hey everyone Dr D here and in this video we are going to be covering chapter 10 from our Campbell's 12th edition biology textbook this chapter covers photosynthesis so let's go ahead and get started I Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D explain stuff all right welcome back this is chapter 10 it covers photosynthesis it's a very interesting chapter so let's Dive Right In photosynthesis is the process that converts solar energy into chemical energy within chloroplasts photosynthesis is responsible for nourishing almost the entire living world either directly or indirectly these photosynthesizers are known as autot troes because they are able to feed themselves they sustain themselves without having to eat anything they don't have to eat other organisms to live they feed themselves by using sunlight and they get their carbon from the air in the form of CO2 autot tropes are the producers of the biosphere they produce organic molecules from CO2 and other inorganic molecules so unlike you and me autot tropes can feed themselves they don't need to consume other organisms to live they get their energy from the sunlight and they get their carbon from CO2 whereas you and I let me just skip ahead here you and I are what's known as heterotrophs or other eaters not self feeders but other feeders we don't get our energy and our CO2 in those ways we get our energy and our CO2 by consuming organic material so we have to eat right we have to consume other organisms to get our energy and to get our carbon right so we are known as heterotrophs there are photosynthesizers which are autotrophs and then there are animals like you and me which are the heterotrophs we consume other living things we also can decompose things or eat dead organic materials okay so again you and I are heterotrophs we depend on the autot tropes to live in fact without these autot tropes without these photosynthesizers we wouldn't have any food any nourishment to eat they really are the bottom of the food chain which is wonderful for us and what are these photosynthesizers they include plants right ukar such as plants ukar such as multicellular algae you know the kelp and seaweed and also unicellular ukar Nots such as ugena or diatoms okay so many different eukaryot are photosynthesizers however you should also realize that there are procaryotic photosynthesizers as well cyanobacteria these are procaryotic bacteria these are photosynthetic bacteria and there's many different types of cyanobacteria and then also there are the purple sulfur bacteria as well so there are many different types of photosynthesizers they all contribute to you know producing sugars and energy for the rest of us to eat so let me show you where the chloroplasts are found in a leaf just to get started here when you have a plant plant cell plants have leaves and the leaves appear green thanks to the chloroplasts if we were to cut a a section of a leaf and take a look at this crosssection of a leaf right here you'll notice that there are cells that are in the middle of the leaf and then there are cells that line the outer the upper surface of the leaf and the underside of the leaf as well the cells that are in the middle see here the cells in the middle of a Leaf are known as the Miso cells miso meaning middle and these are the cells that have chloroplasts inside and each cell can have several chloroplasts inside the chloroplasts are the location where photosynthesis occurs and on the underside of a leaf are these neat structures called stomata which you can think of as breathing uh structures for this for the leaf they can open up to accept net CO2 and to expel net oxygen so they respire kind of the opposite way to you and me we take up oxygen and expel CO2 plants have a net take up of CO2 with a net expelling of oxygen isn't that neat so these are called stamata you can bre you can think of them as little pores that can open and close to allow gas exchange on the bottom of the leaf all right and if we look at a misop cell one of these one of these misop cells up close you can see it it's packed with chloroplasts inside it's those chloroplasts that make the leaf green cuz remember from a previous chapter we talked about the chloroplast here and the structure of the chlorop plast and I told you that a chloroplast has an outer membrane an inner membrane and then it has these stacks of membranes right these Stacks that I call I affectionately call Pancake Stacks right because they remind me of a stack of pancakes each pancake stack of membrane is called a Grom a Grom okay here's the term Grom and each pancake in the stack is called doid okay so a stack of thalloid is a granum and if you look closely there's a membrane here that's called the thid membrane now the fluid immediately outside of these pancake Stacks is called the stroma where is that term here stroma the stroma is the fluid outside of the pancake Stacks now what about the fluid in the pancake Stacks remember that's called the thid space all right so again outer membrane inner membrane pancake Stacks called granum each pancake is aoid the fluid outside is the stroma the fluid inside is the thalloid space and what's this membrane called the membrane of the pancake Stacks it's called the thalloid membrane these are important structures to recall for this chapter so please remember your anatomy of a chloroplast because it's going to come up handy later in this chapter now here is the equation for photosynthesis I want to actually head to the board and go into this equation a little bit with you CU I have some interesting things to share about photosynthesis so here I have written for you the equation for photosynthesis take a look you have light energy CO2 and water as reactants on the left side of the arrow and then you have glucose and oxygen on the right side of the arrow these are your products on the right these are your reactants on the left now I'm going to ask ask you take a close hard look at this equation and answer me this does this equation look familiar to you that's right Wicked wicked's on top of this this looks like cellular respiration doesn't it we just got done in the previous chapter talking about cellular respiration right and the only difference between photosynthesis and cellular respiration is what it looks like The Arrow would be going the other way right so this if the arrow were going the other way what we would have is cellular we'd have aerobic cellular respiration the only difference to would be that instead of you know using glucose and oxygen to make light energy obviously with cellular respiration we would be making ATP energy right so but but other than that what you should realize is photosynthesis is the converse reaction to cellular respiration Converse means opposite okay um photosynthesis and cellular respiration are truly Converse reactions and that leads me to a really really interesting point about photosynthesis I want to share with with you and I hope this blows your mind a little bit I hope it's really interesting for you let me give you a thought experiment okay um now what I'm going to do is I'm going to do a thought experiment with you what if I had like a jug okay and I had a jug and let's say in this jug I put a person okay and here's a person in The Jug right now what do you think would happen to said person in The Jug if we plug the jug right we had a cork here you know and we pluged that jug what would occur here uh well you know if we plug The Jug off from the surrounding air then eventually the person would convert what oxygen right oxygen convert it into what CO2 and unfortunately at some point the person would undergo enough cell respiration right to convert sugar and oxygen into CO2 but at some point the person would not have enough oxygen unfortunately in The Jug correct and the person would end up passing away why because people undergo cellular respiration animals have mitoch Andria and that means that they undergo cellular respiration so now let me give let me give you another example here let me give you another example what if instead of a person in the plugged up jug I did this so now let me show you the second scenario here now The Jug has a plant in it the plant has some soil the plant has some water and the plant has access to sunlight right so but it's plugged up it's plugged up so now let's think about what would happen to our plant in this jug would our plant survive or would our Plant die so think about this look at this let me ask you um if the plant is under going photosynthesis right uh then it is converting CO2 it's converting CO2 and it's using water and sunlight to produce produce what to produce O2 right to produce oxygen now you might think well at some point the plant is going to use up all of its CO2 and convert it to O2 and then the plant is going to pass away right from lack of CO2 right just like the human the human was going this way the human ran out of oxygen and passed away so why would the plant not run out of CO2 and pass away well let me let me make you think a little bit which organel is responsible for photosynthesis doing this reaction here you got it Wicket got it photosynthesis is done by the chloroplasts right do plants have chloroplasts yes plants have chloroplasts chloroplasts do photosynthesis but let me ask you this let me ask you this this should