The Nitrogen Cycle
From the Air We Breath to the Fertilizer We Use, Nitrogen is Everywhere
To Understand the Problem is to Discover the Solution
Nitrogen is all around us. We commonly think of the air that we breathe as being mostly oxygen. In fact it’s actually a mix of gasses and nearly 80% of that mix is nitrogen. Nitrogen in the atmosphere comes in a chemical shape called diatomic, meaning that two nitrogen atoms are bonded together. This bond is one of the strongest on Earth. Think of the two molecules as powerful magnets. When aligned in the right shape they stick together and it’s very hard to pull them apart.
Atmospheric
fixation is probably the most exciting of the three processes. It occurs
when the enormous energy of lightning
breaks apart the nitrogen molecules allowing them to bond with oxygen
in the air forming nitrogen oxides. These chemicals dissolve easily into
rain
that is then carried down to the Earth.
These
critters contain a complex set of enzymes
called nitrogenase,
the only known biological elements capable of breaking the powerful triple
bond of the nitrogen molecule. Imagine this enzyme like a lock where only
a certain key fits. Nitrogenase has two keyholes, one for nitrogen and
one for hydrogen.
When the two elements fit into the keyholes, the nitrogenase enzymes break
the bond between the two nitrogen molecules and connect them with hydrogen.
Using tremendous amount of energy called ATP,
nitrogenase squeezes together one nitrogen molecule and three hydrogen
molecules forming two weak ammonia
molecules (NH3).
Plants take up nitrogen either as ammonia, nitrate, or
nitrite via their roots. Animals get their nitrogen from the food they
consume, passing the nitrogen farther and farther up the food
chain. Ammonia is also a byproduct of metabolism,
the process by which creatures generate energy from food. Ammonia is toxic
and if too much builds up in the body it can be fatal. So creatures have
developed a clever way to remove nitrogen from their bodies. In mammals
and other animals, the kidneys
produce a chemical called urea,
made up of carbon
dioxide, nitrogen and hydrogen. For most birds and reptiles,
ammonia is excreted in the form of uric
acid.
Nitrogen is all around us. We commonly think of the air that we breathe as being mostly oxygen. In fact it’s actually a mix of gasses and nearly 80% of that mix is nitrogen. Nitrogen in the atmosphere comes in a chemical shape called diatomic, meaning that two nitrogen atoms are bonded together. This bond is one of the strongest on Earth. Think of the two molecules as powerful magnets. When aligned in the right shape they stick together and it’s very hard to pull them apart.
Nitrogen, a Cornerstone of Life
Nitrogen is also one of the building blocks of life on this planet. It is one of the major components of amino acids the building blocks of protein. Without protein our bodies could not make muscle. Nitrogen also helps form nucleic acid a vital component of DNA. DNA is the genetic code that creates the blueprint to make the many different types of cells our bodies needs to survive. From the tiniest insect to the largest Blue Whale, DNA guides the formation and growth of these creatures. Without nitrogen life as we know it couldn't exist.What is the Nitrogen Cycle?
We mentioned in an earlier segment of this webpage about the power of the diatomic bond between two nitrogen molecules and how it was one of the strongest bonds on Earth. But somehow, nitrogen has to get from the atmosphere into a form that our body can use. Life on this planet cannot use nitrogen in its most common N2 form. Through one of the most important biogeochemical cycles on the planet called The Nitrogen Cycle this important nutrient is “fixed”.
Fixation
The nitrogen molecule is very inert. The molecules are happy in their N2 form and would like to stay that way. So breaking them apart requires a lot of energy, in a process called fixation. This energy occurs on Earth in these main places: the atmosphere, in tiny microbial bacteria, or with the help of industry.Atmospheric Fixation
Atmospheric
fixation is probably the most exciting of the three processes. It occurs
when the enormous energy of lightning
breaks apart the nitrogen molecules allowing them to bond with oxygen
in the air forming nitrogen oxides. These chemicals dissolve easily into
rain
that is then carried down to the Earth. Biological Fixation
Only a very select few bacteria and archaea (think of these as very primitive bacteria) have the ability to fix nitrogen. Some of these bacteria live symbiotically with plants like soybeans and alfalfa. Cyanobacteria, sometimes called blue green algae, fix nitrogen in aquatic environments. Others might establish a relationship with trees like alders. Still others live inside the bodies of insects like termites or live freely in the soil.These
critters contain a complex set of enzymes
called nitrogenase,
the only known biological elements capable of breaking the powerful triple
bond of the nitrogen molecule. Imagine this enzyme like a lock where only
a certain key fits. Nitrogenase has two keyholes, one for nitrogen and
one for hydrogen.
When the two elements fit into the keyholes, the nitrogenase enzymes break
the bond between the two nitrogen molecules and connect them with hydrogen.
Using tremendous amount of energy called ATP,
nitrogenase squeezes together one nitrogen molecule and three hydrogen
molecules forming two weak ammonia
molecules (NH3). Nitrification
Although ammonia can be used by some plants, most plants use nitrite (NO2) or into Nitrate (NO3). Bacteria species like Nitrobacter and Nitrosomas bacteria - generally called nitrifying bacteria - convert ammonia in the soil into this more usable form.Nitrogen Assimilation
Plants take up nitrogen either as ammonia, nitrate, or
nitrite via their roots. Animals get their nitrogen from the food they
consume, passing the nitrogen farther and farther up the food
chain.