Final answer:
Melatonin is a hormone that helps control sleep-and-wake cycles and circadian rhythms.
Step-by-step explanation:
One hormone that helps control sleep-and-wake cycles and circadian rhythms is melatonin. Melatonin is produced by the pineal gland in the brain and its levels increase in the evening, signaling your body that it is time to sleep. Darkness stimulates the production of melatonin, while light inhibits it.
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