1. The Nitrogen Cycle

2. Why is nitrogen so important?
Nitrogen is required to make PROTEINS
Amino Acid Structure

3. Proteins are found everywhere in living organisms (plants and animals)
Muscles
DNA
Cell membranes
Enzymes

4. Where is nitrogen found in the environment?
The largest single source of nitrogen is the atmosphere
Nitrogen (N2) makes up 79% of the air we breathe.

5. The Problem:
Most living organisms are unable to use nitrogen as it exists in the atmosphere (as N2).
To enter the food chain,
nitrogen must be converted
into nitrates (NO3-1) which
can easily be absorbed by
plants to make DNA and
PROTEINS. -1

6. The Solution: Nitrogen Fixation
Nitrogen Fixation is the process that causes the strong bonds in the N2 molecules to break apart. This requires energy.
Nitrogen is said to be fixed when nitrogen combines with oxygen, forming nitrate ions (NO3-1)
Lightning and nitrogen fixing bacteria are responsible for this process.
Nitrogen + Oxygen + Energy  Nitrates

7. Nitrogen Fixation by Lightning
The energy produced by lightning splits nitrogen gas (N2) in the atmosphere allowing it to react with oxygen (O2) to form nitrates
Nitrates dissolve in rain or surface water and enter the soil where it is absorbed by plants through their roots.

8. Nitrogen Fixation by Bacteria
Nitrogen Fixing Bacteria:
found in the soil or on plant roots of legumes (clover, soybean, peas and alfalfa).
require high levels of oxygen to fix nitrogen.
fix nitrogen more often than lightning.
nodule

9. Nitrogen Movement through the Food Chain
Once nitrates are absorbed by plants, the nitrogen becomes part of the plant tissue as proteins, DNA, enzymes, etc.
Herbivores consume the plants and carnivores consume the animals, all of which have nitrogen stored in their bodies.

10. What happens to nitrogen when plants and animals die or produce waste?
Decomposers break down the dead material and waste and produce ammonia (NH3).
Ammonia is also produced by the waste/dead material itself.

11. Ammonia + Oxygen  Nitrites  Nitrates
Nitrification
Nitrifying bacteria in the soil combine ammonia (NH3) with oxygen (O2) to form nitrites (NO2-1)
Another type of nitrifying bacteria then add more oxygen to the nitrites to form nitrates (NO3-1).
These nitrates can then be absorbed by plants through their roots.
Ammonia + Oxygen  Nitrites  Nitrates
from the decomposition
of dead plants, animals
and waste

12. Nitrification

13. How is nitrogen cycled back into the atmosphere?
Denitrification:
Occurs when oxygen levels in the soil are low, such as in marches, swamps and bogs.
Denitrifying Bacteria convert nitrates back into nitrogen gas which returns to the atmosphere.

14. Review
Name and describe the three (3) processes by which nitrogen is cycled:
1. Nitrogen Fixation – forms nitrates from nitrogen gas (N2) in the atmosphere via:
 Lightning
 Nitrogen Fixing Bacteria (requires O2)
2. Nitrification – forms nitrates from ammonia (dead plants, animals and waste) via:
 Nitrifying Bacteria (requires O2)
3. Denitrification – forms nitrogen gas (N2) from nitrates via:
 Denitrifying Bacteria (does not require O2)

15. Human Impact on the Nitrogen Cycle
Excessive use of fertilizers has added
lots of nitrates (NO3-1) to the soil, leading to:
1. Eutrophication
Nitrates travel in the spring runoff and cause algae to grow rapidly in lakes and ponds.
Bacteria that decompose dead algae consume oxygen, causing less oxygen to be available for aquatic organisms  death

17. Human Impact on the Nitrogen Cycle (cont’d)
2. Acidic Soil and Water
Nitrates react with water (in lakes, ponds and soil) to produce Nitric acid
Crops fail to prosper because they cannot handle the change in pH of the soil
Decreasing pH of water causes aquatic organisms to die

18. The Nitrogen Cycle
High
Oxygen
Low
oxygen

19. Questions: pg. 69 #4,6,8,9
4. Nitrogen fixing bacteria are found in the roots of bean plants. Explain how the bacteria benefit the plant and how the plant benefits the bacteria.
Bacteria create the nitrates so that the plant can grow.
The plant makes glucose which is consumed by the bacteria so it can get energy to live (respiration).
The relationship between the bacteria and the plant is called mutualism (meaning, they both benefit each other)

20. Explain why it is a good practice to aerate lawns.

21. When you aerate your lawn, you are mixing up the soil so that there is more oxygen in it.
This increases the action of the nitrogen fixing bacteria that require oxygen. This leads to:
Increased amounts of nitrate entering the soil which is good for plants.

22. 8. Some farmers alternate crops that require rich supplies of nitrogen, such as corn, with alfalfa. However, alfalfa is usually less valuable in the marketplace than corn. Why would farmers plant a crop that provides less economic value?

23. Alfalfa roots contain Nitrogen Fixing Bacteria which will produce plenty of nitrates for the corn.
By using alfalfa, the corn that grows will be more hearty, and will be easier to sell compared to a lot of corn that is not as hearty.

24. Explain why bogs and swamps are usually low in nitrogen.
Bogs and swamps contain a lot of denitrifying bacteria.
This means that a lot of nitrate is converted into nitrogen gas, leaving very little nitrate for the plants that live in the area.
Since plants are not receiving nitrates from this source, some have evolved over time to have the ability to consume insects.

25. Insect-eating pitcher plant

26. Your Task:
Complete questions #1-3 on pg. 69

27. Pictures from: