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08:18What evidence suggests that ABA from roots can signal guard cells to close?
a. If roots are given sufficient water, guard cells close anyway.
b. If roots are dry, guard cells begin to close—even though leaves may not be experiencing water stress.
c. Applying ABA to guard cells directly causes them to close.
d. If roots are dry, the ABA concentration in leaf cells drops dramatically.
Why was it logical to predict that amyloplasts function as statoliths?
a. They are dense and settle to the bottom of gravity-sensing cells.
b. They are present only in gravity-sensing cells.
c. They make a direct physical connection with membrane proteins that have been shown to be gravity-receptor molecules.
d. Their density changes in response to gravity.
Phytochromes can be considered 'shade detectors,' while phototropins such as PHOT1 can be considered 'sunlight detectors.' Explain why these characterizations are valid.
Suppose that a mutant plant is unable to make methyl salicylate. Explain why it is not likely to survive in the wild.
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.
In many species native to tropical wet forests, seeds do not undergo a period of dormancy. Instead, they germinate immediately. Predict the role of ABA in these seeds. How would you test your prediction?
