Answer:
The nitrogen cycle is a cycle by which the nitrogen is converted into forms which are utilized by the living organisms and these forms circulates among the atmosphere, biosphere, and marine ecosystem. The conversion of nitrogen is through biological and physical processes.
Nitrogen Fixation is the first step in nitrogen cycle. It involves the conversion of atmospheric nitrogen into ammonia. This is done by bacteria like Azotobacter and Rhizobium.
Assimilation involves the absorption of ammonia by the plants from the soil.
Ammonification is the process by which the dead organic remains of plants and animals are decomposed by the soil bacteria to produce ammonia.
Nitrification is the process in which the ammonia is converted into nitrates by the soil bacteria Nitrosomonas and Nitrococcus. The nitrates are again converted into nitrites by the bacteria Nitrobacter.
On the basis of above description, the following is the match of steps of the nitrogen cycle.
A. Nitrification - bacteria convert nitrates into nitrogen gas.
D. Assimilation - plants and animals take in and use nitrogen compounds.
E. Denitrification - bacteria break down waste products and return nitrogen to the soil.
B. Nitrogen fixation - bacteria convert atmospheric nitrogen to ammonia.
C. Ammonification - bacteria convert ammonia to nitrites and nitrates