 Welcome back to the lecture series on bioelectricity. So, we are in the section of plant bioelectricity. So, in the first class in the plant bioelectricity, we talked about overall scheme of things. It is just a brief recap, what we have just talked in our previous lecture. So, what is being considered is in the whole life cycle or in the food chain is in the solar system where we all live. Sun is the major form of energy and this energy is being trapped on the floor of earth by the green plants. And the green plants eventually synthesize food. So, these are ate by the herbivores and the herbivores are being consumed by the carnivores and the carnivore dies and then again all the organic and inorganic matter gets into the soil. And again this whole process continues. So, this is basically the food chain. From the food chain, we took a deviation telling that during 1970s, the discovery of the hydrothermal vents deep under the sea where the no sunlight is reaching kind of set another paradigm of life forms evolving, where most of the bioelectrical phenomena which are taking place are independent of sunlight. That was one paradigm shift. And apart from it, in our previous class we talked about the anatomy of the plant, the gross anatomy, the leaves, the stem, the flowers and in the flowers we talked about we will be talking about the dye sensitized solar cells. And in terms of the xylem and the flowing vessels, once we will be talking about the plant movement with the mimosa and the venous flytrap, we will be talking about those structure and their significance. So, in this class we will start with the basic photosynthetic machinery which is fairly conserved among all the green plants which has evolved on the floor of earth. Of course there are certain plants which follow a certain bit of a shortcut, but the overall scheme of things of electron transfer is fairly same. And the major molecule which involved in the electron in trapping the sunlight is chlorophyll. So, let us start where we left in the last class. Now, let us go to the microscopic details of a leaf or the green pigments or the structure which is involved in trapping the solar energy. So, let us resume the class photosynthesis. Let us get the whole complete basic of photosynthesis under the heading of plant bio electricity. As we have already discussed some point that the whenever we talk about electricity there could be two modes of transport of charges. Either it could be through electrons or it could be through ions. These are the two major modes. In this situation what we are dealing with is essentially the electron transfer and the electron transfer chain across the membrane and which leads to the energy production eventually. So, let us move on to the next slide where we will be talking about the basic structure. So, in the last class we talked about the basic structure of the leaf something like. Now, we will take basically what we will be dealing here is the primary event photosynthesis which is taking place across the leaf. So, if you look at the leaf there will be certain leaves on top of it there will be a slightly waxy coating and underneath is the epidermal layer where basically all these machineries are there. So, all the biological structures are consist of cells. So, the plant cells and animal cell there are some basic differences. The most fundamental difference is the plant cell have something called cell wall where the animal cell does not have it. So, apart from it plant cells have structures called plastics or chloroplast where all this light trapping machinery is being housed whereas animal cell does not have any such structure. So, these are the very gross difference between plant and animal cell. So, if we look at this leaf. So, this leaf essentially consists of a series of cells like this. These are the individual cells if I take a cross section or something like that. So, these cells have something called a cell wall and inside the cell wall you have the whole machinery of everything. So, the nucleus this is the nucleus and then you have certain which I am putting on red these are those small structures which are called your plastics or the structure which are basically holding your light trapping machinery. So, what we will be doing now? So, from the macro structure of the leaf now we are moving into the cellular structure. Within the cellular structure now we are moving into the subcellular structure and the subcellular structures. So, there are I will just take a little backward here how they have probably evolved. So, one of the theories about this particular chloroplast like a structure is this that they were probably at some point of time on the floor of earth these were independent microbial species and some or other they have parasitized on some of these plant like structures and they became part of it. The reason why it is hypothesized like this is the small chloroplast structure what you see they contain their independent DNA and where is the cell itself has it is another set of DNA which ensures that it divides. So, essentially what we are talking about is that within individual cell the nucleus has its own DNA and the chloroplast has its own DNA. So, that set people thinking and the current acceptable mostly acceptable hypothesis is this that at some point or other those microbes parasitize the plants and become part of it somewhere or other. So, now the question arises. So, how the plants were deriving food before that if that is the situation. So, the answer is we