The outer layer of leaves is called the cuticle. The cuticle is a waxy coating that protects the leaf and prevents water loss. In some leaves, the cuticle may be visible due to its shine.
Under the cuticle is the epidermis, which helps to prevent water loss and provides another layer of protection for the leaf. Below the epidermis is the palisade layer, which contains the chloroplasts that allow photosynthesis to occur. The palisade layer is responsible for producing food and oxygen through photosynthesis. The spongy layer is under the palisade layer; it allows for gas exchange in the leaf.