hi and welcome to this lesson while we're going to be looking at module 3.3 from the OCR a level biology syllabus which is all about plant transport it's the first thing you're going to need to do is to get these images you can get them from the PowerPoint that I'm sending you there's a a3 version which looks like this well there's an a4 version which looks like this so what you want to do is to first get those images print them out and then we can use them to construct our mind map so if you need to get those images ready get colorful pens and pencils then we're going to make a quick start if you don't have access to the mind map I'll just disappear for a second so you can take a screen grab okay so where to begin well first of all let's just talk a little bit about plants and why they need transport systems so plants need transport systems to move things around their bodies just like humans do and the two things that plants move around their bodies is they move water and they move sugar from photosynthesis so water comes from the roots and needs to be transported up to the leaves into the rest of the plant and sugars made in photosynthesis are manufactured in the leaves and they need to be transported to the other cells to provide fuel for respiration so we've got two systems that work in plants to move these two things water one way and sugar largely the other way plants don't really have a transport system to move things like oxygen around the body because remember they have a low metabolic demand they don't solve they don't walk they don't move so they don't need a lot of oxygen so oxygen normally gets around plant through a simple diffusion so I think the best place to start is actually if we zoom in and we look here okay so we look at this diagram which sort of shows in outline the movement of water to reply so let's label so here we have water moving into the plot this is the blue arrow here but it's powered by active transport so here mineral ions been a while since I don't know these over half time I've forgotten okay so mineral ions or absorbed by active transport so that means it takes energy and they're moving from a lower to a high concentration so that we can sort of draw I don't know a few dots in here representing high concentration of mineral ions in here because of that water then moves in via osmosis so remember this is down at water potential gradient out here these things are sort of soil particles so I'll do this brown so this is soil particles this is a root hair cell so let's just sort of label that so this this actual cell here this one here you could draw an outline around if you like use a root hair cell and of course it has a very high surface area also we would have quite a few mitochondria to provide the ATP for the active transport so it's quite metabolically active cell mitochondria okay so the water moves down in water potential gradient and it keeps going down of water potential gradient as it moves moves from cell to cell to cell so we could actually label some sort of water potential values let's just kind of make them up so this might be this cell here might have a psy value oh I don't know let's say I don't know - 100 kPa or something and then you know if it's going this way then this one would have to be lower so this would be like psy minus 150 and so on so we're moving down a water potential gradient and so on and so on now there are three ways that water can move from cell to cell so let's briefly go over here and label these three ways water movement cell to cell okay so we've got a B and C pathway a pathway B let's keep the color scheme and proper AC okay so a in this case is the last pathway so the Abacos pathway is water moving through the cell walls so remember a cell wall is really just like a kind of mesh matrix of cellulose fibers but it's very porous it's not a solid structure it's more of a net so water can move around those cellulose fibers so there's a pathway there can kind of go between the cells through the gaps around the cells so that's the a Palast pathway through the cell wall the second pathway is water can move inside the cytoplasm of cells via the symplast pathway I'm going to keep using red because orange isn't great so to write with so simplest and this is so it has to cross a cell membrane so inside the cell and it has to cross the the plasma membrane the cell surface membrane now this can be made a little bit easier if you look at this gap here it this these gaps between these cells are these joins between the cells these are called plasmodesmata singular plasmodesmata cross plasma membrane or via plus modes' martyr and then see equals the vacuolar pathway so you know it's it overlaps with the symplast pathway just happens to go into the actual across the tunnel class which is the membrane around there into the vacuole and then sort of out back into the cytoplasm through to the next cell into the back of it and so on ok so there's three different ways the water can move so if we now go back to this diagram here when the water is moving from this out of route hair cell further and further inside the root it can be going any of those three pathways doesn't matter could be going a class could be going symplast could be going vacuolar and in fact a lot of it goes app applause because that's kind of the fastest way so via any pathway but mainly a Pope last sorry if that's a bit scruffy writing via any pathway but mainly Apple plasters here now that all works fine until it reaches this special layer of cells which has something called the Kasparian strip so this here no way we're down here is the Kasparian strip so this is a is a ring around every single cell so imagine this cell here is a three-dimensional kind of block but there you know there is a ring around that cell i need a prop here i'm going to use my hard drive okay so here is a hard drive let's imagine this is a plant cell it's kind of dimensional the kasparian strip is a bit like a ring my hand is not quite big enough to fit around it but imagine a ring just kind of fitting around that cell like that so that ring around the outside of the cell blocks the the last pathway okay so now the water can't go through the cell wall because there's this ring blocking it and it has to go inside the cell via the either vacuolar or the symplast and pathway so the kasparian strip let's just make a little bit of a note here so it's a ring around all the cells in