hello everyone this is a video regarding photosynthesis which is mainly answering the question where does the food you eat come from so let's go ahead and take a look right away when we take a look at this first of all i'd like to see where you are at in terms of thinking about this so go ahead and read this checkpoint it says plants only photosynthesize in order to process energy while animals use cellular respiration is that true or is that false go ahead and make a note of it okay the correct answer is false and that's because if you look at it first of all look at all those mitochondria in the plant cells and we know mitochondria are what do cellular respiration plus it kind of makes sense that plants do cellular respiration if you think about it for a moment the problem is is that most of our lives we've learned about the fact that plants photosynthesize and we don't really know why other than to make sugar and so but what's done with the sugar what did animals do with the sugar animals are going to break down the sugar to make atp and that is exactly what plants need to do they need to break down that sugar to get the atp out of it so they can do the things that they need to do in their lives like grow produce seeds or fruits any of that kind of thing okay so make sure that you start thinking beyond the kind of the what you learned originally as like kind of a fundamental and let's expand beyond that okay so it says here plants do cellular respiration too as evidenced in mitochondria in plant cells all right so here we can see both cellular respiration and photosynthesis are found in a loop with each other if you think about it it kind of makes sense in a way how they're connected to each other but let's look a little bit more closely okay so first of all looking at this part of the loop what do you notice you've got some items up here that will tell you what we're looking at is this photosynthesis or is this cellular respiration so think about it what do you note that tells you one or the other write those down so you can kind of get an idea write down the reactants write down the products okay so this one is obviously photosynthesis and we can see that because we have chloroplasts here with some sunlight hitting it and then you can see you've got water and co2 that are coming in as reactants and then as a result we're producing glucose and oxygen you're probably already really familiar with all these symbols here because we use them a lot in other areas so use what you know now notice um we also can find out that wow these two items which were the products of photosynthesis also become the reactants so here they're the reactants but of this time of cellular respiration so cellular respiration you can see this is a mitochondrion here it's going to release atp and of course energy in the form of heat and then we also get products water and carbon dioxide as a result of silent respiration okay so let's take a look at these right here when you start to consider these can you identify which is which write them both down and then ask yourself the question which is cellular respiration and which is photosynthesis go ahead and pause here okay now that you've written everything down tell me which one of these or i guess i should say write down which one of these is an anabolic reaction in which one of these is a catabolic reaction go ahead and pause and write that down okay so taking a look at this we can see that the first one right here has glucose plus oxygen yields carbon dioxide and water and atp well that tells you already that if this is glucose that must be cellular respiration because we also take an oxygen after we've eaten or during the temperature all the time i guess and then we produce co2 and water and of course the idea is to get atp out of it and also if you look at this this larger molecule of glucose is being broken down so that is known as catabolic then we also have around the bottom side here we have photosynthesis and photosynthesis we can see that we're producing sugar plants take up water and they take up co2 and fortunately for us they produce oxygen this molecule we're putting other smaller molecules together to make a larger one so that one's going to be anabolic all right so when we think of photosynthetic organisms sometimes people think oh well you know trees and flowering plants and ferns there are some other ones that you might think of like a flower plant like a palm but there are other photosynthetic organisms that we don't think about nearly as much like green algae green algae is not a plant but a protist similarly there is a green seaweed which is also a protist and they do a lot of photosynthesis um in fact much of picking up the co2 that is affecting the climate in terms of climate change um is being taken up fortunately by those little teeny organisms in the ocean then there's also lichens which are not really one organism but two of them put together it's a symbiotic relationship that's mutualistic and it's a fungus and an algae in one and so the algae component is able to do photosynthesis and it provides a little bit of glucose for itself and also for the fungus and then the fungus provides nitrogen for the algae so it's a really nice little relationship there you'd see them on rocks and branches and things like that they're generally decomposers and some of them can excrete acid so that's how they break down rocks which is how you get get the beginnings of soil okay so here's the summary equation of photosynthesis you can see a carbon dioxide we have water of course we know that there's going to be sunlight involved and there's also going to be making glucose and oxygen now in this process too there is going to be a number of enzymes and i'm only writing them on the bottom of the arrow simply because we don't have space on the top and they're going to be involved in photosynthesis every step of the way and then what captures um the sunlight are pigments pigments like the one that you probably know about chlorophyll okay so these are going to be involved too on the left-hand side of the arrow or we should say the stick end of the arrow those are the reactants