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Module 1.5b

®
AP Science Practice Check Your Understanding
Examine the Concept Apply the Concept
▶ Explain the differences among the stages of sleep. ▶ Would you consider yourself a night owl or a morning lark?
▶ Explain the role of the suprachiasmatic nucleus in sleep. Explain how this relates to your circadian rhythm.
▶ Explain how REM sleep relates to dreaming.

Answers to the Examine the Concept questions can be found in Appendix C at the end of the book.

Why Do We Sleep?
1.5-7 What ar e sleep’s TEACH 1.5-7

1.5-7 What are sleep’s functions? functions?
As we’ve just seen, our sleep patterns differ from person to person and from culture to cul- Teaching Tip
ture. But why do we have this need for sleep? Psychologists offer six possible reasons:
Point out to your students how

1. Sleep protects. When darkness shut down the day’s hunting, gathering, and travel, our different qualities have evolved in
distant ancestors were better off asleep in a cave, out of harm’s way. Those who didn’t
wander around dark cliffs were more likely to leave descendants. This fits a broad- animals and humans due to their sleep
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
er principle: A species’ sleep pattern tends to suit its ecological niche ( Siegel, 2009 ). habits. Nocturnal animals typically
Animals with the greatest need to graze and the least ability to hide tend to sleep less. have better night vision and larger
Animals also sleep less, with no ill effects, during times of mating and migration ( Siegel,
2012 ). (For a sampling of animal sleep times, see Figure 1.5-9.) ears than diurnal animals. Animals that

Copyright © Bedford, Freeman & Worth Publishers.
sleep a lot also tend to have faster
metabolisms.
Kruglov_Orda/Shutterstock Andrew D. Myers Utekhina Anna/Shutterstock Steffen Foerster/Shutterstock RubberBall Productions/Getty Eric Isselee/Shutterstock pandapaw/Shutterstock
20 hours 16 hours 12 hours 10 hours 8 hours Images 4 hours 2 hours PRACTICE
2. Sleep restores. Sleep gives your body and brain the chance to repair, rewire, and Figure 1.5-9 Argumentation (SP 4)
reorganize. It helps the body heal from infection and restores the immune system Animal sleep time
( Dimitrov et al., 2019 ). Sleep gives resting neurons time to repair themselves, while Would you rather be a brown bat (20 minutes) Using a jigsaw
pruning or weakening unused connections ( Ascády & Harris, 2017 ; Ding et al., 2016; Li that sleeps 20 hours a day or a classroom technique, divide
et al., 2017 ). Bats and other animals with high waking metabolism burn a lot of calories, giraffe that sleeps 2 hours a day? students into six groups. Assign
producing free radicals, molecules that are toxic to neurons. Sleep sweeps away this toxic (Data from National Institutes of
Health [ NIH], 2010 .)
waste, along with protein fragments that for humans can cause Alzheimer’s disease each group one of the six
( Beil, 2018 ; Xie et al., 2013 ). Imagine that when consciousness leaves your house, clean- functions of sleep, and give them
ers come in and say, “Good night. Sleep tidy.” 10 minutes to discuss and become
3. Sleep aids memory consolidation. Sleep helps restore and rebuild our fading mem- “experts.” Then, form new groups
ories of the day’s experiences. Our memories are consolidated during slow-wave deep
sleep, by replaying recent learning and strengthening neural connections ( Paller & of six that include one student
Oudiette, 2018 ; Todorva & Zugaro, 2019). Sleep reactivates recent experiences stored from each larger group (that is,
in the hippocampus and moves them to permanent storage elsewhere in the cortex one expert for each function).
( Racsmány et al., 2010 ; Urbain et al., 2016). In consequence, adults and children trained
to perform tasks recall them better after a night’s sleep, or even after a short nap, than Have the experts teach each other
after several hours awake ( He et al., 2020 ; Seehagen et al., 2015 ). Older adults’ more for 10 minutes. Be sure they cite
frequently disrupted sleep also disrupts their memory consolidation ( Boyce et al., 2016 ; scientifically derived evidence for
Pace-Schott & Spencer, 2011 ).
their position. This activity can
Sleep: Sleep Stages and Theories Module 1.5b 99 lead to a class discussion of why
we sleep.

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Sleep: Sleep Stages and Theories Module 1.5b 99

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