperature for photosynthesis in most plants is around 300C.
This depends on the natural habitat of the plant.
Some plants in temperate regions have 20°C as their optimum while others in the tropics have 45°C as their optimum temperature.
The rate of photosynthesis decreases with a decrease in temperature below the optimum.
In most plants, photosynthesis stops when temperatures approach O°C although some arctic plant species can photosynthesise at -2°C or even -3°C.
Likewise, increase in temperature above the optimum decreases the rate and finally the reactions stop at temperatures above 40°c due to enzyme denaturation.
However, certain algae that live in hot springs e.g. Oscilatoria can photosynthesis at 75°C
Chlorophyll
Chlorophyll traps or harnesses the energy from light.
Leaves without chlorophyll do not form starch.
Chemical Compounds Which Constitute Living Organisms
All matter is made up of chemical elements, each of which exists in the form of smaller units called atoms.
Some of the elements occur in large amounts in living things.
These include carbon, oxygen, hydrogen, nitrogen, sulphur and phosphorus.
Elements combine together to form compounds.
Some of these compounds are organic.
Organic compounds contain atoms of carbon combined with hydrogen and they are usually complex.
Other compounds are inorganic.
Most inorganic compounds do not contain carbon and hydrogen and they are usually less complex.
Cells contain hundreds of different classes of organic compounds.
However, there are four classes of organic compounds found in all cells.
These are: carbohydrates, lipids, proteins and nucleic acids.
Carbohydrates

• Carbohydrates are compounds of carbon, hydrogen and oxygen.
• Hydrogen and oxygen occur in the ratio of 2: 1 as in water.
• Carbohydrates are classified into three main groups: monosaccharides, disaccharides and polysaccharides.

Monosaccharides

• These are simple sugars.
• The carbon atoms in these sugars form a chain to which hydrogen and oxygen atoms are attached.
• Monosaccharides are classified according to the number of carbon atoms they possess.
• The most common monosaccharides are:
  • Glucose - found free in fruits and vegetables.
  • Fructose - found free in fruits and in bee honey.
  • Galactose - found combined in milk sugar.
• The general formula for these monosaccharides is (CH2O)n where n is 6.
• They have the same number of carbon, hydrogen and oxygen molecules i.e. C6H12O6.

Properties of Monosaccharides

• They are soluble in water.
• They are crystallisable.
• They are sweet.
• The are all reducing sugars.
• This is because they reduce blue copper (II) sulphate solution when heated to copper oxide which is red in colour and insoluble.

Functions of Monosaccharides

• They are oxidised in the cells to produce energy during respiration.
• Formation of important biological molecules e.g. deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
• Some monosaccharides are important metabolic intermediates e.g. in photosynthesis and in respiration.
• Monosaccharides are the units from which other more complex sugars are formed through condensation.

Disaccharides

• These contain two monosaccharide units.
• The chemical process through which a large molecule (e.g. a disaccharide) is formed from smaller molecules is called condensation and it involves loss of water.
• Common examples of disaccharides include sucrose, maltose and lactose.

​Disaccharides are broken into their monosaccharide units by heating with dilute hydrochloric acid.
This is known as hydrolysis and involves addition of water molecules.
The same process takes place inside cells through enzymes.
Sucrose + water + hydrolysis = glucose + fructose

Properties of Disaccharides

• Sweet tasting.
• Soluble in water.
• Crystallisable.
• Maltose and lactose are reducing sugars while sucrose is non-reducing sugar.
• Sucrose is the form in which carbohydrate is transported in plants:
• This is because it is soluble and chernically stable.
• Sucrose is a storage carbohydrate in some plants e.g. sugar-cane and sugar-beet.
• Disaccharides are hydrolysed to produce monosaccharide units which are readily metabolised by cell to provide energy.

Polysaccharides

• If many monosaccharides are joined together through condensation, a polysaccharide is formed.
• Polysaccharides may consist of hundreds or even thousands of monosaccharide units.

