<Tr> <Td> 2 NADH </Td> <Td> 3 or 5 </Td> <Td> Oxidative phosphorylation: Each NADH produces net 1.5 ATP (instead of usual 2.5) due to NADH transport over the mitochondrial membrane </Td> </Tr> <Tr> <Td> Oxidative decarboxylation of pyruvate </Td> <Td> 2 NADH </Td> <Td> 5 </Td> <Td> Oxidative phosphorylation </Td> </Tr> <Tr> <Td> Krebs cycle </Td> <Td> </Td> <Td> </Td> <Td> Substrate - level phosphorylation </Td> </Tr> <Tr> <Td> 6 NADH </Td> <Td> 15 </Td> <Td> Oxidative phosphorylation </Td> </Tr>

Where does the oxygen come from that the cells use for cellular respiration