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UPSC Prelims 2013 · Environment · Nature’s Machinery
With reference to food chains in ecosystems, consider the following statements: Which of the statements given above is/are correct?
- A food chain illustrates the order in which a chain of organisms feed upon each other
- Food chains are found within the populations of a species
- A food chain illustrates the numbers of each organism which are eaten by others
- (a) 1 only
- (b) 1 and 2 only
- (c) 1, 2 and 3
- (d) None
Show the answer and explanation
Answer: (a) 1 only
Only the definition statement is right.
Statement by statement
1. ✓ CORRECT A food chain is the sequence of feeding: grass → grasshopper → frog → snake → eagle.
2. ✗ WRONG — it runs across species Each link is a different species. Members of one population don’t form a chain among themselves.
3. ✗ WRONG — that is a pyramid Numbers of organisms at each level are shown by the pyramid of numbers, not by the chain.
The idea
A food chain is a single line showing who eats whom. Each arrow is a transfer of energy from one species to the next. In nature many chains cross each other and form a food web.
Grass (producer) → Grasshopper (primary consumer) → Frog (secondary consumer) → Snake (tertiary consumer) → Eagle (top consumer)
The trap
Statement 3 describes something real — just a different diagram (the ecological pyramid).
Also know
Two kinds: a grazing chain starts from green plants; a detritus chain starts from dead matter and decomposers. Only about 10% of the energy passes from one level to the next, which is why chains seldom have more than four or five links.
🔒 Chain = order of feeding (who eats whom). Pyramid = numbers / biomass / energy at each level.
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