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Biology Paper 2, May/jun 2010  
Questions:   1 2 3 4 5 6 7 8   Main
General Comments
Weakness/Remedies
Strength












Question 3

(a) Write short notes on each of the following:
(i) ecological niche;
(ii)population density;
(iii)climax community. [12 marks]
(b) Describe briefly the interactions between abiotic and biotic components of an ecosystem. [8 marks]

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OBSERVATION

This question was another popular questions in this section and the performance of candidates on the question was just average.
Most candidates could correctly define Nitche and population density, but in defining population density forgot to state that the organisms they must be of the same species. Many candidates however could not defme climax community and so left the question unanswered.
Expected answers include:
Climax Community
Is established when a stable/unchanging community is attained in ecological succession; the community is in equilibrium with the environment; the vegetation reaches its highest development; and the same species of animals; and plants/organism re-occur from year to year. Most candidates could not properly describe the interactions between the biotic and abiotic components of an ecosystem. Many candidates who attempted it limited their answers to merely naming the biotic and abiotic components. Expected answers were as follows:
Interaction between biotic and abiotic components of an ecosystem
In an ecosystem the abiotic factors are non-living things (carbondioxide, oxygen, sunlight, soil and water etc.) while the biotic componenets are plants and animals. Green plants use carbon dioxide in the presence of sunlight; to produce carbohydrate/starch/food; Animals/herbivores feed on carbohydrates/plants; and release carbondioxide from respiration; decomposers breakdown dead plants/animals/organic matters to release nutrients to the soil; these nutrients are absorbed by plants for use in food production/photosynthesis; plants give out oxygen; during photosynthesis; which is used by animals for respiration.

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