The Nitrogen Cycle
Nitrogen is extremely abundant in the atmosphere. However, it is not easy to acquire directly from the abiotic environment. Nitrogen enters and leaves the atmosphere through a complex biochemical pathway in the nitrogen cycle.
Most of the nitrogen used by living things is taken from the atmosphere by certain bacteria in a process called nitrogen fixation. These micro-organisms convert nitrogen gas into a variety of nitrogencontaining compounds including nitrates, nitrites, and ammonia. Lightning and ultraviolet light also fix small amounts of nitrogen. In addition, humans add nitrogen to the soil as fertilizer.
Once in the soil ecosystem, the nitrogen-rich compounds are available to producers. After the nitrogen is absorbed, it is passed from producer to consumer and on up the food chain. Many animals consume more nitrogen than they can use and excrete the excess in the form of urea and ammonia. A dead organism’s nitrogen-rich compounds are taken in by decomposers or are released back into the environment. These compounds are either recycled again by soil micro-organisms or they are converted by denitrifying bacteria into nitrogen gas which then re-enters the atmosphere.

Questions
1.
In what way do human activities influence the nitrogen cycle?
2.
Plants need nitrogen to produce proteins, DNA and other important chemicals.
Describe how nitrogen in the atmosphere makes its way into plants.
3.
What is the role of decomposers in the nitrogen cycle?
4.
How would aerating your lawn help grass grow greener and fuller?
5.
What do you think is the function of fertilizers? Explain the importance of fertilizers.
6.
Draw a diagram of the nitrogen cycle for a farm or garden where manure is used.
7.
How might the colour of plant leaves indicate the nitrate content of nearby soil?
8.
As a class we have discussed how several elements are cycled through an ecosystem.
Briefly explain what would happen if the following could not be recycled: Carbon,
Nitrogen, Hydrogen, Oxygen.