If an animal with a circadian clock of about 25 hours is kept in the dark without environmental time cues, it will
A) become active one hour later each day.
B) become active at the same time each day.
C) become active one hour earlier each day.
D) become active two hours earlier each day.
E) have an unpredictable pattern of activity.

Question

Quizplus · Accepted Answer

An animal with a circadian clock of about 25 hours will have a natural tendency to cycle through activity and rest periods in a slightly longer-than-24-hour cycle. However, when kept in a dark environment without any external cues, its natural cycle will start to drift with respect to the external day/night cycle. Specifically, the animal's activity period will shift by about one hour each "day" (i.e. 25-hour cycle), so it will become active one hour later each day.

If an Animal with a Circadian Clock of About 25