Biological - NIH Office of Science Education - National Institutes of ...

Do You Y
Have
Rhythm?
Lesson 3
Explore/
Explain
Figure 3.1. Animals, like humans, have biological rhythms that
determine when they are active.
Overview
In this lesson, students explore circadian rhythms and biological clocks.
First, students read about a Frenchman who lived alone for two months in
a cave, and they learn how it affected his sense of time. Second, students
analyze their sleepiness scale responses (from their sleep diaries), graph the
data, and look for a rhythmic variation in sleepiness and alertness. Students
can formulate and test hypotheses using the sleep diary and sleepiness
scale database.
At a Glance
Major Concepts
Humans, and many other animals, have an internal biological clock. This
clock operates on a cycle of just over 24 hours. Environmental cues, especially
light, reset the clock, keeping it in time with the day/night cycles.
The clock directs the rhythmic secretion of hormones, such as melatonin,
that influence our sleep cycle. If the biological clock becomes out of phase
with the environment, various types of sleep problems can result.
Objectives
After completing this lesson, students will
• recognize the existence of biological clocks,
• understand the concept of circadian rhythms,
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