What is the main function of red blood cells?

Red blood cells, also known as erythrocytes, have the primary function of transporting oxygen from the lungs to the tissues throughout the body. This process is critical for cellular respiration, the chemical reaction that provides energy to cells. The oxygen is bound to a protein called hemoglobin within the red blood cells, allowing for efficient delivery to various body parts. In addition to oxygen, red blood cells also help in returning carbon dioxide, a waste product of metabolism, from the tissues back to the lungs for exhalation.

The other options represent functions that are performed by different components of the blood or immune system. Nutrient transport is the primary role of plasma, while antibodies are produced by B cells, a type of white blood cell involved in the immune response. Fighting infections is mainly the role of various white blood cells that actively combat pathogens.