The following compounds are intermediates in the pathway of photorespiration
I) Phosphoglycolate II) Serine
III) glyoxylate IV) glycine
The correct sequence of their appearance in the pathway is

Options

A. I,II, III, IV
B. I,III, IV,II
C. II,I,III,IV
D. II,I,IV,III

Answer

To determine the correct sequence of the intermediates in the pathway of photorespiration, we need to analyze the order in which these compounds appear during the process. The intermediates provided are:

I) Phosphoglycolate
II) Serine
III) Glyoxylate
IV) Glycine

### Step-by-Step Solution:

1. **Phosphoglycolate Formation**:
- Photorespiration begins when ribulose bisphosphate (RuBP) reacts with oxygen (O2) instead of carbon dioxide (CO2) due to the enzyme ribulose bisphosphate carboxylase/oxygenase (RuBisCO). This reaction produces phosphoglycolate as the first intermediate.
- **Hint**: Remember that phosphoglycolate is formed directly from RuBP in the presence of O2.

2. **Conversion to Glycolate**:
- Phosphoglycolate is then converted to glycolate, although glycolate is not listed in the options. This step is crucial as it leads to the next intermediate.
- **Hint**: Glycolate is a transient intermediate that is not part of the final answer.

3. **Formation of Glyoxylate**:
- Glycolate is subsequently converted into glyoxylate. This is the second compound in the sequence.
- **Hint**: Glyoxylate is formed from glycolate in the peroxisomes.

4. **Conversion to Glycine**:
- Glyoxylate is then converted into glycine. This step occurs in the mitochondria.
- **Hint**: Glycine is a key amino acid formed from glyoxylate.

5. **Formation of Serine**:
- Finally, glycine is converted into serine. This is the last step in this sequence of intermediates.
- **Hint**: Serine is formed from glycine through a simple transamination reaction.

### Correct Sequence:
Based on the above steps, the correct sequence of the intermediates in the pathway of photorespiration is:
1) Phosphoglycolate (I)
2) Glyoxylate (III)
3) Glycine (IV)
4) Serine (II)

Thus, the correct order is: **I → III → IV → II**.

### Final Answer:
The correct sequence of their appearance in the pathway is: **I, III, IV, II**.