carbon dioxide and water and on the pointy end we have glucose and oxygen as the products now notice sunlight and enzymes and pigments they are not considered reactants nor are they considered products so we're putting an association with the arrow simply because they are not used up okay now notice here when i clicked on it again what happened was we changed the number in front of some of these molecules the idea here let me go ahead and show that here is kind of generally showing you um what in general is being used and what in general is being produced and then here we're talking about balancing the equation which is something that in chemistry has done a lot so for example here we've got six carbons here to match our six carbons over here and now we have 12 oxygens plus the six over here so here is 12 oxygens and the six over here so by putting the numbers in front that helps us with um with balancing as you can see okay um but in general a lot of times you won't see it with the numbers in front because we're more concerned with what's the overall situation that's happening versus quantifying each amount okay now we can see is that oxygen will lose electrons and hydrogens um when we're looking at water here and that makes that an oxidation from water to oxygen gas and then also we can see that carbon gains electrons and hydrogens going from carbon dioxide to glucose and of course that makes that a reduction from what you've learned before all right so a couple of things we might be interested in is how is it that we get the reactants into the organism into the plant for example and where do the products come out to understand how they come in and out we need to know a little bit about the anatomy of plants so first of all the reactants that we talk about first of all we can look at as water well we know rock water comes in through roots if you've ever watered a plant you have a tendency to water the soil right now you might have experienced a situation where a plant likes to be misted like a fern the real reason why they're missed it is not because that's where the water comes in but it creates a little atmosphere of humidity like the one that they would normally be found in in the wild so burns have a tendency to come from areas that have moisture in the air a little bit more humid and so if you live in a dry area like we do in southern california you might find yourself misting that plant to kind of full it in thinking that it's for a few minutes anyway in a tropical zone and it's a little bit more healthy so um but in general the water comes in through the roots now we also know that there's carbon dioxide and that is going to come in through these little teeny holes called stoma and those stoma have cells around them called guard cells those guard cells help with opening up or closing the stoma and so when they're open carbon dioxide can come in now where do the products go out we know one of the products is oxygen oxygen is going to leave through the stomata which we already talked about when you're looking at transpiration in our biological transport system lab so that's the oxygen coming out and we also noticed it in that lab we were talking about more specifically about how water connect comes out and that can be um you know at the end of the process here so that's not necessarily a reactant but it is something that can lead through the stomata okay so then when you look at a leaf in cross-section it's actually made up of an upper epidermis and a lower epidermis of course you know epidermis means skin so this is the upper surface or skin and then this is the lower epidermis and you'll notice that they do not have any little um guard cells inside of those sorry i said guard cells i meant chloroplasts inside of those epidermis epidermal cells it's only the ones in the middle here so here likewise on the lower epidermis there's no chloroplasts on them so this middle area is called the mesophyll let's write that down meso means middle and fill means fleet so that makes a lot of sense that it's called the mesophyll and when we talked about this in lab we notice that there's two parts to the mesophyll there's the one here that are long kind of column shaped and we refer to those as palisade mesophyll and that's simply because we're looking at the column shaped ones but they're still part of the mesophyll and then the other one that we we noticed were the ones that had lots of air in between kind of like uh cells and then no cells and that's called the spongy mesophyll so there's mesophyll is this whole area and then there's the palisade mesophyll and the sponging is a film so both of those areas are very important the light kind of shines through ultimately through the epidermis and then onto the chloroplasts inside of the mesophyll and so that's where we're going to get all of this amazing photosynthesis happening now when we look at this picture a little bit closer each one of these mesophyll cells that could be palisade or spongy you can see has all these little chloroplasts in them and those chloroplasts look like this if we look inside of them carefully there's actually two membranes that are the outer in the inner membrane and then there are all these little pieces inside of there that to me look like um junior mints or you could say coins or little poker chips something like that they're stacked upon each other we'll take a moment and look at that a little bit closer okay so we know the chloroplast is where all this amazing stuff happens for photosynthesis we learned that when we learn the parts of the cell and this is a major organelle so how it's made up you have first of all these stacks that i was talking about each one of the stacks is called a granum and then each of those sacs within the stack for example this one on the bottom or the next one those are called thylakoids so they're disk like sacs containing chlorophyll and we know chlorophyll is that green color pigment that absorbs light energy it turns out that there are multiple kinds of chlorophyll chlorophyll a b c d e and f and i think i understand that they're working on one that to identify as maybe chlorophyll g so we're