KCSE 2021 Biology Paper 2 (231/2)

SECTION A (40 marks)

Answer all questions in this section in the spaces provided.

1. The photograph below shows an organism from a certain Class of organisms.

a.i. Name the Class to which the organism belongs. (1 mark)

 

  • Diplopoda;ii. Using observable features from the photograph, state two reasons for your answer

     

  • Two pairs or walking legs per segment;
  • Many segments:iii. State two ways in which the organism is important to the environment. (2 marks)

     

  • Decomposes the organic matter/enriches soil fertility
  • Aerates the soil through its movements/burrowingb.i. Name the Kingdom to which bacteria belong. (1 mark)

    Monera

    ii. Name two bacterial diseases in human beings. (2 marks)

    Cholera, Typhoid, Tetenus, Siphillis, Tuberculosis, (first two)

    2.a. State two adaptations of the frog’s skin to gaseous exchange. (2 marks)

     

  • Moist to dissolve respiratory gas for faster gaseous exchange
  • Thin Lined with a one-cell-thick epithelium for faster diffusion of respiratory gases
  • Highly vascularized for faster/efficient transportation of respiratory gases Any twob. Explain how the human nasal cavity is adapted to gaseous exchange. (3 marks)

     

  • Lined with hair; to trap dust particles/foreign materials/purify (the incoming) air,
  • Has mucus; to moisten/warm the incoming airc. Explain why the amoeba does not require an elaborate gaseous exchange system. (2 marks)

     

  • Has a large surface area to volume ratio; diffusion (across its cell membrane) is adequate;d. Name the respiratory disease caused by Bordetella pertussis (1 mark)

    Whooping cough;

    3. The diagram below shows a section through the mammalian skin.

  • a.i. Name the substance produced by the part labelled G. (1 mark)Sebum;

    ii. State two functions of the substance named in 3(a)(i). (2 marks)

     

  • keeps the skin moist/suppletion
  • acts as an antiseptic; – accept kills bacteria makes the skin/hair water repellant / water proofb. Name the part labelled E. (1 mark)

    Sweat pore;

    c. Explain the function of the part labelled F to the mammal.(2 marks)

    Thermoregulation; lies flat or erects (on the skin surface) when hot/cold to conserve heat or emit excess heat;

    d.i. Name one part of the human body where the cornified layer is thickest. (1 mark)

    i. Sole of the feet palm of hands;

    ii. Give a reason for your answer in 3(c)(i). (1 mark)

    Thickest because they encounter high friction/hard-walking (soles of feet) and manual work (palms of hands);

    4.a. Two dogs with black fur mated and produced an offspring with both black and brown fur.Given letter N represents the gene for black fur, determine the phenotypic ratio of the offspring. (5 marks)

b. The photographs below show a hairy pinna in a human ear.

  • i. Explain why this trait is only found in males. (2 marks)The trait is sex-linked; the gene responsible for the hairy pinna is 2 found/attached to the Y-chromosome;

     

  • Hairy nose
  • Duchean musular dystrofyii. Name one other trait that only appears in males(1 mark)

    Premature baldness;

    5.a. State the role of sunlight in the formation of strong bones. (1 mark)

     

  • Sunlight enables the skin to synthesize vitamins Dy which is necessary for the formation of strong bones)b. The photograph below shows the dorsal view of a part of the mammalian vertebral column.

  • i. Name the part of the vertebral column shown. (1 mark)Sacrum/sacral vertebra; Accept sacral vertabrae

    ii. Name the part labelled H.

    coccyx

    iii. State three ways in which the vertebra shown is adapted to its functions.

     

  • Broad transverse processes for articulate with ilium
  • Presence of prezygapophysis to articulate with the lumbar vertebrae
  • Large, broad centrum to offer support
  • Wide neural canal for passage of spinal cord
  • Fused vertebrae to form a rigid/firm structurec. Explain the significance of movement in plants.

    Plants move to reach/access light/water/moisture/carbon (IV) oxide fub (for photosynthesis); they also move to escape harmful environmental conditions/for safety/withstand harsh external forces; as well as for (mechanical) support; To enable fertilization

    SECTION B (40 marks)

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

    6. The table below shows the varying concentration of two hormones, progesterone and luteinizing hormone, determined at seven-day intervals during the human menstrual cycle.

