Final answer:
The hormone released by the pineal gland in response to changes in light is melatonin. Melatonin regulates the sleep-wake cycle and is stimulated by darkness and inhibited by light.
Step-by-step explanation:
The pineal gland is an endocrine gland located in the brain that produces the hormone melatonin. This hormone is crucial for regulating the sleep-wake cycle and is associated with various biological rhythms. The production of melatonin increases in response to darkness, helping to induce drowsiness, and is inhibited by light, which promotes wakefulness. The correct answer to the question 'The pineal gland releases the hormone ______ in response to changes in light.' is b) Melatonin.
Moreover, it's important to understand that the production of melatonin is also influenced by the photoperiod - the relative length of day and night. During the longer nights, or the dark photoperiod, melatonin production is higher. It decreases during the day when the light photoperiod prevails. This hormone's production is innervated by collaterals from the visual pathways and regulated according to light levels detected by the retina and processed by the suprachiasmatic nucleus (SCN).