Photosynthesis turns sunlight, water, and carbon dioxide into sugar, releasing oxygen as a by-product.

The longer version

Inside chloroplasts, light energy is captured by pigments and used to split water molecules. That step releases oxygen as a by-product and provides the electrons needed to build energy-carrying molecules.

In a separate set of reactions that does not need light directly, carbon dioxide from the air is joined onto existing carbon chains and assembled into sugar. The sugar can be used immediately, turned into starch for storage, or built into cellulose for structure. Nearly all the oxygen in the atmosphere comes from this process. Efficiency varies between species, and plants in hot dry places use modified versions of the same chemistry.

Where this entry sits

Plants and Trees gathers ordinary and surprising details about how green things live, from the tallest forest giants down to the moss on a garden wall. Expect notes on flowers, seeds, roots, leaves, fungi, and the quiet tricks plants use to spread and survive. The full list sits on the Plants and Trees page, where every entry is listed in order.