Ammonification: Definition & Nitrogen Cycle

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  • 0:01 What is Nitrogen?
  • 0:42 The Nitrogen Cycle
  • 2:18 Ammonification
  • 3:37 Lesson Summary
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Lesson Transcript
Instructor: Stephanie Matalone

Stephanie taught high school science and math and has a Master's Degree in Secondary Education.

This lesson will cover the basics of the nitrogen cycle. You will learn how nitrogen gets moved around in the environment, with a greater focus on one step of the cycle called ammonification.

What Is Nitrogen?

You are a little tiny nitrogen (N) atom floating around the atmosphere in a gaseous state, the state that you and your nitrogen friends are usually in. You are an element on the periodic table that is very important to life on Earth. You make up DNA, which carries genetic information in organisms.

Image 4

You also make up about 78% of the air surrounding all living things. The problem is, you like to hang really close to your nitrogen boyfriend in the air, joining together as N2. You have a very strong bond to your nitrogen boyfriend, and the two of you are hard to break apart, which makes you unable to be used by living organisms. That is why you must go through the nitrogen cycle in order to be useful.

Nitrogen gas (N2)
Image 1

The Nitrogen Cycle

The nitrogen cycle is composed of four steps: nitrogen fixation, nitrification, ammonification, and denitrification.

Nitrogen Cycle
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During the first step of the nitrogen cycle, nitrogen fixation, you and your boyfriend (N2) are pulled out of the air by bacteria in the soil. The bacteria turns you both into ammonium by mixing you with hydrogen atoms.

Ammonium composed of one nitrogen atom (blue) and four hydrogen atoms (white)
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In the next step, nitrification, is the transition of ammonia to nitrite and then nitrate through oxidation. Look at it this way: you start off as a nitrogen atom in ammonium, surrounded by hydrogen atoms. More bacteria in the soil convert you into nitrite and then nitrate, so you are now surrounded by oxygen atoms. As part of nitrate, you can now be brought into plants through their roots in order to be used. You might then be eaten by an animal and used by it as well.

Nitrate molecule composed of three oxygen atoms (red) and one nitrogen atom (blue)
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During ammonification, the plant or animal that you are a part of dies. You are left to be converted back into ammonium by decomposers (bacteria and fungi that break down dead organisms). You are returned back into the soil and can then reenter the cycle. You can go through nitrification (step two, the previous step) again to be used by more plants and animals, or you can go through the next step, denitrification.

The last step of the cycle is called denitrification, a process in which nitrates in the soil are converted back into nitrogen (N2) to go out into the atmosphere. Bacteria help with this process, which allows the cycle to start all over again. During this step, you get reunited with your boyfriend and hang out in the atmosphere until you go through nitrogen fixation again.

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