Compared to `C_(3)` plants, `C_(4)` plants

Options

A. Remove oxygen from the air spaces between cells in the leaves and thereby avoid photorespiration
B. Fix carbon dioxide into a four carbon sugar at night, and then release the carbon dioxide during the day
C. Concentration oxygen in cells, thereby overcoming the problem of photorespiration
D. Have adaptations which concentrate carbon dioxide in the photosynthetic cells

Answer

### Step-by-Step Solution

1. **Understanding C3 and C4 Plants**:
- C3 plants primarily use the Calvin cycle for photosynthesis, where ribulose-1,5-bisphosphate (RuBP) reacts with carbon dioxide (CO2) to produce 3-phosphoglycerate (3-PGA). However, they are prone to photorespiration, especially in the presence of high oxygen levels.
- C4 plants have evolved a mechanism to minimize photorespiration by concentrating CO2 in their photosynthetic cells.

2. **Photorespiration in C3 Plants**:
- In C3 plants, the enzyme Rubisco can fix both CO2 and oxygen. When oxygen levels are high, Rubisco can react with oxygen instead of CO2, leading to the production of a two-carbon compound called phosphoglycolate, which is not useful for the plant.

3. **Mechanism of C4 Plants**:
- C4 plants utilize a different pathway to fix carbon. They first convert CO2 into a four-carbon compound (oxaloacetic acid) in mesophyll cells using the enzyme phosphoenolpyruvate carboxylase (PEP carboxylase).
- This four-carbon compound is then transported to bundle sheath cells, where it is converted back to CO2 for use in the Calvin cycle, effectively concentrating CO2 around Rubisco and reducing the chances of photorespiration.

4. **Adaptations of C4 Plants**:
- C4 plants have specialized structures (dimorphic chloroplasts) and metabolic pathways that allow them to concentrate CO2 in their photosynthetic cells, which is a significant adaptation to avoid photorespiration.

5. **Evaluating the Options**:
- **Option 1**: "Remove oxygen from the air spaces between the cells in the leaves and thereby avoid photorespiration." - This is not accurate for C4 plants.
- **Option 2**: "Fix carbon dioxide into a four-carbon sugar at night and then release the carbon dioxide during the day." - This describes CAM plants, not C4 plants.
- **Option 3**: "Concentrate oxygen in cells thereby overcoming the problem of photorespiration." - This is incorrect; C4 plants concentrate CO2, not oxygen.
- **Option 4**: "Have adaptations which concentrate carbon dioxide in the photosynthetic cells." - This is the correct statement regarding C4 plants.

6. **Conclusion**:
- The correct answer is **Option 4**: C4 plants have adaptations that concentrate carbon dioxide in the photosynthetic cells, allowing them to minimize photorespiration.