How does phototropism occur in plants ?

Explanation

The growth movement of plants in response to light stimulus is known as phototropism. The shoots show positive phototropism while 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 This happens as follows:
1) When sunlight falls straight on the plant, the auxin hormone synthesised at the tip of the stem spreads uniformly down the stem and due to equal concentration of auxin, stem grows straight
2) When sunlight falls on only one side of the plant, the auxin diffuses towards the shady side of shoot. The concentration of auxiri stimulates the cells of the plant which is not getting sufficient light (shady part) to grow longer. Therefore, the stem appears to bertd towards the source of light.
For E.g- The flower head of sunflower is positively phototropic and hence during a day, it moves from east to west along with the sun.