Welcome back to the lecture series on bio
energy so we are in the module two let us
get back to the slide.
A concept called Hill reaction so what real
reaction is all about so this was in 1939
so while this reactions were clear up in 1941
and1950s 1939 Robert Hill discovered that
isolated chloroplast so he could manage to
isolate the chloroplast isolated chloroplast
led to the evolution of oxygen okay so what
he did so what he observed is that when he
took an isolated chloroplast like this and
illuminated you read light okay in the presence
of and what did they he has a suitable electron
acceptor in the form of Ferrocyanide 
and what he found out that Ferrocyanide is
reduced to Ferrocyanide Ferro and this is
fairy okay.
So there are three points what we detected
out they dissected for synthesis by showing
that oxygen evolution can occur without reduction
of co2 in other words in other word what is
important here CO2+ H2O CH2O + H2 oh sorry
plus oxygen this reaction what you see here
is independent of the other reaction does
it make sense so it means this H2O to oxygen
evolution is totally independent as compared
to the reaction of CO2 forming CH2 this was
one of the landmark thing and that why it
is so significant for us to understand is
that this one reaction leads to the whole
area of in organic chemist who are what pretty
much dedicated all their life many of them
on developing water splitting cluster.
They are developing different kind of water
splitting clusters where they are trying to
generate hydrogen as fuel and we will talk
later about this some of the works which are
done in India as well as abroad by different
people on artificial leaves whereas the other
fragment 
so we get back to the slight if you look at
it so this is the area where tremendous amount
of work is happening across the world in terms
of developing what we call as artificial less
and some of the landmark discovery is were
done in India as well as on a broad and we
will highlight about all those things you
can those of you are very keen you can go
through the website of Daniel Nocera in MIT.
He has done some very seminal work in that
area where is the other side which is so if
you see the sketch in this part of the reaction
this is what falls under another emerging
area of carbon sequestration 
so you see a simple reaction which is happening
in nature which is deceptively simple reaction
as I am telling you from the beginning opens
up some of the most invested areas of research
in the modern science.
How to sequester carbon thumb rule has been
already shown by nature we are converting
carbon dioxide it into carbohydrates whereas
the other reaction which is actually supporting
this reaction in unison where the water is
getting split and evolving oxygen as a by-product
and generating electrons which supports the
other reaction of reduction of CO2 to carbohydrate.
So they are all interlinked and that is one
of the reason why a basic fundamental understanding
of photosynthesis is critical for understanding
the biomass technology now talking about the
hill reaction where we started this let us
explore a little bit further about hill reaction
what are the other areas aspects which will
reaction talked about.
so this is the basic reaction what hill showed
us to H20 + this is where the Ferrocyanide
to Ferrocyanide reaction club in the illuminated
chloroplast leading to oxygen + 4H + which
is the protons + 4 Fe 2+ so here is that reduction
reaction what is happening what was shown
by health.
The second aspect this reaction hill reaction
confirmed was the Evolved oxygen we have already
talked about evolved oxygen comes from water
not from carbon dioxide okay third aspect
which was shown by a reaction is that isolated
chloroplast isolated chloroplast can perform
significant partial reaction of photosynthesis
partial reaction of I am just showing photosynthesis
PS okay and the fourth and most critical point
which will be critical for us to look now
it revealed that the primary event in photosynthesis
is light driven and the transfer of electron
transfer from one substrate to another s stands
for substrate is thermo dynamically uphill
and this is something the gains the gradient.
So it means the electron transfer is happening
not down the gradient all the time it happens
up the gradient so that needs a lot of energy
it is almost like you are pulling a bucket
of water all the way uphill that essentially
what does that mean a thermodynamic thermodynamically
uphill phenomena where you have to invest
energy you know to raise the bucket or raise
the electron to a higher energy State okay
so this is what is very v critical about this
whole process of photosynthesis which was
very nicely summarized by the hill reaction.
Now from here we will move on to the next
aspect what we talked about was two light
reactions interact so now this is so what
we talked about is two light reaction interacting
photosynthesis we have talked about two light
reactions remember we talked about 1 for system
one and for two system two so how this was
being figured out is something like this I
am drawing it so here you have the wavelength
on the x-axis 400 520 600 680 okay and on
the other side we will be talking about the
oxygen evolution or the quantum yield or oxygen
evolved per photon or in other words this
is also called the quantum yield of photosynthesis
okay.
So what you observed in this is a very interesting
aspect init so what you see out here 
and something called a red drop why is it
so now what does this red drop why is it so
signifies 
so what it says is that for synthesis require
interaction of two light reactions as we have
already mentioned okay for system one and
two system two and both of them can be driven
by light of wavelength less than 680 nanometer
but only one of them by light of longer wavelengths
and interestingly the one which is driven
by light of longer wavelength is the one which
is involved in what we call as the dark reaction
driving the dark reaction which is for system
1.
So in the next slide this why you see this
red drop will be very clear to you if I draw
the next just go down on the next slide so
to summarize what does that mean or not this
will make everything clear to you so here
you have photo system 1 PS 1 shining light
on it which is wavelength less than 700 nanometers
okay and you have another photo system PS
2 which is getting light less than 680 nanometer
corrected nanometer okay now what is generated
out here is a strong reductant in the form
of NADPH which is NADPH and one second and
a weak oxidant in the form of ATP where the
for system two you have a weak reductant in
the form of ATP again.