be a quiz from a earlier chapter you remember the uh cell chapter do plant cells also have mitochondria that's right Wicked they do remember I made a big point about that uh plants also have mitochondria mitochondria so what did that tell you that tells you that plants not only can plants do this reaction with their chloroplasts but plants can also do the converse reaction with their mitochondria so guess what when the plant is converting CO2 to oxygen with its chloroplasts it's also converting that oxygen right back into CO2 with its mitochondria so let me ask you again here let's put our thinking caps on right let me ask you again would the plant survive in this jug that's corked or would the plant pass away and the answer is the the plant would live just fine it would just recycle everything it's the perfect green organism green meaning a plant uh in that jug the plant would produce oxygen then use the oxygen to produce more CO2 and the plant could live indefinitely in this jug isn't that neat uh to think about that uh plants are truly amazing plants are self-sufficient plants do not need to consume other organisms to live okay uh in fact plants are so vital photosynthesizers in general are so vital to our existence let me give you three reasons why okay the first reason why is they produce oxygen they they do net more oxygen when not in a jug they do net more oxygen for us to breathe than they then they put out CO2 so the reason why we have lovely oxygen to breathe in our atmosphere is thanks to photosynthesizers photosynthesizers are putting that oxygen in the atmosphere for us to breathe if photosynthesizers were to perish we would soon after perish because we would not have oxygen to breathe reason number two why we depend on photosynthesizers you see what a product of photosynthesis is glucose chemical energy do you remember from chapter one we discussed how energy enters an ecosystem via light then it's that light is captured by producers such as photosynthesizers or autot tropes those photosynthesizers produce chemical energy from that sunlight and then the rest of us animals heterotrofos we are the consumers who consume those an that energy right those sugars and fats that are produced by the plants isn't that neat so if photosynthesizers were to perish we would soon after perish because we would have nothing to eat and the third big reason why we definitely need photosynthesizers around is look at this look what plants do for our environment for our atmosphere plants take CO2 out of the air literally literally you can think of plants as kind of sponges that remove SE CO2 from the air they can take gaseous CO2 from the atmosphere remove the CO2 and use it to produce sugars and other organic molecules so we can thank plants and other photosynthesizers for helping regulate the amount of CO2 in our environment CO2 is a you know greenhouse gas and by plants removing CO2 they help to mitigate that amount of CO2 in the environment and mitigate the problems with global climate change and by the way just for fun look up stories of people who have grown plants inside of closed jars there's even stories of people who have grown plants inside of a closed jar for upwards of decades 50 years or more all right for these reasons I truly believe that plants are fascinating and amazing organisms on the planet they are so highly adapted to living on this planet you know if tomorrow all of us consumers all of us heterotrophs like you and me and all the other animals if we were to perish tomorrow you know the your plant friend would continue to grow the photosynthesizers would continue to grow on this planet Earth and have a great time and and not think a a thought about it right but if the producers if these plants were to perish if these photosynthesizers were to perish tomorrow so would all the rest of us right so isn't that amazing that we 100% depend on these photosynthesizers in fact we breathe their waste product we depend on a waste product of these plants to live and we depend on the sugars that they make make to live and we depend on the fact that they take CO2 out of the environment to live you know what's funny if you think about going to another planet you know like Elon Musk thinks about you know going and inhabiting Mars one day we would have to figure out a way to produce oxygen on Mars you know whereas if we were green people if we were photosynthesizers we could actually go up and produce our own oxygen up there so if plants went up to another planet they they could make their own oxygen their own CO2 however if we went to to another planet we would have to bring a friend we would have to bring a green friend with us so that the green friend a plant a photosynthesizer would produce the oxygen for us to breathe isn't that really neat to think about just how well adapted plants and other photosynthesizers are to living on this planet Earth and and how how uh much we need them for our own Survival all right welcome back from the board I hope that was informative again photosynthesis involves light energy plus 6 CO2 plus six H2O as reactants on the left side and these produce the products glucose and oxygen now you remember what happened during cellular respiration during cellular respiration glucose was oxidized to CO2 remember we took all the H's away from glucose that means we oxidized glucose and when we took all the H's away from glucose what was left of glucose remember it was the six co2's so during cellular respiration glucose was oxidized to CO2 and do you remember what happened to our oxygen during cellular respiration during cellular respiration remember oxygen was our terminal electron acceptor oxygen picked up the electrons at the end of the electron transport chain right so oxygen was reduced to water do you remember that during cellular respiration now this is the converse reaction remember Converse means opposite so in cellular respiration we oxidized glucose to CO2 well guess what during photosynthesis CO2 is gaining H's it's gaining electrons CO2 is getting reduced to glucose and water is losing its H's losing its electrons so water is becoming oxidized to oxygen isn't that really meat so it really is the converse reaction to cellular respiration now do you remember our big overview sheet for cellular respiration how it was a handy overview sheet to look at all the different steps or phases of cellular respiration well here is a comparable image here I really like this image this is an overview a big picture overview of photosynthesis and what's cool about photosynthesis especially if you're trying to learn photosynthesis is that it's only two phases right you have only the light reactions uh as the first part and then you have the Calvin cycle as the second part uh that's it uh remember cellular respiration had three and a half phases right you had glycolysis oxidation of pyrovate then you had the citric acid cycle followed by oxidative phosphorilation remember there was a lot to learn during cellular respiration but here there's only two phases there's the light reactions of photosynthesis which happen in those pancake stacks of the chloroplast this is a chloroplast by the way this is a chloroplast and remember the pancake Stacks called granum well the light reactions occur in the granum and then the Calvin cycle is the second phase of this process and that occurs in the stroma remember stroma is the fluid right outside of those Grom and that's it there's only two phases to learn about so let's delve into these two phases all right so let's delve into photosynthesis and photosynthesis is a lot more straightforward than you might think I'm going to explain it as a big picture and I think you're going to get it it's going to click um it's really not that bad and I just want to show you the big picture picture so that you can see what we're trying to get at before we go into details okay so pay special attention and I think you'll get it there's it's not that bad I promise so take a look here remember at the end of the photosynthesis process you want to make sugar which is some multiple of ch2o you're going to make glucose here well that's what you produce at the end of the Calvin cycle right now what are the building blocks of sugar remember you need carbon you need hydrogen and you need oxygen so think of photosynthesis as a process that wants to make sugar now look at this during the Calin cycle what do we take out of the air right what do we take out of the air we take CO2 out of the air we literally remove CO2 from the air and capture it in the Calvin cycle now what do you think we need from CO2 we need its C's and we need its O's does that make sense because to make sugar we need C's H's and O's and where do we get our C's n O's we get it from CO2 from the air now what else do we need to make a sugar now we have a source of C's and we have a source of O's what else do we need right Wicket we need some hydrogens and where where are we going to get hydrogens from what's another reactant of photosynthesis that has hydrogens that's right Wicket water look at this water is another reactant that's required by the Light reactions okay what does water have it has a couple of hes do you think we could Harvest these hes and take these hes we would like to harvest these hes and where where would we hand hes where do what normally