Question

how does auxin cause a plant to adjust to light?
a it stimulates cells on the dark side of the plant to grow longer, bending it toward light
b it stimulates cells on the light side of the plant to grow longer, bending it toward light
c it stimulates cells on the light side of the plant to grow longer, bending it toward dark
d it stimulates cells on the dark side of the plant to grow longer, bending it toward dark

Explanation:

To determine how auxin causes a plant to adjust to light, we recall the mechanism of phototropism. Auxin is a plant hormone that promotes cell elongation. In phototropism (response to light), auxin moves to the shaded (dark) side of the plant. Here, it stimulates the cells on the dark side to elongate more than the cells on the light side. This differential growth causes the plant to bend toward the light.

• Option a: States auxin stimulates dark - side cells to grow longer, bending toward light. This matches the phototropism mechanism.
• Option b: Says light - side cells are stimulated, which is incorrect as auxin accumulates on the dark side.
• Option c: Claims light - side cells are stimulated and the plant bends toward dark, which is wrong both in cell stimulation location and direction of bending.
• Option d: States dark - side cells are stimulated but the plant bends toward dark, which is incorrect in the direction of bending.

Answer:

a. It stimulates cells on the dark side of the plant to grow longer, bending it toward light