Biology · Bioenergetics

In C4 plants, CO₂ fixation occurs in the mesophyll cells, but it follows a unique pathway compared to C3 plants. C4 plants are adapted to minimize photorespiration by initially fixing CO₂ in the mesophyll cells using the enzyme PEP Carboxylase, forming a four-carbon compound (oxaloacetate). This compound is then transported to the bundle sheath cells, where the Calvin cycle occurs. Therefore, the statement that CO₂ fixation is absent in mesophyll cells is incorrect.

The Calvin cycle is indeed present in C4 plants, but it occurs in the bundle sheath cells, not the mesophyll cells. Bundle sheath cells are essential for the Calvin cycle in C4 plants, and PEP Carboxylase is vital for the initial CO₂ fixation. Thus, options A, B, and C are incorrect.

The Calvin cycle is present in C4 plants. It takes place in the bundle sheath cells, where CO₂ is eventually fixed into sugar.

Bundle sheath cells are present in C4 plants. They play a crucial role in the Calvin cycle by receiving four-carbon compounds from mesophyll cells.

PEP Carboxylase is an enzyme present in C4 plants. It facilitates the initial fixation of CO₂ in mesophyll cells, forming a four-carbon compound.

CO₂ fixation does occur in the mesophyll cells of C4 plants. This is the initial step, using PEP Carboxylase to form a four-carbon compound.