A taxis (plural taxes) is an innate behavioral response by an organism to a directional stimulus. This means the organism automatically moves towards or away from the stimulus.
A taxis differs from a tropism (turning response, often plant growth towards or away from a stimulus) in that the organism has motility and shows movement towards or away from the stimulus source.
- Phototaxis: movement, usually towards light. Shown by many organisms, such as many flying insects.
- Chemotaxis: movement towards desirable chemicals, and away from unpleasant ones.
Even single-celled organisms can show taxis.