Nitrogen Cycle as an Essential

¶ … Nitrogen Cycle

As an essential element in the formation of amino acids and thus proteins -- the basic constituents of all organic matter -- nitrogen is a necessary nutrient to absolutely all life forms on Earth (Killpack & Bulchholz 2010). This is no less true of human beings than it is of other organisms; almost every system in the human body has at least an indirect reliance on proper nitrogen levels being maintained. All life is built of proteins, but nitrogen is even more important in terms of metabolism, growth, and reproduction (Pidwirny 2006). In addition to being one of the basic elemental constituents of amino acids and proteins, nitrogen is also necessary in nucleic acids -- like DNA -- meaning that cellular reproduction and repair cannot occur without adequate nitrogen supplies. It is for this reason that every system in human beings -- and indeed in all animals -- is dependent on nitrogen.

It would seem, then, that nitrogen must be readily available to all of these organisms, but this is not actually the case. Though nitrogen is the most abundant element in the Earth's atmosphere, nitrogen gas -- N2 -- cannot be utilized by most life forms. This is where the nitrogen cycle comes into play. Through a complex series of chemical changes wrought by various organisms and certain other processes, the nitrogen gas in the atmosphere is converted into more usable forms and, after being used as a nutrient by organisms throughout the web of life is eventually returned to the environment and the atmosphere (Elmhurst 2009). There are many different chemical changes that occur at each step in the nitrogen cycle, each of which has major important effects on both the ability for organisms to utilize nitrogen and on the environment as a whole.

It is possible for nitrogen in the atmosphere to interact with oxygen to create nitric oxide (NO) and nitrogen dioxide (NO2), both of which can be utilized by living organisms, and it is further possible for nitrogen dioxide to react with rainwater and create nitric acid (HNO3), which can also be used. The interaction of nitrogen and oxygen in the atmosphere can only occur with the temperatures and pressures associated with lightning, however, and is not the primary means of converting nitrogen to a usable form (Elmhurst 2009). Instead, nitrogen fixing (as the process is known) is carried out by certain bacteria in the soil, which convert nitrogen gas and other forms of nitrogen waste in the soil to usable form of nitrogen, especially ammonia (NH4). Plants then absorb these usable forms of nitrogen and integrate the element into their own structure through growth.