K.C.S.E Biology Q & A - MODEL 2012PP2QN08
Describe how environmental factors increase the rate of transpiration in terrestrial plants.
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
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
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.
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.
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These effector muscles contract; and the finger is withdrawn from the hot object;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.
(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;
(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;
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 2012PP2QN05
Explain the mechanism of stomatal opening.
The osmotic pressure of guard cells increase when sugar is manufactured during photosynthesis/starch is converted to sugar in low acidity/potassium moves into guard cells during the day; water enters guard cells from the surrounding cells by osmosis; because the guard cells are bean shaped with thin outer walls and thick inner walls, the thin outer walls expand faster as the cell becomes turgid; thus the thick inner wall curves; causing the stomatal aperture to open.
K.C.S.E Biology Q & A - MODEL 2012PP2QN05
Describe the process of inhalation.
K.C.S.E Biology Q & A - MODEL 2012PP2QN04
The diagram below illustrates arrangement of bones and muscles of the human arm.
(i) Name the bones labelled K and L.
(ii) Explain how the upward movement of the lower arm is brought about by the, bones and muscles shown in the diagram above.
(b) State three ways in which support is brought about in a leaf.
(a) (i) K - ulna;
L - humerus;
(ii) movement of the lower arm upwards takes place at the elbow/olecranon process which is between the ulna and the humerus; biceps/flexor muscles contract; while the triceps/extensor muscles relax; bringing about the movement of the lower arm upwards. ,
(b) The rigid midrib holds leaf out away from the stem;
Profuse network of veins have lignified cells which support leaf to stay spread out;
Turgidity in spongy mesophyll and palisade cells support the leaf to remain open;
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.
(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 2012PP2QN02
The diagram below illustrates the structure of the kidney nephron.
(a) Name the part labelled E.
(b) How is the part labelled F adapted to its function?
(c) State three physiological mechanisms of controlling the human body temperature during a cold day.
K.C.S.E Biology Q & A - MODEL 2012PP2QN01
In a certain plant species which is normally green, a recessive gene for colour (n) causes the plants to be white in colour. Such plants die at an early age. In the heterozygous state, the plants are pale green in colour but grow to maturity.
(a) Give a reason for the early death of the plants with the homozygous recessive gene.
(b) If a normal green plant was crossed with the pale green plant, what would be the
genotype of the first filial generation (F1 generation)? Show your working.
(c) If heterozygous plants were self-pollinated and the resulting seeds planted, work out the
proportion of their offspring that would grow to maturity.
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
K.C.S.E Biology Q & A - MODEL 2012PP1QN29
Name two nutrients that are absorbed without being digested by enzymes in humans.
K.C.S.E Biology Q & A - MODEL 2012PP1QN28
State two differences between open and closed circulatory systems.
Blood flows in haemocoel Blood confined in vessels;
sinuses/body cavity directly
in contact with cells
Blood flows at low pressure Blood flows at high pressure;
Blood lack pigments Blood has pigments for oxygen and
Carbon (IV) Oxide transportation
K.C.S.E Biology Q & A - MODEL 2012PP1QN27
What is the function of contractile vacuoles in amoeba?
K.C.S.E Biology Q & A - MODEL 2012PP1QN26
(a) State the theories of evolution proposed by the following scientists.
(i) cell organelles
(a) Theory of natural selection;
Theory of environmental influence on inherited characteristics;
(b) (i) Similar organelles performing similar functions in different organisms suggest a common ancestry/cell biology;
(ii) Fossil records/palaeontology/by comparing fossils to show phyllogenetic relationship between organisms/common ancestry;