Sorghum and sugarcane plants show saturation at about

Options

A. 50% of full sunlight
B. 10% of full sunlight
C. 360 ppm of ` CO_(2)`
D. 500 ppm of ` CO_(2)`

Answer

**Step-by-Step Solution:**

1. **Identify the Plants**: The question mentions sorghum and sugarcane, which are both classified as C4 plants.

2. **Understand C4 Photosynthesis**: C4 plants have a unique photosynthetic pathway that allows them to efficiently fix carbon dioxide, especially in hot and dry conditions. This pathway minimizes photorespiration, which is a wasteful process that occurs in some plants when CO2 levels are low.

3. **Krenz Anatomy**: These plants exhibit a specific leaf structure known as Krenz anatomy, which is adapted for their photosynthetic process. This anatomy allows for efficient CO2 capture and reduces photorespiration.

4. **Role of Mesophyll Cells**: In C4 plants like sorghum and sugarcane, mesophyll cells contain an enzyme called PEP carboxylase (often abbreviated as PEPcase). This enzyme allows the plants to continue photosynthesis even when CO2 concentrations are low.

5. **Bundle Sheath Cells**: In addition to mesophyll cells, C4 plants have bundle sheath cells that contain the enzyme RuBisCO, which is involved in the Calvin cycle. This setup allows for effective carbon fixation and minimizes the chances of photorespiration.

6. **Saturation Point**: The question asks about the saturation point for sorghum and sugarcane. The saturation point refers to the level of CO2 concentration at which photosynthesis reaches its maximum rate.

7. **Evaluate Options**:
- Option A (50% of full sunlight) is incorrect.
- Option B (10% of full sunlight) is also incorrect.
- Option C (360 ppm of CO2) indicates a low concentration of CO2, which is suitable for C4 plants, making it a likely candidate.
- Option D (500 ppm of CO2) represents a higher concentration of CO2, which is also not the saturation point for these plants.

8. **Conclusion**: The correct answer is option C (360 ppm of CO2), as C4 plants like sorghum and sugarcane can achieve saturation even at lower CO2 concentrations.

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