Explain why mesophyll cells are the principal site of photosynthesis?

Mesophyll cells are the main centers for photosynthesis because they are rich in chloroplasts—the organelles that contain chlorophyll, responsible for capturing sunlight. These cells are located in the inner leaf tissue, sandwiched between the upper and lower epidermis, allowing them to absorb maximum light. The spongy mesophyll layer also contains air spaces that help carbon dioxide move easily to the photosynthesizing cells.

Key Features of Mesophyll Cells

1. High Chloroplast Content: Mesophyll cells, particularly the palisade mesophyll cells, are densely packed with chloroplasts. These chloroplasts contain chlorophyll, the green pigment essential for converting light energy into chemical energy.

2. Ideal Positioning: Located in the middle layer of the leaf (the mesophyll), these cells are perfectly positioned to capture the most sunlight for photosynthesis.

3. Efficient Gas Exchange: The spongy mesophyll layer beneath the palisade cells has large air spaces. These allow carbon dioxide from the air to diffuse quickly to the photosynthetic cells.

4. Support and Transport: Veins running through the mesophyll contain xylem and phloem, which deliver water and minerals to the cells and carry away the sugars formed during photosynthesis.