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  • Hi. It's Mr. Andersen and in this podcast I'm going to talk about plant

  • nutrition and transport. I'm going to use a number of terms that you should be familiar

  • with. Like monocot, dicot, or ground tissue, vascular tissue. And if you're not sure what

  • I'm talking about, make sure you go back and watch the previous podcast on plant structure.

  • But before we get into that we should talk about what plants need. In other words, what

  • is the nutrition that plants count on? Well it's the same thing as in you. They need CHNOPS.

  • So basically what they need is carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. And

  • so where do they get the carbon? Well, unlike us, they're going to take carbon in in the

  • form of carbon dioxide. So that's going to come in through their leaves. They're going

  • to absorb their water, so they're going to get their hydrogen and oxygen through their

  • roots as well. But the other things like nitrogen, phosphorus and sulfur, they're all going to

  • take in through their roots. Now how does that differ from animals? Well we simply eat

  • things, like plants. Or we eat things that eat plants. And so we can get all of those

  • nutrients. And so basically we are kind of talking about the digestive, circulatory and

  • respiratory system all in one, in relation to plants. And so basically plants live in

  • two worlds. They live in the world above ground and that's the world of the shoots. And then

  • they live in a world below ground. And that's in the world of the roots. And so basically

  • the one thing that they're taking in through their leaves is carbon dioxide. And they are

  • using that carbon dioxide to make sugars. And those sugars are going to make up the

  • bulk of a plant. But they are also going to be used for energy within the plant. Now,

  • as far as roots go, they need water. And so that water is going to flow in through their

  • roots. It's going to move up through the xylem and it's eventually going to evaporate through

  • their leaves. And so they're taking that water in. And the one thing that may puzzle you

  • a little bit on this diagram is that they are also taking in oxygen. They are taking

  • in oxygen through their roots. And you might think that seems a little odd. What do they

  • need oxygen for? Well remember they do photosynthesis. And they're using photosynthesis to take in

  • the energy of the sun and convert that carbon dioxide into sugars. But they are going to

  • use those sugars as well. So they do cellular respiration. What do you require for cellular

  • respiration? You need sugars. And they are going to produce those through photosynthesis.

  • But they also need oxygen. And so any part of a plant that's growing or requires energy

  • is also going to require oxygen. Okay. Let's start at the roots and then kind of work our

  • way up through the shoots. I'm going to have examples here. These are the dicots and the

  • monocots. Remember a quintessential example of a dicot would be like a sunflower. And

  • a monocot is going to be corn. Or a dicot could be a dandelion. And a monocot could

  • be grass. But basically what were going to do is we're going to work our way up from

  • the roots to the stems and then finally to the leaves. And you'll find that there are

  • similarities between the two, but subtle differences. And so if we start in the roots what we are

  • looking at here is a cross -section. So imagine that a root looks kind of like this. And there's

  • going to be root hairs coming out of it. Basically what we'll do is we'll just take a cross-section.

  • So we're cutting right across like that. And that's why we have this kind of a circle.

  • And so basically what do we have here? Well there are three types of tissues. Remember

  • there's going to be an epidermis on the outside. So you can see the epidermis here. There's

  • going to be ground tissue here in the middle. So on the monocots same thing. Epidermis on

  • the outside and then it's going to be ground tissue right here. But you're going to have

  • vascular tissue on the inside. So that vascular tissue is going to be made up of xylem and

  • phloem. And it's kind of hard to see with that color. Likewise here we're going to have

  • xylem and we're going to have phloem. The phloem is going to be right outside of that.

  • And so basically if you think about it, in the roots the vascular tissue, that's going

  • to be the movement of water and the movement of nutrients, is going to be centered in the

  • middle of the root. Now if you think about it, that doesn't make sense. How is the water

  • going to get from the outside to the center? Well every time we build new roots you can

  • see, this is roots actually in a potato, you'll see that they're actually starting at the

  • bottom and then they're growing up from the center. And so it's kind of like a plumbing

  • network where it's going to start on the outside, it's going to move to the inside. And then

  • three dimensionally it's going to go up in the plant. Now if you look at the edge, some

  • of these cells are modified into what are called root hairs. And the function of that

  • is to increase surface area. And a lot of these have fungus that are living in and around

  • them. Symbiotic fungi. It allows them to absorb even more nutrients. Now we're going to go

  • above ground into the shoot system. And we're going to look at the stems. And so what you'll

  • find is that we're still going to have the epidermis on the outside. You could see that.

  • So here's the epidermis on the outside. It's going to have that cuticle on the outside

  • of that. But what we start to see in the dicot is that those vascular tissues moving from

  • the center of the root towards the edge of the stem. And the reason why is that it eventually

  • has to flow out into the leaves. And so right here would be the xylem, closer to the edge.

  • We're going to have the phloem here. So this would be the xylem here, the phloem here in

  • a dicot. Likewise here we're going to have the phloem here, excuse me xylem and then

  • the phloem right here. I've always thought these looked kind of like little monkey heads

  • in a monocot. And then we're going to have the epidermis out here. What are all the other

  • cells then? The other cells are going to be ground tissue. So that's going to be ground

  • tissue here as well. Alright. Let's keep going, because remember those stems are eventually

  • going to bud off and those are going to reach to the leaves. And so if we look at leaves,

  • remember what makes a dicot a dicot is it's going to have this net-like venations. So

  • you can see these nets that are branching off. Those nets, those veins are actually

  • the vascular tissue. And so if we look at a cross section right here of a dicot you

  • could see that vascular tissue moving right through the middle. Likewise, if we go to

  • a monocot, what makes them a monocot? Well one of the characteristics is you're going

