Transcript BIOGEOCHEMICAL CYCLES

BIOGEOCHEMICAL CYCLES
• The flow of energy in the
biosphere is in one
direction only: from the
sun, through living
organisms, into the
environment, and out into
space.
• Matter cycles constantly
from organism to
organism as well as to
and from the
environment, which acts
as a reservoir.
• The cyclic pathways taken by various
elements in passing through living
organisms (biotic) and the earth, its
atmosphere and its bodies of water
(abiotic) are generally called
biogeochemical cycles.
• The NITROGEN CYCLE is one of the
most important.
• Proteins and nucleic acids are essential to
life. In order to make them, living things
must obtain nitrogen in a useable form.
• Nitrogen in the air is diatomic (“2-atom”)
molecules N2, and no animal or plant can
separate them to use them.
• To be useful the nitrogen must be
“fixed”=be attached to atoms of some
other elements to form a compound.
Nitrogen fixation…..
Can occur by:
• Passage of UV light and lightning through
the air = NO3- (nitrate ions) formed
• Volcanoes, combustion of fossil fuels
(coal, oil, natural gas) and forest fires =
nitrate and NH3 (ammonia)
• Rain brings the fixed nitrogen to the soil as
NH4- (ammonium ion)
• The bulk of this is carried out by nitrogen-fixing
bacteria in soil and by cyanophytes (blue-green
bacteria).
• The most efficient nitrogen fixers are bacteria
found in nodules on the roots of certain plants,
notably the legumes (alfalfa, beans, peas, lentils,
clover).
• Fertilizers also add nitrogen to the soil
• Animals must consume Nitrogen in the
form of already formed amino acids in their
food.
• Excretions of animals and the dead
bodies of all organisms are broken down
in the soil by decomposers in the process
of ammonification , which produces
ammonia.
• Nitrifying bacteria convert the ammonia to
NO2- (nitrite ion), then another group of
nitrifying bacteria convert the nitrite ion to
NO3- (nitrate ion). This is know as
nitrification.
• Nitrate is readily taken up by
roots of plants and utilized.
• Denitrifying bacteria convert nitrate to
N2O (nitrous oxide) or N2 (nitrogen gas),
which is then lost to the atmosphere.
• Nitrogen is lost from soil by erosion and
carried into streams, rivers, and ultimately
the ocean.
• It then cycles through aquatic organisms.
• Eventually, some nitrogen is lost to
sediments at the bottoms of oceans or
lakes.
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