The Nitrogen Cycle

1. The Nitrogen Cycle Nycole C. & Deja M.

2. What is Nitrogen? • Nitrogen is the most abundant element in the atmosphere. • Organisms need nitrogen in relatively high amounts. Because of this, nitrogen is often a limiting reagent meaning that a lack of nitrogen constrains the growth of the organism • Nitrogen is used to form amino acids and nucleic acids. • Nitrogen makes about 3% of total body weight in humans • Earth’s atmosphere is 78% by volume.

3. How the cycle works. • Nitrogen is introduced to the soil by precipitation (rain, lighting). Some root nodules can also convert nitrogen in the soil into nitrates. • Plants build up proteins using nitrates absorbed from the soil. • When animals like cows, eat these plants, they in turn use it to build animal protein. • When these animals (cows) poop, pee or die, the urea, excreta or carcass are broken down by decomposers and the nitrogen is re-introduced into the soil in the form of ammonia. • Nitrates in he soil can also be broken down by denitrifying bacteria and sent into the air as nitrogen. • Once nitrogen gets back into the air, the cycle continues.

4. Nitrogen Cycle Steps • 1. Nitrogen Fixation- Converting N2 from atmosphere • 2. Assimilation- Producers take up converted N2 ( Either NH4+ or NO3-) and consumers eat producers. • 3. Ammonification-Decomposers break down bio nitrogen compounds into ammonium. • 4. Nitrification- Nitrifying bacteria convert ammonium. • 5. Denitrification- Denitrifying bacteria convert nitrate into nitrogen gas (N2)

5. Nitrogen Fixation (Biotic) • Since a vast majority of all nitrogen in earth’s atmosphere is in the form of nitrogen gas (N2), most producers can not use it. Very few organisms such as blue green algae and certain bacteria that live within the roots of legumes (peas and beans) can break the N2 bond. These bacteria add hydrogen ions to form NH3.

6. Nitrogen Fixation (Abiotic) • Nitrogen can also be fixed in abiotic ways… • N2 can be fixed in the atmosphere by lightning or combustion processes such as fires and the burning of fossil fuels. These processes convert N2 into nitrate (NO3-), which is usable by plants. The nitrate is carried to Earth’s surface as precipitation. • Humans have also developed techniques for converting N2 gas into ammonia or nitrate to be used in plant fertilizers. Although this technique requires a lot of energy, humans now fix more nitrogen than is fixed in nature. The development of synthetic nitrogen fertilizers has led to large increases in crop yields particularly for crops such as corn that require large amounts of nitrogen.

7. Assimilation • Assimilation occurs after producers take up either ammonium or nitrate and then consumers feed on producers, some of that nitrogen is assimilated into the tissues of the consumers and some is eliminated as waste products.

8. Ammonification and Nitrification • In Ammonification, fungal and bacterial decomposers use nitrogen contain wastes and dead bodies as a food source and excrete ammonium. • After ammonification, Nitrification takes place and the excreted ammonium is converted into nitrite (NO2-) and then into nitrate (NO3-) by specialized nitrifying bacteria.

9. Denitrification • The last step of the nitrogen cycle involves several steps. Because negatively charged particles repel one another, negatively charged nitrite ions do not bond easily to soil particles, most of which are negatively charged. As a result, nitrate is readily transported through the soil with water this is called Leaching. Leached nitrates eventually settle in the bottom of oceans and swamps. Under these conditions, denitrifying bacteria convert nitrate in a series of steps into the gaseous nitrous oxide (N2O) and eventually, N2 which is emitted back into the atmosphere.

10. Human impacts on the nitrogen cycle • One way that humans greatly impact the nitrogen cycle is by adding too much nitrogen to the atmosphere. This occurs from humans combusting fossil fuels at an accelerated rate. Combusting fossil fuels releases nitric oxides into the air. • Another way that humans alter the nitrogen cycle also involves heavy amounts of nitrogen and plants. Increased nitrogen inputs lead to dominance of fast-growing plant species, with associated declines in species richness.

11. Game • How to Play: • 1. Go over Nitrogen Poster to explain movement of nitrogen in an ecosystem. • 2. Student will become nitrogen molecules and travel to various stations and record • their journey. • 3. Handout worksheets, mat boards and pencils. • 4. Assign each student to a station. Have them write this station as #1 on their • worksheet. • 5. When game begins, students will reach into the bowl without peeking and take • out one card. Students look at the picture and write down the next station the • card indicates for them to head as #2. The card is returned to the bowl before the • student leaves the station. Continue the same procedure at each station. • 6. If a student has a “Stay” card, they must write down “stay” and take another turn. • If there is a line waiting at the station, they should go to the end of the line. • 7. When students have completed up to #15, they should move away from the • stations. To finish the worksheet, students need to draw arrows from picture to • picture to represent their journey starting with #1 and ending at #15. They should • indicate a “Stay” at a station by circling the picture.

12. Quiz Time! • What is a limiting reagent? • What percent of Earth’s atmosphere is nitrogen? • What are the 5 steps in the nitrogen cycle? • Name one biotic and one abiotic factor in the nitrogen cycle. • Name one organism that can convert N2 into a form that most producers can use, NH3. • True or False? Animals absorb nitrogen from eating producers. • What is the nitrogen cycle? NH3