1. THE NITROGEN CYCLE
Disclaimer: I do not believe in putting a wall of text in front of the students. I believe in using a PowerPoint as a tool for discussion. The animations and illustrations in this PowerPoint will facilitate such a discussion. I strongly recommend reading through the annotations at the bottom of each page so that you better understand my intent for how this PowerPoint should be used. I also recommend downloading and using the note sheet that accompanies this PowerPoint. Lastly, you will want to go through the PowerPoint several times before using it in the classroom so that you are familiar with the sequence and timing of the animations and how everything is grouped together. Feel free to adapt things to suit your own needs but please do not redistribute any part of this PowerPoint in its original or adapted forms without consent from me, the creator. You can contact me at Now, let’s dive in…
Short intro screen with an animated fluffy cloud and a cow… yes, a cow. The students like to make fun of the cow, which is great, because it acts as a hook. They’ll say things like “where are its utters?” or “why does it have human ears?” or similar. Just roll with the punches and be happy that they are engaged.

2. NITROGEN
I ask them which one is nitrogen, the say number 7, I click the button to confirm. I like to ask them to name something that has nitrogen in it and then to name something does NOT have nitrogen in it. You usually uncover a few misconceptions that the students have about elements.

3. NITROGEN QUICK FACTS N Nitrogen = building blocks7 N
14.01
Nitrogen = building blocks
We use nitrogen to build proteins
We use it to build each piece of DNA
It’s the #1 gas in the atmosphere – 78%
Pretty straightforward, I have them fill out the corresponding part of their notes. I talk about Carbon here because we will have already finished notes about the carbon cycle in my class. When the bird appears I give the disclaimer that sometimes I put things in my PowerPoints that really don’t have much educational value… but look at how cute it is!

4. Where do you find it? Air Live Plants Live Animals Soil Animal Waste
Dead Animals
I like to ask class members for ideas here and we fill out the “major reservoirs” part of the notes together. It’s good to emphasize that reservoirs do not just refer to water, they can refer to any matter cycle. A reservoir is simply a a place where something is temporarily stored. Feel free to comment on the expertly drawn stink lines. The beetle moving and flying off is just another thing that really didn’t need to be done, it’s just for fun. I like to say something afterwards like, “and you thought that was a hole in the tree… suckers!”
& Plants
R.I.P.
“Animal”
R.I.P.
“Plant”

5. Where else is it found? Oceans
Can’t ignore the ocean. I emphasize that everything happening on the land is also happening in the oceans.
Image Source:
Oceans

6. Where else is it found? Fertilizers
Can’t ignore manufactured fertilizers. I like to tell a little bit here about how fertilizer has changed history.
Image Source:
Fertilizers

7. N2 Nitrogen always comes in pairs when in the air…
… we call this atmospheric nitrogen (N2)
Plants and animals CANNOT use N2 to get their nitrogen!
REJECTED N2
REJECTED
Some basics about atmospheric nitrogen leading into the nitrogen cycle. This goes with the portion of the notes entitled “What is atmospheric nitrogen?” I like to recap what we know about the carbon cycle. Plants and other producers can simply pull a form of carbon right out of the air through photosynthesis – not so with nitrogen. I like to ask for class members’ thoughts on how to get around this dilemma. Living things need nitrogen, so how do they get it?

8. Luckily there are some kinds of bacteria that can change the nitrogen in the air…
into forms that plants can use
Animals can then eat those plants so that we get our nitrogen as well! N2
Accepted!
And here is the answer. Bacteria. Nothing to write down in the notes from this page, just keep their attention as you go over the pathway from atmosphere to animal.
Bacteria Image Source: Unknown
Usable
Nitrogen
Accepted!
Bacteria… not to scale

9. Nitrogen Fixing Bacteria
Bacteria changing N2 into a form that can be used by plants is called…
Nitrogen Fixation
And any bacteria that does this we call…
Nitrogen Fixing Bacteria
This covers the parts of the notes called “What is nitrogen fixation?” and “What do you call the bacteria that perform nitrogen fixation?” The sound effect, if it works, is my own lovely voice. If it bothers you feel free to take it out. I like to emphasize here that you can think of nitrogen in the air as “broken”, at least as far as most living things are concerned. These particular types of bacteria are the ones that fix it / change it so that it can be used. You can even go as far as my college professor did and say how these bacteria in the soil breathe in a gassy form of nitrogen and poop out a solid, more usable form. Gross.
(Creative, I know)

10. Nitrogen Fixing Bacteria
Nitrogen fixing bacteria refers to any bacteria that combine nitrogen with oxygen or hydrogen to create useable nitrogen for plants or animals. Useable forms of nitrogen include…
Ammonia (NH4)
Nitrates (NO3)
Rhizobium Bacteria

11. Nitrogen-Fixing Bacteria Nodules

12. N2 Review the animation Accepted! Usable Nitrogen Accepted!
This same slide is repeated 6 times without you having to do anything but pace around the classroom and help the students to draw this first portion of the nitrogen cycle in their notes in the box on the bottom of the front page. If you are using this without the notes then feel free to delete the repeated pages.
Usable
Nitrogen
Accepted!
Bacteria… not to scale

13. N2 Now review it in your notes Accepted! Usable Nitrogen Accepted!
Bacteria… not to scale

14. WRONG That’s it, we’re done, RIGHT? This is a cycle, remember?
This is where I usually end my first day of notes

15. THE NITROGEN CYCLE EPISODE II
Onward! This is where I start the second day of my notes.

16. Option A
Let’s review - see if you can tell me where “Nitrogen Fixation” is taking place in the process below…
Option D N2
Accepted!
Option B
Quick recap of last time to make sure we are all on the same page. The students make their guess on their notes as to where they think nitrogen fixation is taking place. Review what you went over on the front side of the notes and then continue on.
Usable
Nitrogen
Option C
Accepted!
Bacteria… not to scale

17. So what next? Once the nitrogen goes into animals and plants how does it get out to complete the cycle?
1. Waste
As animal waste and dead organisms are broken down by decomposers, their nitrogen is released back into the soil…
2. Death
R.I.P.
“Cow”
R.I.P.
“Plant”
This covers the next part of the notes about how nitrogen gets out of plants and animals to get on to the next stage of the cycle and the role of decomposers in that cycle. There is a lot of stuff packed on this page. Make what you will of the amazing death scene involving the cow or the slow wilting death of the flower. It’s all for student engagement.

