Growth

Hi. In this video, we'll be talking about plant growth, and we'll be focusing in on the various marry systems that plants use now. Most plants experience what's called indeterminant growth, that is, they grow throughout their entire lives and that growth is not terminated. Now plants grow using what are called Mary STEMS. This is a collection of plants stem cells that is able to produce daughter cells and differentiate into any of the necessary mature cell types, meaning that these stem cells conform any of the necessary tissues and structures within the plant. Now primary growth as opposed to secondary growth that we'll talk about a little later in this lesson is when the plants X. When the plant extends its roots through the soil or grows, it's shoots to increase light absorption. Sometimes this can mean sending the shoots down vertically or the stems up. I'm sorry, sending the roots down vertically and sending the shoots up vertically. However, sometimes it's about creating a mawr diffuse root system or shoot system. For example, if there's nothing competing for light above the plant, it might actually send its shoots out to create a wider surface area for sun light absorption, almost like creating a bigger solar panel. You could think of it as now. The a pickle Mary stem is going to be the merest M located at the tip of each route and shoot. And we call the a pickle mayor stem in the shoot. Very creative name. Shoot a pickle, Mayor stem. This gives rise to things like leaves and flowers. And of course, we'll seen you. Stems coming from this. And the route. A pickle marrow stem gives rise to spoiler alert Roots. Here, you can see an example of a shoot a pickle marry stem. We have this little nub, right? And here, that is our Technically, this is our shoot a pickle, mayor stem, And you can see it's surrounded by these young leaves right here. And if we actually take a look at the image over here, you can see that we have our little April marry stem in here. Right? That's gonna be our shoot a pickle, mayor stem. And then over here, get my head out of the way. You can see that, uh, these little regions in the center those our our shoot a pickle mayor stems and surrounding them are these young leaves, so that's actually a young leaf. So moving on, let's actually go ahead and talk about what are called the primary mirror stems. You see these? A pickle Mayor stems will actually differentiate in or to let me say that a different way. Uh, these primary marry stems that air going to form the various tissues of plants differentiate from the A pickle Mary stems and these primary mayor stems are the mayor stems responsible for primary growth. They come in three flavors for our three tissue systems, right? We have the proto durm that's going to give rise to the epidermis. The pro Camby, um, that's going to give rise to the vascular tissue and the ground marry stem, which you guessed it is going to give rise to the ground tissue. So let's take a look at these two figures here on this side. I have a shoot, and on this side I have a root, and let's actually take a look at some of these Mary stems. So the proto Durm, since it gives rise to the epidermis, should come as no surprise that it's found on the exterior of these structures. So this exterior layer of cells here and also on this side had exterior layer of cells and the exterior layer of cells over here is our proto durm, and that's going to give rise to our epidermis. Now the pro Camby, um, which is going to give rise to the vascular tissue, is found inside the proto dream, writes. The program is going to be the most external air. And the pro Camby, um, is going to be a more internal air. And we can see our pro Camby, um uh, in our route as the most central area. This, like core area here and in our shoot, it's actually gonna be this. You can kind of see this darkened line that kind of goes through the middle of the structure here. That's our pro Camby. Um, right that's going to develop into the vascular system now. Lastly, we owe actually, before I get to the ground, Mayor stem really quick. I do want to say that the pro campeon will actually also develop into what's called the vascular Camby. Um, and cork Camby. Um, these air, actually, other types of marist, um, so the pro Camby, um directly develops into vascular tissue, and it also develops into these other types of marry stems that are technically lateral marry stems. And we're gonna talk about those in just a moment. So don't worry. We'll get to that. So let's finish up here with our ground Mary stem and remember that the ground mirror stem will give rise to the ground tissue. And this ground tissue is basically the tissue that's not vascular tissue and not dermal tissue. So it's the everything else stuff, and in our route, it's going to be a the stuff found in this internal area here, of course, also over on this side. I'm just not drying it all the way across and in our shoot. It's actually going to be found in this region as well as this region in here. Um, the you might remember that in the chutes we have the ground tissue divided up as pith and cortex. Right? The stuff that's in, uh, inside the vascular bundles and the stuff That's exterior to the vascular bundles. Well, that's why our ground mayor stem has found on the inside and the outside of our pro Camby in there. All right, with that. Let's actually Oh, my gosh. Let me get my big head out of the waste. You can see where I drew. I'm sorry, you guys. Yeah. So our ground mary stem in the roots. Pardon my fat noodle. You can see that it's this internal tissue here. And I was just drawing it in over here on this side just to be clear that, you know, these things are occurring on both sides. So just to be super crystal clear, let me put some green over here. And just like all in there, that's all ground. Marry stem. Cool. Now let me get my big fat head in the picture and say, Let's turn the page.