handles hes if we were to remove H's like we did during cellular respiration where do those H's go do they go directly to their destination or are they handed to a carrier how about an electron carrier do you guys remember NAD plus and fad were electron carriers or I I prefer to call them hydrogen carriers because that's more accurate um well here there is an electron carrier but it's a it's a plant version uh it's called nadp+ and we hand we're going to oxidize water we're going to take its H's away we're going to use those H's and hand them to nadp+ reducing nadp+ to nadph you see now the now the H went from water right the H's go from water to the carrier reducing the carrier to nadph nadph goes to the Calvin cycle andh the H's to CO2 reducing CO2 to Sugar isn't that interesting so to make sugar our C's and our O's came from CO2 while our hes came from water Isn't that cool now let me ask you this when you oxidize water when you take its H's away as the light reactions did what's left of water when you've taken its hes away you have oxidized water to oxygen isn't that neat you have oxidized water to oxygen do you now see why plants produce oxygen for us to breathe the entire reason why plants produce oxygen for us to breathe is because plants need a source of hydrogens in order to make sugar and they take the hydrogens of water they oxidize water and what's left over is the byproduct called oxygen and that oxygen leaves those little stomata breathing holes and floats around in the atmosphere for us to breathe isn't that neat okay so do you now see the big picture now let me ask you this let's let's go into a little more detail here um let me ask you this do you think it's easy to oxidize water okay think about this real quick when you're taking H's away away from water when you're taking electrons away from water who are you actually taking those H's away from you're taking the H's away from this oxygen what do we know about oxygen does is oxygen fond of its electrons or is oxygen not care about electrons is oxygen electr negative or is oxygen not very electronegative that's right Wicked the oxygen is quite electr negative because it appears at the top right of the periodic table and so it is very electr negative so this is really fascinating isn't it during photosynthesis we are oxidizing water we are taking H's away from water and that's not easy because oxygen doesn't want to give up its hes oxygen doesn't want to give up its o its electrons oxygen is greedy okay in fact oxygen is usually known as a as a thief of electrons it steals electrons from everyone in fact that's where the term oxidation came from it's Oxygen's ability to steal electrons from from other substances isn't that interesting so during photosynthesis uh the the the the the granum in here the the light reactions are capable of stealing from a thief it's like it's like stealing from a thief right uh you're able to take electrons from someone who specializes in stealing electrons and you give those electrons to the electron carrier nadp+ reducing nadp+ to nadph and then nadph transfers those hydrogens and those electrons to the Calvin cycle to make sugar okay isn't that neat so so do you think it's easy do you think it's easy to oxidize water to oxygen if if oxygen doesn't want to give up its hydrogens no it's not easy and it's not spontaneous so we're going to need a source of energy to do that we need a source of energy to oxidize water to oxygen that's not a spontaneous process so we're using light that's why we need light we need sunlight energy uh in order to properly oxidize water into oxygen and steal those hydrogens from water we give those hydrogens to the electron carrier nadp plus reducing it to nadph so that it can carry those electrons and those hydrogens to the Calin cycle and as an added bonus which I'll explain later I'm going to explain this to you we also form some ATP um so I I I'm not going to go into this right now but later in this chapter I'll explain that during the light reactions we also form some ATP okay so what are the so let me ask you this let me ask you this what do you think are the reactants for just the light reactions of photosynthesis what do we need for the light reactions of photosynthesis it looks like we need sunlight we need water okay those are the two main reactants and then what do we what are the products what are the the main products of the light reactions of photosynthesis it looks like the byproduct oxygen as well as some ATP which I'll again I'll explain how we formed this ATP later and because we stole those H's nadph right so now the electron carrier has H's so again the reactants are light and water and the product of the light reactions are ATP nadph and the byproduct oxygen okay now let's turn our attention to the Calvin cycle uh remember the light reactions occurred in the thids of the granum right the pancake Stacks whereas the Calvin cycle occurs in the stroma you know the fluid outside of those Stacks in the chloroplast and now look remember what did I say occurs in the Calvin cycle we want to form sugar right C6 h126 we need a source of C's and O's here is our source of C's and O's it's CO2 it enters the Calvin cycle through the stomata and into the stroma of the chloroplast from the air from just the atmosphere next we need a source of hes we're going to now we have C's and O's we're going to hand the C's and the O's some H's right do we have a source of H's yes right here here's our source of H's n a dph these H's which came from water right so we are going to hand the H's from water to CO2 to make sugar do you think that's a spontaneous process or do you think that requires energy to make sugar that's right Wicket it takes energy to make sugar because breaking down sugar releases energy so if you want to make sugar it's going to cost energy so do you know what we do we use that ATP that's where that ATP is good for from the light reactions we needed ATP we're going to use ATP energy in order to hand the hydrogens from nadph to CO2 to make our lovely sugar right and so what are we truly doing During the Calvin cycle which occurs in the stroma we are using ATP energy in order to reduce CO2 to sugar reduce means we are giving electrons to CO2 to form sugar um those hydrogens contain electrons right so we are reducing CO2 to Sugar awesome so isn't that a cool overview I hope that helped if it's still confusing maybe watch this section again if not let's continue on we've got more details to cover like what exactly is happening in the light reactions and what exactly it's happening during the Calvin cycle we're going to go into more details now but hopefully at this point you have a nice big overview of just how straightforward it really is all right now let's delve a little bit into how light works and what is light uh light is made up of different wavelengths of electromagnetic radiation electromagnetic energy travels in waves and the wavelength is a measure of the distance between the crests of an electromagnetic wave so here you can see there is an electromagnetic spectrum which is the entire range of electromagnetic energy or radiation here is the electromagnetic spectrum you have these energy waves these are known as electromagnetic waves that travel through you know space they travel through uh the universe and these waves are you know some of them are really short waves uh they're 10 to the minus5 nanom which is a very short wavelength these are known as as gamma rays and the longest of the electromagnetic waves are the radio waves which are several meters wide okay uh so you have big wavelength energy uh radio waves and very short wavelength energy gamma rays but in between you have different types of energy you have x-rays UV rays and then this sliver right here in the middle is visible light these are the wavelengths of electromagnetic energy that your eyeball can perceive right so when you are looking at the world and you are seeing the world you are capturing the wavelengths of energy between 380 nanometers which is which corresponds to Violet or Indigo light and all the way through to 700 140 nanometer energy which corresponds to Red Light okay and so your eyeballs are able to perceive every wavelength between about 380 nanometers all the way through 740 nanometers and that's why it's called visible light because it's visible to you and me okay and each wavelength corresponds to a different color so for example 550 is green 500 or less is blue you know three 80 to 400 is more of a violet okay these are different wavelengths of light and white light is made up of all the wavelengths okay all the wavelengths of visible light together constitute white light okay or the light from the sun is all the wavelengths together okay then we have infrared W uh infrared waves which are longer than visible light microwaves which are even longer and finally radio waves which are the longest okay now what you need to know is that the shorter the wavelength the higher the energy right the shorter the wavelength the higher the energy that's important to understand now how does how does it work why are plants green let me explain that real quick plants appear green believe it or not because they do not use green light they do not absorb green light remember the light the white light that comes from the Sun that visible