What is the main role of red blood cells?

The main role of red blood cells is to carry oxygen from the lungs to the body's tissues and return carbon dioxide from the tissues back to the lungs. This function is vital for cellular respiration, which is the process that produces energy in the form of adenosine triphosphate (ATP) necessary for the survival of cells. Red blood cells contain a protein called hemoglobin, which binds to oxygen molecules and facilitates their transport through the bloodstream.

While red blood cells play a critical role in oxygen transport, other cells and systems in the body are responsible for fighting infections, transporting nutrients, and maintaining fluid balance. For example, white blood cells are involved in the immune response and combat infections, while plasma proteins and various cell types manage the transport of nutrients and fluid balance within the body. Thus, the primary and distinctive function of red blood cells is the transportation of oxygen, making this answer the most accurate.