Question

Circadian rhythms are the changes that take place in your body and behavior during each period of approximately 24 hours. Changes in your body temperature and appetite level are examples of circadian rhythms. But the circadian rhythm we’re interested in is your sleep-wake cycle. Part of the sleep-wake cycle is the release of a brain chemical called melatonin into your bloodstream. Melatonin makes you feel sleepy. During your teen years, melatonin is released later in each 24-hour cycle than it was when you were a child. As a result, if you’re a typical teenager, you don’t start getting sleepy until 11:00 p.m. or even later. And since melatonin stops being released around 8:00 a.m., that’s about the time you naturally stop feeling sleepy—no matter what time you go to bed. Teens may brag about getting by on only five hours of sleep. Yet scientists have known for a long time that teens need around 9 hours of sleep each night—that is, if they want to function at their best.

Which supporting detail best supports the main idea?


Yet scientists have known for a long time that teens need around 9 hours of sleep each night—that is, if they want to function at their best.


Circadian rhythms are the changes that take place in your body and behavior during each period of approximately 24 hours.


Part of the sleep-wake cycle is the release of a brain chemical called melatonin into your bloodstream.


Teens may brag about getting by on only five hours of sleep.

Answer 1

"Part of the sleep-wake cycle is the release of a brain chemical called melatonin into your bloodstream."

Explanation: this detail explains the biological mechanism (melatonin release) that causes the shifted sleep-wake cycle in teens, which is the main idea of the passage.