The Nitrogen Cycle
Nitrogen: Unfortunately, this tends to be the most confusing cycle, but (hopefully) the coloring diagram will help to explain it a little easier. For this one, it may be easiest to color as you go to show the steps in order.
First things first, it’s important to understand that nitrogen is everywhere. Approximately 80% of every breath we take is pure nitrogen. However, exactly 100% of the nitrogen we breathe in is completely useless to us. The nitrogen in the air is a nitrogen gas that our bodies cannot use. In order to use nitrogen from our environments, heterotrophs and many autotrophs need to rely on other organisms to “fix” the nitrogen into a form we can use. Fortunately there are numerous ways for this to happen. Let’s explore.
Nitrogen and You: Why You Should Love It
Nitrogen is incredibly important to all living things. Nitrogen is a building block for all proteins that make up who you are. It also helps to make up your DNA, which is, in short, everything of who you are. No need to get into that just yet, we will save the discussion of DNA for another day. Just know that without nitrogen you would have no muscles, skin, nails or hair.
How Nitrogen Cycles
As we had already learned, the nitrogen that we breathe in all the time is useless to the human body. It will all start with the box labeled (I). Label this nitrogen gas.
The three arrows coming off of this box (not squiggly) should be colored red because, remember, this gas is no good for us.
Now, there are three different ways that this can be converted into nitrates, the form we can use to help make us hairy, strong, and covered in skin. The first is through, believe it or not, lightning. This process causes a reaction that converts nitrogen gas into nitrates in the soil, where it can be taken up by plants. If you look at your coloring chart, A shows this conversion. In the box labeled (II) write nitrates. Any arrows that show the conversion of nitrogen gas into nitrates should be colored purple. The process of converting nitrogen gas into a usable form, nitrates, is called nitrification.
The second way this conversion happens is through a special root system of certain plants. Plants known as legumes like peanuts and beans have a special node on their root system. This is labeled as (B). The arrow that points from nitrogen gas to the bean plants should be colored purple.
The third is with the help of nitrogen-fixing bacteria. These special bacteria (at C) help to convert this gas into a nitrate as well. This process is a bit more confusing than this (it’s actually a three step process, involving the conversion of nitrogen gas into ammonium, then nitrites) but I tried to make a confusing cycle less confusing, and let’s face it, I’m sure you don’t mind getting the shorter version of this biogeochemical cycle. The arrow going to the letter C from nitrogen gas should be colored red, the arrow going to nitrates from the letter C should be purple. Can you see how it shows the change?
Use It or Lose It
When this nitrogen is converted into a nitrate, it won’t stay there for long. So how do we get it?
Similar to the phosphorus and carbon cycles, we get it from our food. The producers are able to leech the nitrates from the soil, using it to grow. Without enough nitrogen plants end up looking pretty bad.
Some sorry looking corn due to a lack of Nitrogen.
The process of taking up nitrogen in the form of a nitrate is indicated with the arrow near the letter D. Color this arrow something other than purple or red. The bird is then able to gain the nitrates from eating the producers. When the bird dies, it does not turn into a rabbit as the picture indicates. That was a poor drawing on my part, I am sorry.
However, when a dead organism (like a rabbit) sits in the soil, it will break down. Also, when the rabbit produces waste (like the feces located next to it) this too will break down. There is some nitrogen in these, and with decomposition this nitrogen is returned to the soil. For all purposes, assume that the nitrogen fixing bacteria will get this nitrogen usable for everyone in the form of a nitrate. Color these arrows whatever color you used for arrow D.
Opportunity Only Knocks Once
As we know, there is a lot of useless nitrogen gas in the atmosphere. However, if there are all these processes converting this gas into nitrates then why is there still this useless nitrogen gas?
This is because there are some bacteria, called denitrifying bacteria that will convert nitrates back into nitrogen gas. This process is called denitrification and is indicated with the squiggly line. Color this in with a different color than purple, red, and whatever you chose for the movement of the nitrates.
So there you have it, the nitrogen cycle. Confused yet? Don’t be. All you really need to see here is that nitrogen is useless in the air. With the help of things that fix the nitrogen, we get a usable form called nitrates. These are given to us through our food. However, if not used they undergo denitrification, and are converted into the useless gas again.
Name: ______Period: ______Date: ______
Nitrogen Cycle Questions
You should have colored and labeled already. If you haven’t, read the passage. If you have, color the environment before/during/after answering these.
1. How much of the air we that we breathe in is nitrogen?2. How much of the nitrogen in the air that we breathe can humans use?
3. What are the three ways that nitrogen can be converted into a form that we can use?
4. What is the name of the this process?
5. What is the name of this form of nitrogen we can use?
6. How is nitrogen returned to the soil from dead organisms and wastes?
7. How is nitrogen converted back into nitrogen gas?
8. What is this process called?
9. A scientist has recently created a fertilizer that helps plants to grow with a lot of phosphorus and a chemical that kills bacteria in the soil. However, he noticed that even with a lot of phosphorus the plants are looking overall, pretty terrible. Create a hypothesis explaining why you think this may be happening.