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K.C.S.E Biology Q & A - MODEL 2014PP2QN08
Describe the role of the human skin in homeostasis.
answers
When body temperature is lowered below normal; arterioles in the skin constrict; blood is diverted to a shunt system; less blood flows to the skin/less heat is lost; when body temperature is raised above normal;arterioles in the skin dilate;more blood flows to the skin; more heat is lost by convection and radiation;when body temperature is lowered below normal:erector-pilli muscle s contract, hair stands erect; more air is trapped, air is a bad conductor;and insulates the body against heat loss; when body temperature is raised above normal: erectorpi11i muscles relax, hair lies on skin;less air is trapped, more heat is lost; when body temperature is lowered below normal: less fluids are absorbed by sweat glands;less sweating, less vaporisation of water;
when body temperature is raised above normal:sweat glands are more stimulated and more sweat is produced; water in sweat evaporates and takes up heat from the body;body is cooled/body temperature is lowered;
K.C.S.E Biology Q & A - MODEL 2014PP2QN08
How does excretion take place in plants?
answers
K.C.S.E Biology Q & A - MODEL 2014PP2QN07
Describe the process of carbohydrate digestion in human beings.
answers
​In the mouth;
K.C.S.E Biology Q & A - MODEL 2014PP2QN07
Explain how each of the following factors affects the rate of photosynthesis:
(i) temperature; (ii) chlorophyll concentration.
answers
(i) Reactions in photosynthesis are catalysed by enzymes; at optimum temperature photosynthesis proceeds faster;
Below optimum temperature the rate of photosynthesis decreases because enzymes are inactivated by the low temperatures / above optimum the rate of photosynthesis decreases because enzymes are denatured; (ii) Chlorophyll traps energy from sunlight for photosynthesis; The higher the chlorophyll concentration the higher the rate of photosynthesis and vice versa; K.C.S.E Biology Q & A - MODEL 2014PP2QN06
An experiment was done to determine the uptake of nitrogen from the soil by broad bean seedlings. The experiment was done with one set of seedlings M grown in the atmosphere enriched with carbon (IV) oxide and another set up of seedlings N grown in the normal atmosphere.
The amount of nitrogen in each seedling was measured in milligrams at intervals often days. The table below shows the results obtained. 
​(a) Using the same axis draw line graphs of nitrogen uptake by the two (M and N) sets of broad bean seedlings against time.
(b) Determine the rate of uptake of nitrogen in Set M between 65 and 85 days. (c) (i) What is the relationship between carbon (IV) oxide concentration in the air and nitrogen uptake? (ii) Account for the relationship in (c)(i) above. (d) (i) What would happen to the concentration of nitrogen in the seedlings in set M, if after 75 days the seedlings are transferred to a normal atmosphere. (ii) Explain your answer in (d)(i) above. (e) State three ways in which nitrogen fixation occurs.
answers
(c) (i) The higher the carbon UV) oxide content in air, the higher the nitrogen uptake and vice versa;
(ii) More Carbon (IV) oxide in the air makes the seedlings to photosynthesize more; hence more amino acids/protein; are formed in the dark stage; formation of amino acids/protein requires nitrogen; (d) (i) The concentration of nitrogen would remain constant; (ii) Despite decline in CO,; the nitrogen already absorbed/taken up by the plant will still remain: (iii) Lightning; By free-living bacteria/micro organisms; By Rhizobium (in root nodules of legumes); K.C.S.E Biology Q & A - MODEL 2013PP2QN08
Describe the role of the following organs in excretion and homeostasis.
(a) the liver (b) the skin during hot environmental conditions.
ANSWERS
​(a) Regulation of blood sugar ; when blood sugar is below normal/90 mg/100 cm3 glucagon ; triggers the conversion of glycogen to glucose in the liver ; the glucose is released into the blood stream. When blood sugar is in excess above normal/10 mg/100cm3, insulin; causes the liver to convert glucose excess to glycogen ; which is stored.
