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

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

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.

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

In general, small seeds that have few food reserves must be exposed to red light before they will germinate. (Lettuce is an example.) In contrast, large seeds that have substantial food reserves typically do not depend on red light as a stimulus to trigger germination. State a hypothesis to explain these observations.

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 hoursb. an 8-hour day and 16-hour night with a flash of white light after 8 hoursc. a 13-hour night and 11-hour day with 1 minute of darkness after 6 hoursd. 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?