What is hemoglobin?

• A. the protein that carries oxygen in the blood
• B. the amount of red blood cells in the blood
• C. the percentage of white blood cells in the blood
• D. the rate of blood flow through the vessels

Answer: (B)

Hemoglobin is the protein in red blood cells that binds and carries oxygen from the lungs to tissues throughout the body. Each red blood cell contains many hemoglobin molecules, and when oxygen attaches to the iron-containing heme groups, hemoglobin transports it through the bloodstream as oxyhemoglobin. The amount of red blood cells you have—measured as RBC count or hematocrit—is a separate measurement that tells you how many cells are present, not how much oxygen-carrying protein they contain. Oxygen-carrying capacity depends on both how many red blood cells there are and how much hemoglobin each cell carries. Remember, the iron in hemoglobin is what enables oxygen binding, and this protein gives blood its bright color when oxygen is bound. So the term that describes the protein responsible for carrying oxygen in the blood is hemoglobin.