Photosynthesis

Photosynthesis is how plants and some microorganisms make carbohydrates. It is an endothermic (takes in heat) chemical process which uses sunlight to turn carbon dioxide into sugars. The sugars are used by the cell as energy, and to build other kinds of molecules. Fundamentally, photosynthesis converts light energy into chemical energy.^[1]

Photosynthesis is vital for life on Earth. Before photosynthesis, Earth had no free oxygen in its atmosphere.^[2]

Green plants build themselves using photosynthesis. Algae, protists and some bacteria also use it. Some exceptions are organisms that directly get their energy from chemical reactions; these organisms are called chemoautotrophs.

1. ↑ Schopf J. William 1999. Cradle of life: the discovery of Earth's earliest fossils. p148 et seq.
2. ↑ Zahnle K.; Schaefer L. & Fegley B. 2010. Earth's earliest atmospheres. Cold Spring Harbor Perspectives in Biology. 2 (10): a004895. doi:10.1101/cshperspect.a004895. PMC 2944365. PMID 20573713