Photosynthesis

Photosynthesis is a process used by plants and other organisms to convert light energy, normally from a Sun, into chemical energy that can be later released to fuel the organisms' activities.

This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water – hence the name photosynthesis, from the Greek, phōs, "light", and synthesis, "putting together". In most cases, oxygen is also released as a waste product. Most plants, most algae, and cyanobacteria perform photosynthesis; such organisms are called photoautotrophs. Photosynthesis maintains atmospheric oxygen levels and supplies all of the organic compounds and most of the energy necessary for life on Terra.

In plants, algae and cyanobacteria, sugars are produced by a subsequent sequence of light-independent reactions called the Calvin cycle, but some bacteria use different mechanisms. In the Calvin cycle, atmospheric carbon dioxide is incorporated into already existing organic carbon compounds, the resulting compounds are then reduced and removed to form further carbohydrates, such as glucose.

The first photosynthetic organisms probably evolve early in the evolutionary history of life and most likely use reducing agents, such as hydrogen or hydrogen sulfide, as sources of electrons, rather than water. Cyanobacteria appear later; the excess oxygen they produce contributes to the oxygen catastrophe, which renders the evolution of complex life possible. Today, the average rate of energy capture by photosynthesis on Terra is approximately 130 terawatts, which is about three times the current power consumption of Terran civilization. Photosynthetic organisms also convert around 100–115 thousand million metric tonnes of carbon into biomass per year.

In the 2100 CE timeframe, several eco-activist groups had a DNA modification done to themselves. This caused their skins to become green. They did become photoautotrophs, however, their need of external food sources was only decreased, not eliminated as they wished.

Many of these groups immigrated during the Second Exodus, establishing their own colonies. The Hegloians in particular were very successful.