2. The Nitrogen Cycle My power point presentation is going to be about the nitrogen cycle.

3. The Nitrogen cycle Plants and animals need a supply of nitrogen to make proteins. Proteins are essential for growth and other life processes. The atmosphere of earth contains huge quantities of nitrogen gas. However plants can only obtain their nitrogen from the soil in the form of NITRARES. Animals can get their nitrogen only by eating plants or other animals. The nitrogen in the air can be converted into NITRITES in a variety of ways:

4. Nitrifying bacteria There are at least two types of nitrifying bacteria in the soil: nitrate bacteria ammonium oxygen nitrate bacteria nitrites oxygen = NITRATES By this sequence nitrogen in proteins is changed into a form which can be absorbed by plant roots.

5. Transformation of plant and animal protein Saprotrophic, or putrefying bacteria and fungi decompose proteins in dead animals and plants. In this process ammonia is released and immediately dissolves in soil water. Here, the ammonia combines with soil chemicals to form various ammonium compounds which converted into nitrates by nitrifying bacteria.

6. Picture of Bacteria

7. Nitrogen-fixing bacteria Bacteria of this type use carbohydrates and atmospheric nitrogen to make compounds which are eventually released in the soil as NITRATES. This process is called nitrogen-fixation. Some of these bacteria obtain carbohydrates from the soil humus. Others live inside the root cells of leguminous plants (e.g. peas, beans, clover and vetches) where they cause tiny swellings called root nodules. Here the bacteria obtain both protection and carbohydrate from the plant cells, and in return they release nitrates into the plant tissues and the soil. Leguminous plants are often cultivated in order to increase the nitrate content of agricultural soils.

8. Root nodules on a Legume

9. Lightning During lightning flashes extremely high temperatures is generated. This result in nitrogen combining with oxygen to form nitrous and nitric oxide gases. These gases dissolve in rainwater and form nitrous and nitric acid. These acids soak up into the soil where they react with other chemicals to form NITRATES.

10. Picture

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