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.

his research revealed two genetically different groups of prokaryotes, which justified splitting kingdom monera into two kingdoms. the genetic and cellular differences were so great, that these two kingdoms were eventually placed into different domains in the current three-domain system.