Welcome back to the lecture series on bio
energy, so we are in the module two and we
have finished first two lectures where we
talked about, the overall scheme of, processes
which happens in photosynthesis. We describe
the light reaction, and the dark reaction,
and we talked about for system 1 system 2
and the electron transport, and the proton
gradient which is created across the thylakoid
membrane. So at this stage all my viewers
and listeners have an overall idea of what
are the processes which are happening in photosynthesis.
Now next two classes what we will do so today,
we will be starting our eighth lecture.
Now next to or two three classes our idea
will be to explore each one of those processes,
in greater detail so that what all the next
generation of technologies, which are evolving
by getting inspiration from them can be clear
to all of you. So let us get back to the slide
today.
We are in to that lecture 8, so essentially
in the module 2 and this is basically the
third lecture of module 3 by 2. That is why
you did like this okay.
So now if you remember the first very first
reaction what we have dealt with was co2 +
h2o making ch2o plus oxygen as a by-product.
Now fairly early in the 18th century this
reaction was discovered but this, this reaction
was not discovered in one shot there are few
landmark discoveries or you can say landmark
events which led to the discovery of the fourth
synthesis. So we will just in couple of minutes
we will kind of highlight them that will give
you an idea of the timeline when this discoveries
indeed happen okay.
Now add one more component to this was the
role of light which is light given reaction
so if we look at it, it was the evolving of
oxygen this part this was by Joseph Priestley
just putting the name you can cross-check
you can go online, and you can figure it out,
and around 1700 80 the next major discovery
which happens was the role of light. Which
was described by a Dutch scientist his name
was Jan Ingen Hous so who discovered the rule
of light. The third one was Jean Sengbier
so his discovery was with this carbon dioxide
what he essentially says let me just put the
name Jean Sengbier showed that co2 is taken
up in photosynthesis.
I am just putting PSS photosynthesis not putting
the whole name, then came the role of water
out here you seem just in a different color
code for your understanding role of water
was basically shown by a guy called Theodore
De Saussare. What he said that he demonstrated
that some of the weights of the organic matter
produced by plant and of the oxygen evolved
is much more than the weight of co2 consumed.
And based on the law of conservation of mass
by lavish or It predicted that this is nothing
but the water okay.
And all these so you see Joseph Presley here
this is around 1780 very similar Jan Ingen
Hous worked at the same time Jean Sengbier
just soon after that and the Theodore De Saussare
who talked about the role of water and the
final contribution was made by Julius Robert
Meyer, Julius Robert Meyers. So what Meyer
says was the plant take in one form of power
that is light and produce another form of
power called chemical molecules. So essentially
it was completely summarized by Robert Myer
who said that it is a light energy is converted
into a chemical energy.
And if you will see it very clearly this is
what is happening out here this is the chemical
molecule which is generated and in other words
this is also a process, natural process of
carbon sequestration or carbon capturing because
in the environment there are lot of carbon
layer. So what you are essentially doing you
are capturing the carbon dioxide or the carbon
molecules and converting them into baked carbohydrate
molecules in other words you can call this
whole process. Let me okay, this whole process
could fall under carbon capturing or carbon
sequestration which is one of the very emerging
challenging field currently that how we can
sequester lot of this carbon dioxide in the
form of air pollutant which are present there.
But this brings us to a very different tab
perspective to this whole thing if there is
a way one can emulate the photosynthetic apparatus
then essentially one can think of making food
in an artificial chamber. Think of it you
have carbon dioxide is in abundance your water
in abundance in the sea of the ocean and what
you need and you have light in abundance all
your three commodities are in abundance. Now
if you can push them in one apparatus which
will make carbohydrate as the way a chloroplast
does. And what we are talking about is that
you do not need to grow food in the field
you actually can grow food in a small chamber.
So these are the kind of dream what mankind
is seen in other words, you can actually form
biomass if you know what really photosynthesis
is doing. So think of it why I am putting
trust on this whole area is that the whole
biomass formation is directly related to the
photosynthetic output which is happening on
the floor of Earth as long as the solar energy
is available to us. That is why now what we
will do from this point on our next journey
will take us talking about the architecture
of the organelle which is chloroplast.
We will talk about the structure of the chloroplast,
on next slide we will move on to the structure
of chloroplast shirt off okay before I draw
the structure try to visualize those of you
have seen Food Corporation of India godowns
or something. You must have seen that there
are gunny bag filled with grains they are
stacked over one another like this at some
point or other all of you have seen this if
not in real life or at least in a picture
you have seen it okay. We are stacked over
one another and there is a closed room inside
which these green serving cape exactly visualize
a similar structure chloroplast is a double
membrane structure before I draw this try
to visualize in your brain is a double membrane
structure. In which you will see stacking
of those something like a gunny bags all over
and there are connected between them so now
let me draw it what I was trying to tell you.
