Make your own free website on

The Nitrogen Cycle

Home | Chemical Reactions | Reserviors | Pathway of Movement | Human Intervention | Other Important Stuff | About the Students


The basic steps of the nitrogen cycle....
1) Nitrogen Fixation-- Nitrogen must be fixed in order to be used by plants, its atmospheric form is NOT usable by plants due to the triple bond. Bacteria must "fix" nitrogen into a usable form for plants. These bacteria may be found in the soil (Aztobacter) or in plant root nodules (Rhizobium).
        *So what happens next?....
                    - One of two things can happen there will either be a transfer to dead organisms which will be broken down by decomposers OR the nitrogen will proceed directly to the next step.
        * I think I just saw LIGHTNING....
                    - Did you know lightning actually fixes nitrogen in the atmosphere. I know pretty sweet, I bet you appreciate lightning now!!!
2) Ammonification- Ammonia (NH3)  is made by decomposing bacteria. Some plants are able to use ammonia.
3) Nitrification- For those plants who refuse to settle with ammonia, they undergo nitrification. Specialized aerobic bacteria convert most of the ammonia in soil to nitrite ions (NO2-) and nitrate ions (NO3-).
                *And your like okay so what....
                               - Nitrite (NO2-): is toxic to plants; plants don't want this stuff.
                               - Nitrate (NO3-): is easily taken up by plants as a nutrient; plants DO      want nitrate.
               * How can I remember which is which?
                        Nitrite has a 2 in it's chemical equation and nitrate has a 3 in it's equation. But also consider nitrate has -ate at the end of it think of it as the plant "ate" nitrate...I know brilliant.
4) Assimilation- This is when plants absorb the substances dropped off by nitrogen fixation and nitrification. Plants are able to use these ions to make nitrogen-containing organic molecules such as DNA, amino acids, and proteins.
             * Enough about plants what about the animals?
                       - Animals get their nitrogen by eating plants or plant-eating animals. If an animal wants some nitrogen he has to get through the plant first, figures.
            * Well does all the nitrate undergo assimilation?
                    - Happy you asked. There is a process called denitrification.
5) Denitrification- If the nitrate ions choose not to assimilate they leave the soil and are converted by specialized anaerobic bacteria in water-logged soil, swamps, lakes, etc. from NH3 to NH4+ back into nitrite and nitrate ions and then into nitrogen gas (N2) and nitrous oxide gas (N2O).
          * Okay and then what?
                   - Well these gases find themselves floating right back up to the atmosphere to begin the cycle again. This continues on and on and on and on...Maybe that is why they call it a cycle!

Im pretty sure that some nitrogen is being fixed somewhere in this picture. What do you think?

People shouting at the world over megaphones; Size=240 pixels wide

enjoy the site and what it has to offer


Created by APES Students:
Reshma, Elizabeth, and Darrecia