natural defence

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In biology, the defence against disease provided by natural barriers. In animals this is provided by natural barriers to infection such as the skin, and defence systems of the blood circulation such as the production of antibodies. If the natural defences work, they provide immunity (see immunization) to infection. Plants also have natural defences – for example, spines or poisonous chemicals.

Organisms may also need to defend themselves against being eaten by another organism. Animals and plants use a variety of mechanisms. Animals need to be able to detect a predator (see predation) and take appropriate action. This may involve escaping (for example, rabbits), defending itself using a frightening display (for example, a butterfly opening its wings to reveal eye spots on its wings), or using teeth or claws (for example, a cat). However, many animals and plants rely on camouflage to make them ‘invisible’ – for example, deer or a bulb growing in grassland with leaves looking like grass. Some plants may have defences such as spines (holly), chemicals with unpleasant effects (the stings of nettles), or poisonous chemicals (bracken).

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