hello this is Dr Henna aseel and uh this is a video on transport in Plants this is the biology uh of combined science but it could also apply to the other biology courses of the IGCSE so let's take a look at what we mean by transport in Plants remember that plants take up water from the soil into their roots and then the water has to travel up through the stem to the leaves and then actually it goes out of the leaves so how does water move up the plant this is through the xylem so the xylem vessels are tubes that go through the stem they transport the water and dissolved salts from the root to the leaves so the water goes up the xylem in one direction from root to leaves and the xylem actually has the thick walls which have something called lignin so they are very thick and very stiff so they help to support the plant so when a tree is standing upright to a very uh High uh height then this is due to the presence of the Zion and supporting the plant now when the leaves take the water and carbon dioxide from the air and they make glucose by which process of course by photosynthesis now they make glucose now we need to send this sugar and amino acids that we make from the glucose joining with the nitrates so the leaves make sugar in the form of glucose and they use that to make amino acids in order to make proteins now we want to send all of this to the rest of the plants so that they can use it of course they use the sugar for respiration and the amino acids to make proteins for new cells how are we going to transport it from the leaves to the other parts of the plant first of all the sugar is transported in the form of sucrose not glucose so sucrose is less uh soluble so it will not be lost easily but it is still soluble and can go through the flow so we're going to transport the sugar in the form of sucrose and we're going to transport the amino acids that were made in the leaves to other parts of the plant that means that all of this can go up through the flow to the uh Buds and the flowers at the top of the plant or it needs to go down to the roots all of these cells need the sugar and amino acids so the substance is transported through the phloem actually go both up and down but in the xylem the water and souls go in only one direction from the roots to the leaves are we okay now you need to know the position of the xylem and the phloem in the root and in the stem and in the leaves because it is the different positions in each of them so can you see the root the root is the diagram on the left where is the xylem and where is the flow can you identify that the xylem is that part in the middle in the root and the phloems are Parts on the side of that central part of the root now if we look at the stem where is the xylem and where is the flow now we have uh these in what we call vascular bundles around the stem going round and round the ports that are outside are called phloem and the ports inside are called xylem can you see that so in both of them the xylem is the one in the middle but in the root it is in the central middle of it exactly in the center in the xylem if they're going round and round in the stem the xylem is inside and the phloem is outside please be familiar with which one is xylem and which one is flow okay then we have we said the water will go up to the leaves but when it goes to the leaves it does something called transpiration and you should know that transpiration is the loss of water vapor from the leaves so the water is lost from the leaves in the form of water vapor now how does this happen it happens by evaporation of the water at the surface of the mesophyll cells followed by loss of water through the stomata all of these are Parts in a leaf so let us take a look at the parts in the leaf first of all you should be familiar with the parts of the leaf whether we're talking about transpiration or we're talking about photosynthesis we need to know the parts of the leaf so you should know that the leaf is covered from outside with a waxy cuticle on Top This waxy layer called cuticle prevents loss of water vapor from the surface so that the plant does not dry up then the next layer is a layer of thin transparent cells these are called the upper epidermis and then we have the layer of Palisade mesophyll cells which are cylindrical and they have a lot of chloroplasts the next layer is the spongy mesophyll cells and the spongy mesophyll cells have a lot of air space between them now where is the xylem and where is the phloem in the leaf remember if we draw the leaf like this the xylem is the one on top and the phloem is the one below so the xylem is above the phloem in the leaf the xylem is bringing the water now the water will go from cell to cell until it reaches the spongy mesophyll cells and it evaporates from the surface of the mesophyll cells that means it goes into the air space in the form of water vapor and this water vapor then diffuses out through the hole called the stomata can you see the whole the hole in the middle there is called the stomata one is called stoma menu is called stomata and the water vapor diffuses out of this stomata remember that the stomata are surrounded by gold cells so the cells around that hole are called God cells and the hole in the middle is called the stomach and the stomata and God cells are in the lower epidermis of the leaf are we following okay there are some experiments that we could do to demonstrate that a plant does transpiration remember we said that transpiration is loss of water vapor from the leaves so I can get a leafy plant cover it with a glass jar and surround the pot that has Soil and Water with a cellophane bag that will not allow the water to escape from the soil so if any water goes out then it should go out through the leaves now how do I know that the plant has done