Download The Nitrogen Cycle

The Nitrogen Cycle
The information and the flow charts below gives some of the interrelationships in the
nitrogen cycle.
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All life requires nitrogen-compounds, e.g., proteins and nucleic acids.
Air, which is 79% nitrogen gas (N2), is the major reservoir of nitrogen.
But most organisms cannot use nitrogen in this form.
Plants must secure their nitrogen in "fixed" form, i.e., incorporated in
compounds such as:
o nitrate ions (NO3-)
o ammonia (NH3)
o urea (NH2)2CO
Animals secure their nitrogen (and all other) compounds from plants (or
animals that have fed on plants).
Four processes participate in the cycling of nitrogen through the biosphere:
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nitrogen fixation
decay
nitrification
denitrification
Microorganisms play major roles in all four of these.
Reference
http://helios.bto.ed.ac.uk/bto/microbes/nitrogen.htm
1
Use the flow chart of the nitrogen cycle (and/or any other suitable diagram)
to rearrange these statements into a correct sequence.
It might be a good idea to write out the stages (using the numbers) in the
form of a cycle.
1
Some nitrogen is fixed by lightning The enormous energy of lightning breaks nitrogen molecules and
enables their atoms to combine with oxygen in the air forming nitrogen oxides. These dissolve in
rain, forming nitrates that are carried to the earth.
2
Biological nitrogen fixation requires a complex set of enzymes and a huge expenditure of ATP.
Although the first stable product of the process is ammonia, this is quickly incorporated into protein
and other organic nitrogen compounds.
3
Decomposers break down the molecules in excretions and dead organisms into ammonia.
4
Some bacteria oxidise ammonia (NH3) to nitrites (NO2-).
5
Denitrification reduces nitrates to nitrogen gas, thus replenishing the atmosphere. Denitrifying
bacteria live deep in soil and in aquatic sediments where conditions are anaerobic. They use nitrates
as an alternative to oxygen for the final electron acceptor in their respiration.
6
Animals eat plant protein and digest it into amino acids
7
Animals convert ammonia into urea
8
Bacteria break down animal and plant protein into amino acids
9
Nitrogen fixers convert atmospheric nitrogen into ammonia
10
Some bacteria oxidise nitrites to nitrates (NO3-).
11
Amino acids are absorbed into the blood of animals
12
Amino acids are made into protein in animal cells
13
Plants convert nitrate ions into ammonium ions and use them to make amino acids
14
Amino acids are made into protein in plant cells
15
Urea is filtered from the blood in the kidney
16
Bacteria deaminate amino acids to make ammonia
17
Animals deaminate amino acids to make ammonia
18
Urea passes out of animal bodies in urine
19
Bacteria break down urea to ammonia
20
Urea travels through the blood from the liver to the kidneys
21
Under great pressure, at a temperature of 600°C, and with the use of a catalyst, atmospheric
nitrogen and hydrogen (usually derived from natural gas or petroleum) can be combined to form
ammonia (NH3). Ammonia can be used directly as fertilizer, but most of it is further processed to urea
and ammonium nitrate (NH4NO3).
2
Try to make links between the topics in the cycle and the rest of the your AS
specification.
Can you build up a mind map to help link things together to see the ‘global view’?
Follow up questions.
1
Identify which statements apply to the following bacteria:
Rhizobium
Nitrosomonas
Nitrobacter
2
What are the problems that are created by the use of nitrogen-based
fertilisers?
3
Where are you in the nitrogen cycle?
4.
What happens in the following processes:
nitrification
nitrogen fixation
denitrification
decomposition?
3