we are actually done with how water and minerals move into the soil and Roots root to xylem and then we also talked about how the water and minerals move in the leaf and how water vapor diffuse out of the leaf through transpiration so in this particular video for today we are going to be talking about how water and minerals move up the xylem because that is one important that is also quite important because if the water become because if the water cannot move up the xylem the leaf will not be able to receive the water so before we talk about how water and minerals move up the xylem there are a few things to remember and we have to do a little bit of revision the first important thing to remember is water is a dipole what does it mean by a dipole dipole just means that a water molecule has two charges where it has a the hydrogen at atoms have a partially positive charge and the oxygen atom has the partially negative charge and because water has this polarity one water molecule and another water molecule can bond with each other where the oxygen atom from The partially negative side can bond to the hydrogen atom of another water molecule as I'm showing you there and that bond is known as the hydrogen bonds this phenomenon is called cohesion Co just means the water molecules stick to each other another very important thing to remember is because water has polarity water can also interact with other polar molecules they can bond with other polar molecules for example minerals a lot of minerals have charges like for example uh nitrates nitrates will have a slightly negative charge phosphates also have a negative charge as well when they are absorbed in the roots because the polar substances like minerals can interact with water they can dissolve in water that's why water is referred to as a universal solvent this is all chapter 2 stuff now another very important thing to also remember is the structure of the xylem vessel the xylem vessel themselves are deadified cells they don't have end walls because it's broken down and the xylm vessel elements are joined together to form the vessels that you can see on the left and at specific parts of the xylem vessel there are something known as pits and the pits are just unlignified sections which are made up of cellulose walls and they're permeable to water and minerals we will talk about the importance later one thing I want you to understand is the cellulose wall and the liin has some polarity what do I mean by it has some polarity they do have a little bit of charge and because they have a little bit of charge they can also interact with water so what's the big deal why am I explaining all this before we talk about the movement of water up the xylm because these few things are actually important when we want to explain how water and minerals move up the zum so what I'm going to do now is I'm going to draw out a very oversimplified diagram you can see the root hair cell the cortex and also the endodermis okay just simple stuff and then I'm just going to draw out one xylem vessel now in reality the plant does not have one xylem vessel obviously but to make life simple for us we'll just focus on one xylem vessel those green color Parts where I highlighted they are pits it is very important to have the pits so that water and minerals can enter the xylem and of course the xylem vessel at the top is connected to the leaf cells and you can see the epidermis you can see the parenchima cells which are the palis mesophile spongy mesophile and then you also have the lower epidermis and you can kind of see that kidney shaped cells which are the G cells and between the G cells there is that Gap known as the sto now what I'm going to do is I'm going to represent water as blue dots and I'm going to represent minerals as red dots all right and as you can see I'm just drawing out those minerals and such uh of course they are not exactly like that obviously but it's just to help us understand things so you see the first thing to remember is I told you water and minerals can interact with each other why are they able to interact with each other as I've represented in these bonds this orange color dotted lines I hope you can see them the reason why they able to interact with each other is because water has polarity and they can interact with other polar molecules the second important thing to also know here is as you can kind of see there water those water molecules down here they are also interacting with each other and that is because water also exhibits cohesion right now notice that one dotted line that I drew there that water molecule is bonded to the xylem vessel wall the ligin or cellulose wall now how is that possible that is possible because I told you earlier that the lignin wall and the cellulose wall has some polarity a little bit of polarity it's not much but it has a little bit of polarity enough for the water molecules to also bond to them so why is this all such a big deal and the bonding just goes all the way up before we talk about transport of water and minerals up the xylm the first thing we have to understand is that water molecules can interact or attach to the liin or cellulose wall of the xylem vessels so that means they can stick to the xylem vessel wall because the liin and cellulose has a little bit of polarity that phenomenon is called adhesion adhesion means water sticks to something else due to polarity water can also attach or bond with other water molecules and that phenomenon is called cohesion cohesion just means water molecules stick to each other adhesion means water sticks to something else cohesion means water sticks to each other so what's the big deal if they able to do things like this when water exhibits adhesion and cohesion so what it allows the water and minerals to form a continuous chain within the plant so I'm throwing out this uh pink color highlight to show you where the chain is actually located so you might be thinking okay big so what if it has like this uh continuous chain that still does not explain how water and minerals move up the xylem what I'm going to do here is I'm going to focus on just the water in the leaf as you can