Which one is correct?

Options

A. During the fermentation, 2 molecules of ATP per molecule of glucose is the net gain
B. Oxidative phosphorylation produces the most ATP in the cell
C. During TCA cycle oxidative steps are coupled to the reductions of `e^(-)` carriers
D. All

Answer

To determine which statement is correct regarding respiration in plants, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Analyze Option 1: Fermentation and ATP Production**
- During fermentation, the net gain of ATP per molecule of glucose is indeed 2 ATP. This occurs because, in glycolysis, 4 ATP are produced, but 2 ATP are consumed, resulting in a net gain of 2 ATP.
- **Conclusion**: This statement is correct.

2. **Analyze Option 2: Oxidative Phosphorylation**
- Oxidative phosphorylation is the process that produces the most ATP in cells. According to the chemiosmotic theory, NADH and FADH2 donate electrons to the electron transport chain, leading to the production of ATP. Specifically, one NADH can yield approximately 3 ATP, while one FADH2 can yield about 2 ATP.
- **Conclusion**: This statement is also correct.

3. **Analyze Option 3: TCA Cycle and Electron Carriers**
- The TCA cycle (Krebs cycle) involves oxidation-reduction reactions where oxidation steps are indeed coupled to the reduction of electron carriers like NAD+ and FAD. As one compound is oxidized, another is reduced, which is characteristic of redox reactions.
- **Conclusion**: This statement is correct as well.

4. **Analyze Option 4: All Statements**
- Since all three previous options have been verified as correct, it follows that the option stating "all" is also correct.
- **Conclusion**: This statement is correct.

### Final Answer:
All statements are correct.