 Now we've seen the bigger picture, we can summarize cell respiration. There are three stages to respiration and they each occur in different locations. Glycolysis in the cytosol, the Krebs cycle occurs in the mitochondrial matrix and the electron transport chain occurs across the inner mitochondrial membrane. In glycolysis, the sugars are broken down. The results of glycolysis are 2 pyruvate molecules, 2 ATP molecules, 2 NADH and 2 HDO. The results of the Krebs cycle are 2 more ATP as well as 8 NADH molecules, 2 FADH2 molecules and the 6 carbon dioxide molecules. In the electron transport chain, the NADH and FADH2 release electrons to the protein complexes which transport these to make water and at the same time pump the hydrogen ions, the protons out into the intermembrane space. The end result of the electron transport chain is another 34 molecules of ATP. The first stage of cell respiration, glycolysis, can happen without oxygen present. It's the anaerobic phase. The other two stages require oxygen to go ahead. They are the aerobic stage. Air means air. Big comes from bio, life, so air life and and means without. So without the air for life.