really do not know I mean what was really the I mean how the whole food chain was functioning at that point of time if we really think in that way and that they were parasitized and then the plants then acquire the ability to you know synthesize food. So, but leaving that debate aside let us try to explore this is structure of the chloroplast now and what made this is structure. So, where is special that it can trap the sunlight. So, now the next slide what I will be doing is that I will be getting the cross section of this structure how it looks like. So, this is where we where structure. So, this is the nucleus with n is the cell wall and this is the chloroplast. Now, the chloroplast structure essentially is something like this it is a double membranous structure like this this is how the structure apparently look like in a regular microscope. So, inside this what you will observe is something like a very interesting membranous network many of them out here and these are connected with each other at different level and I will just highlight all the names and everything this may be connected to another set of structures like this at multiple level these are connected I am just simplifying the diagram. So, this kind of a structure what I have just now drawn is basically called thylakoid membrane and this thylakoid membranes are also double structure. So, one of the beauty of most of these structures are these are all you know double membranous structure this is how the structure looks like there are empty space what you people are seeing in this picture this empty space is essentially called a stromal space. So, this is your stromal space and this structure is called thylakoid membrane as a structure thylakoid membrane and this connecting link are called stromal amylase and this whole pile what you see this piled up structure like this this is called granum. And so this is the outer membrane of the chloroplast this is the inner membrane of chloroplast outer membrane inner membrane you have the granum you have the stroma stroma is the space the blank space out there then you have intermembrane is a space in between. So, this is the in the yolo what I am drawing now is a intermembrane is a space and always there is one very interesting thing in all this structure there are lot of intermembrane is a space between all these membranes these are the intermembrane is a space this is the intermembrane is a space. So, this is essentially the whole structure of the chloroplast which is involved in trapping the sunlight now the question arises where exactly it is trapping the sunlight this is very important. So, I have drawn the gross geometry. So, as of now what we have done I am going very slowly because you have to understand this is structure otherwise things will become kind of you know confusing. So, we talked about the whole structure of the leaf then we move down to the structure of the individual cells we talked about the different organelle cell wall chloroplast nucleus and we highlighted the fact that this chloroplast is structure is also called plaster actually the synonymous. So, they have their own set of genome or DNA in them then from there we moved on to the molecular architecture of the chloroplast and now we will be getting into the exact chemical architecture where all these different molecules sun trapping molecules which are setting. So, one thing you always have to remember in this kind of structures most of these membranes or all these membranes are asymmetric that is why I am continuously highlighting which one is the outer membrane which is the inner membrane essentially whenever I am talking about that they are asymmetric it means the property of the membrane it is suppose this is my this is the membrane this my hand is a membrane. So, this side has a different texture as compared to this side. So, just imagine if this is the membrane the property of this side is different from this side that is what we meant by asymmetry of a membrane there are certain molecules which could bind here there are certain molecules which cannot bind here the electron transport may take place from one direction whereas, some molecule may be synthesized in another direction. So, slightly highlighting this is structure what I have drawn for you is the stroma the stromal what you see the vacant spots that is not really a vacant spot there are lot of molecules which are present there which are involved in synthesis of energy rich molecule and carbohydrates and all other things. So, basically the empty space what you see is rich in organic molecules which will help for the synthesis of wide range of molecule and they are coupled with several other structures within this micro architecture of the chloroplast. So, now coming back that where these molecules are sitting. So, most of these molecules which are taking part in the photosynthetic events they are all sitting somewhere like this. So, they are kind of sitting like this out here see I am drawing those pink color dots. So, these are imagine these are series of different molecules which involved in electron transfer and they are all membrane bound. So, they are all membrane bound their structure real integrity is maintained when they are in the membrane as soon as we take them out from the membrane their structural integrity will be lost and that is why they are so very challenging to crystallize and there is understanding their exact structural details. So, this is where all these molecules are sitting and we will be