The document discusses the nitrogen cycle, which includes the processes of nitrogen fixation, nitrification, assimilation, and denitrification. Nitrogen fixation converts nitrogen gas into ammonia through biological and non-biological means. Ammonification converts organic nitrogen into ammonium. Nitrification is a two-step process where ammonia and ammonium are converted to nitrite then nitrate. Denitrification converts nitrates back to nitrogen gas. These processes cycle nitrogen between its gaseous and fixed forms in soil and water.

1. Nitrogen cycle
Group 5
Nida Mushtaq 031
Nabeela shoukat 029
Hifza 030
Mahzaib 014
Sonia 025

2. Contents
• Introduction to nitrogen cycle
• Sources of nitrogen fixcation
• Biological
• Non biologycal
• Steps of nitrogen fixation
• Ammonification
• Nitrification
• Assimilation
• denitrification

21. Nitrogen fixation
 Deposit into soil and surface water- precipitation.
 Once settled undergo changes

 N2 + 8H + 8e → 2NH3 + H2
 Conversion via microorganisms:
 Bacteria in symbiotic relation with plants.
 Free aerobic bacteria/ algea
 cyanobacteria

24. Nitrification
 Two steps process converts NH3 / NH4+ to NO3
 In first step;
 Nitrosomanas / nitrococcus (soil becteria) convert
NH3 to No2

 1: NH3 + O2 +2e → NH2OH + H2O
 2: NH2OH + H2O → NO2 + 5H + 4e

25.  In second step:
 Nitrobacter converts NO2- to NO3-
 Bacteria gain energy known as ( nitrifying bacteria)
 NO2 + ½ O2 → NO3

26. Ammonification
 Many bacteria and fungi convert into ammonium NH4 known as
ammonification
 Converted ammonia become available to take part in other biological
processes.

37. Denitrification:
 Denitrification is the process that converts nitrate to nitrogen gas.
 Some denitrifying bacteria include species in the genera Bacillus,Paracoccus
,Pseudomonas.
 Denitrification is important in that it removes fixed nitrogen from the
ecosystem.