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Green plants and certain bacteria are able to convert inorganic matter into biomass using energy from solar radiation or chemical energy. They are the first link in the food chain and are therefore called the primary producers (autotrophs). All other life depends on the energy fixed by these primary producers. The process of assimilation and fixation of inorganic carbon and other inorganic nutrients into organic matter by autotrophs is called primary production. In calculations of the primary production of an ecosystem the chemical energy source is usually left away. The total amount of energy fixed in living organisms is called the Gross Primary Production (GPP). Through metabolic activities of the plants themselves and by heat loss, 50% or more to the Net Primary Production reduces the GPP. .