This presentation is about Nitrogen Cycle.

1. NITROGEN
CYCLE
PREPARED BY:
JEANELLE A. NEVARES
BSEd 2C Biosci Major

2. What is
Nitrogen? Nitrogen (N) is an essential component of
DNA, RNA, and proteins, the building
blocks of life.
 All organisms require nitrogen to live and
grow.
 The majority (78%) of the Earth’s
atmosphere is N2.

3. Nitrogen’s triple bond
• Although the majority of the air we
breathe is N2, most of the nitrogen in
the atmosphere is unavailable for use
by organisms.
• This is because the strong triple bond
between the N atoms in N2 molecules
makes it relatively inert (like a noble
gas).

4. How Can We Use N2?
• In order for plants and
animals to be able to use
nitrogen, N2 gas must first
be converted to more a
chemically available form
such as ammonia (NH3) or
nitrate (NO3
-).
WE CAN’T!
But it IS POSSIBLE THROUGH
NITROGEN CYCLE!

5. THE NITROGEN CYCLE

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

7. THE FIVE PROCESSES IN THE
NITROGEN CYCLE

8. 1. Nitrogen Fixation
 is the process in which the N2 compound in
the atmosphere breaks and combines with
other compounds. The nitrogen is FIXED when
it combines with HYDROGEN or OXYGEN.
N
N
H
N HH
N2
Ammonia Nitrous Oxide (N2O)

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

10. 2. Nitrogen
Assimilation The process of absorbing Nitrates and
Ammonia into Organic Nitrogen.
 this organic nitrogen is transferred to animal’s
body when plants are eaten by the animals.

11. 3. Ammonification
 Organic N --> NH4
+
 Also called Nitrogen Mineralization.
 Decay of dead things, manure, etc.
 Done by decomposers (bacteria, fungi, etc.)
 During this process, a significant amount of
the nitrogen contained within the dead
organism is converted to ammonium (NH4
+).

12. 4. Nitrification
 NH3 or NH4
+ --> NO2
- --> NO3
-
 (Nitrifying) Bacteria add oxygen to nitrogen in
two steps:
 STEP 1:
Bacteria take in NH3 or NH4
+ & make NO2
- =
nitrite
 Step 2:
Bacteria take in NO2
- & make NO3
- = nitrate

13. 5. Denitrification
 NO3
- --> N2
 (Denitrifying) Bacteria do it.
 removes a limiting nutrient from the
environment and converts it back to
atmospheric N2.

14. Human Impact
• FERTILIZERS!
• Extra nitrogen fertilizer can runoff, where it
contaminates surface water or infiltrates into ground
water.
• In drinking water, excess nitrogen can lead to cancer
in humans and respiratory distress in infants.

15. Human Impact
• In surface waters, extra nitrogen can lead to
nutrient over-enrichment.
• This leads to
– fish-kills,
– harmful algal blooms,
– and species shifts in
aquatic and land
ecosystems.