1. The Nitrogen Cycle A2 OCR Biology

2. Asking questions is a sign of INTELLIGENCE  Unfortunately all questions must wait until the end of the lecture.

3. By the end of this session I will: • be able to describe the importance of nitrogen in living systems. • outline the role of micro-organisms in the cycling of nitrogen • Describe the nitrogen cycle using the appropriate AS/A2 scientific language.  • (k) describe the role of decomposers in the decomposition of organic material; • (l) describe how microorganisms recycle nitrogen within ecosystems. (Only Nitrosomonas, Nitrobacter and Rhizobium need to be identified by name).

4. Nitrogen the basics – needed for • Nitrogen (N) is an element like carbon. All creatures need nitrogen to survive. • Nitrogen is needed for the synthesis of proteins e.g. enzymes. • Nitrogen is also an important component of nucleic acids

5. Nitrogen the basics – chemistry of • There are huge amounts of nitrogen gas in the atmosphere, but most animals and plants have no way of using it as it is very unreactive due to the triple covalent bond. • It needs to be fixed (put into a biologically useful compound). After it is fixed, it can then start to move through the cycles and organisms in an ecosystem.

6. Nitrogen the basics – sources of • Let's start with the main sources of nitrogen. Nitrogen gas is the most abundant element in our atmosphere. • The other main source of nitrogen is in the nitrates of soil. The nitrogen in the atmosphere cannot be used while the nitrates in the soil can be used by plants. Nitrogen can be converted into useful nitrate compounds by bacteria, algae, and even lightning. Once in the soil, the nitrogen becomes biologically accessible.

7. Forms of Nitrogen • Urea  CO(NH2)2 • Ammonia  NH3 (gaseous) • Ammonium  NH4 • Nitrate  NO3 • Nitrite  NO2 • Atmospheric Dinitrogen N2 • Organic N • CHEMISTS WE NOW NEED TO CORRECT SOME OF THESE IONS!!

9. Plant protein Root uptake Nitrate NO3- Nitrates are recycled via microbes Animal protein Soil organic nitrogen Ammonification Ammonium NH4+ Nitrification Nitrite NO2- Nitrification

10. Importance of bacteria in the nitrogen cycle • Nitrogen fixing bacteria • Nitrifying bacteria • Denitrifying bacteria

11. Nitrogen fixing bacteria (Mr M discuss nitrogenase here!!) Function……. …… converts nitrogen into nitrogen containing compounds E.g. …. …… Rhizobium Found in …. ….. Roots nodules of leguminous plants and soil

12. Mutualism

13. Nitrifying bacteria Function…. ….. Convert ammonia in nitrite ions and then into nitrate ions. E.g. ….. …..Nitrosomonas and Nitrobacter. Found in…. ….well aerated soils.

14. Denitrifying bacteria Function…. …. Convert nitrates into nitrogen gas Found in…. …. Sewage works, compost and wet soils

15. Nitrogen in the air nitrogen fixing plant eg pea, clover animal protein plant made protein dead plants & animals urine & faeces denitrifying bacteria root nodules (containing nitrogen fixing bacteria) decomposition by bacteria & fungi nitrates absorbed nitrates ammonia bacteria nitrites bacteria (nitrifying bacteria)

17. Other ways in which nitrogen can be fixed Lightning Haber process

18. Lightning • The electrical energy of lightning causes nitrogen gas (N2) to react with oxygen(O2) in the atmosphere to produce nitrate ions (NO3-) which reach the soil dissolved in precipitation. • Recent research suggests the amount of nitrates produced by lightning may be as high as 50%.

19. Haber process

20. Basic summary of the nitrogen cycle

21. 1) Inorganic fertilisers used on fields are washed into the lake 3) This growth causes overcrowding and many plants die due to lack of enough light or food 2) The fertiliser causes increased growth in water plants Eutrophication Yet another example of pollution, eutrophication is when lakes become stagnant due to careless use of fertiliser. There are six steps:

22. 4) Microorganisms and bacteria increase in number due to the extra dead material 6) The lack of oxygen causes the death of fish and other aquatic animals 5) These microorganisms use up the oxygen in the lake during respiration Eutrophication Can’t…breathe…

23. 4) Microorganisms and bacteria increase in number due to the extra dead material 6) The lack of oxygen causes the death of fish and other aquatic animals 5) These microorganisms use up the oxygen in the lake during respiration Eutrophication