What is the primary function of red blood cells?

The primary function of red blood cells is to transport oxygen throughout the body. These cells, also known as erythrocytes, contain a protein called hemoglobin, which binds to oxygen in the lungs and carries it to various tissues and organs. This is crucial for the survival of cells, as they rely on oxygen for energy production through a process called cellular respiration.

While other options may describe functions related to blood or the immune system, they do not pertain to the primary role of red blood cells. For instance, fighting infections is mainly the role of white blood cells, which are a different type of blood cell responsible for the immune response. Clotting blood is primarily the function of platelets, which play a vital role in preventing excessive bleeding when injuries occur. Regulating temperature is a function of the body's overall homeostatic mechanisms but is not a direct function of red blood cells. Thus, the unique and specific role of red blood cells as oxygen transporters is what sets them apart and is the correct answer.