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biology essay form two

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By the end of form two work, the learner should be able to:

  • Define the term transport
  • List substances transported in plants and animals
  • Link surface area to volume ratio of organisms to the transport system of the organism
  • Explain the necessity of transport in plants
  • Draw the structure of roots and root hairs
  • Relate the structure of the root to their functions
  • Observe prepared slides of roots and root hairs
  • Compare monocotyledons and dicotyledonous root sections
  • Observe charts and drawings of root sections
  • Draw and label the structure of the Xylem Vessel
  • Define Xylem Vessel
  • Relate the structure of the Xylem Vessel to its function
  • Define Tracheid elements
  • Relate the structure of the Tracheid elements to their functions
  • Distinguish between xylem vessels and Tracheid elements
  • Describe water and salt uptake by roots from the soil
  • Explain the physiological process involved in the uptake of water and mineral salts
  • Draw the monocotyledonous and dicotyledonous stem sections
  • Define the term transpiration and relate the structure of xylem to its role in transpiration
  • Draw and label the internal and the external structure of a leaf
  • Describe the functions of the leaf
  • Relate the parts of a leaf to their functions
  • Demonstrate the movement of water in plants
  • Observe prepared leaf sections to identify vascular tissues
  • Discuss the forces involved in movement of water in plants such as transpiration, pull, cohesion and adhesion capillarity and root pressures
  • Demonstrate the forces involved in movement of water in plants
  • Identify the importance of transpiration in plants
  • Discuss the importance of transpiration in plants
  • Explain what the phloem is
  • Draw the structure of the phloem and relate its structure to its function
  • List down materials translocated in the phloem
  • Draw the structure of the phloem
  • Relate the parts of the phloem to its functions
  • Discuss the function of the phloem
  • List down materials translocated and the sites of storage in the phloem
  • Set up an experiment to investigate translocation of food substances in dicotyledonous plants
  • Set up an experiment to investigate translocation of food substances in a monocotyledonous plant
  • Explain the processes involved in the translocation of food in plants Identify unicellular organisms such as amoeba
  • Describe transport of substances in unicellular organisms
  • Explain the necessity of an elaborate transport system in most animals
  • Define an open circulatory system
  • Discuss the open circulatory system
  • Draw the open circulatory system of an insect
  • Define an closed transport system
  • Identify animals with the open circulatory system
  • Distinguish between closed and open circulatory systems
  • Define an Double circulatory system
  • Draw and label circulatory systems in mammals
  • Dissect a rabbit and observe its transport system
  • Draw and label the external parts of the mammalian heart
  • Draw and label the internal structure of the mammalian heart
  • Explain the functions of the heart
  • Relate the structure of the heart to its functions
  • Trace the path taken by blood from the heart to the body parts and back to the heart
  • State the substances supported by the blood of mammals
  • Describe the flow of oxygenated blood in and out of the body through the heart
  • Explain the structure of arteries, veins and capillaries
  • Relate the structure of the arteries, veins and capillaries to their function
  • Name the common diseases of circulatory system such as thrombosis, varicose veins
  • Suggest methods of control/prevention for the diseases.
  • List the components of the blood
  • State the functions of each of the blood components
  • Explain how oxygen and carbon dioxide are transported in the blood
  • Describe the mechanisms of blood clotting and its importance
  • Describe the human blood group system
  • State the importance of blood groups in blood transfusion
  • Discuss the rhesus factor
  • State the role of the rhesus factor in blood transfusion
  • Examine the external and internal structure of a cows heart
  • Investigate pulse rate at the wrist
  • Defining immunity
  • Describe immune response
  • Differentiate between natural and artificial immunity
  • Define vaccination
  • Describe importance of vaccination against diseases such as tuberculosis, poliomyelitis, measles, diphtheria, whooping cough
  • Define allergic reactions and explain their causes
  • Carry out an experiment to demonstrate the unidirectional flow of blood in the cutaneous veins of the forearm
  • Define gaseous exchange
  • Identify the gases that are exchanged in the living organism
  • Explain the importance of gaseous exchange in organisms
  • Describe the stomata
  • Draw and label open and closed stomata
  • Explain stomata and gaseous exchange
  • Investigate the presence of stomata on leaves
  • Investigate the shape of guard cells and the distribution of stomata on leaves
  • Explain the mechanism of opening and closing of stomata
  • Describe photosynthetic/glucose accumulation theory of opening and closing stomata
  • Describe inter-conversion of starch and glucose and ion accumulation theories
  • Investigate the internal structure of stems and leaf stalk in aerial and aquatic plants
  • Investigate tissue distribution in aerial leaves and stems
  • describe Cuticular and lenticular gaseous exchange
  • Draw the structure of the root
  • Describe how gaseous exchange takes place through the epidermis of the roots
  • Examine various types of gaseous exchange structure in different organisms
  • Relate the various types of gaseous exchange structure to their functions in different organisms
  • State the characteristics of gaseous exchange surfaces in different organisms
  • Examine the gaseous exchange structures of a grasshopper or a locust
  • Draw the gaseous exchange structure of an insect
  • Draw and label the structure of gaseous exchange in bony fish
  • Relate the gills to their function
  • describe the mechanism of gaseous exchange in bony fish
  • Examine the location and number of gills in gill chambers of bony fish
  • Examine, draw and label the gill of a bony fish
  • describe the gaseous exchange I a frog through its gills, skin, mouth and lungs.
  • State the structure involved in gaseous exchange in human beings
  • Explain the features of the structures involved in gaseous exchange in human beings
  • Draw and label the structures involved in gaseous exchange in human beings
  • Examine a dissected mammal to locate the gaseous exchange structures
  • Describe the mechanism of breathing in human beings
  • Draw and label the alveoli where gaseous exchange occur in human beings
  • Describe how gaseous exchange occurs in alveoli
  • Explain how human beings are adapted to their functions
  • Able to examine the mammalian lung
  • Demonstrate the breathing mechanism of the lungs and diaphragm in a model thoracic cavity
  • Demonstrate the breathing movement of ribs and muscles by using a model
  • Examine the factors affecting the rate of breathing in human beings
  • Explain the factors which control the rate of breathing in human beings
  • State the causes of respiratory diseases
  • Discuss the symptoms of respiratory disease
  • explain the prevention measures of respiratory diseases
  • demonstrate the effect of exercise on the rate of breathing
  • Define respiration
  • State the significance of respiration
  • Draw and label mitochondria
  • Define Anaerobic respiration
  • Describe Anaerobic respiration in plants
  • Describe Anaerobic respiration in animals
  • Identify the gas given off when food is burnt
  • Investigate the gas produced during fermentation
  • State the economic importance of anaerobic respiration
  • Discuss the economic importance of anaerobic respiration in both plants and animals
  • Explain anaerobic respiration
  • Distinguish between anaerobic and aerobic respiration
  • Compare energy production in anaerobic and aerobic respiration
  • Investigate the production of heat by germinating seeds
  • Demonstrate that respiration takes place in plants
  • Show aerobic respiration in animals
  • Show the aerobic respiration takes place in animals
  • Define terms stated
  • Distinguish between excretion and egestion
  • Explain the necessity of excretion in plants and animals
  • Describe the methods of excretion in plants
  • List down useful and harmful excretory products in plants
  • Identify the uses of excretory products in plants
  • Describe the uses of excretory products in plants
  • Describe excretion and homeostasis in unicellular animals such as amoeba
  • Draw an amoeba
  • Describe excretion in fresh water amoeba
  • Explain the need for complex animals for excretion
  • List down organs involved In excretion in animals
  • List down waste products released by various organs
  • Examine the kidney of a mammal
  • Draw and label the external structure of a kidney
  • Make a vertical section through the kidney
  • Identify the internal parts of the kidney
  • Draw and label parts of the nephron
  • Relate its structure to its role in urine formation
  • Identify the hormones involved in Neuro-endoctrine system and homeostasis eg insulin
  • Explain the process of urine formation in the kidney
  • Describe the role of various hormones in urine formation
  • Describe the components and role of Neuro-endoctrine systems
  • Distinguish between internal and external environments
  • Explain the general working of the homeostatic mechanism
  • Define osmoregulation
  • Describe the role of the kidney in osmoregulation
  • Explain the role of hypothalamus in osmoregulation
  • Explain Diabetes insipidus and other common kidney diseases
  • Describe the causes of Diabetes insipidus and other common kidney diseases
  • State possible control/prevention methods of Diabetes insipidus
  • Draw and label parts of the skin
  • Relate the parts of the skin to their functions
  • Distinguish between osmoregulation and thermoregulation
  • Describe the role of the skin in osmoregulation
  • Describe the role of the skin in thermoregulation
  • Identify behavioral and physiological means of thermoregulation in animals
  • Describe behavioral and physiological means of thermoregulation in animals
  • Explain Heat loss and heat gain
  • Describe the various methods of Heat loss and heat gain in mammals
  • Explain the terms Surface area to volume ratio in relation
  • Relate the body size of mammals to heat loss and heat gain
  • Draw and label the liver and its associated parts
  • Describe the liver and its role in homeostasis
  • List down some of the functions of the liver
  • Describe the functions of the liver
  • Identify all the diseases of the liver
  • Describe the symptoms and possible control of diabetes mellitus and other liver diseases
  • Explain the causes symptoms and diseases of the liver
  • explain catalase enzyme and hydrogen peroxide
  • describe the role of catalase enzyme in breaking down hydrogen peroxide,,use liver and kidney to investigate the reaction
  • Describe the role of the liver in blood sugar control
  • Describe the role of insulin hormone
  • Explain the regulation of blood sugar
  • Describe a flow chart showing the regulation of blood sugar
  • Describe temperature regulation in other animals
  • Relate parts of the lungs to its functions
  • Draw and label parts of the lungs
  • describe the functions of the lungs as discussed during gaseous exchange
  • Identify a mammals lungs
  • Observe and describe structures of lungs in relation to functions

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  • Transport is the movement of substances within an organism.
  • All living cells require oxygen and food for various metabolic processes.
  • These substances must be transported to the cells.
  • Metabolic processes in the cells produce excretory products which should be eliminated before they accumulate.
  • The excretory products should be transported to sites of excretion.
  • Organisms like amoeba are unicellular.
  • They have a large surface area to volume ratio.
  • The body is in contact with the environment.
  • Diffusion is adequate to transport substances across the cell membrane and within the organism.
  • Large multi-cellular organisms have complex structure where cells are far from each other hence diffusion alone cannot meet the demand for supply and removal of substances.
  • Therefore an elaborate transport system is necessary.

Transport in plants

  • Simple plants such as mosses and liverworts lack specialized transport system.
  • Higher plants have specialized transport systems known as the vascular bundle.
  • Xylem transports water and mineral salts .
  • Phloem transports dissolved food substances like sugars.

Internal structure of roots and root hairs

  • The main functions of roots are ;
  • gaseous exchange.
  • The outermost layer in a root is the piliferous layer.
  • This is a special epidermis of young roots whose cells give rise to root hairs.
  • Root hairs are microscopic outgrowths of epidermal cells.
  • They are found just behind the root tip,
  • They are one cell thick for efficient absorption of substances.
  • They are numerous and elongated providing a large surface area for absorption of water and mineral salts.
  • Root hairs penetrate the soil and make close contact with it.
  • Below the piliferous layer is the cortex.
  • This is made up of loosely packed, thin walled parenchyma cells.
  • Water molecules pass through this tissue to reach the vascuiar bundles.
  • In some young plant stems, cortex cells contain chloroplasts.
  • The endodermis (starch sheath) is a single layer of cells with starch grains.
  • The endodermis has a casparian strip which has an impervious deposit controlling the entry of water and mineral salts into xylem vessels.
  • Pericyc1e forms a layer next to the endodermis.
  • Next to the pericycle is the vascular tissue.
  • In the Dicotyledonous root, xylem forms a star shape in the centre, with phloem in between the arms.
  • It has no pith. In monocotyledonous root, xylem alternates with phloem and there is a pith in the centre.

Internal structure of a root hair cell

  • The main functions of the stem are;
  • support and exposure of leaves and flowers to the environment,
  • conducting water and mineral salts
  • conducting manufactured food from leaves to other parts of the plant.
  • In monocotyledonous stems, vascular bundles are scattered all over the stem, while in dicotyledonous stems vascular bundles are arranged in a ring.
  • Vascular bundles are continuous from root to stems and leaves.
  • The epidermis forms a single layer of cells enclosing other tissues.
  • The outer walls of the cells have waxy cuticle to prevent excessive loss of water.
  • The cortex is a layer  next to the epidermis.
  • It has collenchyma, parenchyma and schlerenchyma cells.


  • Is next to the epidermis and has thickened walls at the corners which strengthen the stem.
  • Cells are irregular in shape, thin walled and loosely arranged hence creating intercellular spaces filled with air.
  • They are packing tissues and food storage areas.


  • Cells are closely connected to vascular bundles.
  • These cells are thickened by deposition of lignin and they provide support to plants .
  •   Is the central region having parenchyma cells.

Absorption of Water and Mineral Salts Absorption of Water

  • Root hair cell has solutes in the vacuole and hence a higher osmotic pressure than the surrounding soil water solution.
  • Water moves into the root hair cells by osmosis along a concentration gradient.
  • This makes the sap in the root hair cell to have a lower osmotic pressure than the surrounding cells.
  • Therefore water moves from root hair cells into the surrounding cortex cells by osmosis.
  • The process continues until the water gets into the xylem vessels .

Uptake of Mineral Salts

  • If the concentration of mineral salts in solution is greater than its concentration in root hair cell, the mineral salts enter the root hair cell by diffusion.
  • If the concentration of mineral salts in the root hair cells is greater than in the soil water, the mineral salts enter the root hairs by active transport.
  • Most minerals are absorbed in this way.
  • Mineral salts move from cell to cell by active transport until they reach the xylem vessel.
  • Once inside the xylem vessels, mineral salts are transported in solution as the water moves up due to root pressure, capillary attraction and cohesion and adhesion forces.


  • Transpiration is the process by which plants lose water in the form of water vapour into the atmosphere.
  • Water is lost through stomata, cuticle and lenticels.
  • Stomatal transpiration :
  • This accounts for 80-90% of the total transpiration in plants.
  • Stomata are found on the leaves.
  • Cuticular transpiration:
  • The cuticle is found on the leaves, and a little water is lost through it.
  • Plants with thick cuticles do not lose water through the cuticle.
  • Lenticular transpiration
  • Is loss’ of water through lenticels.
  • These are found on stems of woody plants.
  • Water lost through the stomata and cuticle by evaporation leads to evaporation of water from surfaces of mesophyll cells .
  • The mesophyll cells draw water from the xylem vessels by osmosis.
  • The xylem in the leaf is continuous with xy lem in the stem and root.

