The protein responsible for oxygen transport in blood is hemoglobin. Hemoglobin is found in red blood cells and enables the binding of oxygen in the lungs and its release in tissues. This protein contains iron, which gives blood its red color and facilitates oxygen binding. Hemoglobin's efficient transport mechanism is critical for delivering oxygen to cells throughout the body, supporting cellular respiration and energy production, thus playing a vital role in maintaining overall health and vitality.