2. SEMESTER 2 2012/13 BIOLOGY PRESENTATION BY: HUI SAAN LIM

3. The NitrogenCycleThe NitrogenCycle

4. Nitrogen Nitrogen is important to all life. There is an abundant supply of nitrogen in the earth's atmosphere, nearly 79% of the air is nitrogen. Nitrogen belongs to the 7 th element in the periodic table. It is found in plants and animals. Nitrogen is essential for the formation of amino acids in proteins.

5. How do plants and animals obtain nitrogen?  Nitrogen is so unreactive, it cannot be used directly by plants to make protein.  Most of the plants and animals cannot get the nitrogen they need directly from the air, it must first be fixed to a usable form.  We depend on a special kind of bacteria that can absorb N 2 gas and use it, which involves the conversion of nitrogen gas to nitrates.

6. Nitrogen fixation Nitrogen can be fixed in three ways: Atmospheric fixation This occurs spontaneously due to lightning; only a small amount is fixed this way. Industrial fixation The Haber process is used to make nitrogen fertilizers. Biological fixation Nitrogen-fixing bacteria fix 60% of nitrogen gas.

7. Atmospheric fixation The enormous energy from lightning breaks the nitrogen molecules and enables their atoms to combine with oxygen in the air, forming nitrates. Precipitation carries nitrates to the ground, where they can be assimilated by plants.

8. Industrial fixation (Haber’s process) Ammonia is produced in industry :  Under a high pressure of 200 atmospheres (atm)  Extremely high temperature of 600°C  The use of an iron catalyst Atmospheric nitrogen and hydrogen can be combined to form ammonia (NH 3 ).

9. How the Haber Process works

10. Biological fixation About 60% of nitrogen fixation is done by bacteria. There are two types of nitrogen fixing bacteria :  Free living bacteria Fix significant levels of nitrogen without the direct interaction with other organisms  Symbiotic bacteria Aztobacter

11. Symbiotic Bacteria The plant provides sugars that are used by nitrogen-fixing microorganism. The microbe provides nitrogen to the host plant. Mutualism Rhizobium inhabit the roots of leguminous plants, forming lumps or nodules where the nitrogen fixation takes place. Rhizobium uses enzyme nitrogenase to convert N 2 to NH 4 + using H + and ATP

12. Assimilation  Uptake of nitrogen by plants  The nitrates (NO 3 - ) and ammonia (NH 3 ) resulting from nitrogen fixation are used to produce amino acids.  Animals then ingest these algae and plants, converting them into body organic compounds (eg. Protein)

13. Ammonification The initial form of nitrogen is organic. Soil fungi and bacteria, convert the organic nitrogen back into ammonium (NH 4 + ). Ammonification classically occurs in the soil, in an aerobic environment. Once ammonification has been accomplished, the next stage, nitrification, can occur.

14. Nitrification Most plants cannot utilize ammonium effectively, and they require nitrate as their essential source of nitrogen nutrition. Nitrification is a process conducted by a specialized group of bacteria. Oxidation of ammonium compounds to nitrites and then to nitrates by the nitrifying bacteria.

15. Nitrification.. Nitrification is a two stage process and each stage is performed by a different group of bacteria. Oxidation of ammonium to nitrite is a function carried out by ammonium oxidizing bacteria. Nitrosococcus nitrosus, Nitrosospira briensis, Nitrosovibrio and Nitrococcus

16. Nitrification… Once nitrite is formed, it is rapidly oxidized further to nitrate, by nitrite- oxidizing bacteria. Nitrospira gracilis, Nirosococcus mobilis etc, and several fungi(e.g. Penicillium, Aspergillus) The nitrates can then be taken in by plants.

17. Nitrification Process

18. Denitrification Nitrates are reduced to nitrites and then to nitrogen gas, completing the nitrogen cycle and replenishing the atmosphere. Denitrifying bacteria: Thiobacillus denitrificans, Micrococcus denitrificans, Pseudomonas aeruginosa, etc. Conditions are anaerobic. Bacteria get the oxygen they need for respiration from the breakdown of nitrates. Denitrification can be a harmful process as fixed nitrogen is removed from the soil, making it less fertile.

20. Nitrogen Cycle Overview

22. Video https://www.classzone.com/books/ml_science_share/ vis_sim/em05_pg20_nitrogen/em05_pg20_nitrogen.s wf https://www.classzone.com/books/ml_science_share/ vis_sim/em05_pg20_nitrogen/em05_pg20_nitrogen.s wf

23. Questions 1. The relationship between Rhizobium and Legumes is A. Competitive B. Parasitic C. Predator/ Prey D. Mutualistic

24. 2. The industrial process by which ammonia is made from nitrogen gas is called A. The Ammonia process B. The Haber process C. Electrolysis

25. 3. The conversion of nitrogen gas to nitrates by bacteria is called A. Nitrification B. Nitrogen fixation C. Decay D. Denitrification E. Excretion

26. Figure 4 shows the stages in biological nitrification. 8 (c) (i) Give two ways in which ammonium ions can be produced. 1....................…….. 2............................ (2 marks)

27. Bibliography Glenn Toole(2008),AQA Biology A2 (Chapter 6) Cheltenham p.95-97 http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_ 2011/greenworld/recyclingrev2.shtml http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_ 2011/greenworld/recyclingrev2.shtml http://www.tutorvista.com/content/biology/biology- iv/ecosystem/nitrogen-cycle.php##close_iframe http://www.tutorvista.com/content/biology/biology- iv/ecosystem/nitrogen-cycle.php##close_iframe http://chemistry.about.com/od/geochemistry/ss/nitrogencycle.htm