Revision notes · Infection and response
Plant disease
Detection and identification of plant diseases4.3.3.1
Definition: Plant disease identification is the process of diagnosing a plant health issue by observing physical symptoms and using diagnostic manuals, laboratory testing, or monoclonal antibody kits.
Plants can be infected by viral, bacterial, fungal, or insect pathogens, as well as suffer from mineral deficiency diseases.
- •Symptoms of plant disease include stunted growth, leaf spots, decay or rot, abnormal growths, malformed stems, leaf discolouration, and the presence of pests like aphids.
- •Diseases can be identified by referencing a gardening manual or website, testing infected tissue in a laboratory, or using diagnostic kits containing monoclonal antibodies.
| Deficiency | Effect | Why |
|---|---|---|
| Nitrate | Stunted growth | Nitrate ions are needed to make proteins for growth |
| Magnesium | Chlorosis (yellowing leaves) | Magnesium ions are needed to make chlorophyll |
⚠️ Common mistake: Confusing nitrate deficiency with magnesium deficiency and their specific effects on plant health.
🧠 Remember: Nitrates make New proteins (growth); Magnesium makes chlorophyll (Making leaves green).
Plant defence responses4.3.3.2
Definition: Plant defence responses are the physical, chemical, and mechanical adaptations plants use to resist invasion by pathogens and deter herbivores.
Plants have evolved three main types of defence mechanisms: physical barriers, chemical deterrents, and mechanical adaptations.
| Type | Examples |
|---|---|
| Physical | Cellulose cell walls, a thick waxy cuticle on leaves, layers of dead cells (e.g. bark) that fall off stems |
| Chemical | Antibacterial chemicals to kill bacteria; poisons (e.g. in foxgloves) to deter herbivores |
| Mechanical | Thorns and hairs; leaves that droop or curl when touched; mimicry to trick herbivores |
⚠️ Common mistake: Misclassifying mechanical adaptations (like thorns or drooping leaves) as physical defences.
🧠 Remember: Defences come in PCM: Physical (barriers like bark), Chemical (antibacterials and toxins), and Mechanical (thorns and movement).
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