1. The Nitrogen Cycle Section 1.9 pp. 30-33

2. Nitrogen Cycle Nitrogen is essential to living things for the production of proteins and DNA which are used to pass on the hereditary information from parent to offspring.

3. Nitrogen Cycle Even though the atmosphere is about 78% nitrogen gas, plants and animals are unable to use nitrogen gas directly as a source of nitrogen to make organic nitrogen compounds.

4. Nitrogen Cycle The nitrogen cycle can occur in both land and marine ecosystems. The nitrogen cycle of land ecosystems. Complex cycle involving many species of bacteria. Simplified into 5 steps described below.

5. Nitrogen Cycle

6. Step #1: Plants change the Nitrogen into..... In order for plants to make use of nitrogen it must first be changed into nitrates in the form of nitrate ions (NO3-) dissolved in soil water Two Pathways: A. Nitrogen Fixation by Lightning B. Nitrogen Fixation by Bacteria

7. Step #1: Plants change the Nitrogen into..... A. Nitrogen Fixation by Lightning The electrical energy of lightning causes nitrogen gas (N2) to react with oxygen (O2) in the atmosphere to produce nitrate ions (NO3-) which reach the soil dissolved in precipitation.

8. Step #1: Plants change the Nitrogen into..... B. Nitrogen Fixation by Bacteria Bacteria in the soil can change nitrogen gas (N2) into ammonia (NH3) which then dissolves in water to form ammonium ions (NH4+).

9. Step#2:Nitrification....more involvement of bacteria Nitrification a process in which ammonium ions are converted into nitrate ions. The ammonium ions are changed first into nitrites (NO 2- ) by bacteria. Then the nitrites are converted into nitrates (NO 3- ) by a different group of bacteria which live in the soil.

10. Step#3:Assimilation........the making of proteins for consumer use Assimilation process by which plants use the nitrate ions (NO3-) to make amino acids, proteins, and DNA Only the plants and some bacteria are able to carry out the process of assimilation.

11. Step#4: Ammonification.......breaking down nitrogen in dead bodies Consumer’s body contains nitrogen compounds such as proteins and DNA. Ammonification process by which bacteria and fungi break down nitrogen compounds to make ammonia. The ammonia dissolves in soil water to form ammonium ions.

12. Step#5:Denitrification........returning nitrogen back to the atmosphere During this step, nitrites are changed into nitrogen gas (N 2 ) which returns to the atmosphere. This step is essentially the reverse of nitrogen fixation and nitrification.

13. Nitrogen Cycle