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

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

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

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.

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

Nitrogen Fixing BActeria

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

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

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

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.

Fertilizer Industrial fertilizers convert nitrogen into ammonia Can double crop yields

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

Nitrogen cycle

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.

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

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

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

Phosphorus Cycle