this layer and it's impermeable and it's made I don't think this is on the syllabus but it's made of something called suberin which is just a extra biological molecule that kind of just packs in all the gaps in the cell wall to make it impermeable so the purpose of that is that we make water move via the symplast rapid past pathway now there's another key process that happens so here we could do actually let's draw another arrow in red because it there's a process that's happening here which is the same process as the previous red arrow we drew which is there's active transport okay so that's what's happening here this thing here so more active transport of I of mineral ions into this central part of the route so in this central part of the route we call this the vascular bundle and this is where the xylem are going to be all right strands with neurons into vascular bundle so what's the point of that well you pack more ions into the vascular bundle which means again we lower the water potential the size and water moves via osmosis so then this water moves Vilas Moses here so that's this one I'm gonna label up here water follows via osmosis okay this generates actually a pressure okay so there's loads of mineral ions and water kind of packed in the vascular bundle so then this generates a high pressure environment in this space here I'm gonna kind of do that with a little kind of highlighted blue and then I'm going to try and keep the same vague color and I'm gonna write that I'm gonna write root pressure brackets hi it's high pressure in there okay so that root pressure is part of what pushes water up the stem towards the lease where it needs to go but there's a lot of other factors as well drawing the water up okay so now let's take a look at what that root and what that movement of water through the root looks like in a cross-section of a plant root so if we look over here okay this area now this is a cross-section of what a root would look like so it's actually not the full root okay so let's kind of add to it okay so yeah let's add it down here okay so this is imagine the Roos a circle okay so like this okay and actually on the edges at the root we've got the root hair cells so we've got all these root hair cells like this kind of going around the whole root like back we can add some more over here those are there okay so let's just label that root here cells so we know that water gets absorbed via the root by the root hair cells Osmos this but powered by the active transport so water's coming this way this way this way okay in in in moving vias following the water potential great we talked about here and it goes in here now this is the layer here where the see this layer of sorts right that is the layer where there is this Kasparian strip so I'm actually gonna this here is the layer of cells that contains the Kasparian strip now we also have to give it another name yeah not too bad so this is the endodermis layer so it's pointing to this layer here can you see whoops that's a bit too big but that is called the endodermis and it contains this kasparian strip okay so in from that we have all these cells here are just kind of random packaging cells they contain their two types cells they're called the sclerenchyma and the collenchyma I always forget those and together we just call it the medulla so these cells here okay so this is the medulla here and on the left it's just the cells that are kind of here okay so those cells don't do anything they're just kind of packaging material that cells that are really important here the xylem and phloem cells so let's label okay let's label the phloem in green they flow themselves we're gonna look at flow in great detail later remember the phloem cells transport sugars and we've got the xylem cells that transport water upwards I tried to do green for sugar because sugar is made in photosynthesis and I think of green when I think of fridge senses and blue for water I'm also just gonna highlight that a little bit so first of all let's do this item in blue because that's what transports the water and we could put the phloem in green in a sec okay so that's the design them and the phloem here in green kind of in this kind of just amongst it looks like a starfish basically the silence like a starfish with little blobs of flow in the kind of armpits I suppose of the starfish if a starfish does have an armpit yeah that's that's where the phloem is okay and then the packaging cells I just leave blank this module around the outside now there is another thing there which you need to know there is there is a layer of meristem cells just underneath the endodermis as well it's called the para cycle but let's also just talk about that so men endo domes contains a Kasparian strip meristem underneath and that's called the para cycle peri cycle yeah and the other thing is that the endodermis cells again lots of mitochondria because they're very active they do lots of they do lots of active transport pushing the mineral ions into the vascular bundles souks bundles so that water follows so they have a lot of mitochondrial a reactive active cells mitochondria okay so that is the cross section let's make sure that's we understand what that that is and then out sorry outside the endodermis in the cortex okay so this is outside the vascular bundle so that's kind of this area sort of here the dollar's inside the endodermis so this is a cross-section route cross section okay so so far we've talked about how the water gets into a plant via the root hair cells how its moved into the vascular bundle by the action of the kasparian strip and now we're going to talk about how water moves up the xylem vessels before we do that there there's one thing which I kind of should have stressed a bit more the Kasparian strip what's it about well I've already said that it forces water to go through either the apple plast or the sim sorry the symplast or the vacuolar pathway it blocked the Apple past pathway why is that important well it's really actually about the mineral lines so without the suit without the kasparian strip if you actively transported mineral ions into that vascular bundle across the endodermis then those mineral ions could kind of leak back out through the through the cell walls because it's kind of like a gap so that would mean that you couldn't have this concentration difference where you have more mineral ions in that vascular bundle which draws