What role do erythrocytes primarily serve in the body?

Erythrocytes, commonly known as red blood cells, primarily serve the crucial function of transporting oxygen throughout the body. They contain hemoglobin, a protein that binds to oxygen molecules in the lungs and carries them to various tissues and organs, where oxygen is released for cellular respiration. This process is vital for maintaining the energy levels necessary for bodily functions and sustaining life.

While clotting blood is a role associated with platelets, fighting infection is primarily the function of white blood cells, and hormone regulation does not involve erythrocytes. Thus, the unique and critical role of erythrocytes in oxygen transport distinguishes them from the other options provided.