18. N2 1. It can be reabsorbed by plants
Two things can happen from there…
1. It can be reabsorbed by plants
2. A second kind of bacteria can change the nitrogen back into N2
Nothing to write down in the notes from this page, just keep their attention as you go over the pathway from atmosphere to animal
Bacteria Image Source for the Dr. Mario Viruses (not really bacteria at all, silly): N2
Accepted!

19. Denitrifying Bacteria
The process where bacteria change usable nitrogen back into N2 is called…
Denitrification
This covers the parts of the notes called “What is denitrification?” and “What do you call the bacteria that perform denitrification?” The sound effect, if it works, is my own lovely voice (again, feel free to delete it if it bothers you). I like to emphasize here that you have a mini “cycle within a cycle” here where nitrogen can keep being reused without going back to the atmosphere (plant to animal to waste to plant to animal to waste, etc.), but that doesn’t give us a complete cycle on the larger scale. If we didn’t have some way to get nitrogen BACK to the atmosphere as N2 then the cycle would be broken. These bacteria are the ones that “break” or “free” the nitrogen. You can even go as far as my college professor did and say how these bacteria in the soil eat the solid more usable version of nitrogen and … ahem… “fart”… out a gaseous less usable form. Gross.
And we call the bacteria that do this…
Denitrifying Bacteria

20. N2 N2 We have a cycle… Accepted! Usable Nitrogen Accepted! R.I.P.
“Cow”
R.I.P.
“Plant”
I have them draw the second half of the cycle in the box on their notes at this time. It will automatically repeat 4 times without you having to do anything. If you don’t use the notes then feel free to delete the extra pages. It can be tricky for students to draw a static diagram from this animated version, so I like to pace around the classroom while it’s playing and make sure that they are doing it right. I also like to go over it together on the board afterwards.
Usable
Nitrogen N2
Accepted!
Bacteria… not to scale

21. N2 N2 N2 Atmosphere Nitrogen Fixation Denitrification Decomposers
This is a static version with arrows showing the whole cycle, it might help them to better visualize it for their notes
Consumption
Waste
Nitrogen Fixation
Denitrification
Death
Root Absorption
Decomposers
Nitrogen Fixing Bacteria
Cycle within a cycle
Denitrifying Bacteria

22. 1. Fertilizer Overload So how are humans affecting the Nitrogen Cycle?
You can go as deep or as shallow as you like with the next few pages. With fertilizer overload I focus on Algael Bloom caused from agricultural runoff into marine ecosystems and the potential hazards that may result.

23. Algal Bloom1: http://oceanservice.noaa.gov/hazards/hab/hab.jpg
“Blooms of harmful algae, collectively known as HABs, can deplete the oxygen and block the sunlight that other organisms need to live, and some HAB-causing algae release toxins that are dangerous to animals and humans.”

24. 1. Fertilizer Overload 2. Air Pollutants
So how are humans affecting the Nitrogen Cycle?
1. Fertilizer Overload
2. Air Pollutants
With air pollutants I focus on Nitrogen Dioxide and its health impacts.

25. Car Exhaust: http://assets.slate.wvu.edu/resources/300/1315413746.jpg

26. 1. Fertilizer Overload 2. Air Pollutants 3. Greenhouse Gases
So how are humans affecting the Nitrogen Cycle?
1. Fertilizer Overload
2. Air Pollutants
3. Greenhouse Gases
With greenhouse gases my class will have already had an extensive unit on the carbon cycle and global warming so I just do a quick recap – just like CO2 is a greenhouse gas, so is Nitrous Oxide which is commonly said to be about 300 times more potent than CO2 per unit weight but that there is also 1000’s of times less of it.

27. Laughing Gas Lady: http://www.himisaxenadental.com/serimg/LaughingGas.JPG
Laughing Gas Small:

28. Greenhouse Gas Chart: http://www. eia

29. Legumes Lightning What else should I know about the nitrogen cycle?
LIGHTNINGED!
This is just a bit of “FYI” for the students, it is not on the notes. I talk about the relationship that legumes have with many nitrogen fixing bacteria and I mention how nitrogen fixation occurs naturally in the air by means of lightning

30. Legumes Lightning What else should I know about the nitrogen cycle?
This is just a bit of silliness to wrap things up, feel free to delete it if it’s not your style

31. IT’S OVER! Legumes Lightning
What else should I know about the nitrogen cycle?
Legumes
Lightning
And we close with a beetle departure

32. N2 N2 N2 Atmosphere Nitrogen Fixation Denitrification Decomposers
Here is the whole cycle again for review purpose or questions if desired
Consumption
Waste
Nitrogen Fixation
Denitrification
Death
Root Absorption
Decomposers
Nitrogen Fixing Bacteria
Cycle within a cycle
Denitrifying Bacteria