water in viruses okay so it's actually really to make ace of watertight separate compartment on the inside of the root that's the vascular bundle where you can generate the root pressure so we already talked about route pressure and so that's one part of pushing the water up the xylem but now let's talk about the xylem themselves what are the adaptations of xylem tissue that mean that they are very good at sort of drawing the water up all the way to the top of the tree if it's tree to the leaves of the plant so we're gonna look at this diagram down here which shows both xylem and phloem tissue so I'm gonna talk about the xylem tissue down here and later on I'll sort of leave a little space here for the phloem tissue over here but that's gonna be a little bit later I'm gonna try and keep my xylem stuff down here alright so the first key thing about the xylem is they're dead okay now that may you may be wondering how does a cell have you build a dead cell well they don't start off dead so sign themselves when they're and developing they're alive and once they kind of reached the structure the shape and structure there need to be then we have a final stage where you have something called lignin that's adding of lignin into the cell wall and that really is what kind of kills the cell because once it becomes completely lignified and impermeable then it comedy comedy live is dead so dead cells lignin in cell walls so the wars are have added lignin lignin is basically it's a protein and it's basically what wood is okay so wood is lignin essentially so the xylem get hardened by lignin now lignin in cell rules doesn't have to be fully lignified so let's do a little subheading in here so it could be a pattern so it could be spiral it could be sort of thought it could be what's called a rear annular which basically just means rings or and even if it is fully lignified the whole silent vessel is fully dignified you can have parts of the sides of the cell which aren't liquefied these are called bordered pits and they allow water to move out so so even if it is full you might have bordered pits and that allows lateral movement out of the xylem so let's say let's add in a little actually I'll use red just because it's on blue so let's say you'd have water moving up here up there xylem like so and then here that there's a little gap there okay it might come out okay so this could be a bordered pit here so that allows water to keep moving up the xylem but some of it to exit at different parts to supply the tissues okay so that kind of shows lateral flow out okay because of course if you have a tree you might have a branch here and more up and another branch here so some water needs come out into this barrage and some water knees they come up in this branch and so on so that's the main thing about xylem now the fact that they're dead and the lignin in cell walls means they are a tough essentially straw okay they're basically like a straw they join into end so they the cells fuse okay so dead cells lignin in cell walls and I didn't really see the obvious here that this is strength okay lignin and cell walls give strength now if the tube is fully lignified its strong but it might be brittle it might snap okay so spiral gives it strength but it gives it some flexibility and the same thing for annular so spiral might be flexibility okay right what else so dead cells lignin in cell walls cells fuse end to end okay so they you know one cell and the next the end plays fuse to form a continuous tube continuous tube with no cell contents nothing at all and no divisions between individual xylem vessel elements which fuse together yeah so the reason that this is so important this continuous tube is then it allows the properties of water to kind of take over so you may remember that two properties of water that we looked at in a sort of molecules mind map were so I'm going to underline this continuous tube here and I'm going to put h2o we've got cohesion and which is together water I'm kind of writing this in shorthand cohesion is the force that attracts water molecules to get their cohesive and we also have adhesion which is how water molecules stick to the walls of the xylem and to other things okay so now we have this continuous tube cohesion and adhesion can cause more can kind of allow the water to move up the tube and this is powered really by things that are happening the leaf water is evaporating at the top of the leaf so this pulls water molecules out the top of this eylem but because all the water molecules are kind of sticking together through cohesion when you pull one out the top it draws the water molecules from the lower in the xylem up like that okay so that's cohesion and adhesion also is the water molecules stick to the sides of the xylem and kind of almost crawl up the xylem vessel via capillary action which is another key word so cohesion and adhesion together in the narrow continuous tubes give rise to what is called capillary action okay so I think that's everything about the xylem yeah the other thing so lignin is strong it also prevents the xylem vessel from collapsing in on itself so it keeps it open as a tube so that water can flow so that's the xylem features so this this is the diagrammatic representation here's an actual microscope image where the lignin has been dyed red here so here we can see the kind of ring like or it could be spiral I'm not sure pattern of the lignin of this xylem so okay so this point here is really water flowing in xylem in stem ok so that is the xylem flowing in the sorry the water flowing in the xylem and stem right but we need to again recognize the shape of a cross section so let's go and look at that so here is a stem cross section now this would be a stem cross section not every single plants gonna have exactly the same stem cross section but this is a stem across section in not a tree so sort of like a maybe like a sort of a semi woody plant okay I think it's called yes sorry a non woody plant so something like a green plant bushy which isn't like a tree with a four on trunk in trees would fall on trunks there's a slightly different structure because all the vascular bundles fuse to form a ring which is why you can count tree ages by looking at those rings that get laid down every year so in a non woody plant we have discrete vascular bundles so that's what these are here so let's actually just highlight one that whole thing there and we'll