Explain why energy transfer between trophic levels in a food chain is inefficient, and outline one consequence of this inefficiency for ecosystem structure.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Energy transfer between trophic levels is inefficient because:
1. Not all food is assimilated – some is excreted as faeces or remains uneaten.
2. The assimilated energy is largely lost as heat during cellular respiration and other metabolic processes.
3. Consequently only about 10 % of the energy at one level is passed to the next, giving a transfer efficiency of ~10 %.
A consequence of this inefficiency is that food chains can support only a few trophic levels; biomass and population sizes fall sharply at higher levels, so top predators are far less abundant than primary producers.
1. Not all food is assimilated – some is excreted as faeces or remains uneaten.
2. The assimilated energy is largely lost as heat during cellular respiration and other metabolic processes.
3. Consequently only about 10 % of the energy at one level is passed to the next, giving a transfer efficiency of ~10 %.
A consequence of this inefficiency is that food chains can support only a few trophic levels; biomass and population sizes fall sharply at higher levels, so top predators are far less abundant than primary producers.
Examiner tips
- Use the 10 % rule explicitly; mention loss as heat and faeces; link inefficiency to limited trophic levels and low predator abundance
Common mistakes
- Saying all energy is lost as heat; ignoring faecal loss; stating 100 % transfer efficiency; not linking to top predator scarcity
Mark scheme (4 marks)
- Not all energy consumed by an organism is assimilated; some is lost in faeces/egested matter
- Energy is lost as heat during cellular respiration / metabolic processes
- Only approximately 10% of energy is transferred from one trophic level to the next / transfer efficiency is typically around 10%
- Consequence: food chains are limited to few trophic levels / biomass and population size decrease at higher trophic levels, so top predators are less abundant than primary producers
Key terms in this question
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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