The ` CO_(2)` concetration at which `C_(4)` plants show saturation is about

Options

A. 360 ppm
B. 380 ppm
C. 450 ppm
D. 500 ppm

Answer

To determine the carbon dioxide concentration at which C4 plants show saturation, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding C4 Plants**: C4 plants are unique in their photosynthetic process. They initially fix carbon dioxide into a 4-carbon compound, oxaloacetic acid, which is why they are termed C4 plants.

2. **Role of Mesophyll and Bundle Sheath Cells**: In C4 plants, photosynthesis occurs in two types of cells: mesophyll cells and bundle sheath cells. Mesophyll cells contain the enzyme phosphoenolpyruvate carboxylase (PEPCase) but lack ribulose bisphosphate carboxylase/oxygenase (rubisco), which is essential for the Calvin cycle.

3. **Carbon Fixation Process**: The PEPCase in mesophyll cells converts carbon dioxide into a 4-carbon compound. This compound is then transported to the bundle sheath cells, where it is converted into 3-carbon molecules and carbon dioxide, which enters the Calvin cycle facilitated by rubisco.

4. **Absence of Photorespiration**: C4 plants are efficient because they minimize photorespiration, allowing them to maintain high rates of photosynthesis even at lower carbon dioxide concentrations.

5. **Saturation Point**: The saturation point for C4 plants, where they can effectively utilize carbon dioxide for photosynthesis, is relatively low compared to C3 plants.

6. **Identifying the Correct Concentration**: From the options provided, the lowest concentration of carbon dioxide is 360 ppm. This concentration is significant for C4 plants as they can achieve saturation and high productivity at this level.

### Final Answer:
The carbon dioxide concentration at which C4 plants show saturation is about **360 ppm**.

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