Choose the correct statement for the fixation of one `CO_2` molecule

Options

A. 3ATP & 2 NADPH are required through calvin cycle
B. 5 ATP & 2 NADPH are required through Hatch & slack cycle
C. Photochemical reactions are involved in photolysis of water & phosphorylation of ADP into ATP
D. all of the above

Answer

To solve the question regarding the fixation of one CO₂ molecule, we will analyze each statement provided in the options and determine their correctness step by step.

### Step-by-Step Solution:

1. **Understanding the Kelvin Cycle**:
- The Kelvin cycle, also known as the Calvin cycle, is a crucial part of photosynthesis that occurs in the stroma of chloroplasts.
- It is referred to as the dark reaction because it does not require light directly.
- The cycle involves three main stages: carbon fixation, reduction, and regeneration of ribulose bisphosphate (RuBP).

2. **Analyzing the First Statement**:
- The first statement claims that "3 ATP and 2 NADPH are required through the Kelvin cycle."
- For the fixation of one CO₂ molecule in the Kelvin cycle, it is indeed true that 3 ATP and 2 NADPH are utilized.
- **Conclusion**: This statement is **correct**.

3. **Understanding the Hatch and Slack Cycle**:
- The Hatch and Slack cycle is a pathway used by C4 plants for carbon fixation.
- This cycle involves both mesophyll cells and bundle sheath cells, where CO₂ is initially fixed in the mesophyll and then enters the Calvin cycle in the bundle sheath cells.

4. **Analyzing the Second Statement**:
- The second statement claims that "5 ATP and 2 NADPH are required through the Hatch and Slack cycle."
- It is accurate that the Hatch and Slack cycle requires more energy than the Kelvin cycle, specifically 5 ATP and 2 NADPH for the fixation of one CO₂ molecule.
- **Conclusion**: This statement is **correct**.

5. **Understanding Photochemical Reactions**:
- Photochemical reactions refer to the light-dependent reactions of photosynthesis, which occur in the thylakoid membranes of chloroplasts.
- These reactions involve the photolysis of water (splitting of water molecules) and the phosphorylation of ADP to ATP, both of which require light.

6. **Analyzing the Third Statement**:
- The third statement claims that "photochemical reactions are involved in photolysis of water and phosphorylation of ADP into ATP."
- This statement is true, as these processes are integral to the light reactions of photosynthesis.
- **Conclusion**: This statement is **correct**.

7. **Final Conclusion**:
- Since all three statements are correct, the answer to the question is option D: "All of the above."

### Summary of the Correct Answer:
- The correct answer is **D: All of the above**.