Sleep, Circadian Rhythms and the Clock in the Brain · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Your brain keeps a daily clock

Science · The Human Body · ages 21-22
Name ______________________   Date ____________

  1. When clock proteins pile up inside the cell, what happens next?

    • They switch their own genes off
    • They leave the brain for the blood
    • They freeze the cell for a whole day

  2. Where does your master daily clock live?

    • In the retina that sees shapes and faces
    • A small cluster above where the eye nerves cross
    • In the muscles that move your eyes

  3. Light resets your clock through the same pathway you use to see faces.

    Circle one:   True   False

  4. About how many hours does one turn of the gene loop take?

    Answer: ______________

  5. What does morning light do to a slow clock?

    • It moves the clock later
    • It stops the clock for a day
    • It moves the clock earlier

  6. Which pattern marks the sleep stage of most vivid dreaming?

    • Slow deep waves with no dreaming at all
    • Fast REM activity with vivid dreams
    • No brain activity of any kind

  7. A student claims a lone SCN cell cannot keep time without neighbours. Which finding proves this wrong?

    • SCN damage destroys daily cycles
    • Dish kept SCN cells still fire near every 24 hours
    • Jet lag fades as days pass

  8. Two people cannot see images. One stays synced to the sun and one drifts later each day. What differs?

    • The drifting one lost the brightness to clock pathway
    • The synced one lost that pathway instead
    • Both lost every retinal cell they had
LightMySky · lightmysky.comW1-mt_cXx4SaLJUM-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Your brain keeps a daily clock W1-mt_cXx4SaLJUM-s1

  1. They switch their own genes off · Piled up proteins turn their own genes off until they break down.
  2. A small cluster above where the eye nerves cross · The SCN sits just above where the eye nerves cross and runs the daily rhythm.
  3. False · Brightness cells use their own pathway to the clock, apart from image vision.
  4. 24 · One full loop of making protein, shutting off, and restarting takes near a day.
  5. It moves the clock earlier · Morning light nudges the clock earlier so it lines up with the sun.
  6. Fast REM activity with vivid dreams · REM brings fast patterned activity and most vivid dreaming.
  7. Dish kept SCN cells still fire near every 24 hours · Single cells in a dish hold the rhythm alone, so no neighbours are needed.
  8. The drifting one lost the brightness to clock pathway · Without the brightness signal the clock free runs and bedtime slides later daily.
Worksheet · LightMySky