Whereas there is a strong oxidant 
in the form of oxygen so these weak oxidant
and weekly distant is an ATP now if you look
at this reaction very carefully you realize
so coming back to the slight and let me add
one more point to this which will make you
understand so out here underneath it is the
water splitting cluster 
now this part functions at less than 680 nanometers
which is directly involved in evolution of
oxygen now if you see the previous red drop
graph.
Now you observe what you are how you are quantifying
you are quantifying based on oxygen evolution
so beyond 680 the oxygen evolution is going
to go down there will be a red drop yet the
photo system absorbs light white is absorbing
light now coming back to this picture.
Because between 68 t + 700 682 704 to system
one is functional so what you see a red drop
you see a red drop out here because of this
one out here photo system 2 only functions
at 680 and less and for system to the oxygen
evolution is what we use as a quantifying
or scale for measuring that quantum efficiency
or photosynthetic efficiency but try to understand
the two points here.
But that does not rule out that the chloroplasts
not going to absorb light it is going to absorb
light because between 680 and700 nanometer
for system one is absorbing light where it
is producing a very strong reductant in the
form of NADPH which is eventually taking part
into the CALVIN cycle which will be coming
later where the real biomass formation is
taking place where CO2 the sequestration is
taking place now this brings us to a point
three aspects what we will be dealing.
Now what we will be dealing now is one second
so now at this stage let us draw the three
more aspects what we will be dealing our next
goal will be to 1 outline of electron transfer
between photo system 1and photo system 2 which
of course you can also mention as 680 and
700 sorry let us take a once again 700 or
680 the outline of electron transport with
respect to the radix potential this is one
aspect what we will be dealing with now second
thing we will talk about water splitting cluster
involved in out here at underneath for system
to at 680 okay.
Then we will talk about the third which is
this part and how this one is governing the
CALVIN Cycle for the dark reaction of photosynthesis
where CO2 to carbohydrate or the carbon sequestration
which is happening and from here we will talk
about C3 and C4 plants and what we learn from
them so after crossing through this whole
thing now we have reached to a point where
we will I have already highlighted what always
we are going to discuss we will discuss about
next two classes.
That will be our target area we will discuss
about the transfer of electrons along the
cluster we will talk about the water cluster
process which is happening underneath for
systems too and we will talk about the CALVIN
cycle and that will summarize our this module
so after this these are the three points so
please go through what all we have covered
just to summarize for example so we talked
about the basic architecture of a leaf where
the or of plant cells we have not still talk
show in the plant cell we talked about the
basic architecture of the chloroplast we talked
about the arrangement of thethylakoid membrane
and within thethylakoid membrane okay.
Let me just coming back to the slide once
again and here also we will talk about a little
bit more out here just as the part of this
how proton gradient is created this is very
important we just slipped out so this is another
thing which will be talked about which actually
leads to generation of the ATP so we talked
about the architecture of the chloroplast
we talked about the how it was discovered
that there are four system one and photo system
2 it is further how it was discovered that
there are two different kind of chlorophyll
molecule chlorophyll A and chlorophyll B we
talked about in depth about the reaction center
and how it was observed that after this match
is illumination you only get this much oxygen.
So it means all the chlorophyll molecules
are not involved post excitation into oxygen
evolution then we talked about the hill reaction
where we kind of you know split that whole
reaction of CO2 + H2O into two parts and showed
that they are two independent events where
carbon dioxide is converted into carbohydrate
is one part whereas water is splitting and
it will evolving oxygen is another part which
is part two of it.
So there are two separate events which are
happening altogether which are not interlinked
with each other or quick with each other two
separate events and from there we talked about
the overall scheme of things where we talked
about for system one where it is producing
a very potentially very strong reductant in
the form of NADPH whereas for system two which
is forming a very strong oxidant in the form
of oxygen whereas both of them are generating
a mutually a week reductant and a weak oxidant
in the form of adenosine triphosphate or ATP
molecules.
That got generated because of the proton gradient
which is formed there and in between how you
talked about the red drop why because the
quantum efficiency or the for synthetic efficiency
is a function of oxygen evolution so if you
kind of you know shine light beyond 680 nanometer
there would not be any further evolution of
oxygen instead there were the only absorption
of light and that will only reduce the photosynthetic
efficiency so what you will be observing is
that there will be red drop in terms of oxygen
evolution we talked about it so based on that
we put this outline for the next couple of
classes.
This is what we are going to deal with the
outline of the electron transfer between for
system one and for system two this is what
we will be dealing are part 1 and follow-up
it with respect to the redox potential and
how the gradient is created and out ATP is
generated so again what we will be dealing
what will be the water splitting cluster which
is present underneath photo system 2 or at
PS 680 and the third thing what we will be
dealing with will be NADPH as a strong reductant
driving the CALVIN cycle or the dark reaction
where carbon sequestration taking place and
followed by c3 and c4 plant so these are the
three aspects what we will be dealing with
so I will close in here and we will take up
these three topics in the subsequent two lectures
where we will wind up the module thank you.
