Photosynthesis in C4 plants is relatively less limited by atmospheric ...
In C4 plants, initial fixation of carbon dioxide occurs in mesophyll cells. The primary acceptor of CO2 is phosphoenol pyruvate or PEP. It combines with carbon dioxide in the presence of PEP carboxylase or Pepcase to form oxaloacetate.
C4 plants are more efficient in picking up CO2 even when it is found in low concentration because of the high affinity of PEP case.
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Photosynthesis in C4 plants is relatively less limited by atmospheric ...
Plants such as sorghum and sugarcane fix atmospheric carbondioxide into phosphoenol pyruvic acid to produce oxaloacetic acid in presence of phosphoenol pyruvate carboxylase. Such plants are called C4 plants.
In C4 plants, primary product of OAA is mediated by PEP carboxylase, so it is relatively less limited by atmospheric CO2 levels.
So the correct answer is 'Primary fixation of CO2 is mediated via PEP carboxylase.
Photosynthesis in C4 plants is relatively less limited by atmospheric ...
Photosynthesis in C4 plants is relatively less limited by atmospheric CO2 levels because:
C4 plants have developed a unique carbon fixation pathway that allows them to efficiently capture and concentrate carbon dioxide (CO2) within their leaf tissues. This adaptation enables C4 plants to overcome the limitations imposed by low atmospheric CO2 levels, especially in hot and dry environments.
Primary fixation of CO2 via PEP carboxylase:
In C4 plants, the primary fixation of CO2 occurs in the mesophyll cells, where a four-carbon compound called oxaloacetate is formed through the enzyme phosphoenolpyruvate carboxylase (PEP carboxylase). This enzyme has a higher affinity for CO2 than the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) found in C3 plants.
Effective pumping of CO2 into bundle sheath cells:
The oxaloacetate formed in the mesophyll cells is then converted into malate or aspartate, which are transported to the bundle sheath cells surrounding the leaf veins. The malate or aspartate is decarboxylated in the bundle sheath cells, releasing CO2 and regenerating the four-carbon compound. This process creates a concentration gradient of CO2, with higher levels in the bundle sheath cells.
Higher affinity of Rubisco for CO2:
Unlike C3 plants, where Rubisco directly fixes CO2 in the Calvin cycle, C4 plants have a specialized form of Rubisco in their bundle sheath cells. This form of Rubisco has a higher affinity for CO2 and a lower affinity for oxygen, reducing the wasteful process of photorespiration. This allows C4 plants to continue photosynthesis even when CO2 concentrations are low.
Efficient use of water:
C4 plants also exhibit an advantage in water-use efficiency compared to C3 plants. By concentrating CO2 within the bundle sheath cells, C4 plants can maintain a higher concentration of CO2 while minimizing water loss through stomatal pores. This adaptation is particularly beneficial in arid or drought-prone environments.
Overall, the primary fixation of CO2 via PEP carboxylase, the effective pumping of CO2 into bundle sheath cells, the higher affinity of Rubisco for CO2, and the efficient use of water contribute to the reduced limitation of photosynthesis by atmospheric CO2 levels in C4 plants.
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