Land Plants - 2

by Jason Amores Sumpter
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Hello, everyone. In this lesson, we're going to be talking about the specific adaptations that land plants acquired in their transition from their aquatic environment to their new terrestrial environment. Now plants had to come up with many adaptations because their ecosystems, their environments, drastically changed. You could imagine living in complete aquatic environment to moving to living in a terrestrial environment would be quite dramatically different. So plants evolved many structural features that allowed them to live on land. Now what do you think the majority of these new adaptations are going to do? Well, if you go from living in water to not living in water, you're going to find that the majority of these new adaptations that these plants have is going to help them retain water, going to help them not dry out from living in very dry air. So the majority of these adaptations help them retain water, and some of the major adaptations for retaining water are going to be the cuticle feast Omada and the guard cells. So the cuticle is going to be the main line of defense against desiccation or drying out. This is going to be a waxy film covering the epidermis, or outer layer of cells off many plants. You can actually see the cuticle right here. It actually looks like this, this clear layer of wax, and that's pretty much exactly what it is is it's clear layer of wax that goes directly over the outer layer of plant cells. It's kind of like a raincoat, but instead of keeping the rain out, it wants to keep the water inside of the tissues of the plant. So the cuticles main job is to keep water in, so it keeps the plant cells from losing water. Also, the cuticle is very important for keeping out pathogens, but we'll learn more about that whenever we learn about the immune system that you find inside of plants. All right, so now let's talk about these stone mata so moderate are going to be pores in the tissues of the cells, generally, the leaves that are going to control gas exchange and they're going to regulate water loss. Still, mata are basically pores or holes in the tissues of the plant that air ableto open and are able to close. You can actually see a stone mata or a stoma that is the singular version. Stone Mata is plural. You can actually see a stone MMA right here. This is a stone, This hole in the surface off the leaf. This is a cross section of a leaf. If you guys were wondering, here is the leaf. Here's the cross section of the cells of the leaf, and we have a poor in the bottom of the leaf right there, which is a stone MMA. Now the stone mama are actually able the stone Mott are actually able to open and close. And the way that they're able to open and close is because they have the specialized guard cells and these guard cells air able to change their shape based on their turgid iti, which is going to be the amount of water pressure that they have inside of them. And they're able to open and close the stone. Mama. Now, why would a stone a need to open and close? Well, plants need access to the air to do photosynthesis. Photosynthesis requires co two, and it gets rid of oxygen, so it needs to interact with the gas. Is that air in the air? So the stone mata need toe open for that particular reason for gas exchange for photosynthesis. But because the internal tissues of the plants are interacting with the air, that means that water is actively evaporating out of the leaves, which is bad because we don't want these plants to lose too much water. So this is why Stone Mata opening close. They open so that the plant can do photosynthesis and exchange gasses. But they close so that the plant doesn't lose too much water when it's not doing photosynthesis. In most plants, they're going to close at night when they're not doing photosynthesis because the sun is not out. There are some specialized cases that we will learn about later. Now, I wanted to show you guys how these air actually going to work. So whenever you have these guard cells, whenever they have low water pressure, so low pressure inside of them they are going to be closed. So these are closed guard cells, meaning that the stone model is close. So these guys down here, our guard cells. Now, whenever water is actively pumped into these cells, they're going to become turgid or have a very high water pressure inside of them. and they're going to form this kind of like macaroni shape and this is going to allow the poor to open. So this is gonna have high pressure, and this is going to allow the Stoma Thio open. So now we can have these gas is so we can have co two entering the plants and we can have oh, to leaving the plants because this stone mata or this stone MMA is open. And that's high water pressure versus low water pressure. So this is going to be how the stone mama actually opens and closes. And generally the stone mater are going to be found on the bottom off the leaf, as you guys can see right here. So those were going to be three major adaptations for living on land. Generally toe allow these plants to do gas exchange, but mostly to allow them to retain water Now. Also, we learned that most plants not all land plants, have vascular tissue, but vascular plants did in fact evolve vascular tissue. Vascular tissue is very, very important because it allows these plants to transport water and nutrients throughout the entire body of the plant. This allows plants to grow quite large because they can transport water and nutrients to their extremities. You can kind of think of this particular system. Um, as an analogy to our blood vessel