# DBT JRF 2020 — Question 123

Exam: DBT JRF 2020 · Section: B · Topic: Microbiology · Difficulty: Easy

## Question

An energy generation process in which organic compounds act as both electron donors and terminal electron acceptor in a microbe is called

## Options

- **A.** aerobic process
- **B.** biomass formation process
- **C.** photosynthesis
- **D.** fermentation process

## Answer

Option D

## Explanation

Fermentation (substrate-level phosphorylation, anaerobic): a catabolic process in which: Organic compounds serve as BOTH electron donors (substrate being oxidised — e.g. glucose → pyruvate) AND terminal electron acceptors (the substrate or its derivative accepts electrons — e.g. pyruvate → lactate by LDH; acetaldehyde → ethanol by ADH). No external electron acceptor (O $_2$ , NO $_3^-$ , SO $_4^{2-}$ ) is required. Net ATP from fermentation is substrate-level only (2 ATP from glycolysis). NAD $^+$ is regenerated by the terminal reduction step, allowing glycolysis to continue. Aerobic respiration uses O $_2$ as terminal electron acceptor. Photosynthesis uses light. Biomass formation is a result, not a mechanism. Anaerobic respiration uses external inorganic acceptors (not organic) — distinct from fermentation.

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