The first stage in repiration is glycolysis. It takes place in the cytoplasm of the cell and a 6 carbon sugar is split by a series of reactions into 2 molecultes of a 3 cabon compound - pyruvate. This then enters the Krebs cycle. The glucose for glycolysis may come from the blood or it may be produced by the breakdown of glycogen stores in muscle or liver cells. The first steps in the process actually use up ATP as it is hydrolysed to provide the energy needed to phosphorylate the 6 cabon glucose. This sugar is then split into 2 molecules of GALP which is then converted into a molecule of pyruvate acid. During these reactions 2 hydrpgen atoms are removed from the 3C sugars and taken up by NAD. The reduced NAD then passes through the outer mitrochondrial membrane into the electron carrier system an the energy made available through the electron carrier system is used to phosphorylate ADP and 3 molecules of ATP result from each 3C sugar passing through glycolysis. A small amount of ATP is also made directly from the energy transfer when the 3C sugar is converted to pyruvate. If there is plenty of oxygen the pyruvate will enter the mitrochondria and be used in the aerobic reactions of the Kerbs cycle. If not, the pyruvate is converted to lactic acid with a little ATP produced. This is anaerobic respiration.
If your muscles don't get enough oxygen to supply their needs, the products of glycolysis can't go on to the Krebs cycle. Instead the pyruvate is converted to lactate, another 3C compound. This method only…