AP Biology: Circadian Rhythms Practice Questions
Test yourself on AP Biology: Circadian Rhythms with 12 original AP Exams practice questions. Pick an answer to see instant feedback and a full explanation.
Free original practice questions for study purposes. Open Exam Prep is an independent study resource and is not affiliated with, endorsed by, or sponsored by the makers of AP Exams.
advertisement
Answer the questions below — you get instant feedback and a full explanation for each.
1. Which statement best describes a circadian rhythm?
Explanation. Circadian rhythms are roughly 24-hour biological cycles. They are generated by internal timing mechanisms and can be reset by cues such as light-dark cycles.
2. Light exposure changes the timing of daily activity in a nocturnal animal. Which concept does this example best illustrate?
Explanation. Entrainment means an internal rhythm is adjusted by an external cue. Light is a common cue that synchronizes circadian clocks with the environment.
3. A plant opens its leaves during the day and closes them at night for several days even under constant dim light. What does this observation suggest?
Explanation. Persistence under constant conditions suggests an endogenous rhythm. External cues can set the clock, but the rhythm can continue for some time without the cue.
4. Which result would best support the claim that a gene is involved in circadian timing?
Explanation. A controlled comparison showing that a mutation changes rhythm timing supports a role for that gene. The key evidence is a specific change in period or phase relative to controls.
5. Why are feedback loops useful in molecular models of circadian rhythms?
Explanation. Many circadian systems use feedback loops in which clock proteins affect the expression of clock genes. Delayed feedback can generate regular oscillations.
6. In an experiment, two groups of organisms are kept under identical conditions except that one group receives shifted light-dark cycles. What is the independent variable?
Explanation. The independent variable is what the researcher changes. Here, the light-dark schedule is manipulated, while activity timing would be a dependent variable.
7. Which observation would show that a circadian rhythm is entrained rather than simply eliminated?
Explanation. Entrainment changes the phase of an ongoing rhythm so it aligns with a new cue. It does not mean the rhythm disappears.
8. Why might two species respond differently to the same light cycle?
Explanation. Circadian responses depend on sensory systems, clock components, physiology, and ecological context. Natural selection can favor different timing strategies in different species.
9. A daily hormone pattern peaks before an animal's active period. Which interpretation is most consistent with AP Biology principles?
Explanation. Circadian clocks can coordinate physiology and behavior. Endocrine signals may rise or fall at predictable times to prepare tissues for daily changes in activity.
10. A population lives at high latitude where day length changes strongly across seasons. How could natural selection shape circadian-related traits?
Explanation. If heritable variation in timing systems affects survival or reproduction, natural selection can change allele frequencies. Local environments can favor different rhythm-related traits.
11. What is the best reason to include a control group in a circadian rhythm experiment?
Explanation. A control group provides a baseline for comparison. Without a control, it is harder to attribute rhythm changes to the experimental treatment.
12. Why should students avoid saying that circadian rhythms are controlled only by the environment?
Explanation. The key idea is interaction. Internal biological clocks generate rhythms, and environmental cues such as light can synchronize or shift those rhythms.
📘 Want a full structured course and official-style practice tests? Browse top-rated AP Exams prep books and courses. Some links are affiliate links; we may earn a commission at no cost to you.
advertisement
FAQ
What should I know about circadian rhythms for AP Biology?
Know that circadian rhythms are roughly 24-hour internal cycles, can persist under constant conditions, and are entrained by cues such as light.
How do circadian rhythms connect to gene regulation?
Many models use feedback loops in which gene expression and protein activity rise and fall over time, creating repeated cellular cycles.
What experiment ideas appear in circadian rhythm questions?
Look for independent variables such as light-dark timing, dependent variables such as activity phase or period, and controls that isolate the effect of the cue.