1. The Nitrogen and phosphorus cycles
Unit A: 3.3
The Nitrogen and phosphorus cycles

2. Nitrogen cycle Required so that cells can make proteins
Required to synthesize deoxyribonucleic acid (DNA)

3. Nitrogen Fixation
Nitrogen gas makes up nearly 79% of Earth’s atmosphere
However, nitrogen must be converted into nitrate (NO3) in order to be useful to plants

4. Nitrogen fixation (continued)
Two ways atmospheric nitrogen can be converted into nitrate: 1) Lightning – a small amount of nitrogen gas in the atmosphere is converted, using the energy from lightning to react with oxygen to form nitrate.

5. Nitrogen Fixing Bacteria – produce the majority of nitrates found in ecosystems
Found mostly in soil
Can be found in nodules on the roots of legumes (clover, soybeans, peas and alfalfa)
Aboriginal peoples used the practice of planting the “three sisters” corn, beans and squash to capitalize on the properties of each plant to improve growing conditions of the soil

6. Nitrogen Fixing BActeria

7. Ammonification
Fungi and bacteria (decomposers) convert nitrogen in organic molecules from decomposed organic wastes and dead organisms into ammonia (NH3)

8. Nitrification
Bacteria convert ammonia into nitrites and still other bacteria convert nitrites into nitrates.
These bacteria require oxygen to function
The nitrates are then absorbed by plant roots, converted into plant proteins and then consumed by animals, beginning the cycle again

9. Denitrification
During the decay process, bacteria can break down nitrates into nitrites and then into nitrogen gas that is released back into the atmosphere
These bacteria do not require oxygen

10. Process of aerating
Exposing denitrifying bacteria to oxygen reduces the breakdown of nitrates into nitrogen gas, causing more nitrates to remain in the soil for plant use.

11. Fertilizer Industrial fertilizers convert nitrogen into ammonia
Can double crop yields

12. Negative effects of fertilizer
Too much fertilizer can affect the acidity of soil
Accumulation of nitrogen and phosphate fertilizers can increase algae growth, increase bacteria that feed on dead algae and cause a decrease in the oxygen levels in lakes and ponds. This can lead to the death of fish and other aquatic animals

13. Nitrogen cycle

14. The Phosphorus Cycle
Phosphorus is essential for the formation of cell membranes, DNA, and the calcium phosphate of bones.
The phosphorus cycle has a long-term cycle that involves the rocks of the Earth’s crust and can take millions of years.

15. Long-Term Cycle Phosphorus is found in bedrock
Erodes from rock and dissolves in water
Absorbed in photosynthetic organisms
Passed into food chains
Phosphates eroded from rocks are carried into rivers and then the ocean
Phosphates in the ocean are absorbed by algae, plants and enter the marine food chain

16. Long-Term Cycle (Continued)
Marine animals use phosphates to make bones and shells
Dead marine animals form deposits on the ocean floor and eventually form rock
Geological up-thrusts bring the phosphorus back to Earth’s surface to begin erosion and starts the long-term cycle again

17. Phosphorus Short Cycle
Photosynthetic organisms take in phosphates through their roots
Phosphates enter the food chain
Wastes and dead tissue are recycled by decomposers and release the phosphates which are carried back into the water supply where they are again absorbed by photosynthetic organisms

18. Phosphorus Cycle