light is white okay and when it strikes the Grom when it strikes those thids you have these pigment molecules called chlorophyll which I'll talk to you about in a little bit you know chlorophyll a Chlorophyll B you may have heard of these before but they absorb light right but what's funny is they absorb all the colors except for green green goes right through the chloroplast out the other side which means transmitted light transmitted light is light that passes through and green is also reflected off the surface here that's called reflected light so the when you when you look outside and look at a tree and look at its green leaves the reason those green leaves appear green is because the plant is absorbing the uh the Spectrum all the different colors of light except for green the plant is not using green light the plant is transmitting and reflecting green light plants do not absorb green light right especially these green plants so if you for example if you were trying to grow plants and you used green lights in order to do it uh those plants would not grow what whatsoever isn't that interesting so that's something to understand about how light works now the reason why plants appear green and why plants absorb those colors besides green are because of these pigment molecules these pigments are important for the light reactions of photosynthesis these pigments are vital for capturing sunlight and these pigments exist in The Dore membrane of the granum now look at this there are three types of pigments to know about but the two main ones are called chlorophyll a which is the key light capturing pigment that participates directly in the light reactions of photosynthesis remember phase one of photosynthesis and then there are the you know lesser Chlorophyll B which is an accessory pigment as well as carotenoids which are a separate group of accessory pigments again these pigments are vital vital for absorbing light and allowing the light reactions of photosynthesis to take place especially chlorophyll a so let me show you what the chlorophyll A and B molecules look like what do these pigments look like here you can see the structure the backbone of both chlorophyll A and B remember how I taught you that when you see a structure like this you could fill it in for yourself with carbons and hydrogens so obviously this is a large organic molecule right and look in the middle there is a co-actor magnesium this ring here in the center of chlorophyll A and B is known as a Forin ring with the light absorbing head of the molecule there's a magnesium atom at the center here which which is a co-actor and what's neat is that the only difference between chlorophyll a and Chlorophyll B is this functional group right here here with chlorophyll a there's a methyl group right here on the molecule whereas with Chlorophyll B there's a carbonal group right here on the molecule that's the only difference between the two so let's talk about what these pigment molecules actually do now when a pigment molecule such as chlorophyl a chlorophyl b or one of the carotenoids absorbs light one of its electrons goes from a ground state with a low G value low free energy to an excited state with a high G value a high free energy which is unstable here's kind of what a depiction of that looks like if this is chlorophyll right here this is the pigment molecule chlorophyll a Chlorophyll B this could even be a corat oid here this is a pigment molecule when when a photon of light when Photon hits the chlorophyll molecule remember it absorbs all the colors except for green this causes one of its electrons to go from a ground state with a low free energy low GV value to a higher excited state with a high free energy a high GV value that captures in effect what's happening is the you're capturing that sunlight energy by making this electron hop from a ground state to an excited state when that electron goes in inevitably that electron's going to go back down to the ground state that electron's going to collapse back to a more stable ground state when it does this pigment releases that captured energy so you can think of a chlorophyll molecule kind of like a capacit Itor in electronics you charge up a capacitor and then the capacitor can release that charge here the pigment molecules get charged up with photons of light and then when those electrons collapse back to where they should be they release that energy that trapped energy all right so that's essentially how a chlorophyll molecule works it becomes excited and captures that sunlight energy and then it can release that energy once the electrons travel back to their ground state okay so now it's time to go into a little more detail about what really happens during the light reactions of photosynthesis and then we'll talk about what really happens during the Calvin cycle but first let's start with the light reactions remember the big picture here we want to use sunlight and the granum right the thalloid membrane plays a integral role in the the light reaction so we're going to be focusing on the pancake Stacks we're going to be focusing on those thids those granum okay because that's where the light reactions occur that's where those chlorophyll molecules are right and that's what's very important for capturing sunlight and what happens during the light reactions remember we are using light energy in order to in order to oxidize water to oxygen to produce ATP and produce nadph remember we are stealing hydrogens from water so that we can reduce nadp plus to nadph okay again the hydrogens from water will end up on nadp Plus reducing it to nadph and thanks to our sunlight this this is made possible we also make ATP and oxygen so let's look now I want you to pay special attention to this look remember how thids have a curve to them like a membrane that has a curve to it I just want you to look at this right here imagine this curve right here of the thalico now I'm going to take you to this curve ready just picture this curve okay there is that curve this is the pancake we're looking at the pancake okay this is one phalic coid one pancake of the stack this is the thalloid membrane what's the fluid out here what do you think can you beat Wicket what's the fluid outside of the pancake Stacks that's right Wicket hopefully you got it too this is the stroma that makes this fluid inside of the pancake the thid space I hope you're oriented right thid space aloid membrane stroma okay and remember this is where the magic happens for the light reactions of photosynthesis what you're seeing before you right now is called linear electron flow and I'll explain why in a little bit this is where the pigment molecules play a role this is where light plays a role this is where we you know create ATP and nadph as well as oxygen this is where those light reactions occur so before I explain it in detail I want to show you all the players that are involved here okay I just want to you know don't get bogged down in details at this point I just want you to see the big players here okay um part of this is this guy you guys should all be familiar with this guy down here look at this guy who's this guy we've seen him before this right here is a ATP synthes remember what ATP synthes does we learned about it in the last chapter cellular respiration the top part of ATP synthe spins and Spins so that the bottom part can make ATP right remember that so this is ATP synthes a welcome figure a welcome friend so an enzyme transmembrane protein complex that we know about from before here's another thing we know about from before believe it or not you see this right here PQ cytochrome complex which is transmembrane and PC PQ stands for plastoquinone here you have the cytochrome complex and then PC stands for plastocyanin now this may not look familiar but I guarantee you know how this works these three together are known as an electron transport chain an electron transport chain and we learned about electron transport chains in cellular respiration remember what what do electron transport chains do do you remember what did the four complexes in the mitochondria do do you remember that electrons would flow you see the you see the orange arrows look at this do you remember that electrons can flow through an electron transport chain giving the transport chain the power to do what can you beat Wicket what does the electron transport chain use the electron flow power to do that's right Wicket to pump protons do you remember that electron transport chains they use electron flow in order to power a pump in this case there's only one pump the pump is called cytochrome complex in the case of cellular respiration do you remember there were three pumps pumps 1 three and four which were proton pumps well here you only have one proton pump the transmembrane complex called cytochrome complex and look what it does look what it does you guys it takes protons protons from the stroma the fluid outside of the pancake stacks and it uses that electron flow energy to pump the protons into the pancakes okay it pumps the protons actively into the thid space and it gets the energy for active transport of protons from electron flow does that make sense okay so so far so far we have an ATP synthes we have an electron transport chain those are very similar to components of cellular respiration the concepts