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?

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 except a. increased uptake of solutes. b. gene activation. c. acid-induced denaturation of cell wall proteins. d. cell wall loosening.

Auxin causes a shoot to bend toward 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.

A certain short-day plant flowers only when days are less than 12 hours long. Which of the following would cause it to flower? a. a 9-hour night and 15-hour day with 1 minute of darkness after 7 hours b. an 8-hour day and 16-hour night with a flash of white light after 8 hours c. a 13-hour night and 11-hour day with 1 minute of darkness after 6 hours d. a 12-hour day and 12-hour night with a flash of red light after 6 hours

A plant nursery manager tells the new night security guard to stay out of a room where chrysanthemums (which are short-day plants) are about to flower. Around midnight, the guard accidentally opens the door to the chrysanthemum room and turns on the lights for a moment. How might this affect the chrysanthemums? How could the guard correct the mistake?

SCIENTIFIC THINKING The discovery of auxin is a good example of how scientists build upon each other's work. For each of the three sets of researchers discussed in the chapter (the Darwins, Boyle-Jensen, and Went), write a one-sentence summary of what they discovered. If you were going to credit one person as being the 'discoverer' of auxin, who would it be?