Explain why only a small percentage of the energy available at one trophic level is transferred to the next trophic level in a food chain.

AQA A-Level Biology (7402) — 3.5.3 Energy and Ecosystems · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Only a small percentage of the energy at one trophic level is transferred to the next because:
1. Most of the energy is used for movement and respiration by organisms at that level.
2. The remaining energy is released as heat to the surroundings.
3. Not all of the organism is eaten – some biomass is left uneaten.
4. Undigested material and faeces leave the body, taking energy with them.
5. Consequently, only the energy stored in the biomass of the organisms is available to the next trophic level.

Examiner tips

  • Use the exact terms: respiration, heat, undigested material, biomass

Common mistakes

  • Confusing energy loss with energy transfer; writing that energy is ‘used up’ rather than ‘lost’
  • Omitting the point about undigested material or heat

Mark scheme (5 marks)

  1. Energy is lost through movement / respiration by organisms at each trophic level
  2. Energy is lost as heat (to the surroundings / environment)
  3. Not all of the organism is eaten / some biomass is not consumed
  4. Energy is lost in faeces / undigested material that passes out of the body
  5. Only the energy stored in the biomass of organisms at one trophic level is available to the next trophic level

Key terms in this question

trophic level

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