Production of heat energy ; by increasing the rate of metabolic activities: Excretion of bile pigments ; produced due to breakdown of worn out red blood cells: Deamination/removal of amino group of excess amino acids to form urea: and detoxication/poisonous/toxic substances: (b) Sweat glands excrete urea; excess water; and salts: hence maintaining salt & water balance in the blood. Evaporation of sweat; cools the body due to loss of latent heat of vaporization; when the body temperature rises : blood vessels in the skin vasolidate: allowing more blood to flow near the skin surface: thus heat is lost to the environment radiation/convection. The eretor pili mucle relaxes hair flattens ; in a hot environment reducing insulation: hence heat is lost from the body by radiation! convection; to the environment.
K.C.S.E Biology Q & A - MODEL 2013PP2QN07
How are respiratory surfaces in mammals adapted to their functions?
ANSWERS
Many to provide a large surface area: across which large amounts of gases diffuse: moist surfaces: to dissolve respiratory gases: so as to diffuse. Made of a thin membrane/epithelium/one cell thick wall ; to reduce diffusion distance;
Highly vascularized: to carry away oxygen; and bring in carbon (IV) oxide: creating a steep diffusion gradients.
K.C.S.E Biology Q & A - MODEL 2013PP2QN07
Describe the process of blood clotting in human beings.
ANSWERS
When a blood vessel is cut/injured platelets/thrombocytes/damaged tissue/wound is exposed to the air: they release thrombokinase/thromboplastin ; an enzyme that activates the conversion of prothrombin: to thrombin: in the presence of calcium ions: vitamin K/ phylloquinone ; is needed for the formation of prothrombin; Thrombin converts (soluble blood protein) fibrinogen ; into (the fibrous form) fibrin; which forms a mesh / network across the wound: The clot so formed prevents excessive bleeding: and entry of disease agents/pathogens/micro-organisms/microbes;
K.C.S.E Biology Q & A - MODEL 2013PP2QN06
A scientist carried out an investigation to find out the population growth of mice under laboratory conditions. Twenty young mice were placed in a cage. The results obtained from the investigation were as shown in the table below.
​(a) On the grid provided, draw a graph of the number of mice against time.
GRAPH PAPER (b) Account for the changes in mice population between (i) O to 2 months (ii) 2 to 6 months (iii) 6 to 10 months (iv) 10 to 12 months. (c) (i) Between which two months was the population change greatest? (ii) Calculate the rate of population change over the period in (c)(i) above. (d) What change in population would be expected if the investigation was continued to the 19th month? (e) To obtain the observed results state two variables that were kept constant during the investigation.
answers
(b) (i) No change in population/population is constant: mice still maturing/have not given birth:
(ii) Slow/gradual population growth; few mice have reached sexual maturity; (iii) Faster/rapid rate of population growth/exponential; Many mice sexually matured/reproducing/enough food/space/no competition birth rate higher than death/no diseases: (iv) Population decline; Competition is high / food is limiting / space is limiting/accumulation of toxic waste/disease (outbreak) deathrate higher than birth rate. (c) (i) 6 and 8; (ii) 310-115 = 195 mice per month; (d) Population would increase; (e) Food; space ; cage size; water; Describe how environmental factors increase the rate of transpiration in terrestrial plants.26/6/2020
K.C.S.E Biology Q & A - MODEL 2012PP2QN08
Describe how environmental factors increase the rate of transpiration in terrestrial plants.
ANSWERS
In bright light; stomata are fully/wide open; increasing contact between the atmosphere and air spaces in the leaf; This in turn increases water loss by evaporation through the
open stomata High environmental temperatures; increase the rate of evaporation from the leaf surface thus more water leaves cells due to the increased diffusion gradient; Iii a windy day; air around the leaf is carried away reducing water vapour around the leaf; more water moves into the atmosphere from the leaf air spaces; In low humidity/when the atmosphere is less saturated with water vapour; more water will move from leaf air spaces into the atmosphere; leading to increased rate of transpiration; . Low atmosphere pressure; increases diffusion gradient between atmospheric and leaf increased rate of evaporation;Availability of water; causes turgidity of guard cells hence stomata open; increasing rate of transpiration.
K.C.S.E Biology Q & A - MODEL 2012PP2QN08
Using a relevant example, describe how an allergic reaction occurs in a human being.