just label it we'll just say that is a vascular bundle okay and in fact in your textbook there is a further diagram of a vascular bundle which I am going to try and draw now but maybe you could draw it better than me it's on page 209 in the middle and it kind of looks a little bit like this that's the outside layer this would be this would be a tissue plan okay so I'm just going to draw the the kind of the tissues there and then we have the sort of the phloem like that and then we have the cambium which is a very thin layer like that and then we have the xylem on the inside okay so that is that's kind of this is a more high-power or this is actually a tissue planned zooming in a little bit more so that diagram is showing on page two or nine if you wanted to add that as well you could so let's just quickly label that as well and I'm gonna do it in blue yeah so okay we got this bit this is the sclerenchyma then underneath that we've got the phloem so in plants in the stem the phloem is closer to the surface that goes for non-woody plants and woody plants down here we've got the xylem what's in the middle that is something called the cambium which is basically MERIS themselves okay so cambium meristem now we will learn about this more in year 13 we learn about plant hormones and you need to know a little bit about where the different meristems are in plants and how that causes plants to grow like out and up and that sort of stuff okay so now let's label this diagram a slightly zoomed out version over here so this outer layer is the sclerenchyma then we've got the collenchyma so actually that's the even further outer that's like around that's on the the very outside so that's kind of the protective layer on them on the outside of the plant we've got a bit of cortex in there which is not in the vascular bundle it's between the outer colon summer and then the vascular bundle then we have the phloem and then we have the xylem and then we have this bit down here is the medulla okay like that right let's let's try and keep the same highlight as I did down here so I'm going to be blue for xylem so I'm gonna try and color them all in so xylem is on the inside I won't cut this one which I've highlighted in full because that's the whole vascular bundle so there's the xylem all those little bits what else now we need to do the phloem oh gosh this can be difficult to do it's this middle bit here yeah there we go that's the phloem and now and I'll do the collenchyma sorry the sclerenchyma in yellow here which is that kind of packaging and of course remember in this slightly zoomed out version you can't there's not enough room to label this cambium down here that's also just on my zoomed in version let's do that color code as well and we don't color in biological drawings normally it's just so you can see where everything is okay all right so again you need to recognize this kind of pattern of how where the xylem and phloem are in different parts of the plant where how they arranged in the root how they arranged in the stem okay so we've covered water flow now from the roots into the xylem up the xylem now let's move on to the leaves okay so here we are in the leaf now we're just gonna start by looking at this diagram here which isn't in your textbook but it's very similar to the one which is on page 2 1/4 which is a diagram of the leaf structure so first of all let's just remind ourselves about the different parts of the leaf structure because we do need to know all the different features so at the top here we've got a waxy cuticle is the upper surface of the leaf that I'm laboring waxy cuticle stops water loss from this upper surface stops water last just kind of out of the cells so it's a barrier then we've got this layer these cells here this is the upper epidermis now there's some overlap here within my mat you did the other day so you'll hopefully always remember already remember that these are basically transparent cells they haven't got any chloroplasts and they basically just they form a barrier layer and they let the light through and a little bit of light coming in they let the light through down to the main photosynthetic cells which are here then we've got this this layer this is the photosynthetic layer we've got the palisade mesophyll again we won't go into too much detail because you've already done a kind of bit of work on this but we've got the chloroplasts a tightly packed see these little dots here those are chloroplasts tightly packed with chloroplasts also the central vacuole pushes the chloroplasts to the outside of the cell where they are sort of closer to the incoming light so they can capture the maximum amount of light I'll just write underneath there well here photosynthesis all right these are the ones so these cells are going to be providing sugars for the plot okay we haven't really talked about the phloem and sugar transport but this is the source the Photosynth synthesizing cells in the leaf then underneath that can you remember what it is called this one I hope you can it's the spongy mesophyll and of course we've got all these lots of air spaces it's spongy like a sponge in a sponge you've got bits of whatever the sponge is made of the stuff and then you've got little tiny bubbles of air all over the place little pockets and these are interconnected of course a leaf is a three-dimensional thing it's not just a slice like this so these air spaces here you know are all connected through sort of weaving tunnels and stuff it's a network a spongy network of the air spaces I'll just label that air space and here is where we've got the vascular bundle so I'm actually gonna kind of draw a ring around that there and we shall all why should we label it vascular bundle now in the vascular bundle you've got Salem and phloem typically the xylem I'm just gonna write x4z limb is on top and p4 phloem is on the bottom in the leaf there if you're looking at higher power you might be able to tell the difference because xylem will tend to be slightly larger rounder and hollow than the phloem which are a little bit smaller okay so then we've got this this is the key thing this is the stoma stoma stomata this is the stomata one one is also a stomata stomata for it one yeah I think stomata is both singular and plural stomata yeah so this is the stomata stomatal pore let's call it and these two things here are guard cells so the key feature is that water and I'm gonna try and