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Nitrogen is needed in many biological compounds. It is present in proteins, amino acids, most vitamins, DNA, RNA…etc. In I/GCSE Biology, the following processes are important in cycling nitrogen through ecosystems:
- Feeding and assimilation – passes nitrogen atoms already in organic compounds along food chains.
- Decomposition – produces ammonia from the nitrogen in compounds like proteins, DNA and vitamins.
- The ammonia is oxidized first to nitrite, then to nitrate by nitrifying bacteria. This overall process is called nitrification.
- Absorption – of nitrates by plant roots are combined with carbohydrates from photosynthesis to form amino acids and then proteins, as well as other nitrogen compounds.
Bacteria 🦠
- Denitrifying bacteria – uses nitrates as energy source and converts them into nitrogen gas. Denitrification reduces the amount of nitrate in the soil.
- Free-living nitrogen-fixing bacteria – converts nitrogen gas into ammonia in the soil. This is used by the bacteria to make amino acids and proteins. When the bacteria die, their proteins decompose, releasing ammonia back into the soil.
- Nitrogen-fixing bacteria in root nodules – also make ammonia but this is converted by the plant into amino acids and other organic nitrogen compounds. Death and decomposition of the plant returns the nitrogen to the soil as ammonia.
Summary of Nitrogen Cycle: 👇
- Nitrogen gas in the atmosphere cannot be used directly by plants and animals due to its unreactivity.
- Nitrogen-fixing bacteria in root nodules convert nitrogen gas to ammonia (N2 – NH3).
- This is converted to proteins and amino acids by plants () OR convert nitrogen gas to ammonia and use it as proteins for themselves.
- Both plants (or animals that ate the plants) and bacteria die and their proteins and amino acids become this detritus (dead matter).
- turn these into ammonia.
- Nitrifying bacteria converts NH3 to NO2 (nitrite) and then NO3 (nitrate). This is called nitrification.
That's the end of the topic!
Drafted by Joey (Biology)