Plant defence responsesSpec 4.3.3.2
Plants have defences that resist the invasion of microorganisms and deter animals that might eat them. You need to be able to describe physical and chemical responses, and mechanical adaptations.
| Type | Examples |
|---|---|
| Physical defences against microorganisms | Cellulose cell walls; a tough waxy cuticle on leaves; layers of dead cells around stems (bark on trees) which fall off |
| Chemical defences | Antibacterial chemicals; poisons to deter herbivores |
| Mechanical adaptations | Thorns and hairs deter animals; leaves which droop or curl when touched; mimicry to trick animals |
Layers of dead cells around the stem, such as bark, act as a barrier. They fall off, which helps to remove any pathogens that have settled on them.
Mimicry means looking like something else so that animals are tricked, for example into avoiding the plant.
Quick check
Which ion deficiency causes stunted growth, and why?
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Nitrate. Nitrate ions are needed for protein synthesis and therefore growth.
Which ion deficiency causes chlorosis?
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Magnesium, because magnesium ions are needed to make chlorophyll.
Name three physical plant defences.
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Cellulose cell walls, a tough waxy cuticle on leaves, and layers of dead cells around stems.
Give two mechanical adaptations of plants.
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Any two of: thorns and hairs, leaves that droop or curl when touched, mimicry.