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Biology - What Is A Biological Clock?

What is a biological clock?

First recognized by the Chinese in the third century B.C., the biological clock is a built-in mechanism that controls the rhythm of various life-maintenance activities of plants and animals. Some activities, such as mating, hibernation, and migration, operate on a yearly cycle. Other activities, such as ovulation (the release of eggs) and menstrual cycles of women, follow a lunar month. (A lunar month is the time it takes for the moon to complete a revolution around the Earth, or 29.5 days).

The majority of life-maintenance, or metabolic, activities have a 24-hour, day-night cycle called circadian rhythm. This day-night cycle, first recognized in plants more than 250 years ago and existing in virtually all species of plants and animals, regulates many metabolic functions, including: plants opening and closing their petals or leaves; germination (growing) and flowering functions; changes in human...

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