EnergyMetabolism/NutrientAndEnergyy/EnergyMetabolismWithoutOxygen

The energy metabolism without the use of oxygen is not so efficient. Out of the 6 chemical energy (shown in red lines) inside the nutrient, only 2 are removed and 4 remains in the degradation product.

Please note that the actual degradation is not simply removing connection, but also inserting H and OH, etc. Also, although the substances shown above, do not actually exist, this is a straight-forward illustration to show the essential point of energy metabolism.