A human zygote is diploid (2n = 46), formed by the fusion of a haploid sperm (23) and a haploid ovum (23). It contains 22 pairs of autosomes and one pair of sex chromosomes (XX or XY). Mitotic division then produces all somatic cells. Gametes are haploid (23).
Explanation:
Vitamin D (cholecalciferol) is synthesized in the skin from 7-dehydrocholesterol under UV-B radiation. It then undergoes activation in the liver and kidneys. It regulates calcium and phosphate metabolism.
Explanation:
Melatonin, synthesized from serotonin, is released in darkness, regulating circadian rhythms and promoting sleep. Serotonin is a neurotransmitter, dopamine reward, acetylcholine muscle contraction.
Explanation:
Phosphorus is part of the phosphate backbone of DNA/RNA and the high-energy bonds of ATP. Nitrogen is in bases and amino acids, iron in hemoglobin, sulfur in some amino acids. Phosphorus is essential for energy transfer and genetic material.
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