Describe the role of producers in a food chain and explain what happens to the amount of biomass available as energy is transferred through successive trophic levels.

Pearson Edexcel International GCSE Biology (4BI1) — 4.2 Feeding relationships · Describe · 4 marks · View as Markdown

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

In a pond ecosystem, microscopic algae are eaten by water fleas, which are eaten by small fish, which are in turn eaten by pike.

Model answer (4 marks)

Producers (microscopic algae) are photosynthetic organisms that convert light energy into chemical energy, producing organic biomass.
Only about 10 % of the biomass (or energy) from one trophic level is transferred to the next.
The rest is lost mainly through respiration as heat.
Consequently, the biomass available decreases at each successive trophic level, giving a pyramid of biomass shape.

Examiner tips

  • Use the term ‘producers’ and ‘photosynthetic’. Mention the 10 % transfer efficiency. Explain loss by respiration. Show the pyramid shape of decreasing biomass.

Common mistakes

  • Confusing producers with consumers. Forgetting the 10 % figure. Not linking energy loss to respiration or heat release.

Mark scheme (4 marks)

  1. Producers (algae) are photosynthetic organisms that make/produce biomass / organic matter using light energy
  2. Only around 10% of the energy / biomass is transferred from one trophic level to the next
  3. Energy / biomass is lost through respiration (heat release) at each trophic level
  4. Therefore the biomass available decreases / gets smaller at each successive trophic level, forming a pyramid of biomass shape

Key terms in this question

producer · trophic level · biomass · food chain

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