- (biology) Any of several mechanisms that regulate the periodicity of biological functions.
- The progression from puberty to menopause during which a woman can bear children.
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- 2005 US Department of Health - Your guide to healthy sleep
- Your biological clock is actually a tiny bundle of cells in your brain that responds to light signals received through your eyes.
- 1994 Rugh Winter, Bonnie Eaker-Weil - Adultery, the Forgivable Sin
- Take Linda, a thirty-nine-year-old newscaster who relished her career but began to hear the alarm ringing on her biological clock.