1. Nitrogen Cycle Biology 20

3. Nitrogen Cycle Nitrogen cycle: cycling of nitrogen between organisms and environment. Nitrogen fixation: process of converting nitrogen gas into nitrates and ammonium ions. –Nitrogen-fixing bacteria: bacteria grow in root nodules of legumes. –Examples are: clover, alfalfa –This can then be used by plants.

4. Nitrogen Fixing Bacteria What kind of lawns would you find an abundance of clover? A lawn high in nitrates or low in nitrates? Explain.

5. Nitrogen Cycle Denitrifying bacteria: break down nitrates/nitrites into nitrogen gas. –This nitrogen gas re-enters the atmosphere. –Denitrifying bacteria work best in an anaerobic environment (no air). THOUGHT Question: Why do people aerate their lawns in the spring? How does this help their lawns? Explain.

6. Decaying When plants and animals decay they are turned in to ammonia, then into nitrites and finally into nitrates. These nitrates re-enter the cycle. Question: What organisms are important to the decaying process?

7. Lightning Lightning: Creates nitric acid by reacting with nitrogen gas in the air.