Two Clocks, One Planet: teacher key

Day and Night, grade 11 edition, written for 11th grade. One clock runs inside every living thing and one runs in the sky. Follow the experiments that found both, from a plant kept in the dark to lasers aimed at the Moon.

Read the book. Print this page for the key.

Questions and answers

1. What did Mairan's heliotrope plant show?
   • Its leaves kept opening and closing each day in constant darkness (answer)
   • It grew faster in the dark
   • It lost its leaves
2. Why did scientists still doubt an inner clock after de Candolle's Mimosa result?
   • The leaves cycled every 24 hours exactly
   • For a long time they credited light, temperature or magnetism (answer)
   • Nobody tried the experiment
3. What does melatonin taken in the morning do to the body clock?
   • Stops it
   • Moves it earlier
   • Moves it later (answer)
4. What did Halley's Moon puzzle turn out to be?
   • The Moon speeding up
   • Earth's spin slowing down (answer)
   • A mistake in the eclipse records
5. Where is the twisting effect of a Foucault pendulum greatest?
   • At the equator
   • In Paris only
   • At the poles (answer)
6. In this book, what does eccentricity describe?
   • How sleepy melatonin makes people
   • How oval an orbit is (answer)
   • How fast the Moon moves away

Words

• circadian: about a day
• hypothalamus: brain region
• melanopsin: light-sensing pigment
• melatonin: sleepy hormone
• eccentricity: how oval
• Coriolis: spin deflection