Asked by | 9th Aug, 2009, 11:16: AM
Phototropism is the growth of a plant in the direction of its light source.
There are two kinds of phototropism: positive photropism i.e. growth towards a light source (eg.- plant stem) and negative phototropism i.e. growth away from light (eg- plant roots)
Phototropic responses are caused by auxins. The shoot tip is responsible for directional movement by the plant in response to sunlight, as this is the area where auxins can be found. Auxins are distributed unevenly when the light source comes from only one direction. Sunlight eradicates auxin, meaning that the part of the shoot tip of the plant which is receiving direct sunlight will have the least amount of auxin. Specifically, more auxin flows down the dark side. The extra auxin present on the shaded side promotes more cell division and elongation, meaning that it grows faster than the exposed side of the plant. This unequal or one-sided growth (also called differential growth) brings about the curving or bending of the plant toward the light source.
Answered by | 9th Aug, 2009, 05:31: PM
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