The first reaction in photorespiration is

Options

A. Carboxylation
B. Decarboxylation
C. Oxygenation
D. Phosphorylation

Answer

**Step-by-Step Solution:**

1. **Understanding Photorespiration:**
- Photorespiration is a process that occurs in C3 plants where the enzyme RuBisCO plays a crucial role. It is often referred to as the oxidative photosynthetic carbon cycle.

2. **Role of RuBisCO:**
- RuBisCO (Ribulose bisphosphate carboxylase/oxygenase) is the enzyme that catalyzes the first reaction in photorespiration. It is responsible for the fixation of carbon dioxide in the Calvin cycle but can also react with oxygen.

3. **First Reaction in Photorespiration:**
- The first reaction in photorespiration involves the oxygenation of ribulose bisphosphate (RuBP). This means that RuBisCO catalyzes the reaction where RuBP reacts with oxygen instead of carbon dioxide.

4. **Products of the Reaction:**
- When RuBP is oxygenated by RuBisCO, it produces one molecule of 3-phosphoglycerate (3-PGA) and two molecules of phosphoglycolate (PG). This reaction is considered wasteful because it leads to the loss of energy that could have been used for photosynthesis.

5. **Conclusion:**
- Therefore, the first reaction in photorespiration is the oxygenation of RuBP by the enzyme RuBisCO.

**Final Answer:**
- The first reaction in photorespiration is the **oxygenation of RuBP**.

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