see here what happens is one water molecule is actually going out of the leaf through transpiration and that creates a pulling effect and you can see all the other previous uh water and minerals will actually start moving forward a little bit that is referred to as something called a transpiration pole because every part of them are interacting with each other so what's the big deal if this transpiration pole actually happens so let's talk about it again what I'm going to do is I'm just going to focus on just the water molecules because if I put the minerals it makes things extremely uh confusing so let's just focus on water and I'm going to label each water molecule by number so number one means water molecule number one two is is water molecule number two 3 4 5 6 7 8 and so on and of course uh after8 there's also water molecule number 9 10 and 11 but I'm not going to include them in this diagram now as water molecule one leaves the cell because water is sticking to each other what happens is water molecule 2 3 four and five gets pulled because of cohesion right because the remember I told you that all the water are sticking together so as the leaf loses water it creates a pole and all the water in the leaf also gets pulled as well because the leaf loses water it pulls water out of the xylm as you can see here water molecule number six because there's an empty space over there the water from the xylm will enter the leaf cells through osmosis because the leaf now has a lower water potential why does it have a lower water potential obviously because the leaf has loose has lost some water right it's kind of obvious that way so the water molecule number six moves into the leaf cell by osmosis this is very important because in that highlighted area it creates a tension so what exactly is a tension tension is what happens I'm going to draw out all the xylem at the top and the bottom when the water in the xylem which is the water molecule number six when it goes into the leaf cells there are less water at the top of the xylm it creates a tension and tension just basically means that the top of the xylm now has a lower pressure and the lower pressure like I said is due to the lack of Water by comparison the bottom of the xylm there still has a high pressure earlier the pressure at the top of the xylem and bottom of the xylem were the same but because the top of the xylem has has lost some water the pressure at the top decreased and by comparison the pressure at the bottom is higher okay and this is referred to as something called as a pressure gradient a pressure gradient is important because what happens then is as you can see these arrows over here the water and minerals in the xylem will move up the xylm along the pressure gradient so I still have a few students who I still don't get this could you explain this again I'm going to try to explain this again so that you understand so let's try to draw out the entirety of the xylem vessel I'm going to draw out the leaf cells root cells and also uh you know all the all the um important cells and what I'm just going to do is number 1 3 5 7 9 all the numbers in blue are just water molecules and all the ones in great are just minerals okay they are not exactly like that but but who cares we are just going to represent it like this the first premise is water and minerals form a continuous column or chain in the xylem vessel how are they able to form a continuous chain in the xylem vessel it is due to adhesion and cohesion adhesion means water sticks to the xylem wall at the it interacts with the liin or cellulose and cohesion means water sticks to each other now at number two the Leaf loses water through transpiration and because water molecule number 19 over there has gone out of the leaf it creates a bit of a pull due to cohesion because the water is attached to the minerals look at 17 and 18 they get pulled a little bit and 16 also gets pulled a little bit as well into the leaf okay and I know that 16 are minerals I get it but when 16 gets pulled what actually happens is some water and minerals move out of the xylem and because the water and minerals move move out of the xylem notice the highlighted Parts the highlighted part at the top because it has lost water it has a lower pressure and the highlighted part at the bottom of the xylm vessel has a higher pressure this creates a pressure gradient a pressure gradient just means that one part of the xylem has a higher pressure and another part of the xylem vessel has a lower pressure so what happens then substances will always move from a higher pressure to lower pressure okay so this movement is called mass flow mass flow just means that what happens then look at all the water and minerals they just move upwards as you can see that so number from number 15 to number six they all just move along the pressure gradient and go upwards then you might be thinking hey what happens to the water and minerals in The Roots well because they are all attached to each other like a chain they get pulled into the xylem and because they get pulled into the xylem the root hair cell will continue absorbing more water and minerals that's how it happens that is why transpiration in the leaf is sometimes important because when the leaf loses water it will drive the movement and of it will drive the movement of water and minerals up the sylm uh mass flow itself is just the movement of water and minerals along the pr meure gradient uh and the minerals are dissolved in the water as you can see in this diagram so wherever the water goes the minerals just follow because the minerals are dissolved in water this is just how water and minerals move up the xylm so in the exam question all you just have to talk about is the concept of adhesion and cohesion which allows the water and minerals to form a chain you can then say that the top of the xylem vessel becomes a lower pressure because the leaf loses water and water moves out of the xylm and that creates a gradient a pressure gradient sorry and that drives mass flow to occur because water minerals will just move from a higher pressure to lower pressure thus it moves upwards that's basically it