The role of red blood cells (RBCs) in the human body is primarily to transport oxygen from the lungs to the tissues and to carry carbon dioxide from the tissues back to the lungs for exhalation. These cells contain hemoglobin, a protein that binds oxygen and gives red cells their characteristic color. The efficient transportation of oxygen is crucial for cellular respiration, the process by which cells produce energy. RBCs are produced in the bone marrow and have a lifespan of about 120 days. After aging, they are removed by the spleen and liver, ensuring that the body maintains healthy blood cell levels.