What is the function of red blood cells?

The primary function of red blood cells, also known as erythrocytes, is to carry oxygen from the lungs to the rest of the body and to transport carbon dioxide from the body back to the lungs for exhalation. This process is crucial for maintaining the oxygen supply needed for cellular metabolism, which is vital for energy production and the overall functioning of the body's tissues and organs.

Red blood cells contain hemoglobin, a protein that binds to oxygen. When blood passes through the lungs, hemoglobin picks up oxygen molecules and transports them through the bloodstream. As red blood cells circulate through the body's tissues, hemoglobin releases the oxygen, allowing it to diffuse into cells. Simultaneously, red blood cells collect carbon dioxide produced by cells as a waste product and return it to the lungs, where it can be expelled from the body.

Understanding this function clarifies why the other options do not represent the primary role of red blood cells. While they play an important role in the overall health of the body, fighting infections, transporting nutrients, and helping with blood clotting are primarily functions associated with other components of the blood such as white blood cells, plasma, and platelets, respectively.