hi there everybody so today we are looking at xerophytes and their adaptations so xerophytes are plants that live in very dry very arid areas and therefore water loss is a real problem um so the zero fights of adaptations to try and reduce water loss so if we're talking about water loss then most of these adaptations are going to be to do with water potential so we know that if you've got an area of higher water potential and an area of lower water potential we know that water is going to move down the water potential gradient from high to low water potential and in this situation the high water potential that's in our um in the in the cells of our xerophytes okay and the low water potential is in the air okay so we're in a very dry areas so the air has got very low humidity so anything that the plant can do to decrease the steepness of that water potential gradient is going to help to reduce water loss because the steeper the gradient is the more quickly water will be lost so the plant is trying to reduce the steepness of the water potential gradient okay so the first adaptations we're going to look at are rolled leaves and hairs so here's a picture of a plant which is a zerophyte and this is actually called marum grass hang on let me just get back a little bit so if we look at this diagram obviously you can see that this is rolled okay we don't normally see leaves in this shape and if we look at this what looks like the outside edge there that's actually the lower epidermis it's relatively smooth it's flat this other layer here that i'm drawing around which is very very bumpy this layer here is our upper epidermis and basically then what happens is that the marine grass is able to curve one end and the other end around so that they are rolled and the marine grass is able to do that it's able to roll or unroll depending on the conditions okay now we've got this rolled leaf and another interesting thing about them is that the stomata are all the way here on the upper epidermis now normally with leaves we think about the leaves the stomata being on the lower epidermis but in xerophytes especially ones with rolled leaves we see them on the upper epidermis and then the final thing these ideas are all linked together is that we have all of these little hairs okay so i'm drawing them diagram you can see them if you look okay all of these little hairs here now all of these things together the rolled leaves the hairs and the stomata being on that upper epidermis help to reduce water loss because by having this area here i think that we've got the you know the air is all out here okay the air and then obviously there's wind blowing around by having this area here the air inside the leaf is trapped it's not exposed to the wind and because it's trapped it means that the humidity in here is able to build up and because the humidity is able to build up here that means that the water potential in the air which is right next to the stomata the water potential here is much higher than the water potential of the air out here so what the plant has done by rolling the leaf is reducing the water potential gradient between the cells of the leaf and the air because the air is now very humid and that reduces the rate of water loss because the stomata are all on this upper epidermal surface then again obviously that means that's the only way that water is able to leave the the cells leave the leaves if there were stomata on this surface which is our lower epidermis then the stomata that would mean that the water vapor in the airspace spaces in the leaf was directly in contact with this very very arid very dry air out here so the water potential gradient would be very steep but that's not what happens the stomata are all here and therefore they are next to this very very humid area which has been brought about because we've got rolled leaves and also hairs and the hairs also help to trap the water so we have very high humidity now the other really cool thing about xerophytes is they have sunken stomata so not only are they on the the the side of the leaf which is often rolled um they are also sunken so this diagram here i know that the labels are on their side but this makes it easier to figure out what's going on um this is obviously just a section okay and we can see here this is our stoma okay one of them is a stoma if i just draw out and show you the guard cells there and again i'm going for too far too far ahead then what i've drawn here if you think about drawing the cross section of the leaf then you've got this layer here so all of this this is our epidermis okay on both sides and then here and you can actually see a lot of the chloroplast there this layer would be spongy mesophyll so here we've got our guard cells on either side of the stoma so this is where the um the water vapor will move through so this is what connects the air with the outside air okay the outside air with the air space inside the leaf again because you've got this very sunken stomata this is our airspace now we know that the airspace within a leaf has always got very high humidity there's lots of water vapor because the water is evaporating from the surface of these spongy mesophyll cells okay it's moving out of the cells onto the surface then evaporating but because of this section here this bit is also very high humidity so a little bit like with the rolled leaves this area helps to trap very humid air so again it's decreasing the water potential gradient between in this case the air space and the outside air so the water potential gradient is decreased less water is lost if we just compare it to what it would look like in a non-xerophytic cell so normally you'd have your epidermal layer up here and here are the guard cells so the guard cells lead straight from the outside air straight into the air space so you haven't got this area here where air can be trapped okay there are lots of other adaptations which i've summarized here i'm not going to explain them all because the other ones are much more straightforward so i've explained in a bit more detail some of the ones are a little bit trickier to understand but have a look at this and you'll see the rest of the adaptations that you need to be aware of okay that's it thank you