The exchange of gases between the blood and the cells is called internal respiration. This happens when oxygen from the blood moves into the body’s cells, where it is used for producing energy. At the same time, carbon dioxide, which is the waste product of cellular processes, moves out of the cells and into the blood. From there, the blood carries the carbon dioxide back to the lungs to be released during breathing. Internal respiration is important because it ensures that the cells always receive the oxygen they need while removing harmful waste gases.