It will be something like this, so the structure
is this is outer layer something like this
a structure which dimension is around 2 to
3 micron and on 80 we will see something like
this these are those granny bags which are
present the connector liked it okay. So now
that is was telling you try to imagine where
the grains are kept in gunny bags and these
are those gunny bags that will kind of help
you to visualize how the structure really
looks like, like this now if we label this
a structure let us put the labeling to them.
So this is the this is the inner membrane
and putting the inner membrane 
then the yellow shading what I am doing this
is the outer membrane so two envelopes in
a membrane and the outer membrane then you
have something these structures are called
thylakoid membranes. So 
if you see the cross section of the thylakoid
membrane so you must have seen a pillow. So
imagine you have the cover of the pillow cover
and you remove the cotton from it or any kind
of cushioning agent.
So it is something like this so if I had to
know coming back to the slide if you see this
structure very carefully this is structure
will be something like so there is a hollow
part out here this part is follow okay. So
thylakoid membrane is kind of inflicted it
is kind of you can say it is a saucer-like
inflated structure there are saucers like
this and underneath it is hollow. So and they
have a different function that is one and
all these structures area symmetric in other
words if you look at the outer periphery so
that is why I am putting different colors.
So if this power and this part inner and outer
they have a different property in property
in the sense they are molecular arrangement
of the different kind of proteins which are
present there is entirely different so most
of the biological membrane. What we know off
till this day are a symmetric in nature 
and this asymmetry helps most of them to achieve
some very unique functions okay. So now coming
back to the slides out here so there are a
few other things what we have to mark here
so we talked about the thylakoid membrane
and this is spacing between what you see is
called thylakoid space okay.
Then these kind of connectors are called stoma
or lamellae 
okay and then there is a space in between
these two which is called inter membrane space
okay and this empty space was you see is called
trauma so overall this is the whole architecture
of the chloroplast where these reactions are
taking place and if you guys the number so
where this photo system one and four system
to is located now just let me point out in
so forth system one and four system to is
kind of suppose this is the inner membrane
like this is connecting like this.
So now this is where the four system 1 system
2 what is fitting cluster all these things
are decorated around so what you see essentially
is that so this is where all the, the is 12
water-splitting and all these things are located
so if you see it is essentially a energy transforming
membrane where the lighter energy is falling
and electrons are ejected and all the phenomena
what we have talked in the last two classes
it is all happening at that site so this is
and that of course if we look at the dimension.
So we are talking about a dimension of around
you know 5 4 to 5 micron and the max or maybe
less and within that for 25 micron much, much
smaller are these the smaller units where
these kind of reactions are taking place so
that was telling you that if one can emulate
even ten percent of this kind of structure
and make energy harvesting then pretty much
all our global energy problem will be solved
this is the kind of challenge when mankind
is heading could we emulate a chloroplast
or could you emulate thylakoid membrane is
it really possible maybe someday somewhere
okay.
So this is the overall architecture which
what I want you guys to know kind of you know
keep in mind and if you see wanted to know
the composition of it the composition is something
like this they nearly have equal amount of
lipids and proteins okay almost equal amount
of equal amounts of lipids and proteins and
most of the lipids and the total lipids if
you look at it so there are Galacto lipid
you have sulfa lipid and you have phospholipids.
These are the different kind of lipids which
are present there so this is overall and of
course I have already mentioned you that one
second this structure also has its own genetic
material have already mentioned, and that
is one of the reason why people say, let this
at some point in evolution was and stand alone
organelles which for some XYZ reason parasitized
and other animals.
And today what we see is the plant evolved
the cause of that okay so coming back so the
next thing what we will be dealing with is
once we are done with it so this is what you
have talked about now we will talk about the
structure of the chlorophyll so, so the chlorophyll
molecules how they look like so I told you
that there are similarities between chlorophyll
and hemoglobin told you that if you remove
the iron from the Centers of the poor fire
injuring or then it becomes CEO low because
the whole profile is zero similarly if you
remove the magnesium which makes the chlorophyll
then it remains as yellow the very moment
you put magnesium it retains the green color
the very moment you put iron it attains the
red color okay.
So now let us see the structure of the chlorophylls
the light trapping pigment 
structure of chlorophyll so the structure
of chlorophyll is something like this you
have a coordination out here you have the
magnesium sitting out here like this and this
is the poor fire in structure it is a complex
of structure but just follow it, it will you
see a lot of symmetrical features in the structure
okay. Similarly you have okay, okay, okay,
and in this corner you will see a CH and a
methyl group present here than the methyl
group present here and there is something
called an R.
I am just putting it R here that are essentially
stand for one second bit that are essentially
stand for two situation if it is one second
if it is ch3 then it is so there are two kind
of chlorophyll then it is chlorophyll a and
if it is CH 0 then it is chlorophyll b okay.
