Question

Dropping of tamarind leaves after the sunset is:
A. Phototropism
B. Phototaxis
C. Photonasty
D. Chemotaxis

Answer 1

Hint: The plants interact with their environment and respond to their environment in many ways as well. The phenomenon in which plants respond to their environment or stimulus is called tropism. The common stimuli are light, water, sun, touch and gravity.

Complete answer:
Tropism is a phenomenon in which plants respond to the influences of the environment. These responses are dependent on the direction of stimulus. Tropisms are usually named for the stimulus that causes it. For example, tropism caused by the sun is called phototropism, tropism caused by a host or pathogen is called host tropism or tissue tropism. A great example is sun; sun influences the growth of many plants in a defined direction.
We now know that how tropism affects the activity of a plant. In this case, we are asked why tamarind leaves droop after sunset. This means it is affected by the activity of light i.e. by the phenomenon of photoperiodism.
We can further explain this as: The cells which are present on the farthest side from the sun have a chemical called auxin. This chemical reacts during photoperiodism. It responds by causing the elongation of the cells which are away from light and results in the bending of the stem or leaves towards the direction of the sun.
This explains the drooping of tamarind leaves is caused due to the phenomenon of photoperiodism.

Therefore, the correct answer is option a.

Note: Phototropism is of two types positive and negative. Positive phototropism is growth of plants in direction of the stimulus. For example stem exhibits positive phototropism. In contrast, the growth away from the stimulus is called negative phototropism which is exhibited by roots.