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Biology Paper 2

SECTION A (40 Marks)

Answer all questions in the spaces provided

a) K- eye piece

M-coarse adjustment knob.

b) P-concentrate the light/focuses the light

Q- magnification of the image.

c) i) – N

ii) – Eyepiece magnification X objective lens magnification

d) i) For light to pass through easily;

ii) To make the features more clear and distinguishable;

iii) For cells to remain turgid;

9 marks


a) Excess amino acids are deaminated/amino group is removed amino group is converted into ammonia; ammonia combines with carbon (iv) oxide

(in ornithine cycle to form urea; the carbon group is converted to glucose for respiration/glycogen for storage.;

b) i) production of large dilute amount of urine ;

ii) diabetes inspidus;

c) glomerulus, bowman’s capsule,; proximal convoluted tubule;. (Any two)

8 marks


a) To drive off oxygen/air

b) To avoid killing of yeast (cells)/denaturing of enzymes in yeast cells

c) To prevent air from getting into yeast and glucose suspense/mixture.

d) to supply oxygen; to break down lactic acid;.

e) Alcohol ; energy;

7 marks


Parental phenotype : Black mouse : Brown mouse

Parental genotype : BB : bb ;

Gamete : B B : b b ;

F1 generation : Bb Bb : Bb Bb ;

b) i) F2 offspring’s are BB, Bb, Bb, bb:

Genotypic ratio = 1BB:2Bb:1bb;

ii) Phenotypic ratio -1brown: 3black ;

iii) ¼ x 96 = 28 ;

8 marks


a) Receptors in the skin respond to stimuli forming an impulse. ;

An impulse is transmitted through the sensory neuron,;across the synapse,; to the central nervous system (white matter);through the relay neurons ;In grey matter.;Then to the motor neuron; and finally to the effector muscle;which contracts;

b) Acetylcholine;

8 marks

SECTION B (40 Marks)

Answer question six and any other one question from this section in the spaces provided

a) i) 1968;

ii) Hot water/temperature, sewage, industrial waste

iii) Temperature: high temperature reduces the amount of dissolved oxygen in water suffocating fish.; Sewage: decomposition of organic matter in sewage reduces oxygen concentration in the lakes/sewage provides food for bacteria increasing their population and demand for oxygen leading to depriving fish oxygen.;

The carbon iv oxide produced by decomposition of sewage changes pH of water in the lake interfering with photosynthesis.;

Pathogenic bacteria in sewage may kill fish;

Particles in the sewage may clog fish gills;

Sewage block/decreases light penetration in the lake interfering with producers/photosynthesis thus decreasing food availability.;

Industrial waste: toxic substances in the industrial waste kill producers/and fish ; oil substances in waste may clog gills of fish/oil on the surface reduces availability of oxygen to fish and may change pH of water and oxygen solubility is reduced.;

iv) Because species C became extinct before that year.;

b) Oil spillage from tankers; agricultural effluents,; silting due to soil erosion,;eutrophication;

Total 2o marks

20 marks


a) Breakdown of (complex) food substances by enzymes to simple compound ; which can be absorbed ; ( )2mrks.

b) small intestines are long/coiled to offer large surface area; for digestion;and absorption ; to slow down movement of food to complete digestion and absorption of food;the walls are muscular; for peristalsis ;/inner walls posses mucus glands/ (acc.....goblet cells; that secretes mucus for lubrication;and protection of wall from digestive enzymes.; The inner walls have digestive glands; that secrete (digestive) enzymes;

The inner walls have villi;to increase the surface area for absorption;

The villi posses thin epithelia; to facilitate absorption /diffusion ;/acc...epithelium is one cell thick) The villi have numerous blood vessels;for transport of the end products of digestion ; least two correctly named examples /end products e.g. glucose, amino acids/mineral salts vitamins. The villi also have lactealvessels;for transport of fats/lipids; Acc...illustration of one cell thick epithelium (19mrks) Maxmum 20marks

20 marks


Fossils records;

These are remains of ancient organisms preserved in natural occurring materials for many years ; they show morphological changes of a group of related organisms over a long period of tim e ;e.g. the human skull.;

Geographical distribution;

The theory of continental drift suppose s at one time the present continent formed one large landmass ; which later broke up and its part drifted away from each other due to the continental drifts; animals with common ancestry became isolated and evolved into different species; e.g. camels of S. America resemble those in Africa, the Amazon forest in S. America is inhibited by monkeys with long tails while their counterparts in Africa are short tailed;

Comparative serology;

Analysis of blood proteins with reference to antigen –antibody reaction of different animals reveals some phylogenic reaction;, a group of organisms that are related contains more similar blood proteins e.g. if human serum is injected to the rabbit, the rabbit responds by producing antibodies against the human antigen.; The Rhesus factor, hemoglobin etc are found across a group of organisms and the evidence points towards a common ancestor.;

Cell biology;

Cell of all higher organisms have similar structures and functions this supports that all living things had a common ancestry;e.g. all cells have nucleic acids. ATP and cell membrane enclosing same organelle like mitochondria, Golgi body, lysosomes, ribosome; etc. Comparative embryology; Studies of the development of embryos in different vertebrates like fish, mammals, birds, amphibians,; show that they are morphologically similar during their early stages of development, these points towards a common ancestry ; e.g. all the embryos have gill slits in early stages.;

Comparative anatomy;

When competing the form and structures of different organisms some group show basic structural similarities; this suggests that the organisms have a common ancestral origin example include;

Homologous structures;

This are structures of similar embryonic origin but are modified to perform different functions, this points toward divergent evolution e.g. the pent adactyl limb in vertebrates.; The form and function of the fore limb differ in various vertebrates groups but the basic pent adactyl (5-digits) structure is same, the forelimb of the bat is modified for flight while that of a horse is elongated to enhance speed when running.; The fingers in the monkey are elongated to form a grasping hand for swinging from branch to branch; in a whale the forelimb is modified into a flipper for steering and maintaining equilibrium during swimming; Beaks of the bird also show divergent evolution they have similar embryonic origin but modified to perform different function; seed eaters have short stouts beaks while nectar feeders have long slender beaks and flesh eaters have sharp curved beaks ;

Analogous structures;

These are structures of different embryonic origin modified to perform similar functions ; due to exploitation of similar environments this points towards convergent evolution ;e.g. wings of
birds and insects are modified for flight but those of birds have pent dactyl structures while those of insects do not ;

Vestigial structures;

These are structures that have been reduced in size or have ceased to function during the course of evolution.; Vestigial structures are believed to have been performing normal functions in the ancestor species but have since then reduced to an extent that they have lost their original function; vestigial organs are found among different groups of organisms, these shows some relationship e.g. appendix in man, vestigial tail in man which is small in size, reduced pelvic girdle of the whale.;
Maxmum 20 marks

20 marks

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