A potted plant is kept near a window so that light falls on it from one side. After a few days, the shoot is…

Question

A potted plant is kept near a window so that light falls on it from one side. After a few days, the shoot is seen bending towards the light. Name the hormone responsible for this bending and explain how it brings about the movement.

Accepted Answer

## Model Answer **Hormone responsible:** Auxin **How it brings about bending:** Auxin is synthesised at the shoot tip. When light falls from one side, auxin diffuses towards the **shady side** of the shoot. This higher concentration of auxin on the shady side stimulates those cells to **elongate faster** than the cells on the light-exposed side. Due to unequal growth — faster on the shaded side, slower on the lit side — the shoot **bends towards the light**. This is an example of phototropism. *Source: Control and Coordination, Section 6.2.2 – Movement Due to Growth* --- ## Explanation - The examiner expects three clear points: (1) name the hormone = **auxin**, (2) auxin moves to the shady side, (3) unequal cell elongation causes bending. One mark each. - Do not just say "the plant bends" — explain the *mechanism* (differential growth). - The key phrase is **"cells grow longer on the shady side"** — this is what the textbook specifically states and what examiners look for.

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