Explain why energy is lost as it passes from one trophic level to the next in a food chain.

Cambridge International IGCSE Biology (0610) — 19.1 Energy flow · 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 between trophic levels because:
1. Not all food is digestible – undigested material is excreted and does not transfer energy.
2. Organisms use energy for movement and other life processes.
3. Respiration releases energy as heat, which is lost to the environment.
4. Consequently, less energy reaches the next level, limiting the number of trophic levels.

Examiner tips

Use the four points in order, linking each to the loss of energy.
Show the cause–effect chain: digestion, use, heat loss, reduced energy for next level.
Mention the 10‑20% efficiency rule if time allows.
Keep sentences short and use exam terminology (trophic level, respiration).

Common mistakes

Confusing energy *transfer* with *conversion* – students say energy is ‘converted’ rather than ‘lost’. Misplacing the heat loss step – putting it before the use of energy. Omitting the point about undigested material or the limit on trophic levels.

Mark scheme (4 marks)

Not all material can be digested, so energy in undigested matter is not transferred to the next trophic level
Energy is used for movement / other life processes at each trophic level
Energy is released as heat through respiration and lost to the environment
Because energy is lost at each trophic level, less energy is available for the next organism / this limits the number of trophic levels in a food chain

Key terms in this question

trophic level · food chain · energy