The Nitrogen Cycle
• All life requires nitrogen-compounds, e.g., proteins and nucleic acids.
• Air, which is 79% nitrogen gas (N2), is the major reservoir of nitrogen.
• But most organisms cannot use nitrogen in this form.
• Plants must secure their nitrogen in "fixed" form, i.e., incorporated in compounds such as:
o nitrate ions (NO3'')
o ammonia (NH3)
o urea (NH2)2CO
• Animals secure their nitrogen (and all other) compounds from plants (or animals that have fed on plants).
Four processes participate in the cycling of nitrogen through the biosphere:
• nitrogen fixation
• decay
• nitrification
• denitrification
Microorganisms play major roles in all four of these.

Nitrogen Fixation

The nitrogen molecule (N2) is quite inert. To break it apart so that its atoms can combine with other atoms requires the input of substantial amounts of energy.
Three processes are responsible for most of......

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Title: Nitrogen Cycle
Approximate Word Count: 770
Approximate Pages: 4 (250 words per double-spaced page)

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