Theory question 308
The Ecosystem(a) Define food chain. (b) Describe the energy flow within a terrestrial ecosystem. (c) Highlight three ways by which nitrogen cycle is maintained in the terrestrial ecosystem.
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(a) A food chain is a series of organisms through which food energy passes, each feeding on the one before it, e.g. grass → grasshopper → frog → snake.
(b) Energy comes from the sun; green plants (producers) trap it by photosynthesis; herbivores (primary consumers) eat plants; carnivores (secondary and tertiary consumers) eat herbivores; at each level much energy is lost as heat in respiration, so energy decreases up the chain; decomposers break down dead matter, returning nutrients to the soil; energy flows one way and is not recycled.
(c) Nitrogen-fixing bacteria in root nodules of legumes and in soil turn atmospheric nitrogen into nitrates; lightning fixes nitrogen that rain brings to the soil; decomposers break down dead plants and animals and animal wastes into ammonium and nitrates; plants absorb nitrates and animals eat plants; denitrifying bacteria return nitrogen to the air; farmers add fertilisers and manure.
Show energy decreasing at each level.