Which statement best describes Process C?

• A. It governs circadian rhythm
• B. It governs sleep homeostasis
• C. It is independent of light
• D. It peaks during the day for all individuals

Answer: (A)

Process C refers to the circadian rhythm, the near-24-hour internal clock that times many physiological and behavioral processes such as sleep-wake, hormone release, and body temperature. It is generated by the brain’s master clock in the suprachiasmatic nucleus and is synchronized to the external light-dark cycle primarily through signals from the retina. This makes it the best description because Process C is all about the timing system that governs when we are alert and when we feel sleepy across the day, not about the amount of sleep debt. The idea that it is independent of light is incorrect because light is the main cue that entrains the circadian clock. Saying it peaks during the day for everyone is also inaccurate since individuals have different chronotypes and the timing of various circadian markers can differ, with many physiological signals peaking in the evening or night.