system, our blood vessel system actually transports water and nutrients as well to our extremities. Same thing with the plant, except it's a little bit different. They have vascular tissue and they have one type of vascular tissue that is specific for water on one type of vascular tissue that is specific for nutrients. And these two types of vascular tissue are going to be asylum and flow. Um, xylem is going to be the transport vascular tissue, the transports, water and minerals. This is going to be the one that transports for water. Now, Would is very interesting. It is a form of vascular tissue, specifically xylem, and you can look at the Greek word that xylem came from. So xylem is the English. Word in the Greek word is actually Zylon, and in Greek, it actually means would and would is a form of xylem tissue of water, conducting tissue. Now, xylem tissue is going to have very specific structural components, and one of those is going to be the tray kids. We talked about Trey kids in our lesson whenever we talked about the different types of land plants. And remember that Trey kids are going to be these very important structural cells. But I didn't tell you that they're part of these asylum conducting tissue. So, Trey, kids are gonna be these very long cells that help carry water up from the roots. And they contain secondary cell walls. We know all plant cells have a cell wall, but these trey kid cells have another cell wall on top of that for increased rigidity. Now, what's inside of the secondary cell wall is going to be that lignin component that we talked about increased structural integrity. So because these cells have two walls, their name the primary cell wall, which all plant cells have, which is made of cellulose, and the secondary cell wall which traded specifically, had have, which is made of lignin. Now a great example of a track it seen here in pink. So this is going to be xylem vascular tissue shown in pink, and I hope you guys can see. But those cells in pink actually do have to sell walls So this wall here, which I am highlighting for you guys in blue, is the secondary cell wall, and the secondary cell wall is actually exterior to the primary cell wall. So the primary cell wall, which is still in pink, and the secondary cell wall which is now in blue, which I highlighted for you, are the two cell walls surrounding a TRACON sell. Most plant cells only have a primary cell wall. This is made of cellulose. So this is made of cellulose, which is very important structurally, and the secondary cell wall is made of lignin, which is another strong component. So both of these together make these cells very, very strong, and this allows these plants to grow quite large. Now, the primary cell wall cellulose is gonna be closest to the plant cell. The secondary cell wall. Lignin is going to be on the outside of that primary cell wall, and water and nutrients will be moving through These cells. Look something like that so water will be moving through these cells throughout the plant to distribute needed water. Now the other type of vascular tissue is flow um, flow. Um, is going to transport sugars and amino acids and nutrients. So basically, think of zyla moves water and minerals and flow. Um, moves food for the plant. So flow, um, the word flow, um also comes from another Greek word, and the Greek word for flow, um is actually flow yous. I believe it's how you say it, and this translates to bark and a particular type of flow, um is actually bark the bark on the outside of most trees that, you will see is a type of flow, um, tissue. So this flow, um, tissue is going to transport nutrients and sugars. Specifically, it mostly transports the sugars that were made via photosynthesis to the different areas of the plant that need that energy now flowing is a little more complex than asylum. It's got mawr components, and this depiction here in green is depicting some flow of vascular tissue and flow. Um, is gonna have some major. It's gonna have some major key players and they're going to be the sieve elements which you guys can see here. Let me highlight them for you. This is a sieve element, and it's also going to have these parent came of cells and it is going to have companion cells, so sieve elements are the really important ones here. Sieve elements, which are right here. Let me circle them for you. So this is a sieve element cell right here. Sieve element cells are basically tubes, and the cell has almost nothing inside of it because it's just a transportation tube for sugars and the sieve element. Because it has no real internal structures, it can't take care of itself. It can't metabolize its own sugars, so it's going to have things like companion cells. So a companion cell, which is going to be one of these cells right here a companion cell is basically going to take care of and feed thesis if tube element because it cannot do it itself. So Flown is going to have these tube elements. The transport sugars throughout the body of the plant, and it's going to have these companion cells, and it's also going to have these parent chema cells, which I believe is this cell right here. Thes parent kinda sells basically store the sugars that are being transported by this transportation system. Now that's all I have for you on the specific adaptations off these land plants. Don't worry if the vascular tissue seems a little complex. We do have lessons that specifically go over the vascular tissue and vascular transport of food and water in plants, so we will return to this topic. But now let's go on to the different organs of plants like branches and stems and leaves. Okay, everyone, let's go into our next topic.