A2 BiologyYear 13
Unit 4Populations
and Environment
NITROGEN CYCLE
Identify the microbes involved in ammonification, nitrification, denitrification, and nitrogen fixation
Describe how nitrogen gas can be converted into useful organic forms
Explain why it is important for plants in low nitrate conditions to have symbiotic relationships with bacteria
Explain how ammonification, nitrification, nitrogen fixation and denitrification contribute to the nitrogen cycle
So why do plants struggle to get enough nitrogen?
N2
N2
78% of the Earth’satmosphere is N2
There’s lots of Nitrogen around!It is an inert gas (the triple bond makes it very stable) so not easy to break apart in chemical reactionsPlants and Animals cannot use N2
Plants must secure their nitrogen in "fixed" form, i.e., incorporated in compounds such as:
– nitrate ions (NO3-)
– ammonia (NH3)/ammonium (NH+4)
Look at each of the information cards
Each one talks about one part of the nitrogen cycle (the numbers on the cards indicate which part of the diagram they refer to)
Use the cards to complete the diagram to explain what is happening at each arrow
Words in purple are keywords you should use on your diagram. You must also add extra detail for some steps (eg. Enzymes involved)
The Nitrogen Cycle
Found in
roots
of
legumes
Man
y plan
ts ha
ve a
sym
biotic
relati
onsh
ip with
fung
i call
ed
myc
orrh
izae t
hat i
ncre
ases
the s
urfa
ce ar
ea of
the r
oot
syste
m. A
ctive
tran
spor
t use
d
Nitroge
nase e
nzyme
needed
Protease and
deaminase enzymes
needed
How do plants survive where there
are few microbes to convert nitrogen?
Bacteria on the roots of legumes fix N2 into ammonia, which is
absorbed by plant roots. Explain why nitrogen fixing
bacteria in the root nodules of leguminous
plants are an example of mutualism
The soil is waterlogged. Denitrification by bacteria
returns nitrogen to the atmosphere.
Why are carnivorous plants found in waterlogged soil?
An animal dies and ammonification is carried out by decomposers, turning the nitrogen compounds in their cells into an
ammonium compound. What is the benefit of this to plants?
Ammonia created by saprobionts is made into nitrates by nitrifiying
bacteria during nitrification. What are the 2 steps in nitrification?
Example question and answerExplain why nitrogen fixing bacteria in the root nodules of leguminous plants are an example of mutualismAnswer:Nitrogen fixing bacteria convert nitrogen gas, which is inaccessible to plants directly, into nitrates. This can be taken up directly by the roots of the plant. The bacteria themselves get glucose that the plant makes. This is useful because it can be used in respiration by the bacteria. Nitrogen fixing bacteria need lots of glucose.
A=Add something they have missedB= Build on an idea * that could be more
detailedC= Challenge/Correct anything you disagree
with
Example question and answerExplain why nitrogen fixing bacteria in the root nodules of leguminous plants are an example of mutualismAnswer:Nitrogen fixing bacteria convert nitrogen gas, which is inaccessible to plants directly, into nitrate. This can be taken up directly by the roots of the plant. The bacteria themselves get glucose that the plant makes. This is useful because it can be used in respiration by the bacteria. Nitrogen fixing bacteria need lots of glucose.
A=Add something they have missedB= Build on an idea * that could be more
detailedC= Challenge/Correct anything you disagree
with
Example question and answerDescribe how waterlogged soil can cause nitrate to be removed from the soilAnswer: Flooded wetlands give an opportunity for nitrogen fixation process to take place. In this process, nitrate is converted into nitrogen gas, which is released into the atmosphere. Denitrification requires aerobic conditions. Useful nitrogen fixing bacteria are not able to survive in these conditions.
A=Add something they have missedB= Build on an idea * that could be more
detailedC= Challenge/Correct anything you disagree
with
Example question and answerDescribe how waterlogged soil can cause nitrate to be removed from the soilAnswer: Flooded wetlands give an opportunity for nitrogen fixation process to take place. In this process, nitrate is converted into nitrogen gas, which is released into the atmosphere. Denitrification requires aerobic conditions. Useful nitrogen fixing bacteria are not able to survive in these conditions.
A=Add something they have missedB= Build on an idea * that could be more
detailedC= Challenge/Correct anything you disagree
with