Examples of polysaccharides:

• Starch - storage material in plants.
• Glycogen is a storage carbohydrate in animals like starch, but has longer chains.
• Inulin - a storage carbohydrate in some plants e.g. Dahlia.
• Cellulose - structural carbohydrate in plants.
• Chitin - forms exoskeleton in arthropods.

Importance and Functions of Polysaccharides
They are storage carbohydrates - starch in plants glycogen in animals.
They are hydrolysed to their constituent monosaccharide units and used for respiration. 
They form structural material e.g. cellulose makes cell walls.
Cellulose has wide commercial uses e.g.

• Fibre in cloth industry.
• Cellulose is used to make paper.
• Carbohydrates combine with other molecules to form important structural compounds in living organisms.

Examples are:
Pectins: Combine with calcium ions to form calcium pectate.
Chitin: Combine with (NH) group. Makes the exoskeleton of arthropods, and walls of fungi.

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1. Define nutrition
2. State the importance of nutrition
3. Differentiate the various modes of feeding
4. Define photosynthesis
5. State the importance of photosynthesis
6. Describe the structure and function of chloroplast
7. Give a word equation for photosynthesis
8. describe briefly the process of photosynthesis in plants
9. describe factors that cause high rate of photosynthesis
10. Give the differences between the light and dark reactions during photosynthesis
11. What are chemicals of life?
12. What are organic compounds?
13. List the organic compounds
14. What are carbohydrates?
15. Name the groups of carbohydrates
16. State the general functions of carbohydrates
17. what are proteins?
18. Name the types of amino acids
19. State the classes of proteins
20. Give the functions of proteins
21. What are lipids
22. Name the types of lipids
23. What are the building blocks of lipids?
24. State the functions of lipids
25. What are enzymes?
26. State the properties of enzymes
27. State the factors that affect enzyme action
28. Name the types of enzyme inhibitors
29. What are the functions of enzymes?
30. Explain the various types of heterotrophic nutrition
31. Differentiate between omnivorous, carnivorous and herbivorous modes of nutrition
32. What is dentition?
33. Distinguish between the terms homodont and heterodont
34. Name the types of teeth found in mammals
35. Describe the adaptations and functions of various types of mammalian teeth
36. Draw a labeled diagram to represent internal structure of a mammalian tooth

• This is a mode of nutrition whereby organisms feed on complex organic matter from other plants or animals.
• All animals are heterotrophs.
• Their mode of feeding is also said to be holozoic to distinguish it from other special types of heterotrophic nutrition namely:
  • Saprophytism
  • Parasitism
• Saprophytism/saprotrophysim- occurs in most fungi and some forms of bacteria.
• Saprophytes feed on dead organic matter and cause its decomposition or decay.
• Parasitism is a mode of feeding whereby one organism called the parasite feeds on or lives in another organism called the host and harms it. 

1. Animals have developed various structures to capture and ingest food.
2. The type of structures present depend on the method of feeding and the type of food.
3. Carnivorous animals feed on whole animals or portions of their flesh.
4. Herbivorous animals feed on plant material.
5. Omnivorous animals feed on both plants and animal materials.

• The jaws and teeth of mammals are modified according to the type of food eaten.
• Mammals have different kinds of teeth.
• Each type of teeth has a particular role to play in the feeding process.

• The jaws and teeth of mammals are modified according to the type of food eaten.
• Mammals have different kinds of teeth.
• Each type of teeth has a particular role to play in the feeding process.

• The jaws and teeth of mammals are modified according to the type of food eaten.
• Mammals have different kinds of teeth.
• Each type of teeth has a particular role to play in the feeding process.
• This condition is described as heterodont.
• The teeth of reptiles and amphibians are all similar in shape and carry out the same function.
• They are said to be homodont. 

• Mammals have four kinds of teeth.
• The incisors are found at the front of the jaw.
• They are sharp-edged and are used for biting.
• The canines are located at the sides of the jaw.
• They are pointed and are used for tearing and piercing.
• The premolars are next to the canines and the molars are at the back of the jaw.
• Both premolars and molars are used for crushing and grinding.
• Teeth are replaced only once in a lifetime.
• The first set is the milk or deciduous teeth.
• These are replaced by the second set or the permanent teeth.

