Plant Parts Leaves are the food making factories of green plants. Leaves come in many different shapes and sizes. Leaves can be simple, made of a single leaf blade connected by a petiole to the stem (oak, maple), or compound, in which the leaf blade is divided into separate leaflets attached by a petiole to the stem (ash, locust). Leaves are made to catch light and have openings to allow water and air to come and go. The outer surface of the leaf has a waxy coating called a cuticle which protects the leaf. Veins carry water and nutrients within the leaf. Leaves are the site of the food making process called photosynthesis. In this process, carbon dioxide and water in the presence of chlorophyll (the green pigment) and light energy are changed into glucose (a sugar). This energy rich sugar is the source of food used by most plants. Photosynthesis is special to green plants! Photosynthesis supplies food for the plant and oxygen for other forms of life. A green plant helped make the oxygen you are breathing today.