THE PHOSPHORUS CYCLE
   Biological  importance:  Phosphorus is a constituent of nucleic acids,
   including  ATP,  phospholipids,  and is a a mineral component of bones
   and teeth.

   Forms  available  to  life:  The only biologically important inorganic
   form  of  phosphorus  is phosphate (PO[4]^3-), which plants absorb and
   use to synthesize organic compounds.

   Reservoirs:  The largest accumulators of phosphorus are in sedimentary
   rocks.  There are also quantities of phosphorus in soils, dissolved in
   oceans, and in biomass.

   Key  processes:  Weathering  of  rocks  adds  phosphorus to soil; some
   leaches  into  groundwater  and surface water and find its way to sea.
   Phosphate  taken  up  by  producers  may  be  eaten  by  consumers and
   distributed  through  the  food  web. Phosphate is returned to soil or
   water   through  either  decomposition  of  biomass  or  excretion  by
   consumers.