12/4/2013
What is Nitrogen?
Nitrogen is the MOST abundant element in the Earth’s
atmosphere.
•
• It makes up close to 79% of the Earth’s atmosphere.
The Nitrogen Cycle
• It is required for making DNA and proteins!
• It cannot be absorbed directly by plants and animals
until it is converted into compounds that can be used.
•The usable form of nitrogen is called
a NITRATE ION (NO3-).
How does the Nitrogen Cycle
Work?
Nitrogen Fixation (cont’d)
2) Nitrogen-Fixing Bacteria
STEP 1 – Nitrogen Fixation
Special nitrogen-fixing bacteria can convert the
nitrogen into a form that plants can use.
In order to use Nitrogen for making DNA and proteins we need it to
be in a usable form.
- These bacteria are found either in the soil or roots
of special plants (Example – soybeans, peas, clovers).
- These plants have root NODULES
- A nodule is a lump in the roots that contains the
nitrogen-fixing bacteria.
(*We need to get Nitrogen in a usable form*)
There are TWO ways of doing this:
1) Atmospheric Nitrogen Fixation
2) Nitrogen-Fixing Bacteria
1) Atmospheric nitrogen fixation
Small amounts of Nitrogen can be fixed by
Lightning.
- Nitrogen gas reacts with oxygen in the air, producing nitrates.
-These nitrates dissolve in rain or surface water – where it enters
the soil!
Nitrification
STEP 2 – Nitrification
-All organisms produce wastes and all organisms
eventually die.
-Decomposers break down the nitrogen containing
compounds in the waste or dead bodies of organisms
into AMMONIA.
-So.... Through the process of NITRIFICATION,
ammonia NH3 (from the decomposition of waste/bodies)
is converted into NITRITE ions (NO2-).
So.... We need to convert nitrITEs into nitrATEs.
How does all of this happen?
 BACTERIA!
Decomposers
Nitrogen in
waste/dead
body tissue
Nitrate Bacteria
Ammonia
Nitrite
NO2-
Nitrates
(USABLE
FORM!)
NO3-
Nitrite Bacteria
-BUT...the usable form of nitrogen is NITRATE (NO 3-).
1
12/4/2013
Denitrification
The Nitrogen Cycle
Step 3- Denitrification (The opposite of nitrification!)
-Just like we had bacteria and lightening converting
nitrogen into usable nitrates, the opposite can also occur!
- Denitrifying bacteria convert the simple nitrogen
compounds back into nitrogen gas (N2), which is then
released back into the atmosphere
Nitrates
NO3-
---------> Nitrites -----------> Nitrogen gas
NO2N2
Why do plants need Nitrogen?
Too Much Nitrogen?
2