BioEd Online

Teacher Background

As students learned earlier, most people go to sleep and wake up at about the same times each day. This sleep/wake cycle is regulated by a group of nerve cells inside the brain, called the suprachiasmatic nuclei, which act as a timer, or “biological clock.” These cells receive time cues from the outside environment. For example, special cells in the retina (the part of the eye that has receptors for light) detect sunlight and send messages to the brain in humans and other mammals, saying, “Wake up. It’s daytime.” In fact, daily exposure to sunlight is an important cue to synchronize the body’s sleep cycle.

Abrupt changes in one’s sleep cycle, such those caused by a new work schedule or travel across time zones, can make it difficult to fall asleep or stay awake, because external cues conflict with messages being sent by the body’s internal clock. The brain says, “Sleep,” but outside conditions signal, “Be active, it’s morning!” Other factors that can affect, or interfere with, the sleep cycle include physical exercise, medicines, meal times and stimulants (such as caffeine in coffee, tea and soft drinks).

This activity allows students to investigate their own internal clocks. For one night, students will go to bed one hour earlier than usual. They will observe and record any impacts that this change has on their abilities to fall asleep, and on their usual wake times the next morning.

Objectives and Standards

Life Science

• Behavior is one kind of response an organism can make to an internal or external stimulus.

• Behavioral response is a set of actions determined in part by heredity and in part from experience.

Science in Personal and Social Perspectives

• The potential for accidents and the existence of hazards imposes the need for injury prevention.

• Important personal and social decisions are made based on perceptions of benefits and risks.

Science, Health and Math Skills

• Predicting

• Observing

• Drawing conclusions

Materials and Setup

Materials per Student

• Copy of student sheet (see Lesson pdf)

Setup

1. Lead a class discussion about the steps and purpose of the activity.

2. Have students carry out their own investigations at home and report back the following day.

Procedure and Extensions

Time: 30-60 minutes to conduct initial class discussion; 30-60 minutes to summarize findings the following day.

Day One

1. Remind students of previous activities. Ask, Did the bean plant leaves move the same way each day? How about the animals you observed? Did their behaviors show a daily pattern? Do you do certain things at about the same time each day? Have students refer to their sleep journals. Ask, Do you think a biological clock regulates some of your behaviors?

2. Explain to students that they will be investigating their own biological clocks. One night, they will go to bed one hour earlier than usual, then observe and record what happens.

3. Mention the observations that students will make: whether it was easy or hard to fall asleep at the earlier time and if they woke at the usual time the next morning. Students also should record how they felt the next day: more/less tired than normal, etc. Explain that results will vary from person to person.

4. Distribute copies of the student sheet, on which students will record their data. If possible, have each student enlist the help of a household member to observe and record the actual time the student falls asleep.

Day Two

1. Have students summarize their experiences in short paragraphs. Ask, Did going to bed earlier make it easier or more difficult than usual to fall asleep? When you went to bed, did you notice noises and other people more or less than you usually would? How did you feel the next morning? Did you wake at your usual time?

2. Have students share their paragraphs by reading them aloud, or by posting them in the classroom. Initiate a class discussion of the results. Point out that some students may have had difficulty falling asleep because their bodies were used to a later bedtime. However, students may have woken at their usual times in the morning, even after receiving an extra hour of sleep, due to the programming of their internal clocks. Some students may feel better after receiving the extra sleep.

3. Discuss possible outcomes of going to bed one hour later than usual, instead of earlier. Ask, How do you think you would you feel after getting less sleep than usual? How might a reduction in sleep affect your daily life? Initiate a class discussion about the normal amount of sleep required by people of different ages, and the ways insufficient sleep can impair performance on both mental and physical tasks. For example, lack of sleep, like alcohol intoxication, can make physical reactions slower.

Extensions

• Have students continue with their earlier bedtimes for several days. Do they eventually become programmed to the earlier times?

• Invite another teacher or a parent who has traveled across several time zones (e.g., across the continental US, to Asia, or to Europe) to talk with the class about how he or she felt physically during the first day or two in the new location. Was it easy to sleep? Was he or she more tired or alert than usual? Did he or she have to readjust to the “normal” schedule after returning home?

• Invite a policeman, fireman or someone else who routinely works a night shift to talk to the class about how he or she has adapted to the stresses of a nocturnal work schedule.

Handouts and Downloads

Download color images from The Science of Sleep and Daily Rhythms Teacher's Guide.