ANSWERS
​An allergic reaction is a hypersensitive response; to an antigen by the body immune
system; The body immune system responds by overproducing antibodies; against harmless antigens; The antigen-antibody reaction occurs on the surface of body cells; which burst open; and release histamines; Histamines cause inflammation/itching! swelling/pain, et.c; which damage the body; Allergic people are hypersensitive to materials like dust/pollen grains/some foods/some drugs/some pollutants,
K.C.S.E Biology Q & A - MODEL 2012PP2QN07
Using a relevant example in each case, describe simple and conditional reflex actions.
ANSWERS
Simple reflex action - withdrawal of finger from a sharp object.
Is an automatic response to a specific stimulus; When the finger touches a sharp object, pain receptors in the skin; are stimulated and trigger off a nerve impulse; The nerve impulse is transmitted via the sensory neuron; to the grey matter of the spinal cord; The impulse is then transmitted via a synapse; to the relay neuron; and then through another synapse; to the motor neuron; The impulse is then transmitted to the effector muscles in the hand; These effector muscles contract; and the finger is withdrawn from the hot object; Conditioned reflex action Is an automatic response evoked from an animal by unrelated stimulus; substituted for the one which normally elicits the response; It develops from past experience; and involves modification of behaviour through learning; It weakens with time; and must be reinforced by repeating the unrelated stimulus; Students salivate when the bell for lunch rings; because they have learned to associate the ringing of the bell at lunchtime with food; from experience; every time it rings, they are offered food; K.C.S.E Biology Q & A - MODEL 2012PP2QN06
The data provided below represent populations of a predator and its prey over a fifty years’period.
​(a) (i) Using the same axes, draw graphs of the relative populations of P and Q against time.
(ii) With a reason, identify the curve that represents the prey. (iii) Account for the two populations between 25 arid 32 years. (iv) Which years were the two populations equal? (v) A part from predation, state three biotic factors that may have led to the decline of the prey population. (b) Describe the hazards of air pollution by Sulphur (IV) Oxide.
answers
(a) (i) title - Graph of Prey-predator relationship; (OWTE)
Scales X axis; Graph should cover more than half of the grid provided. Y axis; Graph should cover more than half of the grid provided. correct plotting P; Q; smooth curves P; Q; labelling axes; 
(ii) P represents the prey;
Prey population is initially higher prey population usually starts falling earlier; (iii) Both populations decrease; because prey is not enough to sustain predator/population environmental stress limit population of prey; (iv) at 23±0.5 years; and at 39±0.5; (v) less food for the prey/intra specific competition; emigration of the prey; diseases causing death of the prey; parasitism; human activities b)sulphur dioxide in the air - causes respiratory diseases; poisons plants; forms acid rain which increase soil pi-J; corrodes metals in buildings; K.C.S.E Biology Q & A - MODEL 2012PP2QN03
(a) In an investigation, equal amounts of water was placed in. three test-tubes labelled G, H and J. Pondweeds of equal length were dropped in each test tube. The test-tubes were then placed in identical conditions of light and carbon (IV) oxide at different temperatures for five minutes. After the five minutes, the bubbles produced in each test-tube were counted for one minute. The results were as shown in the table below.
​(i) Name one requirement for this process that is not mentioned in the investigation.
(ii) Name the gas produced in this investigation. (iii) Account for the results in test-tubes H and J. (b) State two ways in which the human intestinal villus is adapted to its function.
answers
​(a) (i) chlorophyll;
(ii) oxygen; (1 mark) (iii) Test tube H is at optimum temperature for enzyme activity; hence high rate of photosynthesis/more bubbles. In test tube J most enzymes have been denaturedby the high temperature; hence low rate of photosynthesis/fewer bubbles. (b) — The villus epithelium is thin; for faster diffusion of dissolved food substances; — The epithelium has goblet cells; which produce mucus to lubricate food passage; — They have microvilli; which further increase their surface area for absorption; Have lacteal; for absorption of fatty acid & glycerol/transportation of lipids; Highly vascularised; for absorption of digested food. K.C.S.E Biology Q & A - MODEL 2012PP1QN30
Name the organelle that is involved in each of the following:
(a) manufacture of lipids (b) formation of lysosomes
answers
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