Question

What is phototropism? Show phototropism in plants with the help of a labelled diagram.

Answer 1

Hint: Tropism is defined as a movement observed in plants in response to certain environmental stimuli. Tropisms are generally gathered with plants, but not limited to them. Tropisms in plants can be present in response to gravity, water or light.

Complete answer:
The biological phenomenon that associates movement of plants and certain pathogens in response to specific stimuli of the environment. Tropism can be either positive or negative. Positive tropisms usually occur when the plant or pathogen moves towards the direction of the stimulus, and negative tropism, if they move away from it.
Phototropism originates from two words - 'photo' meaning light and 'tropism' meaning movement.

Thus, we can say that Phototropism is defined as the movement of plants in the direction of light or towards the source of light. Plants respond positively to phototropism.
The mechanism of phototropism associates plant growth hormones called auxins. Auxin occurs in parts of the plant in different concentrations. Phototropism is known to occur in one of the following ways stated below:
Light can lead to deactivation of auxins present on the side of the leaf exposed to light. This leads to activation of auxins on the shaded part, and the plant grows towards light. Auxin synthesis is activated towards the shaded part of the plant allowing the plant to grow towards light.
Auxin moves between the light exposed area and the shaded area is equal. When light is given on the exposed part of the plant, movement of auxin from the light exposed part to the shaded part increases causing the growth of the plant towards light.

Note: There are two types of phototropism usually present in the environment: positive phototropism and negative phototropism. In positive, the plant shows growth towards the light of the stimuli whereas in the negative phototropism, the plant shows growth in the opposite direction. Fungi such as phycomyces also exhibit positive phototropism. Some vine shoots perfectly show negative phototropism.