The cuticle is a waxy, impermeable layer, like an umbrella. It is the top layer and bottom layer of the leaf and serves as a protection layer, protecting them against viruses and fungus. Water will not be absorbed by the cuticle even if it is underwater. The upper epidermis helps prevent dehydration for the plant. The Palisade layer holds many chloroplasts. The spongy layer enables the molecules to flow easily between cells. The lower epidermis has a group of cells called guard cells. Protective cells.
When there is no water in the plant the guard cells cant open up the stoma and so no oxygen can be produced.