2.81

Describe positive phototropism of stems

Positive Phototropism (growth in response to light, growing towards the light).

When the light source is directly above the plant, the plant grows upwards.

However, if there is a lateral light source (light coming from the side), the plant bends towards the light (like sunflowers!). The light causes the movement of auxin to the darker side. Auxin is a plant hormone that allows more growth to happen on one side of the plant. So the plant bends towards the side with less growth, more light.