CBSE Class 10 Answered

The figure shows a cross-section of a leaf.  

The upper and lower surface layer of the leaf is the epidermis ( the upper end lower epidermis). The epidermal cells have stiff cell walls. They protect the leaf, give it shape, and help to keep the moisture inside. The epidermis is covered by a waxy, water-proof layer of cuticle. In the middle, between the upper and lower epidermis, are the mesophyll cells where the chloroplasts reside. There are two kinds of mesophyll cells in a typical leaf.  These are in the palisade parenchyma region and spongy parenchyma region

Palisade layer is a layer of closely packed cells just below the Upper Epidermis of a leaf whereas Spongy Layer is a layer of loosely arranged cells between the palisade layer and the lower epidermis of the leaf. The cells in the palisade area generally have the most chloroplasts. There are small tight air spaces around the cells in the palisade region whereas the air spaces in the spongy parenchyma region are large and spacious. In the lower epidermis are present the guard cells with stomata, which allow carbon dioxide in and oxygen out.