Taxis

(plural taxes) the movement of a cell or organism in response to a stimulus in environment. This stimulus may be temperature (thermotaxis), light (phototaxis), gravity (geotaxis) or chemical (CHEMOTAXIS).

Taken from Dictionary of Science

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A taxis (plural taxes, pronounced /ˈtæksiːz/) is an innate behavioral response by an organism to a directional stimulus or gradient of stimulus intensity. A taxis differs from a tropism (turning response, often growth towards or away from a stimulus) in that the organism has motility and demonstrates guided movement towards or away from the stimulus source. It is sometimes distinguished from a kinesis, a non-directional change in activity in response to a stimulus that results in the migration toward or away from a stimulus.

Taken from Wikipedia