When we breath, aerobic respiration is occurring. We are using the oxygen that is brought into our lungs when we inhale (“aero” = atmosphere) in a process that is called cellular respiration. Cellular respiration occurs within the mitochondria of eukaryotic cells. During cellular respiration, the oxygen gas that we inhale reacts with the sugar called glucose in order to produce water, carbon dioxide gas, and ATP. ATP stands for adenosine triphosphate. ATP is used as a form of energy in our bodies. Overall, aerobic respiration produces a net of 34-36 ATP.
There are three main parts of aerobic cellular respiration - glycolysis, the Krebs Cycle, and the electron transport chain. Each phase of aerobic respiration uses a different part of the cytoplasm or mitochondria. Here, the processes that occur during each phase of aerobic cellular respiration can be read in greater detail.
Anaerobic respiration is done in the absence of oxygen (“an” = not, “aero” = air or atmosphere). Sometime anaerobic respiration is referred to as fermentation. Fermentation is a metabolic process in which organisms convert carbohydrates, such as starch or sugar, into lactic acid or alcohol. Compared to aerobic respiration, anaerobic respiration produces a net of only 2 ATP.
Ethanol fermentation is the type of fermentation that produces alcohol. It is done by yeast and some strains of bacteria. During ethanol fermentation, pyruvate from glucose metabolism is broken into ethanol and carbon dioxide. Because ethanol fermentation produces alcohol, it is used to produce beer and wine. The carbon dioxide produced by ethanol fermentation is advantageous in the making of breads.
During lactic acid fermentation, six-carbon carbohydrates, such as the pyruvate molecules from glycolysis or lactose, are converted into cellular energy (ATP) and lactic acid. Lactic acid occurs within muscle cells during intense intervals of activity when energy is needed at a faster rate than oxygen can be supplied. The lactic acid produced is the “burn” that athletes feel after an intense workout.