The energy-releasing metabolic process in which substrate is oxidised without an external electron acceptor is called

Step-by-step solution

In fermentation, the incomplete oxidation of glucose is achieved under anaerobic conditions by set of reactions, where pyruvic acid is converted to CO ₂ and ethanol. The enzyme pyruvic acid, decarboxylase and alcohol dehydrogenase catalyse these reactions. In animal cells also, like muscles during exercise, where oxygen is inadequate for cellular respiration, pyruvic acid is reduced to lactic acid by lactate dehydrogenase. The reducing agent is NADH + H ⁺ , which is reoxidised to NAD ⁺ , in both the processes.