Final answer:
Circadian rhythms are controlled by a biological clock and play a role in our daily cycles of behavior.
Step-by-step explanation:
Circadian rhythms are predictable changes that occur on a 24-hour cycle. They are maintained by a biological clock located in the brain's gland. This clock sends signals to the body and controls behaviors and body processes such as sleep-wake cycles, heart rate, blood pressure, blood sugar, and body temperature. The amount of light entering the eyes helps regulate the biological clock. Circadian rhythms are essential for our daily cycles of behavior.