Which of the following describes the mechanism by which a plant stem grows toward light?

Question

A. The plant grows into an open area where it leaves will not be shaded by competing plants.

B. The plant seeks light in order to maximize photosynthesis

C. Cells on the dark side of the stem elongate more than those of the lighted side

D. Nervelike impulses stimulate contractilecells in the lighted side of the stem

E. The greater energy supply on the lighted side of the stem stimulates metabolsim and growth on that side

Answer 1

C. Cells on the dark side of the stem elongate more than those of the lighted side

In the case of positive phototropism (bending toward the light), either hormones that are light sensitive will move away from the light causing cells on that side of the plant to grow longer, or else, other hormones move toward the light side of the plant and cause the growth of shorter cells there. In either case, the plant bends away from the longer cells and toward the shorter ones.

From http://www.biology-online.org/11/10_grow...

"Phototropism, as mentioned, is illustrated by the movement of sprouts in relation to light source direction. Light causes the hormone auxin to move to the shaded side of the shoot. The auxin causes the cells on the shaded side to elongate more than the cells on the illuminated side. As a result, the shoot bends toward the light and exhibits positive phototropism.