1. Learning outcomes Describe the cycle of carbon through the ecosystem Describe how humans have affected the carbon cycle

2. How humans affect the cycle Human activity has affected the balance of the carbon cycle by Think, pair share  Burning down forests – reduces CO 2 absorption by photosynthesis, increases CO 2 formation by combustion  Burning fossil fuels

3. Nitrogen Cycle

4. Nitrogen Essential element Used in proteins, enzymes, antibodies, hormones, cell membranes Often in short supply in biological system Very stable in its molecular form (N 2 )

5. Sources of Nitrogen 1.78% of the atmosphere is made up of nitrogen 2.Ammonia (NH3) from excretion and decay of organic matter (mineralization) Only a few organisms can use it in these forms All others must have it converted to a nitrate ion (NO 3 - )

6. Nitrogen fixation Requires a large amount of energy Can be done by – Lightening strikes – Nitrogen fixing bacteria - Rhizobium – Free living soil bacteria – Blue-green algae (Cyanobacteria) – Industrial processes

7. Atmosphere to Plants – Ammonification Nitrogen fixing bacteria living freely in the soil change atmospheric nitrogen (N 2 ) to ammonia (NH 3 ) E.g. Azotobacter

8. Atmosphere to plants – Nitrification I The ammonia that is free in the soil is then turned into a nitrite ion (NO 2 - ) by nitrifying bacteria such as Nitrosomonas This is an aerobic reaction requiring oxygen

9. Atmosphere to plants – Nitrification II The nirtite ion (NO2-) is then changed into the nitrate ion (NO3-) by a different nitrifying bacteria (Nitrobacter) This is an aerobic reaction requiring oxygen The nitrate ion is now available for plants to absorb

10. Atmosphere to plants – Symbiotic relationship Rhizobium is a bacteria living in a mutualistic relationship in the nodules of legumes. Converts atmospheric nitrogen (N2) into ammonia (NH3) This is then used by the plants to make its own organic compounds In exchange the Rhizobium gets carbohydrates, proteins and environment with the right amount of O2 for the nitrogen fixing reaction

11. Rhizobium

12. Denitrification The reduction of nitrates (NO 3 - ) to nitrogen gas (N 2 ) Replenishes the atmosphere with nitrogen Done by bacteria in anaerobic conditions

13. Human effect on Nitrogen cycle

14. Nitrogen cycle

15. Biozone pages 109 and 110