Untitled Quiz

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