Auxin-Induced Unequal Growth in Shoots

Steps:

• Seedlings grown in dark lack light cues, so growth response is due to auxin from shoot tips.
• Cutting and replacing tips on one side creates asymmetric auxin distribution.
• Auxin concentrates on the side with the tip, promoting cell elongation there.
• Unequal elongation causes the shoot to bend away from the tipped side.

Why D is correct:

• Per the Cholodny-Went theory, auxin diffuses laterally from the offset tip, causing greater growth on the tipped side and curvature to the opposite (right) side.

Why the others are wrong:

• A: Asymmetric auxin prevents straight growth.
• B: No directional light in dark; growth curves, not straight.
• C: Curvature is away from the tipped side, not toward it.

Final answer: D