The lungs are the organs that are most crucial in expelling cellular carbon dioxide waste. Lungs are the most important organ of the respiratory system. They excrete these wastes through the process of diffusion and exhalation. Without the proper excretion of carbon dioxide by the lungs, the blood will be left without oxygen and might be toxic to course through the bloodstream. The lungs are responsible for converting unoxygenated blood into oxygenated blood. Through this process carbon dioxide is expelled as the by-product.