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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
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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
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(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)
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(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
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(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
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(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
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(i)
(ii)
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(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
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Use
solid matter / sludge
dried to producer fertilizer
methane
burnt as fuel
effluent / liquid
discharged into river / stream
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[any 1 set]
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[any 1]
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(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)