transpiration either I weigh the plant from uh at the beginning and at the end or when water vapor comes out it will form water droplets inside the glass jar so you'll find that inside the glass jar there are water droplets and you should remember that the test for water is if I add anhydrous copper sulfate to these droplets it changes from white to Blue now we can do a control for this experiment you understand the meaning of a control a control means repeating the experiment without the substance or the factor that is being tested and if nothing happens then we are sure for example I am saying that the water vapor will come out through the leaves so I repeat the experiment again without leaves without plant without leaves so of course nothing should happen so either the mass of the soil at the beginning and the end will be the same or there will be no water droplets inside the glass jar so this is called the control because this shows me that the water vapor that comes out is coming out from the leaf not from any other uh fact okay another experiment to show that water goes up the plant for example through xylem so I can put this leafy uh stem into colored water leave it for a few hours and then I can see at the end that first of all the leaves the veins in the leaves will uh take the color of the water and if I cut through the stem through the cross section I will find that the xylem in the stem has the color of the colored water it was put in so this shows that water goes up a plant another experiment that we could talk about is something to determine where is the stomata or to determine that water vapor comes out of the stomata you should know that usually in the leaves the stomata are present on the lower part of the leaf so I can put a cobalt chloride paper on the surface on this side and on the other side of the leaf and you should know that cobalt chloride is also a test for water remember another test for water is anhydroscopal chloride changes from Blue to Pink so I will take the time or measure the time taken for the cobalt chloride paper to change from Blue to Pink I will find that the one that was put on the lower side of the leaf will turn faster because this is where we have stomata and this is where the water vapor comes out okay what are the factors that affect transpiration what would make transpiration faster or slower for example temperature remember if I increase the temperature the rate of transpiration will increase do you remember what's transpiration again transpiration is the loss of water vapor from the leaves so the higher the temperature the faster the water vapor will diffuse out the faster the water will evaporate from the mesophyll cells so we will have faster transpiration what about if we're increasing light intensity remember that when light intensity increases the stomata need to open in order to provide the plant with carbon dioxide for uh photosynthesis so when there is more light intensity the stomata are open and of course if the somata are open then more of the water vapor can diffuse out of the leaf so higher light intensity increases the rate of transpiration what else air currents now if it is a windy day then the rate of transpiration will increase because we need to maintain the concentration gradient you remember what's diffusion it's down the concentration gradient so I need inside the leaf to have more water vapor than outside so if the currents air currents or the wind remove the water vapor as it comes out then more and more water vapor will diffuse out so the transpiration will be fast now the only factor that lowers the rate of transpiration is humidity you know what's humidity humidity is the amount of water vapor in the air so if I have high humidity that means I have a lot of water vapor in the air so that means there will be less difference in concentration inside and outside the leaf so less water vapor will diffuse out so if it is high humidity that means more water outside water vapor outside so less transpiration so the more humidity the less the rate of transpiration now in order to measure all of these factors we can use something called apotometer so this is a potometer in which we put a leaf you see the potometer can you see the air bubble well if the um a water vapor goes out of the leaf that means that the plant will pull more of the water into it and that means the air bubble will move faster if the air bubble is not moving fast that means the rate of transpiration is less so it is taking up water at a slower rate okay let's take a look at some questions in transpiration most of the water evaporates at the surface of which Leaf remember we said if this is the layers of the leaf where do we have evaporation of the water it's from the surface of the mesophyll cells because this is these are the cells that are next to the air space the diagram shows a transverse section through a plant root in which tissue is water transported from the root to the leaves you know that water is transported through what through the xylem so basically it's asking you which of these is the xylem that is the one labeled one so my answer is d Which statement explains why the rate of transpiration changes on a hot dry day remember we said if it is hot high temperature what will happen we will have increase in evaporation if we have dry day we will have increase in diffusion so if I have a hot dry day we have increase in evaporation of water from the mesophyll cells not decreasing diffusion so if he if we're talking about diffusion you'll actually have more diffusion on a dry day so all my choices say decrease in diffusion that's wrong decrease in evaporation that's wrong so the only correct choice is increase in evaporation what will give the lowest rate of trans transpiration what would make the rate of transpiration