Nitrogen Cycle
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35 Terms
What percentage of the atmosphere is nitrogen gas?
78%
Why is atmospheric nitrogen gas inaccessible to most organisms?
It must be converted into usable chemical forms
What are the four key processes of the nitrogen cycle?
Nitrogen fixation ammonification nitrification and denitrification
What do detritivores do in the nitrogen cycle?
They feed on detritus and break it into smaller pieces
What do saprobionts do in the nitrogen cycle?
They decompose nitrogen containing molecules into simpler substances such as ammonia
What is assimilation?
The absorption of useful substances by producers and incorporation into other compounds
What is nitrogen fixation?
The conversion of atmospheric nitrogen gas N2 into nitrogen containing compounds such as ammonia
Which bacteria fix nitrogen in root nodules?
Rhizobium
Where are Rhizobium bacteria found?
In the root nodules of leguminous plants
What is the mutualistic relationship between Rhizobium and leguminous plants?
Rhizobium provides nitrogen compounds while the plant provides carbohydrates
What does Rhizobium convert N2 into?
Ammonia NH3
What is ammonia converted into in plants?
Amino acids
Which free living bacteria can fix nitrogen?
Azotobacter
What happens when free living nitrogen fixing bacteria die?
They are decomposed by saprobionts and nitrogen rich compounds are released
What abiotic processes can fix atmospheric nitrogen?
Lightning artificial fertilisers and the Haber process
What is ammonification?
The conversion of organic nitrogen containing compounds into ammonia or ammonium ions
What nitrogen containing substances can be released by death or excretion?
Urea proteins nucleic acids and vitamins
What do saprobionts produce during ammonification?
Ammonium ions NH4+
How can plants obtain nitrogen after ammonification?
They absorb and assimilate ammonium ions
What is nitrification?
The oxidation of ammonia and ammonium ions into nitrites and then nitrates
What do Nitrosomonas bacteria do?
They oxidise ammonia and ammonium ions into nitrites
What do Nitrobacter bacteria do?
They oxidise nitrites into nitrates
What is the first stage of nitrification?
NH3 and NH4+ are oxidised to NO2−
What is the second stage of nitrification?
NO2− is oxidised to NO3−
How do plants obtain nitrates?
They absorb them through their roots and assimilate them
What is denitrification?
The conversion of nitrates into atmospheric nitrogen gas
Which bacteria carry out denitrification?
Denitrifying bacteria
Under what conditions does denitrification occur?
Anaerobic conditions such as waterlogged soils
What can excessive denitrification cause?
Depletion of soil nitrogen and reduced plant growth
Why is the nitrogen cycle important?
It recycles nitrogen needed by organisms
Why is nitrogen essential for organisms?
It is needed to make proteins DNA and RNA
What could happen without the nitrogen cycle?
Ecosystems would run out of usable nitrogen
How can agriculture alter the nitrogen cycle?
It can significantly alter the natural nitrogen cycle
How can fossil fuel combustion affect the nitrogen cycle?
It can significantly alter the natural nitrogen cycle