Food for a plant is made in its leaves through photosynthesis, a process in which light energy is converted into chemical energy. The product of photosynthesis is a sugar called glucose, which is then used to fuel the plant.
The process of photosynthesis consists of two different stages. The first stage comprises the light-dependent reactions and begins when the chlorophyll (a green material that is concentrated in the chloroplasts of plant cells) in a leaf absorbs light from the sun. Chloroplasts are components of a plant cell that are characterized by high concentrations of chlorophyll and are the main manufacturing centers of glucose. The chlorophyll in the chloroplasts absorbs sunlight and uses carbon dioxide from the surrounding air and water to create glucose and oxygen. Some of the glucose is then converted into energy for the plant via a process called respiration. This is the second stage of photosynthesis and is called the light-independent reactions. Some of the excess glucose is subsequently stored in the plant as a starch to be used at a later time, while the rest is expended in building and strengthening the cells in the plant as well as in creating more chlorophyll. Organisms, such as plants, that use photosynthesis to make food are called photoautotrophs.