Structure and function of Xylem

  • Movement of water is through the xylem.
  • Xylem tissue is made up of vessels and tracheids.

Xylem Vessels

  • Xylem vessels are formed from cells that are elongated along the vertical axis and arranged end to end.
  • During development, the cross walls and organelles disappear and a continuous tube is formed.
  • The cells are dead and their walls are strengthened by deposition of lignin.
  • The lignin has been deposited in various ways.
  • This results in different types of thickening
  • Simple spiral.
  • Double spiral.
  • The bordered pits are areas without lignin on xylem vessels and allow passage of water in and out of the lumen to neighbouring cells.
  • Tracheids have cross-walls that are perforated.
  • Their walls are deposited with lignin.
  • Unlike the xylem vessels, their end walls are tapering or chisel-shaped.
  • Their lumen is narrower.
  • Besides transport of water, xylem has another function of strengthening the plant which is provided by xylem fibres and xylem parenchyma.

Xylem fibres ;

  • Are cells that are strengthened with lignin.
  • They form wood.

Xylem parenchyma :

  • These are cells found between vessels.
  • They form the packing tissue.

Forces involved in Transportation of Water and Mineral Salts

Transpiration pull

  • As water vaporises from spongy mesophyll cells into sub-stomatal air spaces, the cell sap of mesophyll cells develop a higher osmotic pressure than adjacent cells.
  • Water is then drawn into mesophyll cells by osmosis from adjacent cells and finally from xylem vessels.
  • A force is created in the leaves which pulls water from xylem vessels in the stem and root.
  • This force is called transpiration pull .

Cohesion and Adhesion :

  • The attraction between water molecules is called cohesion.
  • The attraction between water molecules and the walls of xylem vessels is called adhesion.
  • The forces of cohesion and adhesion maintain a continuous flow of water in the xylem from the root to the leaves.


  • Is the ability of water to rise in fine capillary tubes due to surface tension.
  • Xylem vessels are narrow, so water moves through them by capillarity.

Root Pressure:

  • If the stem of a plant is cut above the ground level, it is observed that cell sap continues to come out of the cut surface.
  • This shows that there is a force in the roots that pushes water up to the stem.
  • This force is known as root pressure.

Importance of Transpiration

  • Transpiration leads to excessive loss of water if unchecked.

Some beneficial effects are:

  • Replacement of water lost during the process.
  • Movement of water up the plant is by continuous absorption of water from the soil.
  • Mineral salts are transported up the plant.
  • Transpiration ensures cooling of the plant in hot weather.
  • Excessive loss of water leads to wilting’ and eventually death if water is not available in the soil.

Factors Affecting Transpiration

The factors that affect transpiration are grouped into two.

  • i.e. environmental and structural.

Environmental factors   


  • High temperature increases the internal temperature of the leaf .
  • which in turn increases kinetic energy of water molecules which increases evaporation.
  • High temperatures dry the air around the leaf surface maintaining a high concentration gradient.
  • More water vapour is therefore lost from the leaf to the air.
  • The higher the humidity of the air around the leaf, the lower the rate of transpiration.
  • The humidity difference between the inside of the leaf and the outside is called the saturation deficit.
  • In dry atmosphere, the saturation deficit is high.
  • At such times, transpiration rate is high.
  • Wind carries away water vapour as fast as it diffuses out of the leaves.
  • This prevents the air around the leaves from becoming saturated with vapour.
  • On a windy day, the rate of transpiration is high.

Light Intensity

  • When light intensity is high; more stomata open hence high rate of transpiration.

Atmospheric Pressure

  • The lower the atmospheric pressure the higher the kinetic energy of water molecules hence more evaporation.
  • Most of the plants at higher altitudes where atmospheric pressure is very low have adaptations to prevent excessive water-loss.

Availability of Water

  • The more water there is in the soil, the more is absorbed by the plant and hence a lot of water is lost by transpiration.

Structural Factors

  • Plants growing in arid or semi-arid areas have leaves covered with a thick waxy cuticle.
  • The more the stomata, the higher the rate of transpiration.
  • Xerophytes have few stomata which reduce water-loss.
  • Some have sunken stomata which reduces the rate of transpiration as the water vapour accumulates in the pits.
  • Others have stomata on the lower leaf surface hence reducing the rate of water-loss.
  • Some plants have reversed stomatal rhythm whereby stomata close during the day and open at night.
  • This helps to reduce water-loss.

Leaf size and shape

  • Plants in wet areas have large surface area for transpiration.
  • Xerophytes have small narrow leaves to reduce water-loss.
  • The photometer can be used to determine transpiration in different environmental conditions.

Translocation of organic compounds

  • Translocation of soluble organic products of photosynthesis within a plant is called translocation.
  • It occurs in phloem in sieve tubes.
  • Substances translocated include glucose, amino acids, vitamins.
  • These are translocated to the growing regions like stem, root apex, storage organs e.g. corms, bulbs and secretory organs such as nectar glands.

phloem is made up of;

  • sieve tubes,
  • companion cells
  • parenchyma, a packing tissue
  • schlerenchyma, a strengthening tissue

Sieve Tubes

  • These are elongated cells arranged end to end along the vertical axis.
  • The cross walls are perforated by many pores to make a sieve plate.
  • Most organelles disappear and those that remain are pushed to the sides of the sieve tube.
  • Cytoplasmic strands pass through the pores in the plate into adjacent cells.
  • Food substances are translocated through cytoplasmic strands.

Companion Cells

  • Companion cells are small cells with large nuclei and many mitochondria.
  • They are found alongside each sieve element.
  • The companion cell is connected to the tube through plasmodesmata.
  • The mitochondria generate energy required for translocation.

Phloem Parenchyma

  • These are parenchyma cells between sieve elements.
  • They act as packing tissue.

Transport in Animals

The Circulatory System

  • 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.

Transport in Insects

  • 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.

Mammalian Circulatory System

  • 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).
  • 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.
  • 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.

Structure and Function of Arteries,Capillaries and Veins

  • 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.
  • 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 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 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.

Diseases and Defects of Circulatory System

  • 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.


  • 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 occurence.

Structure and Function of Blood

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.
  • This is a pale yellow fluid consisting of 90%
  • glucose, amino acids, lipids, salts,
  • hormones, urea, fibrinogen, albumen,
  • 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.
  • Haemoglobin + Oxygen =oxyhaemoglobin
  • (Hb)     + (4O 2 ) __ (HbO g )
  • 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 cu bic 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:
  • Granulocytes (also phagocytes or polymorphs)
  • 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 groups

Blood Transfusion

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 non­virulent 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.


  • Respiration

Meaning and Significance of Respiration

  • Respiration is the process by which energy is liberated from organic compounds such as glucose.
  • It is one of the most important characteristics of living organisms.
  • Energy is expended (used) whenever an organism exhibits characteristics of life, such as feeding, excretion and movement.
  • Respiration occurs all the time and if it stops, cellular activities are disrupted due to lack of energy.
  • This may result in death e.g., if cells in brain lack oxygen that is needed for respiration for a short time, death may occur.
  • This is because living cells need energy in order to perform the numerous activities necessary to maintain life.
  • The energy is used in the cells and much of it is also lost as heat.
  • In humans it is used to maintain a constant body temperature.

Tissue Respiration

  • Respiration takes place inside cells in all tissues.
  • Every living cell requires energy to stay alive.
  • Most organisms require oxygen of the air for respiration and this takes place in the mitochondria.

Mitochondrion Structure and Function

  • Mitochondria are rod-shaped organelles found in the cytoplasm of cells.
  • A mitochondrion has a smooth outer membrane and a folded inner membrane.
  • The folding of the inner membrane is called cristae and the inner compartment is called the matrix.

Adaptations of Mitochondrion to its Function

  • The matrix contains DNA ribosomes for making proteins and has enzymes for the breakdown of pyruvate to carbon (IV) oxide, hydrogen ions and electrons.
  • Cristae increase surface area of mitochondrial inner membranes where attachment of enzymes needed for the transport of hydrogen ions and electrons are found.
  • There are two types of respiration:

Aerobic Respiration

  • This involves breakdown of organic substances in tissue cells in the presence of oxygen .
  • All multicellular organisms and most unicellular organisms e.g. some bactena respire aerobically.
  • In the process, glucose is fully broken down to carbon (IV) oxide and hydrogen which forms water when it combines with the oxygen.
  • Energy produced is used to make an energy rich compound known as adenosine triphosphate (ATP).
  • It consists of adenine, an organic base, five carbon ribose-sugar and three phosphate groups.
  • ATP is synthesised from adenosine diphosphate (ADP) and inorganic phosphate.
  • The last bond connecting the phosphate group is a high-energy bond.
  • Cellular activities depend directly on ATP as an energy source.
  • When an ATP molecule is broken down, it yields energy.

Process of Respiration

  • The breakdown of glucose takes place in many steps.
  • Each step is catalysed by a specific enzyme.
  • Energy is released in some of these steps and as a result molecules of ATP are synthesised.
  • All the steps can be grouped into three main stages:


  • The initial steps in the breakdown of glucose are referred to as glycolysis and they take place in the cytoplasm.
  • Glycolysis consists of reactions in which glucose is gradually broken down into molecules of a carbon compound called pyruvic acid or pyruvate.
  • Before glucose can be broken, it is first activated through addition of energy from ATP and phosphate groups.
  • This is referred to as phosphorylation.
  • The phosphorylated sugar is broken down into two molecules of a 3-carbon sugar (triose sugar) each of which is then converted into pyruvic acid.
  • If oxygen is present, pyruvic acid is converted into a 2-carbon compound called acetyl coenzyme A (acetyl Co A).
  • Glycolysis results in the net production of two molecules of ATP.
  • The next series of reactions involve decarboxylation i.e. removal of carbon as carbon (IV) oxide and dehydrogenation, removal of hydrogen as hydrogen ions and electrons.
  • These reactions occur in the mitochondria and constitute the Tri-carboxylic Acid Cycle (T.C.A.) or Kreb’s citric acid cycle.
  • The acetyl Co A combines with 4-carbon compound with oxalo-acetic acid to form citric acid – a 6 carbon compound.
  • The citric acid is incorporated into a cyclical series of reactions that result in removal of carbon (IV) oxide molecules, four pairs of hydrogen, ions and electrons.
  • Hydrogen ions and electrons are taken to the inner mitochondria membrane where enzymes and electron carriers effect release of a lot of energy.
  • Hydrogen finally combines with oxygen to form water, and 36 molecules of ATP are synthesised.

Anaerobic Respiration

  • Anaerobic respiration involves breakdown of organic substances in the absence of oxygen.
  • It takes place in some bacteria and some fungi.
  • Organisms which obtain energy by anaerobic respiration are referred to as anaerobes.
  • Obligate anaerobes are those organisms which do not require oxygen at all and may even die if oxygen is present.
  • Facultative anaerobes are those organisms which survive either in the absence or in the presence of oxygen.
  • Such organisms tend to thrive better when oxygen is present e.g. yeast.

Products of Anaerobic Respiration

  • The products of anaerobic respiration differ according to whether the process is occurring in plants or animals.

Anaerobic Respiration in Plants

  • Glucose is broken down to an alcohol, (ethanol) and carbon (IV)
  • The breakdown is incomplete.
  • Ethanol is an organic compound, which can be broken down further in the presence of oxygen to provide energy, carbon (IV) oxide and water.

C 6 H I2 0 6 _ 2C 2 H 5 0H + 2C0 2 + Energy

(Glucose) (Ethanol)   (Carbon (IV) oxide)


  • Is the term used to describe formation of ethanol and carbon (IV) oxide from grains.
  • Yeast cells have enzymes that bring about anaerobic respiration.

Lactate Fermentation

  • Is the term given to anaerobic respiration in certain bacteria that results in formation of lactic acid.

Anaerobic Respiration in Animals

  • Anaerobic respiration in animals produces lactic acid and energy.

C 6 H 1 P6 _ 2CH 3 CHOH.COOH + energy

(Glucose) (Lactic acid) + energy

  • When human muscles are involved in very vigorous activity, oxygen cannot be delivered as rapidly as it is required.
  • The muscle respire anaerobically and lactic acid accumulates.
  • A high level of lactic acid is toxic.
  • During the period of exercise, the body builds up an oxygen debt.
  • After vigorous activity, one has to breathe faster and deeper to take in more oxygen.
  • Rapid breathing occurs in order to break down lactic acid into carbon (IV) oxide and water and release more energy.
  • Oxygen debt therefore refers to the extra oxygen the body takes in after vigorous exercise.

Practical Activities

To Show the Gas Produced When the Food is burned

  • A little food substance e.g., maize flour or meat is placed inside a boiling tube.
  • The boiling tube is stoppered using a rubber bung connected to a delivery tube inserted into a test-tube with limewater.
  • The food is heated strongly to bum.
  • Observations are made on the changes in lime water (calcium hydroxide) as gas is produced.
  • The clear lime water turns white due to formation of calcium carbonate precipitate proving that carbon (Iv) oxide is produced.

Experiment to Show the Gas Produced During Fermentation

  • Glucose solution is boiled and cooled. Boiling expels all air.
  • A mixture of glucose and yeast is placed in a boiling tube, and covered with a layer of oil to prevent entry of air.
  • A delivery tube is connected and directed into a test-tube containing lime water.
  • The observations are made immediately and after three days the contents are tested for the presence of ethanol.
  • A control experiment is set in the same way except that yeast which has been boiled and cooled is used.
  • Boiling kills yeast cells.
  • The limewater becomes cloudy within 20 minutes.
  • This proves that carbon (IV) oxide gas is produced.
  • The fermentation process is confirmed after three days when alcohol smell is detected in the mixture.

Experiment to Show Germinating Seeds Produce Heat

  • Soaked bean seeds are placed in a vacuum flask on wet cotton wool.
  • A thermometer is inserted and held in place with cotton wool .
  • The initial temperature is taken and recorded.
  • A control experiment is set in the same way using boiled and cooled bean seeds which have been washed in formalin to kill micro ­
  • Observation is made within three days.
  • Observations show that temperature in the flask with germinating seeds has risen.
  • The one in the control has not risen.

