Which of the following statements about circadian rhythms is true?

• A. They are typically more than 30 hours long.
• B. They are completely unaffected by external cues.
• C. They can be influenced by factors like diet and light exposure.
• D. They only affect sleep patterns.

Answer: (C)

The statement regarding circadian rhythms that is true highlights their susceptibility to external influences, such as diet and light exposure. Circadian rhythms are biological processes that follow a roughly 24-hour cycle, responding to the natural light-dark cycle. This adaptability allows them to synchronize with the environment, optimizing various physiological functions.

For instance, exposure to natural light helps to regulate the production of melatonin, a hormone that promotes sleep. Additionally, dietary habits can impact the timing of these rhythms, such as meal times influencing metabolism and energy levels throughout the day. This interconnectedness underscores the dynamic nature of circadian rhythms, reflecting how they can adjust in response to changes in the environment to maintain bodily homeostasis.

Other options present misconceptions about circadian rhythms: they are generally around 24 hours long, can be strongly affected by external cues, and impact numerous biological processes beyond sleep, including hormone release and alertness.