Taxis

A taxis (from Ancient Greek τάξις (táxis) 'arrangement, order';[1] pl.

: taxes /ˈtæksiːz/)[2][3][4] is the movement of an organism in response to a stimulus such as light or the presence of food.

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.

[5][6] It is sometimes distinguished from a kinesis, a non-directional change in activity in response to a stimulus.

For example, flagellate protozoans of the genus Euglena move towards a light source.