In the study of sleep and biological rhythms, which natural phenomenon is the best example of periodic behavior?

• A. A sudden loud noise triggering the startle reflex
• B. The regular alternation of sleep and wakefulness across a 24-hour day
• C. A random variation in nightly dream content
• D. A once-in-a-lifetime solar eclipse

Answer: (B)

Verified step by step guidance

1. Understand the concept of periodic behavior in the context of sleep and biological rhythms. Periodic behavior refers to events or processes that repeat at regular intervals over time.
2. Identify the options given and analyze whether they represent regular, repeating patterns or irregular, one-time, or random events.
3. Recognize that a sudden loud noise triggering the startle reflex is an immediate, non-repeating response, so it is not periodic.
4. Note that a random variation in nightly dream content lacks a consistent, repeating pattern, so it is not periodic.
5. Understand that the regular alternation of sleep and wakefulness across a 24-hour day is a classic example of a circadian rhythm, which is a natural, periodic biological process repeating roughly every 24 hours.