The Nitrogen Cycle:
Who Cares?
Nitrogen is an essential
component of the amino acids
that make up proteins and is a
basic element of living things.
Elements Essential for Life

Carbon, Oxygen, and Hydrogen: needed to
create sugars (C6H12O6)& carbohydrates.
These are used for energy by living things

Carbon, Oxygen, Hydrogen, and Nitrogen:
needed to create amino acids & proteins.
These are used for building tissue by living
things.
Nitrogen, Nitrogen
Everywhere!




78% of our atmosphere is made up of nitrogen.
Atmospheric nitrogen is N2
Most organisms can NOT use N2 because of its
strong triple bonds (N=N)
Nitrogen in the atmosphere must be chemically
changed into a form that living things can
absorb
Nitrogen must be changed into nitrates (NO3)
or ammonia (NH4)
How Nitrogen is Fixed into a
Usable Form

Nitrogen Fixation: the process used to transform
atmospheric nitrogen in to a usable form

Accomplished by bacteria like (i.e. Rhizobia) and bluegreen algae

A group of nitrogen-fixing bacteria in soil converts
nitrogen into nitrate (NO3)

Rhizobia are the most important of the nitrogenfixing bacteria that live in nodules on the roots of
legumes like the pod-bearing plants such as
soybeans, peas, beans, and alfalfa
Rhizobia
Watch this!
Atmosphere
Nitrogen-fixingBacteria
Bacteria
Nitrogen-fixing
Denitrifying
nitrates to
change
NBacteria
to roots
Nitrate
(NO3)again…
ofconvert
2on
And(Rhizobia)
so begins
the cycle
legumes
nitrogen
gas in(Nnodules
2) and return it back to the
atmosphere (70% of air is made of N2)
N2 (Nitrogen Gas)
Legume Plant
(Nitrogen Gas)
Nitrate
NO
NO33
N2
Denitrifying Bacteria
Atmosphere
Nitrogen-fixingBacteria
Bacteria
Nitrogen-fixing
Denitrifying
nitrates to
change
NBacteria
to roots
Nitrate
(NO3)again…
ofconvert
2on
And(Rhizobia)
so begins
the cycle
legumes
nodules
gas (N
return
nitrogen to the
2) and in
atmosphere
N2 (Nitrogen Gas)
Legume Plant
(Nitrogen Gas)
Nitrate
NO
NO33
N2
Denitrifying Bacteria
Nitrogen Cycle
Like legume plants, lightning can fix nitrogen too
N2
Nitric
Acid
N2O
Nitrifying Bacteria

Other specialized bacteria convert the
ammonia into nitrites (NO2 ) and then nitrates
(NO3 )

Plants can only absorb nitrates or ammonium

This happens through their roots and are then
passed on to organisms that eat them
Denitrifying Bacteria


All of these activities would tend to stockpile
nitrogen in the soil if it were not for another
set of microorganisms
Denitrifying bacteria are organisms that
break down nitrogen-containing substances
and return N2 gas back into the atmosphere
More Bacteria in the Nitrogen
Cycle!

One of the major sources of nitrogen containing
materials comes from waste products of animals
(feces and urine) and from the decomposition of
dead animals and plants.

Bacteria convert these nitrogen-containing wastes
into ammonia (NH3 ) and ammonium (NH4 )
Nitrogen Cycle
A Smaller Cycle within the Nitrogen Cycle
Legume Plant
NO3 Nitrate
Wastes or
dead
Animal
animal/plant
matter is/are
decomposed
Nitrifying Bacteria
Feces &
Urine (NH4)
Eutrophication

Watch this…
Homework!


Read pages 57-60 and 63
Answer the following questions


What are the 5 human impacts and how do
they affect the nitrogen cycle?
Name three ways in which nitrogen can be
fixed