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Ecology-Answer.doc S5 Biology Revision Test – Answer 1. (a) (i) (ii) 1-2 km downstream (1) There is a sudden increase in the concentration of organic matter owing to the introduction of organic sewage (2) The concentration of organic matter decreases slowly because decomposition of organic matter by decomposers / dilution of organic matter down the river. (iii) (1) The oxygen concentration decreases rapidly because introduction of sewage / decrease in the population of algae rapid consumption of oxygen as / increased respiratory activity as 1 1 1 1 bacterial population increases (2) The oxygen concentration increases because decreased consumption by as bacteria population decreases / increased oxygen production as algal population increases (iv) (1) The population of shrimp decreases rapidly because of oxygen shortage / accumulation of toxic products (2) The population of shrimp increases steadily because of dilution of sewage/toxins by water / increased oxygen content 1 1 1 1 1 1 1 1 1 1 1 (Total: 15 marks) 2. (a) (i) Sunlight/solar energy Terrestrial insects (ii) herbivores/detritivores/primary consumers They feed on plant materials (living or dead) (iii) The rest of the sun’s energy is absorbed by water / reflected as light (iv) Dead plant materials and decomposers Midge larvae Terrestrial insects (v) 780+95+17+615+4+60+45+2000 = 3616 (kJ) 1 1 1 1 1 1 1 1 1 (vi) The difference is 3616 – 3500 = 116 kJm-2year-1 Some energy is used for formation of new tissue of the older fish which are locked up/ not oxidized in respiration Some energy is trapped in indigestible materials (e.g. cellulose, insect body parts) which are egested out of the older fish’s gut as faeces 1 1 1 1 (Total: 13 marks) Ecology-Answer.doc 3. (a) phytoplankton zooplankton shrimp fish sea bird The concentration of DDT increases along the food chain DDT is non-biodegradable It will accumulate in the body of organisms / not be excreted and pass from one trophic level to another during feeding As predators feed on a large number of prey in each trophic level the concentration of DDT increases along the food chain. (iii) (3) insecticides / pesticides (4) Pest may develop resistance to DDT / Natural predators may be eliminated 1 1 1 1 1 1 (iv) DDT is fat soluble / not excreted by the animal and remains in the dead bodies after the animal dies (v) Some organisms in the habitat are eaten by human and enters the human body resulting in the accumulation of DDT in the fatty tissue of the body 1 1 1 1 (i) (ii) 1 1 (Total: 12 marks) 1. (a) (i) (ii) To avoid the accumulation of wastes / prevent growth of harmful bacteria / to keep the farm clean. [any 2] filtration / sedimentation (iii) (5) (6) (7) (8) (iv) (1) (2) oxidation of organic matter / respiration / biodegradation To supply oxygen to the bacteria / to promote aerobic respiration Fungi / bacteria To decompose organic matter into inorganic matter anaerobic bacteria methane (v) Product 1 1 1 1 1 1 Use solid matter / sludge dried to producer fertilizer methane burnt as fuel effluent / liquid discharged into river / stream 1 1 1 [any 1 set] 1 1 [any 1] 1 (vi) To kill microorganisms present in the effluent (vii) It causes a foul smell Danger of transmission of diseases / poor hygiene condition Reduction of oxygen content in water Death of aquatic life in water (Total: 12 marks)