The Nitrogen Cycle

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The Nitrogen Cycle

• An essential part of proteins, DNA and other
  compounds needed for life

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Nitrogen Cycle Nitrogen Cycle Nitrogen Cycle

N2
atmosphere
lightning fixed Fertilizer Factory Fertilizer Factory
Denitrifying bacteria Denitrifying bacteria
Nitrates
Plants Bacteria
Decay Waste
Animals Ammonia
Decomposers

Bacteria in Nodules
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• Plants use nitrogen (N), phosphorus (P) and
  potassium (K) for growth.
• Earths atmosphere is 80 nitrogen gas (N2).
• Nitrogen gas is a form that very few organisms
  can use (they cant absorb it directly).
• In order to be used by organisms, nitrogen gas
  must be fixed

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Nitrogen Cycle Explained

• Nitrogen is critically important to life, as it
  is a basic building block for amino acids and
  proteins.
• Nitrogen gas in the atmosphere is composed of two
  nitrogen atoms bound to each other. Nitrogen is a
  fairly non-reactive gas it takes a lot of energy
  to get nitrogen gas to break up and combine with
  other elements, such as carbon or oxygen.

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Nitrogen Fixation

• Nitrogen gas can be taken from the atmosphere
  (fixed - reacted) in two basic ways.
• 1. Lightning provides enough energy to "burn" the
  nitrogen and fix it in the form of nitrate, NO3-.
  This process is duplicated in fertilizer
  factories to produce nitrogen fertilizers.
• 2. Nitrogen fixing bacteria use special enzymes
  to fix nitrogen (react the nitrogen with oxygen
  or hydrogen).

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Nitrogen Fixation continued

• Nitrogen gas is bound to other elements to make
  it usable by living organisms.
• add to oxygen to form NO3-- nitrate
• add to hydrogen to form NH4 ammonium
• The job of fixing nitrogen is up to certain
  bacteria that are found in the soil and water.
  The most important of these is Rhizobium, a
  bacterium that lives in nodules on the roots of
  plants like legumes (peas, beans, alfalfa and
  clover).
• Plants can absorb the fixed nitrogen through
  their roots, animals must get nitrogen by eating
  plants or other animals.

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The Cycle Begins

• 1. Most plants can take up nitrates and convert
  it to amino acids and then possibly proteins.
• 2. Animals acquire all of their amino acids when
  they eat plants (or other animals).
• 3. When plants or animals die (or release waste)
  the nitrogen is returned to the soil.
• 4. The nitrogen that is usually returned to the
  soil in animal wastes or in the output of the
  decomposers, is ammonia. Ammonia is rather toxic.
• 5. Nitrifying bacteria in soil or water convert
  ammonia to nitrates, which are taken up by plants
  to continue the cycle.

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Questions

• Page 65, 1-6
• Page 71, 13-14