The Energy Budget of Respiration:

1. Each NADH molecule is generated in the link step (between glycolysis and Krebs cycle) and the Krebs cycle produces three ATP molecules in the electron transport chain. 

2. While each NADH generated in glycolysis gives a profit of two ATP molecules because it has to be transported across the mitochondrial membrane and it costs one ATP
3. Each FADH2 molecule produces two ATP molecules.
4. Note that during anaerobic oxidation of a glucose molecule only 2 ATP molecules are gained as the net profit. It is because there is no Krebs cycle and electron transport chain in anaerobic respiration. In this way, the respiratory energy is used in the body of organisms