Answer
✅ Correct Statement:
RuBisCO catalyzes the carboxylation of RuBP (Ribulose-1,5-bisphosphate).
🔍 Explanation:
RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is a vital enzyme in the Calvin cycle, responsible for catalyzing the carboxylation of RuBP. This reaction fixes carbon dioxide (CO2) into an organic compound by producing two molecules of 3-phosphoglycerate (3-PGA).
Although RuBisCO can also react with oxygen (O2) in a process called photorespiration, it generally has a higher affinity for CO2, especially when the CO2:O2 ratio is nearly equal.
❌ Why the Other Statements Are Incorrect:
- “It is active only in the dark” – RuBisCO works in the Calvin cycle, which depends on ATP and NADPH from light reactions; it is not exclusive to darkness.
- “It has higher affinity for oxygen than carbon dioxide” – RuBisCO has a greater affinity for CO2 under normal atmospheric conditions.
- “It is an enzyme involved in the photolysis of water” – Photolysis is part of the light-dependent reactions and is performed by Photosystem II, not RuBisCO.
🧠 Summary Table
| Statement | Accuracy | Reason |
|---|---|---|
| Catalyzes carboxylation of RuBP | ✅ Correct | Primary function of RuBisCO in the Calvin cycle |
| Active only in the dark | ❌ Incorrect | Not exclusive to dark; functions when ATP/NADPH are available |
| Higher affinity for O₂ than CO₂ | ❌ Incorrect | RuBisCO has greater affinity for CO₂ |
| Involved in photolysis of water | ❌ Incorrect | Photolysis is performed by Photosystem II |