The Nitrogen Cycle
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How is nitrogen stored within organisms
Within amino acids
What is deamination?
Ammonia found in excess proteins is released in the liver and converted to urea through the ornithine cycle, finally being excreted
What is saprobiotic digestion?
Proteins found in dead matter are broken sown into amino acids by decomposing bacteria and fungi
What is ammonification?
The conversion of amino acids to ammonium ions
Give the three stages of nitrification
Ammonium ions > Nitrate ions > Nitrate ions
How are ammonium ions converted into nitrates
Through nitrification carried out by nitrifying bacteria
How is the energy released from nitrification used?
Bacteria use the energy released from the oxidisation reactions for their own metabolism
What are the nitrates taken up into?
Root hair cells
Through which process are nitrates absorbed?
How are nitrates converted into amino acids?
They are reacted with glucose
Give one use for amino acids
Where does denitrification of soil occur?
Within waterlogged soil in which there is no oxygen to support aerobic nitrifying bacteria
What are nitrates converted into during denitrification and by what are they converted?
- Nitrogen gas
- Denitrifying bacteria
What happens to nitrogen gas produced during denitrification?
It escapes into the atmosphere and is lost
How is nitrogen gas converted into ammonia?
Through a reduction reaction known as nitrogen fixation
Where do nitrogen fixing bacteria live?
Within root nodules of leguminous plants such as clover and pea
How is the relationship between nitrogen fixing bacteria and leguminous plants an example of mutualism?
- Both organisms benefit:
- The plant obtains ammonia that can be used to synthesise amino acids
- The bacteria obtain sugars that can be used as an energy source
Why must fertiliser be added to crops?
In nitrate levels fall productivity is limited
What effects does rain have on nitrates?
Soluble nitrates are leeched into fresh water sources
Why are artificial fertilisers less likely to be leeched?
They are less water soluble
State two actions that increase the rate of leeching
- Removal of hedgerows
- Loss of organic matter and humus of soil
Describe the process of eutrophication
- Nitrates are leeched into fresh water
- This causes excessive growth of algae
- This mass of algae blocks light to organisms at greater depths
- Water plants and algae lower in the water can no longer photosynthesise
- Algae and water plants eventually die and sink to the bottom of the water
- Aerobic saprobiotic bacteria decay the algae and reproduce rapidly
- Increased numbers of bacteria absorb the oxygen in the water for use in respiration eventually depleting it as no photosynthesis is occurring
- Aquatic animals cannot respire aerobically and die
What effects does the presence of sewage in a water source have?
- Bacteria will feed directly from the organic matter contained within
- This decreases oxygen levels
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