Question

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

• A. Photorespiration
• B. Glycolysis
• C. Fermentation
• D. Aerobic respiration

Answer 1

The Correct Option is C

The given question asks about a metabolic process where the substrate is oxidized without an external electron acceptor.

1. Definition and Context:
   • The key characteristic of this process is that it does not utilize an external electron acceptor.
   • In metabolic processes, oxidation involves loss of electrons, and typically, an electron acceptor is required to complete the reaction cycle.
   • The process in question here is fermentation.
2. Understanding Fermentation:
   • Fermentation is an anaerobic process, meaning it occurs without oxygen.
   • In fermentation, substrates like glucose are partially oxidized, and the energy is released in the absence of an electron transport chain.
   • The electrons released during oxidation reduce organic molecules (such as pyruvate to lactate or ethanol), instead of reducing molecular oxygen or other external electron acceptors.
3. Eliminating Other Options:
   • Photorespiration: This process occurs in plants and involves the uptake of oxygen and release of carbon dioxide, usually without releasing energy. It is not primarily about substrate oxidation for energy release.
   • Glycolysis: Although it includes substrate oxidation, glycolysis itself is part of both aerobic and anaerobic pathways. Alone, it doesn’t conclude an energy-releasing process as it eventually needs an electron acceptor in aerobic respiration.
   • Aerobic Respiration: This process requires oxygen as the terminal electron acceptor, which contradicts the requirement of having no external electron acceptor.

Conclusion: From the analysis above, the correct answer is Fermentation.