For which substrate `RuBisCO` shows greater affinity?

Answer

### Step-by-Step Solution:

1. **Understanding RuBisCO**: RuBisCO stands for Ribulose-1,5-bisphosphate carboxylase/oxygenase. It is an enzyme that plays a crucial role in the process of photosynthesis, specifically in the Calvin cycle.

2. **Substrates of RuBisCO**: RuBisCO can catalyze two different reactions based on the substrates available: carboxylation (with carbon dioxide) and oxygenation (with oxygen).

3. **Affinity for Substrates**: The enzyme RuBisCO has an active site that can bind both carbon dioxide (CO2) and oxygen (O2). However, it has a greater affinity for carbon dioxide compared to oxygen.

4. **Conditions for Oxygenation**: The process of oxygenation (where RuBisCO reacts with oxygen) only occurs under specific conditions, particularly when the ratio of carbon dioxide to oxygen is low. This means that under normal conditions, RuBisCO will preferentially bind to carbon dioxide.

5. **Conclusion**: Therefore, the substrate for which RuBisCO shows greater affinity is carbon dioxide.

### Final Answer:
RuBisCO shows greater affinity for carbon dioxide (CO2) compared to oxygen (O2).