Welcome back to the lecture series in bio
energy so in the last class we finished with
the Calvin cycle and we talked about the energy
expenditure and we concluded the class with
the fact that for synthetic efficiencies 30-person
we talked about how many ATP molecules are
required how many NADP features required how
many water molecules and how many carbon dioxide
and what is the end product of six carbon
glucose or starch molecules okay start your
sucrose molecule.
So today what we will do is if you guys remember
that at some point I was telling you about
the Rubisco and the problems with Rubisco
so today's lecture will be about C3 and C4
plants but the way I will move is that first
o fall I will give you an idea exactly where
is the significance of this so actually Rubisco
as per the evolutionary chemist or evolutionary
biologist Rubisco possibly evolved in an environment
in a distant past at some point which was
rich in carbon dioxide Rubisco as an enzyme
was never really made by nature or a no engineered
by nature to handle a situation of high oxygen.
And as we have already discussed that Rubisco
has both ways of binding it can bind to oxygen
it can bind to carbon dioxide okay so now
it has been observed that at higher temperature
if the main temperature goes up say for example
somewhere in the tropics or semiarid tropics
where the temperature during the summer goes
to like a 45 degree centigrade or at least
even 42 or you know however between 45 to
50 degree centigrade it has been observed
with the increase in temperature Rubisco affinity
for oxygen increases what does that mean that
means Rubisco which was supposed to bind to
carbon dioxide and promote carbon dioxide
sequestration or carbon capture instead utilizes
the oxygen that means instead of synthesizing
it is now utilizing oxygen.
So there is no evolved divorcing of oxygen
instead it is consuming oxygen a process which
is also called photorespiration so now if
you just think let us do not go to the details
first of all try to get the philosophy of
it if you think that an enzyme which is so
critical for the plant to carryout photosynthesis
is now involved in consuming oxygen so what
we have talked about the thirty percent efficiency
of photosynthesis is going to go down because
part of the energy is we consume the respiration
process and that thing whole thing or photo
expression and this that whole thing will
continue till the temperature comes down.
But then how in all these semiarid tropics
and tropical areas or the places on the earth
where there is huge amount of incoming solar
radiation how the plants grow there are several
crawfish growth okay interestingly meaning
of those plants many of those crop plants
have developed or devised a very interesting
technique to compensate for it how they do
so before we get into the detail of water
there is those mechanisms and everything let
us talk about a little bit about the anatomy
of the leaf.
So if you see a leaf suppose this is a lead
okay you are doing so on top surface if we
take a microscope and you take a section of
the leaf you will see there are very small
structure called stomata okay.
So it looks something like this coming back
to the slide you see a structure of the leaf
something like this okay so if you take a
cross-section of it so if I take a cross section
like this so in the cross section what will
you see there are cells like this these are
the plant cells with the cell wall like this
and in between these are all the plant cells
what I am drawing you see certain structures
like this 
okay something like this these are essentially
the one which I drown in red color these are
essentially called the estimator so these
are called stomata so stomata are small pores
which regulates exchange of gases and regulate
movement of water regulate and just train
movement of water I am just showing by arrow
in the moment okay.
So now if this is structure regulated a moment
of water certain high temperature this is
stomata spores closes because it cannot afford
to lose water now think of situation if this
stomata closes at a higher temperature automatically
gaseous exchange is kind of now prevented
because I told you the Kiska matter has two
functions one function is that it allows the
gas to slide in slide out glass molecule diffuses
through the stomata and the water molecules
moves out in the form of vapor and some of
the water molecules will come inside through
that okay.
Now at a high temperature what is happening
is this stomata spores is shut down so automatically
carbon dioxide which is supposed for the plant
is supposed to know trap the carbon dioxide
does not happen so now correlate the two situation
first let me put it together the first point
what I mentioned to you was the Rubisco the
first the beginning so Rubisco become more
oxygen binding okay when the temperature is
higher right point one point two when the
temperature is higher the stomata closes okay.
