[Campbell Biology P.1143] A group of humans is kept in a laboratory environment with constant... | Practice Question

A group of humans is kept in a laboratory environment with constant dim light and no external time cues for several weeks. Based on the information provided, what would be the most likely observation regarding their sleep-wake cycles?

  • A: Their sleep-wake cycles would become completely random and unpredictable due to the lack of light/dark cycles.
  • B: Their sleep-wake cycles would gradually shift to a period slightly longer than 24 hours, still maintaining a rhythm.
  • C: Their sleep-wake cycles would become perfectly synchronized to exactly 24 hours, as their biological clocks take over.
  • D: They would experience continuous wakefulness as their SCN would cease to function without light input.

Explanation

The text states: 'Although biological clocks are typically synchronized to the cycles of light and dark in the environment, they can maintain a roughly 24-hour cycle even in the absence of environmental cues see Figure 40.9 . For example, in a constant environment humans exhibit a sleep/wake cycle of 24.2 hours, with very little variation among individuals.' This directly supports that their internal clocks would continue to function, but would drift slightly from a precise 24-hour cycle.