What does phototactically mean?
Phototactically means in response to light, especially by moving or orienting toward or away from a light source. The term is used chiefly in biology and related sciences to describe organisms whose movement is influenced by light. For example, certain microorganisms move phototactically toward a light source, while others retreat from it. The direction of the response can be positive, meaning movement toward light, or negative, meaning movement away from it. The word should not be confused with “phototropically,” which normally refers to the bending or growth of a plant in response to light. Although “phototactically” is relatively uncommon outside scientific writing, it provides a precise term for movement governed by light.
adverbIn a phototactic manner, by moving or orienting in response to light.
- In response to light, especially by moving or orienting in a light-dependent direction.
"Many single-celled organisms move phototactically toward light of an appropriate intensity."
"The microorganisms moved phototactically toward the illuminated part of the chamber."
"A change in the light source caused the larvae to turn phototactically."
Some tiny organisms can effectively navigate by light, moving toward brightness or away from it depending on their phototactic response.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does phototactically come from?
The word is formed from the combining form photo-, relating to light, and the taxonomic element -tactic, associated with arrangement, orientation, or response. Its underlying noun, phototaxis, was coined in the nineteenth century from the same Greek roots for light and movement or arrangement. Closely related scientific terms include photosynthesis, phototropism, and phototherapy.
Related word forms
How phototactically is actually used
This is a specialized scientific adverb, most often used in biology, botany, and descriptions of microorganisms. It describes the manner of a phototactic response rather than the response itself.
Easily confused with phototactically
Phototactically describes movement or orientation in response to light, whereas phototropically describes growth or bending toward or away from light.