What does phototaxis mean?
Phototaxis is the directional movement of an organism or cell in response to light. It differs from phototropism because phototaxis concerns movement rather than growth: an organism may swim or crawl toward a light source, or move away from it. Positive phototaxis is the tendency to move toward light, while negative phototaxis indicates movement away. The term is especially useful in discussions of microorganisms, including algae, bacteria, and protozoa, as well as in studies of animal behaviour and plant responses to light. Although phototaxis sounds like a specialized term, it describes a widespread principle of orientation: organisms can detect differences in light intensity and alter their movement accordingly. The word comes from the combining form photo-, relating to light, and taxis, meaning movement or arrangement.
nounThe movement of an organism or cell in response to light, either toward a light source (positive phototaxis) or away from it (negative phototaxis).
- The movement of an organism or cell in response to light, either toward or away from the light source.
"The microorganisms exhibited positive phototaxis, moving toward the illuminated area of the microscope slide."
"The algae showed clear phototaxis toward the light."
"Negative phototaxis can cause microorganisms to retreat from an exposed surface."
Used when referring to multiple examples of the phenomenon or to distinct types of light-directed movement.
"Researchers compared the phototaxes of several species of algae."
Phototaxis lets tiny organisms navigate by light, even when the difference between brightness and darkness is too subtle for human eyes to perceive.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does phototaxis come from?
Phototaxis is a modern scientific formation built from Greek photo-, meaning light, and taxis, meaning movement, arrangement, or orientation. The underlying sense is therefore movement in response to light. Its components are also familiar in words such as photosynthesis and phototropism, while taxis itself is the common source of related terms in biology and movement.
Related word forms
How phototaxis is actually used
This is a technical biological term, used chiefly in microbiology, botany, zoology, and related sciences. The modifiers positive and negative indicate movement toward and away from light, respectively.
Easily confused with phototaxis
Phototaxis is movement of an organism or cell in response to light, whereas phototropism is growth or bending of a plant or organism in response to light.