The tips of leaves are the first to mature, development progressing toward the base, which when reached causes the cells to stop growing and dividing. Although leaves may live for a few years, depending on the species, they are of little use to the plant once the first year has passed.

The primary function of leaves is to be the foremost location of photosynthesis in the plant, which is made possible by their physical structure. Leaves are covered in a thin epidermal layer of tissue that secretes a fatty substance called cutin, which forms a waterproof outer layer called the cuticle. Pores, or stomates, are present in the epidermis and are formed by specialized paired guard cells. The tissue between the upper and lower epidermis is known as the mesophyll and is lined with veins. The cells of the mesophyll contain photosynthetic pigments.

Stomates enable a leaf to exchange vapor and gases through the waxy cuticle barrier. The guard cells regulate the opening and closing of the stomates in response to various environmental conditions. For instance, stimuli such as darkness or an internal water deficit have a propensity to close stomates and decrease transpiration. Alternatively, bright sunlight or an abundant supply of water typically causes stomates to open, increasing transpiration.