37. Plant Sensation and Response

A conformational change in a substance called phytochrome __________.

What happens immediately after a phytochrome is activated by light?

You are interested in determining what part of a plant senses the light, which leads to phototropism. A good first experiment would be to __________.

Some seeds require light for germination. This process is controlled by the phytochrome system. Which of the following germination treatments would inhibit germination of such seeds?

Photoperiodism is __________.

An Alaskan trapper worried about being attacked by grizzly bears left the lights on in his cabin all the time. Plants just outside the cabin flowered a month early. Which of the following best explains this?

A certain short-day plant flowers when days are less than 12 hours long. Which of the following treatments will result in flowering?

What are circadian rhythms?

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 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.

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.

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