Describe how energy is lost from a food chain at each trophic level, and explain why this means food chains rarely have more than five trophic levels.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Energy is lost as heat during respiration at each trophic level.
Energy is also lost as waste (urine, faeces) and undigested material.
Only a small proportion of the energy taken in is transferred to the next trophic level.
Thus the amount of energy available decreases at each successive trophic level.
After several trophic levels there is insufficient energy remaining to support another level, so food chains rarely have more than five trophic levels.
Energy is also lost as waste (urine, faeces) and undigested material.
Only a small proportion of the energy taken in is transferred to the next trophic level.
Thus the amount of energy available decreases at each successive trophic level.
After several trophic levels there is insufficient energy remaining to support another level, so food chains rarely have more than five trophic levels.
Examiner tips
- Use the exact phrases ‘heat produced during respiration’, ‘waste materials’, ‘small proportion of energy’, ‘decreases at each successive trophic level’, and ‘insufficient energy remaining’ to match the mark scheme.
- Show the sequence of loss (heat → waste → small transfer) to demonstrate understanding of the energy flow.
- Mention the 10‑20 % transfer efficiency to justify the limit of five levels.
Common mistakes
- Confusing energy loss with energy gain; students may say energy is gained at higher levels.
- Using vague terms like ‘energy is used up’ instead of specifying heat, waste, and small transfer.
- Failing to explain that the cumulative loss limits the number of trophic levels.
Mark scheme (5 marks)
- Energy is lost through heat produced during respiration
- Energy is lost in waste materials such as urine or faeces / undigested material in faeces is not absorbed
- Only a small proportion / percentage of energy taken in is passed on to the next trophic level
- So the amount of energy available decreases at each successive trophic level
- After several trophic levels there is insufficient energy remaining to support another level / organism at the next level
Key terms in this question
Related
- All AQA A-Level Biology (7402) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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