And in this stomata closes so automatically
there will be fall in CO2 intake so essentially
these two situations where the CO2 intake
is reduced and this stomata is closed and
the Rubisco this essentially promotes in a
way something like this where the Rubisco
is binding to oxygen now what is the strategy
the plant kingdom developed in order to ensure
that Rubisco functions so one strategy could
be if some way or other some way or other
in that local vicinity just underneath the
stomata spores it somewhere or other they
could tap a lot of carbon dioxide.
So it means you have a store of carbon dioxide
which you are holding out there okay if you
could trap those carbon dioxide and transform
them obviously just think of it you cannot
track car with because there is no cylinder
there okay there is no so you have to transform
carbon dioxide into some other form there
if you have a mechanism by virtue of which
say for example CO2 is transform into a product
X and then that X product you have some way
or other again make it CO2.
Now say something I strategy like this so
there is lot of ambient CO2 okay so this CO2
is being picked up suppose this is the plant
cell it is picking up this CO2and concentrating
it at one point and this CO2it is converting
into an x compound which by another process
could again release CO2 okay something like
this so in other words this vessels what I
have drawn here is acting as a kind of reservoir
to trap CO2and the idea is to maintain a high
CO2 level such that the Rubisco is more affinity
has more affinity for CO2 okay.
So this is the strategy then how the plant
does it here comes a catch let us say for
example if this is the leaf and so we are
taking the cross section so if you see the
cross section it has an upper layer and it
has a lower layer okay so now the upper in
the lower layer is filled with us so we will
call the epidermis okay something like this
these are called the epidermal layers upper
epidermis which is the top of the plant okay.
And this is the so this is up epidermis upper
epidermis and you have the lower epidermis
okay and in the center of it here the xylem
phloem vessels which are rolling through okay
so this is the xylem flame X and P that is
essentially for xylem and phloem vessels around
that now I will show in light green are a
series of cell where most of the Calvin cycle
is happening okay those are called is the
name from called bundle sheath cells 
okay and between the bundle sheath cells and
the epidermis and by the way on the epidermis
layer you are having those stomata and all
those things which are sitting out there which
is in direct contact with the air underneath
this now put a blue color or there are cells
which are arranged something like this these
are called the mesophyll cells or mesophyll
cell okay.
So the cross section if you look at it so
you have the upper layer of epidermis underneath
you on the epidermis you are having these
estimator underneath you are having the mesophyll
cells lining or mesophyll cells underneath
you are have the vascular cheat layer and
then underneath you are having the xylem flame
again that repeats further in the same pattern
okay now coming back to the slide so the catch
line out here in this layer this layer what
you see I am just putting it the one which
I am talking now in the mesophyll layer.
So there are two categories of plants I will
explain it why they are called one is called
C3 plants the other one is called C4 plants
and in a C3 and C4 plant that different lies
in that mesophyll layer these mesophyll layers
are very intensely packed in C4 plants like
this okay almost like as if like a cylinder
they are standing out there so this is how
they are packed so instead of these blue you
have to replace it by a and they are in very
close proximity with on the epidermal layer
the estimator like this okay something like
this and some of them even are in direct contact
with air.
And you are having the epidermal lining like
this which is I am putting in the light green
color okay whereas on the country these mesophyll
lining is something like this crinkle shape
like this and underneath you are having the
stomata like something like this once again
okay first emitter is like okay so now what
happens by specialization lies in this layer
of the mesophyll cells these mesophyll cells
what they do is that they are direct contact
with air or through the stomata this is that
reservoir what just coming back to the slide
these mesophyll cells for the C4 plant.
If this reservoir like this that CO2reservoir
so what is happening inside these mesophyll
cells because it is underneath the mesophyll
cells you're having the layer of bundle sheath
cells which are sitting here is where all
the Calvin cycle is taking place okay I am
coming to the camp pathway after this okay
so an out here so this is the reserve voice
where something is happening and what is happening
in that mesophyll point.
So in that reservoir is CO2 is getting accumulated
and transformed into certain 4 carbon molecules
called mallets okay and there is a series
of transformation let me put it down on the
slide it will make more sense.
