Explanation:

Palisade parenchyma is a layer of cells found in the mesophyll of leaves. These cells are rich in chloroplasts, which are essential for photosynthesis—the process by which plants convert light energy into chemical energy (glucose).

• The elongated shape of palisade cells allows them to absorb maximum sunlight.
• The high concentration of chloroplasts makes them the primary site for light-dependent reactions of photosynthesis.

Thus, the main function of palisade parenchyma is photosynthesis, making option (D) the correct answer.