BIOLOGY Paper 2 Questions and Answers - KCSE 2022 Past Papers

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SECTION A (40 marks)

Answer all the questions in this section in the spaces provided.

  1. The set-up below was used to investigate a certain factor necessary for seed germination.
      1. Identify the factor under investigation. (1 mark)
      2. Give a reason for your answer in 1(a)(i) (1mark)
    2. Explain why it was necessary to:
      1. maintain the water bath at 35°C (1 mark)
      2. use soaked bean seeds (1mark)
      1. Explain the expected observations at the end of the experiment in test tubes E and F. (2 marks)
      2. Explain what is likely to happen if set-up F was maintained for 7 days. (2 marks)
  2.  A fresh water lake surrounded by agricultural farms has the following organisms:
    1. State the roles of each of the following organisms in the lake ecosystem:
      1. hippopotamus (2 marks)
      2. algae   (2 marks)
    2. Explain the likely positive and negative effects of the surrounding agricultural farms on the lake ecosystem.
      1. Positive effects (2 marks)
      2. Negative effects (2 marks)
    1. Two tall garden pea plants were crossed and of the resulting offspring, 750 were tall and 250 were short. Using letter T to represent the dominant gene, determine the genotypic ratio of the off-spring. (5 marks)
    2. Besides height in the garden pea plants, state two other contrasting seed traits that Mendel focused on in his genetic studies. (2 marks)
    3. State how the genetic knowledge has been used to improve pea plant farming. (1 mark)
    1. Explain how each of the following factors affect uptake of mineral ions in plants:
      1. temperature   (3 marks)
      2. glucose concentration in root hair cell sap (3 marks)
    2. State two characteristics of the root hairs that increase their surface area for absorption of mineral ions. (2 marks)
    1. State two main functions of the ear ossicles. (2 marks)
    2. Explain how each of the following parts of the ear are structurally adapted to their functions:
      1. tymphanic membrane (1 mark)
      2. cochlea  (1 mark)
    3. State the function of the eustachian tube in the mammalian ear. (1 mark)
    4. State the importance of each of the following in the mammalian ear:
      1. wax (1 mark)
      2. endolymph and perilymph (2 marks

SECTION B (40 marks)

Answer question 6 (compulsory) and either question 7 or 8 in the space provided after question 8.

  1. A shoot of an aquatic plant was exposed to different light intensities and the rate of photosynthesis estimated by counting the number of bubbles of a gas leaving the shoot per minute. The results were tabulated as shown below.
     No. of bubbles per minute  0 9  16  22  28  31  32  32 32
    Light intensity (arbitrary units) 0 1 2 3 4 5 6 7 8
    1. On the grid below, draw the graph of the number of bubbles produced per minute against light intensity. (6 marks)
    2. State how the identity of the gas produced can be determined in the laboratory. (I mark)
    3. Name the apparatus used for measuring light intensity. (1 mark)
    4. Why was it necessary to get the shoot from an aquatic plant? (1 mark)
    5. Account for the number of bubbles produced between the following units of light intensities.
      1. 0-6 (3 marks)
      2. 6-8(3 marks)
    6. State two modifications one would make on the experimental set up to increase the rate of gas bubble production. (2 marks)
    7. Explain the limitations of using gas bubbles to determine the rate of photosynthesis. (2 marks)
    8. With a reason, predict the number of bubbles that would have been produced at 15 units of light intensity. (1 mark)
    1. Describe how plants eliminate waste products. (8 marks)
    2. Describe the structure and function of the mammalian nephron. (12 marks)
    1. Describe five tropic responses in plants and their survival values. (15 marks)
    2. Describe how the mammalian heart beat is controlled. (5 marks)