Comparison Between Aerobic and Anaerobic Respiration

Comparison Between Energy Output in Aerobic and Anaerobic Respiration

  • Aerobic respiration results in the formation of simple inorganic molecules, water and carbon (Iv) oxide as the by­
  • These cannot be broken down further. A lot of energy is produced.
  • When a molecule of glucose is broken down in the presence of oxygen, 2880 KJ of energy are produced (38 molecules of ATP).
  • In anaerobic respiration the by products are organic compounds.
  • These can be broken down further in the presence of oxygen to give more energy.
  • Far less energy is thus produced.
  • The process is not economical as far as energy production is concerned.
  • When a molecule of glucose is broken down in the absence of oxygen in plants, 210 KJ are produced (2 molecule ATP).
  • In animals, anaerobic respiration yields 150 kJ of energy.

Substrates for Respiration

  • Carbohydrate, mainly glucose is the main substrate inside cells.
  • Lipids i.e. fatty acids and glycerol are also used.
  • Fatty acids are used when the carbohydrates are exhausted.
  • A molecule of lipid yields much more energy than a molecule of glucose.
  • Proteins are not normally used for respiration.
  • However during starvation they are hydrolysed to amino acids, dearnination follows and the products enter Kreb’s cycle as urea is formed.
  • Use of body protein in respiration result to body wasting, as observed during prolonged sickness or starvation.
  • The ratio of the amount of carbon (IV) oxide produced to the amount of oxygen used for each substrate is referred to as Respiratory Quotient (RQ) and is calculated as follows:

R.Q. = Amount of carbon (IV) oxide produced

Amount of oxygen used

  • Carbohydrates have a respiratory quotient of 1.0 lipids 0.7 and proteins 0.8.
  • Respiratory quotient value can thus give an indication of types of substrate used.
  • Besides values higher than one indicate that some anaerobic respiration is taking place.

Application of Anaerobic Respiration in Industry and at Home

  • Making of beer and wines.
  • Ethanol in beer comes from fermentation of sugar(maltose) in germinating barley seeds.
  • Sugar in fruits is broken down anaerobically to produce ethanol in wines.
  • In the dairy industry, bacterial fermentation occurs in the production of several dairy products such as cheese, butter and yoghurt.
  • In production of organic acids e.g., acetic acid, that are used in industry e.g., in preservation of foods.
  • Fermentation of grains is used to produce all kinds of beverages e.g., traditional beer and sour porridge.
  • Fermentation of milk.

End of Topic


Necessity for Gaseous Exchange in Living Organisms

  • Living organisms require energy to perform cellular activities.
  • The energy comes from breakdown of food in respiration.
  • Carbon (IV) oxide is a by product 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.

Gaseous Exchange in Plants

  • 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.

Structure of Guard Cells

  • 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.

Mechanism of 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.

Proposed causes of turgor changes in guard cells.

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.

Explanation is based on accumulation of potassium  

  • 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.

Process of Gaseous Exchange in Root Stem and Leaves of Aquatic and Terrestrial Plants

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.
  • When stomata are open,carbon(IV)oxide from the atmosphere diffuses into the substomatal air chambers.
  • From here, it moves into the intercellular space in the spongy mesophyll layer.
  • The CO2 goes into solution when it comes into contact with the cell surface and diffuses into the cytoplasm.
  • A concentration gradient is maintained between the cytoplasm  of the cells and  the intercellular spaces.
  • CO2 therefore continues to diffuse into the cells.
  • The oxygen produced during photosynthesis moves out of the cells and into the intercellular spaces.
  • From here it moves to the substomatal air chambers and eventually diffuses out of the leaf through the stomata.
  • At night oxygen enters the cells while CO2 moves out.

Gaseous exchange in the leaves of aquatic(floating)plants

  • 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 ie.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.

Gaseous Exchange Through Stems

Terrestrial Plants

  • Stems of woody plants have narrow openings or slits at intervals called
  • 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.

Aquatic Plant Stems

  • 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.

Gaseous Exchange in Roots

  • 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.

Gaseous Exchange in Animals

  • 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.

Types and Characteristics of Respiratory surfaces

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.

Characteristics of Respiratory Surfaces

  • They are permeable to allow entry of gases.
  • They have a large surface area in order to increase diffusion.
  • They are usually thin in order to reduce the distance of diffusion.
  • They are moist to allow gases to dissolve.
  • They are well-supplied with blood to transport gases and maintain a concentration gradient.

Gaseous Exchange in Amoeba

  • 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

  • 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 Bony Fish (e.g, Tilapia)

  • 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 branchial 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 ftlaments.
  • 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.


  • 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.

Gaseous Exchange in an Amphibian – Frog

  • 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.
  • 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.
  • 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 foldings to increase surface area for gaseous exchange.
  • A rich supply of blood capillaries for efficient transport of gases.
  • Moisture lining for gases to dissolve.


  • 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.
  • 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.          

Gaseous Exchange in a Mammal -Human

  • 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 intercostals 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.
  • 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.
  • 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.
  • 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.

Table 7.1: Comparison of Inspired and Expired

 Air (% by volume)

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 cm 3 of air when fully inflated.
  • However, during normal breathing only about 500 cm 3 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.
  • Emotions like anger, flight

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.

Diseases of the Respiratory System

  • Asthma is a chronic disease characterised by narrowing of air passages.
  •   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.
  • 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.

Emotional or mental stress

  • Strains the body immune system hence predisposes to asthma attack.


  • 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.
  • This is due to an infection of bronchi and bronchioles by bacteria and viruses.
  • Difficulty in breathing.
  • Antibiotics are administered.

Pulmonary Tuberculosis

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


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


  • 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 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.
  • Pain in the chest accompanied by a fever, high body temperatures (39-40°C) and general body weakness.
  • Maintain good health through proper feeding.
  • Avoid extreme cold.


  • 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

  • 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.


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


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


  • 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 Diptheria, Pertusis and Tetanus ( DPT).
  • To reduce the coughing, the patient should be given drugs.


Observation of permanent slides of terrestrial and aquatic leaves and stems

  • 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.
  • 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:
  • Lenticels on terrestrial stems.
  • Large air spaces (aerenchyma) in aquatic stems.

Excretion and Homeostasis

  • 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

Excretion in Plants

  • 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.

Plant Excretory Products their source and uses

Excretory products in animals

Excretion and Homeostasis in Unicellular Organisms

  • Protozoa such as amoeba depend on diffusion as a means of excretion.
  • They have a large surface area to volume ratio for efficient diffusion.
  • Nitrogenous waste and carbon (IV) oxide are highly concentrated in the organism hence they diffuse out.
  • In amoeba excess water and chemicals accumulation in the contractile vacuole.
  • When it reaches maximum size the contractile vacuole moves to the cell membrane, bursts open releasing its contents to the surroundings.

Excretion in Human Beings

  • Excretion in humans is carried out by an elaborate system of specialised organs.
  • Their bodies are complex, so simple diffusion cannot suffice.
  • Excretory products include nitrogenous wastes which originate from deamination of excess amino acids.
  • The main excretory organs in mammals such as human beings include lungs, kidneys, skin and liver.

Structure and function of the human skin

Nerve Endings :

  • These are nerve cells which detect changes from the external environment thus making the body to be sensitive to touch, cold, heat and pressure.

Subcutaneous Fat:

  •  Is a layer beneath the dermis.
  •  It stores fat and acts as an insulator against heat loss.
  • The skin helps in elimination of urea, lactic acid and sodium chloride which are released in sweat.
  • Carbon (IV) oxide formed during tissue respiration is removed from the body by the lungs.
  • Mammalian lungs have many alveoli which are the sites of gaseous exchange.
  • Alveoli are richly supplied with blood and have a thin epithelium.
  • Blood capillaries around the alveoli have a high concentration of carbon (Iv) oxide than the alveoli lumen.
  • The concentration gradient created causes carbon (IV) oxide to diffuse into the alveoli lumen.
  • The carbon (IV) oxide is eliminated through expiration.

Structure and Functions of the Kidneys

  • The kidneys are organs whose functions are excretion, osmoregulation and regulation of pH.
  • Kidneys are located at the back of the abdominal cavity.
  • Each kidney receives oxygenated blood from renal artery,
  • while deoxygenated blood leaves through the renal vein.
  • Urine is carried by the ureter from the kidney to the bladder, which temporarily stores it.
  • From the bladder, the urine is released to the outside via the urethra.
  • The opening from the urethra is controlled by a ring-like sphincter muscle.
  •  A longitudinal section of the kidney shows three distinct regions: a darker outer cortex, a lighter inner medulla and the pelvis.
  • The pelvis is a collecting space leading to the ureter which takes the urine to the bladder from where it is eliminated through the urethra.

The Nephron

  • A nephron is a coiled tubule at one end of which is a cup-shaped structure called the Bowman’s capsule.
  • The capsule encloses a bunch of capillaries called the glomerulus.
  • The glomerulus receives blood from an afferent arteriole a branch of the renal artery.
  • Blood is taken away from the glomerulus by efferent arteriole leading to the renal vein.
  • The Bowman’s capsule leads to the proximal convoluted tubule that is coiled and extends into a U-shaped part called loop of Henle.
  • From the loop of Henle is the distal convoluted tubule that is also coiled.
  • This leads to the collecting duct which receives contents of many nephrons.
  • Collecting ducts lead to the pelvis of the kidney.

Mechanism of Excretion

  • Excretion takes place in three steps:
  • Filtration, reabsorption and removal.
  • The kidneys receive blood from renal artery a branch of the aorta.
  • This blood is rich in nitrogenous waste e.g. urea.
  • It contains dissolved food substances, plasma proteins,hormones and oxygen.
  • Blood flow in capillaries is under pressure due to the narrowness of the capillaries.
  • The afferent arteriole entering the glomerulus is wider than the efferent arteriole leaving it.
  • This creates pressure in the glomerulus.
  • Due to this pressure, dissolved substances such as urea, uric acid, glucose, mineral salts and amino acids are forced out of the glomerulus into the Bowman’s capsule.
  • Large sized molecules in the plasma such as proteins and red blood cells are not filtered out because they are too large.
  • This process of filtration is called ultra-filtration or pressure filtration and the filtrate is called glomerular filtrate.

Selective Reabsorption

  • As the filtrate flows through the renal tubules the useful substances are selectively reabsorbed back into the blood.
  • In the proximal convoluted tube all the glucose, all amino acids and some mineral salts are actively reabsorbed by active transport.
  • The cells lining this tubule have numerous mitochondria which provide the energy needed.
  • Cells of the tubule have microvilli which increases the surface area for re-absorption.
  • The tubule is coiled, which reduces the speed of flow of the filtrate e.g. giving more time for efficient re-absorption.
  • The tubule is well supplied with blood capillaries for transportation of reabsorbed substances.
  • The ascending loop has thick wall and is impermeable to water.
  • Sodium is actively pumped out of it towards the descending loop.
  • As glomerular filtrate moves down the descending loop, water is reabsorbed into the blood by osmosis in the distal convoluted tubule and in the collecting duct.
  • Permeability of the collecting duct and proximal convoluted tubule is increased by anti-diuretic hormone (ADH) whose secretion is influenced by the osmotic pressure of the blood.
  • The remaining fluid consisting of water, urea, uric acid and some mineral salts is called urine.
  • The urine is discharged into the collecting d ct and carried to the pelvis.
  • The loop of Henle is short in semi­-aquatic mammals, and long in some mammals like the desert rat.
  • The urine is conveyed from the pelvis to the ureter.
  • The ureter carries the urine to the bladder where it is stored temporarily and discharged to the outside through the urethra at intervals.

Common Kidney Diseases

  • This is a condition in which concentration of urea in the blood.
  • It may be due to formation of cysts in tubules or reduction in blood supply to the glomeruli as a result of contraction of renal artery.
  • Symptoms include yellow colouration of skin, smell of urine in breath, nausea and vomiting.
  • Treatment includes dialysis to remove excess urea and a diet low in proteins and salts especially sodium and potassium.

Kidney Stones

  • Kidney stones are solid deposits of calcium and other saIts.
  • They are usually formed in the pelvis of the kidney where they may obstruct the flow of urine.
  • Causes : the stones are formed due to crystallisation of salts around pus, blood or dead tissue.
  • Symptoms: include blood in urine, frequent urination, pain, chills and fever. Severe pain when urinating.
  • Use of laser beams to disintegrate the stones.
  • Pain killing drugs like morphine.
  • Stones can be removed by surgery.
  • Taking hot baths and massage.
  • Nephritis is the inflation of glomerulus of the kidney.
  • Causes: Bacterial infection, sore throat or tonsillitis, blockage of glomeruli by antibody-antigen complex.
  • Signs and Symptoms : include headaches, fever, vomiting, oedema.
  • Control includes dietary restrictions especially salt and proteins.
  • Prompt treatment of bacterial infections.

Role of Liver in Excretion

  • The liver lies below the diaphragm and it receives blood from hepatic artery and hepatic portal vein.
  • Blood flows out of the liver through hepatic vein.
  • Excretion of Nitrogenous Wastes
  • Excess amino acids cannot be stored in the body, they are deaminated in the liver.
  • Hydrogen is added to amino group to form ammonia which combines with carbon (IV) oxide to form urea.
  • The urea is carried in the blood stream to the kidneys.
  • The remaining carboxyl group, after removal of amino group, is either oxidised to provide energy in respiration.
  • or built up into carbohydrate reserve and stored as glycogen or converted into fat and stored.

Breakdown and Elimination of Haemoglobin

  • Haemoglobin is released from dead or old red blood cells which are broken down in the liver and spleen.
  • Haemoglobin is broken down in the liver and a green pigment biliverdin results which is converted to yellow bilirubin.
  • This is taken to the gall bladder and eliminated as bile.

Elimination of Sex Hormones

  • Once they have completed their functions, sex hormones are chemically altered by the liver and then taken to the kidney for excretion.

Common Liver Diseases

  • Cirrhosis is a condition in which liver cells degenerate and are replaced by scar tissue .
  • This causes the liver to shrink, harden, become fibrous and fail to carry out its functions.
  • Chronic alcohol abuse, schistosomiasis infection, obstruction of gall-bladder.
  • Headache, nausea, vomiting of blood and lack of appetite, weight loss, indigestion and jaundice.

Control and Treatment

  • Avoid alcohol consumption and fatty diet.
  • Use drugs to kill the schistosomes if that is the cause.
  • This is a yellow colouration of the skin and eyes.
  •   Presence of excess bile pigments.
  • This happens due to blockage of bile duct or destruction of liver.
  • Yellow pigmentation of skin and eyes, nausea, vomiting and lack of appetite. Itching of skin.
  • Removal of stones from the gall bladder by surgery.
  • Give patient fat-free diet, reduced amount of proteins.
  • Give antihistamines to reduce itching.