talking about these individual molecule one by one as we will be highlighting the whole process of electron transfer along this. So, for a layman understanding what exactly is happening is overall thing is this I will use the black and so light falls out here like this and through a series of oxidation reduction reaction the electron flows along this follow my arrow something say for example like this let us do it and in that process of electron flow this is h nu or this is sun. So, this is where the electron transport chain is moving this electron transport chain eventually leading to synthesis of the electron flow molecules essentially what is happening here this electron transport chain out there is creating a potential difference across that asymmetric membrane. So, across this membrane what you see out here there is a potential difference it almost functions like a battery or something like a device which can you know generate sufficient energy to synthesize molecules. So, now we have to go one by one to figure out the molecules which are involved in this game before we do that let us revisit the basic reaction of what synthesis. So, which is essentially your CO 2 plus H 2 O forming carbohydrate plus oxygen. So, which is essentially what you are talking about is C u H 2 O it will be N. So, this is N obviously. So, your raw material is carbon dioxide and water which is abundant water is very abundant carbon dioxide is also very abundant and your output is carbohydrate the glucose the major source of energy and oxygen which ensures that we all breathe the first challenging question in this equation which haunted for a while was who is supplying the oxygen is it the carbon dioxide or is it the water it was found out that it is the water which contributes in the generation of oxygen. And that discovery of the carbon dioxide helps us to figure out that for synthesis could be divided into two stages one stage where water is getting a split the other stage is where energy rich molecules are synthesized through a process. So, broadly speaking the whole for synthesis even could be classified into two parts one part is purely electron transverse and the other. So, let us kind of put it like this sun is falling the sun rays are falling we are being trapped by we will be talking about the details of this structure chlorophyll molecules and this leads to a series of electron motion this whole process falls under light reaction within light reaction are existent for the reaction there are two stages one is called photosystem one p s one other one is called p s two there is a p s two where water is getting split at this whole electron transfer leading to generation of energy rich molecules which is essentially the carbohydrates this part falls under something called dark reaction is not dependent on sunlight as such this part falls under light reaction which is essentially dependent on sunlight there is no sunlight the light reaction will not proceed any further. So, under the broad umbrella for synthesis you have light reaction and dark reaction in this course we are not dealing with the dark reaction. I will just give you one example of dark reaction just in terms of the C three and C four plants about their efficiency and why some plants are efficient some plants are not in terms of photosynthetic output but I will be what will be doing will be mostly talking about will be talking about the light reaction. So, within the light reaction let us enumerate what all we are going to cover the first thing we have already covered is light reaction first thing is structure of chloroplast. Which we have already dealt with the second thing will be dealing with basic history of photosynthesis or rather first of all the basic reaction of photosynthesis which we have already I have kind of highlighted CO 2 plus H 2 O forming C H 2 O plus oxygen. So, now third thing will be the will be dealing will be the discovery of the basic equation of photosynthesis all the reactions we led to the point where we are now and that will take you from the point of Levisure all the way up to the 19th century when photosystems were being discovered. So, next thing what we will be dealing with is the structure of chlorophyll and how they trap energy structure of chlorophylls trap solar energy and followed by that we will be talking about a very interesting unsolved concept called reaction center of we are putting p s as photosynthesis reaction center of photosynthesis and 6th will be dealing this phase will be oxygen evolved coming from water. This is the next thing what we are going to deal with how the oxygen is coming after this once we gone this far in this we will be talking about the actual physical electron transfer how the electron transfer is taking place. So, essentially next 2 to 3 classes that is what we are going to deal with and before I move into that I will have I will be taking 2 classes where I will be dealing with how you that very basic concept of the electron transfer your reduction potential because this reduction potential concept will be very essential for you to understand how the electron transport is taking place. So, we have done with the structure of the chloroplast we are done with the basic reaction of it next what we will be doing you know next lecture will be the discovery discovery of the basic equation of photosynthesis and the structure of the chlorophyll which are there to you know trap the sunlight. So, closing here in the next class we will resume these 2. Thank you.