How do plants produce food?

Plants produce food through photosynthesis. In this process, chlorophyll in chloroplasts captures light energy and helps convert carbon dioxide from the air and water from the soil into sugars, especially glucose. Oxygen is released as a by-product.

Photosynthesis has two linked stages. Light-dependent reactions use sunlight to split water and make energy-carrying molecules, while the Calvin cycle uses those molecules to incorporate carbon dioxide into carbohydrates. Plants then use these sugars for energy, growth, and building materials such as cellulose, or store them as starch.

The process was clarified through experiments by Joseph Priestley, Jan Ingenhousz, Jean Senebier, and Nicolas-Théodore de Saussure in the 18th century. Ingenhousz showed in 1779 that light and green plant tissue were essential to restoring air.

A common mix-up is that plants also respire: cellular respiration breaks down sugars to release usable energy, but it does not make the food. Transpiration is water loss through leaf pores, not food production. Photosynthesis usually occurs in leaves, although green stems and algae can perform it too.