  • Homeostasis is the maintenance of a constant internal environment.
  • The internal environment consists of intercellular or tissue fluid.
  • This fluid is the medium in the space surrounding cells.
  • Tissue fluid is made by ultra-filtration in the capillaries.
  • Dissolved substances in the blood are forced out of the capillaries and into intercellular spaces.
  • Cells obtain their requirements from tissue fluid while waste products from cells diffuse out into the tissue fluid.
  • Some of the fluid gets back into the blood capillaries while excess fluid is drained into the lymph vessels.
  • Cells function efficiently if there is little or no fluctuation in the internal environment.
  •  The factors that need to be regulated include temperature, osmotic pressure and pH.
  • The body works as a self-regulating system and can detect changes in its working conditions bringing about corrective responses.
  • This requires a negative feedback mechanism e.g. when body temperature falls below normal, mechanisms are set in place that bring about increase in temperature.
  • And when the increase is above normal, mechanisms that lower the temperature are set in place.
  • This is called a negative feedback and it restores the conditions to normal.

Neuro-Endocrine System and Homeostasis

  • Homeostatic mechanisms are brought about by an interaction between nervous and endocrine systems.
  • Nerve endings detect changes in the internal and external environment and relay the information to the brain.
  • The hypothalamus and pituitary are endocrine glands situated in the brain.
  • The  hypothalamus detect changes in the blood.
  • The pituitary secretes a number of hormones involved in homeostasis e.g. anti-duretic hormone (ADH).
  • The discussion below shows the nature of these interactions.

The Skin and Temperature Regulation

  • The optimum human body temperature is 36.8°C.
  • A constant body temperature favours efficient enzyme reaction.
  • Temperatures above optimum denature enzymes, while temperature below the optimum range inactivate enzymes.
  • The skin is involved in regulation of body temperature as follows:
  • The skin has receptors that detect changes in the temperature of the external environment.

When the body temperature is above optimum the following takes place:

  • Sweat glands secrete sweat onto the skin surface.
  • As sweat evaporates it takes latent heat from the body, thus lowering the temperature.

Vasodilation of Arterioles:

  • The arterioles near the surface become wider in diameter.
  • More blood flows near the surface and more heat is lost to the surrounding by convection and radiation.

Relaxation of hair erector muscle:

  • When hair erector muscles relax, the hair lies flat thus allowing heat to escape from the skin surface.

When body temperature is below optimum the following takes place:

     Vasoconstriction of Arterioles:

  • The arterioles near the surface of the skin become narrower.
  • Blood supply to the skin is reduced and less heat is lost to the surroundings.

Contraction of hair erector muscles.

  • When hair erector muscles contract, the hair is raised.
  • Air is trapped between the hairs forming an insulating layer.
  • Animals in cold areas have a thick layer of subcutaneous fat , which helps to insulate the body.
  • Besides the role of the skin in thermoregulation as discussed above, the rate of metabolism is lowered when temperature is above optimum and increased when temperature is below optimum.
  • The latter increases the temperature to the optimum.
  • When this fails, shivering occurs.
  • Shivering is involuntary contraction of muscles which helps to generate heat thus raising the body temperature.

Homeostatic Control of Body Temperature in Humans

Body size and Heat Loss

  • The amount of heat produced by metabolic reactions in an animal body is proportional to its mass.
  • Large animals produce more heat but they lose less due to small surface area to volume ratio.
  • Small animals produce less heat and lose a lot, due to large surface area to volume ratio.
  • Small animals eat a lot of food in relation .to their size in order to raise their metabolic rate.

Behavioural and Physiological Responses to Temperature Changes

  • Animals gain or lose heat to the environment by conduction, radiation and convection.
  • Birds and mammals maintain a constant body temperature regardless of the changes in the environment.
  • They do this mainly by internally installed physiological mechanisms hence they are endotherms, also known as homoiotherms.
  • At the same time behavioural activities like moving to shaded areas when it is too hot assist in regulating their body temperature.
  • Other animals do not maintain a constant body temperature e.g. lizards.
  • They are poikilotherms (ectotherms) as their temperature varies according to that of surroundings.
  • They only regulate body temperature through behavioural means.
  • Lizards bask on the rocks to gain heat and hide under rocks when it is too hot.
  • Some animals have adaptive features e.g. animals in extreme cold climates have fur and a thick layer of subcutaneous fat like polar bear.
  • Those in extremely hot areas have tissue that tolerate high temperatures e.g. camels.
  • Some animals avoid cold conditions by hibernating e.g. the frog while others avoid dry hot conditions by aestivation e.g. kangaroo rat.
  • This involves decreasing their metabolic activities.

Skin and Osmoregulation

  • Osmoregulation is the control of salt and water balance in the body to maintain the appropriate osmotic pressure for proper cell functioning.
  • Sweat glands produce sweat and thus eliminate water and salt from the body.

The Kidney and Osmoregulation

  • The kidney is the main organ that regulates the salt and water balance in the body.
  • The amount of salt or water reabsorbed into the bloodstream is dependent on the osmotic pressure of the blood.
  • When the osmotic pressure of the blood rises above normal due to dehydration or excessive consumption of salt, the osmo-receptors in the hypothalamus are stimulated.
  • These cells relay impulses to the pituitary gland which produces a hormone called anti-diuretic hormone – ADH (vasopressin) which is taken by the blood to the kidneys.
  • The hormone (ADH) makes the distal convoluted tubule and collecting duct more permeable to water hence more water is reabsorbed into the body by the kidney tubules lowering the osmotic pressure in the blood.
  • When the osmotic pressure of the blood falls below normal due to intake of a large quantity of water, osmoreceptors in the hypothalamus are less stimulated.
  • Less antidiuretic hormone is produced, and the kidney tubules reabsorb less water hence large quantities of water is lost producing dilute urine (diuressis).
  •  The osmotic pressure of the blood is raised to normal.
  • If little or no ADH is produced, the body may become dehydrated unless large quantities of water are consumed regularly.
  • Diabetes insipidus is a disease that results from the failure of the pituitary gland to produce ADH and the body gets dehydrated.
  • A hormone called Aldosterone produced by the adrenal cortex regulates the level of sodium ions.
  • When the level of sodium ions in the blood is low, adrenal cortex releases aldosterone into the blood.
  • This stimulates the loop of Henle to reabsorb sodium ions into the blood.
  • Chloride ions flow to neutralise the charge on sodium ions.
  • Aldosterone also stimulates the colon to absorb more sodium ions into the blood.
  • If the sodium ion concentration rises above optimum level, adrenal cortex

Notes missing

  • Formation of Red Blood Cells.
  • In the embryo, red blood cells are formed in the liver.
  • Breakdown and elimination of old and dead blood cells.
  • Dead red blood cells are broken down in the liver and the pigments eliminated in bile.
  • Manufacture of Plasma Proteins.
  • Plasma proteins like albumen, fibrinogen and globulin are manufactured in the liver.
  • Storage of blood, vitamins A, K, BI2 and D and mineral salts such as iron’ and potassium ions.
  • Toxic substances ingested e.g. drugs or produced from metabolic reactions in the body are converted to harmless substances in a process called detoxification.


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KCSE 2023 Biology Essay Questions and Answers (KCSE 2023 Prediction Questions)

Here are KCSES 2022/2023 Biology Essay Questions and Answers (KCSE 2022 Prediction Questions). Content: 31 pages with 60 questions and answers.

BIOLOGY (231/2) Revision Questions (Essays): Expected Responses

Q1. Explain the various ways in which a typical cell is adapted to its functions

   Has a cell membrane; with pores; that regulates substances entering and leaving the cell; cytoplasm; contain sugars and salts; for maintaining its osmotic pressure; also has a liquid medium; for all biochemical reactions; nucleus; contain chromosomes having hereditary material; and controls all the activities of the cell; ribosomes; are sites for protein synthesis; golgi bodies/apparatus; for secretion of hormones and enzymes; formation of lysosomes; lysosomes; contain lytic enzymes for breaking down worn-out organelles; secretory vesicles; formed from golgi apparatus for secreting substances; smooth endoplasmic reticulum; synthesizes and transports lipids; rough endoplasmic reticulum; transport proteins; nucleolus; controls the activities of the nucleus; produces ribosomes; mitochondria; form sites for energy production; centrioles; formation of cilia and flagella; forms spindle fibres used in cell division; plant sap vacuoles; store salts and other dissolved substances; controls osmotic pressure and turgidity of cells; food vacuoles involved in digestion of engulfed food; chloroplasts; form sites for photosynthesis in plant cells;  Max. 20 mks

Q2. Explain how the various specialized cells are modified to carry out their functions in plants and animals

   Animal cells: Sperm cell; has acrosome containing lytic enzymes; that digest the egg membranes for penetration during fertilization; has a long tail; containing numerous mitochondria; to generate maximum energy for propulsion/swimming in the vaginal fluid after ejaculation; Red blood cells; are flattened, circular/spherical biconcave in shape; to increase the surface area for packaging of haemoglobin; has haemoglobin; that combines with respiratory gases; for transport to and from body tissues; White blood cells; are amoeboid in shape hence able to change shape; to engulf pathogens through phagocytosis; lymphocytes produce antibodies to fight pathogens; Nerve cell; has extensions/dentrites; to receive and send information for sensation; Ciliated epithelial cells; have cilia for propulsion of mucus that traps dust and micro-organisms in the respiratory tract; Muscle cells; elongated, striated and contractile; to bring about movement; Plant cells: Guard cells; bean-shaped; to regulate the size of the stomata allowing gaseous exchange; and control water loss; has chloroplasts with chlorophyll; for photosynthesis; Root hair cell; elongated; thin-walled; with dense cytoplasm for absorption of water and mineral salts; Epidermal cell; thin; for protection of inner tissues from mechanical and micro-organism attack; Palisade cell; contains numerous chloroplasts with chlorophyll; for photosynthesis; elongated; to increase surface area for trapping maximum amounts of light energy; Meristematic cell; thin-walled; with dense cytoplasm; for primary and secondary growth; Max. 20 mks

Q3. Describe how the mammalian body protects itself against infections

   Pathogenic microbes are found on the skin, respiratory tract, mouth, vagina and the intestinal tract; the skin; has a keratinised and waterproof cornified outer layer; that provides a mechanical barrier to microbes/prevents entry of microbes; sebaceous gland; produces sebum; which has antiseptic properties; the respiratory tract; produce mucus secretions that trap dust; cilia sweep/waft/propel the microbes to the pharynx for swallowing or to be coughed out; reflex actions of coughing/sneezing/vomiting help remove foreign materials from the respiratory tract/digestive tract; lysozymes/enzymes in saliva/nasal secretions/tears; digest walls of bacteria destroying them; gastric secretions such as hydrochloric acid lowers the pH in the stomach killing micro-organisms; clotting of blood; prevents entry of microbes after damage of blood vessels; phagocytosis; by phagocytes engulf and destroy microbes and other foreign bodies; lymphocytes are stimulated to produce antibodies; by proteins present in microbes protecting the body; antibodies destroy/kill micro-organisms through various ways: agglutinins; bind to pathogens making them clump together; killing them; Lysins; bind to pathogens and make them burst or disintegrate; opsonins; bind to pathogens making them easily recognized hence be engulfed/destroyed by other lymphocytes; anti-toxins; bind and neutralize toxins produced by micro-organisms; vagina is acidic; hence making it not conducive for growth and reproduction of micro-organisms; Max: 20 mks

Q4. How are the leaves of higher plants adapted to their functions?

    Broad and flattened lamina; to increase surface area; for absorption of light; thin blade; to reduce distance for diffusion of gases and penetration of light waves; transparent epidermis and cuticle; to allow light to penetrate to tissues; cuticle layer absent on stomata; to allow for gaseous exchange; one-cell thick epidermal layer; to reduce the distance over which sunlight penetrates; palisade cells have numerous chloroplasts containing chlorophyll; to trap maximum amounts of light energy; have stomata on the epidermis; to allow for gaseous exchange; and control of water loss through transpiration; palisade layer have elongated cells located at right angles to the leaf surface; for maximum absorption of light energy; spongy mesophyll; consists of spherical and loosely-packed cells; to create air spaces; which communicate with the atmosphere through stomata; for purposes of gaseous exchange and control of water loss; veins have conducting tissues: xylem; for movement of water and dissolved mineral salts; phloem; for translocation of manufactured food; Max. 20 mks

Q5.  Explain how the various teeth adapt mammals for nutrition

   Incisor; sharp; chisel-shaped; for biting; and cutting food; one root for support in the jaw bone; Canines; long; sharp; pointed; for holding prey; piercing; and tearing flesh from prey; single root; for support in the jaw bone; Premolars; large/wide; to increase surface area for grinding food; highly cusped; to increase surface area for grinding food; two roots; for firm support/anchorage in the jaw bone; molars; large/wide; to increase surface area for grinding food; highly cusped; to increase surface area for grinding food; Max. 20 mks

Q6. Describe what happens to a meal of oily beans and maize from the time of ingestion up to the time of absorption

   In the mouth; starch in maize; is digested by salivary amylase/ptyalin/diastase into maltose; food is chewed and mixed by teeth and the tongue; rolled into boluses by peristalsis; it enters into the stomach via the cardiac sphincter; in the stomach, gastric juice containing pepsinogen that is activated to pepsin; digests proteins in the beans; into shorter peptides; food is churned and allowed into the duodenum; via the pyloric sphincter muscle; in the duodenum; bile juice secreted by the gall bladder; emulsifies the oils in the beans into tiny oil droplets; pancreatic juice; secreted by the pancrease; contains pancreatic amylase; that digests starch to maltose; pancreatic lipase; that digests the oil in the beans to fatty acids and glycerol; trypsin; digests proteins into shorter peptides;  food enters into the ileum; where succus entericus is secreted; it contains maltase enzyme; that digests the maltose into glucose; that is absorbed; peptidase; digests peptides into amino acids; lipase digests the remaining lipids (oil) into fatty acids and glycerol; which is absorbed through the lacteals of the villi; Max. 20 mks

Q7. How are the small intestines in mammals adapted to their functions?