do a nice light blue and let's do a different color water moves out of the xylem here down a water potential gradient so it can move into these cells where it's needed for photosynthesis it can move through these cells and it will evaporate okay it will evaporate into this it's a bit difficult to see here this color but it evaporates into this air space so this air space here if you focus with my pen is is moist it is humid is your packed with moisture that moist air can diffuse out of the stomata pour into the environment and Dennett's may be blown away by the wind washing over the leaf so is this process of evaporation and then the diffusion of water out of the stomata that powers the whole process of transpiration this provides the pull so we've got the pull of the water leaving us tomato we've got the cohesion and the adhesion in the xylem best we've got a little bit of Route pressure coming from the roots and all those things together kind of equal transpiration so let's label those two or three key points here this diagram is in your book so we've got here this is water moves out of xylem remember this could be through something like some boarded pits you know because of the lignin it has to have a way out to the lateral movement and then the water when it's moving from cell to cell to cell this is osmosis because we're talking about the movement of water my high water potential to a lower water potential here this arrow is evaporation okay that's that's kind of key so I'm gonna do that in red because it's a something which you might go wrong evaporation because it's evaporation of water from the surface of the cell into the airspace now we've got water vapor a gas and so now we're talking about a gas it's no longer osmosis but this is diffusion out of the stomata okay so just a slight difference there evaporation diffusion and osmosis we're going to use those words at the right time to describe the right process so that is transpiration this can be regulated and stopped by the closing of the guard cells so the guard cells here let's just put a little note underneath can close pour in times of water stress okay so if the plant senses that it is running out of water then the stomata will close yeah and if the plant senses it's got enough water and it wants to be photosynthesizing there are also mechanisms that kind of mean that when the plant starts photosynthesizing that sends like rapidly it sends a message to the guard cells to open pour well investigate that a little bit more in year 13 so here's a little overview animation just so you can kind of visualize that whole process of transpiration of the transpiration stream once again so here we can see at the top that the whole process is powered principally by the evaporation of water from the leaves out the stomata let's zoom in let's look back at the route so here we've got the route hair water moving in by osmosis down a water potential gradient now the cells are interconnected so water is moving through the plasma desmo plasmodesmata via the symplast pathway mainly or the apple plast pathway sorry the apple a swather is mainly its main pathway and that's through cell wall now that carries on through the simplest and the upper class all the way till we get to this endodermis layout the endodermis layer has the kasparian strip which blocks the apple plast pathway and there is that protein called suberin that kind of makes that cell wall impermeable this allows the active transport of mineral ions into the vascular bundle so that there is a high concentration of solutes there and a low water potential which means that water will flow into that vascular bundle via osmosis this sets up a bit of a route pressure and now when we're talking about route pressure that kind of pushes the water up a little bit but the main thing that pulls water up is really cohesion of water molecules so here we see this nice animation showing that water molecules are held together via a hydrogen bond Network so as water molecules are removed at the top of the transpiration stream all the way up in the leaf it pulls water molecules up from lower down in the plant so we can follow that transpiration stream all the way up to the xylem and in all the way up the xylem and into the leaf now in the leaf here the xylem loses water down a little potential gradient into the into the cells in the leaf and eventually that water will evaporate into the air spaces within the leaf and it will then leave via diffusion out of the guard cells which is the whole thing this disappears called transpiration the whole thing is called the transfer a stream so as I said this whole process transpiration is super super important transpiration supplies water for photosynthesis in the cell straight in the leaf cells because the leaf needs water it's one of the raw materials for its senses supplies water to maintain the turgor pressure to keep the cells inflated with water throughout the plant and it also cools down the leaves when they're in the Sun this evaporation of water and and some diffusion that they slaughter cools down believes as well so transpiration is very very important and we can measure transpiration which is technically speaking just the loss of water vapor from the leaves let's just label that we can measure the rate of this using something called a potometer which is this device here okay so to investigate transpiration we use a pedometer so to use a pedometer first you need a piece of of a branch or a piece of a plant that you want to investigate now here's how we set this up first of all well there's kind of two types actually there's one one which is a bubble potometer and one which is a mass potometer so let's just have a little look at this one we're not going to talk about it in detail but this mass potometer basically works by measuring oops go back this mass potometer here basically works by measuring the mass of water lost now here there's a little bit of a layer of oil across the top of this beaker is water here below and basically as water moves up the xylem and out the leaves the mass is going to go down now the water can't evaporate through the oil layer which is essential if your results are going to be valid so we just measure the mass loss over time now the bubble potometer is a bit better and here we go let's look at this bubble potometer so first of all if you want to compare different rates of transpiration you're going to need