Plant defence

What physical barriers do plants have against pathogens?

• Cellulose cell walls → strengthen cells and resist pathogen entry.

• Tough waxy cuticle → waterproof barrier on leaves.

• Layers of dead cells/bark → protective outer barrier on stems (shed to remove pathogens).

What chemical defences do plants use?

• Antibacterial chemicals → e.g., mint, witch hazel.

• Poisons → deter herbivores (e.g., tobacco plants, foxglove, deadly nightshade).

What mechanical defences do plants have?

• Thorns and hairs → deter animals from eating them.

• Leaves that curl or droop when touched → dislodge insects or scare herbivores.

• Mimicry → plants look like unhealthy plants or mimic insect eggs to avoid being eaten.

How do plants defend themselves against herbivores (beyond poisons and thorns)?

• Some plants produce toxins that make them taste bad.

• Some release chemicals into the air to warn neighbouring plants or attract predators of herbivores (e.g., parasitic wasps that attack caterpillars).

How can plant diseases be identified?

• Observing symptoms (spots, wilting, abnormal growth).

• Laboratory testing of samples.

• Monoclonal antibody testing kits for specific pathogens.

Give an example of a plant’s defence against insect attack.

Some plants produce sticky resins or hairs that trap insects, preventing feeding or egg-laying.