Question

Negative phototropism occurs in
A. Root
B. stem
C. Leaf
D. Flower

Answer 1

Hint: Phototropism is the orientation of a plant in response to light. It is of two types; positive and negative. There are many other responses that occur in plants. Some plants grow in response to a chemical called chemotaxis. The aerial parts of the plants show negative phototropism.

Complete answer:
Negative phototropism is defined as the orientation of the plant or maybe any other organism away from the light. Most of the plant shoots exhibit positive phototropism, i.e. oriented towards the light source and they rearrange their chloroplast in the leaves to maximize photosynthetic energy and also promote growth. The present study shows that negative phototropism can occur when the level of auxin signalling is reduced to a minimal level. The negative phototropism is the basal response to unilateral blue-light irradiation in plant axial organs. It can be seen in the roots of plants. They grow downwards and do not show positive phototropism.
i. Leaf: They grow on stems, therefore, they also show positive phototropism.
ii. Flower: They also grow on stems, therefore, they show positive phototropism. They grow towards the light.
Hence, the correct answer is Option (A).

Note: Phototropisms are caused by an unequal distribution of auxins. This makes the plant grow either towards or away from the light, depending on which part of the plant receives the light. In a stem, the cells on the shaded side contain more auxin and grow longer than the cells on the light side.