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Photosynthesis

Added Oct 14, 2013 •

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View the video to review the light dependent reactions and the Calvin Cycle (Dark Reactions)

Show Transcript

hi it's mr. Anderson and in this podcast I'm going to talk about photosynthesis I love listen to this because it gives me two things that I need I need to breathe so give me oxygen and I need to eat and so it's going to give me food and so I love photosynthesis on you might think only found in these things plants but it's also found in bacterial its founded LG and so it's found in protists is found everywhere it so photosynthesis been around a long time the super important the you understand how it works and so let's start with the site in eukaryotic cells of photosynthesis and that's the chloroplast so this is a number of you can see how many chloroplasts we could have in a typical cell so there's a whole bunch of them there are a few turns you should be familiar with and where they are first one is a thylakoid membrane thylakoid when is going to be organized like this and basically that's where the light reactions going to take place if you got a stack of thylakoids like this together we call that a granite the other big what time does Stan photosynthesis is this is filled with a liquid in that liquid is called the stroma that's going to be the site of the Calvin cycle if we were to grind Wendell Lee food fight is not only one pigment chlorophyll a the does photosynthesis but there's a number of them that are working together and so if you grind Alief into some chromatography paper and then you put it in in solvent what you'll get is chromatography it's going to separate into all the different parts and so this right here and be clear a and clarfield be in the city like carotene and xanthophyll and they're all working together you'll see these other pigments in the fall when the chlorophyll moves back is it a lease and is reabsorbed but if we look at what light they absorb here's chlorophyll a and here's beef this is what's called their absorption Spectrum what color of light they're able to absorb and you can see did they absorb a lot of the blue a lot of the red but they don't absorb a lot of this in the middle of the screen and so a quick question could be what is there least favorite are plants in the right answer would be green because they reflect that green light now this is actually puzzled scientists for a long time and we really don't have a definitive answer as to why plants are green no this it if they were black they probably would get a little bit too hot they would have too much alike that's a let's start with an equation cuz this is simply a chemical reaction to chemical reaction number of steps but what are the reactants water and carbon dioxide and so how does a plant grow it's basically taking water and from its roots and it's taking open dioxide in through its leaves through the stomata the other thing it needs is light and so it's just taking these simple ingredients and then it's a weeding those together into glucose this monster molecule here and then oxygen and said this is the food that I get and this is the oxygen that I breathe now are plants just nice they're making this sugar for themselves so they can break it down using cellular respiration and in fact if I put this arrow in the other direction that become cellular so they're making food for themselves and they're also going to make some of the structures so like the cellulose in the in the cell walls of a plant is made from that as well what are the different steps in photosynthesis and always imagined this picture right here there's photo and synthesis in the word photo means light and synthesis means to make and so are two steps in photosynthesis the light reaction and those are going to take place in the thylakoid membrane and then the Calvin cycle we used to call this the dark react is Arches a silly term doesn't happen train the dark it happens during the light and so basically the person who work this all out is Melvin Calvin and so we named it after him where's this take place you guess it takes place in the stroma or this liquid portion and so let's kind of do a cartoon version of photosynthesis what are the what Dance Again water light in carbon dioxide what are going to be the products that come out of this it's going to be oxygen and glucose let's watch what happens in the light dependent reaction Water and Light going to the thylakoid membrane and they produce two things they produce oxygen oxygen simply waste product and then I'm going to produce these chemicals and AD pH in ATP so they have energy now let's watch what happens to them while the energy is going to transfer to the Calvin cycle where carbon dioxide comes in and then glucose goes out in so this is the big picture of photosynthesis but now it's kind of digging in a little bit deeper and talk about the light reaction okay so where are we were Tyler coin membranes over in this membrane Roar so if we were to zoom into that membrane right here that's what this diagram is okay so what are the two things coming in will the first one's going to be light so lights coming in here lights coming in here what's the next thing that we're going to have coming in and that's going to be water okay so let's look at some of the other features in this style koi membrane so this is the outside of the stroma in this is going to be the Lumen or the inside and so there's a couple of big things right here what's in here while these are base play going to be proteins with chlorophyll in the inside of it and so we call that whole thing together a photo system so this first one is actually called photosystem 2 and then we photosystem 1 and the reason we go backwards is it photosystem 1 was discovered first so basically what comes in light what's that light used to do what light is you how are the movement of an electron through an electron transport chain so that electron is going through proteins carrier proteins and eventually that electron is going to go to hear it go to any dph cuz remember that's one of the products of the light dependent reaction what happens to the water then so the water is going to be split right away if you split water what do you get will you get oxygen so that's the O2 that's going to diffuse out of a sound that's the oxygen that you actually breathing right now never going to have these protons which are simply hydrogen ions so their hydrogen atoms that have lost their electron okay so this is getting kind of messy so let's look what happens