Theory question 103
Feeding Relationships and Energy Flow(a)(i) What is a habitat? (ii) Explain briefly three roles of a decomposer in an ecosystem. (b) Explain briefly energy flow in a freshwater habitat. (c)(i) State three harmful effects of microorganisms to plants. (ii) State six beneficial effects of microorganisms to humans.
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(a)(i) A habitat is the natural place where an organism lives.
(ii) Any three: break down dead plants and animals and their wastes; release mineral nutrients back into the soil or water (nutrient recycling); form humus that improves soil; clear away dead matter; release carbon (IV) oxide for photosynthesis.
(b) The sun is the source of energy. Producers (phytoplankton, algae, water plants) trap light energy in photosynthesis. Primary consumers (zooplankton, tadpoles, small fish) eat the producers; secondary and tertiary consumers (bigger fish, birds) eat them. Energy flows in one direction along the chain; at each step much is lost as heat (respiration) and in wastes, so less energy reaches each higher level. Decomposers get energy from dead matter at every level.
(c)(i) Any three: cause plant diseases (e.g. rusts, blights, mosaic); rot fruits and stored produce; lower crop yield; denitrifying bacteria remove nitrates from the soil.
(ii) Any six: decay of dead matter recycles nutrients; nitrogen-fixing bacteria enrich the soil; yeast used in baking and brewing; bacteria used in making yoghurt, cheese and vinegar; making antibiotics (e.g. penicillin) and vaccines; bacteria in the gut make vitamins (B, K); sewage treatment; making biogas; retting of fibres and tanning of leather; used in genetic engineering (e.g. insulin).
For energy flow, start from the sun and name a trophic level at each step.