- an innate mechanism of the body that regulates its rhythmic and periodic cycles, as that of sleeping and waking.
- an inherent periodicity in the physiological processes of living organisms that is not dependent on the periodicity of external factors
- the hypothetical mechanism responsible for this periodicity
- An internal mechanism of the body that is thought to regulate physical and mental functions in rhythm with normal daily activities.
- An innate mechanism in living organisms that controls the periodicity or rhythm of various physiological functions or activities.
- An internal system that controls an organism’s circadian rhythms, the cycles of behavior that occur regularly in a day. In mammals, the biological clock is located near the point in the brain where the two optic nerves cross. In many birds, the biological clock is located in the pineal gland. In protists and fungi, the individual cells themselves regulate circadian rhythms.
The innate rhythm of behavior and body activity in living things. A twenty-four-hour cycle of body activity, which operates in some organisms, is called the circadian rhythm.