Explain how energy enters and is transferred through a food chain in an ecosystem.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In a meadow ecosystem, grass is eaten by grasshoppers, which are eaten by frogs, which are eaten by herons.
Model answer (4 marks)
Energy enters the ecosystem when the grass (a producer) uses photosynthesis to convert sunlight into chemical energy.
Energy is transferred to the next trophic level when a grasshopper eats the grass, and then to frogs when the frog eats the grasshopper, and finally to herons when the heron eats the frog.
Only about 10 % of the energy is passed on at each step; the rest is lost as heat, waste or used for metabolism.
Thus the Sun is the original source of all the energy in the food chain.
Energy is transferred to the next trophic level when a grasshopper eats the grass, and then to frogs when the frog eats the grasshopper, and finally to herons when the heron eats the frog.
Only about 10 % of the energy is passed on at each step; the rest is lost as heat, waste or used for metabolism.
Thus the Sun is the original source of all the energy in the food chain.
Examiner tips
- Use the word ‘photosynthesis’ to show the source of energy.
- Show the step‑by‑step transfer from grass to grasshopper to frog to heron.
- Mention the 10 % transfer efficiency and loss of energy as heat.
- Include the Sun as the ultimate energy source.
Common mistakes
- Confusing producers with consumers; not stating photosynthesis.
- Forgetting to mention the loss of energy or the 10 % rule.
- Using vague terms like ‘food’ instead of ‘energy transfer’.
Mark scheme (4 marks)
- Energy enters the ecosystem via photosynthesis (in producers/grass)
- Energy is passed to consumers when organisms are eaten
- Not all energy is transferred to the next level — some is lost
- The original source of all energy in the food chain is the Sun/sunlight
Key terms in this question
Related
- All Eduqas GCSE Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →