Question

Plants bend toward the light because
(A) They need light for photosynthesis
(B) They need light for respiration
(C) Light attracts them
(D) Cells on the shaded side elongate more

Answer 1

Auxin is a growth hormone that gets produced on the other side of the stem which is receiving light and the part in which the hormone auxin is secreted, shows an increase in the number of cells.

Complete step by step answer:
Plants bend toward the light because cells on the shaded side elongate more, this happens just because of the action of the hormone Auxin. When only one part is receiving the light, the Auxin hormone through diffusion moves to the part which is receiving less sunlight and helps in the elongation of cells that are receiving less sunlight.
So, the correct answer is ‘Cells on the shaded side elongate more’

Additional Information: Auxins are a class of plant hormones which has some morphogen-like characteristics also in it. Auxins play a very important role in the coordination of many growths and behavioral processes in plant life cycles and are essential for plant body development. It is a plant hormone produced in the stem tip and helps in the promotion of cell elongation.
Other than Auxin, plant hormones also include abscisic acid, ethylene, gibberellins, cytokinins, salicylic acid, strigolactones, brassinosteroids, and nitrous (nitric) oxide. Gibberellins are known as one of the most important and primary plant hormones, which have physiological functions such as stimulating organ growth through the enhancement of cell elongation and cell division.

Note: When the plant bends towards the light, the process is known as phototropism. This reveals that stem and leaves show phototropism. As light is one of the factors, the other factor is gravity. The upward growth of plant parts like the stem is an example of negative geotropism and the downward growth of roots is an example of positive geotropism.