Question

mention the role of the plant harmone (a)auxin

Answer 1

The plant stem responds to light and bend towards it due to the action of 'Auxin hormone'.
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Answer 2

Auxin is synthesized at shoot apices in response to light. Unidirectional exposure to light at shoot apex results in diffusion of auxin towards the shaded region of the shoot. This thereby leads to more growth on the shaded side as compared to the illuminated region. So the stem bends towards the source of light.

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