THE CARBON CYCLE
   Biological  importance:  Carbon  forms  the  framework for the organic
   molecules essential to all organisms.

   Forms  available  to  life:  Photosynthetic organisms convert CO[2] to
   organic forms used by consumers.

   Reservoirs:  The major reservoirs include fossil fuels, soils, aquatic
   sediments, oceans (dissolved compounds), plant and animal biomass, and
   the  atmosphere.  The  largest  reservoir is sedimentary rocks such as
   limestone, though this pool turns over very slowly.

   Key  processes:  Photosynthesis  by  plants  and phytoplankton removes
   substantial  amounts  of  CO[2]  each year, balanced by CO[2] released
   through  cellular  respiration.  The burning of fossil fuels is adding
   significant amounts of additional CO[2].