Final answer:
Erythrocytes, or red blood cells, primarily function to transport oxygen from the lungs to the body's tissues and carry carbon dioxide back to the lungs. They are specialized, numerous, and contain hemoglobin which binds and transports oxygen and carbon dioxide.
Step-by-step explanation:
The main function of erythrocytes, also known as red blood cells (RBCs), is to transport oxygen and carbon dioxide within the body. These cells are abundant in the blood, with millions present in just a microliter. Erythrocytes contain a high concentration of hemoglobin, an iron-containing protein essential for oxygen transport. Hemoglobin molecules within erythrocytes bind oxygen in the lungs and carry it to the body's tissues while also picking up carbon dioxide from the tissues and transporting it back to the lungs for exhalation. Erythrocytes are adapted for their oxygen transport role by being small, biconcave, and, in mammals, lacking a nucleus and mitochondria, which provides maximum space for hemoglobin and prevents the use of oxygen for metabolic processes within the red blood cells.