still learning a lot um over time about something like chloroplasts which are so fundamental to way things work now the other part of the chloroplast is all of the liquid that is inside of these two membranes and that is called the stroma now be careful we learned the term stoma which are the little holes stomata or pores that are found in the leaves and then this word is stroma with an art inside of there so two very different things so be very very careful that you um pay attention to which one you're writing or you could be something saying something very different than you intended okay so now there's overview of photosynthesis it actually takes only two stages which is nice to think about when you consider that cellular respiration took um three or four depending on your perspective so first of all there is the set called the light reactions and you can see um this is happening in the chloroplast and it's referring to this left-hand side clearly because there's light associated with it now where is this happening it's in the thylakoid you can see it's each of these little sacs here that are being struck by a photon of light as they say they're the calvin cycle on the other half and on the other hand is happening in the fluid or the stroma in in the chloroplast now in terms of the light reactions we refer to that as light dependent and of course that means that it requires light it's dependent on light to happen in the calvin cycle it has been referred to as light independent or historically dark reactions but when we see the word dark reactions what you should do is just get rid of that idea that gives a false understanding that it has to happen in the dark well in reality it can happen in the light or in the dark so as you can see it's independent of whether or not life is present so that's the main thing we're going to be taking a look at here we're going to be looking at what's happening in terms of these two stages a little bit more later on as well okay so since sunlight is so important it's part of the light reactions we really do need to consider something about the nature of sunlight sunlight as you know is a part of what's called the electromagnetic spectrum the electromagnetic spectrum is a range of of different wavelengths of light um where you're looking at things like x-ray and gamma rays and infrared and so forth um it's a full range of radiation and the way that we talk about radiation is in their wavelengths so if you can imagine this kind of thinking about it as though we're in the ocean you know that wavelengths like this if we were measuring one way to the next it would be easiest to kind of measure the distance between the waves by looking at well here is the press of one wave here is the press of another one and then what is the distance between them and so if they're coming in quicker you get them closer together it would have a short wavelength or they could be spread out a lot more so it's a full range of radiation measured as wavelengths now when we look at the electromagnetic spectrum it consists of all kinds of radiation as i mentioned like i said x-ray gamma ray and so forth and one portion of it we refer to as the visible light spectrum and those are the colors um of light that we can see with our particular eyes and it's those particular wavelengths however it's kind of a funny term because what is visible to you and to me is not necessarily what's visible to other organisms in fact organisms like bees actually have a broader ability to see they can see down in the uv section which is why some flowers have wonderful markings on them that we can't even see until you put them under uv light and then you can see they look like little air traffic controllers waving their wands to let um airplanes of course that means the bees here into where they need to park that is where the nectar is or the pollen is it's kind of fun in any case um this is looking at the whole electromagnetic spectrum as i mentioned before all of these different kinds of wavelengths gamma x-ray uv visible light infrared microwaves and radio waves and what we see here is that they have their own set of wavelengths now you know in an ocean that that wavelength would be measured as say in meters right but when we're talking about looking at it in in light this can be very very small so we're going to be using generally um you know the nanometer range is what we're really referring to so really really really tiny something that's smaller than we can see um you know on with our naked eye so in any case we're looking at this that's nanometers here and so that's generally the unit we're talking about so we've got meters some of them get to be bigger like one meter or a thousand meters but a lot of it is down in the nanometer range now when you take a look at this the lower the wavelength down here okay what that means is that it's going to have a shorter distance so let me draw this again here say for instance we're talking about uh a person who is going to be running okay so let's have an example here this is a little bit lower here so this is the distance a person needs to run and for whatever reason they run like this and let's see if i can do this with a mouse not beautiful that you get the idea okay so those are really really short ways right from press to crest is a very short distance in contrast now if i have a different person or even maybe the same person i don't know and that person runs the same length here but decides to run it like this right that one's going to have a much longer wavelength so which one do you think is going to take more energy to run the top one or the bottom well i imagine i picture my son doing his running and when he was doing cross-country or track and if he had to run all of this to get to here you know that's going to take more energy than somebody's running like this right so the lower the wavelength like this the top one that means that we're going to have higher the energy it's going to take more energy to run like this than to run like this so that is something kind of interesting when we're looking at what's happening with the electromagnetic spectrum this is what