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1.Describe how the mammalian body protects itself against

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;

2.Outline and explain the various homeostatic functions of the liver in



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) oxide to 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;


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;

3 a. What is homeostasis?

Mechanisms of control and maintenance of a constant internal environment regardless of the external conditions;

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;

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;

4. 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 airspace.

5.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;

6.Describe double circulation in mammals - KCSE Biology Essay

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;

7.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;

8.Explain the role of the following hormones during homeostasis

a. 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; concentratedand 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;

b. Insulin

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;

c. Glucagon

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;

9(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;

b. Explain how mammalian bodies regulate glucose and protein levels in their blood

When glucose level is high (above 90mg/100cm3), the brain sends impulses to the (β cells of islets of Langerhans) pancrease cells; to release insulin hormone; the hormone 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;

However, when the glucose level falls below normal (below 90mg/100cm3); the brain sends impulses to the (α cells of the islets of Langerhans) pancrease cells; which are stimulated to release glucagon hormone; the hormone 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 to avail more glucose; the glucose formed is released to the bloodstream causing a rise of blood glucose level to normal;

The level of plasma proteins such as prothrombin, globulins, albumins and fibrinogen; which play a major role in osmoregulation and blood clotting; are controlled by the liver; which manufactures them using the amino acids found in the liver; when their levels reduce,more is produced; but when the level is high, less of the proteins is produced in the liver; excess amino acids are deaminated; as the body is not able to store them; the process involves removal of an amino group from an amino acid molecule; the amino group enters the ornithine cycle; where it is combined with carbon (IV) oxide to form urea; which is excreted in urine through the kidneys;

10. Describe the structure and function of the mammalian skin

It has a cornified layer ;made up of dead cells and is tough and impermeable to water; to protect the skin against mechanical damage; bacterial infections and water loss; granular layer; whose cells divide to form the cornified layer;

Malpighian layer; which is made up of diving cells that give rise to a new granular layer;

Contains melanin; to protect skin against ultra-violet rays/radiations;

Sebaceous glands; which secrete sebum; to make the skin supple/soft and waterproof; sebum is also antiseptic;

Blood vessels; dilate during hot weather; increasing blood flow near the skin surface; heat loss is enhanced;constrict; in cold weather; less blood flow; minimize heat loss;

Sensory nerve endings and receptors; enable detection of external environmental changes;

Highly coiled sweat glands; secrete sweat; to control body temperature; when hot sweat evaporates cooling the body; sweat contains excretory products;

Subcutaneous fat/adipose tissue in dermis; for insulation; hair; to regulate body temperature; in cold weather erector pili muscles contract; hair is raised, air trapped to insulate the body; in hot weather, erector pili muscles relax; hair lies flat reducing insulation;

Dense network of blood capillaries; supply nutrients/oxygen to skin tissues; as well as carrying away wastes and carbon (IV) oxide away from the skin tissues; adipose tissue/sub-cutaneous layer; serves as an insulator;helping in temperature control; helps in manufacture of vitamin D;

11. Discuss the various mechanisms of opening and closing of stomata

Photosynthetic theory;

During the day, guard cells carry out photosynthesis manufacturing glucose; This increases the osmotic pressure of the sap vacuole; which becomes higher than that of the neighbouring epidermal cells; guard cells therefore take in water by osmosis; and become turgid; the outer thin wall stretches easily; pulling the thicker inner wall outwards; thus the stomata opens;

At night, there is no light hence no photosynthesis takes place; plant cells respire using up more glucose; the osmotic pressure of the sap vacuole of the guard cells reduces; becoming lower than the neighbouring epidermal cells; the guard cells lose water by osmosis; to adjacent epidermal cells; they then become flaccid; pulling together the thick inner walls; and stomata closes;

Enzymatic inter-conversion between starch and glucose/sugar;

At day time, plants continuously use carbon (IV) oxide for photosynthesis; leading to an increase in the pH of the guard cells; this causes starch to be converted to sugar/glucose; the glucose increases the osmotic pressure of the guard cells; hence water is taken in by osmosis; the cells become turgid and bulge outwards; causing the stomata to open;

At night, no photosynthesis occurs but respiration takes place; carbon (IV) oxide accumulates in guard cells;lowering the pH; the low pH favours conversion of glucose into starch; starch is osmotically inactive;this lowers the osmotic pressure of guard cells; guard cells therefore lose water by osmosis to the adjacent epidermal cells; become flaccid; pulling together the thick inner walls; and the stomata closes;

Active ion exudation;

During the day, there’s an accumulation of potassium and sodium ions; as aresult of active pumping of the ions by the ATP formed through photosynthesis; carbon (IV) oxide fixation occurs in the guard cells; the guard cells become turgid; and stomata open;

At night, before the stomata close, the ions diffuse out of the guard cells into epidermal cells; the osmoticpressure of guard cells is lowered; they lose water to epidermal cells by osmosis; and become flaccid; thereby closing the stomata;

12 Explain how the following blood cells are adapted to their functions - KCSE

Biology Essays

a. Explain how the following blood cells are adapted to their functions

i. Red Blood Cell

Presence of haemoglobin molecules; with a high affinity to combine with oxygen as/to form oxyhaemoglobin;bi-concave shape; to increase the surface area for packaging of haemoglobin;absence of nucleus; to accommodate maximum/more haemoglobin molecules;thin membrane; for faster diffusion of gases;

ii. White blood cell

Irregular in shape/amoeboid; which changes to enable the cell to squeeze through the capillaries;lymphocytes produce antibodies; which help to prevent diseases;phagocytes are amoeboid-shaped; to change shape and engulf bacteria cells;

b. Explain the different ways in which Carbon (IV) Oxide is transported by blood

-Carbon (IV) oxide diffuses out of the tissues into the red blood cells where it reacts with water; in the presence of carbonic anhydrase enzyme; to produce carbonic acid;