Small intestines consists of the duodenum and the ileum; most digestion of food occurs in the duodenum; bile from the gall bladder of the liver is secreted through the bile ducts; and it is used to emulsify fats/break fat particles into tiny droplets; to increase the surface area for enzyme action; the pancreas secretes pancreatic juice to the duodenum; the juice contains pancreatic amylase; that helps to breakdown the remaining starch into maltose; trypsin; (that is secreted in its inactive form, trypsinogen , and activated by enterokinase enzyme); hydrolyses proteins into shorter peptides; pancreatic lipase; converts lipids into fatty acids and glycerol; sodium hydrogen carbonate is also produced; to neutralize the acidic chyme from the stomach; and provide a suitable alkaline medium for pancreatic and other intestinal enzymes; the ileum is long; and narrow; to increase the surface area for complete digestion of food; and maximum absorption of digested food; highly-coiled; to reduce speed of food flow; for maximum digestion; and absorption; presence of villi; and microvilli; to increase surface area; for maximum absorption; dense network of capillaries; to transport blood; for efficient transport of absorbed food; presence of lacteals in the villi; for absorption of fatty acids and glycerol molecules; presence of enzymes: Lipase; for digestion of lipids into fatty acids and glycerol; maltase; for digestion of maltose to glucose molecules; peptidase; for breakdown of peptides into amino acids; sucrase; for digestion of sucrose into glucose and fructose; lactase; for digestion of lactose into glucose and galactose; goblet cells; produce mucus; to lubricate the walls of the ileum; for smooth flow of food; coats the walls of ileum to prevent digestion by peptidase enzyme; Max. 20 mks

Q8. Outline and explain the various homeostatic functions of the liver in mammals

   Deamination; process of removal of an amino group from an amino acid molecule; the process gets rid of excess amino acids in the body; as the body is not able to store them; the amino group enters the ornithine cycle; where it is combined with carbon (IV) oxideto form urea; which is excreted in urine through the kidney; Heat production; many metabolic activities take place in the liver; releasing heat energy; that is distributed by the blood to other parts of the body; this helps in thermoregulation; Storage of vitamins and mineral salts; Vitamins A, B, D, E and K; are stored in the liver; worn-out red blood cells, are broken down to yield iron; which is stored in the liver in form of ferritin; this is used later in case of shortage; Formation of red blood cells; occurs in the liver of the foetus; the liver also breaks down old/exhausted red blood cells; leading to formation of more in the bone marrow to replace the worn-out cells; to enhance oxygen and carbon (IV) oxide distribution; Regulation of blood sugar level; liver cells convert excess glucose into glycogen and fats under the influence of insulin hormone; the stored glycogen is however converted back to glucose; when glucose levels are low; by the liver cells; under the influence of glucagon hormone; Regulation of plasma proteins; plasma proteins such as prothrombin and fibrinogen are manufactured in the liver using the amino acids found in the liver; they play a major role in blood clotting; that prevents excessive blood loss and infection at the injured area; other plasma proteins produced by the liver such as serum and albumen; contribute to the maintenance of osmotic pressure in the body; non-essential amino acids are also synthesized by the liver; for use by the body; Storage of blood; the liver is highly vascularised; hence it is capable of holding a large volume of blood when the blood vessels dilate during hot conditions; when the temperatures are low, the blood vessels constrict under the influence of the endocrine and nervous systems; hence less blood is stored in the liver; this contributes to thermoregulation; Detoxification; this is the process where harmful compounds such as drugs and poisons; are converted to less toxic compounds in the liver; toxicity is caused by medication, drugs and microorganisms; the toxic compounds are later excreted in urine; detoxification prevents the accumulation of toxins in body cells; which could lead to death or malfunctioning of the body cells; Max. 20 mks

Q9. Explain why the following conditions are necessary for photosynthesis

  • Carbon (IV) Oxide

Required in the dark stage of photosynthesis; it combines with the hydrogen ion from the light stage; to form glucose, proteins and lipids; low concentrations reduces the rate of production of energy and food; while high concentrations leads to an increase in the amount of energy and food formed;

It is used to break down water molecules (through photolysis); into hydrogen ions, oxygen and energy; the energy and hydrogen ions formed are used in the dark stage;

  • Chlorophyll

Green pigment that traps light energy from the sun; that is used in photolysis of water molecules;

  • Suitable temperature and pH

Temperature affects the enzymes involved in photosynthesis; suitable/optimum temperatures activate enzymes; for maximum production of food; while extremely low temperatures inactivate enzymes; leading to less or no production of food; high temperatures denature enzymes; stopping the process of photosynthesis; photosynthetic enzymes work well in low pH; so the rate is high; while higher pH reduces enzyme activity; lowering the rate of photosynthesis;

Forms a medium for the chemical reactions; it is split to yield hydrogen ions, oxygen and energy for use in the dark stage; solvent for the materials used in photosynthesis; Max. 20 mks

Q10. How is the ileum adapted to its functions?

      Long; and narrow; to increase the surface area for complete digestion of food; and maximum absorption of digested food; highly-coiled; to reduce speed of food flow; for maximum digestion; and absorption; presence of villi; and microvilli; to increase surface area; for maximum absorption; dense network of capillaries; to transport blood; for efficient transport of absorbed food; presence of lacteals; for absorption of fatty acids and glycerol molecules; presence of enzymes: Lipase; for digestion of lipids into fatty acids and glycerol; maltase; for digestion of maltose to glucose molecules; peptidase; for breakdown of peptides into amino acids; sucrase; for digestion of sucrose into glucose and fructose; lactase; for digestion of lactose into glucose and galactose; goblet cells; produce mucus; to lubricate the walls of the ileum; for smooth flow of food; coats the walls of ileum to prevent digestion by peptidase enzyme; Max. 20 mks

Q11. a) What is homeostasis?

         (Mechanisms of) control and maintenance of a constant internal environment regardless of the external conditions; 2 mks

  • b) Name any three factors that must be maintained constant in mammalian bodies

          Temperature; Water; Salt or ion content; Carbon (IV) oxide; Glucose; amino acids; Max. 3 mks

  • c) Explain how endotherms respond to heat and cold conditions in their environment

         Heat/hot conditions: Increased sweating; to lose heat through latent heat of vaporization; dilation of arterioles under the skin; to bring more blood to the skin surface to lose heat to the atmosphere; decreased body metabolism; to reduce heat generation; erector pili muscles relax; making hair follicles to relax hence hair lies flat on skin, no air is trapped; to lose heat; slow/reduced muscular activity due to slow metabolism; to reduce heat production; panting to expose tongue and mouth; to release heat; moving to shades to avoid direct heat; aestivation; to escape the extreme heat; flapping of ears to create currents to carry away heat; Cold conditions: stamping of feet; to generate heat; basking in the sun to gain heat directly; less production of sweat; to reduce water loss through latent heat of vaporization; vasoconstriction of arterioles; hence less blood flow to the skin surface to reduce heat loss; increased metabolism through release of more thyroxine hormone; to generate heat; erector pili muscles contract; pulling hair follicles hence hair is raised; to trap a layer of moist air; to prevent heat loss; shivering/rapid contraction of muscles; to yield heat to warm body; Max. 15 mks

Q12. Describe the route taken by water from the soil up to the evaporating surface of a plant

      Water is drawn into the root hair cells by osmosis; due to the presence of dissolved substances in the cell sap of root hairs, the concentration of cell sap is greater than that of the surrounding solution in the soil/concentration gradient; this exerts a higher osmotic pressure, thus drawing the water molecules across the cell wall and cell membrane into the root hair cells; more water drawn into the root hair cells dilutes the cell sap; making it less concentrated than that in the adjacent cortex cell of the root; due to osmotic gradient, water moves from the adjacent cells to the next by osmosis; until it enters the xylem vessels located in the center of the root; the xylem vessels of the root then conduct the water up into the xylem vessels in the stem into the leaves; there is a force in the roots which pushes water up the stem; this force is known as root pressure; and can be considerably high in some plants; energy from the endodermal cells of the root is responsible for driving this force; in the xylem vessels, water would rise up by capillarity; to some extent because the vessels are narrower and there is  a high attractive force between the water molecules and the cell walls; the cohesive; and adhesive forces are important in the maintenance of a continuous and uninterrupted water column in the xylem vessels up the tree to the leaves; water vaporizes from the spongy mesophyll cells; their cell sap becomes concentrated than the adjacent cells. This increases the osmotic pressure of the spongy mesophyll cells; as a result of this, water flows into the cell from other surrounding cell, which in turn takes in water from xylem vessels within the leaf veins; this creates a pull/suction force that pulls a stream of water from xylem vessels in the stem and roots. This force, known as transpiration pull; helps in maintaining a continuous column of water from the roots to the leaves; water flows from the midrib into leaf veins from where it enters leaf cells; from the mesophyll cells, it enters the airspaces; then the substomatal air chambers; from where it evaporates through the stomata; to the atmosphere; Max. 20 mks

Q13. How is the mammalian heart adapted to its functions?

Heart is enclosed in a pericardial membrane/pericardium; that produces a fluid; to lubricate it; the membrane also keeps the heart in position; It is covered in a fatty layer; that acts as a shock absorber; made up of cardiac muscles; which are interconnected/interacted hence contract and relax without fatigue or nervous stimulation/myogenic; for continuous pumping of blood throughout the lifespan of the animal; the muscles are supplied by nutrients and oxygen; by the coronary arteries; and the coronary veins take away wastes and carbon (IV) oxide; heart is divided into 4 chambers; for efficient double circulation/ avoid mixing of oxygenated and deoxygenated blood/carry large volume of blood; has interventricular septum; to separate oxygenated and deoxygenated blood; ventricles are thick/muscular; to generate high pressure to pump blood out of the heart; left ventricle has thick muscles/more muscular; to pump blood to all body tissues; heart has bicuspid; and tricuspid valves; to prevent back flow of blood to left auricle; and right auricle respectively; valves have tendinous cords/valve tendons; to prevent them from turning inside out; semi lunar valves located at the beginning of major arteries; prevent backflow of blood into the ventricles; has sino-artrio node located in the muscles of the right auricle; to initiate heart beat/contractions of heart muscles/cardiac muscles, rate of heart beat is controlled by nerves; vagus nerve; slows down heartbeat; while sympathetic nerve; speeds up the heartbeat; has aorta; to transport oxygenated blood to all body parts; has pulmonary artery; that transports deoxygenated blood from right ventricles to lungs for oxygenation; has pulmonary vein; that transports oxygenated blood from lungs to the left ventricles; for distribution to all body parts; has the venacava; that  receives deoxygenated blood from all body parts to right ventricles; Max. 20 mks

Q14. Describe double circulation in mammals

 Deoxygenated blood from body tissues (except lungs); enters the heart via the right auricle; through the venacava; it flows to the right ventricle; via the tricuspid valve; the right ventricle contracts; pumping blood; via the semi lunar valves; through the pulmonary artery; to the lungs for oxygenation; the oxygenated blood from the lungs; flow through the pulmonary vein; to the left auricle; via the bicuspid valve; to the left ventricle; the left ventricle contracts; pumping blood via the semi lunar valves; through the aorta; to the rest of the body tissues; Max. 20 mks

Q15. Describe the process of urine formation in the mammalian kidneys

      The afferent arteriole which is a branch of the renal artery supplies blood to the glomerulus; the afferent arteriole has a wider lumen/diameter than the efferent arteriole; which takes away blood from the glomerulus; the differences in the diameter of the afferent and the afferent vessels causes high pressure; leading to ultrafiltration of blood; the walls of the blood capillaries are one-cell thick; hence glucose, amino acids, vitamins, hormones, salts, creatine, urea and water filter into the Bowman’s capsule; to form glomerular filtrate; white blood cells, red blood cells, plasma proteins such as globulin and platelets are too large to pass through the capillary wall; hence remain in the blood capillaries; useful substances in the human body are selectively reabsorbed; back into the blood stream at the proximal convoluted tubule; the tubule is highly coiled; to increase the surface area for reabsorption of the substances; the useful substances include amino acids, glucose, vitamins, hormones, sodium chloride and water; many mitochondria found at the proximal convoluted tubule; provide energy for reabsorption of these substances against a concentration gradient; the glomerular filtrate flows into the descending and the ascending limb of the loop of Henle; blood in the capillaries and the glomerular filtrate in the loop of Henle move in opposite directions/counter-current flow; this provides a steep concentration gradient that leads to maximum absorption of water through osmosis; sodium chloride is actively absorbed from the ascending limb into the blood capillaries; under the influence of aldosterone hormone; the glomerular filtrate flows into the collecting tubule from where, more water is reabsorbed into the blood stream; antidiuretic hormone influences the amount of water to be reabsorbed depending on the osmotic pressure of the blood; the glomerular filtrate from several collecting tubules now referred to as urine; is emptied into the collecting duct; the urine passes through pyramid, pelvis and ureter into the bladder; where it is stored for some time. The sphincter on the urethra relaxes to allow urine to be released from the body; Max. 20 mks

Q16. Explain the role of the following hormones during homeostasis

  • Antidiuretic Hormone (ADH)

Secreted by the (posterior lobe/end) pituitary gland; in response to an increase in the osmotic pressure of blood; the hormone stimulates the distal convoluted tubules and the collecting ducts; to increase their permeability to water; this increases the reabsorption of water into the bloodstream; concentrated and less urine is excreted; when the osmotic pressure decreases, less or no hormone is produced; hence the tubules become impermeable to water; less water is reabsorbed into the bloodstream; hence more dilute urine is excreted; fluctuations in the osmotic pressure is detected by the hypothalamus;

Secreted by the pancrease; in response to a rise in blood sugar level; it stimulates liver cells to convert the excess glucose into glycogen and fats for storage in the liver and muscle cells; increases the oxidation of glucose in respiration to yield water energy and carbon (IV) oxide/increases metabolism in the body; this leads to a fall in blood glucose to normal level;

Secreted by the pancrease; in response to a decline in blood glucose level; it stimulates liver cells to convert the stored glycogen and fats back to glucose; stimulates the conversion of amino acids to glucose; and stops the oxidation of glucose in the body cells; the glucose formed is released to the bloodsteream causing a rise of blood glucose level to normal; Max. 20 mks

Q17. a) Distinguish between Diabetes mellitus and Diabetes insipidus

            Diabetes mellitus is a condition/disease caused by failure of the pancrease to produce adequate insulin hormone; leading to excess glucose levels in the body some of which is released in urine while diabetes insipidus is a condition caused by failure/inability of the kidney tubules to control the amount of water in urine as a result of a defect in production of antidiuretic hormone (ADH) leading to production of more dilute urine; Max. 2 mks

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Biology notes for form two - all topics.

biology essay form two


6. Reduce Sitting and Screen Time

Exercise can’t immunize you from your sedentary time. Even people who exercise regularly could be at increased risk for diabetes and heart disease and stroke if they spend lots of time sitting behind computers. Practically speaking, you could consider taking breaks from sedentary time, such as walking around the office/room a couple of times in a day.

