07 Mar Nitrogen Cycle- Suitable for A-Level and IB Biology
▪79% of the atmosphere is made up of nitrogen.
▪Plants are unable to absorb nitrogen gas directly.
▪Absorption of nitrogen into plants is only as ammonium ions and nitrates.
▪ animals fulfill their nitrogen requirements from other plants and animals.
▪Nitrogen is obtain in soil in the following ways
- artificial fertilizers.
- nitric acid formed due to lightning.
- Due to biological assimilation.
This is when nitrogen gas in the atmosphere changes nitrogen containing compounds.
Biological fixation is carried out in two ways.
Non symbiotic fixation: following organisms convert N2(g) into
ammonium ions: azotobacter and clostridium,
- Plants absorb ammonium ions and synthesise nitrogenous compounds including amino acids and proteins.
- These are passed into other animals.
- Ultimately these compounds are added again to the soil by their death.
Ammonification: the above products are converted to ammonium ions by saprophytic bacteria and fungi.
- ammonium compounds in the soil are changed to nitrogen compounds.
- Ammonium ions are converted into nitrites by Nitrosomonas.
- Then nitrites are converted into nitrates by Nitrobacter
- nitrates in the soil are converted into nitrogen gas this occurs by denitrifying bacteria.
- This occurs in under anaerobic conditions.