A taxis (plural taxes /ˈtæksz/, from Ancient Greek τάξις (taxis), meaning 'arrangement') is the movement of an organism in response to a stimulus such as light or the presence of food. Taxes are innate behavioural responses. A taxis differs from a tropism (turning response, often growth towards or away from a stimulus) in that in the case of taxis, 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.

Taxes are classified based on the type of stimulus, and on whether the organism's response is to move towards or away from the stimulus. If the organism moves towards the stimulus the taxis is positive, while if it moves away the taxis is negative. For example, flagellate protozoans of the genus Euglena move towards a light source. This reaction or behaviour is called positive phototaxis, since phototaxis refers to a response to light and the organism is moving towards the stimulus.

Many types of taxis have been identified, including:

Depending on the type of sensory organs present, a taxis can be classified as a klinotaxis, where an organism continuously samples the environment to determine the direction of a stimulus; a tropotaxis, where bilateral sense organs are used to determine the stimulus direction; and a telotaxis, where a single organ suffices to establish the orientation of stimulus.

There are five types of taxis based on the movement of organisms.

This page was last edited on 16 April 2018, at 21:22.
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