In leaf anatomy, which two cell types comprise the mesophyll to optimize photosynthesis?

• A. Guard cells and epidermis
• B. Palisade and spongy mesophyll cells
• C. Vascular bundle cells
• D. Sclerenchyma

Answer: (B)

Leaf mesophyll is built to maximize photosynthesis by combining two specialized cell types. The palisade mesophyll cells are close to the upper surface, are tightly packed, and are rich in chloroplasts, so they capture most of the light that enters the leaf and drive most of the photosynthetic activity. Below them, the spongy mesophyll cells are more loosely arranged with many air spaces between them, which creates a network that facilitates diffusion of carbon dioxide to the photosynthetic cells and the release of oxygen. This arrangement—efficient light capture from the palisade layer and effective gas diffusion through the air spaces in the spongy layer—lets the leaf optimize photosynthesis. The other options refer to tissues outside the mesophyll and don’t serve this combined role in light capture and gas exchange.