Nitrogen is essential for life but is predominantly found as unusable atmospheric N2. The nitrogen cycle converts N2 into biologically available forms through four processes: nitrogen fixation by bacteria and lightning, ammonification by decomposer bacteria, nitrification by more bacteria, and denitrification by yet more bacteria or burning of fossil fuels which converts it back to N2. Human activities like combustion, use of commercial fertilizers, and sewage discharge disrupt the natural nitrogen cycle.

1. What is Nitrogen?
Nitrogen makes up about 78%
of our atmosphere.
Nitrogen in the atmosphere it is mostly in the
N2
form of ______, which is a compound that plants
and animals cannot use.
The process of converting nitrogen into
compounds that can be used by plants and
Nitrogen Cycle
animals is called the ______________________.

2. Why we care about nitrogen…
Nitrogen is an essential
component of
DNA, RNA and Proteins
_____________________.
The building blocks of life.

3. How does atmospheric nitrogen (N2) get
changed into a form that can be used by
most living organisms?
Four
By traveling through one of the ________
processes in the Nitrogen Cycle!
(1) Nitrogen Fixation
(4) Denitrification
Nitrogen
Cycle
(3) Nitrification
(2) Ammonification

4. Process 1: Nitrogen Fixation
Nitrogen Fixation
___________________ is the process in
which the N2 compound in the atmosphere
breaks and combines with other compounds.
“fixed”
The nitrogen is _________ when it combines
hydrogen
oxyge
with ______________ or _______________.
n
N
H
H
N
N
N2
H
Ammonia (NH3)
Nitrous Oxide (N2O)

5. Three ways to “fix” Nitrogen
bacteria
Main process: Special ____________
convert the nitrogen gas (N2) to
some
ammonia (NH3), which only ________
plants can use (peas, beans).
Lightning
_________________ strikes convert
N2 to N2O or NO3.
Chemical
Industrial production. ____________
manipulation turns N2 into NH3
(Fertilizer)

6. Process 2: Ammonification
Ammonification
_____________________ - After all the living
organic nitrogen
organisms have used the ___________________,
decomposer bacteria convert the nitrogen to
ammonia
_______________.
H
N
H
Bacteria
Organic Nitrogen (proteins)
H
Ammonia

7. Process 3: Nitrification
Nitrification
_______________ is the process that
converts ammonia (NH3) into nitrites
most
(NO2) and nitrates (NO3) which ____
can
plants _______ use.
Both
Note: Ammonia comes from ______
nitrogen fixation and ammonification
How is it done?
Bacteria!
_____________________
H
H
O
N
H
N
O
O
O
N
O

8. Process 4: Denitrification
Denitrification
_______________: Process in which nitrogen
convert back
compounds _____________________ into
atmospheric nitrogen (N2 or N2O).
The main process is performed by
bacteria
_____________________ in the soil. It can
burning
also happen by _____________ fossil fuels.
N2
NO3
N2O

9. N2
N2O
(1) Nitrogen Fixation
(4) Denitrification
Nitrogen
Cycle
(2) Ammonification
(3) Nitrification
Ammonia is converted
to nitrites and nitrates.
NO3
NH3
Nitrates in Soil
Organic nitrogen is
converted to ammonia.

10. Nitrogen in
the air
nitrogen fixing
plant
eg pea, clover plant made
animal protein
protein
root nodules
(containing nitrogen
fixing bacteria)
denitrifying
bacteria
nitrates absorbed
dead plants & animals
urine & feces
decomposition by bacteria & fungi
nitrates
bacteria
(nitrifying bacteria)
ammonia
nitrites
bacteria

11. Human Impact
Combustion
___________________, releases toxic nitrogen
compounds into the atmosphere.
Commercial Fertilizers
____________________________ release
nitrous oxide into the atmosphere and introduce
excess nitrogen into the environment.
Remove nitrogen from the soil when we mine it
mineral deposits
for nitrogen rich __________________________.
Discharge of ___________________________
municipal sewage
releases excess nitrogen into the water ecosystems
which disrupts the aquatic balance and kills fish.

12. Commercial Fertilizers
Are the ______ contributor of new nitrogen in
#1
the nitrogen cycle.
limiting factor
Added because nitrogen is a ________________
for plant growth.
Problems: hard to apply fertilizer and keep it in
one area. Runoff, evaporation, etc.. So farmers
twice as much
apply about ___________________ as they
need.
food chain
Extra nitrogen disrupts the ________________.