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THE NITROGEN CYCLE for highschool student
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- 2. Learning Objective Describe hownitrogen is cycled within an ecosystem, including the roles of nitrogen-fixing bacteria (e.g. Rhizobium) and nitrifying bacteria (Nitrosomonas and Nitrobacter)
- 3. Keywords Nitrogen Nitrogenfixation Ammonification Nitrification Denitrification Bacteria Process
- 4. What is aNitrogen??
- 5. Nitrogen isin the atmosphere as N2 The majority (78%) of the Earth’s atmosphere is N2. All organisms require nitrogen to live and grow N2 is an inert gas and cannot be used by plants or animals Nitrogen limits plant growth Nitrogen is easily lost from biological systems Nitrogen
- 6. Forms of Nitrogen Urea CO(NH2)2 Ammonia NH3 (gaseous) Ammonium NH4 Nitrate NO3 Nitrite NO2 Atmospheric Dinitrogen N2 Organic N
- 7. How Can WeUse N2? In order for plants and animals to be able to use nitrogen, N2 gas must first be converted to more a chemically available form such as ammonium (NH4 + ) or nitrate (NO3 -). WE CAN’T!
- 8. Roles of Nitrogen Plants and bacteria use nitrogen in the form of NH4 + or NO3 - It serves as an electron acceptor in anaerobic environment Nitrogen is often the most limiting nutrient in soil and water
- 9. Nitrogen is akey element for: amino acids nucleic acids (purine, pyrimidine) cell wall components of bacteria
- 10. Nitrogen Cycling Processes 1.Nitrogen Fixation – bacteria convert nitrogen gas (N2) to ammonia (NH3). 2. Ammonification – bacteria and fungi decompose dead plants and animals and release excess NH3 and ammonium ions (NH4 + ). 3. Nitrification – type of chemosynthesis where NH3 or NH4 + is converted to nitrite (NO2 -) ; other bacteria convert NO2 - to nitrate (NO3 -) . 4. Denitrification – bacteria convert NO2 - and NO3 - to N2.
- 11. Nitrogen Fixation 1) HumanManufacturing Of Synthetic Fertilizers 2) Environmental 3) Nitrogen-fixing Bacteria And Cyanobacteria Means of Nitrogen Fixation:
- 12. Nitrogen Fixation HUMAN IMPACT Burning fossil fuels, Using synthetic nitrogen fertilizers, Cultivation of legumes all fix nitrogen.
- 13. Nitrate NO3 - Atmospheric fixation Out gassin g Plant protein Atmospheric Nitrogen Ammonium NH4 + Soilorganic nitrogen The human impact Biological fixation Industrial fixation
- 14. Industrial N-Fixation TheHaber-Bosch Process N2 + 3H2 2NH3 The Haber process uses an iron catalyst High temperatures (500°C) High pressures (250 atmospheres) The energy require comes from burning fossil fuels (coal, gas or oil) Hydrogen is produced from natural gas (methane) or other hydrocarbon
- 15. The future ofindustrial nitrogen fixation Food production relies heavily upon synthetic fertilisers made by consuming a lot of fossil energy Food will become more expensive to produce Nitrogen fixing microbes, using an enzyme system, do the same process at standard temperatures and pressures essentially using solar energy
- 16. Nitrogen Fixation Environmental High-energy NaturalEvents Which Break The Bond N2 Examples: Lightning Forest Fires Hot Lava Flows
- 17. Root uptake Nitrate NO3 - Plant protein Soilorganic nitrogen Nitrogen from the atmosphere Biological fixation Atmospheric fixation Out gassing Atmospheric Nitrogen 4 000 000 000 Gt
- 18. Atmospheric nitrogen fixation Electrical storms Lightning provides sufficient energy to split the nitrogen atoms of nitrogen gas, Forming oxides of nitrogen NOx and NO2
- 19. Atmospheric Pollution Thisalso happens inside the internal combustion engines of cars The exhaust emissions of cars contribute a lot to atmospheric pollution in the form of NOx These compounds form photochemical smogs They are green house gases They dissolve in rain to contribute to acid rain in the form of nitric acid The rain falling on soil and running into rivers They contribute to the eutrophication of water bodies
- 20. Nitrogen-fixing Bacteria and Cyanobacteria These bacteria form symbiotic relationships with host plants The bacteria live in nodules found in the roots of the legume family of plants (e.g. beans, peas, and clover)
