Plant Defences
Biology: AQA GCSE Higher, topic 3.3.2
Plant Defences
Plants have lots of defences against infections and harm from other organisms. They include:
Physical defences
- Bark is made of dead cells that acts as a barrier of protection for the stem against pathogens and pests (like aphids).
- Waxy cuticle is a barrier on the surface of leaves and stems to stop pathogens invading leaf tissue.
- Cell walls, which are made of cellulose, are a physical barrier to stop pathogens entering cells.
Chemical defences
- Antibacterial chemicals are produced by some plants, such as mint, garlic and witch hazel. They work like antibiotics to stop populations of bacteria from growing.
- Poisons are produced by many plants, including foxglove and deadly nightshade, to deter (put off) herbivores.
Mechanical defences
- Thorns or hairs stop animals eating the plants.
- Leaves that close up rapidly when touched decrease the surface area available to herbivores. They may also dislodge smaller herbivores already on the plant.
- Some plants use mimicry (copying) to trick animals.
- An example is a pattern on leaves that resembles the presence of insect eggs. Insects avoid laying their eggs on them in order to avoid competition.
Test yourself on Plant Defences
Why does bark protect a plant's stem from harm?
How does a leaf's waxy cuticle protect it from disease?
Why do plant cell walls help defend a cell against pathogens?
What type of chemical defence does foxglove use to protect itself?
Why do the leaves of some plants close up rapidly when touched?