What is the role of hemoglobin in oxygen transport?

• A. The molecule that carries most carbon dioxide in the blood
• B. The enzyme that digests fats in plasma
• C. The protein that allows oxygen to bind to red blood cells
• D. The molecule that forms antibodies

Answer: (C)

Hemoglobin is the protein in red blood cells that carries oxygen. In the lungs, oxygen binds to the iron in the heme groups of hemoglobin, forming oxyhemoglobin, and is then carried through the bloodstream to tissues. In tissues, where oxygen is scarce and carbon dioxide and hydrogen ions are higher, hemoglobin changes shape to release the oxygen where it’s needed. Each molecule of hemoglobin can carry up to four oxygen molecules, which greatly increases the blood’s oxygen-carrying capacity. While hemoglobin does transport some carbon dioxide back to the lungs, most CO2 is carried as bicarbonate in plasma, and the other options describe functions unrelated to oxygen transport.