What is the primary function of red blood cells?

The primary function of red blood cells is to carry oxygen from the lungs to the rest of the body. They contain a protein called hemoglobin, which binds to oxygen molecules. When red blood cells pass through the lungs, they pick up oxygen and transport it through the bloodstream, delivering it to tissues and organs where it is needed for cellular respiration and energy production.

In addition to transporting oxygen, red blood cells also play a role in transporting some carbon dioxide, which is a waste product of metabolism, back to the lungs for exhalation. This dual function of oxygen delivery and carbon dioxide removal is vital for maintaining the body's overall homeostasis and ensuring efficient metabolic processes.

While nutrients are transported by the bloodstream, that is primarily the function of plasma and not red blood cells specifically. The immune system is responsible for fighting infections, with white blood cells playing the major role in this process. Clotting blood is mainly the function of platelets and certain proteins in plasma, not red blood cells. Therefore, the correct identification of the primary function of red blood cells as carrying oxygen is foundational to understanding their critical role in the circulatory and respiratory systems.