      1. Oxygen (is necessary for seed germination);
      2. Presence/inclusion of pyrogallic acid (in set-up E) absorbs oxygen in experimental set-ups);
      1. (35°C) is the optimum temperature required for functioning of (most) enzymes;
      2. To soften the seed coat/testa (for ease of emergence of the radicle)/ water activates germination enzymes/hydrolyses stored food/enhancing the rate of germination/solvent/medium of transport;
        • Set-up E- germination will not occur due to lack of energy/ oxygen;
        • Set-up F-germination will take place since the seed coat/testa is softened/there is oxygen (that was initially in the apparatus)/ temperature is optimum;
      2. Germination/growth process stagnates/slows down then seedlings wither/die/dry up; the oxygen/moisture in the test tube will be depleted;
      1. Hippopotamus exhale carbon (IV) oxide which is used up by the algae/reeds to photosynthesize; their dung released into the water enriches it, favouring the growth of algae/ phytoplanktons/reeds; the dung is also fed on by fish;
      2. Algae are the primary producers for the lake ecosystem; release oxygen for use by organisms (in the lake ecosystem); purifies the ecosystem by using up the carbon (IV) oxide (produced by the fish/hippopotamus/other animals; regulates the pH of the water-by using up the carbon (IV) oxide; provide breeding grounds for fish; algae is fed on by fish/hippopotamus;
      1. Portions of fertilizers\/organic manure applied on the farms find themselves deposited in the lake (due to surface run-off/ siltation); enriching the lake ecosystem, favouring growth of plants/algae/phytoplanktons(in the lake ecosystem);
        • Excessive use of fertilizers/organic manure on the farms and their eventual deposition into lake ecosystem into the lake ecosystem results in nthe overgrowth of phytoplanktons/leads to eutrophication;
        • Some agrochemicals (pesticides/herbicides) used in the farms may be toxic/poisonous to the aquatic organisms;
        • Extensive surface run-off/soil erosion and deposition into the ake blocks/clogs gaseous exchange surfaces of aquatic life; it increases turbidity, reducing visibility/light penetration in the water;
      Accept correctly done Punnet square
      • Texture (of seed coat);
      • Colour (of seed coat/cotyledon/ testa);
      • Form/shape of the seed;
    3. Artificial selection/ cross breeding/ polyploidy/ genetic engineering (resulting in varieties with desirable traits);
      1. At temperatures below optimum, the rate (of mineral ions uptake) is slow due to inactive respiratory enzymes; at optimum temperature, the rate (of mineral ions uptake) is highest since respiratory enzymes are most active; at temperatures beyond optimum, the rate (of mineral ions uptake) slows since the respiratory enzymes are destroyed/denatured;
      2. Glucose is a respiratory substrate (which when oxidized releases energy); needed for active uptake of mineral ions; high glucose concentration produces more energy; while low glucose concentration produces less energy;
      • Are long/elongated (to penetrate through the soil) to reach more mineral ions;
      • Are numerous/ many;
      • Transmission of sound vibrations (from the tympanic membrane to the oval window);
      • Amplification of sound vibrations;
      1. Thin/tight/pliable membrane that vibrates/converts sound waves into vibrations;
        • Highly coiled to accommodate a larger number of sensory cells; 
        • Has numerous sensory cells (to perceive sound vibrations)
        • Filled with a fluid to enhance transmission of sound vibrations;
    3. To balance pressure between the atmosphere and middle ear/on both sides of the eardrum/middle and outer ear;
        • Trap dust particles/prevent entry of solid/ foreign particles/ bacteria/(micro)organisms;
        • Maintain the pliability/ flexibility of tymphanic membrane;
        • Absorbs (mechanical) shock;
        • Transmission of vibrations in the inner ear;
      Plotting(P) - 1 mark
      Labelling axes (L)   - 2 marks
      Smooth curve (SC) - 1 mark
      Scale (S) - 2 marks
      Total           6 marks
    2. (Using a glowing splint) it relights a glowing splint;
    3. Photometre/light metre/ exposure metre/ photographic light metre;
    4. Aquatic plants are adapted to photosysnthesizing under the water/ in low light intensity; it can utilize carbon(IV)oxide in solution form; it is easier to collect the gas produced by aquatic plants under the water; OWTTE
      1. Rapid increase in the number of bubbles produced; due to increased light intensity which increased the rate of photosynthesis;
