1. What is the Nitrogen cycle The nitrogen cycle is the biogeochemical cycle that describes the transformations of nitrogen and nitrogen- containing compounds in nature biogeochemical cycle nitrogen

2. Importance of Nitrogen Nitrogen is essential for many biological processes; and is crucial for any life here on Earth. It is in all amino acids, is incorporated into proteins, and is present in the bases that make up nucleic acids, such as DNA and RNA.amino acids proteinsnucleic acidsDNA RNA In plants, much of the nitrogen is used in chlorophyll molecules which are essential for photosynthesis and further growth.plants chlorophyllphotosynthesis

3. Processes of the nitrogen cycle Nitrogen fixation The conversion of nitrogen (N 2 ) from the atmosphere into a form readily available to plants and hence to animals and humans.

4. Conversion of Atmospheric Nitrogen There are three main ways to convert N 2 (atmospheric nitrogen gas) into more chemically reactive forms Biological fixation Industrial N-fixation Atmospheric fixation (lightning)

5. Biological fixation some symbiotic bacteria (most often associated with leguminous plants) and some free-living bacteria are able to fix nitrogen and assimilate it as organic nitrogen.

6. Industrial N-fixation Under great pressure, at a temperature of 600 C, and with the use of a catalyst, atmospheric nitrogen and hydrogen can be combined to form ammonia (NH 3 ). which is used to make fertilizer and explosives.

7. Atmospheric Fixation The enormous energy of lightning breaks nitrogen molecules and enables their atoms to combine with oxygen in the air forming nitrogen oxides. These dissolve in rain, forming nitrates, that are carried to the earth.

8. Assimilation Plants can absorb nitrate or ammonium ions from the soil via their root hairs. If nitrate is absorbed, it is first reduced to nitrite ions and then ammonium ions for incorporation into amino acids, nucleic acids, and chlorophyll

9. Ammonification When a plant or animal dies, or an animal excretes, the initial form of nitrogen is organic. Bacteria, or in some cases, fungi, converts the organic nitrogen within the remains back into ammonia, a process called ammonification

10. Nitrification The conversion of ammonia to nitrates is performed primarily by soil-living bacteria and other nitrifying bacteria. The primary stage of nitrification, the oxidation of ammonia (NH 3 ) is performed by bacteria such as the Nitrosomonas species, which converts ammonia to nitrites (NO 2 - ). Nitrosomonas

11. Other bacterial species, such as the Nitrobacter, are responsible for the oxidation of the nitrites into nitrates (NO 3 - ).It is important for the nitrites to be converted to nitrates because accumulated nitrites are toxic to plant life. Nitrobacter

12. Denitrification Denitrification is the reduction of nitrites back into the largely inert nitrogen gas (N 2 ), completing the nitrogen cycle. This process is performed by bacterial species such as Pseudomonas and Clostridium in anaerobic conditionsPseudomonas Clostridium

13. Human influences on the nitrogen cycle Extraction Growing of legumes Industrial extraction for fertilizer Release Burning fossil fuels Untreated sewage release Fertilizer run off

15. QUESTIONS