The first reaction in photorespiration is

Options

A. phosphorylation
B. decarboxylation
C. oxygenation
D. carboxylation

Answer

**Step-by-Step Solution:**

1. **Understanding Photorespiration**: Photorespiration is a process that occurs in plants where oxygen is taken in and carbon dioxide is released in the presence of sunlight. It is considered a wasteful process because it does not produce ATP, which is the energy currency of the cell.

2. **Identifying the First Reaction**: The first reaction in photorespiration involves the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (commonly known as rubisco). This enzyme catalyzes the reaction between ribulose-1,5-bisphosphate (RUBP) and oxygen.

3. **RUBP and Oxygen**: In this initial step, RUBP, which is a 5-carbon compound, reacts with an oxygen molecule. RUBP has the ability to fix both carbon dioxide and oxygen.

4. **Formation of Phosphoglycolate**: When RUBP reacts with oxygen, it produces a 2-carbon compound called phosphoglycolate. This reaction is termed "oxygenation" because it involves the fixation of oxygen.

5. **Conclusion**: Therefore, the first reaction in photorespiration is the oxygenation of RUBP, leading to the formation of phosphoglycolate.

**Final Answer**: The first reaction in photorespiration is oxygenation.

---