• Dentition refers to the type of teeth, the number and their arrangement in the jaw.
• A dental formula shows the type and number of teeth in each half of the jaw.
• The number of teeth in half of the upper jaw is represented above a line and those on the lower jaw below the line.
• The first letter of each type of teeth is used in the formula i.e. i = incisors, c = canines, pm = premolars and m = molars.
• The total number is obtained by multiplying by two (for the two halves of each jaw).

Adaptation of Teeth to Feeding
In general, incisors are for cutting, canines for tearing while premolars and molars are for grinding.
However, specific modifications are observed in different mammals as an adaptation to the type of food they eat.
Teeth of Herbivores

• Incisors are long and flat with a sharp chisel like edge for cutting.
• The enamel coating is thicker in front than at the back so that as the tooth wears out, a sharp edge is maintained.
• Canines are reduced or absent.
• If absent, the space left is called the diastema.
• The diastema allows the tongue to hold food and push it to the grinding teeth at the back of the mouth.

Premolars and molars:

• These are transversely ridged.
• The ridges on the upper teeth fit into grooves on the lower ones.
• This gives a sideways grinding surface.
• The teeth of herbivores have open roots i.e., wide opening into the pulp cavity.
• This ensures a continued adequate supply of food and oxygen to the tooth.
• In some herbivores, such as rabbits and elephants, the incisors continue to grow throughout life.

Teeth of Carnivores

• Incisors are reduced in size and pointed.
• They are well suited for grasping food and holding prey.
• Canines are long, pointed and curved.
• They are used for piercing and tearing flesh as well as for attack and defence.
• Premolars and molars: In general, they are long and longitudinally ridged to increase surface area for crushing.
• Carnassial Teeth: These are the last premolars on the upper jaw and the first molars on the lower one.
• They are enlarged for cutting flesh.
• They act as a pair of shears.
• They also crush bones.
• The teeth of carnivores have closed roots i.e., only a very small opening of the pulp cavity to allow food and oxygen to keep teeth alive.
• Once broken, no re-growth can take place.

Teeth of Omnivores

• Incisors have a wide surface for cutting.
• Canines are bluntly pointed for tearing.
• Premolars and molars have cusps for crushing and grinding.
• The premolars have two blunt cusps while the molars have three to four.

​The tooth consists of two main parts:
Crown: The portion above the gum; it is covered by the enamel.
Root: The portion below the gum; it is covered by the cement.
The tooth has two roots.
Neck: Is the region at the same level with the gum.

• It forms the junction between the crown and the root.
• It is covered by enamel. Incisors and canines have one root only.
• Premolars have one or two roots while molars have two to three roots each.
• Internally, the bulk of the tooth is made up of dentine which consists of living cells and extends to the root.
• It is composed of calcium salts, collagen and water.
• It is harder than bone but wears out with use.
• This is why it is covered by enamel which is the hardest substance in a mammal's body.

Pulp Cavity: Contains blood vessels which provide nutrients to the dentine and remove waste products. It also contains nerve endings which detect heat, cold and pain.
Cement: Fixes the tooth firmly to the jaw bone.

Dental Carries
Dental carries are the holes or cavities that are formed as acid corrodes enamel and eventually the dentine.
Causes

• This is caused by bacteria acting on the food left between teeth and on the cusp.
• Acids are formed that eventually corrode the enamel.
• The pulp cavity is eventually reached.
• A lot of pain is experienced then.
• The bacteria then infect the pulp cavity and the whole tooth decays.

Treatment
Treatment depends on the extent of the dental caries:
Extraction of Tooth.
Filling
This involves replacing the dentine with amalgam, a mixture of hard elements e.g. silver and tin.
Root Canal Treatment
This involves surgery and reconstruction.
It saves severely damaged teeth.
The nerves in the root canal are surgically severed.
The tooth is cleaned and filled up with amalgam.
Periodontal Diseases

• These are diseases of the gum.
• The gum becomes inflamed, and starts bleeding.
• Progression of the disease leads to infection of the fibres in the periodontal membranes and the tooth becomes loose.
• This condition is known as pyorrhoea.
• The diseases are caused by poor cleaning of the teeth.
• The accumulation of food particles leading to formation of plaque, lack of adequate vitamin A and C in the diet.

