Carbon dioxide is one of the most abundant gases in the atmosphere. Carbon dioxide plays an important part in vital plant and animal process, such as photosynthesis and respiration. Photosynthesis and respiration play an important role in the carbon cycle and are at equilibrium with one another.

Carbon dioxide is essential for internal respiration in a human body. Internal respiration is a process, by which oxygen is transported to body tissues and carbon dioxide is carried away from them. Carbon dioxide is a guardian of the pH of the blood, which is essential for survival.