KCSE 2019 Biology Paper 2

2019 Biology Paper 2

Answer all the questions in the spaces provided.

1. In an experiment to investigate the effect of Sodium chloride on the growth rate in a spinach seedling. seeds were treated with different concentrations of sodium chloride. The results are as recorded in the table below.

(a) From the results in the table above, explain the effect of increasing the concentration of sodium chloride. (3 marks)

Increased Sodium chloride concentration/having more sodium and chloride ions solutes decreases osmotic potential/makes water potential more negative outside the seed/seedling in the surrounding solution/the surrounding solution to be hypertonic to the cell sap in the seedling/ seed cells; seeds take in less water by osmosis/are dehydrated/lose water molecules to the surrounding solution; reducing the (growth) enzyme activity, hence reduced growth rate; OWTTE

(b) Apart from a ruler, state two other equipment one would need to determine the rate of growth in the roots. (2 marks)


  • Thread;
  • Marker pen;
  • Dye(c) With a reason, state one other part of the seedling the students would focus on to determine the effect of sodium chloride on growth. (2 marks)

    (Rate of growth/increase in length of) the shoot tip/apex; It is a region of (active) cell division/growth;

    (d) State the likely effect on the seedling of increasing the seedling of increasing the concentration of sodium chloride to 2.20 mol/I . (1 mark)

    The seedling will be dehydrated, hence wither/die

    2. The table below shows results of blood cell counts per mm° of blood from a sample of people living at different altitudes.


  • (a) Explain the relationship between:(i) Red blood cells count and the altitude;(3 mark)

    (i) The number of red blood cells count increase with the increase in altitude; to increase the oxygen carrying capacity (by the hemoglobin molecules in blood); since oxygen concentration is lower at higher altitudes

    (ii) White blood cells count and the altitude.(3 mark)

    White blood cells serve to protect the body against harmful micro-organisms/pathogens; the quantities of pathogens or vulnerability of the body to microbial attack is not dependent on the altitude (to be countered by the white blood cells); hence the number of white blood cells’ count is constant at whatever

    (b) Explain why chances of nose-bleeding increase with altitude in humans. (2 marks)

    Atmospheric pressure decreases with the increase in altitude; the imbalance between the (outer) atmospheric pressure at high altitude and the internal blood pressure (generated by the heart) results in one nose bleeding at higher altitudes/internal blood pressure is higher than the (outer) atmospheric pressure .

    3. (a) State one importance of irritability to living organism. ( 1 mark)


  • Enables living organisms to avoid dangerous/harmful/harsh climatic/environmental conditions; 
  • Enable living organisms obtain/access favourable environmental conditions (light, water, oxygen); any one(b) ln an experiment, students treated seedlings as illustrated below.

(i) Account for the observations made in seedling 1 (3 marks)

(i) Positive phototropism/tip bends towards light light causes migration of auxins (produced at the tip); to darker side of the shoot resulting in faster division of cells/elongation on the darker/ opposite side of the shoot, hence bending towards light;

(ii) Explain the similarity in the end results made in seedlings II and II (2 marks)

(ii) Both seedlings remain upright; seedling II does not have the tip while in III the tip has been covered by an opaque material preventing light from causing unequal distribution of auxins;

(iii) State the likely treatment that would make seedlings II and III respond like seedling I. (2 marks)

Fitting an agar block treated with auxins at the decapitated end of seedling II; removing the opaque material covering the tip of seedling III Replacing the opaque cap with a transparent one;

4. In cats, the gene for fur colour is sex-linked. Letter G represents the gene for ginger fur colour while letter B represents the gene for black fur colour in a given cot species.

These genes are codominant.

Heterozygous females have ginger and black patches of fur rind their phenotype is described as tortoise-shell.

(a) With reference to the information given above, what is meant by the term codominance? (1 mark)

Both alleles are expressed/shown equally in the phenotype (of the offspring) /non suppresses the other/ gene for ginger and black fur colour express themselves equally in the phenotype of the offspring.

(b) Explain why male cats with a tortoise-shell phenotype do not usually occur. (2 marks)

The gene for coat colour is sex-linked; contained in the X-chromosome; males have only (inherit) one X-chromosome (from females/mothers)/Y-chromosome does not carry genes;

(c) A tortoise-shell female was crossed with a black male. Determine the genotypes and phenotypes of the offspring. (5 marks)

5. A person accidentally touches a hot pan and responds as illustrated in the diagram below.

(a) Explain how the response illustrated above occurs. (6 marks)

The stimulus/heat/pain is detected by temperature/pain receptors (in the skin/dermis); impulses transmitted along sensory neurone to the Central Nervous System/spinal cord; (chemical) transmission across synapses; to relay neurone; across a synapse to motor neurone/across another synapse /via motor neurone; to muscles/effectors via motor neurone; muscles/effectors contract, (hand moves away); This is known as a reflex action;

(b) Explain how auxins are utilised as selective weed killers in agriculture. (2 marks)

Selective weed killers contain auxins which are absorbed by the weeds (than desired/beneficial/plants); making the weeds to grow abnormally faster/die out (ahead of the desired plants);

SECTION B (40 Marks)

