Final answer:
Circadian rhythms are physiological cycles that occur over a 24-hour period and include daily fluctuations in various bodily processes. They are controlled by a biological clock and influenced by the light-dark cycle of the environment.
Step-by-step explanation:
Circadian rhythms are physiological cycles that occur over a 24-hour period. They include daily fluctuations in heart rate, blood pressure, blood sugar, body temperature, and our sleep-wake cycle. These rhythms are influenced by our environment's natural light-dark cycle and are controlled by a biological clock located in the brain. Examples of circadian rhythms in animals include changes in behavior and body processes that occur at specific times of day.