Photorespiration is favoured by

Options

A. High oxygen and low carbon dioxide
B. High carbon dioxide and low oxygen
C. High temperature and low oxygen
D. High humidity and temperature.

Answer

**Step-by-Step Solution:**

1. **Understanding Photorespiration**:
- Photorespiration is a metabolic process in plants where the enzyme Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) plays a crucial role. It primarily fixes carbon dioxide during photosynthesis but can also react with oxygen.

2. **Role of Rubisco**:
- Under normal conditions, Rubisco catalyzes the carboxylation reaction, where it combines carbon dioxide with ribulose bisphosphate (RuBP) to produce 3-phosphoglycerate (3-PGA). However, under certain conditions, it can catalyze an oxygenation reaction instead, where it reacts with oxygen and leads to the production of a two-carbon compound, which is less useful for the plant.

3. **Conditions Favoring Photorespiration**:
- Photorespiration is favored by specific environmental conditions:
- High levels of oxygen.
- Low levels of carbon dioxide.
- These conditions lead to an increased likelihood of Rubisco engaging in the oxygenation reaction instead of the carboxylation reaction.

4. **Analyzing the Options**:
- **Option A**: High oxygen and low carbon dioxide - This is the correct condition that favors photorespiration.
- **Option B**: High carbon dioxide and low oxygen - This condition would not favor photorespiration as it promotes carboxylation.
- **Option C**: High temperature and low oxygen - While high temperature can increase photorespiration, low oxygen does not favor it.
- **Option D**: High humidity and temperature - This is incorrect as photorespiration is more common in hot and dry conditions, not humid.

5. **Conclusion**:
- The correct answer is **Option A: high oxygen and low carbon dioxide**, as these conditions lead to increased photorespiration in plants, particularly in C3 plants.

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