<P> The negative ΔG indicates that the reaction can occur spontaneously . </P> <P> The potential of NADH and FADH is converted to more ATP through an electron transport chain with oxygen as the "terminal electron acceptor". Most of the ATP produced by aerobic cellular respiration is made by oxidative phosphorylation . This works by the energy released in the consumption of pyruvate being used to create a chemiosmotic potential by pumping protons across a membrane . This potential is then used to drive ATP synthase and produce ATP from ADP and a phosphate group . Biology textbooks often state that 38 ATP molecules can be made per oxidised glucose molecule during cellular respiration (2 from glycolysis, 2 from the Krebs cycle, and about 34 from the electron transport system). However, this maximum yield is never quite reached because of losses due to leaky membranes as well as the cost of moving pyruvate and ADP into the mitochondrial matrix, and current estimates range around 29 to 30 ATP per glucose . </P> <P> Aerobic metabolism is up to 15 times more efficient than anaerobic metabolism (which yields 2 molecules ATP per 1 molecule glucose). However some anaerobic organisms, such as methanogens are able to continue with anaerobic respiration, yielding more ATP by using other inorganic molecules (not oxygen) as final electron acceptors in the electron transport chain . They share the initial pathway of glycolysis but aerobic metabolism continues with the Krebs cycle and oxidative phosphorylation . The post-glycolytic reactions take place in the mitochondria in eukaryotic cells, and in the cytoplasm in prokaryotic cells . </P> <P> Glycolysis is a metabolic pathway that takes place in the cytosol of cells in all living organisms . This pathway can function with or without the presence of oxygen . In humans, aerobic conditions produce pyruvate and anaerobic conditions produce lactate . In aerobic conditions, the process converts one molecule of glucose into two molecules of pyruvate (pyruvic acid), generating energy in the form of two net molecules of ATP . Four molecules of ATP per glucose are actually produced, however, two are consumed as part of the preparatory phase . The initial phosphorylation of glucose is required to increase the reactivity (decrease its stability) in order for the molecule to be cleaved into two pyruvate molecules by the enzyme aldolase . During the pay - off phase of glycolysis, four phosphate groups are transferred to ADP by substrate - level phosphorylation to make four ATP, and two NADH are produced when the pyruvate are oxidized . The overall reaction can be expressed this way: </P>

Where does electron transport take place in cellular respiration