The Biotiming Tutorial, created by the National Science Foundation's Center for Biological Timing, offers an excellent review of biological clocks—the internal timepieces that drive daily rhythms in nearly all organisms. In humans, for example, these clocks help govern when we feel like sleeping and eating. The Web site explains how light therapy or the hormone melatonin can adjust the human clock. It also reveals how the biological clocks of plants allowed the taxonomist Carolus Linnaeus to create a garden in which he could tell time by which flowers were open. Learn about the sleep-wake cycle, jet lag, the restless elderly, and much more.

Go to: http://www.cbt.virginia.edu/tutorial/TUTORIALMAIN.html