root growth occurs in three areas, which were found behind the protective covering called the root cap. This protects the A pickle. Marist, um, and amazingly senses gravity so that the plant knows which direction to grow its roots in. It also secretes a lubricating Polly Sacha ride that allows the growing route to push through the soil more easily. Now these three areas are known as the zone, sometimes called area. You know it doesn't really matter what term you want to use their zone area, whatever. But it's the zone of cellular division on this is where the A pickle and primary mayor stems air found, and this is where cells air actively dividing. We also have behind that the zone of elongation. This is where these primary Mary stem tissues, or rather, tissues derived from the primary mary stems are elongated, actually elongate by swelling with water. And this swelling with water provides force to actually push the root cap through the soil so the root cap is actually forced through the soil by the swelling of the cells in the zone of elongation. Pretty incredible, huh? Then you have, lastly, what's called the zone of cellular maturation. Basically, this is where the cells go. Thio complete their differentiation into whatever tissue type they're going to become, you know, like dermal vascular, ground tissues, whatever. And it's it's actually from this area that we see these epidermal outgrowths called root hairs. These are super important there, the sites of water and nutrient absorption. And here, in our diagram, you can see all of these areas labeled. We have our Route Kappa at the bottom. Then behind that the area of cell division find that elongation and lastly, the area of cell differentiation, or zone of cell maturation. It's the same thing. So this is also the same Aziz zone of maturation. And this is the area where you'll find the root hairs growing. All right, looking over here, we can see some of the particular primary marry stems we covered and they've been labeled. So of course as we saw in the last page, that central area is going to be our here. It's labeled vascular Camby. Um, I want you guys to think of this as our pro Camby. Um and also we have our proto derm on the outside. And then, of course, the ground marry stem in between those two layers looking down at this think image here. Um, it's a really nice picture of the route cap. That's basically what we're looking at here. This is really just a route cap photo and what I want you to notice. Here's the root cap, right? It's this this area in here. Notice all of these dead cells slough ing off the route cap in this last external area that's marked by the number four there, right as the root cap. Rather, as the root grows and extends the root cap is actually going to slough off the dead cells. Um, now, lastly, I just want to turn your attention to this image behind my head. Get out of the way. Here. You can see our route ape Marist n labeled in this area. It's, of course, found behind our route cap. And I also want you to notice all of these internal tissues, right. So here in red and blue, that's our vascular tissue. That's our zeile. Um, and it's actually the red stuff Is the flow in there? So put that in red asylum and flow. Um, And then, of course, we also have our ground tissues in thes layers here. That's our ground tissue. So really, all I want you to see is how in the root, how the root grows, how those primary marry stems are, how they're found, how they're located in there. And then, of course, the tissues that they're going to develop into all right with that, let's flip the page and talk about secondary growth.

primary growth is all about extending the roots and the shoots. But secondary growth, actually, Onley occurs in places that no longer grow in length and secondary growth is all about expanding the circumference of the plant. Usually, we only see this in woody plants. There are some other types of plants that experience secondary growth. But we're just gonna focus on woody plants is our example now, uh, the merest M responsible for secondary growth is called a lateral mary stem, and we're actually gonna look at two types of lateral mary stems, both of which are derived from the pro Camby in which you might remember is one of those primary marry stems that gives rise to the vascular tissue system. Now, vascular Camby, um, is one of those lateral mayor stems and its job is to produce xylem and flow. Um, no, you might recall the pro Camby, um, also produces island flow. Um, we call those asylum and flown produced by the pro Camby, um, primaries. I'll, um, and primary flow him. What does thieve ask Euler Campion produces is known as secondary asylum and flow. Um, now, the growth pattern here is kind of interesting you see the vascular Camby in produces xylem and foam both to the outside and inside of where it's located. I'm highlighting the vascular Camby, Um, as this layer of cells here in blue, that's our vascular Camby, um, cells that it produces towards the outside of the plant. Here is the outside. Here's the inside cells that are produced towards the outside our secondary flow. Um, whereas these cells produce towards the inside our secondary xylem. Now, what this results in is an actually pretty interesting growth pattern. Uh, you've probably seen a tree cut in half, and it has those growth rings, right? Those rings that those concentric circles that continue all the way from the outside of the tree to the interior Well, what's actually happening is the vascular Camby, um, stays on, uh, the basically like the outer layer of the tree. The vascular can be, um, is going to stay towards the outside. It's going to leave behind lots of older asylum on the inside, right? So these are all from the previous year's growth, as you can see, whereas this layer right here is the current year's growth, and again, these air older years seen in here. Well, these Xilin that move, or rather due to the fact that the court court Camby, um continually produces thes cells but keeps moving towards the outside or rather keeps its position on the periphery of the plant. We get this build up of old xylem on the inter portions of the rings, we'll get back to those in a 2nd. 1st, I want to quickly mention the cork Camby, um, that other lateral mayor stem. And this one is actually located even mawr towards the outside than the vascular Camby. Um, we actually highlight the cork Camby. Um, here in red, it's this lateral mirror. Step there. That's our cork, Camby. Um and it's going to produce cells towards the outside. That air, called cork, sells these air non living cells that are highly impermeable to gas and water and actually will form the structure known as bark. Now I want to get back to those interiors Island. See those interiors? I'll, um, have a name that's much more common. That you've probably heard of it's called would write. Would is that poorest structural tissue that's derived from those secondary xylem. Uh, it's it should be noted that it's on Lee the outer layers of asylum that actually transport water. The inner layers accumulate various gums and resins to resist decay. And we actually have two names for these different regions of asylum. We have the heartwood, which I'm gonna jump out of the image. Here is this darker internal area. So this is our heartwood. Then we also have the SEC would which is this lighter colored external air? That's the sap wood. So three heartwood is the layer that's accumulated all these gums and resins in order to resist decay. And it's no longer actively transporting anything. You know, effectively. It is just structural support. At that point, the sap with these lighter outer regions, those will have actively that layer will have actively transporting xylem in it. Now, we also said that that bark is formed from those cork sells. It actually is also made in part from the secondary flow. Um, remember that the vascular Camby, um produces island to the inside and flow into the outside. Well, some of those flow um, the non active ones will become bark in addition with cork cells. So this layer this park because it has these cork cells in it. It's super impermeable to water and gas. But trees have evolved or say woody plants have evolved a way of dealing with that impermeable ity. They have these things called lent ical zin their bark. Basically, it's ah, poorest tissue that creates little openings to allow for gas exchange. And in this birch bark that you see right here we have these horizontal lines that are very characteristic of birch bark. You've ever seen it in the wild. Those are lent ical. So these horizontal lines are our Len tickles. All right, That's all I have for this video. I'll see you guys next time.