PATHOLOGY

Detailed explanation-1: -The hemoglobin molecule has four binding sites for oxygen molecules: the iron atoms in the four heme groups. Thus, each Hb tetramer can bind four oxygen molecules.

Detailed explanation-2: -The mammalian hemoglobin molecule can bind (carry) up to four oxygen molecules.

Detailed explanation-3: -Hemoglobin can bind to four molecules of carbon dioxide. The carbon dioxide molecules form a carbamate with the four terminal-amine groups of the four protein chains in the deoxy form of the molecule.