Food chain

In the syllabus and the exam

A food chain shows a single, linear pathway of feeding relationships and energy transfer, always drawn starting with a producer and using arrows that point in the direction energy flows, from the organism being eaten to the organism eating it, never the reverse. Candidates are commonly asked to label each organism's trophic level (producer, primary consumer, secondary consumer, tertiary consumer) and, at a higher level, to explain why a food chain rarely extends beyond four or five links, because only a small fraction of the energy at one trophic level is transferred to the next, with the rest lost mainly as heat through respiration; this reasoning should be applied without stating a specific percentage as a memorised fact unless a numeric value is given in the question. A very common error is drawing the arrow backwards, pointing from predator to prey, which reverses the actual direction of energy flow and is marked wrong even if the sequence of organisms is otherwise correct. Candidates should also avoid confusing a food chain with a pyramid of numbers or biomass, which are separate diagrams built from the same feeding data but plotted as bars whose width represents a quantity, not simply arrows connecting organisms. Removing or introducing a species at any point in a food chain is a frequent structured-question scenario, requiring candidates to trace the resulting effect on populations both above and below that point.

Example

Grass to grasshopper to frog to snake to eagle is a food chain showing the one-way transfer of energy from a producer through three consumers to a top predator.

Related terms

Food webProducerDecomposer

Source:SRC-DSKP-EN