Explain how plants detect and respond to damage caused by insects.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Some plants produce chemicals in their leaves when insects begin to eat them. These chemicals can also affect neighbouring plants of the same species.
Model answer (4 marks)
Plants sense insect damage by detecting changes in cell integrity and ion fluxes at the cellular level.
They then synthesise and release defensive compounds such as alkaloids or terpenoids that are toxic or unpalatable to the insects.
These chemicals are emitted into the air or leached into the soil, where they are detected by neighbouring plants of the same species.
The neighbouring plants respond by producing the same defensive compounds in advance, thereby protecting themselves before an attack occurs.
They then synthesise and release defensive compounds such as alkaloids or terpenoids that are toxic or unpalatable to the insects.
These chemicals are emitted into the air or leached into the soil, where they are detected by neighbouring plants of the same species.
The neighbouring plants respond by producing the same defensive compounds in advance, thereby protecting themselves before an attack occurs.
Examiner tips
- Use the phrase ‘sense damage at the cellular level’ to show detection. Mention ‘toxic or unpalatable compounds’ for the response. Explain the release into air/soil and the neighbour’s pre‑emptive production. Keep each point concise to cover all four marks.
Common mistakes
- Confusing plant response with insect behaviour. Omitting the ‘neighbouring plants’ aspect. Using vague terms like ‘defence’ without specifying chemicals or mode of release.
Mark scheme (4 marks)
- Plants detect changes at the cellular level / detect damage caused by insects
- Damaged plants produce chemicals that are toxic / taste unpleasant to insects
- These chemicals can be released into the air / soil and detected by neighbouring plants
- Neighbouring plants then produce the same defensive chemicals before being attacked / as a precaution
Key terms in this question
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