4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria (specific names of bacteria are not required).

• Nitrogen fixing bacteria - these fix the N2 in the air into useful nitrogen compounds which the plants can use. 
• Nitrifying bacteria - these turn ammonia in decaying matter into nitrates.
• Decomposers - these break down proteins and urea (from decaying matter and faeces) into ammonia.
• Denitrifying bacteria - these convert nitrates back into N2 gas. These are of no use to us.