Final answer:
Both the palisade mesophyll and the spongy mesophyll layers of dicot leaves contain chloroplasts and play a role in photosynthesis, making option C) Both palisade and spongy mesophyll the correct answer.
Step-by-step explanation:
The layers of cells below the epidermis of dicot leaves that have a role in photosynthesis are known as the mesophyll. The mesophyll consists of two specific layers: the palisade mesophyll and the spongy mesophyll. The palisade layer is made up of column-shaped, tightly packed cells, and the spongy layer comprises loosely packed, irregularly shaped cells. Both layers contain many chloroplasts, which are the sites of photosynthesis. Therefore, the correct answer to which leaf mesophyll layers have a role in photosynthesis is C) Both palisade and spongy mesophyll.