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 compounds in the pathway of photorespiration, we need to understand the order in which these intermediates appear during the process. Here’s a step-by-step breakdown:

### Step 1: Identify the Starting Compound
The photorespiration process begins with the fixation of oxygen by ribulose-1,5-bisphosphate (RuBP) in the chloroplast. This reaction produces the first intermediate, which is **phosphoglycolate**.

### Step 2: Conversion of Phosphoglycolate
Phosphoglycolate (a 2-carbon compound) is then converted into **glycolate** by the release of inorganic phosphate. This step occurs in the chloroplast.

### Step 3: Formation of Glyoxylate
The glycolate is transported to the peroxisome, where it undergoes further conversion to form **glyoxylate**. This is still a 2-carbon compound.

### Step 4: Conversion to Glycine
Next, glyoxylate is converted into **glycine** (also a 2-carbon compound) in the mitochondria.

### Step 5: Formation of Serine
Finally, glycine is converted into **serine**, which is a 3-carbon compound. This step also occurs in the mitochondria and releases one molecule of carbon dioxide.

### Summary of Sequence
Thus, the correct sequence of the intermediates in the pathway of photorespiration is:
1. Phosphoglycolate
2. Glyoxylate
3. Glycine
4. Serine

### Final Answer
The correct sequence of their appearance in the pathway is:
**I. Phosphoglycolate → III. Glyoxylate → IV. Glycine → II. Serine**