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Question

Difficulty: EasyHormonal Coordination in Plants and Animals

When a growing plant shoot is exposed to light coming from one direction, it bends towards the light source. Which of the following statements correctly explains the distribution of auxin responsible for this growth response?

  1. Auxin accumulates on the shaded side of the stem, promoting cell elongation on that side.Answer
  2. B
    Auxin accumulates on the illuminated side of the stem, promoting cell elongation on that side.
  3. C
    Auxin accumulates on the illuminated side of the stem, inhibiting cell growth on that side.
  4. D
    Auxin breaks down completely on the shaded side, causing the illuminated side to grow faster.

Answer

Auxin accumulates on the shaded side of the stem, promoting cell elongation on that side.
In shoot phototropism, light from one side causes auxin to move laterally from the illuminated side to the shaded side. The increased auxin concentration on the shaded side stimulates greater cell elongation compared to the illuminated side, bending the shoot toward the light.

Step-by-Step Solution

1
Identify the phototropic movement mechanism
Unilateral light causes lateral translocation of auxin in the shoot tip.
Plant shoots display positive phototropism regulated by differential auxin concentrations.
2
Determine auxin distribution and its cellular effect
Auxin concentration increases on the shaded side, stimulating cell elongation.
Unequal elongation rates between the shaded and illuminated sides result in bending toward the light source.

Key Concept

Auxin Redistribution in Shoot Phototropism
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Topics

Hormonal Coordination in Plants and Animals

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