1. Nitrogen Cycle
Teacher Copy

2. Mineralization

3. Processes of Nitrogen Cycle
Nitrogen Fixation (includes Ammonification)
Nitrification
Assimilation (nitrogen uptake)
Mineralization (decay)
Denitrification

4. 1. Nitrogen Fixation
Fixation= turning N2 into a usable form for plants and animals
Fixation happens mostly from bacteria in the soil or in root nodules of legumes (like beans or peas)
Can also happen from lightning or volcanic activity

6. 1. Nitrogen Fixation
The bacteria in the soil or roots turn N2 into Ammonium (NH4+)
This is also known as ammonification
Plants can then absorb this ammonium (although it is not their preferred way to absorb N because ammonium is toxic in large quantities).

7. 2. Nitrification NH4+ into NO3-
Nitrifying bacteria turn ammonium (NH4+) into nitrites (NO2-) and then into nitrates (NO3-)
Nitrates are the compounds that plants usually use to gain N.
** Teacher notes
Nitrites are used to preserve processed foods (nitrogen dioxide). Nitrites kill most bacteria.

8. Mineralization

9. 2. Nitrification
NO3- is easily dissolved into water, which makes it easy for plants to absorb it through their roots but it also makes it easy to get washed out (leached) of the soil into nearby water sources
This leaching can lead to eutrophication and loss of soil nutrients

10. Checks for Understanding
1. What is the formula for atmospheric N?
2. What does it mean when we fix N?
3. List 2 ways that nitrogen can be fixed.
4. What form is N converted into when it is “fixed?”
5. What is the term for turning N2 into NH4+? N2
It is turned into a form that plants/animals can use
Lightning, volcanoes, N. fixing bacteria (mostly)
NH4+
Ammonification or Nitrogen Fixation

11. Checks for Understanding
It is turned into a form that plants/animals can use
Lightning, volcanoes, N. fixing bacteria (mostly)
NH4+
Ammonification or Nitrogen Fixation N2
It is turned into a form that plants/animals can use
Lightning, volcanoes, N. fixing bacteria (mostly)
NH4+
Ammonification or Nitrogen Fixation

12. Checks for Understanding
6. What is the term for turning NH4+ into NO3-?
7. What does NH4+ stand for?
8. What does NO3- stand for?
9. What organisms cause nitrification?
10. What form of N do plants prefer to absorb?
11. Which form of N is easily leached out of soil?
6. Nitrification
7. Ammonium
8. Nitrates
9. Nitrifying bacteria in the soil
10. NO3-
11. NO3-

13. Checks for Understanding
6. Nitrification
7. Ammonium
8. Nitrates
9. Nitrifying bacteria in the soil
10. NO3-
11. NO3-
6. Nitrification
7. Ammonium
8. Nitrates
9. Nitrifying bacteria in the soil
10. NO3-
11. NO3-

14. 3. Assimilation (Uptake)
Turns NH4+ or NO3- into organic Nitrogen (N in living things)
The ammonium or nitrates produced by N-fixing bacteria are absorbed by a plant, which turns it into organic Nitrogen by incorporating it into proteins or DNA.
When animals eat plants (or other animals), they gain organic nitrogen from the organisms they are eating
Emphasize that it’s when both plants & animals take in Nitrogen, not only plants.

15. Mineralization

16. 4. Mineralization Organic N into NH4+
When organisms die, bacteria or fungi decompose the organism and convert the organic N into NH4+ (ammonium)
This is called mineralization.
The NH4+ can either be absorbed by a plant or nitrified into NO3-

17. 5. Denitrification NO3- into N2
Denitrifying bacteria turn nitrates (NO3-) into atmospheric N2
It can also turn into small amounts of nitrous oxide (N2O), which leads to acid rain
This is the only process that removes N from the fixed reservoirs within ecosystems.
It should balance the amount of nitrogen fixed.

18. Nitrogen Cycle Animation
** There isn’t any one way for Nitrogen to move through the cycle.
There are multiple pathways that a N atom can take.
Why is the Nitrogen Cycle Important?
Nitrogen is essential for life. Without Nitrogen to make proteins and DNA, organisms will not survive.

19. HOW NITROGEN GETS INTO WATER
Runoff – Washes fertilizers/manure/urine into water
Acid rain
From either denitrifying bacteria or burning fossil fuels releasing N2O into the air, eventually forming acid rain
Animal waste
Urea is found in animal urine, which can be found in waterways or leached from the soil into waterways
Soil Leaching
Nitrates are leached from the soil into nearby waterways

21. Human Impact on Nitrogen Cycle
Fertilizers add synthetic N into water and soil
Can cause eutrophication
Burning Fossil Fuels
Releases nitrous oxides into atmosphere, leading to acid rain
Sewage & Livestock
Animal and human waste adds nitrogen to soil & water
Excess N leads to eutrophication, which leads to dead zones (no life). This can destroy fishing industries and can be potentially dangerous for tourism (swimming/boating etc)

23. Checks for Understanding
1. What is the term for plant/animal uptake of N?
2. In what two forms can plants absorb N?
3. What do plants and animals turn N into?
4. Mineralization turns ____ into ____.
5. When does mineralization occur?
6. What organisms cause mineralization?
Assimilation
NH4+ and NO3-
Proteins and DNA
Organic N into NH4+
During decomposition of organisms
Bacteria or fungi

24. Checks for Understanding
Assimilation
NH4+ and NO3-
Proteins and DNA
Organic N into NH4+
During decomposition of organisms
Bacteria or fungi

25. Checks for Understanding
Denitrification turns _____ into ________ or _________.
What organisms cause denitrification?
Why is denitrification important?
How does N get into rivers or lakes?
List 3 ways that humans impact the N cycle.
7. NO3- into N2 or N2O
8. Denitrifying bacteria
9. It balances out the amount of N2 in the atmosphere and the N fixed.
10. Runoff, leaching, animal urine & acid rain
11. Fertilizers add N, burning fossil fuels (adds N2O) and Livestock/sewage (adds N)

26. Checks for Understanding
7. NO3- into N2 or N2O 8. Denitrifying bacteria 9. It balances out the amount of N2 in the atmosphere and the N fixed. 10. Runoff, leaching, animal urine & acid rain 11. Fertilizers add N, burning fossil fuels (adds N2O) and Livestock/sewage (adds N)