What is carried by the red blood cells

• A. White blood cells
• B. Nutrients
• C. Carbon dioxide
• D. Oxygen and hemoglobin

Answer: (D)

Red blood cells specialize in moving gases. They house hemoglobin, the protein that binds oxygen in the lungs and releases it to tissues throughout the body. Because oxygen is carried bound to hemoglobin inside these cells, red blood cells effectively transport both oxygen and the hemoglobin molecule itself as part of that process. While carbon dioxide is also carried back to the lungs, the defining function of red blood cells is transporting oxygen via hemoglobin, making the combination of oxygen and hemoglobin the best description. White blood cells serve immunity, nutrients travel mainly in plasma, and carbon dioxide is carried in part by hemoglobin but is not the defining carrier described here.