How many oxygen molecules can be transported by one hemoglobin molecule?

A single hemoglobin molecule is capable of binding and transporting four oxygen molecules. This is due to its structure, which includes four heme groups, each containing an iron atom. These heme groups are the sites where oxygen binding occurs. When oxygen binds to the iron in the heme groups, it causes a conformational change in the hemoglobin molecule that increases its affinity for additional oxygen molecules. This cooperative binding mechanism allows one hemoglobin molecule to effectively transport up to four oxygen molecules from the lungs to the tissues. Thus, the option indicating that a hemoglobin molecule can transport four oxygen molecules is accurate.