According to the chemiosmotic hypothesis of ATP formation in the chloroplast, which one does not contribute to the development of proton gradient across the thylakoid membrane?

Options

A. Splitting of water
B. Reduction of `NADP^(+)` to `NADPH + H^(+)`
C. Reduction of `NAD^(+)` to `NADPH + H^(+)`
D. Removal of `H^(+)` from stroma while transporting electron

Answer

To solve the question regarding the chemiosmotic hypothesis of ATP formation in chloroplasts and identify which process does not contribute to the development of the proton gradient across the thylakoid membrane, we can analyze each of the given options step by step.

### Step-by-Step Solution:

1. **Understanding the Chemiosmotic Hypothesis**:
- The chemiosmotic hypothesis explains how ATP is synthesized in chloroplasts. It involves the creation of a proton gradient across the thylakoid membrane, which is essential for ATP production.

2. **Identifying the Processes**:
- We need to evaluate the following processes to determine which one does not contribute to the proton gradient:
- A) Splitting of water (photolysis)
- B) Reduction of NADP+ to NADPH + H+
- C) Reduction of NAD+ to NADPH + H+
- D) Removal of H+ from stroma while transporting electrons

3. **Analyzing Each Process**:
- **A) Splitting of Water**:
- This process occurs during photosynthesis where water molecules are split into oxygen, protons (H+), and electrons. The protons contribute to the proton gradient in the thylakoid lumen.
- **Conclusion**: This process contributes to the proton gradient.

- **B) Reduction of NADP+ to NADPH + H+**:
- This reaction involves the addition of protons to NADP+ to form NADPH. While it does involve protons, it does not directly contribute to the proton gradient across the thylakoid membrane.
- **Conclusion**: This process does not contribute to the proton gradient.

- **C) Reduction of NAD+ to NADPH + H+**:
- This option is incorrect in the context of chloroplasts because NAD+ is not directly involved in the light reactions. Instead, NADP+ is the relevant molecule. Thus, this process is not applicable in the context of the chemiosmotic hypothesis in chloroplasts.
- **Conclusion**: This process is not relevant to the proton gradient.

- **D) Removal of H+ from Stroma while transporting electrons**:
- This process involves the movement of protons from the stroma into the thylakoid lumen, which helps establish the proton gradient necessary for ATP synthesis.
- **Conclusion**: This process contributes to the proton gradient.

4. **Final Answer**:
- Based on the analysis, the process that does not contribute to the development of the proton gradient across the thylakoid membrane is **C) Reduction of NAD+ to NADPH + H+**.