Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
SAF Archives  search ask the scientists in the classroom cool science

Guide Index

Why Are Peppers Hot?

Can You Beat Jet Lag?

How Do Bees Fly?

Why Does Traffic Jam?

Sand to Nuts

Viewer Challenge
in the classroom

Life's Little Questions:
Can You Beat Jet Lag?

Attempts to fool our bodies into beating jet lag have created entire industries. The scientific explanation involves light and hormones. Alan Alda finds out, when he subjects himself to a sleep experiment, that the ultimate solution to resetting the human biological clock is not quite as easy as it might appear. But the findings could have useful applications to millions of troubled sleepers.

Curriculum Links
National Science Education Standards
Activity: Hey, Turn Out the Light!



biological clock, nervous system




circadian rhythms




5-8: Structure and Function in Living Systems, Reproduction and Heredity, Regulation and Behavior, Diversity and Adaptations of Organisms
9-12: The Cell, Biological Evolution, Behavior of Organisms
5-8: Science as a Human Endeavor, Nature of Science
9-12: Science as a Human Endeavor, Nature of Scientific Knowledge
5-8: Personal Health, Science and Technology in Society
9-12: Personal and Community Health, Science and Technology in Local, National and Global Challenges


If you've ever traveled across time zones and felt disoriented during and after your travels, you've probably experienced jet lag. Evolution hasn't caught up with our modern lives. Science tells us that all animals and plants have a biological clock that does not quite match our clocks and calendars. For most people, the natural internal clock follows a cycle that is about 30 minutes longer than the planetary day/night cycle.

As you see on Frontiers, upsetting the human biological clock can have significant effects on the body. Other animals also have a biological clock that is set for a "normal" day of light and dark cycles.

In this activity, you'll test the effect of light on the development of mealworm larvae into adults.

If you cannot conduct a long-term experiment with mealworms, how else could you test the effects of light on other animals, such as cats, hamsters, dogs, birds or fish? Design your own experiment and give it a try!

  • plant grow light and timer
  • king mealworms (may be purchased at a bait or pet store)

Mealworms take a week or more, depending on variables, to reach the pupa stage and another week to hatch into adult beetles when kept in covered containers and at room temperature. In this experiment you will subject two populations of mealworms to different cycles of light and dark to see if changing the normal cycle speeds up this development. Development in insects is subject to temperature, so mealworms need to be kept at the same temperature.

  1. Obtain two containers of mealworms for use in this experiment. Make sure each container has the same number of mealworms (transfer mealworms from one container to another if necessary to equalize the population). Record the number of larvae in each container.

  2. Enclose one container of mealworms in a box in your classroom that is not directly in the sun. (Note: Make sure each container is kept at room temperature to minimize temperature as a variable.)

  3. For the second mealworm container, set up a grow light with a timer. Set the timer for twelve hours of light and twelve hours of darkness. This group should be covered so the only light they receive is from the grow light. (See drawing for setup.)

  4. Each day, note any changes you observe in your mealworm population. Be sure to record the total number of adult beetles versus larvae in your data table.

  5. As adults appear, remove them from the container so they do not interfere with the development of the larvae. Continue to record data until all the larvae have turned into adults. (You can release the grown beetles outside or use them as food for reptile pets.)

  1. Did the grow light seem to affect the development of the larvae into adults?

  2. Do you think there is an "optimal" amount of light versus dark to speed up the development of the larvae? Design an experiment to prove or disprove your theory.


  • Studies have shown that age may influence what time of day people are most active. Design a questionnaire to find out what time of day students like to wake up and what time of day they feel they can get the most work done. How do the answers vary? Research the efforts of some school districts to change the hours of the school day.

  • With your teacher's permission, interview people who work nights (police, reporters, grocery store clerks, factory workers) to see how they adjust to working at night and if they consider themselves a night or day person and why.

  • Take part in the online science experiment in biological timing and find out more at

  • Investigate circadian rhythms and the effects of light in people who are blind.


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.