we refer to as an inverse relationship right because we talked about situations where um when you have lower something there's higher something here right so um the lower the wavelength the higher the energy um and then the higher the wavelength the lower the energy and this becomes important for plants because it turns out that if a plant is doing photosynthesis it has to be the right kind of amount of energy if it's too low of energy photosynthesis won't basically happen you can't get it going but on the other hand if it's too high high of energy it could damage the plant tissue so it's got to be kind of in that goldilocks range just right okay so that's the nature of light and specifically we're talking about with the visible spectrum okay now when we talk about like uh this is going to be an associated in association with the things that we see right imagine that you have um a person in the room and they're wearing a bright purple sweater well if they're wearing that sweater the reason why you see the purple is because that is the wavelength that is being reflected to your eye if they're wearing a yellow sweater then that means that it's the yellow wavelengths that are reflected to your eye and you kind of already have intuitive sense about this if you think about it say for instance if you're talking about taking a hike and it's a hot hot day would you choose to wear your black t-shirt or your white t-shirt well of course you're going to use your white t-shirt i mean the black one looks so nice but it might make you a lot hotter because the white will reflect all that sunlight off the black will soak it in will absorb it and therefore you're going to feel a lot hotter save that black t-shirt for a nice cold day and you're going to feel so much better you'll look great you'll have your black t-shirt on and you'll be warm enough even though it's cool outside okay so we know that light can be reflected and that's what we will see let's write that down what we see okay and then the other thing that happens is what about all the other wavelengths of light that are not reflected well it really depends on what is the nature of the thing that's being struck by light if it's something opaque like a t-shirt and say for instance you're wearing a purple one we know that that is going to be the reflected light that appears but the rest of the wavelengths will be absorbed into um into the t-shirt okay the same thing will happen with chloroplasts so of course as i was mentioning that the green from the chlorophyll will be reflected that's what we'll see and make the plant leaves look green but all the rest of the wavelengths of light that are visible are going to be absorbed and that is what is really beneficial for the plant the plant can use this there we go so the plant can use absorb light okay now it turns out that if you're talking about something different like um something that's kind of transparent say you're talking about a glass of apple juice or a glass of iced tea and if you place it on a desk that is in the light and the light comes into it you'll notice that on the side of the opposite of where the sunlight is coming in you'll see this beautiful color of yellow or orange depending on what you're talking about and if it's a kind of an orange tea it'll repair up here orange on the desktop or if it's the apple juice it'll appear 11. a yellow that's funny so um that's what happens with transmitted light is that the other light will pass through so those are the three things that can happen with light now in terms of using that light this is going to be important to plants in those molecules that we talked about called pigments well here you've got a really dark green leaf right and so you can imagine it's going to have pigments that are green however even though you're talking about a dark green leaf there are other pigments as well so for example there are carotenes which are the kind of orange color so that's what's going to be reflected is the orange color this is also the pigment that is found in high amounts in carrot in carrots which is where carotenes get their name from xanthophils xantho means yellow and so these are kind of a slightly greenish yellow color and that's what you end up seeing and then chlorophyll a is the one that we usually think about the most that's the one that is the one that appears like the green leaf and then there's chlorophyll b which is a slightly green color but slightly yellow so more on the green side and this one's more on the yellow side and what we can do here is take a solution like we did in lab and grind it up and then from there we can allow um for the acetone that we put in there with petroleum ether to take the plant material and wick it up as we're going along over time and those molecules that are most have a most affinity are most attractive to the solvent in this case the keratins will go up the highest and then those that are least attractive like chlorophyll b will stay down to the original part where it was at near the solution um at the base of the paper so we can see the reflected colors here again but it turns out each of these absorbs slightly different wavelengths and that is really beneficial because then that means the plant can use most of the spectrum to do something with it although the chlorophyll a is going to be the most important one how is that the case well chlorophyll a is the one that's involved directly in the light reactions and so it absorbs violet blue or blue violet and red light and it's the one of course that we know reflects that really kind of bluish dark green the other photosynthetic pigments will get the other parts of the light right but what they will do is absorb that and dissipate any excessive light energy so that way chlorophyll a is protected and it doesn't damage it because otherwise it'll stop being photosynthesis okay so how do we see them if you've ever lived in a very cold area um then you might have seen when the leaves change color in the fall we don't get that so much here in san diego there are a few plants that will do that for example there's one called liquid amber which turns some really beautiful