Download Nitrogen Cycle Power Point

Background

All life requires Nitrogen
–
–
–

Proteins
Amino Acids
Nucleic Acid
79% of the air is N2
–
–
This form cannot be used by most organisms
Organisms need a fixed form (incorporated into a
compound)
Usable Nitrogen

Plants secure Nitrogen in
a fixed form
–
–

nitrate ions (NO3−)
ammonium (NH4+)
Assimilation- Animals
secure Nitrogen from
plants and other animals
that have eaten plants in
organic material
Nitrogen Fixation


The breaking apart of N2 so that the atoms
can combine with other atoms
3 processes:
–
–
–
1) atmospheric fixation
2) biological fixation
3) industrial fixation
Atmospheric Fixation



Energy in lighting breaks apart N2 molecule and
N combines with Oxygen in the air
Nitrates (NO3-) forms in rainwater and falls to
the earth
5-8% of the total nitrogen fixed
Biological Fixation



Some species of bacteria
can fix atmospheric N2 into
ammonium (NH4)
Can be free living bacteria
or symbiotically associated
with plants
Legumes form a symbiotic
relationship with bacteria
from the genus: Rhizobium
Industrial Fixation




Haber-Bosch Process
Creates 500 million tons
artificial fertilizer/year
High pressure and intense
heat (750-1200 degrees F)
cause atmospheric
Nitrogen and Hydrogen to
form Ammonia (NH3)
most of its is further
processed to urea and
ammonium nitrate
(NH4NO3).
Decomposition



Proteins made by plants and animals pass
through the food web
Excretions and Dead animals get broken
down by decomposing microorganisms
Creates ammonia (NH3)
Nitrification


Ammonia from decay can be taken up
directly by plants but usually converted first
to nitrates (NO3-)
Bacteria break down NH3 to nitrites (NO2−)
and then to nitrates (NO3-).
Denitrification



Bacteria living deep in soils and aquatic
Reduce Nitrates to Nitrogen gas (N2) so it
returns to the atmosphere
Can they keep up with the agricultural
production?
Eutrophication





Excess Nitrates leach into ground water and get into
bodies of water
Algal blooms do well with the added nutrients
(sometimes toxic)
Prevent light from hitting deeper plants that produce
O2, and their decomposition requires O2 use by the
bacteria
Reduced O2 in the water results
Nitrates are harmful to humans and other organisms
(amphibians)