Phototaxis

Article By:

Whippo, Craig W. Department of Natural Sciences, Dickinson State University, Dickinson, North Dakota.

Last reviewed:April 2021

DOI:https://doi.org/10.1036/1097-8542.511760

Movement of a motile organism or free plant part in response to light stimulation. Light provides many organisms with both energy and information about their surroundings, which is why these organisms commonly display motile responses to light. Such movements of motile organisms or free plant parts in response to light stimulation are forms of phototaxis. Movements directed toward or away from sources of light are further described respectively as positive or negative types of phototaxis. For example, a moth's flight toward a shining lamp is a type of positive phototaxis (see illustration), whereas the tendency of a ciliate cell to swim toward darker waters exhibits negative phototaxis. Organisms can respond not just to the direction of light, but also to its intensity. Typically, phototactic movement allows organisms to maintain optimal physiological and growth conditions. Certain defensive behaviors, especially those of insects, are also considered to be forms of phototaxis. See also: Cell motility; Environment; Light; Plant movement; Plant physiology; Taxis

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