The answer is D.
Melatonin is a molecule that is produced in the pineal gland and secreted into the blood. Melatonin then travels to different parts of the brain. It tells the brain and the rest of the body about the time of wake and sleep. It causes drowsiness and decreases body temperature to assist in the regulation of the sleep/wake cycle. The melatonin secretion into the blood is regulated by the endocrine system, by the hypothalamus which on gets stimulated by the light.
The greatest surface area for gas exchange is found in the Alveoli
Endorphins sound correct.
Please vote my answer brainliest! thanks.
The answer to your question is solar radiation hitting the earth, a sphere which is tilted on its axis, puts into effect differential heating of the earth's surface. This affects weather and climate all across the globe. For example, the tropics along the equator get a lot more heat than at the poles. The air at the equator is heated.
<span>In organisms that breed sexually, the body cells have a diploid number, or 2n, and the gametes have a haploid number, n. The diploid number of chromosomes is double that of the haploid number. So the the diploid number would be 24 and it is produced when the pollen, containing the sperm, fertilizes the egg.</span>
