Phototropism
Phototropism
Phototropism (/foʊˈtɒtrəˌpɪzəm/; from the Greek phōs (φῶς), meaning "light", and tropos (τρόπος), meaning "turn") is the orientation of a plant or other organism in response to light, either towards the source of light (positive phototropism) or away from it (negative phototropism).
Etymology
The term "phototropism" is derived from the Greek phōs (φῶς), meaning "light", and tropos (τρόπος), meaning "turn". It was first used in the late 19th century to describe the phenomenon observed in plants.
Explanation
Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Growth towards a light source is a positive phototropism, while growth away from light is a negative phototropism. Most plant shoots exhibit positive phototropism, and rearrange their chloroplasts in the leaves to maximize photosynthetic energy and promote growth.
Mechanism
Phototropism is driven by the plant hormone auxin. Light causes the plant to produce auxin on the side of the stem that is furthest from the light, causing cells on that side to elongate and the stem to bend towards the light.
Related Terms
- Heliotropism: A form of phototropism, heliotropism is a plant's growth in response to the direction of the sun.
- Gravitropism: This is a turning or growth movement by a plant in response to gravity.
- Thigmotropism: This is the turning or bending of a plant or other organism in response to a touch stimulus.
- Hydrotropism: This is a plant's growth response in which the direction of growth is determined by a stimulus or gradient in water concentration.
- Chemotropism: This is the growth of organisms navigated by chemical stimulus.
External links
- Medical encyclopedia article on Phototropism
- Wikipedia's article - Phototropism
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