this is the nitrogen cycle universally
hated questions can be quite complicated
this is really not as bad as most
teachers make it out to be okay so I'm
going to start with a series of four
boxes connected by arrows on the top
this is going to be the direction of
flow pretty much and it should all make
a little bit more sense so let me draw
the boxes first so far so good
these are squares are going to represent
inorganic so if you don't know what that
means it means not containing carbon the
inorganic forms of nitrogen that flows
through ecosystems I'm going to start
here with the letter A easy to remember
the difficult thing often about these
questions and exams is that they will
always give you a different diagram and
it's always going to look slightly
different every textbooks going to
represent it differently I would have
your version
ie my version in your head crystal clear
you'll see there's not like this one and
know what's what in terms of C sometimes
they're going to skip it
sometimes they're going to change the
layout but if you are confident of
what's wearing your head then you can
remap the question so that it makes
sense to you and I always start here
with a so this is ammonium ions and
ammonium ions as I said the direction of
flow is going to be in this direction
ammonium ions are going to be
transformed into nitrite this is an eye
and what I usually do is write this
underneath with a number one because it
comes first because the next thing that
comes after this is pretty similar and
you're gonna have to spell them
correctly because they are very easily
confused as nitrate and usually I put in
here late so nitrate comes after nitrite
we start with a at the beginning
alphabet nitrites nitrates and then the
evil form that we do not
is nitrogen gas in the atmosphere so
this is very unreactive in that it's
almost impossible for things to use I
might even put a little nasty cross in
there because that's not what we want
that's not mr. Foreman action that
biological things want nitrogen in okay
so what do we want nitrogen in well the
easiest form of nitrogen to absorb the
plants are nitrates so plants are going
to absorb these things so this is gonna
be plants and you need to know which
kind of compounds contain nitrogen in
plants what any living thing is going to
have nitrogen containing compounds in a
couple of fours I'm just going to put
them in green so see if you can guess
what they are
think test yourself they are proteins or
amino acids you can also have DNA or RNA
so these is often the inference of the
question is about what do the biological
ramifications of this mean in plants or
animals so I'm doing a circle around
this circles are going to be organic
life forms and living things basically
organic forms of nitrogen well these are
I'm going to put this arrow in black
actually because this is not an arrow
that you need to know in terms of you're
going to need to know the names of which
of these it all going to have a name in
fact this one is just absorption not the
most important this one is going to be
animals how do animals get their
nitrogen well they eat plants and where
are the nitrogenous compounds in animals
well all living things I'm going to
repeat this a lot of times protein and
DNA again animals are living they're
going to go in a round circle okay so
what happens to the nitrogen compounds
from animals and plants when they die or
maybe they excrete we just these things
well they're going to be broken down by
decomposers or Sephirah by on source a
probiotic bacteria microorganisms so
disaffected label for the stages
afterwards so I'm going to call these
decomposes
and I'm going to add a little note to
that fat probiotic micronus
microbes where do they have their
nitrogenous compounds well you guessed
it proteins and DNA and are they living
yes they are they go in a round bubble
okay
so we're more or less done and then we
need to conjoin the end of the cycle and
they're going to add a few other little
bits and pieces as well but from here we
go back to ammonium and there's a few
other bits and pieces but effectively
the cycle but we're most interested in
is living things we want to do this as
much as possible or if when animal we
want to do this as much as possible so
one of the names of these stages the
names of these stages are this one we
are the process of making ammonia so
this is ammonification specification the
process of making ammonia pretty
straightforward
these two both have the same name these
are nitrification and this one so this
not forgetting because it's the process
of making sort of good nitrogen useful
nitrogen so nitrites and nitrates are
soluble they can be absorbed by plants
and they can do useful fun stuff with
them like to make proteins this stage
here we're converting it back into a
form of nitrogen that we don't want the
nitrogen in the atmosphere and so we
call this the nitrification we're
removing nitrogen from the biological
system and the last stage that we need
to learn about during this stage almost
two more I'm lying to you we're going to
we're going to go from nitrogen gas in
the atmosphere straight into plants but
not everything can do this whenever
we're taking nitrogen gas and converting
into a soluble form so apply something
that a plant can use we're going to call
that nitrogen fixation
we're fixing it we're taking it from a
useless form and putting it fixing it
into a good form now this is done
generally speaking by bacteria in a meat
mystic relationship with Lake goo-
plants so legumes is the French word
vegetables as an example of legumes are
going to be pea plants lentils beans
things that vegetarians eat to get lots
of protein why do they have lots protein
because they can do this they can take
nitrogen out of the air they I have a
higher ratio of nitrogen in them so they
have higher amount of proteins and this
is generally done by bacteria in the
root nodules something else that I'm
going to put in here about
denitrification the way that they tend
to ask this in exam questions this is
nearly always under anaerobic conditions
and the way that question is usually
asked is to do with how aerated the
soils or how waterlogged the soil is
that's how that question is usually
asked and the last state that you need
to know about is called separable tick
nutrition and well is it going to be a
key term this is digestion or decay of
dead organic matter by extracellular
enzymes
okay so what is extra cellular enzymes
or x-rays outside of the cell so these
these micro naeun's basically booze out
their enzymes onto the substances the
enzymes catalyze reactions hydrolyze
them break them down into simple
molecules which can then be absorbed
through the membrane and this is how
they do their digestion so a quick
summary remember you start with a you go
to nitrites because you could put an eye
in it the second eye it can be a one
then it goes into nitrates
this is nitrification making useful
nitrogen soluble it can be absorbed by
plants where two plants animals and all
living things have their nitrogen in
proteins and DNA basically this process
is evil denitrification it's removing
nitrogen from the biological system it's
under anaerobic conditions and it's
usually waterlogged soils there are a
magic group of bacteria that live in
association with legumes legume plants
which can fix nitrogen nitrogen fixation
and convert the nitrogen gas they
actually convert it into ammonium ions
and then they do some fancy chemistry
but in terms of what you need to know
its nitrogen fixation and it's done by
bacteria in association with legumes how
does it get recycled back into ammonium
well superb antic nutrition is basically
digestion and decay by extracellular
enzymes and this process is
ammonification okay so we've done Arthur
Murray but there's one more thing that
you need to know and as the names of the
bacteria which do a couple of these
processes not all of them so here this
bacteria that does this is called
nitrosomonas Lytro so you're just gonna
have to learn these but there is a
little bit of a trick that we can use to
remember these so nitrosomonas has more
letters in it than this one this is
nitrobacter
so we're going from long in to short and
then this one here nitrogen fixation is
done by where am I going to squeeze him
in it's going to be done by rhizobian so
rhizome or mycorrhizae is something you
going to study probably as well a
rhizome means like root
so these these live in the roots that's
a little bit of a clue in there and then
the last stage that there's actually one
that I'm going to add on for you
lucky extra people and it's another form
of nitrogen fixation and this one with
nitrogen fixation because we're going
from nitrogen gas into ammonia nitrogen
fixation is done by a Zota bacter these
are bacteria that live in the soil they
do exactly the same as the Rhizobium but
they don't do it in association with
leguminous plants
okay so that is the full detail there's
not huge amount of writing on that page
I suggest you write this out as a
skeleton so just the boxes and the
arrows no writing
photocopy it I might even get somebody
to do that nicely and scan it and send
it to me so then you guys can print it
out ten times it'll take you two minutes
to fill that in once you get good at it
and you will not forget it and then
again the key is just mapping the
diagram they give you in the exam - the
one you've got clear in your head so
that you know what's happening each step
of the way
