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Anaerobic respiration uses a respiratory electron transport chain with a final electron acceptor other than molecular oxygen. External acceptors can include sulfate, depending on the organism. “External” distinguishes a supplied terminal acceptor from the fuel-derived organic intermediates used in fermentation; it does not mean that the reduction must take place outside the biological cell. In fermentation, regeneration of carriers such as NADH to their oxidized form permits glycolysis to continue without a respiratory electron transport chain. Both routes can operate without molecular oxygen, but they are different mechanisms.^[ref]