Question

The organelles involved in the process of photorespiration are
(A). Chloroplast
(B). Mitochondria
(C). Peroxisomes
(D). Vacuole
Choose the correct answer from the options given below:

• A. (A), (B) and (C)
• B. (A), (B) and (D)
• C. (A), (B), (C) and (D)
• D. (B), (C) and (D)

Hint:

Remember the sequential order of organelles in photorespiration:
\[ \textbf{Chloroplast} \rightarrow \textbf{Peroxisome} \rightarrow \textbf{Mitochondria} \] (Mnemonic: CPM - Chloroplast, Peroxisome, Mitochondria).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Photorespiration (the $\text{C}_2$ oxidative photosynthetic carbon cycle) is a metabolic pathway that occurs when the Rubisco enzyme fixes oxygen ($\text{O}_2$) instead of carbon dioxide ($\text{CO}_2$). This pathway involves several organelle compartments.

Step 2: Detailed Explanation:
- Photorespiration is a multi-step pathway that requires the coordinated activity of three organelles in a specific physical arrangement:
1. Chloroplast (A): Rubisco fixes $\text{O}_2$ to ribulose-1,5-bisphosphate (RuBP), forming 3-phosphoglycerate (3-PGA) and 2-phosphoglycolate. The 2-phosphoglycolate is dephosphorylated to glycolate, which is exported.
2. Peroxisome (C): Glycolate is imported and oxidized to glyoxylate, releasing hydrogen peroxide ($\text{H}_2\text{O}_2$, which is degraded by catalase). Glyoxylate is then transaminated to glycine.
3. Mitochondria (B): Glycine is imported. Two molecules of glycine are decarboxylated and deaminated by glycine decarboxylase to form one molecule of serine, releasing $\text{CO}_2$ and $\text{NH}_3$.
- Serine is then transported back to the peroxisome, converted to glycerate, and returned to the chloroplast to re-enter the Calvin cycle.
- The vacuole (D) is not involved in the photorespiratory pathway.
Thus, only (A), (B), and (C) are involved in photorespiration.

Step 3: Final Answer:
The correct option is (A).