are the same okay now here's a little enzyme that's friendly over here look at this enzyme over here at the top top right this enzyme is called nadp+ reductase okay that means it's the remember Ace means enzyme so it's the enzyme that reduces nadp plus so what this little enzyme does is that when it receives electrons it gives those electrons to n a dp+ which is the electron carrier you see this is an electron carrier kind of like nad+ or fad remember nadp+ is the electron carrier and nadp+ reductase reduces nadp+ to nadph okay so again we have three components we just discussed the ATP synthase an electron transport chain and an enzyme called natp plus reductase which hands electrons to the electron carrier nadp plus reducing it to nadph now there's two more structures here which we need to look at look at this thing that looks kind of like an apple right you see this thing it kind of looks like an apple okay that looks like the core of the apple right and here's another one here's another one of these structures that looks like an apple it's drawn like an apple those are the two new things that you know need more explanation okay the these things that look like apples are also part of the light reactions of photosynthesis and very very important for photosynthesis these are known as the photo systems okay this one here is called photo system 2 and this one here is called photo system one and both are integral so important for the light reactions of photosynthesis because these this is where those chlorophyll molecules exist this is where those pigment molecules exist you see in fact these green dots are all pigments okay these green dots are all pigment molecules like chlorophyll a Chlorophyll B right so very very important the reason why light is captured is thanks to these photo systems right like photos system 2 now what's funny is that photos system 2 appears first in this in this chain right photos system 2 appears first and later on down the road you're dealing with photo system one and the only reason for that this trips up students all the time because students think how come the first one how come the first photo system isn't called photo system one and it's simply because this one was discovered first right so photo system one was discovered first and then photo system 2 was discovered later uh even though it's more Upstream it's it's at the beginning of this process okay so we don't know how these photo systems work yet do we we don't know what these Apple looking things do do we Okay so I'm going to explain that next but I just want you to know ahead of time that they're so important for capturing light and letting the process of the light reactions occur but now look at this apple okay look at this one photo system right look at these photo systems let's go into detail about how these photo systems work so in so in the next little segment I'm going to explain exactly how these little photo systems work all right let's delve into those apple looking things that are called photo systems so remember this this is what I was talking about the photo system now photo systems have two major parts let's just break this down real quick there's the purple part that surrounds the blue part you see this the purple part is really where the Story begins this purple part of the protein comp complex is called the light harvesting complex right actually there are several complexes there these are the light harvesting complexes and they surround the blue part the blue part in the center is called the reaction Center complex okay those are the two main parts to a apple right to a photosystem the light harvesting complexes which surround a reaction Center complex okay so let's break it down now let's break it down let's start in the purple part let's start in one of these light harvesting complexes cuz that's really where the Story begins okay now focus in on this look what look what we have in the light harvesting complex look at this these green things are pigment molecules such as chlorophyll right like chlorophyll a for for instance so here you have several pigments inside of the light harvesting complex you have many of them okay and here's how it works ready light travels from the Sun and strikes a pigment molecule remember like chlorophyll a and if you recall from a previous slide this has an effect on chlorophyll a right chlorophyll a its electrons get excited and move to a higher energy State and then when those electrons collapse back to their ground state this pigment molecule actually releases that captured energy and look what it does it releases that captured energy and passes it to its neighbor okay I want you to see what what's going on here again light struck this pigment this let's say chlorophyll a this pigment its electron went to a higher energy State capturing that sunlight energy and when that electron goes back to ground this pigment releases that captured energy to its neighbor it's not okay let me let me just clarify it's not passing the light to its neighbor it's not passing electrons to its neighbor it's passing the trapped energy the captured energy from that Photon to its neighbor so it's only passing energy to its neighbor okay um now what's really cool is that there's this Domino action that happens now like a Cascade look at this the light excites this pigment this pigment then releases that trapped energy to excite its neighbor now its neighbor is excited look look this chlorophyll molecule got excited but not directly from light right this second chlorophyll pigment did not get excited by light it got excited from its neighbor who was excited by light so all you needed was light to start this reaction look light only had to excite this pigment which then sent the energy to the next pigment and guess what he does that's right he sends the energy to the next pigment and then the next pigment and then the next pigment it's almost like doing the wave at a sporting event right when someone starts the wave well that's it you got to go with it and everyone's going to do the wave right so only one person has to get excited enough to start the wave and then the wave carries on around the stadium right so kind of like the analogy I like to share with my students but again the light only had to excite the first pigment which then excites its neighbor who excites his neighbor who excites its neighbor who excites his neighbor but look what happens eventually the energy the excitement the energy reaches the blue part okay the blue part of the complex let's talk about this okay let's move on to What's called the reaction Center complex the blue part of the uh photo system here the blue part always has two special chlorophyll A's and they're literally called the special pair of chlorophyll a molecules in fact they have even more special names the special pair on photos system 2 is called p680 and the special pair on photos system one is called p700 so when I say p680 I'm talking about the special pair on photosystem 2 when I say p700 I'm talking about the special pair on Chlor photos system one and they really are just a pair of chlorophylls but these are special because they exist in the blue part the reaction Center and they do something special let me explain what they do when the excitement the energy when the energy reaches the special pair the special pair of chlorophyll a molecules either p680 or p700 this actually it these behave kind of like a electro negativity switch okay depending on your class you may or may not need to know this level of Det detail but what happens is when excitement reaches this pair this pair goes from very electr negative to not very Electro negative and when they switch to not very Electro Negative they give away their electrons so electrons move not energy this time not the black lines are energy right but this time when the energy reaches the special pair the special pair becomes uh it switches to not very electr negative and it so it gives away its electrons you see the yellow arrow okay it gives away the electrons to its neighbor this box okay this box represents the primary electron acceptor so the special pair once excited give away electrons so they pass not energy to the neighbor they're special because they pass electrons to the neighbor and once the electrons reach this box those electrons are free to leave the whole photo system those electrons are free to go on a journey and abandon the photo system and go on a journey okay again one more time the light harvesting complex the purple part is where the Story begins a photon of light strikes a pigment molecule in the light harvesting complex exciting it which then releases that excitement to excite its neighbor with energy who can then become excited and excite his neighbor with energy and then it's neighbor with energy and then it's neighbor with energy when the energy reaches the special chlorophyll pair the special chlorophyll pair switches to uh a state which is not very electr negative and is more than willing to give up its electrons those electrons hop to this box which is the primary electron acceptor and then those electrons go on a journey okay so knowing that knowing that now you know how a photosystem works and now you have all the key Concepts to understand and the light reactions of photosynthesis so let's hop back to the