What does phototropism mean?
Phototropism is the directional growth of a plant or other organism in response to light. It commonly describes the way shoots curve toward a light source, a response called positive phototropism, although roots may show the opposite pattern, known as negative phototropism. The process is distinct from phototaxis, which concerns movement rather than growth, and from heliotropism, which is closely related but more specifically associated with orientation toward or away from the sun or a light source. Phototropism is especially important in the study of plant development because it shows how organisms detect light and alter their growth in response to their surroundings. The term is used chiefly in biology, horticulture, and related scientific discussion.
nounThe growth or movement of a plant or other organism in response to light, usually in a direction determined by the light source. Growth toward light is called positive phototropism, while growth away from it is called negative phototropism.
- The directional growth of a plant or other organism in response to light.
- The tendency of a plant to grow toward a light source, especially when the response is described as positive.
"The shoot displays positive phototropism as it bends toward the window."
"The seedlings exhibited strong phototropism as they leaned toward the lamp."
"Researchers studied phototropism in fungi under controlled lighting conditions."
The plural is uncommon in general use but follows the regular plural rule.
"The experiment compared different phototropisms in young seedlings."
Plants have a built-in compass for light: their shoots usually bend toward it, while roots often grow away from it.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does phototropism come from?
Phototropism combines the Greek roots phōtós, meaning “light,” and trópos, meaning “turn” or “direction.” The word developed in the scientific vocabulary of botany to describe plant growth directed by light. Its etymological relatives include photosynthesis, phototaxis, and photometer, all of which use the same element meaning light.
Related word forms
How phototropism is actually used
The term is primarily used in biology and is less common in general language. In technical writing, the direction of the response is often specified as positive or negative.
Easily confused with phototropism
Heliotropism is the turning of a plant or part of a plant toward or away from the sun or another light source, whereas phototropism more generally describes growth in response to light.
Phototropism is a growth response, while phototaxis is the movement of an organism, such as a microorganism, toward or away from light.