Question
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The bending of stem towards light is due to the action of :
A. Gibberellins
B. Abscisic acid
C. Cytokinin
D. Auxin

Answer
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Hint: Auxin is the chemical which helps the plant to move towards the sunlight.

Complete answer: Phototropism also known as bending or moving away of the stem with respect to light is mainly due to action of Auxin.
1. It is most commonly observed in plants but can also be seen in fungi.
2. The cells that are most far away have a chemical called auxin which react when phototropism occurs.
3. Photo morphogenesis is the process by which plant development occurs due to action of light.
4. Sunlight completely destroys auxin meaning the part of the shoot tip of the plant which is receiving direct sunlight will have the least amount of auxin.
5. The spare auxin which is not destroyed present on the shaded side promotes more cell division and elongation, causing plants to bend towards sunlight.

Additional information: Auxin moves to the darker side which results in an increase of size of the cell present there in correspondence to other cells which are present on the
1. lighter side of the plant.
2. This effect causes curving of the stem tip towards the light.
3. Apart from this auxin also maintains the apical dominance of the plant.

The correct option is, (D)

Note: Gibberellins promotes plant growth by initiating germination of the plant.
Abscisic acid inhibits plant growth by wilting the leaves of the plant.
Cytokinin also promotes plant growth by promoting cell division.