A closed system maintains itself on a limited amount of resources that are entrenched in that particular system. Energy can be exchanged with other systems, but not any actual matter. Therefore, some of what goes on in the environment is considered a closed system, but not a whole lot. Open systems are much more common. In an open system, necessary resources are renewed and exchanged on a regular basis. Many ecosystems, for example, rely on the sun to constantly import energy into their basic cycles. Then there's a limited amount of nutrients to go around -- such as carbon, nitrogen and phosphorous -- and they're constantly cycled around. Some common cycles include the hydrological cycle, rock cycle and the carbon cycle.
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