light reactions of photosynthesis so we can truly once and for all figure out what is happening during those steps all right we're back remember this curved membrane is the membrane of a pancake athal coid right so this is the thalloid membrane remember this is the stroma out here this is the thalloid space down inside of here and so really what we're looking at is mainly what's going on in the pancake right what's going on in the thalloid now again remember the Story begins right here so let's start our story here with photo system 2 photosystem 2 as all photos systems light travels from the Sun remember let's zoom in here light travels from the Sun and Strikes this pigment molecule this pigment remember becomes excited and then it can pass that energy onto its neighbor which then becomes excited and passes its energy onto its neighbor which passes its energy onto its neighbor which passes the energy to its neighbor which passes the energy to who what is this that's right Wicket this is is p680 the special pair of chlorophyll a on photosystem 2 now what was special about the special pair when energy reaches the special pair what can the special pair pass on that's right see this Arrow right here this orange arrow this is electrons being passed from the special pair to the box right to the primary electron acceptor the Box now now um what what happens when the box when the special pair receives the electrons what can those electrons do do you remember what I said before of course you're right Wicket the electrons can leave uh the photosystem AL together and go on a journey remember the electrons can now go and leave the whole photo system and that's what this orange arrow is showing those electrons can now leave the photos system so let's follow their Journey here we go the electrons are leaving the photo system they're traveling through plastoquinone remember and this is an electron transport chain so this is a spontaneous flow of electrons by the way the electrons are stolen by plastoquinone then they're stolen by cytochrome complex then they go through plastocyanin and then they get stuck let's say they get stuck right here on p700 the special pair of chlorophyll a on photosystem 1 but let's go back to this let's go back to this part here let's not skip through this too fast again the electrons went spontaneously through this electron transport chain and that's a spontaneous process right which releases energy energy that you can use to do work via energy coupling remember what's the job of an of a electron transport chain remember electron transport chains have a proton pumps remember proton pumps so cytochrome complex here is a proton pump it actively pumps protons in this case from the stroma out here you see the red arrow protons are being pumped from the stroma out here into the thalloid space in here isn't that neat and that's an active transport of protons and the more more electrons flow the more protons are actively pumped so would you agree then if this is the case you would end up with a high concentration of protons in the aloid space again why because cytochrome complex is actively pumping protons into the thalloid space so we should be getting a high concentration of protons in the phal coid space are you with me but let me show you something else if protons are high in concentration in the thalloid space but relatively low in concentration in the stroma doesn't that mean the protons would like to I don't know diffuse out of the out of the thid think about it wouldn't the protons want to diffuse out into the stroma but let me ask you this from what we've learned so far can protons which are positively charged can protons diffuse through a membrane directly that's right wick it no they cannot right they cannot because they are charged charged things can't just cross a membrane but what is this character over here remember this guy over at the bottom right what is this guy we learned about them in the previous chapter this is ATP synthes ATP synth says sure come on protons go ahead and squeeze on by but remember at a cost right remember what happens ATP synthes is a carrier for protons it allows protons to squeeze by it it it allows protons to attach to the rotating head then that provides uh a proton motive Force remember to spin ATP synthes as the protons squeeze their way out okay um so essentially what's happening is just like in cellular respiration the protons are doing chemiosmosis which means diffusion of protons across the membrane exerting a force called the proton motive force and that is what's providing the energy to spin the top of ATP synthes right that's what's so the protons leaving uh diffusing out is what's spinning the top of ATP synthes and that means the bottom part is doing what that's right the bottom part has the power now it needs to join a DP along with inorganic phosphate to form ATP isn't that neat so the energy for production of ATP during the light reactions of photosynthesis is provided by chemiosmosis of protons through ATP synthes and by the way uh on the exam if they ask how was this ATP synthesized how was this ATP made the technical term for this is actually photo phosphorilation isn't that neat because photons of light were required for this ATP to be made so this is known as photo phosphorilation resulting in ATP production and remember that ATP is made and now it's going to make its way through the stroma right where it was made the ATP was made in the stroma that ATP is on its way to the next phase remember the next phase of the photosynthesis is called Calvin cycle so that's where the ATP is headed okay so isn't that neat again those electrons went through the electron transport chain the electron transport chain actively pumped protons those protons chem OS back out spinning ATP synthes allowing ATP synthes to make ATP via photo phosphorilation the ATP went to the Calvin cycle but where did we leave off where did we leave off weren't the electrons stuck here at the central chlorophyll pair on photosystem one see the electrons I said they got stuck right here at p700 the special chlorophyll pair of chlorophyll a on photosystem one and they're going to be stuck there until what until look at this until light traveling from the Sun strikes a pigment molecule in the light harvesting complex of photosystem one exciting this pigment molecule which then releases the excitement to excite its neighbor who excites its neighbor who releases its energy to excite its neighbor and again the excitement reaches who it reaches the special chlorophyll pair of photosystem one called p700 and what does the special pair do once it's uh energized once it receives that energy that's right it switches to a very non- electronegative State it's called a negative EO state which can then which can then release those elect R remember the special pair doesn't release energy it actually releases those trapped electrons passing the electrons to the box right the primary electron acceptor and where what happens to those electrons once they get passed to the primary electron acceptor that's right those electrons are free to leave the photosystem all together and that's what you see here the electrons leave the photosystem they go through this carrier to our friend here remember I told you about this enzyme this special enzyme that's attached to the outside of the thalloid membrane this enzyme is called the enzyme that reduces nadp+ or nadp plus reductase so I asked my students I asked my students is this enzyme nadp+ no that's right Wicket this enzyme is not nadp+ this is the enzyme that reduces nadp plus what does reduce mean that's right Wicked it means give electrons to so when those electrons look when those electrons reach nadp+ reductase nadp+ reductases job is to hand those electrons to n a dp+ the electron carrier the electron carrier in addition to picking up uh the electrons also picks up picks up a proton from the stroma and it becomes reduced nadp+ picks up those electrons and a proton to become reduced to nadph here's your H okay and remember that nadph now goes to the Kelvin cycle isn't that neat all right now not so fast we're not quite done there's one more part of this uh process to talk about remember the these are known as the light reactions the uh light reactions of photosynthesis which is the first part of photosynthesis okay there's one more part to talk about here and it's at the very beginning okay let's focus in on the very beginning remember what happened remember energy from the Sun struck a a pigment molecule which then excited its neighbor who excited its neighbor who excited its neighbor who excited its neighbor and remember when the excitement reached p680 the special chlorophyll pair the special chlorophyll pair released those electrons to the primary electron acceptor on the reaction Center and then those electrons went on that wild ride right but doesn't that mean that p680 is now oxidized doesn't that mean that P6 80 is missing uh those electrons now so what that should tell you is we need don't we need to reload p680 with electrons so it can do this again because think about it p680 just let go of its electrons and those electrons went on this wild ride right so we need to reload p680 with electrons in fact at this point p680 because it's missing those electrons is called p P 680 plus