next what is that electron moves through the electron transport chain and again it's powered by the introduction of light here and light hear that electron is going to be all the way down here and every time I go through one of these proteins it's pumping protons to the inside so it's pumping protons to inside now protons have a positive charge so basically what's happening is that you're building up a positive charge on the inside so there's a positive charging here you know how cellular respiration works you realize that this is the opposite of that so now we have all these positive charges on the inside where do they go while there's only one hole that they can go through MadAss to go through this protein here has those protons move out there moving through a protein called ATP synthase and works almost like a little rotor and every time what time does through we make another ATP so what if we made in the light dependent reaction we've made nadph and we've made ATP and what's nice about is there now just sitting right here in the stroma and so they're able to go on to the Calvin cycle which is going to be the next step in this process and so who's providing the energy light who's providing the electrons water and then a base or a waste product of that is simply going to be oxygen let's go to the Calvin cycle then so what's happened turn the Calvin cycle you can see here's those reacting so we've got our ATP here ATP here and nadph what are they providing simply energy we also have molecule here it's called rubp  basically it's a five carbon molecule and then we have carbon dioxide coming in so it moves through the stomata the Jason is going to diffuse its way in carbon dioxide is a 1 carbon molecule so basically there's an enzyme here called rubisco and it's going to attach this one carbon molecule to A5 carbon joke it immediately breaks into two three-carbon molecules and then it gets energy from ATP and nadph and when we're done it's creating this chemical down here called 3 peat what does g3p become well it can be assembled quickly into glucose or sucrose or maltose or whatever they need to do that's going to produced writing here by the g3p so that's where we're synthesizing another was were taking carbon and we're fixing it we're making it usable now some of that g3p to release but a lot of it is recycled again to make more of this rubp and so that's why it's a cycle over and over again what's the big picture if we don't have a teepee we do what nadph then this process is going to shut down what's the other thing that could shut it down if we don't have carbon dioxide okay so that's basically photosynthesis and again it's been working for billions of years but there's a slight problem and that problem is called photorespiration what is photorespiration Will photorespiration occurs only when we don't have enough carbon dioxide so if we don't have enough carbon dioxide let me cross that out  so we certainly can't make our g3p but something worse happened messaging can actually jump into the Calvin cycle and using rubisco can form another chemical now that chemical doesn't do anything in other words it has no it's in the cell actually has to break it down and so as a result of that plants and we call almost all plants C3 plants and the reason we call him three plants is this g3p is going to be a 3 carbon molecule so these C3 plants photorespiration is in other words they don't get anything out of it and so they're going to lose based on that oxygen kind of jumping into the Calvin cycle I think evolutionarily why would this have even involved well remember photosynthesis shows up first and then oxygen in the atmosphere shows up much later into wasn't a problem initially but it became a problem another question you might think as what when are we not going to have enough carbon dioxide when would we have carbon dioxide well how do they get carbon ox plant is going to have a stomata and it's surrounded by guard cells and so basically when a plant opens up at stomata carbon dioxide can diffuse in and so the only time the plan wouldn't have dioxide cuz we have tons of carbon dioxide in the atmosphere is when it's actually closed and when would it be closed in a plant the only time is closed is when it's really really hot plant doesn't want to lose water cuz you're transpiration you're constantly losing water and so if you're playing you have this if it's a hot day you have this really tough choice if you if you turn up your stomata you're going to lose water you could shrivel up if you close it you can't get carbon dioxide in and then you're going to start doing photorespiration and so of course nature is comes with set time up with solutions to this overtime and it's only going to be found in plants that live in really hot environment so here's the first solution and this totally makes sense so this is in Camp can plants example be a jade plant or like a pineapple basically what they do is they only open their stomata at night and tonight they open up there stomata and then the carbon dioxide over come in and they'll create malic acid out of it so they're going to store it in vacuoles inside the cell okay so now when it's date what they can do is they can close the stomata because they don't want to lose water and now they can actually take that carbon dioxide out of the malic acid and they can use it in the Calvin to make sugars so the great thing about a cam plant is again they're only taking and carbon dioxide at night when it's cool and then during the day they can close their stomata and they don't lose water another example of this would be in C4 plants what they do is instead of doing it day and night what they'll do is I'll take that carbon dioxide in and they'll actually use times to make a 4 carbon molecule out of it that for carbon molecule move to some cells on the inside of Aleve called the bundle sheath cells and then they can simply reduce carbon dioxide in the Calvin cycle here and so again both of these Solutions are basically taking carbon dioxide when you can get it creating a chemical out of it you can introduce at chemical into the Calvin cycle and they don't have to wait for a carbon dioxide to do fuse in now of course there's going to be extra steps in here so it's going to require more energy and so we own see this in areas where it's really really warm but an example of a C4 plant that we all eat and use a hot of in fact most of us are just made out of this stuff is corn pencil that's photosynthesis a simple problem is photorespiration but I

Uploaded by Darcy Milam.

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