colors but in general if you wanted to see this you have to go to another colder area of the united states such as the north east like new hampshire and vermont in that area and there's a particular reason for that chloroplasts with their chlorophyll in them are very susceptible to degrading when it's cold and when that happens the other pigments like the ones that will show different colors will be unmasked and then you get to see them very well before that it's mostly the chlorophyll is what you're seeing and the reality is here in san diego we love the the mellow uh weather but we don't get it cold enough and that's why we don't see those brilliant colors however if you ever have experienced a very cold that is relatively speaking here winter in san diego then um you will have seen um situations where there can be more of these reds and yellows um and oranges than in other times but it's not very often simply because of the of the temperature all right so let's take a look at what's happening with photosynthesis in detail looking at what's happening at the cellular level okay so what we talked about before were that there were two um two major reactions in photosynthesis so there was the light reactions and the calvin cycle the basic idea of the light reactions is to convert solar energy into chemical energy so into an energy that can be used right it's a potential energy so take a moment and let's look at this left-hand side of the chloroplast and what do you see as the major reactant and what's the major product pause this for a moment and write that down okay so now you'll notice that water is the major reactant and oxygen is the major product it often seems like light would be the way it's written in here but if you think about it as it's not really getting affected it doesn't get broken down like the water is it doesn't have molecules that are being broken apart or anything so in that way this is like catalyst it's not exactly like an enzyme but it's what gets things going right so i wouldn't count light as a reactant i would count the water and the oxygen okay but then you can also see that there are other reactants and products that are involved here in order to get things going for the light reactions um we know this that we have plus nadp plus phosphate the phosphorus in the form of phosphate one thing i want to point out though is that sounds pretty familiar doesn't it what does it remind you of this should be something that we talked about in cellular respiration what was it if you remember there was nad plus and what was nab plus go back in your notes to try to figure that out if you can't remember at the moment or write them down if you do remember it okay so nad plus was an electron carrier it just didn't have the electrons in it at the moment so that's very much like what nadp plus is this is just the plant form of it so here we're looking at a different molecule but with a similar kind of thing that is an electric care oh it was an electron carrier now in terms of light reactions we can also see there's two major products that's nadph and you probably recognize that now as well when this electron carrier gets full and it adds in the two electrons plus the hydrogen so that's the electron carrier that is full and that's what's happening here is that the light reaction is producing that so that way it can be used in this calvin cycle the other thing is that we've definitely phosphorylated the adp to become atp right we've added a phosphate on here where there were two phosphates and now there are three so that's the other thing that clearly we need to have in the calvin cycle all right so that's what's happening there we can see chemical energy we're dealing with that in terms of the electrons going to be involved in phosphorus right and then over here on this side it's about making sugar from carbon dioxide well we know sugar usually is glucose and that is c6h12o6 so we're talking about the carbons right this is the carbon here the other hydrogens and oxygens can be involved too because look at there's our oxygen right so our major reactants what are they and what's our major product take a moment write those down for the calvin cycle okay so here's the major reactive we have carbon dioxide and then here is our major product and so what we've done is we've accomplished our task we've made sugar that was the goal making glucose in photosynthesis now let's see how this all happens right now it's a little bit magical so let's take a look at more specifically what's happening to these molecules and how they're getting to be the way that they need to be so they become an actual glucose so if you've gone through your cellular respiration then this picture should look awfully familiar it should look a lot like something we've seen in cellular respiration of course it's not happening in the mitochondrion it's happening in a chloroplast instead and you can see more specifically it's happening within one of these thylakoids along its membrane so it's inside the sack and then the membrane is uh kind of around it and all of these purple things are in the membrane so based on what we've seen before you should be able to identify various kinds of things in this picture they're using the same symbols so when you hear them write down or say out loud what the parts are so what is this yellow arrow that's squiggly supposed to represent yep those are photons of light what is this uh gray and yellow thing well it's a phospholipid um bilayer which is the membrane right it's a membrane of the thylakoid we talked about so we've got a bilayer there what are these purple things what have we been using purple for and kind of in general well those are proteins and those proteins are going to do something looks like moving things across which we've seen before right okay what is this blue oval usually represent yep you know it's going to be water and water can be broken apart into these things right what does the red sphere represent it's going to represent oxygen o2 right and then of course the other part is going to be the other part of water which would be hydrogen so that's what these must be all hydrogen