The presence of light waves activates the suprachiasmatic nucleus and the secretion of promoting the wake cycle, while the absence of light waves activates the pineal gland and secretion of promoting the sleep cycle.

The activation of the suprachiasmatic nucleus is stimulated by the presence of the light waves. This activation leads to the release of the hormone serotonin. Serotonin promotes the wake cycle of the person along with his internal clock. However, when the light is absent, then the pineal gland, which is present at the top of the middle of the brain, secretes the hormone melatonin. The melatonin regulates the sleep cycle of the person.

Hence, the blanks can be filled with 'serotonin and melatonin' respectively.

Serotonin is released when the suprachiasmatic nucleus gets activated due to the presence of light waves. Whereas, secretion of melatonin promotes the sleep cycle.

Further Explanation:

Serotonin refers to a happy hormone which contributes to the wellbeing as well as happiness in an individual. This chemical is usually found in the blood platelets, bowels, and brain. The actual function is complex and includes learning, reward, memory, and modulation cognition. Suprachiasmatic nucleus refers to the small segment of the brain found in the hypothalamus region and is found directly above the optic chiasm. This is responsible for managing the circadian rhythms.

Sunlight or light waves activate this part of the brain and release serotonin. Exposure to the sunlight is known to elevate the release of this hormone. Serotonin is linked with boosting the mood as well as helping an individual feel calm as well as focused.

Melatonin is considered to be the only hormone which is generated by the pineal gland. It is produced in response to the darkness. Therefore, it has a name called “hormone of darkness”. The mechanism is simple; darkness regulates the pineal gland which produces melatonin while exposure to the light blocks this mechanism.

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Answer Details:

Grade: High School

Subject: Biology

Chapter: Hormones

Keywords:

Serotonin, melatonin, darkness, sleep cycle, happiness, darkness, nucleus, light, sunlight, waves, optic chiasm, hormone, circadian rhythms.

biology is the study of life. it is the study of living organism.