1. Nitrogen Cycle
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2. Molecular Forms of Nitrogen
Nitrogen gas N2
NH4+
NO3-
NO2-
Ammonium
Nitrate
Nitrite

3. Nitrogen Changing Processes
The process by which nitrogen-fixing bacteria in the roots of legumes change atmospheric nitrogen to nitrates is called _______________________
The process by which N2 or organic nitrogen is changed to ammonium is called____________________
The two-step process of changing ammonium to nitrate is called _______________________
The process of changing nitrate into atmospheric nitrogen is called __________________
The process of changing nitrates into organic nitrogen is called ______________________
Nitrogen fixation
Ammonification
Nitrification
Denitrification
Assimilation

4. Background Information

5. Nitrogen Fixation by nitrogen-fixing bacteria in the roots of legumes

6. Ammonification by soil bacteria and fungi

7. Nitrification: Step 1

8. Nitrification: Step 2

9. Assimilation

10. Ammonification by Decomposers - decomposing bacteria and fungi

11. Denitrification

12. The Whole Cycle

13. Nitrogen Cycle Summary
Process
Bacteria
N Changed from
N changed to
Nitrogen Fixation
Ammonification
Nitrification step 1
Nitrification step 2
Assimilation
N/A
Denitrification
Nitrogen-fixing bacteria in legume roots
Nitrogen in air
Nitrate
Nitrogen-fixing bacteria in soil
Nitrogen in air
Ammonium
Organic nitrogen
Decay bacteria and fungi
Ammonium
Nitrite
Nitrifiying bacteria
Nitrite
Nitrate
Organic nitrogen
Nitrate
Denitrifying bacteria
Nitrogen in air
Nitrate

14. Discussion Questions
1. The atmosphere is 78% nitrogen: why do you think plants and animals can't use nitrogen as it is found in the atmosphere?
2. Explain what is meant by nitrogen fixation.
3. What is the role of bacteria in the nitrogen cycle?
4. Why don't legumes need nitrogen-containing fertilizers?
5. Why is nitrogen so important for living things?

15. Nitrogen gas nitrates organic nitrogen gas Ammomium Ammonification
Nitrogen fixation is the process that changes nitrogen from ______________
. The type of bacteria able to “fix” nitrogen are called
___________________________. Nitrogen fixing bacteria in legume roots allow
for nitrogen to be used by legume plants and become ____________________
nitrogen.
2. Nitrogen fixing bacteria in the soil change nitrogen from _________________
to ____________________ by a process called _________________________.
3. The nitrifying bacteria in the first white circle change nitrogen from
__________________________ to _____________________________ in a
process called ________________________________.
nitrates
organic
nitrogen gas
Ammomium
Ammonification
Ammomium
nitrite
nitrification

16. nitrates nitrite assimilated organic decay bacteria fungi ammonium
4. This process is continued by a second group of nitrifying bacteria that change
nitrogen from _________________________ to _________________________.
5. Nitrates can follow one of two paths. If it is taken into a plant, it will be
_____________________________ into _____________________ nitrogen.
The chipmunk gets the nitrogen it needs by eating plants. Nitrogen containing
organic wastes from either plants or animals will be broken down by
___________________________ and ___________________________ into
__________________________________.
6. Denitrifying bacteria change nitrogen from ______________________________ to
_______________________________ returning it to the atmosphere.
nitrates
nitrite
assimilated
organic
decay bacteria
fungi
ammonium
nitrate
nitrogen gas