survival and response

responding to the environment

• - organisms increase their chances of survival by responding to changes in their external environment. animals and plants respond in different ways:
• for example, animals can move away from harmful environments such as places which are too hot or too cold.
• plants cannot actually move themselves, but they can change the way they grow in an attempt to find more favourable environmental conditions. e.g. seedlings growing in dark conditions can rapidly develop very long, thin stems to increase their chances of finding light.
• - organisms also respond to changes in their internal environment to make sure that the conditions are always optimal for their metabolism (all the chemical reactions that go on inside them).
• - any change in the internal or external environment, e.g. a change in temperature, light intensity or pressure is called a stimulus.

simple responses

• - simple mobile organisms, e.g. woodlice, have simple responses to keep them in a favourable environment. their responses can either be tactic or kinetic :
• tactic responses (taxis) - directional movement in response to a stimulus. the direction of the stimulus affects the response.
• kinetic response (kinesis) - non-directional (random) movement in response to a stimulus. the intensity of the stimulus affects the response.

Slide 3

• investigating simple animal responses