4.3.2 The Nitrogen Cycle Flashcards
What is Nitrogen, as an element required for?
to make proteins
Why can’t neither plants nor animals absorb nitrogen from the air?
as N2 gas is very stable and the bonds holding the nitrogen atoms together would need massive amounts of energy to break
- the two nitrogen atoms in a nitrogen molecule are held together by a triple covalent bond
There are two ways Nitrogen can be taken out of the air and converted into something easier to absorb, what are they?
1. Nitrogen fixing bacteria found ‘free living’ in soil and also in the root nodules of certain plants (peas, beans, clover – we call them leguminous plants) take N2 gas and change it into nitrates in the soil
Plants absorb the nitrates they find in the soil and use them for what?
the nitrogen in them to make proteins
Animals eat the plants (or other animals) and get the nitrogen they need from the, what?
proteins in the plant or animal
Waste (urine and faeces) from animals sends nitrogen back into the soil as, what?
ammonium compounds (the urea in urine contains nitrogen)
When the animals and plants die, what happens?
they decay and all the proteins inside them are broken down into ammonium compounds and put back into the soil by decomposers
The plants can’t absorb ammonium compounds though, so a second type of soil bacteria, called?
nitrifying bacteria
What does nitrifying bacteria do?
It converts the ammonium compounds to nitrites and then to nitrates, which can then be absorbed by plants – and so the cycle goes on
Finally, there is a third, unhelpful type of (anaerobic) bacteria called, what?
denitrifying bacteria
Where is denitrifying bacteria found?
found in poorly aerated soil (ie not much oxygen)
These bacteria take the nitrates out of the soil and convert them into what?
back into N2 gas
Farmers can help reduce the amount of these unhelpful bacteria by, doing what?
ploughing and turning over soil
