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.

Content Standard C:
Organisms have behavioral responses to internal changes and to external stimuli.

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.

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.

8. Give each student a copy of the bottom half of Master 3.2, The Rhythms of Sleep, and ask them to read it.
9. Ask the class what they think happened to Michel Siffre’s sleep cycle after he left the cave.

Students should predict that light cues reset his biological clock and his sleep cycle returned to normal.

1. Give each student a copy of Master 3.3, Sleepiness Scale Graph Template. Have them refer to their sleepiness scale entries in their sleep diaries (from Lesson 1) and graph the average of their scores for each time point (for example, wake time).

If you have time, you may consider having students calculate the average sleepiness scale scores using all of the class data. Doing this emphasizes the nature of science since there is a greater likelihood of seeing a rhythm when using more data for analysis. Students can then compare their own data with the average class data.

2. Ask students to describe the graph of their sleepiness scale data. Is a pattern detectable?

Ideally, students will observe that their sleepiness scale graph resembles the following example:

Figure 3.2. Sample sleepiness scale graph.

Alertness first increases (sleepiness decreases) in midmorning, then alertness decreases during the afternoon. Alertness then increases again in the early evening before sleepiness takes over at bedtime.

3. For those classrooms with access to the Internet, you may access your class data at http://science.education.nih.gov/supplements/sleep/student. Click on “Lesson 1—What Is Sleep?” and then enter your class code. Click on “Generate Report” and select one of the sleepiness scale options.

For classrooms without access to the Internet, collect students’ sleepiness scale data on the board and calculate class averages for each time point.

4. Instruct students to work individually or in small teams. They should develop a hypothesis, test it by using the data in the sleep database, and provide a short written summary of their findings.

As in Lesson 1, students can formulate hypotheses, build a custom report, and evaluate the data presented in the report. Classes without Internet access can test their hypotheses using the class data set. Classes not using the sleep database have less data available for their use. Therefore, it is important that you also provide them with the sleep diary data used in Lesson 1. Students can then test hypotheses that relate data from the sleep diary to those from the sleepiness scale.

Make sure that students are testing answerable questions using information in the database. Some appropriate hypotheses include

1. there are male/female differences in the cycling of alertness during the day;
2. school start time has an effect on the timing of the dips in alertness and peaks of sleepiness during the day;
3. latitude affects the timing of the dips in alertness and peaks of sleepiness during the day; and
4. total sleep time affects the timing of the dips in alertness and peaks of sleepiness during the day.

5. After the class has had the opportunity to test their questions, ask for volunteers to share their hypothesis and findings. Ask students why they asked the questions they did.
6. If students can’t determine whether the data support their hypothesis, ask what additional data could help resolve the questions.

This is an opportunity to assess whether students have asked a question that can be answered using information in the database. Even if students have asked appropriate questions of the database, there may be too few cases to allow them to reach a firm conclusion. This is an opportunity to discuss what type of data are needed to properly analyze their hypotheses.

7. Give each student a copy of Master 3.4, Thinking about Sleepiness and Sleep Cycles, and ask them to respond to the questions.

Answers to questions on Master 3.4, Thinking about Sleepiness and Sleep Cycles.

Question 1. The graph below contains sleepiness scale data from an individual who recorded entries every waking hour during a Monday and a Thursday. Describe how the data for Monday differ from those for Thursday. Can you suggest an explanation for this difference?

Assessment:
Having students write their answers before sharing their thoughts with the class gives you an opportunity to evaluate each student’s understanding. It also helps students organize their thoughts before class discussion.

Students should observe that the morning increase in alertness and the afternoon increase in sleepiness occur later on Monday as compared to Thursday. This “phase shift” may occur if an individual sleeps later on Saturday and Sunday than he or she does on weekdays. In effect, the change in sleep habits on the weekend may cause a resetting of the individual’s biological clock. The reason for having the students record data on two Mondays is so that any difference between the first Monday’s data and Thursday’s data may be confirmed with data from the second Monday. This point can be made as a means of indicating how science is done. Ask students if their data showed such a phase shift.

Question 2. During the past several activities, you have learned about different types of cycles associated with sleep. List three different cycles and provide a brief description of each one.

Three cycles associated with sleep are 1) the NREM/REM cycles that occur during sleep (ultradian rhythm); 2) the cycling of the need to sleep (homeostatic regulation); and 3) the circadian rhythm governing our propensity to sleep. It is more important that students recognize that there are different rhythms associated with sleep than that they remember the technical names for them.