when parallel light rays exit a concave lens, the light rays diverge converge come together

Why is it important to reduce the number of chromosomes in half when forming gametes for sexual reproduction?

Aboy jumps into a cold swimming pool and his body tempature goes down hus muscles ,blood vessels

Amino acids contain the elements carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. of the 20 amino acids found in humans, 11 are called "nonessential" because they can be manufactured by the body when needed. which elements in these 11 amino acids are commonly obtained from the metabolism of sugar molecules?