Question

The curvature of coleoptile towards the source of light is due to ______.

Options

• Enlargement of the cell on the illuminated side.

• Enlargement of the cell on the shaded side.

• Enlargement of the cells on both sides.

• No enlargement.

Answer 1

The curvature of coleoptile towards the source of light is due to enlargement of the cell on the shaded side.

Explanation:

When a plant coleoptile is exposed to a unilateral (one-sided) light source, the growth hormone auxin is laterally redistributed and accumulates on the shaded side of the shoot. Because higher concentrations of auxin actively stimulate cell elongation and expansion, the cells on the darker, shaded side grow significantly longer than those on the illuminated side. This unequal, differential growth rate between the two sides mechanically forces the coleoptile to curve and bend directly toward the light.