What does phototropy mean?
Phototropy is the biological tendency of an organism or plant to grow toward or away from a light source. When the response is toward light, it is called positive phototropy; growth in the opposite direction is negative phototropy. The effect is especially noticeable in plants, whose stems and shoots commonly bend toward a brighter area, helping them capture light for photosynthesis. Not every organism responds in the same way, and some roots, microorganisms, and fungi grow away from light under certain conditions. Phototropy is therefore part of the wider study of how living things respond to environmental stimuli. Although the word appears in plant physiology and related biological literature, phototropism is generally the more familiar term for the directional growth response itself.
nounThe tendency of an organism or plant to grow toward or away from light. It may be positive, involving growth toward light, or negative, involving growth away from it.
- The tendency of an organism or plant to grow or bend directionally in response to light, either toward it (positive phototropy) or away from it (negative phototropy).
"The seedlings display clear phototropy, bending toward the window."
"The young shoots show positive phototropy as they lean toward the bright side of the greenhouse."
"The fungus exhibits negative phototropy, growing away from the strongest source of light."
The plural is used in technical contexts but is much less common than the singular.
"The study compares phototropies in different plant species."
Not all growing things follow the light: some organisms turn toward it, while others deliberately grow away.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does phototropy come from?
Phototropy combines Greek phōtos, meaning “light,” with a form of Greek trope, meaning “turn” or “direction.” The term follows the same conceptual pattern as other biological words such as heliotropism and thermotropism, which describe orientation in response to light and temperature respectively. Its scientific development belongs to the tradition of describing biological responses with Greek-derived combining forms.
Related word forms
How phototropy is actually used
This is a specialized biological term. In general writing, phototropism is often used because it more directly denotes the process of directional growth in response to light.
Easily confused with phototropy
Phototropy names the underlying tendency to grow toward or away from light, while phototropism usually names the observable growth response itself.