    Time in days 1 7 14 21 28
    Concentration
    of progesterone
    (mg/cm3
    of blood)
    2 2 24 100 20
    Concentration of luteinizing
    hormone
    (mg/cm3
    of
    blood)
    46 40 100 84 40

    a. On the same axis, draw graphs of concentration of hormones against time.(8 marks)

  • Plotting- 02 marksScale – 02 marks

    Smooth curves – 02 marks

    Appropriate labelling of axes – 02 marks

    b.i. Name the physiological process taking place when the concentration of luteinizing hormone is highest. (1 mark)

     

  • Ovulation;ii. State the significance of the process named in 6 (b) (i). (1 mark)

     

  • Releases the ovumc.i. Determine the concentration of progesterone hormone at which the endometrium is thickest. (1 mark)
  • 100mg/cm3 bf blood; Accept without unitsii. Explain your answer in 6(c)(i). (1 mark);

    Endometrium is thickest when the concentration of progester highest (in preparation for implantation);

    d. State two roles of progesterone hormone in humans. (2 marks)

     

  • Inhibits production of luteinizing and follicle stimulating hormones
  • Stimulating the thickening of the endometrial lining(for implantation)
  • Maintains pregnancy; -Mause the fust 12 c).e. Name two sites where progesterone hormone is produced in the human body. (2 marks)

     

  • Corpus luteum/ovary;
  • Placenta;f. Name another hormone, apart from the luteinizing hormone, that inhibits the secretion of progesterone hormone. (1 mark)
  • Prolactin hormone;g.i. Predict the concentration of progesterone hormone seen days after the study period if fertilization did not take place. (1 mark)
  • Will remain low/keep decreasing any value below 20 mg/cm3ii. Give a reason for your answer in 6(b)(i). (1 mark)
  • The Corpus luteum will have broken down/degeneratedh. Name the part of the human body where the luteinizing hormone is produced. (1 mark)
  • (Anterior) pituitary gland;7.a. Explain the role of the placenta during pregnancy. (10 marks)

     

  • The placenta plays the respiratory, excretory; nutritive ndocrine xorine/ gland juar barrier; and immunological functions;
  • Exchange of respiratory gases, supply of oxygen-to the foetus’ tissues and removal of carbon (IV) oxide from the foetus takes place across the placenta; Nutrients/food substances are also released into the foetus from the mother’s system through the placenta;
  • The placenta also serves as a barrier, preventing the mixing of maternal and foetus’ blood/poisonous/harmful substances from the mother; Some hormones/enzymesy needed for the foetus’ development are also passed from the mother to the foetus through the placenta;
  • Some antibodies needed for the protection of the foetus from infections are also passed from the mother to the focus through the placenta;
  • Some waste products, like urea, are also passed from the foetus through the placenta;b. Explain features and mechanisms that hinder self pollination and self fertilisation. (10marks)

     

  • Dichogamy is mechanisms where either the male or female parts of the plant reproductive organs ripen at different times in some plants;
  • Protandry is when stamens ripen earlier and anthers release their pollen before the stigma is mature while protogyny-refers to where the stigma matures earlier hence becomes ready to receive pollen grains (common in plants of the grass family);
  • Self-sterility/incompatibility; is where pollen grains cannot germinate on the stigma of the same plant but only germinate on a different plant of the same species, hindering self- pollination;
  • Heterostyly; is a condition where stigma, is higher/above the anthem/stamen making it impossible for the pollen to land, accumulate and fertilize the ovules of the same flower)
  • Dioecious; plants have reproductive parts located separately on different plants of the same species discouraging self-pollination) Monoecious; plants have the reproductive parts located at different parts on the same plant, discouraging self-pollination;8.a. Describe how the xylem tissue is structurally adapted to its functions.(5marks)

     

  • Xylem tissue consists of xylem vessels; and tracheids;
  • Xylem vessels are tubular, long/hollow structures/running loy coudu continuously from the roots through the stem to the leaves, its walls are strengthened with lignin; preventing them from collapsing;
  • The Xylem vessels have bordered pits; to allow passage of water;
  • Tracheids have chisel-shaped ends and perforated cross-walls;b. Describe the functions of blood in the human body.(15 marks)

     

  • It transports vitamins, mineral salts and digested food materials to tissues of the body where they are needed) hormones are also transported by blood from the secretory sites to the target tissues/organs” (to bring about the needed hormonal responses);
  • plasma also transports enzymes to tissues where they are required to catalyze certain reactions; waste products (urealcletnia /carbon (IV) oxide) are also transported in the plasma to the excertory organs Erythrocytes are important in the transportation of oxygen from the lungs to different body tissues; and carbon (IV) oxide from (respiring) tissues to the lungs (for purification);
  • by haemoglobin (a protein in the erythrocytes);
  • Plasma also plays a thermoregulatory role; by distribution of heat
  • Leucocytes protect the body against infections (from bacteria/viruses);
  • The plasma also transports antibodies; throughout the body for defense against pathogens;
  • Platelets play a role in clotting of blood protect damaged body tissues; preventing excessive loss of blood
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