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

Activity 2
Students should have their sleep diaries containing sleepiness scale data
available. The day before you do this activity in class, ask students to complete
the graphing exercise described in Step 1 of the procedure (page 90).
Activity 1: Michel Siffre Story
Procedure
1. Introduce this activity by reminding students of statements 1,
“Everyone has a biological clock” (true), and 9, “The body quickly
adjusts to different sleep schedules” (false), on Master 1.1. How
did students respond to these statements and why?
This activity and the next will allow students to investigate biological
clocks and our ability to adapt to changing environmental cues.
2. Give each student a copy of Master 3.1, Michel Siffre Story, and ask
them to read it.
3. Ask students to explain why Siffre’s “day” varied so much, and
why his average “day” was longer than 24 hours.
4. If students are having trouble understanding why Siffre’s days
became so long, ask them how they know when it is time to sleep.
Of course, students will mention that they use a clock. Ask them to
think about how our body can tell what time of day it is.
5. Give each student a copy of the top half of Master 3.2, The
Rhythms of Sleep, and ask them to read it.
6. Ask students if the information in their handout helps them understand
why Siffre’s day began to grow longer than 24 hours.
The important point made in the handout is that the circadian clock
operates on a cycle that is a bit longer than 24 hours (more like
24.5 hours). Students should appreciate that this helps explain why
Siffre’s day grew longer. Although the circadian clock can be reset
using artificial light, Siffre had no way of telling time and his use of
artificial light did not help him maintain regular sleep/wake cycles.
Content Standard C:
Organisms have behavioral
responses to
internal changes and
to external stimuli.
7. Next, ask the students, Why don’t you experience a day-lengthening
effect similar to Michel Siffre’s?
If students have trouble answering this question, direct the discussion
toward how our body uses light to sense the time of day. Light
is the signal that resets our clock.
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Student Lesson 3