Daily rhythms keep going in the dark
- The idea
- Predict
- See it
- Why
- Check
The idea
“Daily rhythms happen because light switches activity on and off each day.”
Mice get busy at dusk and birds sing at dawn, so light looks like the switch. Take the light away and the rhythm keeps going.
The short version
The mistake: Daily rhythms happen because light switches activity on and off each day.
What's actually true: An internal clock runs daily rhythms on its own. Light resets that clock each day so it matches the real day.
- A circadian rhythm is a roughly 24-hour cycle run by an internal clock, a loop of genes and proteins inside cells.
- In constant darkness the clock free-runs at its own period, rarely exactly 24 hours. So the start time drifts.
- Outdoors, light at dawn and dusk resets the clock a little each day to match the real day. This is called entrainment.
On the exam: If a rhythm keeps going without light cues, an internal clock runs it. Light only resets it.