      2. Number of bubbles produced remain constant; since the rate of photosynthesis had reached the maximum; due to optimum light intensity; other factors (such as carbon (IV) had oxide concentration) became limiting;
      • Supply sodium hydrogen carbonates in the set-up/ any other source of carbon (IV) oxide;
      • Increase the number of shoots of aquatic plants;
      • Increase temperature to optimum;
    7. Photosynthesis and respiration occur simultaneously in plants/gases produced during one process are used in the other; not all bubbles may be accounted for/some gas dissolves in the water;
    8. 32 or any other value less than 32 but not more than 32, photosynthesis had reached the peak/maximum/less than 32-bleaching of chlorophyll;
      • Plants eliminate vapour through the stoma/cuticle/lenticels during the process of transpiration;
      • Some other wastes are eliminated in form of gases (oxygen/carbon (IV) oxide through diffusion/through lenticels/ stoma/ pneumatophores during photosynthesis;
      • Some plants also get rid of excess water in form of water droplets-jor guttation through hydathodes in their leaves;
      • Some plants eliminate their wastes by shedding their leaves;
      • Plants also recycle/reuse their wastes, for instance the carbon (IV) oxide produced during respiration being used in photosynthesis; as the oxygen produced during photosynthesis is used up during respiration; Other plants store their wastes in vacuoles; while others deposit them in stems/roots;
      • Some waste products like gum, resins, oils are removed by exudation through the bark;
        Max - 8 marks
      • It has kidney/renal tubule; and glomerulus/ a network of blood capillaries;
      • Bowman's capsule; (with a capsular space between inner and outer wall); and a glomerulus where ultrafiltration occurs; due to the difference in diameters of the blood vessels serving it; afferent vessel (wider lumen); and efferent vessel (narrower lumen);
      • The proximal convoluted tubule; extend from the Bowman's capsule. The filtrate flows through the proximal convoluted tubule where useful substances/ glucose, amino acids, some water and mineral salts/ ions are selectively reabsorbed into the bloodstream; by diffusion/active transport;
      • Ascending and descending/The Loop of Henle has a descending arm for water reabsoption; and an ascending arm where salts are reabsorbed;
      • The (filtrate empties into the) distal convoluted tubule; where (more) water is reabsorbed into the blood by osmosis/under the influence of Antidiuretic Hormone (ADH) and (more) mineral salts are reabsorbed by diffusion/active transport under the influence of aldosterone;
        Max-12 marks
      • Phototropism; growth curvature in response to direction/ unidirectional light; shoots are positively phototropic while roots are negative; phototropism enables plant shoots reach light for photosynthesis;
      • Chemotropism; is growth response to a gradient of chemical substance/mineral ions/salts concentration; for instance, the growth of pollen tube towards the embryo sac for fertilization/ growth of roots towards certain mineral salts (for absorption);
      • Geotropism; is the growth response to gravity; shoots are negatively geotropic while roots are positively geotropic; geotropism enables the roots reach water/mineral ions for absorption/enables roots to grow into the soil for anchorage;
      • Hydrotropism; is the growth response to water? moisture-joi roots are positively hydrotropic, enabling roots reach water for absorption;
      • Thigmotropism/haptotropism; is the growth response due to contact with solid objects; observed in climbing stems/ tendrils/plants with weaker stems to enable them reach light for photosynthesis/exposing flowers for pollination/fruit dispersal; Max-15 marks
    2. Mammalian heartbeat is controlled in two ways, non-nervous; and through nervous control;
      During the non-nervous control, the cardiac muscles are myogenic/ initiate their own contractions/relaxations;(stimulation/electrical charges/excitations originate from within, in the Sino Atrial Node (SAN), stimulus/ excitation spreads through auricles leading to their contraction, stimulus/ excitation proceeds to the atrioventricular node into the Purkinje tissue to all ventricles (right/left) which contract; During the nervous control, the blood pressure and chemical composition of blood is monitored by the cardiovascular centre of the brain;/the heartbeat rate can be increased through sympathetic nerve; heartbeat rate lowered through vagus nerve/parasympathetic nerve;
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