7. Consume less salt and sugar

Most people get their sodium through salt. Reduce your salt intake to 5g per day, equivalent to about one teaspoon. It’s easier to do this by limiting the amount of salt, soy sauce, fish sauce and other high-sodium condiments when preparing meals; removing salt, seasonings and condiments from your meal table; avoiding salty snacks; and choosing low-sodium products. On the other hand, consuming excessive amounts of sugars increases the risk of tooth decay and unhealthy weight gain. In both adults and children, the intake of free sugars should be reduced to less than 10% of total energy intake. This is equivalent to 50g or about 12 teaspoons for an adult. WHO recommends consuming less than 5% of total energy intake for additional health benefits. You can reduce your sugar intake by limiting the consumption of sugary snacks, candies and sugar-sweetened beverages.

8. If you drink alcohol, do so responsibly

While an occasional alcoholic drink likely won’t affect your health, drinking too much alcohol can take a heavy toll on many of your organs.

Overconsumption of alcohol can damage your liver, brain, and heart, and also increase the risk Trusted Source of several types of cancer, including breast, colorectal, and liver cancer. Heavy drinking can also negatively impact your mental health.

- Drinking too much can interfere with the brain’s communication pathways, and can affect the way the brain looks and works.

- Heavy drinking takes a toll on the liver, and can lead to a variety of problems and liver inflammations

biology essay form two

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BIOLOGY Paper 2 Questions and Answers - KCSE 2022 Past Papers

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SECTION A (40 marks)

Answer all the questions in this section in the spaces provided.


  • Identify the factor under investigation. (1 mark)
  • Give a reason for your answer in 1(a)(i) (1mark)
  • maintain the water bath at 35°C (1 mark)
  • use soaked bean seeds (1mark)
  • Explain the expected observations at the end of the experiment in test tubes E and F. (2 marks)
  • Explain what is likely to happen if set-up F was maintained for 7 days. (2 marks)
  • hippopotamus (2 marks)
  • algae   (2 marks)
  • Positive effects (2 marks)
  • Negative effects (2 marks)
  • Two tall garden pea plants were crossed and of the resulting offspring, 750 were tall and 250 were short. Using letter T to represent the dominant gene, determine the genotypic ratio of the off-spring. (5 marks)
  • Besides height in the garden pea plants, state two other contrasting seed traits that Mendel focused on in his genetic studies. (2 marks)
  • State how the genetic knowledge has been used to improve pea plant farming. (1 mark)
  • temperature   (3 marks)
  • glucose concentration in root hair cell sap (3 marks)
  • State two characteristics of the root hairs that increase their surface area for absorption of mineral ions. (2 marks)
  • State two main functions of the ear ossicles. (2 marks)
  • tymphanic membrane (1 mark)
  • cochlea  (1 mark)
  • State the function of the eustachian tube in the mammalian ear. (1 mark)
  • wax (1 mark)
  • endolymph and perilymph (2 marks

SECTION B (40 marks)

Answer question 6 (compulsory) and either question 7 or 8 in the space provided after question 8.

  • On the grid below, draw the graph of the number of bubbles produced per minute against light intensity. (6 marks)
  • State how the identity of the gas produced can be determined in the laboratory. (I mark)
  • Name the apparatus used for measuring light intensity. (1 mark)
  • Why was it necessary to get the shoot from an aquatic plant? (1 mark)
  • 0-6 (3 marks)
  • 6-8(3 marks)
  • State two modifications one would make on the experimental set up to increase the rate of gas bubble production. (2 marks)
  • Explain the limitations of using gas bubbles to determine the rate of photosynthesis. (2 marks)
  • With a reason, predict the number of bubbles that would have been produced at 15 units of light intensity. (1 mark)
  • Describe how plants eliminate waste products. (8 marks)
  • Describe the structure and function of the mammalian nephron. (12 marks)
  • Describe five tropic responses in plants and their survival values. (15 marks)
  • Describe how the mammalian heart beat is controlled. (5 marks)


  • Oxygen (is necessary for seed germination);
  • Presence/inclusion of pyrogallic acid (in set-up E) absorbs oxygen in experimental set-ups);
  • (35°C) is the optimum temperature required for functioning of (most) enzymes;
  • To soften the seed coat/testa (for ease of emergence of the radicle)/ water activates germination enzymes/hydrolyses stored food/enhancing the rate of germination/solvent/medium of transport;
  • Set-up E- germination will not occur due to lack of energy/ oxygen;
  • Set-up F-germination will take place since the seed coat/testa is softened/there is oxygen (that was initially in the apparatus)/ temperature is optimum;
  • Germination/growth process stagnates/slows down then seedlings wither/die/dry up; the oxygen/moisture in the test tube will be depleted;
  • Hippopotamus exhale carbon (IV) oxide which is used up by the algae/reeds to photosynthesize; their dung released into the water enriches it, favouring the growth of algae/ phytoplanktons/reeds; the dung is also fed on by fish;
  • Algae are the primary producers for the lake ecosystem; release oxygen for use by organisms (in the lake ecosystem); purifies the ecosystem by using up the carbon (IV) oxide (produced by the fish/hippopotamus/other animals; regulates the pH of the water-by using up the carbon (IV) oxide; provide breeding grounds for fish; algae is fed on by fish/hippopotamus;
  • Portions of fertilizers\/organic manure applied on the farms find themselves deposited in the lake (due to surface run-off/ siltation); enriching the lake ecosystem, favouring growth of plants/algae/phytoplanktons(in the lake ecosystem);
  • Excessive use of fertilizers/organic manure on the farms and their eventual deposition into lake ecosystem into the lake ecosystem results in nthe overgrowth of phytoplanktons/leads to eutrophication;
  • Some agrochemicals (pesticides/herbicides) used in the farms may be toxic/poisonous to the aquatic organisms;
  • Extensive surface run-off/soil erosion and deposition into the ake blocks/clogs gaseous exchange surfaces of aquatic life; it increases turbidity, reducing visibility/light penetration in the water;


  • Texture (of seed coat);
  • Colour (of seed coat/cotyledon/ testa);
  • Form/shape of the seed;
  • Artificial selection/ cross breeding/ polyploidy/ genetic engineering (resulting in varieties with desirable traits);
  • At temperatures below optimum, the rate (of mineral ions uptake) is slow due to inactive respiratory enzymes; at optimum temperature, the rate (of mineral ions uptake) is highest since respiratory enzymes are most active; at temperatures beyond optimum, the rate (of mineral ions uptake) slows since the respiratory enzymes are destroyed/denatured;
  • Glucose is a respiratory substrate (which when oxidized releases energy); needed for active uptake of mineral ions; high glucose concentration produces more energy; while low glucose concentration produces less energy;
  • Are long/elongated (to penetrate through the soil) to reach more mineral ions;
  • Are numerous/ many;
  • Transmission of sound vibrations (from the tympanic membrane to the oval window);
  • Amplification of sound vibrations;
  • Thin/tight/pliable membrane that vibrates/converts sound waves into vibrations;
  • Highly coiled to accommodate a larger number of sensory cells; 
  • Has numerous sensory cells (to perceive sound vibrations)
  • Filled with a fluid to enhance transmission of sound vibrations;
  • To balance pressure between the atmosphere and middle ear/on both sides of the eardrum/middle and outer ear;
  • Trap dust particles/prevent entry of solid/ foreign particles/ bacteria/(micro)organisms;
  • Maintain the pliability/ flexibility of tymphanic membrane;
  • Absorbs (mechanical) shock;
  • Transmission of vibrations in the inner ear;


  • (Using a glowing splint) it relights a glowing splint;
  • Photometre/light metre/ exposure metre/ photographic light metre;
  • Aquatic plants are adapted to photosysnthesizing under the water/ in low light intensity; it can utilize carbon(IV)oxide in solution form; it is easier to collect the gas produced by aquatic plants under the water; OWTTE
  • Rapid increase in the number of bubbles produced; due to increased light intensity which increased the rate of photosynthesis;
  • Number of bubbles produced remain constant; since the rate of photosynthesis had reached the maximum; due to optimum light intensity; other factors (such as carbon (IV) had oxide concentration) became limiting;
  • Supply sodium hydrogen carbonates in the set-up/ any other source of carbon (IV) oxide;
  • Increase the number of shoots of aquatic plants;
  • Increase temperature to optimum;
  • Photosynthesis and respiration occur simultaneously in plants/gases produced during one process are used in the other; not all bubbles may be accounted for/some gas dissolves in the water;
  • 32 or any other value less than 32 but not more than 32, photosynthesis had reached the peak/maximum/less than 32-bleaching of chlorophyll;
  • Plants eliminate vapour through the stoma/cuticle/lenticels during the process of transpiration;
  • Some other wastes are eliminated in form of gases (oxygen/carbon (IV) oxide through diffusion/through lenticels/ stoma/ pneumatophores during photosynthesis;
  • Some plants also get rid of excess water in form of water droplets-jor guttation through hydathodes in their leaves;
  • Some plants eliminate their wastes by shedding their leaves;
  • Plants also recycle/reuse their wastes, for instance the carbon (IV) oxide produced during respiration being used in photosynthesis; as the oxygen produced during photosynthesis is used up during respiration; Other plants store their wastes in vacuoles; while others deposit them in stems/roots;
  • Some waste products like gum, resins, oils are removed by exudation through the bark; Max - 8 marks
  • It has kidney/renal tubule; and glomerulus/ a network of blood capillaries;
  • Bowman's capsule; (with a capsular space between inner and outer wall); and a glomerulus where ultrafiltration occurs; due to the difference in diameters of the blood vessels serving it; afferent vessel (wider lumen); and efferent vessel (narrower lumen);
  • The proximal convoluted tubule; extend from the Bowman's capsule. The filtrate flows through the proximal convoluted tubule where useful substances/ glucose, amino acids, some water and mineral salts/ ions are selectively reabsorbed into the bloodstream; by diffusion/active transport;
  • Ascending and descending/The Loop of Henle has a descending arm for water reabsoption; and an ascending arm where salts are reabsorbed;
  • The (filtrate empties into the) distal convoluted tubule; where (more) water is reabsorbed into the blood by osmosis/under the influence of Antidiuretic Hormone (ADH) and (more) mineral salts are reabsorbed by diffusion/active transport under the influence of aldosterone; Max-12 marks
  • Phototropism; growth curvature in response to direction/ unidirectional light; shoots are positively phototropic while roots are negative; phototropism enables plant shoots reach light for photosynthesis;
  • Chemotropism; is growth response to a gradient of chemical substance/mineral ions/salts concentration; for instance, the growth of pollen tube towards the embryo sac for fertilization/ growth of roots towards certain mineral salts (for absorption);
  • Geotropism; is the growth response to gravity; shoots are negatively geotropic while roots are positively geotropic; geotropism enables the roots reach water/mineral ions for absorption/enables roots to grow into the soil for anchorage;
  • Hydrotropism; is the growth response to water? moisture-joi roots are positively hydrotropic, enabling roots reach water for absorption;
  • Thigmotropism/haptotropism; is the growth response due to contact with solid objects; observed in climbing stems/ tendrils/plants with weaker stems to enable them reach light for photosynthesis/exposing flowers for pollination/fruit dispersal; Max-15 marks
  • Mammalian heartbeat is controlled in two ways, non-nervous; and through nervous control; During the non-nervous control, the cardiac muscles are myogenic/ initiate their own contractions/relaxations;(stimulation/electrical charges/excitations originate from within, in the Sino Atrial Node (SAN), stimulus/ excitation spreads through auricles leading to their contraction, stimulus/ excitation proceeds to the atrioventricular node into the Purkinje tissue to all ventricles (right/left) which contract; During the nervous control, the blood pressure and chemical composition of blood is monitored by the cardiovascular centre of the brain;/the heartbeat rate can be increased through sympathetic nerve; heartbeat rate lowered through vagus nerve/parasympathetic nerve;

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Biology library

Course: biology library   >   unit 1.

  • Preparing to study biology
  • Biology overview

What is life?

Introduction, properties of life, 1. organization, 2. metabolism, 3. homeostasis, 5. reproduction, 6. response, 7. evolution, is this the definitive list, separating living and non-living things, what counts as life is still being defined., what do you think, want to join the conversation.

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How to get into tie online library  .

Getting into Tie online library (www.tie.go.tz vitabu) is so much easy, just tap on the green button below and you will be redirected to Tie library. https //ol.tie.go.tz login

To find Tie books in the library, you are required to login to your account, enter your username and password. 

If you forgot your login password tap on forgot password to recover or create new password. 

If you are new to Tie online library (https //ol.tie.go.tz login) you need to register first before access Tie online books. You can fill a registration form or one-click login by Google email. 

Tanzania Institute of Education TIE Online Library service | TET Maktaba Mtandao  

The Tanzania Institute of Education (TIE) is a Parastatal Organization under the Ministry of Education and Vocational Training (MOEVT) charged with the responsibility of ensuring the quality of education in Tanzania at the pre-school, primary, secondary and teacher training levels.

The Tanzania Institute of Education Launched Free Online Library Services to Help Tanzanians and None Tanzanians to find Learning materials  Easily in Distance way Especially for those who had no Access to physical Library service.

Kalenda ya utekelezaji Awali na shule Msingi  OPEN

What are the Tie books Available  

In this page you are going to find Tie library books . These Tie library books at https //ol.tie.go.tz login or Http ol tie go tz are only available for online use. Tie books pdf download is not available. 

This page acts as alternative to Tie library. All Tie library books are available here, but you won't be able to download Tie books pdf. 

To find this page you may go to your browser then on google, search Tie library, Tie books,  Tie library books,  Tie books pdf download, Tie vitabu online, www.tie.go.tz vitabu or https //ol.tie.go.tz login or Http ol tie go tz

Also you can download Tie library APK in your android phone . Tie library apk is available for free.

  Form Two Books

Strategies for answering exam and test questions

Click on the accordions below to see more information about how best to tackle the following question types in your exam.

Multi-choice questions

Things to remember about multi-choice questions

  • Read through the options and try to eliminate the ones that aren’t right . Multi-choice questions usually have one option that is obviously wrong, and three or four others that are similar.  It is important to look carefully at how they are worded in order to select the correct  answer.
  • Don’t struggle over a question . Do all of the easy questions first and come back to harder ones later to maximise efficient use of test/exam time.
  • Answer all the questions . Even if you are not sure, your educated guess may well be correct. It is better to have a go at answering a question than potentially miss out on a mark.
  • When you check back through your paper and think an answer is wrong - change the answer . Research indicates that you will probably be correct in doing so.

Short answer questions

Short answer questions range from a sentence or two through to a paragraph in length.

