Plant leaf structure. Cutaway computer illustration showing the structure of a typical plant leaf. In most plants, leaves are the major site of photosynthesis. Chloroplasts within the leave's cells use chlorophyll to convert the energy in sunlight into chemical energy that the plant can use as food in the form of glucose. Each leaf is made of many layers sandwiched between two layers of tough epidermal skin cells, which also secrete a waxy substance that forms the cuticle. These layers protect the leaf from pests. Within the epidermal cells are pairs of guard cells, which form a pore (stoma), the site of gas exchange. Most food production takes place in the palisade mesophyll. Gas exchange occurs in the air spaces between the cells of the spongy