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Nitrogen Cycle
A. Nitrogen Facts
 Makes up DNA & proteins
(muscle function).
 Help plants grow.
Where Nitrogen is Found (store):
 Atmosphere (78% is N2)
 Oceans
 Organic matter in soil

Lakes, marshes, organisms
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B. How Nitrogen Changes Form:
- N2 is not usable by plants or animals, so it has to be
converted to other forms.
- Plants can use NO3- (nitrate) and NH4+ (ammonium)
Part I. Making nitrogen into usable form (3 steps)
1. Nitrogen Fixation
 process in which nitrogen gas (N2) is converted into
a compound that contains ammonium (NH4+) or
nitrates (NO3-)
 Occurs in 3 ways:
 Atmosphere:N2  NO3 -(lightening)
 Soil: N2  NH4 + (Nitrogen fixing bacteria eg. Rhizobium)
 Water: N2  NH4 + (Cyanobacteria)
Not in the Data
Booklet
2. Nitrification


done by nitrifying bacteria.
2 Stages:
NH4+ (ammonium)  NO2- (nitrite)  NO3- (nitrate)
Step 1
Step 2
3. Uptake
 The process of taking up usable nitrogen by
plants and incorporated into plant DNA
 NO3- is sucked into plants & used for growth.
 Herbivores eat plants & use N for making
proteins & DNA.
Part II. Return N2 to ecosystem
1.Denitrification
done by denitrifying bacteria & volcanic eruptions
NO3-  N2
2.
Decomposition:
nitrogen from DNA/protein of dead organism  NH4+
(Bacteria and Fungi)
Volcanic Ash:
Return ammonia (NH3) to atmosphere
3.
C.
Human activities affect the nitrogen cycle.
1. Burning fossil fuels + Land clearing
►
NO & NO2 produced
 lead to Acid Rain
Question: Leaching of nitrogen into water ways, what
problem could this make?
Algal Bloom
2. Overfertilization
NH4+ & NO3- leach into soil
& waterways.
► huge growth in
aquatic algae =
eutrophication
Algal blooms use up all CO2
& O2, blocking sunlight and
therefore kill many aquatic
organisms.
Algal blooms can produce
neurotoxin that poison the
animals
The Phosphorous Cycle
Phosphorous Facts
 In Plant, Phosphorous contributes to root growth, stem
strength and seed production.
 In animals/human, phosphorous is important for bone
development and DNA.
Where Phosphorous is Found (storage):
 Found in phosphate rocks (PO43–, HPO42–, H2PO4-) and
sediments on the ocean floor; Not in the Atmosphere
The Phosphorous Cycle
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B.
How Phosphorous Changes Form.
1. Weathering (breaking down rock into smaller pieces).
a) Chemical weathering (Chemical reaction) :
acid rain or lichens releases phosphates (PO43- )
b) Physical weathering (physical process) :
wind, water and freezing release the phosphates.
2. Uptake: plants suck up PO43-, then are eaten by animals.
3. Decomposition: Bacteria break down organic matter &
phosphorous is returned to soil.
4. Geologic Uplift: when rocks under the ground are pushed
up  mountains  weathering (mountain building).
C. Human activities affect the Phosphorous Cycle.
1. Fertilizer, P-containing detergents, animal waste
(bird’s dropping or guano),industrial waste,
untreated human waste add additional phosphate to
the phosphorous cycle.
2. Guano: dried excrement of fish-eating sea birds,
deposited in rocky coastal regions
Q. How much phosphorus does guano contribute to
the phosphorus cycle?
2. Too much phosphorous can cause death in some
animals (Eutrophication)
How Changes in Nutrient Cycles
Affect Biodiversity
To Review:
Any significant changes to any of these nutrients (C, H, O, N
or P) can greatly impact biodiversity.
1. Carbon cycle changes  climate change & global
warming.
2. Too much nitrogen can allow certain plant species to
out-compete other species.
3. Decreased levels of phosphorous 
slow growth of algae
(important producers).
► Homework:
Pg 91 # All
► Handout from yesterday.
► Chapter 2 Test on Friday.