Closed ecological systems (CES) are ecosystems in which matter exchange does not take place with any part outside the system.
The term most often describes small manmade ecosystems. Scientifically, such systems are quite interesting and can potentially serve as a life support system in space stations, during space flights or space habitats.
In a closed ecological system, if one species produces waste products, it must be utilized by at least one other species. If the purpose is to maintain a life form, such as a human or a mouse, waste products such as feces, urine, and carbon-di-oxide must eventually be converted into food, water, and oxygen.
There must be at least one autotrophic organism in a closed ecological system. Though phototrophic and chemotrophic organisms, both are plausible, almost every ecological system to date is based on a phototroph like green algae.
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