GCSE Biology · AQA 8461 · Topic 4.3.3
Plant disease
Key points
- Plant diseases: TMV (virus, mottled leaves), rose black spot (fungus, black spots and early leaf fall), aphids (insect pests feeding on phloem).
- Mineral deficiencies: lack of nitrate ions causes stunted growth (less protein); lack of magnesium causes chlorosis (yellow leaves, less chlorophyll).
- Disease can be identified from symptoms, location, pattern on the crop, testing kits with monoclonal antibodies, and lab tests.
- Physical defences: cellulose cell walls, a waxy cuticle and layers of dead cells (bark) that fall off.
- Chemical defences: antibacterial chemicals and poisons that deter herbivores.
- Mechanical adaptations: thorns and hairs, leaves that droop or curl when touched, and mimicry to trick animals.
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Plants get ill too, and because they cannot move away from danger they depend on being recognised and treated early and on their own built-in defences. This sub-topic covers the signs of plant disease, its causes and the many ways plants…
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