The steps required for aerobic cellular respiration are, in order of their occurrence: glucose —> glycosis —> TCA cycle —> electron transport reactions —> denosine triphosphate, or ATP. The sequence starts with the carbohydrate glucose, which contains stored energy, and moves through a series of biochemical reactions that ends with the production of ATP, which is the energy currency used by cells to fuel their metabolic processes. Oxygen is required for aerobic respiration to occur, and in eukaryotic cells, most of the reactions take place within a cell's mitochondria.
During the aerobic respiration process, each molecule of glucose entering the reaction produces two net molecules of ATP, which the cell will use for energy. Four molecules of ATP are actually produced during the course of the process, but two are used up during the sequence of reactions.
Cellular respiration can also take place without the presence of oxygen and is referred to as anaerobic respiration. The glycosis step, or metabolic pathway, of the process is different when oxygen is unavailable. Anaerobic conditions will produce lactate during glycosis instead of the pyruvate produced under aerobic conditions. Overall, aerobic respiration is a much more efficient process than anaerobic respiration.
Cellular respiration is considered an exothermic reaction because it releases energy in the form of heat. Although similar in nature to a combustion reaction, the heat release occurring within a living cell takes place very slowly.