Some animals use oxygen to break-down glucose completely into carbon dioxide and water. Some use other pathways that do not involve oxygen. In all cases the first step is the break-down of Glucose, a six carbon molecule into a three-carbon molecule called pyruvate. This process takes place in the cytoplasm. Further, the pyruvate may be converted into ethanol and carbon dioxide.
This process takes .place in yeast during fermentation. Since this process takes place in the absence of air (oxygen), it is called anaerobic respiration. Break down of pyruvate using oxygen takes place in the mitochondria. This process breaks up the three carbon pyruvate molecule to give three molecules of carbon dioxide. The other product is water. Since the process takes place in the presence of air (oxygen), it is called aerobic respiration. The release of energy in this aerobic process is a lot greater than the anaerobic process.