Treatment

• Nutrition - by taking adequate balanced diet rich in vitamins A and C.
• Antibiotics are used to kill bacteria.
• Anti-inflammatory drugs are given.
• Antiseptic is prescribed to use in cleaning the mouth daily to prevent further proliferation of bacteria.
• The plaque is removed-drilled away - a procedure known as scaling.

In order to maintain healthy teeth the following points should be observed:

• A proper diet that includes calcium and vitamins, particularly vitamin D is essential.
• The diet should also contain very small quantities of fluorine to strengthen the enamel.
• Large quantities of fluorine are harmful.
• The enamel becomes brown, a condition known as dental fluorosis.
• Chewing of hard fibrous foods like carrots and sugar cane to strengthen and cleanse the teeth.
• Proper use of teeth e.g. not using teeth to open bottles and cut thread.
• Regular and thorough brushing of teeth after meals.
• Dental floss can be used to clean between the teeth.
• Not eating sweets and sugary foods between meals.
• Regular visits to the dentist for checkups.
• Washing the mouth with strong salt solution or with any other mouth wash with antiseptic properties. 

Digestive System and Digestion in Humans
Organs that are involved with feeding in humans constitute the digestive system.
Digestive System and Associated Glands

• Human digestive system starts at the mouth and ends at the anus.
• This is the alimentary canal.
• Digestion takes place inside the lumen of the alimentary canal.
• The epithelial wall that faces the lumen has mucus glands (goblet cells).
• These secrete mucus that lubricate food and prevent the wall from being digested by digestive enzymes.
• Present at specific regions are glands that secrete digestive enzymes.
• The liver and pancreas are organs that are closely associated with the alimentary canal.
• Their secretions get into the lumen and assist in digestions.

Digestive system consists of:

• Mouth.
• Oesophagus.
• Stomach.
• Small intestines - consist of duodenum, the first part next to the stomach, ileum - the last part that ends up in a vestigial caecum and appendix which are nonfunctional.
• Large intestines consist of: colon and rectum that ends in the anus. 

Ingestion, Digestion and Absorption

• Feeding in humans involves the following processes:
• Ingestion: This is the introduction of the food into the mouth.
• Digestion: This is the mechanical and chemical breakdown of the food into simpler, soluble and absorbable units.
• Absorption: Taking into blood the digested products.
• Assimilation: Use of food in body cells.
• Mechanical breakdown of the food takes place with the help of the teeth.
• Chemical digestion involves enzymes.

Digestion in the Mouth

• In the mouth, both mechanical and chemical digestion takes place.
• Food is mixed with saliva and is broken into smaller particles by the action of teeth.
• Saliva contains the enzyme amylase.
• It also contains water and mucus which lubricate and soften food in order to make swallowing easy.
• Saliva is slightly alkaline and thus provides a suitable pH for amylase to act on cooked starch, changing it to maltose.
• The food is then swallowed in the form of semisolid balls known as boluses.
• Each bolus moves down the oesophagus by a process known as peristalsis.
• Circular and longitudinal muscles along the wall of the alimentary canal contract and relax pushing the food along.

Digestion in the Stomach

• In the stomach, the food is mixed with gastric juice secreted by gastric glands in the stomach wall.
• Gastric juice contains pepsin, rennin and hydrochloric acid.
• The acid provides a low pH of 1.5-2.0 suitable for the action of pepsin.
• Pepsin breaks down protein into peptides.
• Rennin coagulates the milk protein casein.
• The stomach wall has strong circular and longitudinal muscles whose contraction mixes the food with digestive juices in the stomach. 

