Plant defence responses: Mechanical adaptations.

The idea

Mechanical adaptations are physical features of a plant that deter herbivores. Unlike physical plant defences, which resist invasion by microorganisms, mechanical adaptations specifically protect against animals. Examples include thorns and hairs, which make the plant difficult or painful to eat. Leaves that droop or curl when touched can dislodge insects or frighten larger animals. Mimicry is another mechanical adaptation, where a plant resembles another organism or object to trick herbivores, such as looking like a pebble or having patterns that resemble butterfly eggs to deter egg-laying. These features are inherited adaptations that increase survival.

What earns the marks

• Mechanical adaptations are physical features that deter herbivores from eating the plant.
• Examples include thorns and hairs, which can wound or deter animals.
• Leaves which droop or curl when touched act to dislodge insects or frighten herbivores.
• Mimicry tricks animals, for example by resembling stones or mimicking the presence of insect eggs.
• Mechanical adaptations are distinct from physical defences, which protect against microorganisms.

Common mistakes and how to put them right

• Conflating mechanical adaptations with physical defences.

  Put it right by remembering mechanical adaptations deter herbivores, while physical defences resist microorganisms.

• Forgetting mimicry is a mechanical adaptation.

  Put it right by including examples like plants that look like pebbles to avoid being eaten.

• Thinking thorns protect against pathogens.

  Put it right by stating thorns deter herbivores, not microscopic pathogens.

Exam tips

• Clearly distinguish between mechanical adaptations (against herbivores) and physical defences (against pathogens).
• Name specific examples like thorns, hairs, drooping leaves, or mimicry when asked for mechanical adaptations.