Phosphorus Cycle.
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   Biological  importance:  Phosphorus  is  a component of nucleic acids,
   phospholipids, as well as bones and teeth.
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   Forms available to life: Inorganic phosphate (PO[4]^3-) is absorbed by
   plants.
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   Reservoirs: The largest reservoirs are in sedimentary rocks.
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   Key  processes:  Weathering  of  rocks  adds  phosphorus to soil; some
   leaches into groundwater and soil and find its way to sea.
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   Phosphate  taken  up  by  producers  cycle  through  the  food web via
   consumers.
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