Which can move easily across the membrane without facilitated diffusion?

What causes darkening of the skin as melanin production increases

How is transcription similar to translation in terms of base pairing?

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?