Download Ecological Cycles Part 3

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Environmental Science: The Nitrogen Cycle – Major Assessment
DIRECTIONS: On an 11’ x 17” sheet of paper, draw an illustrated diagram of the Nitrogen cycle according to
the following directions and answer the closing questions. Use erasable pencil at first, and then color it in with
crayons, colored pencils and/or pens.
BACKGROUND
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.
DIRECTIONS
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.
(15pts)
1. Put all the forms of nitrogen from the Background section into your diagram. Add some
chemical formulas where you have room, for instance draw plenty of N2 in the air.
(5pts)
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.
(5pts)
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 the ground labeled “Nitrogen
Fixation” and the chemical reaction: N2 + O2  NO3(5pts)
4. 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+
(10pts)
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.
(5pts)
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 animal waste (tastefully!) Draw an
arrow from the animal waste into the soil and label that arrow “Decomposition releases NO3- ,
NO2- and NH4+“
(10pts)
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 “NO3- NO2- and NH4+ washes downstream.”
(5pts)
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
(5pts)
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”
(5pts)
CLOSING QUESTIONS
(20pts)
1- How does nitrogen enter the atmosphere?
2- How does nitrogen return from the atmosphere?
3- What is “Fixing Nitrogen” or Nitrogen Fixation?
4- What is denitrifying?
NEATNESS/EFFORT
(10pts)
TOTAL
PARNTERS with work done (no more than 3people in the group)
Partner
Work done
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