to use same cutting several different times because the different cuttings are going to have different surface areas of leaf and different amounts of leaves and and so on so we're gonna need to use the same piece of leaf and just repeat the experiment several times now when we cut the branch which we're going to investigate it should be cut with a sharp knife underwater okay that is so we don't get any air bubbles introduced into the xylem which would block the flow of water up the xylem if you get Bob on the xylem you can't have that cohesion of water molecules going up in so we've got to cut it under water then we have to place the new newly cut shoot into the potometer also all whilst it's under water again with this is just to stop the bubbles getting into the xylem so this whole thing is now filled with water now we're almost ready to go so the leaf is started to do some transpiration I'm just gonna back it up there for a second the leaf has started to do some transpiration and therefore air is drawn it okay air is drawn in here watch very closely right here air is drawn in so you let a little bubble go and then you put it in the water then you just track how fast this bubble is moving you do that on a scale and you watch the bubble go you know you time it you know maybe 10 minutes maybe 20 minutes and you record the distance the bubble moves so you probably wouldn't sit there and watch it for every single second you might look at it every three minutes for 30 minutes sounds about sensible okay then you could sort of plot a graph of this so over time you watch the bubble move as it moves along and you record the time and you plot a graph so the slope of this graph is going to become the rate of transpiration basically okay now what you might do is then you might use this as your reference point that's basically your control how much transpiration happens with the branch as it is but now let's change some factors let's see what happens if the leaf is illuminated with a bright light now as a control here we place a heat shield okay so this could be a piece of perspex which is specially designed to block infrared radiation or it could be kind of a small almost like a small fish tank with water in okay so the water basically absorbs the infrared and it allows the light to go through onto the fly so we're not changing two factors light and temperature we're just affecting the light so now let's run this experiment again with a higher light intensity and we can see here that variability the date is kind of going up and down a little bit there but basically it's gonna look like we've got a higher rate of transpiration now the reason for that as I sort of mentioned earlier in year 13 there is a direct link between photosynthesis and the stomatal opening so it just means that the stomata will be more likely to be open therefore more transpiration light energy also can directly kind of help the evaporation of water all right what about air movement let's put a fan next to this piece of branch here now the air is going to blow any diff any moist air there's recently come out of the stomata and it's just sitting near the surface of the leaf the fan is gonna blow it away so this is going to increase the rate of transpiration because it means that humid air does not sort of cluster around the leaf it's gonna maintain the actually what it's doing is maintaining the concentration gradient in terms of moist air into an ounce of the leaf because it's blowing away the moist air out of the leaf okay so that's also gonna increase the rate of transpiration not quite so much there what about humidity well if it's a humid day now to model this we could just place a plastic bag around the whole barrage set up this means that water vapor when it gets into the plastic bag it can't be blown away by the air so the air and the bag becomes quite humid so does that affect the rate of transpiration well yeah it clearly does and this time is going to reduce the rate of transpiration because it means the difference in humidity in and out of the leaf is less so there's a lower concentration gradient in terms of the moisture in the air from inside to the outside of the leaf okay so we can summarize that like this okay tada so let's add this diagram to to the to the mind map here it is just move it across and then now let's talk about a few of the key points from that potometer experiment that we need to remember okay so red here was high light intensity blue here was windy replicated with a fan black was control and green was high humidity and humidity lowers the effect of transitory low as the rate of transpiration wind enos or air movement increases the rate of transpiration and high light intensity increases it a lot key facts about the potometer use there was same branch cut underwater was just a cut plus setup underwater and the reason for that was really kind of no no bubbles in the xylem that is but you do track the movement of this bubble here by the way you can also if you know the distance the bubble has moved you can calculate the volume of water that has been lost now how do you do that well if you know that the diameter and the radius of the capillary tube you can work out the volume of water that has been lost out of that tube so it is the distance in millimeters times PI R squared which is the area because remember the capillary tube is circular cylindrical so that's the area inside times the length so it's basically the volume of a cylinder okay so almost finished on transpiration now we're just going to look at how do two different types of plant kind of work with transpiration - you know because they live in weird or extreme environments okay so we're going to just going to touch on these two two different plan adaptations I'm going to look at zero fights and we're gonna get Hydra fights now it's fair to say that plants normal terrestrial plants typical plants also have adaptations to stop water loss we've kind of already looked to those up here with the leaf for example the waxy cuticle but if you want to add more information here you can on page 2a you've got a bit more information about terrestrial prawns so zero fights are plants that live in arid environment okay so here is a zero fight cactus is a zero a fight or marram grass okay so this one the one that we're seeing here is marram grass and a cactus is another one now I think hopefully as a level students you're familiar with