During photorespiratin RUBisCo uses _______ as a substrate-

Options

A. `CO_(2)`
B. NADPH
C. `O_(2)`
D. 3-PGA

Answer

**Step-by-Step Solution:**

1. **Understanding the Process of Photorespiration**:
- Photorespiration is a process that occurs in plants, particularly when the concentration of oxygen is high and carbon dioxide is low. It is often considered a wasteful pathway because it does not produce energy-rich molecules like ATP or NADPH.

2. **Role of Rubisco**:
- Rubisco, which stands for Ribulose 1,5-Bisphosphate Carboxylase/Oxygenase, is the key enzyme involved in this process. It has two main activities: carboxylase activity (binding with CO2) and oxygenase activity (binding with O2).

3. **Substrates Used by Rubisco**:
- During photorespiration, Rubisco primarily uses oxygen (O2) as a substrate. This is in contrast to its carboxylase activity, where it uses carbon dioxide (CO2).

4. **Products of Photorespiration**:
- When Rubisco binds with oxygen, it produces one molecule of phosphoglycolate and one molecule of 3-phosphoglycerate (3-PGA). This process is less efficient than when it binds with carbon dioxide.

5. **Conclusion**:
- Therefore, during photorespiration, Rubisco uses **O2 (oxygen)** as a substrate.

**Final Answer**: During photorespiration, RUBisCo uses **O2 (oxygen)** as a substrate.

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