Theory question 103
Feeding Relationships and Energy Flow(a) What is meant by the term Food chain?
(b) Draw a food chain involving four trophic levels which can be found in a terrestrial habitat.
(c) Explain (i) the flow of energy through the food chain drawn in 3(b) above;
(ii) how energy in the chain is lost to the environment.
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(a) A linear feeding relationship in which energy passes from a producer through a series of organisms, each feeding on the one before it.
(b) e.g. Grass (producer) → Grasshopper (primary consumer) → Lizard (secondary consumer) → Hawk (tertiary consumer), with arrows pointing towards the eater.
(c)(i) Sun's light energy is trapped by chlorophyll in grass and stored as chemical energy in food (photosynthesis); the grasshopper gets it by eating grass; the lizard by eating the grasshopper; the hawk by eating the lizard; flow is one-way (non-cyclic), and decomposers finally obtain energy from dead remains.
(ii) At each level energy is lost as heat in respiration; in movement and other activities; in undigested food (faeces) and excretory products; parts of the organism are not eaten (bones, roots); so only about 10% passes on to the next level.
Remember: energy flows one way and decreases at each trophic level.