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TRANS NZOIA WEST DISTRICT MOCK EXAMINATION – 2008 Kenya Certificate of Secondary Education (K.C.S.E) 231/2 BIOLOGY PAPAR 2 MARKING SCHEME CONFIDENTIAL 1. 2. a) b) c) c) e) a) b) c) d) 3. a) b) c.i) ii) d) 4. a) b) Endotherm/ Homeoiotherm (1mk) It ensures that metabolism occurs without being affected by external factor; Sweating; excretion; breathing; defecation; (any 2mks) - Erector filli muscles relax; thus body hair lies flat decreasing insulation and increasing heat loss; - Vasodilation occurs; - it increases blood flow in superficial blood vessels, hence increasing heat loss by convection and radiation; - Sweat glands secrete more sweat; which evaporates increasing loss of heat through latent heat of vaporization. (3mks) To prevent overheating in the body / to prevent heat stroke (1mk) A – Gill filament B – Gill bar (2mks) Filter solid particles/ food particles from inflowing water (1mk) Water in the gill filament flow in opposite direction to the flow of the blood in the filaments; creating a steep diffusion gradient for faster/ maximum gaseous exchange; Concentration of O2 in water is higher than its concentration in the protozoa; O2 diffusises a cross the cell membrane into the protozoa ; concentration of CO 2 in the protozoa is higher than in the water surrounding due to respiration ; CO2 diffuses out into the water across the cell membrane; (Any 3 mks for any 3 points) Curve Y; - it starts with a higher population than X, the predator; (2mk) The number of predators dropped due to increase competition for food; as a result of a decrease in the number of prey; (2mks) Prey – predator relationship or predation (1mk) It maintains the numbers of prey and predators at the carrying capacity of the habitat; It removes weak organism from the population by natural selection; There would be an increase in the herbivorous population due to reduced predation; Herbivores would feed on a lot of vegetation which would reduce primary productivity – hence causing soil erosion; ( 2mks) Aa; Aa; (2mks) Parental phenotype P. genotype Normal Aa Normal Aa1 ½ Gametes Fusion Genotype of normal pigmented children :AA; Aa; Genotype of albino child – aa; Trans-Nzoia West Examination Panel (2mks) (1mk) 1 Biology 231/2 5. c) a) 1/5 (1mk) Oestrogen - Heals and repairs uterine wall - together with progesterone causes prolifenation of the uterine lining in preparation for implantation; - Makes uterine muscle more sensitive to oxytocine; (any 1 pint, 1mk) Progesterone: - Causes prolifenation of the uterine wall; - Maintains thickening of the uterine wall; - Prevents miscarriage / maintains pregnancy; ( any 1 pt 1mk) b)i ii) Umbilical artery; Umbilical vein; c) -Umbilical artery – Co2; Nitrogenous wastes - Umbilical vein – Oxygen; food nutrients; - Antibodies; (any 1 pt, 1mk) Oestrogen inhibits the production of FSH, no follide grows; - Progesterone inhibits the production of FSH and LH. No ovulation can occur; (2mks) Nitric acid; carbonic acid; (2mk) on the graph; Title - ½ mk Scale - ½ mk Correct curves ( 2mks) Y axis – mean length in mm (2mks) X axis – acid concentration (mol dm x 10) (2mks) Growth of shoot – as the acid conc. increases, growth of the shoot decreases; due to the low pH which is toxic to the cells; (2mks) The length of the root increases slightly at the beginning; but as the acid concentration increase, the growth of the root decreases; low pH is not suitable for the growth of root; (2mks) At 5 x 10-3 - Mean shoot length 2.0mm ± 0.1; - Mean root length 2.0 mm ± o.1; (2mks) - Kills organisms in water and soil; - Corrodes walls and roofs of buildings; - Causes leaching of aluminum from soil; (any 2 points 2mks) - Use of substances that extract sulphur from sulphur containing substances; - Fitting chimneys with scrubbers that dissolve gases like sulphur dioxide and nitrogendioxide; - More use of electricity instead of fossil fuels; - Fitting automobiles with filters and catalytic converters in their exhaust pipes to reduce emission of sulpur oxides; ( any 3 points, 3mks) d) 6. a) b) c)i ii) d) e) f) Trans-Nzoia West Examination Panel (1mk) (1mk) 2 Biology 231/2 SECTION B 7. In the mouth; There is mechanical breakdown of food using teeth; to increase the surface arae for enzyme action; food is moistened; and lubricated by saliva; for easy swallowing; The enzyme ptyalin; converts starch; to maltose; food is then rolled into bolluses; and pushed down the gullet by the tongue; There is no chemical digestion of protein in the mouth; since no protein digesting enzymes are there; Trans-Nzoia West Examination Panel 3 Biology 231/2 In the stomach HCL acid provides a suitable PH; to activate pepsinogen; to pepsin; protein in the egg is converted by pepsin; to peptides; and peptones; No digestion of starch; because the pH is not suitable for ptyalin to continue acting on starch; Food is churned; by rhythmical contraction of the muscular wall of the stomach; to form chyme; In the duodenum; Bile; provides a suitable PH and neutralizes the acid chime; Pancreatic amylase; converts starch to maltose; Trypsin; converts proteins into peptides and peptones; Bile salts; emulsify the fats in the egg; pancreatic lipase; digests fat to fatty acids and glycerol’s; In the ileum; Maltase; converts maltose into glucose; Peptidase; convert peptides into amino acids; Lipase converts fats to fatty acids and glycerol; 8. ( Any 20 points 20mks) Evidences of evolution Comparative anatomy/ Taxonomy; Members of a phylum/ group show similarities; organisms have similar structures/ similar organs performing the same functions; eg digestive system, urinary system, nervous system/ any correct example; vestigial organs e.g appendix, coccyx tail; vertebrate heart; The pendactyl limb/ any correct example; Analogous structures/ different structures performing the same function; e.g wings of insects bats and birds – show convergent evolution; Homologous structures/ structures with same origin but performing different functions; show divergent evolution; Fossilrecord / palaentology; These are remains of organisms preserved in naturally occurring materials for many years; show morphological changes of organisms over a long period of time; e.g skull of man, leg of horse; (4 mks) Comparative embryology; Vertebrate embryos are morphologically similar; suggesting the organisms have a common origin / ancestry; ( 3mks) Geographical distribution; Present continents are thought to have been a large land mass joined together; and as a result of continental drift isolation occurred; bringing about different patterns of evolution; eg kangaroos in Australia, Jaquar in South America, Liama in Amazon; (any correct example) Coparative serology/ physiology; Antigen – antibody reactions/ Rh. Factors blood group/ haemoglobin structure; reveal some relationship among organisms/ common ancestry; (2mks) (Total 23 max, 20mks) Trans-Nzoia West Examination Panel 4 Biology 231/2