KCSE Past Papers 2018 Biology Paper 2 (231/2)

Biology Paper 2 (231/2)

1. The diagram below illustrates a section of the mammalian kidney.

(a) Name the structures labelled E and F. Region H (1 marks)

E Glomerulus;

F Artery/branch of renal artery

(b) Explain the processes that take place in the regions labelled G and H. Region G (3 marks)

At the (glomerulus), the afferent arteriole which brings blood to the glomerulus is wider than the efferent arteriole; this creates high pressure; leading to ultrafiltration;

At the proximal convoluted tubule /distal convoluted tubule, substances required by the body/amino acid substances required by the body (amino acids/glucose/vitamins/ some water; are selectively re-absorbed (into the blood stream); hence selective reabsorption

Region H (3 marks)

At the descending arm or/limb of the Loop of Henle, water is selectively reabsorbed; At the ascending arm/limb of the Loop of Henle, sodium ions/salts are actively/selectively reabsorbed; At the collecting duct, water is (selectively) reabsorbed:

2. Below is a graphical representation of students’ height in a classroom.

(a) Name the type of curve illustrated.

Normal distribution curve

(b) (i) State the type of variation represented by the curve.

Continuous (variation);

(ii) State two meiotic processes that lead to variation among organisms. (2 marks)

 

  • Independent assortment;
  • Crossing over;(iii) Explain the role of variation in organisms. (2 marks)

    Organisms/individuals with advantageous traits/variations are favoured/selected by nature; and survive to reproduce/pass on/propagate the advantageous/favourable traits to their off-spring

    (c) Explain the need for genetic counselling in present day health facilities. (2 marks)

     

  • Variation ensures propagation of desirable/favourable traits; to the future generations/off-spring, ensuring improved/quality population3. The amount of blood flowing through certain parts in the mammalian body at different activity levels was measured and results tabulated as shown in the table below.

  • (a) Account for:(i) the high blood-flow through the cardiac and skeletal muscles during strenuous exercises. (4 marks)

    During strenuous exercises, the heart beat/pulse rate is increased (more contraction/relaxation of cardiac muscles);

    while the rate of contraction and Telaxation of skeletal muscles is increased;

    hence more blood flows to supply more oxygen/nutrients; and for removal of metabolic waste products (carbon (IV) oxide/urea);

    (ii) the results obtained for the alimentary canal at rest. (2 marks)

    At rest, more blood flows through the alimentary canal/gut/gastral intestinal tract (since digestion is at optimum at rest); to transport digested/absorbed food materials/eliminate metabolic wastes;

    (b) Name two waste materials excreted by both the skin and the kidneys. (2 marks)

     

  • Urea;
  • Water;
  • Salts;4. The diagram below illustrates the arrangement of bones in a human arm.

  • (a) Name:(i) The type of joints formed at points H and M.

    Ball and socket (joint); (1 mark)

    M Gliding/planar/plane (joint) (1 mark)

    (ii) bone G (1 mark)

    ii. Clavicle

    (b) Name bone J and state how it is adapted to its functions. Name: (1 mark)

    – Scapula;

    Adaptation (3 marks)

     

  • Has a spine to increase surface area for muscle attachment; I-t is broad/flat to increase the surface area for muscle attachment;
  • Forms flexible attachment above the ribs that allows movement of the arms;
  • Has a glenoid cavity/depression for articulation wlth the humerus/forming the ball and socket joint;
  • Has acromion for articulation with clavicle/for muscle attachment;
  • Has coracoid process to increase surface area for muscle attachment(c) State one functional difference between a tendon and a ligament. ( 1 mark)

    Ligaments hold the bones together (at a joint) while tendons attach muscles to bones;

    5. The photograph below represents a plant in a certain Division.

  • (a) (i) Name the Division to which the plant belongs. (1 marks) 
  • Bryophyta(ii) With reference to the photograph, state three observable features of the Division named in a (i) above. (3 marks)

     

  • Has capsules (for enclosing spores);
  • Has (long) setae (for supporting the capsules/for effective propagation of spores);
  • (Developed) rhizoids (for anchorage/absorption of water/mineral salts);
  • Thalloid in nature/Thallus/undifferentiated;(b) Name the parts labelled N and P.

    N = Capsule(1 marks)

    P = Seta(1 marks)

    (c) Explain how the part labelled Q is adapted to its functions. (2 marks)

     

  • Numerous/hair-like to increase the surface area for absorption;/to enhance rate of absorption of water/nutrients/dissolved mineral salts;
  • Numerous/hair-like to hold firmly on the surface/not to be easily blown away/displaced/anchorageSection B (40 marks)

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

    6. The effect of auxin concentration on growth response of two parts of a plant, X and Y was investigated over a period of time. The results were tabulated as shown in the table below.

