Read the passage below and then answer the following questions.
Your body's biological clock, or the suprachiasmatic nucleus (SCN), determines when you feel tired and when you feel awake. There are generally two periods of the day during which the body feels like sleeping— at night and in the early part of the afternoon, between 1 p.m. and 3 p.m. In many cultures, the early part of the afternoon is a dedicated rest time, or siesta.
The SCN works in two ways to regulate sleep. First, it monitors the amount of light in the environment. It leads the body to be more active when there is more light and less active when there is less light. It also releases the hormone melatonin during the late evening, which increases feelings of relaxation and sleepiness, and signals that it is time to go to sleep. Compared with adults, teenagers' melatonin is typically released later in the evening and remains at high levels in the blood until later in the morning. This biological difference contributes to the difficulty teenagers have falling asleep earlier in the evening and waking up early the next morning.