How many molecules of NADH are left at the end of anaerobic respiration
(a) 2
(b) 4
(c) 6
(d) 0

Options

A. 2
B. 4
C. 6
D. 0

Answer

To determine how many molecules of NADH are left at the end of anaerobic respiration, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Anaerobic Respiration**:
- Anaerobic respiration occurs in the absence of oxygen. In this process, glucose is converted into pyruvate through glycolysis.

2. **Glycolysis and NADH Production**:
- During glycolysis, for each molecule of glucose that is broken down, 2 molecules of NADH are produced. This is a crucial step in both aerobic and anaerobic respiration.

3. **Pathway After Glycolysis**:
- In aerobic respiration, pyruvate would enter the Krebs cycle (TCA cycle) to further produce ATP and NADH. However, in anaerobic respiration, pyruvate does not enter the Krebs cycle.

4. **Fermentation Process**:
- Instead, pyruvate undergoes fermentation. There are two main types of fermentation: alcoholic fermentation (in yeast) and lactic acid fermentation (in animal cells).
- During fermentation, pyruvate is converted into either ethanol (in yeast) or lactic acid (in animal cells).

5. **NADH Usage in Fermentation**:
- The conversion of pyruvate to ethanol or lactic acid requires the use of NADH. Specifically, NADH is oxidized back to NAD+ in the process, which is essential for glycolysis to continue.

6. **Net Result of NADH**:
- Since the NADH produced during glycolysis is used up in the fermentation process, there are no NADH molecules left at the end of anaerobic respiration.

7. **Conclusion**:
- Therefore, the answer to the question of how many molecules of NADH are left at the end of anaerobic respiration is **0**.

### Final Answer:
(d) 0

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