[Music] so we know all about the xylm and the floam but now we need to know exactly how water and minerals move around the plant you should already know about the structure of the leaf but if not watch this video to remind you let's have a look at transpiration and the xylem transpiration is the evaporation of water from the aerial parts of the plant so the leaves and stems by water evaporating out of these parts mostly the leaves a suction pressure is created which draws up the water through the plant this is called the transpiration pool but what exactly happens in transpiration let's start with the roots Roots have root hairs giving them a large surface area for water absorption water passes in from the soil by osmosis passing down the concentration gradient and into the root hair cell cytoplasm and then onto the xylm vessels water moves through the xylon vessels from the root to the stem to the leaf transpiration at the leaf causes a transpiration pull and because water molecules are cohesive water is pulled up through the plant in the transpiration stream as well as the leaf cells needing water for photosynthesis water also keeps the cells turg which supports the plant inside the leaves water is drawn out of the xylm cells to replace the water lost through transpiration because of the cohesive nature of water which also pulls the water through the plant as water leaves the xylm and moves into the leaf it again pulls more water molecules behind it but it isn't just about water the transpiration stream also transports mineral ions that are dissolved in the water from the roots to the leaves the transpiration rate isn't constant there are many different factors that affect it the environmental factors are similar to those that make you sweaty the temperature the humidity but also wind and light intensity then there are also physical factors like does it have a waxy cuticle how many stomata does it have the nature of the guard cells how large is the leaf surface area and if the leaf is folded or flat if the rate of transpiration increases then the rate of water absorption by The Roots needs needs to increase too when water is scarce or if the roots are damaged the plant needs to reduce its transpiration rate by closing some of this tomata there are God cells on either side of the stata which regulate this during daylight hours chloroplasts produce sugar this lowers the water potential of the god cells and they take in Water by osmosis this makes the god cells turgid because the god cells have a different cell wall thickness when turgid they Bend more on the outside into sausage shapes this opens the stomata or the pole water can then be lost during the night all the sugar produced by the chloroplasts gets used up so the water potential of the guard cells increases more water less sugar the guard cells lose water by osmosis and become flaccid and the stomata starts to close this reduces water loss so you now know about water movement through the plant up the sylm and pulled along the transpiration stream by the transpiration pull and unsurprisingly the plant has methods to control water loss by closing the stomata based upon how flaccid or turgid the guard cells are so in the final part of this video we are going to look at the movement of glucose after all water may be important but so is food