All of the substances that occur in organisms cycle through ecosystems in a cyclic path involving both biological and chemical processes termed biogeochemical cycle Generally, the bulk of these substances are not contained within the bodies of organisms but rather exist in the atmosphere, water or in rocks. Carbon (in form of carbon dioxide), nitrogen and oxygen primarily enter bodies of organisms from the atmosphere while phosphorus potassium, sulfur, magnesium, calcium, sodium, iron and cobalt all of which are required for plant growth come from rocks.
The cycling of materials in ecosystems begins when they are incorporated from the atmosphere or from weathered rock into the bodies of organisms. Some times, they pass from these organisms into the bodies of other organisms that feed on them and ultimately through decomposition, they are returned to the non-living world. After this occurs, the nutrients may begin the cycle again by being incorporated into bodies of other organisms. This process goes on over and over again.
There are many nutrient cycles, but the well known and important cycles include the water cycle, the carbon cycle, the nitrogen cycle, the oxygen cycle, the phosphorus cycle and the sulphur cycle.