How Do Plants Defend Themselves Against Disease?
Learn how plants defend themselves against disease using physical barriers, antibacterial chemicals and mechanical adaptations for AQA GCSE Biology revision.
Plants defend themselves using physical barriers, chemical defences and mechanical adaptations. These prevent pathogens entering or spreading and can deter animals that might damage the plant.
Physical barriers
Physical barriers make it difficult for disease-causing microorganisms to enter:
- Cellulose cell walls form a strong barrier around plant cells.
- A tough, waxy cuticle covers leaves and prevents many pathogens from entering.
- Layers of dead cells, such as bark around tree stems, form a protective barrier. These layers can fall off, helping to remove pathogens.
A pathogen is a microorganism that causes infectious disease, such as a virus, bacterium or fungus.
Chemical defences
Plants can produce chemicals that protect them:
- Antibacterial chemicals kill bacteria or stop them growing.
- Poisons deter herbivores from eating the plant.
Reducing damage from herbivores is useful because damaged tissue can provide an easier route for pathogens to enter.
Mechanical adaptations
Some plant structures or responses discourage animals from feeding on them:
- Thorns and hairs deter animals.
- Some leaves droop or curl when touched.
- Mimicry allows a plant to resemble something that animals avoid.
Worked example
Question: Explain how a waxy cuticle helps defend a leaf against disease.
Answer: The waxy cuticle forms a physical barrier that makes it more difficult for pathogens to enter the leaf tissue.
Common exam mistake
Do not simply list a feature such as “cell wall”. Link the feature to its protective effect: the cellulose cell wall forms a barrier that reduces pathogen entry.
This content applies to both Foundation and Higher tiers of AQA GCSE Biology, but it is biology-only content, so it is not required for AQA Combined Science.