What is happening inside this now we are into
the C4 plants in the C4 plants so let us put
the two cell layer so this is the mesophyll
cell layer out here and I am just drawing
it horizontally there I drew it vertically
now I am drawing it horizontally and adjutant
to it you are having the bundle sheath layer
which is in closed touch with it so this is
the bundle sheath layer bundle sheath cells
where the Calvin cycle is happening okay so
this is why Calvin cycle is happening and
this is the bundle sheath so this is the bundle
sheath cells whereas out here you're having
these are the mesophyll cells.
Okay so in the midst of yourself they are
in direct contact with the air so here one
second if you are having CO2 coming from outside
so this is the environment either okay so
CO2 is entering a fall entering the CO2 is
converted into something called oxolao acetate
okay from oxolo acetate it forms molecule
called malate okay and this malate is transferred
or transported into the bundle sheath cells
where Malate transform into a Pyruvate and
in that process it releases the carbon dioxide.
And this carbon dioxide eventually takes part
in to the Calvin cycle okay Calvin cycle whereas
this pyruvate which is formed here is brought
back transported back here I am just putting
P by the weight this fire weight goes to a
very intricate reaction which I am not getting
into detail where it is consuming so this
is where it consuming a lot of ATP molecules
and transformed it into ANP this is the interesting
part is that adenosine triphosphate so this
has three phosphate groups and ANP it has
the one phosphate group so in other word it
is losing two phosphate in that process okay
TI plus TI okay it goes through to transition
and form phosphoe in all pyruvate PEP phospho
in all pyruvate okay and this phospho pyruvate
again transform into auxiliary acetate and
again this whole reaction continues now interestingly
the first clue of the existence of such cycle
or something different was given by a Russian
scientist okay.
Followed by that there this was further so
coming back to the flight this was further
back in nineteen sixty this idea was thrown
that there is something different is happening
after that two scientist explored this pathway
which is called or rather discovered this
pathway one is name is hatch and the other
one is CR slack and that is what is this also
called hatch slack pathway what they said
is that Celvin side the first clue of the
existence CO2 transport mechanism came from
studies showing that the radioactivity from
a pulse 14 co2 remember what we have talked
in beginning 14 co2 appeared initial in oxolo
acetate and malate and other 4 carbon.
So what you see here that will see here this
is oxolo acetate malate these are all four
carbon chains okay and you remember in the
previous situation we talked about three carbons
which was starting the process so what you
are getting is starting point here is the
four carbon okay.
So comparison here is that oxalo acetate verses
phosphoglycerate this is where C3 and oxalo
acetate being C4 to the starting point these
are called C4 plants okay and there is a decarboxylation
of the C4 compound in the burned cheap cell
maintains the high concentration of basically
of the CO2 at the site of Calvin cycle and
theC3 compounds returned to the mesophyll
cellsanother round of carboxylation so this
whole thing continued and enzymes which are
involved in this process one of them is called
phosphoenol pyruvate carboxylase 
and there are few other which are not really
significant at this point but what is important
for you people to understand is what is exactly
happening here.
The reaction is something like this I am just
putting down the reaction so you have co2
in 
mesophyll cells okay plus ATP remember that
I told you that there is a consumption of
ATP plus water which is making it CO2 in bundle
sheath cells 
and plus AMP I told you ATP gives away two
phosphate and becoming in 2Pi because those
two phosphate serving lost and a proton and
two high energy phosphate bonds are consumed
in transporting CO2 to the chloroplast of
the bundle sheath cells okay.
Now what we will do after talking about this
basic pathway of C4 cells let us talk about
the what is the total consumption of energy
in this whole process so now 6C02 now this
is that comparison +30 ATP now here you see
the difference is 30 ATP as compared to where
you are using if you talk about the C3 pathway
you are using18 ATP so you are needing more
energy for 33 okay it is 43 you need less
energy whereas here you need more energy now
coming back next twelve NADPH +12 H2O giving
away C6H12O6 +30 ADP because you know process
having lost the 30 Pi that is phosphate 12
in ADP + 18 proton moieties which are coming
out of it.
