AP BIOLOGY

Detailed explanation-1: -Promotes Tropism: Auxin induces phototropism, gravitropism and thigmotropism, i.e. movement in response to light, gravity and touch, respectively.

Detailed explanation-2: -Phototropism is the growth of an organism in response to a light stimulus. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light contain a hormone called auxin that reacts when phototropism occurs.

Detailed explanation-3: -Phototropic movement in plants in response to light is stimulated by the concentration of auxin, the plant growth hormone.

Detailed explanation-4: -Phototropisms. In a stem, the shaded side contains more auxin and grows longer, which causes the stem to grow towards the light. The plant does NOT bend towards the light. It grows because the auxin causes the cells to elongate on the shaded side, so this side grows more.

Detailed explanation-5: -Both phototropism and geotropism are controlled by the distribution of auxin within the plant cells: In geotropism, auxin will accumulate on the lower side of the plant in response to the force of gravity. In phototropism, light receptors (phototropins) trigger the redistribution of auxin to the dark side of the plant.