Photosynthesis is the process of generating high-energy biomolecules from lower-energy substances by means of light energy. Plants, algae and some bacteria perform photosynthesis. In this biochemical process, the light energy is first converted into chemical energy by means of light-absorbing pigments such as chlorophyll or bacteriochlorophyll. Among other things, this is used to create energy-rich organic compounds (mostly carbohydrates) from low-energy inorganic substances (carbon dioxide CO2). Their synthesis is called assimilation because the energy-rich organic substances become components of the living being. A distinction is made between oxygenic and anoxygenic photosynthesis. While molecular oxygen (O2) is produced in the oxygenic variant, this is not the case with anoxygenic photosynthesis. As a result of the latter, however, other inorganic substances such as elemental sulfur (S) may be generated. Oxygenic photosynthesis is the most important biogeochemical process occurring on Earth, and also one of the oldest. Due to its property to form organic matter by means of solar energy and thus supply a variety of living organisms with energy-rich building material and energy sources, it directly or indirectly drives almost all existing ecosystems.