  • to have one of these parallel veins that are going through the leaf. And so you can see

  • that those veins are vascular tissue that's moving right through the leaf, if I kind of

  • try to draw this three dimensionally. But both of them are going to have essentially

  • the same characteristics when you get to the level of the leaves. And now we're taking

  • a cross section of the leaf. We've got our epidermis on the top. You got the waxy cuticle

  • above that. We're going to have epidermis on the bottom. You can see right here that

  • there's a stomata there. What the stomata for? That's to take in carbon dioxide and

  • also to lose water. Some of the other levels that we have in here is this. We're going

  • to call this the palisade mesophyll. And then we're going to have this down here which is

  • going to be the spongy mesophyll. And so basically what is that? And it's organized different

  • in dicots and monocots. But basically this palisade mesophyll is like palisades, like

  • a waterfall, is going to be an area where we have photosynthesis going on. So we're

  • going to have light coming in and that light is hitting chloroplasts. And that's where

  • the photosynthesis is taking place. But what else do we need for photosynthesis. Well,

  • we need that water. That's going to come through the vascular tissue. And then we need carbon

  • dioxide. And so the bottom part here, all of that space down here is for the carbon

  • dioxide gas to diffuse in and then can be used in photosynthesis. One quick thing I

  • should mention going way back down to the roots again, our immune system kind of protects

  • us from it's environment. And also our skin is going to protect us and is going to allow

  • things in that we want and and things out that we don't. And so basically the way it

  • works in the roots of a plant is a little bit different. And so imagine now we're down

  • right in here. We're down in the root hairs like this. So how is water getting in? Water

  • is flowing in through osmosis. So it's flowing in here to the middle. And remember it's going

  • to go to the center of the root and then it's going to work it's way up. But we don't want

  • to let just anything come in. And the way water flows is kind of odd. Some of the water

  • is going to flow, so this is one cell and this is another cell, so some of the water

  • is going to flow within the cell. So it will go across a membrane. And it will flow through

  • these little pores between the cells called plasmodesmata. But some of it will actually

  • move through the cell wall. So you can see this water right here would be moving through

  • the cell wall and it's never having to go across a cell membrane. And so basically what

  • plants have, now let me do a quick cross-section. So if this is the epidermis and this is the

  • vascular tissue on the inside of a root, so the water is going to flow in like this, basically

  • we don't want it to flow up in a plant unless we have had some say over what has coming

  • in. And remember what protects our cells, what allows certain things in and certain

  • things out, that's going to be the cell membrane. And if you look at this water, since it's

  • going all the way across here, we call that apoplectically. It's moving through the cell

  • wall. It's never had to go across this cell membrane. And so basically what happens is

  • you're going to have an endodermis here. This has a lining around it. And there's going

  • to be a waxy cuticle called the casparian strip. You can kind of see it right here.

  • This is that casparian strip that's connecting all of the cells. And basically what it does

  • is it acts almost as, I don't know if you've seen the Lord of the Rings, but there's a

  • scene where Gandolf, you know, puts his staff down and says, "You shall not pass". Basically

  • what the casparian strip is doing is it's this strip that's goes all the way across

  • here and it's basically forcing that water that's made it all the way to the inside of

  • the vascular tissue, it can't keep sneaking through this cell wall. It will have to force

  • its way into the cell. And it has to go symplastically at that point. So the function of the casparian

  • strip is to force the water eventually to go across the membrane so we have control.

  • And so we just have two things left to talk about. And that's basically how water moves

  • up a plant and then how sugar moves in a plant. And we've talked about transpiration before.

  • But I want you to think about it as a pull. In other words there's going to be xylem,

  • which are these vascular tissues that go all the way from the roots, all the way up in

  • the tree. It's going to go all the way up the inside of the bark. All the way up to

  • the leaves. And eventually evaporate. And so there's a connection all the way up from

  • the roots to the leaves. But there's also something important you should know about

  • water. Water is slightly charged. And that means that this right here, the oxygen is

  • going to have a slightly negative charge. And the hydrogen is going to have a slightly

  • positive charge. And so basically water will line up so the negative oxygen is attached

  • to the positive hydrogen. And we call this bond right here a hydrogen bond. And so basically

  • water is all connected through these hydrogen bonds. And so once one bit of water starts

  • flowing up the tree, the ones are going to follow. And we call that process, or we call

  • that phenomena cohesion. There would also be some adhesion to the inside of the xylem.

  • So two quick things you should know about xylem. It's dead at maturity. So these are

  • cells that are now empty. They're not alive anymore. It's simple just a container or a

  • vessel for the water to flow through. But basically if we go all the up here to the

  • leaf, water is evaporating out. So the H2 is evaporating out. That water is connected

  • all the way back through the vascular tissue through the leaves, through the veins. All

  • the way back down through down here to the root hairs. And so we have a continuous pathway

  • all the way up of water. And so every time one water molecule evaporates here in the

  • leaf, that's going to pull this whole chain up. And so really xylem and the water is moved

  • through a pulling process. What's generating all of that energy to pull it up? It's going

  • to be the sun is pulling it all the up like that. Okay. Now last thing then is how does

  • phloem move? Well phloem is different. Phloem are cells. So here is one cell. Here's another

  • cell. Here's another cell. They're empty. And so how do you be alive as a cell and be

  • empty? Well basically they'll have these companion cells that are going to have a nuclei. And

  • they're connected to the phloem cells. And they're going to provide the metabolic support

  • for phloem. But phloem is a living cell. And xylem we said is dead. They're going to be

  • little connecting holes all the way through here. And same thing over here. It will be

  • connectors like that. And so basically I like to think of it