Photosynthesis occurs primarily in the mesophyll, which is the middle layer of a leaf. The mesophyll contains cells called chloroplasts, which convert sunlight into a stable chemical energy source the plant can utilize.
The mesophyll is protected by upper and lower outer layers. The outer layer of a leaf and its stem are not typically responsible for photosynthesis. Systems of veins called vascular bundles are found throughout the leaf and serve to transport nutrients to the rest of the plant. Pores located on the leaf's surface, known as stomates, allow for the intake of carbon dioxide, which is converted into sugar, and the release of oxygen into the air.