Phototaxis

Phototaxis is directed movement toward or away from a light source or light gradient. It is positive when movement is toward light and negative when movement is away.

Photoreceptor: A cell or molecule that detects light and initiates a biological response. Photoreceptors provide the light signal that guides phototactic movement.
Taxis: Directional movement of an organism in response to a stimulus. Phototaxis is the light-directed member of this broader class of responses.
Phototaxis in insects: Light-oriented movement in insects, including attraction or avoidance of light sources. Insects provide familiar cases of light-guided movement with varied ecological causes.
Phototropism: Directional growth of an organism or organ in response to light. Phototropism changes growth direction, whereas phototaxis changes movement direction.
Eyespot apparatus: A light-sensing structure in some microorganisms, often combining pigment with nearby photoreceptors. In organisms such as Euglena, this structure helps determine light direction.
Light gradient: A spatial change in light intensity or other light properties. A gradient supplies the directional information that phototaxis follows.
Phototaxis in zooplankton: Light-directed movement by small animals drifting or swimming in aquatic environments. Light responses can influence where zooplankton occur in the water column.
Photoperiodism: A biological response to the length and timing of day and night. It responds to light schedules rather than steering movement along a gradient.
Phototactic response in Chlamydomonas: The light-guided swimming response of the green alga Chlamydomonas reinhardtii. Its eyespot and flagella show how sensing can steer a swimming cell.
Positive and negative taxis: Directional responses in which movement is respectively toward or away from a stimulus source. The terms specify whether phototactic movement approaches or avoids light.

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