Answer question 6 (compulsory) and either 7 or 8

6. The table below shows the rate of product formation for two enzymes, H and J over a range of pH values.


(a) On the same axis, plot graphs of the rate of product formation against pH. (8 marks)

  • (b) Account for the rate of product formation for enzyme H between:(i) pH 1.0 and 3.0 (3 marks)

    Rate of product formation increases with the increase in pH up to the optimum/then decreases; pH 2.0 is the optimum pH value for the activity of enzyme ii; between pH 1 and 2, the enzyme molecules are activated;

    (ii) pH 3.0 and 7.0. (3 marks)

    Rate of product formation (sharply) decreases with the increase in pH; enzyme IN is not favoured by the increase in pH, hence is denatured; no product forms above/beyond pH 4.0 to 7.0 (all enzyme molecules will have been denatured);

    (c) From the graph, determine:

    (i) The pH value at which the rate of product formation of the two enzymes was the same (l mark)

    pH 4.0

    (ii) The value of the rate of product formation for enzymes H and I at the pH value stated in (G)(i) above (1 mark)

    15.0 mg/hour;

    (iii) The optimum pH value for enzyme J (l mark)

    (d) State one variable that may lead to the change in the optimum rate of product-formation of the two enzymes. (l mark)


  • Temperature (increasing beyond 40°C or extremely lowering it);
  • (Varying) substrate concentration;
  • Enzyme concentration;(e) Suggest with a reason, the likely part of the human alimentary canal where enzyme H would be found. (2 marks)


  • Stomach;
  • Acidic medium/low pH;7.Giving examples,describe the following interactions among organism: (20 marks)

    Predator-prey relationship

    A predator is an animal that hunts/kills another/other animals (prey) for food; example, a dog and a hare; preys devise survival mechanisms in their habitats not to be eaten/killed; to survive and reproduce/propagate their lineage; to this end, they run faster (strong hind leg muscles); camouflage with environments; mimic the predators; or strong sense of smell to detect the predator; some emit chemicals/smell that turn away from the predators; while others, like porcupines, use quills/spines/ spikes to fight off predators; on the other hand, predators also evolve/ device means to be able to survive in such an ecosystem, for instance, running faster/camouflaging with the environment/mimicking preys/ sharp eyesight; some produce venom/poison; sharp/strong/long claws;


    Is a close, (long-term) association between two organisms of different species where the two mutually benefit from each other; for example, the bacteria in the rumen/gut/colon of herbivores; which help the herbivores digest cellulose; as they are sheltered by the herbivores; the bacteria found in the human digestive system/gut; are also sheltered by humans as they ensure microbial balance; the nitrogen-fixing bacteria on the root nodules of leguminous plants; benefit from the shelter offered by the plants; as they facilitate conversion of free atmospheric nitrogen into forms that can be readily absorbed by the plants;


    Is a kind of(inter-specific) relationship/association where one member/ organism, the parasite, benefits while the other, the host is harmed/ loses; (also called antagonistic/antipathetic symbiosis) for example, a tick (parasite); sucking blood from a cow (host), making the cow to be anaemic/skin destroyed/malnourished; parasites can be external/ecto- parasite; or internal/endo-parasite; endo-parasites,for instance, liver fluke, suck blood/nutrients from the host and can cause death/bodily harm on the internal organs of the host, including blocking blood vessels;

    8. Explain the effects of increased physical activity on the following organ systems: (20 marks)

    (a) Heart

    Increased physical activity results in increased heart beat/rate/cardiac frequency/increased blood pressure; pumping more blood to the muscles/peripheral blood vessels at a faster rate; supplying oxygen; nutrients; for continued oxidation/respiration; to yield energy needed to sustain the (vigorous) contraction/relaxation of muscles (during the physical activity); carbon (IV) oxide/lactic acids/other nitrogenous/ metabolic wastes produced during the process are also eliminated/ transported to the relevant excretory organs for elimination; the wastes, if left to accumulate, can also poison cells/cause muscle crump/ fatigue/pain;

    (b) Lungs

    The panting/increased breathing rate (during the physical activity) influences the lung volume/lungs expand/increase in volume, to take in more amount of air/oxygen retained (for the activity) or expelled (during the activity); they expand to take in more air/oxygen (into the body) and deflate to expel more carbon (IV); more oxygen is taken in (during exercise) to sustain the process of muscle respiration/to produce the required energy (for the constant muscle contraction and relaxation);

    (C) Kidneys

    Kidneys also maintain the blood plasma pH; and osmotic balance; by eliminating excess hydrogen ions(H“) that accumulate for instance, through the production of lactic acid/carbon (IV) oxide during exercise; to maintain the osmotic balance, the kidneys conserve sodium ions and reabsorb water (in the kidney tubules); leading to reduction in the volume of urine produced; during exercises, the kidneys tend to filter out more urea, releasing more in the urine;

    (d) Skin.

    Due to the increased muscle activity during physical exercises, one sweats (more); eliminating nitrogenous wastes/excess water (through the skin)/sweat pores; cooling the body; after water in the sweat evaporates; the increased internal body temperature also leads to the dilation of superficial blood vessels (vaso-dilation)/blood flowing to the skin; leading to loss of excess heat (to the atmosphere) by radiation/ convection; the hair on the skin surface also lie flat to allow for loss of heat (to the environment) by radiation/convection;


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