Respiration is a mechanical process, while cellular respiration involves biochemical reactions through enzymatic action. Respiration is broadly classified into two types: external and internal; cellular respiration consumes the oxygen taken into the body after internal respiration occurs. External respiration is the mechanism whereby the gaseous metabolic waste product of cellular respiration, which is carbon dioxide, is expelled from the body.
All organisms undergo respiration and cellular respiration to support life. External respiration pertains to the inhalation of atmospheric oxygen and the exhalation of carbon dioxide into the environment. It involves three processes that primarily occur in the lungs, including ventilation, diffusion and perfusion. Internal respiration, meanwhile, refers to the exchange of oxygen carried by the red blood cells in the blood and the carbon dioxide produced by metabolic cells.
Cellular respiration is categorized as either aerobic and anaerobic. The oxygen received by the cells during internal respiration is used during aerobic cellular respiration. The primary bio-fuel in the body, which is glucose, chemically combines with oxygen through a series of metabolic pathways. The biochemical energy stored in the bonds of glucose is then transformed into usable energy in the form of adenosine triphosphate, or ATP. These high-energy molecules power essential life processes carried out by the cells, such as muscle contraction and synthesis of macromolecules.