  • Keep to the point . Short answers are usually two-three sentences.
  • Main ideas . Your answers should incorporate the key points, words, ideas and phrases the marker will be looking for.
  • Leave one or two lines after each answer . This is so you can add important points later on.
  • Try to answer all the questions .  If you don’t know the complete answer, put down what you do know, as this is likely to get you some marks.

Exam essay questions

The advice here is in four parts: Time allocation | Task analysis | Planning | Presentation

Time allocation

  • Use the reading time at the start of the exam to choose which essay questions you will answer .
  • Check how much time you might have to answer each essay question , and stick to it. You can come back and add more to your answer in your revision time at the end of the exam session.
  • If you haven’t finished your answer, jot down the rest in note form . This will show the marker what you know, and you might get some marks for it.

Task analysis

  • Read the question carefully .
  • Underline or highlight the content words . What is the topic?
  • Pick out the instruction words in the question, e.g. identify, describe, compare and contrast, evaluate. What are you being asked to do with the topic?
  • Take some time to think and plan your answer . For example: use the reading time to select which essay questions you will answer. Then use the start of the writing time (5-20mins) to make notes of all the points you remember that are relevant to the essay. General guide for timing: for 30 minutes of writing, allow 5-7 minutes for planning .
  • Plan out the structure by organising your points into a logical order :e.g. by numbering them according to intended sequence.
  • General writing rule for exam essays - one paragraph = one point . Follow standard essay-writing procedure, e.g. start with a topic sentence that contains your key point, and then support this with examples, explanations, and evidence.


  • Make sure your handwriting is legible . Markers should not have to decipher your handwriting. If your handwriting is illegible, it could compromise your marks.
  • Make sure that you can express ideas effectively in terms of sentence structure and word use .  Incoherent sentences and incorrect terminology will likely result in the marker not being able to understand your answer properly.
  • Don’t worry too much about punctuation, grammar and spelling . Getting your ideas down is more important than ‘perfect’ writing (and markers usually take this into account given that students are writing under pressure in an exam situation). However, you do need a basic level of competency in these areas: an answer that lacks any punctuation and is full of spelling mistakes will probably be incoherent for the marker.
  • Don't waffle . Get straight to the point in terms of your answer so that you don’t waste time and word space on unessential or irrelevant detail. Planning your essay beforehand is key to avoiding waffle.

Problem solving questions

Usually these types of questions target formulae, steps in a process, or rules.

  • Make sure you write down relevant formulas, equations, and rules . Important: For numerical problems involving computation, make sure you include the appropriate mathematical units in your final answer (e.g. ml, m/sec).
  • Clearly show the steps you have taken in working out the answers.
  • If necessary, write notes to explain your answers .
  • Do the easier answers first , and return to the difficult ones later.
  • Explain the general and distinctive features of the kingdom Fungi
  • State the phyla of the Kingdom Fungi
  • Describe the structure of mosses
  • Outline advantage and disadvantages of Mosses
  • Explain general and distinctive features of the division Filicinophyta
  • Describe the structure of Ferns
  • Outline advantages and disadvantages of ferns
  • Explain the concepts of nutrition and food nutrients
  • Outline the importance of nutrition in living things
  • Identify different types of food substances and their functions in human Body
  • Explain the concept of balanced diet in terms of food quality and quantity
  • Explain nutritional requirement for different groups of people
  • Outline different types of nutritional deficiencies and disorders in human beings
  • Explain the causes , symptoms, effect and control measures of nutritional deficiencies and disorders
  • Identify parts of the human digestive System and their adaptive features
  • Explain the digestion process in process in human being
  • Compare the human digestive system with that of other mammals
  • Outline common disorders and diseases of the human digestive System
  • Explain causes, symptoms, effects and control measures of common disorders and diseases of the human digestive system
  • Mention essential mineral element in plant nutrition
  • Investigate the roles of essential elements in plant nutrition
  • Explain the concept of photosynthesis
  • Describe the structure of the leaf in relation to photosynthesis
  • Explain the process of photosynthesis
  • Outline the importance of photosynthesis in the real life situation
  • Mention the basic food substances and their properties
  • Identify common reagents and chemicals used to determine food Properties
  • Carryout food tests for reducing sugars, non reducing sugars, starch, proteins and lipids (Fats and Oil)
  • Explain the concept of food processing , food preservation and food storage
  • Explain the importance of food processing, preservation and storage
  • Differentiate between traditional and modern methods of processing, preserving and storing food
  • Balance Of Nature
  • Explain the concept of natural environment
  • Describe biotic and abiotic components of the environment
  • Identify various organism in their natural environment in the community
  • Explain the importance of the natural environment
  • Identify ways in which living organisms interact with the non living component of the environment
  • Explain the interaction of organisms among themselves
  • Explain the meaning of food chain and food web
  • Mention the components of a food chain and food web
  • Distinguish food chain from food web
  • Explain the significance of food chain and food web in real life situation
  • Transportation Of Materials In Living Things
  • Explain the concept of transportation of materials in living things
  • Outline the importance of materials in living things
  • Explain the meaning of osmosis, diffusion and mass- flow
  • Carryout experiments to demonstrate the process of diffusion, osmosis and mass flow
  • Outline the differences between diffusion, osmosis and mass flow
  • Explain the roles of diffusion, osmosis and mass flow in movement of materials in living organisms
  • Explain the functions of the external and internal parts of the mammalian heart
  • Explain the adaptations of the parts of the mammalian heart to their functions
  • Describe the structure of arteries, veins and capillaries
  • Carry out simple experiments to determine pulse rates in human being
  • Explain the function of major blood components
  • Explain the effects of HIV on white blood cells
  • Explain the concepts of blood group and blood transfusion
  • Outline the relationship between blood groups and blood transfusion
  • Explain the advantages and disadvantages for blood transfusion
  • Outline precautions to be taken during blood transfusion
  • Explain the importance of blood circulation in humans
  • Mention disorders and diseases of the human blood circulatory system
  • Outline the causes, symptoms and effects and control/measures of the disorders and diseases of the human blood circulatory system
  • Carry out practical exercises to measure human pulse rate and blood pressure
  • Explain the concept of lymphatics
  • Describe the components of the human lymphatic system
  • Mention the common disorders and diseases of the lymphatic system
  • Explain causes, symptoms, effects and prevention of disorders and diseases of the human lymphatic system
  • Explain the concept of vascular system
  • Describe components of vascular system
  • Explain the function of vascular system in plants
  • Explain the functions of root hairs in absorption and movement of water and mineral salts in plants
  • Outline the movement of water and dissolved mineral salts in plants
  • Explain the concept of transpiration
  • Outline the significance of transpiration in plants
  • Outline factors affecting the rate of transpiration in plants
  • Identify organs responsible for gaseous exchange in living organisms
  • Explain the concept of gaseous exchange
  • Identify parts of the respiratory system
  • Describe the features of different parts of the respiratory system and their adaptive features
  • Describe the mechanism of gaseous exchange in mammals
  • Describe gaseous exchange across the alveolus
  • Outline factors affecting gaseous exchange in mammals
  • Identify parts of plant responsible for gaseous exchange
  • Describe the process of gaseous exchange in plants
  • Explain the importance of gaseous exchange in plants
  • Explain the concept of respiration
  • Mention types of respiration
  • Explain the concept of aerobic respiration
  • Outline the mechanism of aerobic respiration
  • Carry out experiments on aerobic respiration
  • Describe factors which affect the rate of respiration
  • Explain the concept of anaerobic respiration
  • Outline the mechanism of anaerobic respiration
  • Mention the end products of anaerobic respiration
  • Carry out an experiment to demonstrate the application of anaerobic respiration
  • Distinguish between aerobic respiration and anaerobic respiration
  • Mention common airborne infections and diseases which affect the respiratory system
  • Explain the causes, symptoms, effects and control measures of common infections and diseases of the respiratory system
  • Mention disorders of the respiratory system
  • Explain causes, symptoms and effects of the disorders of the respiratory system
  • Suggest ways of preventing and controlling disorders of the respiratory system

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Free Biology Essay Examples & Writing Tips

Don’t know what to write about in your essay on biology? Looking for good biology essay examples for inspiration? This article has all you need!

A biology essay is a type of academic paper that focuses on a particular topic of biology. It can discuss animal life, cycles in biology, or a botanic subject. You will need to demonstrate your critical thinking skills and provide relevant evidence to support your perspective.

On this page, you will find examples of biology essays. You will also find here tips and topics prepared by our experts . They can assist you in nailing your short or extended essay.

Areas of Research for Biology Essays

If you’ve been assigned to write a biology essay, you probably know which area of research you have to choose. However, it might be beneficial to explore other available scopes. It’s useful for both interdisciplinary study and the cases when you are free to pick your area of research. In this section, let’s figure out what you can study in biology.

Here are biological areas of research you should be familiar with:

  • Cancer Biology studies this type of disease to prevent, detect, diagnose and cure it. The ultimate goal of such biologists is to eliminate cancer.
  • Cell Biology is a branch that studies the structure, function, and behavior of cells. Here, biologists study healthy and sick cells to produce vaccines, medication, etc.
  • Biochemistry is an application of chemistry to the study of biological processes on cell and molecular levels. It is a cross-discipline between chemistry and biology. The focus is on the chemical processes of living organisms.
  • Computation Biology is a study of biological data that develops algorithms and models to understand biological systems. Here, scientists either work for institutions or research for private enterprises.
  • Genetics is an area that focuses on the study of genes and genetic variations for health benefits. It looks at the way DNA affects certain diseases.
  • Human Disease is an area within which scientists study different diseases. The field covers cancer, developmental disorders, disease genes, etc.
  • Immunology is a branch of biology that focuses on immunity. Immunologists look at the way the body responds to viruses as a way to protect the organism.
  • Microbiology studies all living organisms that are too small for our eye to see. It includes bacteria, viruses, fungi, and other microorganisms.
  • Neurobiology is the study of the nervous system. Biologists examine the way the brain works and look into brain illnesses.
  • Stem Cell and Developmental Biology seeks to examine how the processes behind stem cell’s ability transform cells. The biologists in this area use the power of stem cells to model human illnesses.

Essay on Biology: Writing Tips

Want to know how to start a biology essay? Wondering about the best way to write your essay on biology? Then check out the following tips.

When you’re writing about biology, pay attention to the following features:

  • Introduction . Just as in any other form of academic writing, the first section of your paper introduces the subject. Here, explain why your ideas are relevant to biology as a science.
  • Thesis Statement. The final one or two sentences of the first paragraph should include your original hypothesis and experiment. You will be proving them in the main body. You do not have to include the results as the reader will encounter them later. If you’re struggling with this part, try our thesis generator .
  • Main Body. In this part, write about all the experiments in detail. Often, teachers require to include visual aid to prove your point. For Zoology, Anatomy, Botany, it is pretty easy to find some photos and illustrations.
  • Conclusion. Here, restate your thesis. Reemphasize the most critical aspects described in the main body. You can do it by using our summarizing tool . The goal of this last paragraph is to leave an everlasting impression on the reader.

Thank you for reading our article. We hope you found it helpful. Share it with your class peers who also study biology. Additionally, have a look at the biological essay examples below.

780 Best Essay Examples on Biology

“the egg and the sperm” by martin: article review.

  • Words: 1401

Bacteria Classification and Assessment

Crop genetic erosion: understanding and responding to loss of crop diversity, the breakdown and recycling of neurotransmitters, the genomics of adaptation in birds by campagna & toews, the human family tree development, streptococcus pyogenes overview, a light microscope: function and usage, disorders of thyroid gland vs. normal structure, menopause and associated anatomical changes, cognitive neuroscience: methods and studies, metabolic responses to exercise, meiosis and mitosis and mendel’s law of independent assortment, the human body as a site of active conflict, biology: analysis of egg experiment, operant and respondent conditioning, the origin of olives and their medicinal uses.

  • Words: 1524

Yersinia Pestis: Mechanism of Streptomycin Resistance

Absorption and digestion of carbohydrates, “pécis: sociobiology” by c. nickerson, winogradsky’s contribution to biology, the nature of dna structure discovery, the discovery of the deoxyribonucleic acid (dna) structure, biology kingdom: fungi, plantae and animalia, body and atom relationship description, energy balance and expenditure, aspects of lactic acid bacteria in wine, ruth patrick, an american biologist and ecologist, eukaryotes: infections in travelers and migrants, food macromolecules – lipids, carbohydrates, and proteins, cervical, thoracic, and lumbosacral spinal cord cross-section levels, mitochondria and power companies, lucid dreams aspects nature analysis, natural history of farber, linnaeus, and buffon, stuttering and its neurobiological causes, protein structure and functions, somatosensory cortex and perception of touch, developmental stuttering in children, bacteria cells calculation and categorization, antimicrobial action mechanisms, animal self-medication article review, femoral nerve and functional movements associated with muscles, the botanical evidence: the general description and the analysis, streptomycetes among prokaryotes important in society, anatomy of neuron and neuroplasticity, is earthworm beneficial or harmful to humans, cellular respiration in context of human biology, history of potatoes, their vatiety, and popularity.

  • Words: 1233

A Biological Science Innovation Article Analysis

Streptococcus mutans: the pathogen of dental caries.

  • Words: 1016

Review of Eukaryote Cells Role in Organism

Aspects of hermaphroditism and self-fertilization, the thermoregulation is and its importance, fluid imbalance effects on gaseous exchange, diversity and extinction of cyclura lewisi, the swallowing process analysis, halophila stipulacea: dynamic changes in salinity levels, non-trophic interaction in marine species, aloe vera: composition, main biological activities, and use, the tridacnids species in a coral reef ecosystem, interesting aspects of brain development, cell signaling, intracellular signaling, and insulin signaling.

  • Words: 1120

The Psychological Nature of Memory

  • Words: 1223

Distribution of the Native Natural Species in Australia

  • Words: 1707

The Role of the Olive in Human History and Lives

  • Words: 1653

Planting Bamboo: The Role of Photosynthesis

Methods of finding and identifying dinosaur fossils.

  • Words: 2816

Occupational Exposure Limit of COVID-19 and Other Biological Agents

The occupational exposure of crude oil tank cleaning workers, how to identify ohio wild mushrooms, the function and structures of the human heart, the definition of etc and chemiosmosis, experiment on the bacteriophages, discussion of body image concerns problem.

  • Words: 2025

Epithelial Tissue: Structure and Functions

Nitrobacter’s features and position in the ecosystem, neural stem cells in therapeutic purposes, is vitamin d the new super nutrient, anatomy of the pituitary gland, the reproductive attractiveness of junco birds, triplet nature of the genetic code, microbial staining techniques, the importance of sleeping and dreaming, practical report: determination of a bacteriophage titer, the beginning of life: stages and participants, evolutionary biology and darwin.

