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Nitrogen cycle

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Nitrogen cycle

  1. 1. NITROGEN CYCLE Submitted by: Syed Usman Abdulah Roll No: 2712 (148077) Department: BS-Zoology Semester: 6th (Evening)
  2. 2. Nitrogen Cycle The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmosphere, terrestrial and marine ecosystem.
  3. 3. Nitrogen Cycle Fig.
  4. 4. Importance of Nitrogen  Nitrogen is an essential nutrient for the production of amino acids, proteins, nucleic acids, etc., and stone fruit trees require an adequate annual supply for proper growth and productivity.  Nitrogen is so vital because it is a major component of chlorophyll, the compound by which plants use sunlight energy to produce sugars from water and carbon dioxide (i.e., photosynthesis).
  5. 5. Different forms of Nitrogen  In the atmosphere, nitrogen exists as a gas (N2),  In the soils it exists as nitrogen oxide, NO, and nitrogen dioxide, NO2,  When nitrogen is used as a fertilizer, can be found in other forms, such as ammonia, NH3,
  6. 6. Reservoir of Nitrogen  The major reservoir of nitrogen is the atmosphere, where the nitrogen exists.  Atmosphere contains 78.9% nitrogen by volume.  Nitrogen is also stored in: watershed in soil, groundwater, ocean water, sediment and plant matter (dead and living).
  7. 7. Stages of Nitrogen Cycle Process of Nitrogen Cycle consists of the following steps – 1. Nitrogen fixation (N2 to NH3/ NH4+ or NO3) 2. Assimilation (Incorporation of NH3 and NO3 into biological tissues) 3. Ammonification (Organic nitrogen compound to NH3) 4. Nitrification (NH3 to NO3) 5. De-nitrification (NO3- to N2)
  8. 8. 1.Nitrogen Fixation  The conversion of free or gaseous nitrogen into nitrate compounds or ammonia is called Nitrogen Fixation.  These are three principal ways in which nitrogen fixation can occur: A. Atmospheric fixation B. Biological fixation C. Industrial fixation
  9. 9. A. Atmospheric fixation: o A natural phenomenon where the energy of lightning breaks the nitrogen into nitrates or nitric acid. o These are dissolved in rain and carried to earth. o Plants acquire these when they absorb water and other minerals through their roots. o It has been estimated that about 10% of nitrates are added to sail in this manner.
  10. 10. B. Biological fixation: The second method, which contributes 90% of fixed nitrogen to earth, is biological. It is accomplished by either, i. Free living bacteria in the soil: Among the free living bacteria responsible for nitrogen fixation are azobacter, Clostridium, Derxia and so on. These bacteria take up nitrogen from atmosphere and form ammonia. ii. Free living blue green algae: In aquatic systems Cynobacteria like, Nostoc, Anabena are important nitrogen fixer. iii. Symbiotic bacteria: Symbiotic bacteria fix far greater amount of atmosheric nitrogen than do any other organsim. E.g Rhizobium
  11. 11. C. Industrial fixation: Today large quantities of fixed nitrogen are artificially added to the agriculture soil in the form of fertilizers. The production of nitrogen fertilizers is achieved in large factories by combining nitrogen and hydrogen in the presence of heat (about 600° 𝑐 ) and high pressure. This process has increased the fertility of soil but requires large amounts of energy.
  12. 12. 2.Assimilation  Plants can absorb nitrate or ammonium from the soil by 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.  The plants may be eaten by animals that turn use the amino acids from the plants proteins in synthesizing their own protoplasm.
  13. 13. 3.Ammonification  When plants or animal die, the nitrogen present in the organic matter is released back into the soil. The decomposers, namely bacteria or fungi present in the soil, convert the organic matter back into ammonium. This process is known as Ammonification.  The bacteria responsible for ammonification are mostly Actinomycetes and species of Bacillus.  The ammonia so formed is either released to atmosphere or retained in the soil to be absorbed by plants or converted into nitrate compounds.
  14. 14. 4.Nitification  Most of the ammonia is converted into nitrate compounds by a process called Nitrification.  The Nitrification is completed into two steps, I. Firstly the ammonia is converted into nitrites (NO2). The first phase is completed by bacteria which collectively known as Nitrosofying bacteria. II. In the second phase the nitrites are converted into nitrates (NO3). Second phase is completed by nitrifying bacteria. E.g Nitrocystis,  Some nitrates are reabsorbed by plants while others are carried in streams and rivers to the oceans, where they become part of the dead sea sediments.
  15. 15. 5.De-Nitrification  Denitrification is the reduction of nitrates back into nitrogen gas (N2), completing the nitrogen cycle.  This process is performed by bacterial species such as Pseudomonas, under aerobic condition.  They use the nitrate as an electron acceptor in the place of oxygen during respiration.
  16. 16. Thank You

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