What special molecule does a red blood cell have?

Red blood cells contain a special molecule called hemoglobin, which is responsible for transporting oxygen from the lungs to the body's tissues and facilitating the return transport of carbon dioxide back to the lungs. Hemoglobin is a protein composed of four subunits, each containing an iron atom that binds oxygen, giving red blood cells their characteristic red color. This efficient oxygen-carrying capacity is crucial for maintaining cellular respiration and overall bodily function.