okay and then we also see this going to that so what are these a picture of so these are electron carriers and we remember that the electron carrier here is a little bit different in the plant in terms of its name and molecule but they do the same thing so this is nadp plus and this is nadph and you can see that the two little seats here when they're empty in the empty form of this taxi that this is now the full form so they're sitting right in there okay and then finally what is this star well that is as you know atp so this must be an enzyme and it looks like stuff is moving through it right and we learned about an enzyme that has something to do with atp if you guess atp synthase you've got it so that's atp synthase all right so picture this as though it's like a dam and we're looking from the top of the dam like we're flying a helicopter over it okay so what we're gonna look at in the light reactions are the three parts these purple um proteins we're going to refer to as photosystems photo of course meaning light and then the other part we're going to look at is this part which should look pretty familiar it's an etc or an electron transport chain and then finally the third part is chemiosmosis and osmosis should sound familiar that is the movement of what across a what so if you remember the term osmosis it's moving water across a semi-permeable membrane but here they've changed the name just a little bit kidney osmosis so maybe it's not water but something very much like water and remember it moves from an area of blank concentration to an area of length concentration so which way is that high to low or low to high if you remember high to low you're correct because we're talking about something moving from an area of high concentration to low concentration without the use of energy so we'll talk about that a little bit later let's focus a little bit more on those photo systems so we can see what's happening there now currently in this picture you can see that it is in tact meaning it's a part of a leaf a part of a chloroplast what i'm going to show you next is if we were to take it and in its simplest kind of grind it down so it doesn't have all the parts the membranes aren't all there and so forth but what we could see is that light is able to strike it so we're going to see a very simplified version of it that's what this is right here now notice what we have is a chlorophyll molecule that's the main important molecule in the light reactions and what we saw was that light is striking those purple proteins in which the chlorophyll molecule is located you get a photon or wave particle of light that strikes it and what that does is it kind of energizes everything so it wiggles things around and then an electron jumps up into this location up here so where is there more potential energy where do you think there'd be more potential energy in the excited state or in the ground state what do you guys think well think of it just like if you were considering uh the snowboarder right we talked about where he or she has the highest potential energy it'd be up at the top of the hill right the same thing here the excited state has more potential energy than the ground state and then um what can happen is that snowboarder will slide down the hill and it'll transform the potential energy into kinetic energy now if this plant were more intact then we could use that kinetic energy to do something so what is released when the electrons fall down what do you see from the picture here so probably you're going to see heat and light that's what's going to come out of this you know that heat is kind of randomized energy it's useless or relatively useless comparatively speaking and in terms of fluorescence that is just the extra entropy as it were the energy that is released as a as a result of this now the weird thing about this is that it creates this fluorescence and if you remember in lab we got to see a picture of that it turned out to be this crazy blood red color it wasn't as obvious in our particular situation it wasn't as concentrated but it was very strange to see something that is naturally green colored and when you shine a white light on it it turns red that's the fluorescence that's given off when that energy isn't used so i guess the next question is what happens when we put this intact what can we do with that energy that is in fluorescence typically well we can see if we have an intact photosystem we still have our sunlight there's still our chlorophyll a molecule and now we've got it in place where it has the protein photosystem it's which is placed inside of a membrane right and we can see that a photon of light strikes um the parts of the protein right here where there are molecules these are all pigment molecules and when it strikes a pigment molecule that pigment molecule bumps into another molecule and that one bumps into another they kind of just get rattled and basically what ends up happening is the last one bumps into chlorophyll a and what it does that chlorophyll-a molecule is excited and the electron jumps up into the excited state right which is going to be what we call the primary electron acceptor in that part of the protein now if you remember from photosynthesis we have primary electron acceptor but in cellular respiration we referred to as the final electron acceptor do you remember where the final electron acceptor was where was it in which of the stages and what molecule was it well hopefully you remember that in the very last stage in oxidative phosphorylation that final electron acceptor was oxygen and it's where the electrons came down from the etc and when the oxygen received that then it was able to form water so if you don't really remember that go back just for a moment and you can visualize it by seeing the picture of it now in this situation here we're looking at the electron going into the primary electrons acceptor within the reaction center of this protein and so at this point it has very high potential energy and it has potential to just do pretty much anything it just falls down and what it's going to fall down is like the snowboarder it's going to change that the