What is the primary function of red blood cells?

Red blood cells, or erythrocytes, primarily function to transport oxygen from the lungs to the tissues throughout the body. This is achieved through the protein hemoglobin, which binds to oxygen molecules. Each red blood cell is uniquely structured to optimize this function: they are biconcave discs that provide a large surface area for gas exchange, and they have no nucleus, allowing for more space to carry hemoglobin.

The capacity to efficiently deliver oxygen to organs and tissues is vital for cellular respiration and energy production. While red blood cells also play a minor role in transporting carbon dioxide back to the lungs for exhalation, their primary role remains oxygen transport. The other choices, such as fighting infections and clotting blood, are primarily functions of white blood cells and platelets, respectively, highlighting the specialized roles of different cell types in the circulatory system.