Tuesday, 21 June 2011

4.10 Nitrogen Cycle

describe the stages in the in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria
N2 
Nitrogen consists of 78.324% of the atmosphere
Unreactive, abundant

Uses of nitrogen in plants:
Plant takes in N03(Nitrates) to make amino acids(CHON) and then made into protein. DNA contains nitrogen.


How does nitrogen in the atmosphere transfer into the soil?
Lightening can combine atmospheric nitrogen and oxygen to form nitrate, lightening has sufficient energy to do so however, this is rare, does not give enough nitrates for plants to grow.

Food Chain
Nitrogen can pass through trophic levels in the form of protein.

Excretion
In animals the urea+water=>urine which is a return of nitrogen to the soil

Decomposition
Decomposers can take urine/urea along with the decaying organic molecules and break them down to ammonia (NH3) However, this cannot be used for growth of plants.

Nitrifying bacteria
It changes NH3 (ammonia) into No2-(nitrite) and then into No3 (nitrate) which can be used

Freeliving Bacteria
Freeliving bacteria in the soil (not directly related to the plant) can turn atmospheric nitrogen into nitrate in the soil that plant uses. N2=>NO3-

Nodules
There are some plants structures on the roots called nodules, e.g. Legumi (beans, clover), these are capable of taking atmospheric nitrogen into nitrate.

Denitrifying bacteria
They take nitrate back to nitrogen.

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