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Nitrogen Cycle_ SlideShare
- 1. NITROGEN CYCLE Presented byShanza Maryam
- 2. Introduction Nitrogen is absolutelynecessary for the existence of life, as it is essential component of proteins and nucleic acids, which are vital to living organisms. Luckily the earth’s atmosphere has 78.9% of nitrogen by volume
- 3. Although nitrogen isso important for organisms and present in huge quantity in atmosphere, it cannot be used by plants and animals in gaseous and elemental form. Plants can only use nitrogen is present in the form of nitrate(NO3), nitrite (NO2) or ammonium ions(NH4).
- 4. The plants absorbnitrate compounds and ammonium ions from the soil and make proteins and nucleic acids. whereas animals get their nitrogen already fixed in plant tissues they eat. The major reservoir of nitrogen is atmosphere where nitrogen exist
- 5. Process of nitrogencycle Nitrogen cycle consists of following steps namely: 1.Nitrogen Fixation 2.Assimilation 3.Ammonification/ Decay 4.Nitrification 5.De-nitrification It is important to note that microorganisms play an important role in each of these steps.
- 6. 1.Nitrogen Fixation Theconversion of free or gaseous nitrogen into nitrate compounds or ammonia is called Nitrogen Fixation. There are three principal ways in which nitrogen fixation can occur.
- 7. (a)Atmospheric fixation: When lightningor thunderstorms occur, greater quantities of atmospheric nitrogen are turned into nitrates or nitric acid These are dissolved in rain and carried to earth. Plants acquire these when they absorb water and other minerals through their roots.
- 8. (b)Biological fixation Microorganisms capableof transforming atmospheric nitrogen into fixed nitrogen (inorganic compounds usable by plants). More than 90 percent of all nitrogen fixation is effected by these organisms, which thus play an important role in the nitrogen cycle.
- 9. Two kindsof nitrogen-fixing bacteria are recognized. The first kind, the free-living (nonsymbiotic) bacteria, includes the cyanobacteria Anabaena and Nostoc. The second kind comprises the mutualistic (symbiotic) bacteria; examples include Rhizobium,
- 10. The symbiotic nitrogen- fixingbacteria invade the root hairs of host plants, where they multiply and stimulate formation of root nodules,Within the nodules the bacteria convert free nitrogen to ammonia, which the host plant utilizes for its development.
- 11. Nitrogenase is an enzymeresponsible for catalyzing nitrogen fixation, Nitrogenase catalyzes the breaking of triple bonds between nitrogen atoms and the addition of three hydrogen atoms to each nitrogen atom.
- 12. (c)Industrial fixation It isa man-made alternative that aids in nitrogen fixation by the use of ammonia. Ammonia is produced by the direct combination of nitrogen and hydrogen. Later, it is converted into various fertilizers such as urea.
- 13. 2.Assimilation Once the nitrogenhas been fixed in the soil, plants can absorb nitrogen through their roots. This process of absorption is known as assimilation.
- 14. 3.Ammonification This is anotherprocess by which ammonia can be generated. Organic remains of plants and animals are broken down in the soil by some bacteria to release ammonia into the soil. These dead and waste matter is used by these microorganisms as food and they release ammonia into the soil
- 16. 4. Nitrification Nitrification isa two-step process in which NH3/ NH4+ is converted to NO3– . First, the soil bacteria Nitrosomonas and Nitrococcus convert NH3 to NO2– (nitrites), and then another soil bacterium, Nitrobacter, oxidizes NO2– to NO3–(nitrates).
- 17. The reaction involvedin the process of Nitrification is as follows: 2NH3 + 3O2 → 2NO2 – + 2H+ + 2H2O 2NO2 – + O2 → 2NO3 –
- 18. 6.Denitrification Most nitrate orammonia compounds in the soil are reduced again to free molecular nitrogen (N2) which is released back to the atmosphere. Reduction of nitrates into free molecular nitrogen is called De-nitrification.