Auxin redistribution drives phototropism

Steps:

• Light from one side triggers uneven auxin distribution in the shoot tip.
• Auxin moves laterally to the shaded (darker) side of the stem.
• Higher auxin concentration on the darker side promotes cell elongation there.
• Uneven elongation bends the shoot towards the light source.

Why C is correct:

• Per the Cholodny-Went theory, light causes auxin to accumulate on the darker side, stimulating elongation and bending the shoot phototropically toward light.

Why the others are wrong:

• A: Auxin promotes, rather than inhibits, cell elongation on the side where it accumulates.
• B: Auxin accumulates on the darker side, not the lighter side, to cause bending.
• D: Auxin primarily stimulates cell elongation, not division, in phototropism.

Final answer: C