Assertion : Dark reactions of photosynthesis are temperauture -controlled processes.
Reason : Most of the reactions are enzymatic in nature.

Options

A. If both Assertion % Reson ar true and the reason is the correct explanation of the asserition the mark (1)
B. If both Assertion % Reason are true but the reason, is not the correct explanation of the assertion ,then mark (2)
C. If Assetion is true statement but Reason is false , The mark (3)
D. If both Assertion and Reason are false statements, the mark (4)

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "Dark reactions of photosynthesis are temperature-controlled processes." This means that the processes that occur during the dark reactions, which include the Calvin cycle, are influenced by temperature.

2. **Understanding the Reason**: The reason provided is that "Most of the reactions are enzymatic in nature." This indicates that the reactions occurring during the dark reactions are primarily driven by enzymes, which are biological catalysts.

3. **Linking Assertion and Reason**: The assertion is true because temperature does influence the rate of enzymatic reactions. Enzymes have optimal temperature ranges in which they function effectively. If the temperature is too high or too low, it can lead to enzyme denaturation or reduced activity, thereby affecting the dark reactions.

4. **Conclusion**: Both the assertion and the reason are true. Furthermore, the reason explains why the assertion is true, as the enzymatic nature of the reactions in the dark cycle makes them sensitive to temperature changes.

5. **Final Answer**: Therefore, the correct conclusion is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.