Which process produces both NADH and `FADH_2`?

Options

A. Krebs cycle
B. Glycolysis
C. Electron transport system
D. Fermentation

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which process produces both NADH and FADH2. These molecules are important energy carriers in cellular respiration.

2. **Identifying Key Processes**: In cellular respiration, there are several key processes where energy molecules are produced. The main processes to consider are glycolysis, the Krebs cycle, the electron transport chain, and fermentation.

3. **Analyzing Glycolysis**: Glycolysis is the first step in cellular respiration, where glucose is broken down into two molecules of pyruvate. During this process, NADH is produced, but FADH2 is not.

4. **Analyzing the Krebs Cycle**: The Krebs cycle (also known as the citric acid cycle) occurs after glycolysis. In this cycle, acetyl-CoA (derived from pyruvate) is processed, and both NADH and FADH2 are produced along with ATP.

5. **Analyzing the Electron Transport Chain**: The electron transport chain does not produce NADH or FADH2; instead, it uses these molecules to generate ATP.

6. **Analyzing Fermentation**: Fermentation is an anaerobic process that occurs in the absence of oxygen. It primarily produces ATP and does not generate NADH or FADH2.

7. **Conclusion**: Based on the analysis, the process that produces both NADH and FADH2 is the Krebs cycle.

**Final Answer**: The correct answer is the Krebs cycle.

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