Ecosystem, Closed

a functionally unified assemblage of organisms (plants, animals, and microorganisms) inhabiting a common territory and capable of prolonged existence under conditions of a closed cycle of matter (that is, in the absence of matter exchange across the boundaries).

The ecosystem principle is used in the development of life-support systems to maintain human life in places other than the earth’s biosphere, for example, in spacecraft or underwater craft. Such an artificially created ecosystem is based on plants, which in the process of photosynthesis use light energy to absorb carbon dioxide and release oxygen, that is, regenerate the atmosphere. The plant biomass can be used as food by man and by other heterotrophic organisms, which themselves, in turn, can serve as food for man. The unused plant biomass and the metabolic wastes of man and other components of the artificial biocenosis are decomposed by microorganisms to form water, carbon dioxide, and mineral substances, which are reused by the plants.

Experimental closed ecosystems have been created in the USSR consisting of man, unicellular algae, higher plants (cabbages, carrots, beets, tomatoes, wheat), and microorganisms, which act as mineralizers. Regeneration in such ecosystems fully satisfies man’s requirements for oxygen and water and provides 20 percent of his food. Natural ecolosystems usually are referred to simply as ecosystems.