The enzyme RuBisCO has

Options

A. (a) more affinity for `CO_(2)` than for `O_(2)`
B. (b) more affinity for `O_(2)` than for `CO_(2)`
C. (c) equal affinity for both
D. (d) more affinity for sugars than for `CO_(2)`

Explanation

**Step-by-Step Solution:**

1. **Understanding RuBisCO**: RuBisCO (Ribulose bisphosphate carboxylase/oxygenase) is an enzyme that plays a crucial role in the process of photosynthesis, specifically in the Calvin cycle where it helps fix carbon dioxide into organic molecules.

2. **Active Site Functionality**: The active site of RuBisCO is where the substrate (carbon dioxide or oxygen) binds. This active site is responsible for the enzyme's ability to catalyze reactions involving these gases.

3. **Affinity for Substrates**: The question asks about the affinity of RuBisCO for carbon dioxide compared to oxygen. It is known that RuBisCO has a higher affinity for carbon dioxide than for oxygen. This means that it preferentially binds to carbon dioxide when both gases are present.

4. **Oxygenation vs. Carboxylation**: The active site of RuBisCO can facilitate both carboxylation (fixing carbon dioxide) and oxygenation (fixing oxygen). However, the enzyme primarily operates in carboxylation mode under normal conditions because of its higher affinity for carbon dioxide.

5. **Conditions for Oxygen Binding**: RuBisCO can bind to oxygen, but this occurs mainly when the concentration of oxygen is significantly higher than that of carbon dioxide. Under typical conditions, carbon dioxide is more abundant, leading to preferential binding.

6. **Conclusion**: Based on the information gathered, we conclude that RuBisCO has more affinity for carbon dioxide than for oxygen.

7. **Final Answer**: Therefore, the correct answer to the question is option A: "more affinity for carbon dioxide than for oxygen."

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