-The acid dissociates into hydrogen and hydrogen carbonate ions; the hydrogen carbonate ions then diffuse out of the red blood cells into the plasma; where it further dissociates to produce carbon (IV) oxide on reaching the alveolar cavities of the lungs and diffuses into the alveoli; some carbon (IV)oxide combines with the amine group in the haemoglobin molecule forming carbaminohaemoglobin; which dissociates in the lungs producing carbon (IV) oxide;

-Some carbon (IV) oxide dissolves in the blood plasma forming carbonic acid, which dissociates to carbon (IV) oxide on reaching the lungs;

13. a. What is transpiration?

Process by which plants lose water to the atmosphere; in form of vapour (through lenticels, stomata and cuticle);

b. Explain how the various environmental factors affect the rate of transpiration

Temperature; an increase in temperature increase the water vapour holding capacity of air in the spaces between mesophyll cells due to increased evaporation; therefore more water diffuses from the cells increasing the water vapour pressure; this causes an increase in the diffusion gradient between the intercellular spaces and the atmosphere; hence increasing the rate of transpiration; low temperature decreases water vapour pressure and the diffusion gradient hence; lowering the rate of transpiration;

Light intensity; high light intensity increases the rate of photosynthesis in the guard cells; causing the opening of stomata; leading to increased water loss; it also increases the internal temperature of the leaf; that increases the evaporation rate in the intercellular spaces; leading to a higher rate of transpiration; low light intensity; reduces the rate of water loss;

Humidity; a humid atmosphere lowers the water vapour diffusion gradient; hence lowering the rate of water loss; in a less humid/dry atmosphere, water diffusion gradient is high/steep; hence the rate of transpiration increases;

Availability of water in the soil; more water will diffuse to the atmosphere when there is adequate or excess water; as more will be absorbed; increasing the rate of water loss; the guard cell will also remain turgid; hence stomata are open; leading to more water loss; however, less water in the soil leads to a reduced diffusion gradient between the mesophyll cells and the atmosphere; thereby reducing the rate of transpiration;

Wind/air currents; wind blowing over a leaf surface carries pockets of moisture away from the leaf;creating a steep diffusion gradient between the atmosphere and the leaf; increasing the rate of water loss; in still air/on a calm day however, water vapour at the leaf area becomes saturated; and the diffusion gradient is lowered; reducing the rate of transpiration;

Atmospheric pressure; low atmospheric pressure leads to a high rate of diffusion of water vapour;since air molecules move at a faster rate; and this increases the rate of water loss; in high atmospheric pressure conditions however, there is low rate of diffusion of water vapour; hence the rate of water loss is lowered;

14. Discuss the various ways in which anaerobic respiration is utilized in industries and homes .

Bread making; yeast is used to ferment sugar in wheat flour into carbon (IV) oxide and energy; the carbon (IV) oxide is produced in form of bubbles that causes the dough to rise and become porous;

Beer making; yeast is used to ferment sugars in malt/grapes/fruits; to form beer, wines and spirits;

Sewage treatment; anaerobes break down raw sewage and harmful industrial effluents; to harmless products of water, energy/heat and carbon (IV) oxide;

Silage formation; vegetation is fermented by bacteria to produce nutritious and good-scented/flavoured animal feed that increases production/yields;

Production of acids and strong liquors; special bacteria and fungi ferment food products; to produce acids such as citric acid, oxalic acid and vinegar; the products are used as food preservatives and flavouring agents;

Manufacture of dairy products; under controlled environments; anaerobes help in fermentation hence manufacture of milk products such as butter, cheese, ghee and yogurt;

Production of fuels such as biogas and gasohol; cane sugar is fermented by yeast; to produce gasohol for running engines or operating machinery; animal wastes such as guano and cow dung; can be used to produce a mixture of methane and carbon (IV) oxide gas; by exposing it to fermentation agents; methane is used to run simple machines such as water pumps and for cooking;

Production of fermented porridge and milk; maize or wheat flour and milk is exposed to microbes in the air which ferment it; to produce sour and sweet tasting porridge or milk;

15. Discuss the composition and functions of mammalian

Mammalian blood consists of two main components: Blood plasma; and the blood cells; (Red bloodcells/Erythrocytes, White blood cells/Leucocytes and Platelets/Thrombocytes);

Blood plasma transport nutrients (glucose, amino acids, vitamins, fatty acids and glycerol, dissolved oxygen)to tissues; transports hormones, enzymes/metabolic regulators to target organs and tissues; Transport excretory substances/wastes from the cells; to excretory organs for elimination from the body; Distribute heatenergy; helping in thermoregulation; Transports/contains water, plasma proteins and dissolved mineral salts;important in osmoregulation; Suspends blood cells;

Red blood cells transport oxygen; and dissolved carbon (IV) oxide; helps in regulation of pH;

White blood cells help in protection/immunity; by engulfing or producing antibodies to kill/destroy invading micro-organisms/pathogens;

Platelets help in blood clotting; preventing excessive blood loss; entry of pathogens; and promotes healing of wounds;