i didn't mention um oxygen yet.
why and that is because
um in order to get these electrons and
these hydrogen ions- they don't come from
nadh and fadh2 or the nadph -
they come from water there's so
much energy involved here that it
splits water and when the water is
split that releases
oxygen molecules they join together and
we get o2
that we breathe thank you photosynthetic
organisms
and we get uh the
hydrogen ions and the electrons
that are part of these electron
transports chains. so
initially new electrons come from water
and for photosystem 2 for photosystem 1
they come from photosystem two so
there's just this constant splitting of
water.
and we have there are the plants always
have
a supply of
hydrogen ions and electrons okay.
so let's break this down a little more.
we call these light dependent reactions
so
light absorption that excites and this
is for electrons
so a different picture of photosystem 2
in photosystem 1 and ATP
synthase but you see the light
that is being absorbed by both
photo systems this doesn't happen
this one first and then this one - it's
going on at the same time
and what happens is that excites
the electrons and they
pass their excitement until it gets
to the special electrons that are
in the reaction center complex, don't
worry about
learning reaction center complex.  just
realize there are special electrons
and those will be the ones that
ultimately jump ship. okay
same thing over here light energy
exciting electrons
until we get to the um
special electrons that can enter the
electron transport
chain. okay so light absorption
that excites electrons
whoops so
excited electrons pop
out of the photo systems and move
through the electron transport chains or
electron transport systems
and water is split so this is a nice
diagram showing you where the water and
this is the water
that the plant is pulling up if it's a
tree for example from
the roots all the way up to maybe
30 feet up from the surface
to the leaves that's that water
that they need.so the water then
provides the electrons and the hydrogen
ions
and then the oxygen that we use.
so you see the electrons you see the
hydrogen hydrogen ions and you see
the oxygen then
at the end of photosystem one we
see that is where that electron
system is where NADP+
is reduced to NADPH and
what's not shown here is the ATp
synthase
but that's okay in fact i shouldn't be
there yet i should be with
the electron transfer and the splitting
of water
going on here
and this just is part of my explanation
about
the source of the electrons for both
photosystem
ii and photosystem one. so
the source for photosystem 2 for
electrons
and for hydrogen ions will be from
water being split, the source of
electrons
for photosystem ones
um for photo system one
is from photo system two.
the last part so we've had light
absorption exciting electrons
electrons being transferred
and water being split we
also then have the ATP
production again ATP synthase is
not here but we know that that we do
have
well what is that
i don't believe that's ATP synthase but
ATp synthase
should be over here.   ATP synthase
for the production of ATP
and here the electrons we have to have a
final electron acceptor and in this case
it's NADP+
not oxygen, NADP+
and that then
gives us the NADPH.
the ATp and the NADPH
will be substrates for
the calvin cycle
i have an overall equation for the light
dependent reactions. water
+ light energy someone asked is if
is it really a substrate
uh we can call it a substrate, light
+ water + light energy + NADP+
 
+ ADP + Pi
gives us oxygen that we breathe
NADPH and ATP.
so far we don't have any sugar
so far the energy from the sun is
temporarily stored
here. you might wonder why do the
photosynthesis
at all well if you're going to get some
atp
here it's not enough plus it doesn't
allow for
storage plus it doesn't allow for
building carbohydrates that become part
of the structure
of the plants so it is not enough
energy for the plant.
the light independent reactions they're
not
technically independent of light because
they need the ATP
and the NADPH from
the light dependent reactions,
but they don't directly need an input of
light you don't see
an input of light.   here instead
what we have is this calvin cycle we
start with RuBP
and we end with RuBP so there's an
input of co2 this is really simplified
by the way
so are you RuBP plus the co2
results in these rearranging to three
carbon compounds of
phosphoglycerate
and then
we call that carbon fixation because
a gas is brought in well
i'll talk about that some more in a
minute. so let's just ignore that for now
so co2 comes in
joins or bonds to RuBP and there are
multiple RuBPs so
again not as simple as this is showing
forming
several of these uh
phosphoglycerates and
then the phospho
glycerate another intermediate is reduced
and we get uh-
what is it i've got it written down
in the next one it's i usually don't use
the name- but this intermediate
some of them leave and notice three
carbons not six
takes two turns of this to get a six
carbon
sugar and then
the rest of these G3P's and i'll
tell you what that stands for when i
look-
are eventually regenerated to RuBP
so again it's a cycle.
now let me fix this
by telling you what's going on here
carbon fixation there are three steps or
stages to the calvin cycle carbon
fixation
co2 that's a gas binds to RuBP
and that forms that phosphoglycerate you
know that name i could remember
and this one is a
three carbon compound okay
 this transfers
oh and this should be transfers this
transfers it from a gaseous form to a
solid.
that is the definition of
fixation and in this case it's carbon
fixation.
so reduction
the NADPH
has already been reduced in the light
dependent reactions it is now oxidized
so that the hydrogen ions and the
electrons end up
in and this is that g3p glyceraldehyde
3-phosphate.
okay it takes some energy for all this
to happen so now this
has so the energy from the ATP
and that produces half of a sugar
each time this thing turns
then there's regeneration
of the RuBP which is what we started with.
okay so
there's your equation for the light
independent reactions RuBP
+ co2 it's an overall equation
+ atp + nadph yields
rubp it's a cycle half a sugar
nadp+
that can go back to the light dependent
reactions and
adp + p that can go back to the light
dependent reactions this shows a little
more
of the detail of what is going
on and also assumes
there have been the two turns
so that we get the glucose or the
other sugar.
what i have been explaining up until now
would be c3 photosynthesis
that occurs in what we call c3
plants okay and this is related to the
carbon fixation part
so because see it when co2 is fixed
when co2 bonds RuBP
and that first intermediate
it has three carbons that's where the c3
comes from,
three carbons in the first intermediate
of the calvin cycle. okay
so these are
80 something percent of the plants 80
some
 percent of the plants that we that
inhabit our world
are c3 plants and you can see
some examples right here okay
most plants are c3 plants
but there are environments
that are hotter and drier so there
are two adaptations to that.
one would be c4 plants
during the day it gets hotter and drier
in these environments and these plants
partially close those stomata those
holes
and those holes are so important because
they allow the co2 to
enter the leaf they also allow the
oxygen
to leave the leaf
but for the purposes of photosynthesis
we have to have co2 we have to have it
to be fixed
to make the sugar in the calvin cycle
so they keep their
stomata open partially
during the day and anytime
they have a little extra co2
they fix it in a different
type of cell and instead of
ultimately forming the carbohydrate
because they need to catch up
with the atp and the nadph
they store it as a four
carbon compound hey you want to know
what that four carbon compound is
it's oxaloacetate that's interesting as
well
but they say this as
as a four carbon compound and then
as the calvin cycle
multiple calvin cycles are running
obviously
as they need the co2 input
the co2 is released from the
oxaloacetate
and the co2 then is available for carbon
fixation
cool huh so a couple of
uh examples are corn
and sugar cane there aren't that many of
these remember
80 something percent of the plants
are c3.
then there are the cam plants
so both c4 plants and cam plants
fix carbon twice
c4 plants do it during the day keeping
any excess co2
as this oxaloacetate so that they have a
storage
of co2 okay cam plants
it's even neater what cam plants do
is they open their stomata at night
when there's no light
so photosynthesis can't proceed because
it means
the light for the light dependent parts
of photosynthesis
so it's so cool what these plants do
they
