What is the role of large bundle shealth cells found around the vascul...
The role of large bundle sheath cells in C4 plants
C4 plants have a unique mechanism to enhance photosynthesis efficiency in hot and dry environments. They have specialized anatomy and biochemistry that separate the initial carbon fixation step from the Calvin cycle, which occurs in the chloroplasts of mesophyll cells and bundle sheath cells, respectively. The large bundle sheath cells play a crucial role in the C4 pathway.
1. Carbon fixation in mesophyll cells:
- In C4 plants, the initial carbon fixation occurs in the mesophyll cells, where the enzyme phosphoenolpyruvate carboxylase (PEPCase) incorporates CO2 into phosphoenolpyruvate (PEP) to form oxaloacetate (OAA).
- This process occurs even when the stomata are partially closed, reducing water loss through transpiration.
2. Transfer of carbon to bundle sheath cells:
- The OAA formed in the mesophyll cells is converted into malate or aspartate before being transported to the bundle sheath cells through plasmodesmata.
- This transfer of carbon compounds allows the bundle sheath cells to concentrate CO2 around the enzyme Rubisco, which minimizes photorespiration and enhances photosynthesis efficiency.
3. Carbon fixation in bundle sheath cells:
- In the bundle sheath cells, the malate or aspartate is decarboxylated to release CO2, which is then used in the Calvin cycle.
- The Calvin cycle occurs exclusively in the bundle sheath cells of C4 plants, ensuring that Rubisco functions efficiently without being inhibited by oxygen.
4. Enrichment of chloroplasts in bundle sheath cells:
- The large bundle sheath cells have an abundance of chloroplasts, which maximize the efficiency of the Calvin cycle.
- This enrichment allows for a higher concentration of Rubisco in the bundle sheath cells, improving the overall photosynthetic capacity of C4 plants.
Conclusion:
The large bundle sheath cells found around the vascular bundles in C4 plants play a critical role in the C4 pathway by concentrating CO2 around Rubisco, minimizing photorespiration, and enhancing the efficiency of the Calvin cycle. The abundance of chloroplasts in the bundle sheath cells allows for increased photosynthetic capacity, ultimately improving the plant's ability to fix carbon and thrive in hot and dry environments.
What is the role of large bundle shealth cells found around the vascul...
C4 plants have a specialized carbon fixation mechanism that involves spatial separation of initial carbon fixation and the Calvin cycle. Bundle sheath cells play a crucial role in this process. They are large, tightly packed cells that surround the vascular bundles.
In C4 plants, the initial carbon fixation occurs in mesophyll cells, where the enzyme PEP carboxylase captures carbon dioxide to form a four-carbon compound. This compound is then transported to the bundle sheath cells, where it releases carbon dioxide, which is then fixed by the enzyme Rubisco through the Calvin cycle.
The large bundle sheath cells in C4 plants are rich in chloroplasts, which provide the site for the Calvin cycle to operate efficiently. The high concentration of chloroplasts in the bundle sheath cells allows for a higher capacity of carbon dioxide fixation and efficient functioning of the Calvin cycle, leading to increased photosynthetic efficiency.
Therefore, the correct answer is (a) To increase the number of chloroplasts for the operation of the Calvin cycle.
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