<P> Phosphorus is an essential nutrient for plants and animals . Phosphorus is a limiting nutrient for aquatic organisms . Phosphorus forms parts of important life - sustaining molecules that are very common in the biosphere . Phosphorus does not enter the atmosphere, remaining mostly on land and in rock and soil minerals . Eighty percent of the mined phosphorus is used to make fertilizers . Phosphates from fertilizers, sewage and detergents can cause pollution in lakes and streams . Overenrichment of phosphate in both fresh and inshore marine waters can lead to massive algae blooms which, when they die and decay, leads to eutrophication of fresh waters only . An example of this is the Canadian Experimental Lakes Area . These freshwater algal blooms should not be confused with those in saltwater environments . Recent research suggests that the predominant pollutant responsible for algal blooms in salt water estuaries and coastal marine habitats is Nitrogen . </P> <P> Phosphorus occurs most abundantly in nature as part of the orthophosphate ion (PO), consisting of a P atom and 4 oxygen atoms . On land most phosphorus is found in rocks and minerals . Phosphorus rich deposits have generally formed in the ocean or from guano, and over time, geologic processes bring ocean sediments to land . Weathering of rocks and minerals release phosphorus in a soluble form where it is taken up by plants, and it is transformed into organic compounds . The plants may then be consumed by herbivores and the phosphorus is either incorporated into their tissues or excreted . After death, the animal or plant decays, and phosphorus is returned to the soil where a large part of the phosphorus is transformed into insoluble compounds . Runoff may carry a small part of the phosphorus back to the ocean . Generally with time (thousands of years) soils become deficient in phosphorus leading to ecosystem retrogression . </P> <P> The primary biological importance of phosphates is as a component of nucleotides, which serve as energy storage within cells (ATP) or when linked together, form the nucleic acids DNA and RNA . The double helix of our DNA is only possible because of the phosphate ester bridge that binds the helix . Besides making biomolecules, phosphorus is also found in bone and the enamel of mammalian teeth, whose strength is derived from calcium phosphate in the form of Hydroxylapatite . It is also found in the exoskeleton of insects, and phospholipids (found in all biological membranes). It also functions as a buffering agent in maintaining acid base homeostasis in the human body . </P> <P> Phosphates move quickly through plants and animals; however, the processes that move them through the soil or ocean are very slow, making the phosphorus cycle overall one of the slowest biogeochemical cycles . </P>

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