Question: All of the following are elements of red blood cells (RBC) except which description? Hemoglobin is the oxygen-carrying protein molecule in RBC. Young RBCs are referred to as erythrocytes and mature RBCs are reticulocytes. RBCs live 120 days before being destroyed through phagocytosis. They carry oxygen from the lungs to body tissues and transfer carbon dioxide from the tissue to the lungs.