Question

How does phototropism occur in plants?

Answer 1

The growth movement in plants in response to light stimulus is known as phototropism. 
Leaf tips and stem tips have a hormone called auxin which is sensitive to light.
The shoots show positive phototropism, and the roots show negative phototropism. This means that the shoots bend towards the source of light whereas the roots bend away from the light source. 
For Example: The flower head of sunflower is positively phototropic and hence it moves from east to west along with the sun.