potential energy into kinetic energy there's going to be a transferring and so at that point we'll talk about that if you need to review this again because we're going to see this again in a few minutes over and over okay so what we can see here is that we're putting our photosystems the two of them inside of the membrane now so like we saw before we had uh the photon that was was striking the protein and it strikes the pigment molecules which makes them jostle back and forth knocking into each other until the last one knocks into this particular chlorophyll we call it p680 because it's talking about the wavelength of light that really gets this energized the most and is more likely to release that electron so that electron ends up in the primary electron acceptor and as a result of that now this chlorophyll is missing an electron so in order to lose an electron this is going to have to gain it right so there's an oxidation going on here there's going to have to be a reduction and so here the reduction is the electron is going to come from water splitting water from water to oxygen and hydrogen so now it's replaced that electron now the electrons are going to fall down this etc and we haven't talked about this yet and we will in a moment but we're going to see that this is going to somehow um provide some energy so we can get atp but we haven't done that yet it's not in this picture so we can see there's a second photosystem and in that photosystem there's a photon of light that strikes these pigment molecules and they jostle around the last one is going to knock the electron out of p 700 which that chlorophyll is going to lose an electron here and ultimately go down its etc this electron comes down here and replaces that one that was in the chlorophyll so what i'd like you to do is take a moment and go through and try to write down what are the reactants here and what are the products remember to look for arrows the stick end and the pointy end this one's kind of strange looking but try it for just a moment go ahead and put it on pause and then you can pick it back up once you're done writing okay so let's see if you figured it out this is really a weird one because you have all these arrows but which ones are these are reactants and which ones are products and so we know that photon of light is not because that's just kind of assisting getting things going here kind of like a catalyst and we can see this is just movement of these electrons right but what we can see is the end of an arrow here so the main reactant here and this side is going to be water and the products will be on the pointy end the half o2 plus um 2h plus now if you're wondering why it says half o2 well that's because we know when you see oxygen in the environment because of the octet rule it's an oxygen oxygen molecule two oxygen atoms hooked together right um and when we see that that's how they're normally found but if we were trying to figure out well we have one oxygen here that must mean that there's a half of it in there so um i suppose they could have written this differently and you'll have to pardon me since i can't write this with the appropriate um with the appropriate subscripts but they could have written that i suppose like 2 h2o right and then yields and then do their uh oxygen and then plus four h plus let's try this again plus four h plus so if they wanted to say it this way then they could say well here we've got two waters so that means there's one h2 what two to h2 let's try to get two h's in one water so if we have two h2os that would be four hydrogens right and there's four hydrogens and then if we said o2 well then there's two o's in two waters so this is another way of saying the same thing they just chose to illustrate it this way basically it's an issue of showing it as a balanced reaction not really that important the main thing is that water breaks apart and releases oxygen and hydrogen ions okay so that's one thing did you find the other reactant in product set the other reaction if you did that should have been up here with the nad plus plus hydrogen ions and then yields the nadph so that's that okay good so what we have here is a process we can see that the electrons are moving out and down this etc so to finish off the light reactions we just have one more part we've talked about the um uh the two parts right here where we have a photosystem two and one and then we also have briefly looked at the fact that this is an etc right so an etc electron transport system helped us out with something last time when we talked about it inside the respiration what did it help with well it turned out it had everything to do with a concentration gradient and we're doing the same thing here this is going to be a concentration gradient again of hydrogen ions so you can see what happens here is that we have photosystem 2 and we have the light strikes there we get the pigment molecules jostle back and forth until we release an electron the electron is reintroduced to this chlorophyll by water which splits here and then what we do is we have that electron in a place of high potential energy and it starts to fall down and as it does it provides the kinetic energy to change the shape of this protein so that way we can actually get the hydrogen ions moving from an area of low to an area high thereby creating a concentration gradient you see on this side we have lots of hydrogen on this one we have very little so we created that then we also are able to create at this point ah nadph so that was one of the things that we needed to get out of the whole deal was nadph the other thing that we needed to get out of it was atp and that's going to happen just as it happened with cellular respiration it's happening the same way notice the high concentration is on this side and the low concentration is this side so since there are no other openings that allow for hydrogen to flow this is the only opening that allows for the hydrogen to flow through the enzyme and it kind of turns around like a turbine until an active site for adp and p come available and then that allows for them to come together to make atp as the hydrogen flows