1. The Nitrogen Cycle
Chapter 16.3

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

3. What is the nitrogen cycle?
Nitrogen from the atmosphere gets fixed, used by plants and animals, and later returned to the atmosphere.

4. It is one of nature’s great ironies…
Nitrogen is an essential component of
DNA, RNA, and Proteins.
Most living organisms are unable to use nitrogen as it exists in the atmosphere!

5. Simple Nitrogen Cycle Animation

6. End Show

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

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

9. How does atmospheric nitrogen get changed into a usable form?

10. decomposition by bacteria & fungi
Nitrogen in
the air
nitrogen fixing plant
eg pea, clover
animal protein
plant made
protein
dead plants & animals
urine & feces
denitrifying
bacteria
root nodules
(containing nitrogen
fixing bacteria)
decomposition by bacteria & fungi
nitrates absorbed
nitrates
ammonia
bacteria
nitrites
bacteria
(nitrifying bacteria)

11. Other ways that nitrogen returns to the atmosphere…
Emissions from industrial combustion and gasoline engines
Volcano eruptions

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

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

14. Biological Fixation “Nitrogen Fixing Bacteria”
Symbiotic Relationship
(“fixes” 70% of N2)

15. What is “nitrogen fixation” and what does it mean nitrogen gets “fixed”?

16. “Nitrogen Fixation” the process that breaks strong (3 covalent bonds) two-atom nitrogen molecules apart so they can combine with oxygen or hydrogen.
Oxygen
Hydrogen N N
Hydrogen N N N N
Oxygen

17. Atmospheric Fixation (5 to 8% of the Process) Lightning breaks nitrogen molecules apart . Combines with oxygen forming nitrogen oxides (N2O). N2O dissolves in rain, forming nitrates. Nitrates (NO3) are carried to the ground with the rain.
Lightning “fixes” Nitrogen! N N O
Nitrogen combines with Oxygen
Nitrogen oxides forms
Nitrogen oxides dissolve in rain and change to nitrates
(N2O)
(NO3)
Plants use nitrates to grow!

18. Industrial Fixation N N H N H3
Industrial Plant combines nitrogen and hydrogen
Ammonia is formed
(NH3)
Ammonia is used a fertilizer in soil

19. Symbiotic Relationship Bacteria Bacteria on 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.

20. 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?

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

22. What is ammonification?

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

24. Why is ammonification necessary?

25. Plants cannot use the organic forms of nitrogen which are a result of: (1) wastes (manure and sewage) (2) compost and decomposing roots and leaves

26. How does ammonification occur?

27. Bacteria converts organic nitrogen to ammonium (NH4)
Ammonium (NH4) is used by some plants
Ammonium (NH4) is stored in soil.

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

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

30. Nitrifying bacteria in soil combine ammonia with oxygen
Ammonia changes to nitrites
Nitrifying bacteria in soil convert nitrites to nitrates
Plants absorb nitrates and grow!
Ammonia
Nitrites
Nitrates
(NH3)
(NO2)
(NO3)

31. How does nitrogen re- enter the atmosphere in the nitrogen cycle?

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

33. What does denitrification do?

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

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

36. Denitrifying bacteria live deep in soil and in aquatic sediments where it is difficult for them to get oxygen. They use nitrates instead of oxygen, leaving nitrogen gas as a byproduct…completing the nitrogen cycle!
(N2)
(NO3)

37. Ammonia is converted to nitrites and nitrates.
(b)
N2O
(4) Denitrification
(1) Nitrogen Fixation
(c)
Nitrogen Cycle
(3) Nitrification
(2) Ammonification
NO3
NH3
Ammonia is converted to nitrites and nitrates.
Organic nitrogen is converted to ammonium.
Nitrates in Soil