Jeff is writing a term paper on the role of melatonin. he decides to emphasize the important role that this hormone plays in regards to

The melatonin is a hormone responsible for the regulation of the sleep cycles. this hormone is secreted by the pineal glands.

The amount of the melatonin helps the body to regulate the sleeping pattern. The levels of the melatonin is higher at night and it promotes sleeping. During daytime the level of melatonin is comparatively low.

So, the correct answer is sleeping cycle.

thinking it would be physical characteristics

the most common type of reef is the fringing reef. this type of reef grows seaward directly from the shore. they form borders along the shoreline and surrounding islands.