Which hormone is secreted more in dark conditions?

Identify the hormone with its correct matching of source and function.

Which of the following helps in the maintenance of the normal rhythm of the sleep-wake cycle?

The structure surrounding the pineal gland in the forebrain is located at:

$P$ is a small,round,reddish structure located on the dorsal side of the forebrain. It contains a stalk and releases a hormone $Q$ which controls the diurnal rhythm of the body. $P$ and $Q$ are

George comes on a vacation to India from the $U.S.$ The long journey disturbs his biological system and he suffers from jet lag. What is the cause of his discomfort?