The most abundant enzyme on earth

Options

A. Has much greater affinity for `CO_2` than `O_2`
B. Has active site for O_2 only
C. Has carboxylase activity only
D. Both (1) & (3)

Answer

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks for the most abundant enzyme on Earth.

2. **Recall the Enzyme**: The most abundant enzyme on Earth is RuBisCO (Ribulose bisphosphate carboxylase/oxygenase).

3. **Analyze the Given Statements**:
- **Statement A**: "Has much greater affinity for carbon dioxide than oxygen."
- **Statement B**: "Has active site only for oxygen."
- **Statement C**: "Has carboxylase activity only."
- **Statement D**: "Both A and C."

4. **Evaluate Statement A**: RuBisCO does indeed have a greater affinity for carbon dioxide than for oxygen, especially in conditions where both gases are present.

5. **Evaluate Statement B**: This statement is incorrect because RuBisCO has active sites for both carbon dioxide and oxygen, not just for oxygen.

6. **Evaluate Statement C**: This statement is also incorrect. RuBisCO has both carboxylase activity (fixing carbon dioxide) and oxygenase activity (fixing oxygen) depending on the conditions.

7. **Evaluate Statement D**: Since Statement C is incorrect, Statement D (which states both A and C) is also incorrect.

8. **Conclusion**: The correct answer is Statement A: "Has much greater affinity for carbon dioxide than oxygen."

**Final Answer**: The most abundant enzyme on Earth is RuBisCO, which has much greater affinity for carbon dioxide than oxygen.

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