The Nitrogen Cycle

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The Nitrogen Cycle

Ammonification

NH

Assimilation

NO

NO

NH

Nitrification

Reveal

Nitrogen (N )

About 78% of the atmosphere is nitrogen gas.

• Organisms can not use nitrogen in this gaseous form.
• A process called nitrogen fixation converts nitrogen into a form living things can use.

Nitrate Ion (No )

• Form that plants can use.

• Absorb nitrates from soil into roots.

Ammonia (NH )

Nitrogen-fixing bacteria convert the nitrogen gas into ammonia as a waste product of nitrogen fixation.

Ammonia is toxic to most living things.

Nitrogen Fixation

• Nitrogen most abundant element on Earth.
• Necessary step in order for organisms to use nitrogen to build proteins.
• Lightning in atmosphere can only fix some nitrogen,.

• Important part of cells.
• Necessary for amino acids, proteins and DNA, make chlorophyll in plants.

Ammonium (NH )

• Part of decaying process
• Plant or animal dies and decomposers like fungi and bacteria turn nitrogen back into ammonium.

• Human activity has altered cycle, adding extra nitrogen into the soil with fertilizer and other activities that result in more nitrogen entering the atmosphere.

Denitrification

• Not all nitrogen in soil is used by plants.
• Denitrifying bacteria take excess nitrogen and convert it back into nitrogen gas during this process.

Nitrogen dioxide (NO ) also known as a nitrite.

Nitrifying Bacteria

Two step process:

1) Bacteria convert ammonia into nitrite (NO2-) 2) Bacteria convert nitrite into nitrate (NO3-)