low high temperature no we said high temperature will increase the rate high humidity yes High rate of movement no So my answer is high humidity this is the one that will give the lowest rate of transpiration are we following the graph shows the uptake of Water by root hair cells over many hours during a day what could have caused the change in the rate of optic act T now what's happening at T the rate of uptick is starting to decrease so why do you think the rate of uptake is decreasing that means that the rate of transpiration is decreasing which of these will cause rate of transpiration to decrease while decrease in temperature would cause the rates of transpiration to decrease but decrease in humidity no more water vapor will come out and increase in light intensity and increase in temperature will cause more water vapor to come up so the only thing that would cause the rate of water object to decrease is a decrease in temperature which statement describes transpiration we said what do we mean by transpiration transpiration is evaporation of water from the leaf mesophyll cells that is transpiration a tree has lost most of its leaves how does this affect the rate at which water is taken up by the trees well if we lose most of its leaves then it cannot um have more transpiration so it will have less transpiration and that means less water uptick so but we're going to say our um choices would be water uptake decreases not increases or Remains the Same all stops it will decrease but it will not stop if we have lost most of the leaves the graph shows rate of water loss what could cause the change in the rate of water loss between X and Y again the rate of water loss is decreasing less transpiration so which of these would make less transpiration again the air becomes cooler so less temperature less transpiration the table shows how humidity may affect the rate of diffusion of water vapor from a plant to the surrounding air which row will result in the highest rate of transpiration so if I want more transpiration do I want high humidity or low humidity but I want low humidity he said if I have low humidity that means there is less water vapor in the air that means more of the water vapor will diffuse out so I need low humidity for higher rate of transport what do I need with respect to diffusion gradient do I want the diffusion gradient to be high or low I want it to be high if there is less water vapor outside than inside then more of the water vapor will diffuse the diagram shows a plant in a controlled environment the list gives three ways in which environment can be altered which changes will cause an increase in the rate of transpiration so let's take them one by one humidity increases no that would cause decrease light intensity increases yes the stomata will open more water vapor comes out temperature increases yes more temperature higher temperature means the molecules will have more kinetic energy and evaporate faster and diffuse out faster so my answer is d were you able to answer all of this the diagram shows the transverse sections through different parts of a plant so we have through the leaf and through the stem and through the root which tissues transport water so basically which of these are xylem remember in the leaf we said where is the xylem the xylem is the one on top so Q in the stem where is the xylem the one inside so that's s in The Roots where is the xylem the one inside so that is you so my answer is d the diagram shows a plant in a container of water the layer of oil stops the water in the container evaporating the initial mass of the container and contents is 296. after two hours the mass of the container and contents is 292. that means how much water evaporated in the two hours 296 minus 292 that's 4 grams so 4 grams of water evaporated in two hours so what is the rate of transpiration per hour he's looking for per out so four evaporated in two hours so for each hour we lost two grams of water the diagram shows a green plant most of the plant is enclosed in a black plastic bag only one part is exposed to the light and can photosynthesize how is the sugar produced by the exposed part transported to the rest of the plant so we have a leaf that is exposed to light it did photosynthesis so it made sugar we we make the sugar into sucrose and we need to transport it to the rest of the plant now remember that the sugar is transported through the to the rest of the plant in phloem now in phloem we said we go downwards only or we go upwards and downwards remember that we said in the phloem we go upwards and down which graph shows how atmospheric humidity affects the rate of transpiration of a green plant we said humidity if the humidity increases what happens to the rate it decreases so it is that graph in C not any of the others it simply decreases with increase in humidity the mesophyll cells and stomata of the leaf are involved in transpiration describe the process of transpiration use the terms mesophyll cells and stomata in your answer we said what is definition of transpiration you should remember transpiration is loss of water vapor from plant leaves now how does this happen by evaporation of water at the surface of the mesophyll cells followed by loss of water vapor through the stomata okay complete the sentences below using words or phrases from the list so he says in the plant water travels upwards in the we said water travels in xylem dissolved sugar drought travels in what flower and moves how upwards and downwards remember in the phloem the sugar and amino acids go up and down evaporation of water from the surfaces of the mesophile cells is called transpiration are you okay with all of this okay thank you this was basics of transports in plants and this is for IGCSE uh biology combined science thank you for listening