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

• fermentation

• photorespiration

• aerobic respiration

• glycolysis

D.

glycolysis

Glycolysis is the first stage of the breakdown of glucose in the cytoplasm of the cell without using oxygen (electron acceptor). It is a stepwise process in which one molecule of glucose breaks into two molecules of pyruvic acid and a net gain of energy is 2 ATP and 2NADH₂ molecules.
The stepwise breakdown of the respiratory substrate to CO₂ and H₂O in presence of oxygen is referred as aerobic respiration. It is a catabolic process and generates a large amount of energy to form ATP.
Anaerobic respiration n micro-organisms are called fermentation. Alcoholic fermentation is a breakdown of glucose into ethyl alcohol and CO₂ in presence of enzyme of micro-organism. Photorespiration is light-induced oxidation of photosynthetic intermediates with the help of oxygen without releasing energy.