biological clock
- any of the various natural cycles in organisms that are related to the tides, sun, moon, light, temperature, etc. and that control breeding, feeding, migration, etc.
- Informal a person's life cycle; specif., the period of human fertility: her biological clock was ticking away
See biological clock in American Heritage Dictionary 4
noun- An internal mechanism in organisms that controls the periodicity of various functions or activities, such as metabolic changes, sleep cycles, or photosynthesis.
- The progression or time period from puberty to menopause, marking a woman's ability to bear children.
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