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

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

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

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.