Digestion in the Duodenum

• In the duodenum the food is mixed with bile and pancreatic juice.
• Bile contains bile salts and bile pigments.
• The salts emulsify fats, thus providing a large surface area for action of lipase.
• Pancreatic juice contains three enzymes:
  • Trypsin which breaks down proteins into peptides and amino acids,
  • Amylase which breaks down starch into maltose, and
  • Lipase which breaks down lipids into fatty acids and glycerol.
• These enzymes act best in an alkaline medium which is provided for by the bile.

Digestion in ileum

• Epithelial cells in ileum secrete intestinal juice, also known as succus entericus.
• This contains enzymes which complete the digestion of protein into amino acids, carbohydrates into monosaccharides and lipids into fatty acids and glycerol.

Absorption

• This is the diffusion of the products of digestion into the blood of the animal.
• It takes place mainly in the small intestines though alcohol and some glucose are absorbed in the stomach.

The ileum is adapted for absorption in the following ways:

• It is highly coiled.
• The coiling ensures that food moves along slowly to allow time for its digestion and absorption.
• It is long to provide a large surface area for absorption.
• The epithelium has many finger-like projections called villi (singular villus).
• They greatly increase the surface area for absorption.
• Villi have microvilli that further increase the surface area for absorption.
• The wall of villi has thin epithelial lining to facilitate fast diffusion of products of digestion.
• Has numerous blood vessels for transport of the end products of digestion.
• Has lacteal vessels; for absorption of fatty acids and glycerol and transport of lipids.

Absorption of Glucose and Amino Acids

• Glucose and other monosaccharides as well as amino acids are absorbed through the villi epithelium and directly into the blood capillaries.
• First they are carried to the liver through the hepatic portal vein, then taken to all organs via circulatory system. 

Absorption of Fatty Acids and Glycerol

• Fatty acids and glycerol diffuse through the epithelial cells of villi and into the lacteal.
• When inside the villi epithelial cells, the fatty acids combine with glycerol to make tiny fat droplets which give the lacteal a milky appearance.
• The lacteals join the main lymph vessel that empties its contents into the bloodstream in the thoracic region.
• Once inside the blood, the lipid droplets are hydrolysed to fatty acids and glycerol.

Absorption of Vitamins and Mineral Salts

• Vitamins and mineral salts are absorbed into the blood capillaries in' the villi. Water is mainly absorbed in the colon.
• As a result the undigested food is in a semi-solid form (faeces) when it reaches the rectum.
• Egestion: This is removal of undigested or indigestible material from the body. Faeces are temporarily stored in the rectum then voided through the anus. Opening of the anus is controlled by sphincter muscles
• Assimilation: This is the incorporation of the food into the cells where it is used for various chemical processes.

Carbohydrates

• Carbohydrates are used to provide energy for the body.
• Excess glucose is converted to glycogen and stored in the liver and muscles.
• Some of the excess carbohydrates are also converted into fat in the liver and stored in the adipose tissue' (fat storage tissue), in the mesenteries and in the connective tissue under the skin, around the heart and other internal organs.

Proteins

• Amino acids are used to build new cells and repair worn out ones.
• They are also used for the synthesis of protein compounds.
• Excess amino acids are deaminated in the liver.
• Urea is formed from the nitrogen part.
• The remaining carbohydrate portion is used for energy or it is converted to glycogen or fat and stored.

Lipids

• Fats are primarily stored in the fat storage tissues.
• When carbohydrates intake is low in the body, fats are oxidised to provide energy.
• They are also used as structural materials e.g. phospholipids in cell membrane. They act as cushion, protecting delicate organs like the heart.
• Stored fats under the skin act as heat insulators.

Vitamins

• These are organic compounds that are essential for proper growth, development and functioning of the body.
• Vitamins are required in very small quantities.
• They are not stored and must be included in the diet.
• Vitamins Band C are soluble in water, the rest are soluble in fat.
• Various vitamins are used in different ways.

Mineral Salts

• Mineral ions are needed in the human body.
• Some are needed in small amounts while others are needed in very small amounts (trace).
• All are vital to human health.
• Nevertheless, their absence results in noticeable malfunction of the body processes.

