What is the primary function of red blood cells?

The primary function of red blood cells is transporting oxygen. These cells, also known as erythrocytes, contain hemoglobin, a protein that binds to oxygen in the lungs and carries it throughout the body to tissues and organs. This process is crucial for cellular respiration, which is how cells produce the energy they need to function. Red blood cells also play a minor role in transporting carbon dioxide, a waste product from metabolism, back to the lungs for exhalation.

While other options are functions carried out by different types of cells—such as nerve impulses being transmitted by neurons, hormones produced by glands, and infections fought off by white blood cells—these do not pertain to the function of red blood cells.