The `C_(4)` plants are photosynthetically more efficient than `C_(3)` plants because

Options

A. the carbon dioxide efflux is not prevented
B. photorespiration is negligible
C. the carbon dioxide compensation point is more
D. `CO_(2)` generated during photorespiration is trapped and recycled through PEP carboxylase

Answer

### Step-by-Step Solution

1. **Understanding C3 and C4 Plants**:
- C3 plants use the Calvin cycle for photosynthesis, where the enzyme Rubisco fixes carbon dioxide. However, Rubisco can also bind to oxygen, especially when carbon dioxide levels are low, leading to photorespiration, which reduces the efficiency of photosynthesis.
- C4 plants have a different mechanism that minimizes photorespiration.

2. **Mechanism of C4 Photosynthesis**:
- In C4 plants, carbon dioxide is initially fixed into a 4-carbon compound (oxaloacetic acid) in the mesophyll cells. This process involves the enzyme phosphoenolpyruvate carboxylase (PEP carboxylase), which has a higher affinity for carbon dioxide than Rubisco.
- The oxaloacetic acid is then converted to malic acid and transported to bundle sheath cells.

3. **Reduction of Photorespiration**:
- In the bundle sheath cells, the malic acid releases carbon dioxide, which is then fixed by Rubisco in a high concentration of carbon dioxide, significantly reducing the chances of photorespiration.
- This high concentration of carbon dioxide at the site of Rubisco in C4 plants leads to a much lower rate of photorespiration compared to C3 plants.

4. **Conclusion**:
- The main reason C4 plants are more photosynthetically efficient than C3 plants is that photorespiration is negligible in C4 plants due to the high concentration of carbon dioxide at the site of Rubisco, allowing for more effective carbon fixation.

### Answer:
C4 plants are photosynthetically more efficient than C3 plants because photorespiration is negligible in C4 plants.