What is the primary 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 transport carbon dioxide from the body back to the lungs for exhalation. This process is critical for sustaining life, as cells throughout the body require oxygen for metabolism and energy production. Hemoglobin, the protein in red blood cells, binds oxygen molecules in the lungs and releases them in tissues where oxygen levels are low.

While red blood cells are essential for the respiratory process, the other functions mentioned in the incorrect options are carried out by different cell types. For instance, fighting infections is primarily the role of white blood cells; clotting blood is the function of platelets; and transporting hormones is generally the job of plasma proteins. This highlights the specialized functions of various components of blood and underscores the unique, vital role red blood cells play in maintaining overall health.