Ecological Cycles Part 3- An illustrated Diagram of The Nitrogen Cycle
Take an 11’ x 17” sheet of paper and draw an illustrated diagram of the Nitrogen
cycle according to the following directions. Use erasable pencil at first, then color
it in with crayons, colored pencils and/or pens.
This assignment is DIFFERENT from the Carbon cycle diagram because
different chemical reactions are involved. Other than that, it is very similar.
Draw a landscape showing plenty of atmosphere, ocean, and land (both above
and below sea level). Be sure to include a lake or swamp, and soil and
sediments.
Most of the nitrogen on earth takes the following forms:
In the atmosphere:
N2 = Nitrogen molecule.
(The two nitrogen atoms are held together by a triple bond, which is very
hard to break. In fact, only a few bacteria have ever learned how. Turning
N2 into other chemical forms that organisms can use is called FIXING
NITROGEN.)
Dissolved in seawater, freshwater, and in soil:
N2 = Nitrogen molecule
NO3- = nitrate ion
NO2- = nitrite ion
NH4+ = ammonium ion
(The last three are the forms that plants can use)
In the Biomass (mostly trees, grass, and plankton)
Living organic tissue (Nitrogen is an important part of DNA, chlorophyll
and proteins.) Write “DNA, proteins and chlorophyll” inside a tree or plant.
Dead organic matter
1. Put all these forms of nitrogen into your diagram. Add some chemical
formulas where you have room, for instance draw plenty of N2 in the air.
2. Bacteria living in the roots of certain plants like beans and alfalfa FIX
nitrogen from the atmosphere. So draw an arrow from the air going into
some clover or beans and label it “Nitrogen Fixation” and include the
chemical reaction: N2  Living organic tissue.
3. Lightning bolts in the atmosphere also fix nitrogen. The nitrate rains out
with raindrops. So draw a lightning bolt, some rain, and an arrow down to
drake.marin.k12.ca.us/academics/rock/nitrogen_cycle.doc
the ground labeled “Nitrogen Fixation” and the chemical reaction: N2 + O2
 NO34. Fertilizer factories turn N2 from the atmosphere into ammonium. So draw
a fertilizer factory (any industrial-looking building) and an arrow going from
the air through the building and into the ground. Label the arrow “Nitrogen
fixation” and include the chemical reaction: N2 + H2  NH4+
5. Plants take up nitrogen through their roots. Draw arrows from the soil into
the plants, label the arrows “Plants take up NO3- , NO2- and NH4+” Draw
arrows to the proteins, DNA and chlorophyll molecules in plants.
6. Animals eat plants, and each other. Living animal tissue becomes dead
organic tissue. Bacteria and Fungi decompose the dead tissue and
release the nitrogen into the soil and water. So, draw an animal eating
some of the plants. Draw the animal pooping (tastefully!) Draw an arrow
from the animal poop into the soil and label that arrow “Decomposition
releases NO3- , NO2- and NH4+“
7. NO3- , NO2- and NH4+ also wash downstream into lakes, swamps, and
oceans, so draw an arrow from the soil into the wetlands and label it “NO 3NO2- and NH4+ washes downstream.”
8. In swamps and sediments where there is no oxygen, a type of bacteria
called DENITRIFYING BACTERIA take the oxygen from NO3- and turn it
back into N2, which goes back into the atmosphere. So draw an arrow
from a swamp into the air labeled “Denitrification” and include the
chemical reaction: NO3-  N2
9. N2 moves freely between the atmosphere and water and soil, so draw a
double-headed arrow between water and soil and label it “N2 exchange”
Your Instructor will show you some examples
drake.marin.k12.ca.us/academics/rock/nitrogen_cycle.doc