a cactus okay cactus cacti don't have leaves that's the key thing they minimize water less by losing all that water lost by losing all their leaves so where do they do photosynthesis in the stem the stem is green they protect the stem with spikes from herbivores that want to kind of eat the plant and get the water inside and the stem itself is kind of very spongy and can store water but America marram grass is a slightly different thing so first of all here's a picture of Marion Ross for real okay looks pretty much like grass but what happens is the leaf okay imagine my hand is a blade of a leaf the leaf is not flat it is curled up like this okay and that's what we see here so the outer surface of the leaf is on the outside of the curl and the inner surface is inside there okay so this is our outer surface which has got the standard waxy cuticle so now the inner surface is here so the inner surface is all curled round and this means that any water vapor that is kind of coming out of the stomata and the stomata are actually way down in these sunken pits here okay so the stomata are way down in there so water vapor has a long way to go to get out kind of in the leaf and the water vapor I'm gonna change to a little slightly darker blue so we can sort of picture you know water molecules knocking around here as water vapor so they kind of get trapped inside that space and it means that they don't know water vapor doesn't diffuse out and away from the leaf so quickly so this reduces the sort of the concentration gradient in terms of the moisture of the air between the kind of inside of the leaf and it's and the outside of leaf because the outside of the leaf is this protected environment protected from wind and which keeps some of the humid air in so marram grass reduces the loss of water and the stomata I'm just looking where they are in pits in the lower epidermis okay so how what are the key things that we could say here so stomata in pits and the lower surface lower surface of leaf is roll plus it's extra hairy hairy pits essentially nice so yeah Marin brass got hairy pits and yeah and it's got stomata there as well so that all prevents what prevents so much water for being lost so Marin rose typically lives on sand jeans and stuff the outer surface also has you know an extra thick waxy cuticle okay extra waxy cuticle so that's a zero fight what's the opposite of the zero fight zero I think is Greek by the way for dry so zero fight means dry loving the opposite of a zero fight is a hydro fight ten can you guess what this one loves well hope you did its water so hydro water fight likes it okay water loving plot now water loving plants they don't really care about transpiration because they live in water okay so water water loving plants there's an infinite amount of water essentially if you're sitting in a lake or a river you don't need to worry about losing water out of your leaves because there's just loads of water everywhere so hydro fights don't really have to conserve as much water now one thing about let's just actually draw all plant here okay alright so here's I'm gonna do a cross-section supply okay bear with me this is the surface of some water on it we have a lovely water lily okay water lily like that now water lily has a stem that goes down like that into let's say a you know a pot okay this is what this is actually a model of my mum's pond okay she's got a pond it's great I spent hours looking at it and trying to find out all the nature that's inside of it and it's got water lives in it okay so the water there's a plant in the pot at the bottom of I was born and they've got these big stem things like this they kind of curl up to the surface and the leaves are floating on the surface so one thing that the leaf has to do differently is that actually schemata on the upper surface which is weird because normally they're on the lower surface so the reason that is essential is because the lower surface is water so to do gas exchange with the air to get carbon dioxide from the air the plants need to have the stomata on the upper surface so that's one the key thing also the leaves and the stem need to float up to the surface so that's what these things are ok these are air spaces and they cause the leaf to float so it helps for buoyancy and it keeps the Leafs of float and it also allows oxygen to diffuse down those if you this these kind of air spaces are actually actually channels for air for oxygen to diffuse down the stem and to get to the roots okay because sometimes the water may not have enough oxygen for the roots to kind of continue their metabolic processes so as air spaces two things here gosh can I spell this buoyancy is a tough one boy and c plus o2 diffusion okay so that's hard to fight that's zero fight this is my mum's water lilies and this is the bottom of the planter okay so that's everything about water movement through the plant we're so nearly done but we just got one little bit more to do which is about sugar movement in a plant okay so we already said if I pinch out slightly that sugar is made by photosynthesis up here in the palisade mesophyll mainly of the leaf how does it get everywhere else every single cell in a plant needs to do respiration but the sugar is only made in the photosynthesizing cells so how does sugar move well it moves in the phloem so let's go down here talk about that first let's talk about the adaptations of phloem cells so phloem unlike xylem like move across here is alive just I say just because the cells are kind of clinging on to life living cells why are they clinging well because there's nothing in them really ok the nucleus the mitochondria all that stuff that's normally in the cell has been cleared out in their development process unlike the xylem they don't go full fully and completely die but they you know there's not much in the middle so living cells most of contents have sort of been cleared out how does it say in the textbook ya know just to say most of contents cleared out and literally just the little cytoplasm left so we can see that here okay there's not much in there there's no nucleus there's no mitochondria it's just a tiny bit of cytoplasm so this leaves room for mass flow there's a key word okay mass flow the plain capitals mass flow the other thing that helps mass flow is that the the phloem cells the barrier where one clumps I'll meets the next is like a sieve like a sip so it's called a sieve