Even though a very few cells in a C4 plant carry out the biosynthetic - Calvin pathway, yet they are highly productive. Can you discuss why

Even though only a small number of cells in a C4 plant are involved in the biosynthetic - Calvin pathway, they are still highly productive. This can be attributed to the unique anatomical and biochemical adaptations of C4 plants.

1. Anatomical Adaptations: C4 plants have specialized leaf anatomy that separates the initial carbon fixation step from the Calvin cycle. They possess two distinct types of photosynthetic cells: mesophyll cells and bundle sheath cells.

2. Mesophyll Cells: These cells are responsible for the initial carbon fixation step, which occurs through the C4 pathway. They contain high levels of the enzyme phosphoenolpyruvate carboxylase (PEP carboxylase), which has a high affinity for carbon dioxide (CO2). This allows them to efficiently capture CO2 even at low concentrations.

3. Bundle Sheath Cells: After the initial carbon fixation, the C4 acids produced in the mesophyll cells are transported to the bundle sheath cells. These cells surround the vascular tissue and contain high levels of the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), which is involved in the Calvin cycle. Rubisco has a lower affinity for CO2 but a higher specificity for oxygen. By concentrating CO2 in the bundle sheath cells, C4 plants minimize the oxygenation of Rubisco and reduce photorespiration.

4. Biochemical Adaptations: The separation of the initial carbon fixation and the Calvin cycle in different cells allows C4 plants to optimize photosynthesis. The C4 pathway enables them to efficiently capture and concentrate CO2, enhancing the efficiency of Rubisco and reducing energy loss through photorespiration.

5. Higher Productivity: Due to these anatomical and biochemical adaptations, C4 plants have a higher photosynthetic efficiency and productivity compared to C3 plants. The concentration of CO2 in the bundle sheath cells ensures that Rubisco is primarily exposed to CO2, leading to increased carbon fixation and biomass production.

In summary, even though only a few cells in a C4 plant carry out the Calvin pathway, their high productivity can be attributed to the anatomical and biochemical adaptations that optimize photosynthesis and minimize energy loss.