okay p680 plus and what's really neat about p680 plus is that now p680 plus along with an enzyme is one of the most oxidative forces in the world uh they they call p680 a electro negativity switch remember because when p680 has electrons and it becomes excited it becomes not very Electro negative in fact it's so not Electro negative it gives away its electrons but once it gives away its electrons it's almost like it has like remorse you know it's it now that it gives away its electrons and it's p680 plus it switches to Super greedy you know off the chart super greedy for electrons right so greedy that it's one of the most oxidative forces on the planet and it can actually steal electrons from from who remember this guy right here who's this guy water remember water was required for the light reactions of photosynthesis in fact water is the source of the electrons those hydrogens right so p680 plus with the help of an enzyme steals electrons literally steals electrons from the master Thief oxygen giving those electrons to p680 plus reducing p68 80 plus back to p680 so that we've reloaded this photosystem so that it can send more electrons down the road okay and when you've oxidized water when you've taken water's electrons away in order to reload p680 plus with electrons what's left of your water that's right uh2 or you know oxygen oxygen is a byproduct okay isn't that neat so the reason why plants need water the reason why photosynthesis requires water is because water is the source of the electrons the electrons needed to reload p680 plus with electrons so that those electrons can go on this Wild Ride those electrons can be used in uh photosynthesis and oxygen is a byproduct of oxidizing water isn't that neat so so let's just let's just sum this up real quick let's sum this up what if I were to ask you let's see if you can beat Wicket what are the reactants for just the light reactions of photosynthesis that's right reactants that's right Wicket reactants mean what do you need you need light and you need water right now what if I were to ask you what are the three products of the light reactions of photosynthesis what would you say that's right hopefully you beat Wicket oxygen is the byproduct we also have nadph and we have ATP via photo phosphorilation okay and it's the ATP and the nadph which are on their way to phase two of the photosynthesis process known as Calin cycle in the stroma oxygen is not needed by the you know system anymore by photosynthesis anymore and again I just want to show you the big picture right the big picture here is that we took electrons from water right so watch this this is the story of the Journey of electrons the electrons began on water those electrons were transferred to p680 plus those electrons made their way from photosystem 2 through the electron transport chain all the way to photosystem 1 and then released from photosystem one all the way to our enzyme friend nadp plus reductase who handed those electrons to the electron carrier nadp+ reducing it to nadph and here are those electrons these electrons were from water right and those electrons in the form of hydrogen here those electrons are going on their way to the Calvin cycle in order to help form sugar for us all right let's go back to our nice overview figure here and just kind of look at the big picture again remember the whole point of photosynthesis is to make sugar for sugars we need C's H's and O's and during the light reactions we actually captured some hes right do you remember what we did we took H's we took electrons from water with the help of sunlight we took those H's and who did we hand it to we gave the electrons to nadp+ which then reduced nadp+ to nadp so here's our H's our H's went from water to to nadph which are on their way to the Calvin cycle do you remember we ALS o form some ATP via photo phosphorilation and do you remember when we oxidized H2O we we were left with the byproduct of oxygen and this is what plants breathe out right now we're done with the story of the thids right the granum the rest of the story picks up where at the celvin cycle which takes place in the stroma remember this is the fluid outside of these pancake stacks these granum okay here in the Calvin cycle I'm going to show you how sugar is made by taking CO2 out of the air and by reducing it to Sugar so let's talk about the Calin cycle and how the Calin cycle makes sugar for the plant all right the Calvin cycle which takes place in the stroma is almost like a reverse KB cycle or citric acid cycle cycle let me ask you this before we before we delve into the Calvin cycle do you recall what happened during the citric acid cycle of cellular respiration in a mitochondrion do you remember we took a sugar and we oxidized it until there was nothing left except CO2 right so the citric acid cycle took a sugar and ox ized it stole its H's took its H's away until there was nothing left but CO2 well the Calvin cycle is like an inverse citric acid cycle it's like the opposite what's the opposite of taking a sugar and stealing all of its electrons until there's nothing left but CO2 well the opposite of that would be taking CO2 and handing it H's handing it hydrogens until it became sugar isn't that neat so we're reducing CO2 to Sugar um that's what's ultimately happening during the Calin cycle let me show you exactly how it works and hopefully that makes better sense in a little bit there are three phases to the Calvin cycle phase one is called carbon fixation which relies on this enzyme called rabisco I'm going to show you how that works in a minute but phase one is called carbon fixation phase two is called reduction and phase three is the Regeneration of this CO2 acceptor rubp or ribulosebisphosphate this sounds very complicated but it's really not I'm going to show you how it works just in the next step and again recall that the Calvin cycle occurs in the stroma of the chloroplast so here's how it works okay um I know again I know it looks complicated and convoluted but it's really not that bad I'm going to explain it in detail so that you fully get it um so this is a cycle and remember biochemical Cycles are metabolic processes where the end product remember what a cycle is the end product is required for the beginning of the cycle okay that's what makes a cycle remember in um cellular respiration dur during the citric acid cycle we had to regenerate oxaloacetate because we needed it to start a new cycle well here at the end of the cycle you have to regenerate this guy this organic molecule right here look at this you every time you do a Calvin cycle at the end of the Calvin cycle you have to regenerate this molecule this molecule is very important this molecule is called RP also known as ribulosebisphosphate okay and what's so special about rubp ribulosebisphosphate what's so special about it that we have to regenerate it at the end of every Calvin cycle well let me tell you ribulosebisphosphate is a uh five carbon sugar see 1 2 3 four five it's a five carbon sugar that needs to be replenished at the end of every Calvin cycle it is also known as the carbon acceptor it's called the CO2 acceptor the CO2 acceptor so when someone's talking about the Calvin cycle and the CO2 acceptor this is what they're referring to they're referring to rubp now okay what's so special about rubp well watch this okay here's how it works you ready rubp is this five carbon molecule and here's what's happening what's entering what's entering the Calvin cycle you see here at the top what enters the Calvin cycle CO2 right remember the Calvin cycle is able to take CO2 out of thin air out of the atmosphere out out of just air and it's able to capture that CO2 and do you know how it does it an enzyme called rubisco and I know this is kind of confusing because usually enzymes end in Ace and rubisco is just one of those rare enzymes that doesn't end in Ace but this very very important and um abundant enzyme called rubisco what it does is it literally takes CO2 out of thin air and adds it onto rubp it takes CO2 from the air and connects it to the solid molecule rubp so so in essence carbon dioxide goes from a gas State and once you attach it to rubp it's in a solid state okay and this is known as carbon fixation phase one is called carbon fixation during carbon fixation just to summarize the enzyme Risco takes CO2 and connects it to the to the CO2 acceptor molecule rubp also known as rulos bis phosphate and this causes ribulosebisphosphate to kind of enter this transition state and then get cleaved in half into glycerol uh sorry three phosphoglycerate you don't need to know all these baby steps you don't you just need to know for my class anyway you need to know the main concept what was the main concept during phase one rabisco uh fixed the carbon took CO2 out of the air added it to rubp okay now haven't we captured C's and O's from the atmosphere we have captured CO2 we have captured C's and O's have we made sugar yet no that's right Wicket we have not made sugar yet we've captured C's and O's in order to make sugar we need C's H's and O's right do we have a source of hes that's right wick we have a source of hes in the form of remember n a dph those H's are what we need those H's were from water remember those H's those electrons were from water originally now we have the H's because this nice