Science Fair Project Encyclopedia
Phototropia or heliotropia is a botanical term for an organism's movement (tropism) in response to light (in the case of heliotrophism specifically the Sun). Growth toward a light source is positive phototropia, while the reverse is skototropism. Leaves and other parts of the plant that require light for photosynthesis exhibit positive phototropism, while roots, shoots, and other parts needing shelter use negative phototropism to some small extent, but gravitropism usually plays a larger role in their development. Plants that move toward sunlight are sometimes referred to as "heliotropic", but now that it is known that they respond to artificial light, a more general term is often used.
Different organs (parts of the plant) may exhibit different phototropic reactions to different wavelengths (colors) of light. Stem tips exhibit positive phototropic growth to blue light, while root tips exhibit negative phototropic growth to blue light. Both root tips and stem tips exhibit positive phototropism to red light. Not all phototropic effects are visible. Chloroplasts change their positions within cells depending on red-light intensity.
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details