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

  • glycolysis

  • fermentation

  • aerobic respiration

  • photorespiration

Answer

B.

fermentation

In fermentation, the incomplete oxidation of glucose is achieved under anaerobic conditions by a set of reactions, where pyruvic acid is converted to CO2 and ethanol. The enzyme pyruvic acid, decarboxylase and alcohol dehydrogenase catalyse these reactions. In animals 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 reoxidized to NAD+, in both the processes. 

In fermentation, the incomplete oxidation of glucose is achieved under anaerobic conditions by a set of reactions, where pyruvic acid is converted to CO2 and ethanol. The enzyme pyruvic acid, decarboxylase and alcohol dehydrogenase catalyse these reactions. In animals 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 reoxidized to NAD+, in both the processes.