through yay so what we've done is we've made what we need chemical energy so that way we can go on to the next part for the calvin cycle and we can actually make the glucose that we need all right so taking a look at that part let me erase these little things here okay so that was chemi osmosis as you know that's the process by which atp is made through atp synthase okay so the calvin cycle you're going to notice is not too bad when you compare to what we've already seen before so we can see that we have carbon dioxide that's going to come in and it's going to come in as you know from the outside air into the leaf of the plant through the stomata inside of the leaf already in the stroma is this molecule called rubp we could spell it all out but it's got this huge long beam and why bother let's call it rudp now notice as we've drawn it before it also has carbons in this case it is a five carbon molecule but there happen to be three of them okay so that means there's a total of 15 carbons here okay we know that carbon dioxide has one but there are three of them so um we can see there's 15 and there's three here now what's going to happen is these two are going to come together and get reorganized into this three pga again you don't need to know all these intermediate names like rudp and 3pga it's not so much necessary however what you do notice is that well there's one two three carbons for one molecule times six of them that's eighteen just like we saw a moment ago right three plus fifteen so it's eighteen they're all just rearranged into this other shape now what ends up happening is you have a particular molecule called rubisco ribisco is surprisingly the name of an enzyme because what do enzymes normally have at the end of their names do you remember if you remember it's ase that's what helps us know that it's an enzyme however nobody calls rubisco the thing with its a and c at the end because it's such a long name here let me give it to you the name you is ribulose one five bisphosphate carboxylase oxygen oxygenase right almost messed it up myself there so you can see there is an ase at the end um but it's just such a long name that people don't even call that whole thing they just take parts of this whole thing to give it a name so that is an enzyme and be aware of that enzyme it happens to be the most common enzyme known on the planet and it's just to do this little part of the calvin cycle for visco okay so remember each of these steps is mediated by an enzyme so the next part that's going to happen is these six three carbon molecules are going to have a few things done to them so first of all we're going to energize them so there's going to be atp that is going to energize them and then it breaks apart into adp plus p and of course this came from the previous situation in the light reactions and also we have nadph yields nadp plus well what is that called going from nadph to nadp plus think about it this way did nadph gain or did it lose electrons to become nadp plus well clearly it lost because here's two electrons and now there aren't any right so if you lose electrons what do we call that remember that's that crazy oil rig thing that means it's going to be an oxidation okay well if this is the oxidation there has to be reduction who gave them turns out it's going to be this process here going from 3pga to this thing called g3p so that is the reduction see how sometimes without having the whole drawing there you can't see a whole lot of what's happening so it's sometimes just better to follow what you can see and then you know the other member of the coupled reaction the reduction for example here is in there even though you can't see it at least not the way it's shown right now okay so now we have this molecule called g3p we actually have six of them it turns out g3p is basically half of a glucose and so what we're going to do is we're going to steal one of them right here and hold on to it for a moment and the other five are going to go back here well why can't we just steal two of them and then make a glucose because there's a half each well if we did this wouldn't be a cycle because at this point with five of them we've got a total of 15 carbons if we had four of these we'd only have 12 so we couldn't make this again and we couldn't start over again so got to be a little patient in this case what we'll do is we'll take one out re-invest five of these three carbon molecules so 15 of them right and then uh from there we can put a little energy onto them there they are and now we're ready to restart when we need to so basically if you think about that then all you need to do is double what you have here do this twice and you'll get a glucose molecule all right so what i want you to do is take a moment do the reactants and do the products and then you will see um you know what's left over here so take a moment pause here write down the possible reactants and products you can combine like terms too like if you have atp here combine it with that one the numbers as well okay go ahead and do that pause here and then try it all right so hopefully you've got here six co2 well it says three here why is it six well remember if we want to make glucose we have to double it that means this has to go through twice so all the numbers we need to double so here we've got three let's make it six atp's here we've got six here and we've got three here so that's nine times two that's our eighteen and then our nadphs we have six here times two that'll make it twelve and then our products will be the same thing and of course our original product will be two g3ps which will make our glucose ultimately so if you wrote glucose here that's okay too and then uh but the original main product is actually g3p and then that just gets made into glucose and then of course you're going to have the same amounts of phosphates and adps and nadp pluses all right so and that's because we had to multiply it times two because we're going to go through the cycle twice all right i hope that was useful to you and you can connect it to your concepts associated with photosynthesis from lab have a good time everybody thank you for listening