Functions of Leaves
The process by which plants make food from carbon dioxide, water, and energy of sunlight is called photosynthesis. This process is begun by the chlorophyll. In the higher plants photosynthesis occurs chiefly in the leaves, in which chlorophyll is contained in the mesophyll.
Plants use only a tiny fraction of the water they obtain through their roots. The remainder they give off chiefly as water vapor, through their stomata, by the process of transpiration. Plants transpire huge quantities of water. A large apple tree can give off an average of 10 gallons (38 l) a day.