Explain why the extinction of one species in an ecosystem can lead to the decline of other species in the same ecosystem.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Species in an ecosystem are interdependent, relying on each other for food or resources.
If one species is lost, the species that feed on it lose a food source or prey species.
This causes the population of those dependent species to decrease or decline.
The effect can spread through the food web, affecting further species – a knock‑on or cascade effect.
If one species is lost, the species that feed on it lose a food source or prey species.
This causes the population of those dependent species to decrease or decline.
The effect can spread through the food web, affecting further species – a knock‑on or cascade effect.
Examiner tips
- Use the word ‘interdependent’ or ‘depend on each other’.
- Show the chain: loss → loss of food → population decline → further effects.
- Mention ‘cascade effect’ to hit the last point.
Common mistakes
- Confusing cause and effect – saying the species declines because of the loss, rather than the loss causing the decline.
- Using vague terms like ‘change’ instead of ‘decline’ or ‘cascade’.
Mark scheme (4 marks)
- Species in an ecosystem are interdependent / depend on each other for food or resources
- If one species is lost, species that feed on it lose a food source / prey species
- This causes the population of those dependent species to decrease / decline
- The effect can spread through the food web, affecting further species (knock-on / cascade effect)
Key terms in this question
Related
- All Eduqas GCSE Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →