Auxin causes a shoot to bend toward light bya. 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.

A barley mutant lacking a gibberellic acid receptor would (A) fail to make GA. (B) catalyze starch more quickly. (C) fail to make a-amylase. (D) fail to take up water.

Auxin enhances cell elongation in all of these ways excepta. 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.

Charles and Francis Darwin discovered thata. 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.

How may a plant respond to severe heat stress?a. by reorienting leaves to increase evaporative coolingb. by creating air tubes for ventilationc. by producing heat-shock proteins, which may protect the plant's proteins from denaturingd. 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 ofa. 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 darkb. 14 hours light/10 hours darkc. 4 hours light/8 hours dark/4 hours light/8 hours darkd. 8 hours light/8 hours dark/light flash/8 hours dark

Phytochromes can be considered 'shade detectors,' while phototropins such as PHOT1 can be considered 'sunlight detectors.' Explain why these characterizations are valid.