- 21. The nitrogen fixers Cyanobacteria are nitrogen fixers that also fix carbon (these are photosynthetic) Rhizobium bacteria are mutualistic with certain plant species e.g. Legumes They grow in root nodules Azotobacter are bacteria associated with the rooting/soil zone (the rhizosphere) of plants in grasslands
- 22. Some arefree-living in soil (E.g., Nostoc, Azotobacter); others live symbiotically with plants (E.g., Frankia, Rhizobium). These organisms have nitrogenase, an enzyme that uses N2 as a substrate. N2 + 8e- + 8H+ + 16ATP -> 2NH3 + H2 + 16ADP + 16Pi NH3 is immediately converted to NH4+ . Bacterial enzymes sensitive to O2. Symbiotic fixation rate depends on plant stage. Nitrogen Fixing Bacteria and Cyanobacteria
- 23. In aquatic environments (like fishtanks),blue-green algae (cyanobacteria) is an important free- living nitrogen fixer. Nitrogen-fixing bacteria and cyanobacteria
- 24. Biological Nitrogen Fixation TreatmentsYield / g Oats Peas No nitrate & sterile soil 0.6 0.8 Nitrate added & sterile soil 12.0 12.9 No nitrate & non-sterile soil 0.7 16.4 Nitrate added & non-sterile soil 11.6 15.3
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- 27. The different sourcesof fixed nitrogen Sources of fixed nitrogen Production / M tonnes a-1 Biological 175 Industrial 50 Internal Combustion 20 Atmospheric 10
- 28. Mineralization or Ammonification Decomposers: earthworms, termites, slugs, snails, bacteria, and fungi Uses extracellular enzymes initiate degradation of plant polymers Microorganisms uses: Proteases, lysozymes, nucleases to degrade nitrogen containing molecules
- 29. Ammonification Process Nitrogenenters the soil through the decomposition of protein in dead organic matter Amino acids + 11 /2O2 CO2 + H2O + NH3 This process liberates a lot of energy which can be used by the saprotrophic microbes
- 30. Mineralization or Ammonification R-NH2 NH4NO2 NO3 NO2 NO N2O N2
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- 32. Nitrification (Nitrifying) Bacteria addoxygen to nitrogen in two steps: 1rst step catalyzed by Nitrosomonas. They oxidise it to nitrite: 2 NH4 + + 3 O2 2 NO2 - +2 H2O+ 4 H+ 2nd step catalyzed by Nitrobacter. They oxidise the nitrite to nitrate: 2 NO2 - + O2 2 NO3 -
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- 36. Denitrification Removes nitrogenfrom ecosystems, and converts it back to atmospheric N2. Nitrates and nitrites can be used a source of oxygen for Pseudomonas bacteria 4NO3 - + C6H12O6 2N2 + 6 H20
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- 38. Have You EverStarted a Fishtank? Why must you wait to add a bunch of fish? Like all living creatures, fish give off waste products (pee and poo). These nitrogenous waste products break down into ammonia (NH3), which is highly toxic to most fishes.
- 42. Eutrophication Nutrient enrichmentof water bodies Nitrates and ammonia are very soluble in water They are easily washed (leached) from free draining soils These soils tend to be deficient in nitrogen When fertiliser is added to these soils it too will be washed out into water bodies There algae benefit from the extra nitrogen This leads to a serious form of water pollution
- 43. Fertilisers washed intoriver or lake New limiting factor imposes itself Sewage or other organic waste Eutrophication
- 44. Increased Biochemical Oxygen Demand(BOD) Hot water from industry (Thermal pollution) Pollution from oil or detergents Reduction in dissolved O2 Making things worse!
- 45. The death ofa lake Death/emigration of freshwater fauna Methaemoglobinaemia in infants Stomach cancer link (WHO limit for nitrates 10mg dm-3 ) Increased nitrite levels NO3 - NO2 - Reduction in dissolved O2
- 46. Making things better The need for synthetic fertilisers can be reduced by cultural practices Avoiding the use of soluble fertilisers in sandy (free draining soil) prevents leaching Rotating crops permits the soil to recover from nitrogen hungry crops (e.g. wheat) Adding a nitrogen fixing crop into the rotation cycle Ploughing aerates the soil and reduces denitrification Draining water logged soil also helps reduce denitrification
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