plate but at the end is perforated with lots of little holes many plasmodesmata to the next one so this is the sieve plate here so sieve plate between cells and there is that okay now the phloem cells have to be lied because there are physical metabolic processes that have to happen for them to do their job and those metabolic processes are largely done by something called a companion cell okay so this here is a companion cell to the phloem cells without the companion cells the phloem cells would die okay so the companion cells and the phloem cells are connected by these plasma Dez Dez martyr so the plasma as the companion cells are kind of doing all the proteins since this or the respiration all that stuff to support their neighboring phloem so all these cells here actually around would be companion cells as well so I'll label that next to the phloem so what do the companion cells do the companion cells help load and unload sugar into the phloem where it's been made in the leaves and then out of the phloem where it's being stored let's say in a underground sugar storage organ like a potato stored sugar as starch so first of all it's let's look at the loading so the loading process of sugar okay so let's look at this companion cells loading how did the companion cells stuff sugar into the phloem well it's a bit of an old process it's kind of a bit of a roundabout process first thing H+ pumped out okay seemed strange we start with pumping something out hold on a minute this creates gradient okay so we've got lots of H+ outside not aligned then H+ flows back in okay it flows back into the companion cell but this involves something called Co transport so every time an H+ ion wants to come back into the cell it goes via a carrier protein and it carries with it sugar so each one we enter if it brings sugar with it so this is co-transport co-transport of H+ and sugar together does it suit crows together sucrose okay so now we've got lots of sugar then the sugar because this is high sugar here some of the sugar is just going to move into the the phloem via the plasmodesmata so sucrose moves into flow so now we've got loads of sugar in here loads of sugar in the Fleur what happens when you've got lots of sugar in one place water follows via osmosis okay this sets up kind of a platter pressure kind of a pressure in the phloem at the source so this loading is happening at the source to fully understand the whole bit of foam we got just move across here and also look at the sink so this is the source okay we've talked about this specific details of the loading process so this red arrow here so sugar being loaded into the phloem and then we can see that water follows these two blue arrows so water follows like that it also follows from xylem which typically run next to the phloem so this is h2o moving from the xylem so this is xylem into the flow so this generates a high hydrostatic pressure there's physical pressure there now what's happening at the sink okay this down here is the sink in this diagram here we've got a beetroot okay so a beetroot has leaves that's where the photosynthesis happens and the beetroot is on the ground so the soil is kind of here the beetroot is buried and it's where the beetroot stores make sugar for the winter for example so in the sink we have active unloading yep so in the sink we have active unloading of the of the sucrose you don't need to know the full details of this like the the biological mechanism but there's active unloading of sucrose at sink so what happens there well again that means that we're going to decrease sorry we're gonna increase the water potential here you can see this diagram here that we kind of the sugar is being moved out but crucially in this one is then probably going to be converted to start so it won't have much of an osmotic effect because it's insoluble starch so it's moved out converted to start quite quickly so that means that the water potential here is now quite high and remember now we're kind of down in the roots and remember that also at the same time in the roots we've got mineral ions being pushed in there so that's why this diagram shows water moving from the phloem back into the xylem because you know helping to build up that root pressure partially caused by the mineral ions being pushed in there so what's going on to move the actual fluid in the phloem well we've got water pressure sort of building up here water in to be phloem at the source and water out of the phloem at the sink this causes something called mass flow so mass flow is right here I'm going to label that mass flow caused by the kind of water pressure so the water going in at the source and coming out of the sink which is also caused by the other sugar okay so that's the phloem all right so I think we've looked at everything there so I'll just zoom out so we can kind of get the whole view now what I'll do because I there was a one or two more animations I wanted to kind of put in but I'll leave them up to you whether you look at them what I'll do is I'll link in my favorite two or three animations about transpiration and the phloem underneath the video in the description so if you want to have a look at that you certainly can but that is plant transport very briefly I'm going to summarize in about 20 seconds okay xylem dead cells lignin could be different patterns like spiral or ring thickening phloem living cells most of the contents is gone there's a little cytoplasm in there and they're kind of kept alive by the companion cells which have a role in loading sucrose overall water moves from the roots through the cortex into the vascular bundle where as route pressure generated then the water moves up the xylem which we just talked about and then out of the leaves this whole process is called transpiration and we can measure it with a pedometer suddenly you have slight adaptations to kind of minimize or maximize transpiration so zero fights and hydro fights have slightly different leaf structure and then finally we talked about the phloem the the specific mechanism of loading which is kind of H+ and then Co transport sugar back in and then this idea of mass flow do also need to know cross-section diagrams of the root and the stem and how the different tissues are arranged so that's everything on plant transport hope that was useful and then the next moment we're going to look at this week is going to be on disease okay so I'll see you then Thanks