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Questions and Answers
What is the primary role of nitrogen-fixing bacteria in the nitrogen cycle?
What is the primary role of nitrogen-fixing bacteria in the nitrogen cycle?
Which process involves the conversion of ammonia into nitrates?
Which process involves the conversion of ammonia into nitrates?
What is a significant environmental effect of nitrogen oversupply?
What is a significant environmental effect of nitrogen oversupply?
What process describes the return of nitrogen to the atmosphere from nitrates?
What process describes the return of nitrogen to the atmosphere from nitrates?
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How does the excessive use of nitrogen fertilizers affect aquatic ecosystems?
How does the excessive use of nitrogen fertilizers affect aquatic ecosystems?
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Study Notes
Nitrogen Cycle Overview
- Nitrogen is essential for life, forming DNA and proteins
- The atmosphere is primarily nitrogen (78%), but most organisms can't use it directly
- The nitrogen cycle involves processes transforming nitrogen into usable forms for life
Nitrogen Fixation
- The largest single source of nitrogen is in the atmosphere
- Nitrogen fixation is the first process in the nitrogen cycle, converting atmospheric nitrogen into ammonia or nitrates
- Three ways nitrogen is fixed:
- Atmospheric Fixation: Lightning energy breaks nitrogen molecules, forming nitrogen oxides which dissolve in rain to create nitrates.
- Industrial Fixation: High pressure and temperature, with a catalyst, combine atmospheric nitrogen and hydrogen to form ammonia.
- Biological Fixation: Bacteria in soil and plant roots convert atmospheric nitrogen into ammonia. Two types of bacteria involved include free-living bacteria, and symbiotic relationship bacteria.
Ammonification
- Microorganisms break down dead organisms and waste products (organic nitrogen) into ammonia (NH3), a source of nitrogen suitable for plants.
- This process is essential for making nitrogen accessible to plants as well as for soil health in general.
Nitrification
- Nitrifying bacteria convert ammonia to nitrites and then to nitrates
- Nitrates are the form of nitrogen most useful to plants
Denitrification
- Denitrifying bacteria convert nitrates back into atmospheric nitrogen (N2), completing the cycle
- Helps return atmospheric nitrogen to the environment for use in nitrogen fixation
Effects of Over Supply of Nitrogen
- Leaches nitrogen from fertilized croplands
- Environmental problems including:
- Acidification of soils and water
- Acid rain
- Increased nitrous oxide (N2O), a greenhouse gas
- Ozone depletion
- Transport of nitrogen into estuaries and coastal waters, leading to pollutants
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