little electron carrier carried those H's from the light reactions to the Calvin cycle so what we want to do at this point is hand those H's to our captured C's and O's right so that way we have C's H's and O's so if we want to give H's okay we want to hand look we want to hand these H's to our CO2 right to our captured C's and o's um that's called reduction right because we're giving electrons to the C's and O's remember G gain of electrons means reduced so what do you think Phase 2 is called phase two is called reduction why because we are reducing the carbon dioxide we are giving hydrogens Which contain electrons we are giving them to the C's and the O's that we captured that we fixed that's known as uction and when we do that what have we formed we formed C's H's and O's which is sugar first we make a three carbon sugar usually and then two of these stick together to make a glucose a six carbon sugar Isn't that cool as well as other organic compounds as well isn't that fantastic so again during phase one we've captured our C's and our O's during phase two we've then given those C's and the O's H's we've reduced the C's and O owes in in effect we have reduced CO2 to sugar okay and that's called reduction and by the way do you think it's easy to make sugar and by easy I mean spontaneous I mean negative Delta G do you think it's a negative delto G process to hand hydrogens to carbon dioxide to make sugar oh that's right Wicket it is not breaking down sugar is spontaneous and that releases a lot of energy but not making sugar making sugar is non-spontaneous making sugar is positive Delta G so we need a source of energy do we have a source of energy right again Wicket we have ATP right remember this ATP MOS long got here from the light reactions of photosynthesis right remember this ATP was made by photo phosphorilation during the light reactions of photosynthesis so we're using ATP energy in order to reduce our C's and our O's to Sugar isn't that neat now we're not done because remember what's the what happens at the end of every cycle you have to replenish something at the end of every cycle to start a new cycle so the phase three is regenerating what phase three involves regenerating rubp we need to make another ribulosebisphosphate another CO2 acceptor so that it can go along and accept another CO2 from rubisco isn't that neat so again the point of Calvin cycle is to make sugar it gets its C's and its O's from CO2 and then it gets its H's from nadph which is from water originally isn't that neat so sugars are C H2O right some multiple of CH H2O glucose is C6 h206 those C's and those o came from CO2 and those H's came from water originally from water to nadph from nadph to the sugar okay and that's how the overall process works isn't that neat now you fully understand photosynthesis all right before I let you go there are a couple more Concepts that you may want to know about about photosynthesis and that has to do with first of all the light reactions do you remember the light reactions I told you about how light and water are used to form nadph ATP and oxygen well this is known as not just the light reactions but linear electron flow during the light reactions what's linear electron flow mean well it just everything I explained is linear electron flow you see how the electon R began on water and then the electrons were passed to p680 plus and then the electrons were passed from photos system 2 through the electron transport chain to photos system 1 and then the electrons were passed to the enzyme nadp plus reductase and then the electrons were passed to nadp plus reducing it to nadph which then left well that's linear electron flow why because the electrons are flowing in a linear fashion right so if I ask you on the exam what are the three products of a linear electron flow of the light reactions you would say what you would say nadph ATP and oxygen okay great but did you know there was a thing called cyclic electron flow that's right cyclic electron flow in cyclic electron flow photo exited electrons cycle back from FD to the cytochrome complex instead of being transferred to nadp+ that sounds like a mouthful so let's explore what that means here you can kind of see what they're talking about when the electrons reach photos system 1 at p700 and remember normally during linear electron flow the electrons go to the enzyme uh nadp plus reductase however during cyclic electron flow those electrons are able to cycle back through the electron transport chain and then do it over and over and over again so it's this is known as Clic electron flow because the electrons flow around and around in a cycle they don't actually get to the end they they go around and around and around so let me show you how that looks on our previous example Le all right do you recall linear electron flow the electrons started on water the electrons went on this journey see the electrons I told you at some point the electrons reached p700 right you see here the electrons reached p700 and normally when light strikes and excites all these neighbors remember what happens during linear electron flow the electrons go towards the right right the electrons go to this enzy nadp+ however plants can switch from linear electron flow to cyclic electron flow in this case what happens is instead of those electrons going up from p700 off to the right the electrons will transfer back they'll cycle back through FD they'll cycle back through the electron transport chain so they'll do this look they'll go from p700 then when they leave leave p700 they'll cycle back you see that's why it's called cyclic because it just Cycles back and then it'll cycle back every time light every time light excites these pigments the electrons leave p700 and they cycle back through the electron transport chain then they cycle back through the electron transport chain then they cycle back through the electron transport chain and the plants they can switch from linear electron flow to cyclic electron flow um to make more at P okay so think about it what's the only product if if I'm only doing this over and over again I've kind of short circuited this process right and the electrons just keep going around and around and as long as there's light as long as there's light the electrons just keep going around and around and around let me ask you this maybe you can beat Wicket what's the only product of cyclic electron flow what's the only product if I'm doing this over and over again than think about it that's right wick it just ATP because think about it every time the electrons flow through the electron transport chain what does the electron transport chain do that's right it pumps protons actively and that builds protons in the in in the thalloid space which then chem Osmos and exert a proton motive Force spinning ATP synthes allowing us to make ATP via photo phosphorilation so what you need to know is that during cyclic electron flow the only product is ATP and we finally reached the final concept that I need you to know okay this is the final concept I promise of chapter 10 and that is the the the ju Theos of the mitochondrion and the chloroplasts I want you to know about these important things they have in common on the left you see a drawing of a mitochondrion and on the right there is a drawing of a chloroplast and what I want you to know is that there are so many similarities between these two organel first of all both of them have a very important membrane in which uh there is an electron transport chain as well as an at P synthes so think about it in the mitochondrion which membrane possessed both the electron transport chain and an ATP synthes it was the inner membrane right remember the highly convoluted chiste of the inner membrane that's where you found an electron transport chain as well as an ATP synthes but in a chloroplast where did you find the electron transport chain and an ATP synthes that's right it was the thid membrane right the membrane of the pancake Stacks okay now another thing you need to know both the mitochondrion and the chloroplast have areas of high proton concentration where is the proton concentration high in a mitochondrion that's right Wicket it was the intermembrane space the dark gray area is where the proton concentration was high and what about in the chloroplast where was the proton concentration High that's right the dark gray area the in this case the thid space the space inside of the Grom great now also in both there was an area where ATP was synthesized where was the actual ATP synthesized in the mitochondrion the light gray area The Matrix and where was the actual ATP synthesized in the chloroplast the light gray area the stroma okay so what I want you to be able to do is just like I did jxap pose compare and contrast the mitochondrion and the chloroplast based on what based on where are the electron transport chain and ATP synthese where is the proton concentration high and where is ATP synthesized and with that we reached the end of chapter 10 thank you so much for joining me hopefully it was understandable I tried to break things down as straightforward as I can please leave any questions you have in the comment box below and I'll see you guys next time Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D A Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D Dr D