Write concisely on all of the following aspects of the Nitrogen cycle to illustrate the importance of biogeochemical cycling:  Explain what you understand by term biogeochemical cycling. 2. Why is nitrogen fixation important and under what circumstances does it occur? 3. Describe the two-step process that makes up nitrification. 4. Assimilation of NH3 (ammonia) into organic nitrogen-containing compounds (amino acids - glutamate and glutamine) 5. Denitrification