Water

• Water is a constituent of blood and intercellular fluid.
• It is also a constituent of cytoplasm.
• Water makes up to 60-70% of total fresh weight in humans.
• No life can exist without water.

Functions of Water

• Acts as a medium in which chemical reactions in the body takes place.
• Acts as a solvent and it is used to transport materials within the body.
• Acts as a coolant due to its high latent heat of vaporisation.
• Hence, evaporation of sweat lowers body temperature.
• Takes part in chemical reactions i.e. hydrolysis. 

Roughage

• Roughage is dietary fibre and it consists mainly of cellulose.
• It adds bulk to the food and provides grip for the gut muscles to enhance peristalsis.
• Roughage does not provide any nutritional value because humans and all animals not produce cellulase enzyme to digest cellulose.
• In herbivores symbiotic bacteria in the gut produce cellulase that digests cellulose.

Factors Determining Energy Requirements in Humans

• Age: Infants, for instance, need a greater proportion of protein than adults.
• Sex: males generally require more carbohydrates than females.
• The requirements of specific nutrients for females depends on the stage of development in the life cycle.
• Adolescent girls require more iron in their diet; expectant and nursing mothers require a lot of proteins and mineral salts.
• State of Health: A sick individual requires more of certain nutrients e.g. proteins, than a healthy one.
• Occupation: An office worker needs less nutrients than a manual worker.

Balanced Diet
A diet is balanced when it contains all the body's nutrient requirements and in the right amounts or proportions.
A balanced diet should contain the following:

• Carbohydrates
• Proteins
• Lipids
• Vitamins
• Mineral Salts  
• Water
• Dietary fibre or roughage

Malnutrition
This is faulty or bad feeding where the intake of either less or more than the required amount of food or total lack of some food components.
Deficiency Diseases
Deficiency diseases result from prolonged absence of certain components in the diet.
Examples are:
Marasmus:
Lack of enough food results in thin arms and legs, severe loss of fluid, general body wasting, sunken eyes.
Kwashiorkor
Lack of protein in the diet of children. The symptoms of kwashiorkor include wasting of the body, red thin hair, swollen abdomen and scaly skin.
Other deficiency diseases are due to lack of accessory food factors (vitamins and mineral salts.). Such diseases include rickets, goitre and anaemia.
Treatment of these deficiency diseases is by supplying the patient with the component missing in the diet. 

• Experiments to show that Carbon (IV) Oxide is necessary for Photosynthesis
• Experiment to Show Effect of Light on Photosynthesis
• Experiment to Show the Effect of Chlorophyll on Photosynthesis
• Experiment To Observe Stomata Distribution in Different Leaves
• Test for Reducing Sugar
• Test for non-reducing sugar
• Test for Lipids;

         a)      Grease Spot Test         b)      Emulsion Test

• Test for Proteins -Biuret Test
• Experiment To Investigate Presence of Enzyme in Living Tissue
• Dissection of a Rabbit to show the Digestive System

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TOPIC 5 - NUTRITION IN PLANTS AND ANIMALS [KCSE NOTES].pdf
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By the end of the topic, the learner should be able to:

1. use the magnifying lens to observe the external features of plants and animals
2. record observations of the main external characteristics of living organisms, preserved specimens and photographs
3. state the necessity and significance of classification
4. name the major units of classification
5. state the application of Binomial nomenclature in naming organisms. 

​Introduction 
Classification is putting organisms into groups.
Classification is based on the study of external characteristics of organisms.
It involves detailed observation of structure and functions of organisms.
Organisms with similar characteristics are put in one group.
Differences in structure are used to distinguish one group from another.
The magnifying lens is an instrument that assists in the observation of fine structure e.g. hairs by enlarging them. 

A specimen is placed on the bench or held by hand,
Then the magnifying lens is moved towards the eye until the object is dearly focused and an enlarged image is seen.
The magnification can be worked out as follows:
Note: magnification has no units. 

​To be able to identify organisms into their taxonomic groups.
To enable easier and systematic study of organisms.
To show evolutionary relationships in organisms. 

