1. Nitrogen Cycle
The nitrogen cycle is the biogeochemical cycle by which nitrogen is exchanged between the biosphere and living organisms.
The Earth's atmosphere is about 78% nitrogen; however, it is in the form of nitrogen gas and is unusable by most living organisms.
Nitrogen is essential for many biological processes; and is crucial for any life here on Earth.
Nitrogen helps build our proteins!

2. Nitrogen Cycle Important Vocabulary Legumes Root Nodules
Nitrogen-Fixing Bacteria

3. Nitrogen Cycle
Nitrogen in the atmosphere is unusable to plants and animals.
In order for nitrogen gas to be usable, it needs to be “FIXED.”
Nitrogen-fixing bacteria create usable forms.
Lightning also “fixes” atmospheric nitrogen.

4. Nitrogen-Fixing Bacteria
Without Nitrogen-fixing bacteria, there would not be enough usable nitrogen available to living organisms.
Nitrogen-fixing bacteria “fix,” or change the nitrogen gas from the atmosphere into a usable form for living organisms.

5. Nitrogen-Fixing Bacteria
Nitrogen-fixing bacteria live on the root nodules of legumes.
Legume plants include: beans, peas, and clover
The legumes provide habitat for the bacteria while the bacteria provide nitrogen to the plant.

6. Human Impacts on the Nitrogen Cycle
Increased global concentrations of nitrous oxide (N2O) creates acid rain.
Increased use of fertilizers increases nitrogen runoff into our waterways and contributes to eutrophication.

7. REMEMBER THIS!!!
Atmospheric nitrogen (gas) is unusable by most living organisms.
Nitrogen-fixing bacteria provide most of the usable nitrogen.
Nitrogen-fixing bacteria are found on the root nodules of legumes.

8. Nitrogen Cycle Summary
Now you have learned about the nitrogen cycle, check out the:
Nitrogen Cycle Animation

9. Questions??? Question 8: Where is most nitrogen found?
Question 9: Where does usable nitrogen come from?
Question 10: What type of relationship exists between nitrogen-fixing bacteria and legumes?