Why do lower leaf cells have air spaces?

Lower leaf cells, particularly those in the spongy mesophyll, contain air spaces to facilitate gas exchange. These air spaces allow carbon dioxide to diffuse in for photosynthesis and oxygen to diffuse out as a byproduct. Additionally, the presence of air spaces helps maintain humidity within the leaf, reducing water loss while still enabling efficient gas exchange. This structure is crucial for the plant's overall respiratory and photosynthetic processes.