Which of the following substances is the determinant of an individual's skin color?

A. The kidneys do not play a role in the chemical breakdown of protein. Their primary function is filtration and regulation of blood composition.

B. The mouth is where mechanical digestion (chewing) occurs, but chemical digestion of proteins does not begin there. Enzymes like amylase break down carbohydrates, not proteins.

C. The stomach is where protein digestion begins. The enzyme pepsin, activated by stomach acid (HCl), starts breaking down proteins into smaller peptides. This is the correct answer.

D. The small intestine continues the digestion of proteins, but the initial breakdown occurs in the stomach. The pancreas also releases digestive enzymes, including trypsin, to further digest proteins in the small intestine.

A. While phagocytes can move to areas of damage, their primary function is not to clump together and adhere to tissues, but rather to engulf and digest foreign materials.

B. Phagocytes, such as macrophages and neutrophils, are specialized white blood cells that ingest and digest foreign pathogens, dead cells, and debris within damaged tissues. This is their main characteristic and function.

C. The release of histamine is typically associated with mast cells, not phagocytes. Histamine helps to initiate inflammatory responses, but phagocytes are involved in engulfing pathogens rather than releasing histamine.

D. Transporting oxygen from the lungs to tissues is the role of red blood cells, not phagocytes. Phagocytes are involved in immune defense, not oxygen transport.