Charles and Francis Darwin discovered that
a. Auxin is responsible for phototropic curvature
b. Red light is most effective in shoot phototropism
c. Light destroys auxin
d. Light is perceived by the tips of coleoptiles

Evaluate the following assertions about phototropism. Select True or False for each statement.

T/F Cells on the illuminated side of a stem elongate more than cells on the shaded side.

T/F Phototropism is triggered by blue light.

T/F Phototropins play a significant role in phototropism.

T/F The bending of the plant is due to cell elongation in response to auxin.

A barley mutant lacking a gibberellic acid receptor would

a. Fail to make GA.

b. Catalyze starch more quickly.

c. Fail to make α-amylase.

d. Fail to take up water.

Auxin enhances cell elongation in all of these ways except:

a. Increased uptake of solutes

b. Gene activation

c. Acid-induced denaturation of cell wall proteins

d. Cell wall loosening

Which of the following statements about phytochrome is not correct?

a. It is photoreversible.

b. Its function was understood long before the protein itself was isolated.

c. The Pfr form activates the responses to red light.

d. It is involved in guard-cell opening.

Auxin causes a shoot to bend toward the light by

a. Causing cells to shrink on the dark side of the shoot

b. Stimulating growth on the dark side of the shoot

c. Causing cells to shrink on the lighted side of the shoot

d. Stimulating growth on the lighted side of the shoot

How may a plant respond to severe heat stress?

a. By reorienting leaves to increase evaporative cooling

b. By creating air tubes for ventilation

c. By producing heat-shock proteins, which may protect the plant's proteins from denaturing

d. By increasing the proportion of unsaturated fatty acids in cell membranes, reducing their fluidity

The signaling molecule for flowering might be released earlier than usual in a long-day plant exposed to flashes of:

a. Far-red light during the night

b. Red light during the night

c. Red light followed by far-red light during the night.

d. Far-red light during the day

If a long-day plant has a critical night length of 9 hours, which 24-hour cycle would prevent flowering?

a. 16 hours light/8 hours dark

b. 14 hours light/10 hours dark

c. 4 hours light/8 hours dark/4 hours light/8 hours dark

d. 8 hours light/8 hours dark/light flash/8 hours dark