So these are the two chlorophyll generally
used in very small letter just correct that
colorful be out here another methyl group
present here at this point you have complex
structure out here where you see carbon and
ch3 and out here you have an oxygen attached
to it on the other side okay.
So of the plane you have a methyl group hydrogen
out here under hydrogen and out here this
is where the second level of modification
comes and there is something called an R this
R is again very important for you guys to
keep tap and I will talk about the arch just
in few minutes and it is one small this, this
bond is wrongly placed here actually this
should happen here. So now you see this complex
structure and I have not explained you about
our what that are it stands for now what I
will do just follow up this pictures.
And let us put what that are means in the
next slide so that r is equal to 
CH 2 CH another CH 3 CH 2, CH 2, CH 2, CH
then of the ch3, ch2 twice and here 
you have ch2, ch2, ch3, ch3 so this is what
the R group stand for so what you have talked
about is there is a chlorophyll a and a chlorophyll
b based on that particular position. Where
we talked about where whether it will be CH0
or it will be a ch3 now we will talk about
what distinguishes a chlorophyll a and chlorophyll
b let us coming back to the slide so this
is the second our group. What we have talked
about so there are two zones one our group
I told you out here the box top and the other
our group out here which I shown in all right
okay.
Now so what you see is the absorption spectra
so if you if I draw the absorption spectra
it will be it will look like something like
this okay. So here you have absorption coefficient
which is shown in mole and say around out
here 10 to the power 5 and absorption 400,
500, 600 and ending at 700 these are in wave
length in nanometers okay. So for chlorophyll
a if you look at it we put it in green so
for the chlorophyll a the absorption peak
is something like this 
if you see this is what is the chlorophyll
is absorption is going okay.
Now if you look at chlorophyll b which I am
so let me just this so this is chlorophyll
a and for chlorophyll b you see the absorption
it is something different it will be something
like this it is slightly shifting 
and 
so one second business today Lotus will be
okay. So what you observe is that and there
is a slight staggering and the wavelength
at where chlorophyll a and chlorophyll b are
absorbing but what is interesting to know
that there are a huge vast part of the spectrum
where there are no absorption.
These are the peak absorbed them which are
taking place at that particular wavelength
now to summarize this particular slide it
is so what we are observing is that the absorption
spectra of chlorophyll a b and b are different.
So absorption these are the take-home message
absorption spectra of chlorophyll a and b
are different this is the first conclusion
you have to draw from this and secondly light
is not appreciably absorbed by chlorophyll-a
at 460 nanometer that you can see at 460 nanometers
light is not appreciably absorbed by chlorophyll-a
whereas it is captured by chlorophyll b which
has intense absorption at that wavelength.
That you can see out here so if you see it
around 460 nanometer so there is a better
absorption of chlorophyll, chlorophyll b as
kind of to as compared to chlorophyll a and
these two kinds of chlorophyll complement
each other in absorbing incident light okay.
So this is the major take-home message and
the spectral region from 500 to 600 nanometer
is only weakly absorbed by this chlorophyll
that you can see out here as far as trying
to tell you in the beginning. So if you look
at this zone there is hardly any kind of absorbance
which is happening at that region okay.
But this does not pose a problem for most
green plants okay by contrast light is often
limiting factor for cyano bacteria or blue-green
algae red algae the poses accessory so for
such blue-green algae or the red algae for
them there are other accessory molecules which
Nature has devised which ensures that they
absorb light at those kind of different kind
of wavelengths. So having said this let us
summarize this so what we have observed is
that there are two kind of chlorophyll, chlorophyll
a and chlorophyll b and their absorption spectra
is slightly started but there is a huge shown
between 500 and 600.
Where there is hardly any kind of absorbance
which is taking place but apart from it there
are several accessory molecules which are
available to different species whether it
is a blue-green alga cyano bacteria read by
red algae or whatever they are supplemented
with a series of such different dyes which
absorbs wavelengths at different wave which
absorbs light of different wavelengths. So
in other words if you have to can you imagine
it, it is to be something like this as if
there are different kind of say you know.
So this is the solar energy which is falling
on different kind of life form and they have
a different kind of you know 
so wave length one wave length two wave length
three wave lengths 45. So Nature has equipped
most of the light form with wide array or
spectrum of light harvesting pigment by virtue
of which it complements the existing panels
of chlorophyll a and chlorophyll b but this
particular aspect is an inspiration for one
of the advanced topic. What we will be dealing
with is called dye-sensitized solar cells
we will be right in so tight solar cell we
talk about this later but at this stage just
remember there are wide array of such pigments
available in nature.
So these are the if I these are the different
pigments or natural pigments and dyes available
in nature which otherwise have a role to support
the living systems which are there but those
could be an inspiration to develop different
kind of another series of solar cells okay
we will come later into this so this is the
overall understanding what I wanted for you
whistles for chlorophyll a and chlorophyll
b but what is the significance of this chlorophyll
a and chlorophyll b. So I will close in here
thank you.