​Taxonomy is the study of the characteristics of organisms for the purpose of classifying them.
The groups are Taxa (singular Taxon).
The taxonomic groups include:

1. Species: This is the smallest unit of classification. Organisms of the same species resemble each other. The number of chromosomes in their cells is the same. Members of a species interbreed to produce fertile offspring.
2. Genus (plural genera): A genus is made up of a number of species that share several characteristics. Members of a genus cannot interbreed and if they do, the offspring are infertile.
3. Family: A family is made up of a number of genera that share several characteristics.
4. Order: A number of families with common characteristics make an order.
5. Class: Orders that share a number of characteristics make up a class.
6. Phylum/Division: A number of classes with similar characteristics make up a phylum (plural phyla) in animals. In plants this is called a division.
7. Kingdom: This is made up of several phyla (in animals) or divisions (in plants). It is the largest taxonomic unit in classification. 

Some are unicellular while others are multicellular.
They have no chlorophyll.
Most are saprophytic e.g. yeasts, moulds and mushrooms.
A few are parasitic e.g. Puccinia graminae.

These are very small unicellular organisms.
They lack a nuclear membrane
do not have any bound membrane organelles.
Hence the name Prokaryota.
They are mainly bacteria, e.g. Vibrio cholerae.

​They are unicellular organisms.
Their nucleus and organelles are surrounded by membranes (eukaryotic).
They include algae, slime moulds - fungi-like and protozoa 

They are all multicellular.
They contain chlorophyll and are all autotrophic.
They include; Bryophyta (moss plant), Pteridophyta (ferns) and Spermatophyta (seed bearing plants).

​These are all multicellular and heterotrophic.
Examples are annelida (earthworms), mollusca (snails),athropoda, chordata .
Example of Arthropods are ticks, butterflies.
Members of Chordata are fish, frogs and humans. 

In plants we should look for:-
Spore capsule and rhizoids in moss plants.
Sori and fronds in ferns.
Stem, leaves, roots, flowers, fruits and seeds in plants.
In animals, some important features to look for are:
Segmentation, presence of limbs and, number of body parts, presence and number of antennae. These are found in phylum arthropoda:
Visceral clefts, notochord, nerve tube, fur or hair, scales, fins, mammary glands, feathers and wings.
These are found in chordata. 

Organisms are known by their local names.
Scientists use scientific names to be able to communicate easily among themselves.
This method of naming uses two names, and is called Binomial nomenclature.
The first name is the name of the genus: (generic name) which starts with a capital letter.
The second name is the name of the species (specific name) which starts with a small letter.
The two names are underlined or written in italics.
Man belongs to the genus Homo, and the species, sapiens.
The scientific name of man is therefore Homo sapiens.
Maize belongs to the genus Zea, and the species mays.
The scientific name of maize is Zea mays.

​Use of Collecting Nets, Cutting Instruments and Hand Lens.
Forceps are used to collect crawling and slow moving animals.
Sweep nets are used to catch flying insects.
Cutting instrument like scapel is used to cut specimen e.g. making sections.
Hand lens is used to magnify small plants and animals.
Drawing of the magnified organism are made and the linear magnification of each calculated. 

 E.g. moss, ferns, bean.
Look for the following:
Moss plants: Rhizoids and spore capsules.
Fern plants: Rhizomes with adventitious roots; large leaves (fronds) with Sori (clusters of sporangia).
Seed plants: Tree/shrub (woody) or non-woody (herbs) e.g. bean.
Root system - fibrous, adventitious and tap root.
Stem - position and length of internodes.
Type of leaves - simple or compound; arranged as alternate, opposite or whorled.
Flower - colour, number of parts, size and relative position of each:
Fruits - fleshy or dry; edible or not edible.
Seeds - monocotyledonous or dicotyledonous.
Small animals e.g. earthworms, tick, grasshopper, butterfly, beetles.
Observe these animals to see:

1. Number of legs.
2. Presence or absence of wings.
3. Number of antennae.
4. Body covering.
5. Body parts.