Arrange the following sequential steps of a shoot's phototropic response to unidirectional light in the correct order from initial stimulus to the resulting growth movement.
- 1Unidirectional light strikes one side of the plant shoot tip.
- 2Auxin diffuses laterally from the illuminated side to the shaded side of the shoot tip.
- 3Cells on the shaded side undergo increased cell elongation compared to those on the light side.
- 4The stem bends towards the light source due to differential growth rates.
Answer
The correct sequence begins with unidirectional light striking the shoot tip, followed by lateral diffusion of auxin to the shaded side, increased cell elongation on the shaded side, and finally the bending of the stem toward the light source.
Phototropism in plant shoots is driven by the asymmetric distribution of auxin. Exposure to unilateral light causes auxin to migrate laterally from the illuminated side to the shaded side of the shoot tip. The higher concentration of auxin on the shaded side accelerates cell elongation on that side, creating a growth differential that causes the stem to bend toward the light source.
Step-by-Step Solution
Key Concept
Auxin lateral redistribution and differential cell elongation in phototropism