Mimosa plants spread their leaflets during the day and fold them at night. You decide to design an experiment to test whether Mimosa's leaf movements are controlled by a biological clock. Which experiment would be the best test of your hypothesis?
A) Growing the plant indoors and turning the lights on in the middle of the night. If a biological clock is controlling leaf movement, the leaves will open.
B) Putting the plant under a bright light in the middle of the day. If the leaves close, a biological clock mechanism is ruled out.
C) Subjecting the plant to a flash of red light in the middle of the night. If the leaves open at the usual time the next morning, a biological clock mechanism is ruled out.
D) Putting the plant in a dark closet at nightfall. Check on the plant at noon the next day, while the plant is still in the closet. If the leaves are open, a biological clock is indicated.

Question

Quizplus · Accepted Answer

Option D is the best test because it eliminates the possibility of external cues such as light and allows for observation over an extended period of time. Mimosa plants fold their leaves at night, so if the leaves are open the next day, it suggests the timing of their movements is regulated by an internal biological clock. Choice A is not a good test because turning on the lights in the middle of the night could be an external cue that triggers leaf opening. Choice B is not a good test because the response to light does not necessarily indicate the absence of an internal biological clock mechanism. Choice C is not a good test because a flash of red light can also act as an external cue that triggers leaf movement.

Mimosa Plants Spread Their Leaflets During the Day and Fold