So in other word to put it summarize this
whole thing does this mean the tropical plants
with C4 pathway do little for photorespiration
because it has a high concentration of CO2
in the bundle sheath cells and accelerate
the carboxylase reaction related to the oxygenase
reaction so this is the challenge carboxylase
and oxygenase reaction of Rubisco so by this
process you are increasing the carboxylase
reaction because you are trapping more co2
making this environment in spite of having
high temperature you are making this environment
more and local concentration of co2 is much
more higher.
So there are plants like sugarcane in most
common plant which follows a C4 pathway and
I request you to look for what are the other
C4 so one of the objectives of a lot of bio
energy research directed towards plant genetic
engineering is that if we could have more
and more plants with C4 plackets think of
it philosophically what does that that means
we will be sequestering more carbon dioxide
because they have a mechanism of kind of a
cylinder where they can trap it.
There are lot of efforts happening across
the world how the plant could have more co2
so that they can transform them into hexose
sugar so this is where all the way from the
basic reaction of photosynthesis we reach
to the C3 and C4 and this is where we will
be concluding the photosynthesis part where
how old is different bio energy resources
are being produced so what we see.
Now this is the driving force for producing
wide range of sugars driving the whole machinery
of the plant and with having lot of protein
and lipids and all sorts of complex sugar
long-chain sugar shortchange sugars likewise
series of them so low they can non cellulosic
starch and all that stuff so now since we
know pretty much with all these lectures as
of now that this is how the biology is producing
all over the world whatever vegetation you
see which are dependent on light we are not
talking about the hydrothermal where there
is no like light.
Light independent system produces it biomass
through this whole chain of photosynthesis
using light synthesizing a series of molecules
on next our goal is in the next class what
will be starting is that how again these could
be transformed from here to energy rich well
one aspect what we will be dealing with and
the second thing how these materials could
be utilized for making charge storage or energy
harvesting directly okay which will be our
advanced topics and we will talk about all
this.
So to conclude this journey of photosynthesis
or the most fundamental mechanism by virtue
of which the light-dependent synthesis of
these molecules are happening we started with
basic architecture then we talked about for
system one and system two we talked about
water splitting cluster where the part of
the reaction CO2 + H2O making CH2ON which
is the carbohydrate plus oxygen.
So H2O 42 which is essentially the water splitting
which is happening underneath for system to
in the manganese cluster is taking care of
that from there that electron which is the
infinite source of electron in the form of
water is supplying electron to the for system
two in order to bring it back to its ground
state where because of the four photon electron
is being ejected out from the chlorophyll
molecules that chlorophyll molecule which
is devoid of the electron is brought back
to its ground state than the electron hops
to for system 2 for system 1 for system 2
for system1 simultaneously as series of chlorophyll
molecules which are devoid of electron.
Because we have ejected out electron is balanced
out they are being brought back to their ground
state and that electron which is donated by
the for system one then supplies fun of that
electron to NADP to make it NADPH which is
a very strong reductant and then once that
how that NADPH takes care of using C3 carbons
how the whole glucose moieties are being formed
and now today we concluded that that is not
the only one route there is another route
where C4 carbons are being there so in other
words there are nana cylinders in the form
of mesophyll cells in the plan which has this
ability to you know trap and carbon dioxide
and transform them into four carbon molecules
which could release again carbon dioxide and
which was being funneled into the Calvin cycle.
So this is the whole summary of photosynthesis
encoding what I just forget to mention in
this whole thing all the redox potential and
how the electrons are hopping through so again
please go through so this was quite an intensive
photosynthesis part what we covered so next
we will be all the processing of all this
plant product which are formed now in the
form of sugars proteins and lipids and what
all the technologies the next class see you
back in the next class with the phase 2 of
X where we will be doing all the processing
of generating energy rich flues and some of
the very interesting energy harvesting as
well as energy storage products made from
biological sources thank you.