  • Words: 1406

Characterizing Antibiotic Resistance of Hafnia Alvei and Citrobacter Freundii

  • Words: 2478

Microbiology: Influenza Viruses

Biowarfare and bioterrorism: history and origin, hippocampus-dependent memories during sleep, mitosis in onion root and whitefish blastula, biology of neuronal impulses interaction, clinical testing of naegleria fowleri amoeba, case study: human body water balance, prefrontal cortex and effects of stress exposure, possibility of improving gluten tolerance using necator americanus, nervous system: the main functions, how nematodes are beneficial to humans, escherichia coli: a deeply studied prokaryote, photosynthetic organism: aesculus hippocastanum, the question of determining species: the morphological species concept, pseudomonas aeruginosa: a more detailed study, memory: its functions, types, and stages of storage, acroptilon repens: plant description, the relationship between the working memory and non-conscious experiences, biology lab report: biodiversity study of lichens, consciousness: the link between working memory and unconscious experience.

  • Words: 1869

A Statistical Experiment: Junco Birds

Researching the basics of biology, high temperature and ultraviolet rays’ effect on different types of bacteria.

  • Words: 1346

Evaluating the Effect of Vitamin B12 on Athletic Performance and Strength

Digestive journey of cheeseburger, how people receive information from their environment, computational biology as an essential research area, the memory formation process: key issues, american crow subspecies and interesting facts, researching and analysis of peppered moths, adaptation to stress of endocrine and sympathetic nervous system, stem cells applications in bone and tooth repair and regeneration, mitosis and genetic makeup of different species.

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Writing help, paraphrasing tool, biology - free essay examples and topic ideas, biology and signaling alterations in ad.

The Rho-associated coiled-coil containing kinases (ROCKs) are ubiquitously expressed serine/threonine kinases that are downstream effectors of the RhoA GTPase (Ishizaki et al., 1996b; Leung et al., 1996a; Leung et al., 1995a; Matsui et al., 1996a; Nakagawa et al., 1996a; Schackmann et al., 2011). ROCKs are key regulators of the actomyosin cytoskeleton dynamics, as well as neuronal morphology and synaptic plasticity (Schubert and Dotti, 2007). The two ROCK homologs (ROCK1 and ROCK2) share high homology in their kinase domains (92%) and […]

Who Killed Yew Case Study Answers

Introduction The purpose of this case study is to find out the basic process of mitosis, which focuses on the basic cellular processes that occur during each stages of interphase, prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis. Mitosis is the process of cell division. It plays an important part in the life for example to growth of tissue, repair and replace damage or death cell, regeneration or asexual reproduction. Besides, this case is framed by solving a murder. The murder […]

Respiratory and Circulatory System

The human body is comprised of multiple separate systems that work together to maintain homeostasis, regular, stable internal conditions. The maintenance of internal function depends on a variety of variables: body temperature, fluid balance, concentration of sodium, potassium and calcium ions, and blood sugar levels. The respiratory system is responsible for the function of a series of organ in taking in oxygen and expelling carbon dioxide. The circulatory system, also known as the cardiovascular system, is responsible for the organ […]

Effect of Exercise on the Rate of Respiration and the Heart Rate

How does increase the number of jumping jacks affect the rate of respiration and the heart rate per minute in teenagers aged 17-18? Background Information: Different types of activity will have a different effect on the rate of respiration as well as the heart rate because of certain factors. These include the level of intensity and difficulty of the exercise, as well as determining whether it is an aerobic or anaerobic activity. Aerobic respiration requires the presence of oxygen. (Haldane, […]

Photosynthesis Vs. Cellular Respiration the Major Processess in a Global Balance

There are two key processes that occur in nature to obtain energy, they are photosynthesis and cellular respiration. The derivative of the word photosynthesis is the process in which energy of sunlight is converted by plants to store chemical energy in carbohydrate bonds. Photosynthesis is known to be performed by plants, as is cellular respiration. Cellular respiration is organisms obtaining energy from a conversation that releases energy when oxygen is present. These two processes work together hand in hand as […]

We will write an essay sample crafted to your needs.

Benefits of Starting School Later

Waking up before 6 in general- for most people is dreadful, so imagine being up at 7:00 to sit in a classroom. Fighting to get out of bed early in the morning is a hassle for a lot of people. School starting times are way too early and should be changed to a later times because students are affected negatively by these start time. This would promote focus and improve student performance and behavior. By going to the UCPS board […]

Photosynthesis and Energy

Energy is very important and plays a substantial role in life itself, but where does energy come from, and how does energy work? Of course, the answer is simple: photosynthesis. With this reading, you will learn what photosynthesis is, how it works, the energy it creates, and how energy is stored and used. Finally, you will learn about different types of energy and the benefits those energy sources have. The process of photosynthesis begins when a plant receives carbon dioxide […]

Process of Photosynthesis

Presentation Photosynthesis, process by which green plants and certain different living beings utilize the vitality of light to change over carbon dioxide and water into the basic sugar glucose. In this manner, photosynthesis gives the fundamental vitality source to basically all life forms. A critical result of photosynthesis is oxygen, on which most living beings depend. Photosynthesis happens in green plants, ocean growth, green growth, and certain microscopic organisms. These living beings are veritable sugar plants, creating a huge number […]

Idea of Photosynthesis by Jan Ingenhousz

To begin, the idea of photosynthesis was created by, according to Encyclopaedia Britannica, ""A Dutch scientist, Jan Ingenhousz. (Ingenhousz 1.) He was born in the Netherlands on December 8, 1730. Ingenhousz, is most known for his discovery of photosynthesis. According, to Encyclopedia Britannica, ""Ingenhousz discovered that light is necessary for photosynthesis, only the green parts of the plant perform photosynthesis, and all living parts of the plant can potentially damage the air."" (Ingenhousz 1.) Photosynthesis occurs in two steps inside […]

Exploring the Intricacies of Genetics through DNA

Introduction The hereditary molecule that is tasked with carrying genetic instructions that are used in all living things in development, growth, reproduction and functioning is referred to as deoxyribonucleic acid (DNA). DNA molecules consist of two strands which are bipolar and are mostly coiled near to one another to form a spiral. This strands are referred to as polynucleotides simply because they are made of small units known as nucleotides. The information of the DNA is stored in this nucleotides. […]

Climate Change and Genetically Modified Food

Social issues are the factors that affect how human beings live. One of the most prominent social issues in the twenty first century is climate change and genetically modified food. The two issues are somewhat related since climate change has changed weather patterns, forcing human beings to change their farming methods one way to adapt to climate change has been genetically modified food. Both climate change and genetically modified food have subject to rigorous debate and there lacks consensus regarding […]

Photosynthesis in Living Leaves

Abstract The rate of photosynthesis can be measured by examining the amount of reactants and the buildup of products. Oxygen is a product of photosynthesis and is stored in the spongy mesophyll. This gives the organism the ability to float. In this experiment, oxygen is taken out of the spongy mesophyll. The leaves are then placed into the bicarbonate solution with soapy water. The spongy mesophyll fills with the solution, causing the leaves to sink. A light source was placed […]

Hardy Weinberg Lab Analysis

How does migration affect the allele frequency of the dominant allele? A genetic population can be described as the sum of allelic frequencies of all genes that are represented in the population. This implies that for an evolution of a species to take place a change in the gene frequency has to take place. This can be influenced by some factors like the fitness of organisms, fertility or even the viability of the organisms. When the fitness of an organism […]

Energy Efficiency of Photosynthesis

Photosynthesis is the process in which plants use the energy from the sunlight to make glucose (a type of sugar), which they then use as food. The equation for photosynthesis is: 6CO2 (carbon dioxide) +6H2O (water) -->(Sunlight) C6H12O6 (glucose) +6O2 (oxygen). Plants, algae, and cyanobacteria are photosynthetic organisms. In plants and algae, light is absorbed by chlorophyll—a molecule present in the cytoplasmic organelle called the chloroplast. Chlorophyll has a porphyrin ring with a magnesium cofactor at its center. Plants have […]

What is Sustainability in Business?

The first aspect business looks when thinking about sustainability is the operational aspect and saving cost as it is easy to measure.Most of the resource we are using are non-renewable resources,from our energy need to the consumption of oil.But all these resources are bound to get over in the future.There is a term called peak oil,after which production of oil reduces due to reduce reserves.There is already an alert for helium gas which is used in many areas like filling […]

Factors Influencing Sustainability of Electronic Manufacturing Company in Laguna

The 5S program is a technique originated in Japan and was introduced by Takashi Osada in 1980. 5S is consist of five phases from Japanese words: Seiri (sort), Seiton (set in order), Seiso (shine), Seiketso (standardize) and Shitsuke (sustain). 5S is a step by step process of housekeeping to achieve a safe, clean and organized environment in the work area involving the employees with a commitment to sincerely implement and practice housekeeping. When the workplace is unorganized and dirty, the […]

The Sustainability of Bottled Water

Water is a valuable resource that all living things including human beings require in order to survive. It is believed that the realities of the environment will soon hit us to an extent of making us change the behavior regarding the costly use of resources (Earle, 2009). The changes are most likely going to affect the manner in which we use water and hence cause alterations both in quantity and water usage. Privatization of water resources as well as selling […]

What is Photosynthesis?

Photosynthesis is the process that transforms organisms from light energy into chemical energy. In order for photosynthesis to take place, it needs these three things: Water, carbon dioxide, and sunlight. As humans, in order to live plants, must take in gases. Plants are known as ""autotrophs, which means organisms that can make their own food. The process of photosynthesis was created and developed Jan Ingenhousz, a British physician and scientist. Joseph Priestley was another scientist who contributed to the discovery […]

Photosynthesis Virtual Lab

Hypothesis: all of the colors in the light spectrum are most effective in the growth process of photosynthesis except for green. We tested our hypothesis by plugging in the different colors as well as the different types of plants into the simulation. After running the simulation we gathered the info of the averages in lengths of the plants after 30 days. The variables we controlled in this experiment were the pot, type of soil, location, and amount of water given. […]

Why is Photosynthesis Important?

"Photosynthesis is an important process which allows organisms to produce food without the intervention of any other organisms. This specialized reaction, occurring only in autotrophs, has several key features that are fundamental for understanding the process as a whole. Factors of where the process takes place, the reactants and products of the reactions, and what happens in the process are all important elements in the success of photosynthesis. Photosynthesis occurs in the chloroplast, an organelle found only in plant cells. […]

DNA and Mutations

Occurrence of mutation. Mutation is the process that produces a gene or a chromosome set different from the wild type. For instance this allows us to measure the frequency of mutation occurance.a cell caring mutation can be used as probes to disassemble the constituent parts of a biological function and to examine their workings and interrelations.For a recessive mutation to give rise to a mutant phenotype in a diploid organism both alleles must carry the mutation but one copy of […]

Sustainability in Architecture

Sustainability in architecture is a concept that has been spread across the United States of America for decades now. For some time now the public has acknowledged that if we don't take care of the world we live in then soon it will be gone. The first signs that warned the people in urban areas were not only the in your face issue of global warming but also the increase in the price of energy. Building and business owners found […]

The Case for Urban Agriculture as a Driver of Environmental Sustainability

Abstract As a result of the growing global population, many cities around the world are experiencing rapid urbanization. With that comes a growing demand for food and increasing challenges in food production. One solution increasing in popularity is urban agriculture (UA), simply defined as the production of food in an urban environment. UA can operate on different scales (micro, meso, and macro) have various objectives (recreational, subsistence, or commercial), and take place across landscapes in the form of backyard gardens, […]

Sustainability and Social Responsibility in Companies and People

Social responsibility is the belief that businesses have an obligation to balance profit-making practices with activities that benefit their community. This is also referred to as corporate social responsibility (CSR). Sustainability is the ability to supply necessities for the population without compromising the availability of the resources for those in the future. Throughout this essay, the popularity of sustainability and social responsibility in corporate companies will be examined and explained. In addition, the demographics, including race and religion, of CSR […]

Effects of Sweet Cassava Polysaccharide

The study I researched was the ""Effects of sweet cassava polysaccharide extracts on endurance exercise in rats. Sweet cassava is a major carbohydrate in many countries and it contains monosaccharides and polysaccharides. It was found that high-carbohydrate foods could increase muscle glycogen content, which can allow one to exercise for a longer time and not tire as quickly. The aim of the study was to examine the effects of the sweet cassava polysaccharides (SCP) on exercise performance in rats. The […]

Sustainability Community Engagement and Diversity Inclusion Review BA

Introduction: Southern Company is an energy holding company that produces and sells electricity through various southern power subsidiaries. It's headquarters is located in Atlanta, GA and the company has been a part of the Fortune 500 list for 24 years. It's current rank is 126, up 19 spots from its ranking in 2017. The CEO is Thomas A. Fanning and he is in charge of 31,344 employees. Southern Company operates 11 regulated utilities serving an estimated 9 million people in […]

JOR Study on the Emerging Trend of Green-Banking and Environment-Sustainability through PSBSIN India

ABSTRACT The problem related to the environment, the maintenance of ecological balance and environmental-sustainability have become topics of debate throughout the world. Both organizations and consumers have understood the importance of the environment for the survival of human beings. The banking sector plays an important role in the economic growth of a nation. Given that public sectors banks (PSBs) are among one of the main sources of financing for commercial projects, they can play an important role in promoting environmental-sustainability […]

Compare and Contrast about Cats and Dogs

 Dogs and cats have several similarities, but even more distinctions. Both animals are easily loved by mankind and will display love and affection in return for good treatment. Some people enjoy the presence of a cat, and others are simply dog lovers. Based on the history, characteristics, and similarities of the two creatures, dogs are considered to be man's best friend- but most likely it's the feline who is. Thousands of years ago, a man trapped wolves and used a […]

How the Body Remains at Homeostasis

The body goes through many challenges throughout life, but the body always manages to stay at a stable equilibrium which is known as homeostasis. Homeostasis is the body's ability to adjust its internal environment in order to stay within a stable state in order for the body to function properly. Homeostasis processes may differ depending on what is going on in the body and how positive and negative feedback may affect it. In addition, some people may have deficiencies or […]

Endangered Species: Arctic Wolf

Why I chose the Arctic Wolf? The reason I am choosing the Arctic Wolf because I love wolves and I would hate them to go extinct. They are unique animals especially just listening to that beautiful spine-tingling howl, which they use to communicate. I also, like how they are territorial and could hear up to six miles away. Wolves are very much family-oriented, they have a good system of leadership, and they are beautiful animals and very powerful. They are […]

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