The Nitrogen Cycle

Biological Importance

Nitrogen is a constituent of amino acids, proteins, nucleic acid as well as a plant nutrient.

Different Forms of nitrogen

Used by plants

1.       Ammonium 

2.       Nitrate 

3.       Amino acids

Used by bacteria

1.       Ammonium

2.       Nitrate

3.       Amino acids

4.       Nitrite 

Used by animals (only organic forms)

1.       Amino acids

Since different organisms require different forms of nitrogen, there is the nitrogen cycle that provides them with the appropriate forms.

Sources of Nitrogen

·         Nitrogen gas – atmosphere which consist of 78% nitrogen

·         Bound nitrogen – soils, sediments of lakes, rivers and oceans

·         Dissolved nitrogen – surface water and ground water

Key processes

Nitrogen Fixation

Nitrogen rich waste from animals is converted into nitrates by nitrifying bacteria.

Nitrogen is also fixed by nitrifying bacteria in soil and by symbiotic (recall: a relationship between two types of animal or plant in which each provides for the other the conditions necessary for its continued existence) bacteria that live in nodules. The bacteria convert nitrogen gas in the atmosphere into ammonia. This passes out of the root nodules, dissolves in soil water and is then taken up by plant roots.

(Do you see why this relationship between the bacteria and the plant is symbiotic? Both parties benefit as the plant get a steady supply of nitrogen and the bacteria get a constant supply of sugars from the plant)

Some nitrogen is also fixed by lightning, known as atmospheric nitrogen fixation.Lightning discharges ozidize nitrogen gas to nitrate, which ends up in the soil.

Ammonification

Ammoification decomposes organic nitrogen to ammonium. Bacteria and fungi carry out most of the ammonification in the nitrogen cycle.

Nitrification
Ammonium is oxidized to nitrate by nitrifying bacteria such as Nitrosomonas while other bacteria such as Nitrobacter oxidize nitrite to nitrate .

Denitrification

Denitrifying bacteria such as Pseudomonas denitrificans reverse the process and return fixed nitrogen to the atmosphere

Feelings

Learning the nitrogen cycle has allowed me to realize the importance of nitrogen in our daily life. Before this lesson, I did not know that different organisms is only suited to certain forms of nitrogen. For example, animals can only used organic forms of nitrogen. It is also interesting that organisms on earth share such intimate relationships, where they depend on one another for survival. If the nitrogen cycle lacks any one of the organism, it would result in many implications. I believe many other biological process in life also work the same whay, where one cannot do without another.