Question

How does phototropism occur in plants?

Answer 1

It refers to the growth of an organism in response to the light stimulus. It is the directional movement of a plant. The movement can be either towards the light or away from the sunlight.

Complete answer:
Phototropism is more often observed in plants but it can also occur in fungi. The process of phototropism refers to the directional movement of an organism in response to light stimuli. Plant cells contain a chemical known as auxin that are very active. They are far from the light and when these active chemicals react, phototropism takes place in plants.
In phototropism, the shoot responds by bending towards light whereas the root responds bending away from the light. When sunlight falls directly on the plant, the auxin hormone synthesizes at the tip of stem which spreads uniformly down the stem and due to equal concentration of auxin hormone, the stem grows straight.
When sunlight falls only on one side of the plant then the auxin diffuses towards the shady side of the shoot. The auxin concentration stimulates the cells to grow longer. Therefore, the stem appears to bend towards the light source. When a plant grows in the opposite direction then it is called negative phototropism.

Note: There are two types of phototropism i.e. positive phototropism and negative phototropism. In positive, the plant grows towards the light of the stimuli whereas in the negative phototropism, the plant grows in the opposite direction. Fungi like phycomyces also exhibit positive phototropism. Some vine shoots are examples of negative phototropism.