Positive effect of photorespiration

Options

A. reduces `O_(2)` injury to chloroplast in `C_(3)` plant
B. balance the `O_(2)//CO-(2)` ratio of plant
C. increase the yield of plant
D. do not have any positive effect

Answer

### Step-by-Step Solution

1. **Understanding Photorespiration**:
- Photorespiration is a process that occurs primarily in C3 plants. It happens under specific conditions, particularly when there is a low concentration of carbon dioxide (CO2) and a high concentration of oxygen (O2).

2. **Conditions Favoring Photorespiration**:
- The process is more likely to occur when temperatures are high. Under these conditions, the enzyme ribulose bisphosphate carboxylase/oxygenase (rubisco) has a higher affinity for oxygen than for carbon dioxide.

3. **Process of Photorespiration**:
- In normal photosynthesis, rubisco catalyzes the reaction between ribulose bisphosphate (RuBP) and carbon dioxide to produce two molecules of 3-phosphoglycerate (3-PGA).
- However, during photorespiration, when CO2 levels are low, RuBP combines with oxygen instead, resulting in the production of one molecule of 3-PGA and one molecule of phosphoglycolate.

4. **Products of Photorespiration**:
- The products of photorespiration (3-PGA and phosphoglycolate) indicate that the process does not yield the same energy-rich compounds as normal photosynthesis, leading to a net loss of energy.

5. **Conclusion on Positive Effects**:
- Generally, photorespiration is considered a wasteful process as it does not contribute positively to the plant's energy production. It is often viewed as a negative aspect of plant metabolism, especially in C3 plants.

### Final Answer:
- In conclusion, photorespiration does not have any significant positive effects; it is primarily a wasteful process that reduces the efficiency of photosynthesis in C3 plants.