3.3.2: Plant defence responses
Not started yet — this one needs some love.
Physical defences (structural barriers against microorganism invasion):
Cellulose cell walls: provide a physical barrier.
Tough waxy cuticle: covers leaves; waterproof; prevents pathogen entry.
Bark (layers of dead cells around stems): physical barrier; cells fall off taking pathogens with them.
Chemical defences:
Antibacterial chemicals: kill or inhibit bacteria.
Poisons (secondary metabolites): deter herbivores (e.g. tannins, alkaloids).
Mechanical adaptations:
Thorns and hairs: physically deter animals from eating the plant.
Leaves that droop or curl when touched: reduces palatability or exposes feeding insects.
Mimicry: tricking animals (e.g. resembling a less palatable species).
Common exam mistakes
Plant defences are largely passive/structural — do not describe them as active immune responses like in animals.
Bark is a layer of dead cells that falls off — do not say bark 'fights' pathogens actively; it simply provides a physical barrier.
Chemical defences include both antibacterial chemicals AND poisons for herbivores — these are different things.