Assertion :- In Stroma lamellae cyclic photophosphorylation is the only mean of ATP synthesis
Reason :- In stroma lamellae both PS-II and NADP reductase enzyme are absent.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Answer

**Step-by-Step Solution:**

1. **Understanding the Assertion**: The assertion states that in stroma lamellae, cyclic photophosphorylation is the only means of ATP synthesis. This means that within the stroma lamellae of chloroplasts, the process of generating ATP occurs solely through cyclic photophosphorylation.

2. **Understanding the Reason**: The reason given is that in stroma lamellae, both Photosystem II (PS-II) and NADP reductase enzyme are absent. This is significant because PS-II and NADP reductase are essential for non-cyclic photophosphorylation, which is another method of ATP synthesis that also produces NADPH.

3. **Cyclic vs. Non-Cyclic Photophosphorylation**:
- **Cyclic Photophosphorylation**: Involves only Photosystem I (PS-I) and does not require water or produce NADPH. It generates ATP by cycling electrons back to PS-I.
- **Non-Cyclic Photophosphorylation**: Involves both PS-I and PS-II, requires water (which is split to provide electrons), and produces both ATP and NADPH.

4. **Location of Processes**: The stroma lamellae are the regions of the chloroplast where cyclic photophosphorylation occurs. Since they lack PS-II and NADP reductase, non-cyclic photophosphorylation cannot take place here.

5. **Conclusion**: Since cyclic photophosphorylation is indeed the only method of ATP synthesis in the stroma lamellae due to the absence of PS-II and NADP reductase, both the assertion and reason are correct. Therefore, the assertion is justified by the reason provided.

**Final Answer**: Both the assertion and the reason are correct, and the reason correctly explains the assertion.

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