`NADH_(2)` generated in glycolysis produces ATP in ETS in presence of `O_(2)`. In absence of `O_(2)` this `NADH_(2)` functions as

Options

A. Oxidising agent
B. Phosphorylating agent
C. Reducing agent
D. Carboxylating agent

Answer

To answer the question, "NADH₂ generated in glycolysis produces ATP in ETS in presence of O₂. In absence of O₂ this NADH₂ functions as," we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Glycolysis**:
- Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing ATP and NADH in the process. NADH is generated when NAD⁺ (Nicotinamide adenine dinucleotide) accepts electrons during the oxidation of glucose.

2. **Role of Oxygen**:
- In the presence of oxygen (aerobic conditions), NADH produced in glycolysis enters the Electron Transport System (ETS), where it is oxidized back to NAD⁺. This process allows for the production of ATP through oxidative phosphorylation, yielding approximately 3 ATP molecules per NADH.

3. **Absence of Oxygen**:
- When oxygen is not available (anaerobic conditions), the NADH cannot enter the ETS. Instead, it must be re-oxidized to NAD⁺ through alternative pathways.

4. **Function of NADH in Anaerobic Conditions**:
- In the absence of oxygen, NADH acts as a reducing agent. It donates electrons (and protons) to other molecules, which allows the regeneration of NAD⁺. This is crucial for glycolysis to continue, as glycolysis requires NAD⁺ to function.

5. **Fermentation Process**:
- The re-oxidation of NADH occurs during fermentation. There are two main types of fermentation:
- **Lactic Acid Fermentation**: In this process, NADH donates electrons to pyruvate, converting it into lactic acid and regenerating NAD⁺.
- **Alcoholic Fermentation**: Here, NADH donates electrons to acetaldehyde, converting it into ethanol (ethyl alcohol) and regenerating NAD⁺.

6. **Conclusion**:
- Therefore, in the absence of oxygen, NADH functions as a reducing agent, facilitating the fermentation process and allowing glycolysis to continue by regenerating NAD⁺.

### Final Answer:
In the absence of O₂, NADH₂ functions as a reducing agent in fermentation processes.

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