3.1. Leaf

Leaves are specialized and highly evolved organs that are the sites for photosynthesis in plants. The stem elevates leaves from the ground so that the leaves can better absorb sunlight, and use the energy to build sugars from atmospheric carbon dioxide. Generally speaking, a leaf’s flat form allows it to have a large surface area to volume ratio and reflects its ability to efficiently capture sunlight and exchange carbon dioxide and water vapor. Leaves produce nearly all of a plant’s sugars through photosynthesis. The light that falls upon leaves is absorbed by chloroplast-rich mesophyll cells, and the energy is used to drive the photosynthetic reactions. Leaves are also perforated on the surface with tiny pores called stomata that allow air to diffuse into intercellular airspaces, providing the chloroplasts with a supply of carbon dioxide, the carbon from which is the primary building block of sugar molecules. Leaves, with the energy, materials, and biochemical machinery needed for photosynthesis, can be considered green sugar factories.