     

(a) On the same axis, draw line graphs of the effect on growth of the two parts, X and Y (percentage inhibition or stimulation) against the concentration. (8 marks)

  • (b) With reasons, name the two parts of the plant, X and Y.X Root

    Reasons

     

  • Low auxin Concentration stimulates(rapid/faster)cell division and elongation/growth in roots
  • High Concentration of auxins inhibits growth in rootsY Shoot

    Reasons

    Low auxins concentration has little effect on the growth of shoots/shoots are stimulated to grow with high auxin concentration (upto given optimum)

    (c) From the graph identify:

    (i) the point at which the percentage stimulation was the same for both X and Y. (1 marks)

    33% ± 2

    (ii) the optimum concentration of auxins required for part Y (1 marks)

    1.0 parts per million

    (d) State three ways in which the effects of auxins on plants is applied in flower farming.(3 marks)

     

  • Faster maturity of flowers/earlier flower formation/flowering;
  • Prunning/decapitating shoot tips to allow sprouting of lateral buds, hence more yield;
  • Keeping flowers fresh;
  • Stimulate formation/development of (adventitious) roots;(e) Distinguish between simple and conditioned reflex action (3 marks)

     

    Simple reflex action Conditioned reflex action
    Is not learned (over time)/is inborn Is learned (over time);
    Primary
    stimulus involved
    Secondary stimulus  involved
    Impulse
    follows appropriate sensory and motor neurone/sensory and motor components are
    the same all the time;
    Impulse follows inappropriate sensory but appropriate motor neurone
    Single stimulus brings about the desired  response Repeated  stimulus  needed to bring about a response

     

    7. (a) Describe the mode of reproduction in a named fungus. (5 marks)

    Rhizopus/mucor/mould; reproduce asexually; by sporulation; spores develop from a single cell forming sporangium; which bursts on maturity releasing spores; which are dispersed by air currents/wind germinating; to form new generation/ form a mycelium (if it lands on a suitable medium); Or Yeast/Saccharomyces/Schizosaccharomyces; reproduce asexual1y;by budding; parent cell forms an outgrowth/projection/bud; this is followed by division of the nucleus into two; one of the nuclei moves into the bud; which grows and develops into a new cell;

    (b) Describe the role of hormones in the human menstrual cycle. (15 marks)

     

  • After/at the onset of menstruation, (the anterior lobe of) the pituitary gland; secretes follicle stimulating hormone (FSH); the FSH causes the Graafian follicle; to develop into the ovary; and stimulate the Ovary tissues to secrete oestrogen hormone; Oestrogen brings about repair/healing of the endometrium/uterine wall; its concentration increases to a level which stimulates the (anterior) pituitary gland; to secrete lutenizing hormone (L.H.) and stops fiirther secretion of FSH;
  • The L.H. stimulates the maturation of the Graafian follicle; LH also stimulates the Graafian follicle to release an ovum into the (funnel of the) fallopian tube/causes ovulation; it also stimulates the remains of the Graafian follicle to form a yellow body/corpus luteum (in the ovary;
  • The corpus luteum is stimulated by the L.H. to produce progesterone; Progesterone then stimulates the thickening of the endometrium/inner lining of the uterine wall; in readiness for implantation; as progesterone level increases, it inhibits (the pituitary gland) from secreting FSH; further increase in progesterone level inhibits the pituitary gland from secreting L.H. This causes the corpus Luteum to degenerate; this reduces the amount of progesterone; the sudden drop in secretion of progesterone causes the endometrium to slough off/menstruation occurs; and the cycle is repeated8. Describe what happens to a meal rich in proteins along the alimentary canal from ingestion to egestion. (20 marks)

     

  • The meal is ingested through the mouth; (In the mouth), it is chewed/masttcated (by teeth); to reduce/break it into smaller particles; mixed with saliva (from salivary gland); The food is then rolled (by the tongue) into boluses; and pushed down/ into the oesophaghus/swallowed; The boluses move by peristalsis (into the stomach);
  • Constant contractions/relaxations of the stomach walls mix the food, (giving rise to chime); Presence of food in the stomach further stimulates production of gastric juice; which contains pepsinogen; and rennin/chymosln; Pepsinogen is activated to pepsin; by hydrochloric acid; (contained in the gastric juice). Pepsin breaks down proteins to peptides;
  • Rennin converts/coagulates the protein, caseinogen; in milk to casein; (which is abundant in young children). It is then pushed into the duodenum (through the pyloric sphincter): Pancreatic juice in the duodenum contains trypsin; which digests proteins into peptides; (secreted in an inactive form, trypsinogen)
  • In the ileum, intestinal juice/succus antericus iz secreted; It contains peptidase enzymes; which breaks down polypeptides into amino acids; It also contains polypeptidase enzyme; which breaks down peptides to amino acids, completing the process of digestion of the proteins;
  • The amino acids are absorbed into the bloodstream/pass through the epithelia of the villi, and the capillary walls into the blood-stream; by active transport; The undigested/indigestible proteins/food substances pass through to the colon/large intestines; where water is absorbed; leaving a semi-solid waste material being passed on to the rectum; then out through the anus (as faeces);

 

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