1. The Nitrogen Cycle

2. Where is nitrogen found in the environment?

3. The largest single source of nitrogen is in the atmosphere.
Nitrogen makes up 78% of our air!

4. What happens to atmospheric nitrogen (N2) in the nitrogen cycle?

5. Atmospheric nitrogen is converted to ammonia or nitrates.
Atmospheric Nitrogen (N2) N N
Nitrates (NO3)
Nitrogen combines with Oxygen to make Nitrates
Ammonia (NH3)
Nitrogen combines with Hydrogen to make Ammonia

6. Why does atmospheric nitrogen need to be converted?

7. It is one of nature’s great ironies…
Nitrogen is an essential component of DNA, RNA, and proteins—the building blocks of life.
Although the majority of the air we breathe is nitrogen, most living organisms are unable to use nitrogen as it exists in the atmosphere!

8. How does atmospheric nitrogen get changed into a form that can be used by most living organisms?

9. By traveling through one of the four processes in the Nitrogen Cycle!
(1) Nitrogen Fixation
(4) Denitrification
Nitrogen Cycle
(3) Nitrification
(2) Ammonification

10. The first process in the nitrogen cycle is… Nitrogen Fixation!

11. What is “nitrogen fixation” and what does it mean to say nitrogen gets “fixed”?

12. “Nitrogen Fixation” is the process that breaks apart the N2 n molecules found in the atmosphere so they can combine with oxygen or hydrogen. N N
Oxygen
Hydrogen
Hydrogen N N N N
Oxygen

13. There are three ways that nitrogen gets “fixed”!
(a) Atmospheric Fixation
(b) Industrial Fixation
(c) Biological Fixation
Bacteria

14. Lightning “fixes” Nitrogen!
Atmospheric Fixation (Only 5 to 8% of the Fixation Process) The enormous energy of lightning breaks nitrogen molecules apart and enables the nitrogen atoms to combine with oxygen forming nitrogen oxides (N2O). Nitrogen oxides dissolve in rain, forming nitrates. Nitrates (NO3) are carried to the ground with the rain for plants to use to grow. N N O
Nitrogen combines with Oxygen
Nitrogen oxides forms
(N2O)
Nitrogen oxides dissolve in rain and change to nitrates
(NO3)
Plants use nitrates to grow!

15. N N H
Industrial Fixation Under great pressure, at a temperature of 600 degrees Celcius, and with the use of a catalyst, atmospheric nitrogen (N2) and hydrogen are combined to form ammonia (NH3). Ammonia can be used as a fertilizer. N H3
Industrial Plant combines nitrogen and hydrogen
Ammonia is formed
(NH3)
Ammonia is used a fertilizer in soil

16. Symbiotic Relationship Bacteria
Biological Fixation (where MOST nitrogen fixing is completed) There are two types of “Nitrogen Fixing Bacteria”
Free Living Bacteria
(“fixes” 30% of N2)
Symbiotic Relationship Bacteria
(“fixes” 70% of N2)

17. Free Living Bacteria Highly specialized bacteria live in the soil and have the ability to combine atmospheric nitrogen with hydrogen to make ammonia (NH3). N N H N H3
Free-living bacteria live in soil and combine atmospheric nitrogen with hydrogen
(NH3)
Nitrogen changes into ammonia
Bacteria

18. Symbiotic Relationship Bacteria Bacteria live in the roots of legume family plants and provide the plants with ammonia (NH3) in exchange for the plant’s carbon and a protected home.
Legume plants N
NH3 N
Roots with nodules where bacteria live
Nitrogen changes into ammonia.

19. Most atmospheric nitrogen (N2) is “fixed” and changed to ammonia (NH3)
Most atmospheric nitrogen (N2) is “fixed” and changed to ammonia (NH3). Ammonia is highly toxic to many organisms. Can plants use ammonia?

20. Very few plants can use ammonia (NH3)… …but, fortunately the second process Ammonification can help!
(1) Nitrogen Fixation
(2) Ammonification

21. What is ammonification?

22. Ammonification: Bacteria decomposers break down amino acids from dead animals and wastes into nitrogen ammonium.
Bacteria decomposers break down amino acids into ammonium

23. What happens to ammonium (NH4) stored in the soil?

24. It travels through the third process of the nitrogen cycle called Nitrification!
(1) Nitrogen Fixation
(3) Nitrification
(2) Ammonification

25. Nitrifying bacteria in the ground convert the ammonium to nitrites then nitrates which green plants can absorb and use!
Nitrifying bacteria in soil combine ammonia with oxygen
Ammonia changes to nitrites
Nitrifying bacteria in soil convert nitrites to nitrates
Ammonia
Nitrites
Nitrates
Plants absorb nitrates and grow!
(NH3)
(NO2)
(NO3)

26. How does nitrogen reenter the atmosphere in the nitrogen cycle?

27. Through the fourth process called denitrification!
(1) Nitrogen Fixation
(4) Denitrification
(2) Nitrification
(3) Ammonification

28. What does denitrification do?

29. Denitrification converts nitrates (NO3) in the soil to atmospheric nitrogen (N2) replenishing the atmosphere.
Nitrogen in atmosphere (N2)
Nitrates (NO3) in Soil

30. How does the denitrification process work?
Nitrates in soil

31. Denitrifying bacteria live deep in soil and in aquatic sediments where conditions make it difficult for them to get oxygen. The denitrifying bacteria use nitrates as an alternative to oxygen, leaving free nitrogen gas as a byproduct. They close the nitrogen cycle!
Nitrogen in atmosphere closes the nitrogen cycle!
(N2)
(NO3)
Denitrifying bacteria live deep in soil and use nitrates as an alternative to oxygen making a byproduct of nitrogen gas.

32. Other ways that nitrogen returns to the atmosphere…
Emissions from industrial combustion and gasoline engines create nitrous oxides gas (N2O).
Volcano eruptions emit nitrous oxides gas (N2O).