Briefly describe the nitrogen cycle
What will be an ideal response?
Answer: In the nitrogen cycle nitrogen is taken from the atmosphere and fixed, or converted to forms that can be used by plants and animals to build proteins and other molecules. Nitrogen fixation occurs by both natural and human processes.
Most natural nitrogen fixation takes place in the soil, by bacteria, and is then taken up in plants and incorporated in plant tissue. This nitrogen then passes from plants to the animals that consume them, before being broken down and released back to the atmosphere. Bacteria play a major role in converting nitrogen contained in biomass into mobile forms such as ammonium (NH4) and nitrate (NO3), which are readily dissolved in water. Water moving through the soil can carry this soluble nitrogen to streams and to the ocean.
Humans fix nitrogen through chemical fertilizer use. This nitrogen is added to agricultural systems from which it is spread through the environment. Vehicles and fossil-fuel fired power plants also emit large amounts of nitrogen oxides that are returned to the surface in precipitation nitrates. Today more nitrogen is fixed by humans than by natural processes.
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