Certain compounds cycle through the abiotic portion
and the biotic communities of ecosystems. These compounds contain elements that
are necessary to the biochemical processes that are carried out in living cells.
Among these elements are carbon, hydrogen, oxygen, and nitrogen. In elemental
form, they are useless to cells and must be combined in chemical compounds. Let
us trace the pathways of some of the vital compounds from the earth to living
organisms to the atmosphere and back to earth. This cycle of events is best
described
by the term biogeochemical cycles.
