The energy-releasing metabolic process in which substrate is oxidised without an external electron acceptor is called
- glycolysis
- fermentation
- aerobic respiration
- photorespiration
Answer
(2) fermentation
Solution
In fermentation, NADH formed during glycolysis is reoxidised by an organic intermediate of the same pathway (pyruvic acid or acetaldehyde), so no external electron acceptor is needed; as per NCERT, it gives ethanol + CO2 (yeast) or lactic acid (muscle) under anaerobic conditions.
∵ Aerobic respiration uses O2 as the external terminal electron acceptor, glycolysis is only the first part of a process and photorespiration releases no useful energy,
∴ the process is fermentation.
Answer: (2)