Explain why energy is lost as it passes along a food chain, and state one consequence of this energy loss for the number of trophic levels in a food chain.

Cambridge International IGCSE Biology (0610) — 19.2 Food chains and food webs · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Energy is lost because not all material can be digested – for example fur, bones and cellulose are indigestible and are excreted.
Energy is also lost through respiration, movement and maintaining body temperature.
Energy is lost through excretion and decay of dead material.
Because energy is lost at each trophic level, a food chain normally has no more than five trophic levels – there would be insufficient energy to support a longer chain.

Examiner tips

  • Use the phrase "energy is lost" and give at least two mechanisms (digestion, respiration, excretion).
  • Mention the 5‑level limit to show understanding of the consequence.

Common mistakes

  • Writing that energy is "transferred" rather than lost, or omitting the digestion point.
  • Failing to state the consequence (maximum of five trophic levels).

Mark scheme (4 marks)

  1. Energy is lost because not all material can be digested (e.g. fur, bones, cellulose)
  2. Energy is lost through respiration / used for movement / maintaining body temperature
  3. Energy is lost through excretion / decay
  4. Because energy is lost at each trophic level, there is usually a maximum of five trophic levels / food chains are rarely longer than five trophic levels, as there would be insufficient energy to support further levels

Key terms in this question

food chain · trophic level

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