Lesson video

Hello and welcome to this lesson from the unit stem cells and differentiation.

The title of today's lesson is meristem cells in plants.

And in today's lesson what we're going to be looking at is those stem cells that are in plants that can differentiate into other types of specialised cells that make up the different tissues in a plan.

My name's Mrs. Barnard and I'm going to be taking you through today's lesson.

So by the end of today's lesson, you should be able to explain what meristem cells are and give examples of where they are found in plants.

And our key terms for today's lesson are meristem, shoot, root, xylem, and phloem.

So if you would like to write down the definitions, you can just pause the video.

Otherwise we'll be going through them as we go through today's lesson.

So our lesson today is in three parts.

The first part is stem cells in plants.

So where about those stem cells are and what they are.

Differentiation, so what kind of cells those stem cells differentiate into in plants.

And finally, the use of meristem in agriculture and conservation.

So let's get started with the first part of today's lesson, which is stem cells in plants.

So stem cells are cells that are not specialised for a particular function.

They can differentiate into any type of cell.

So can you recall the main structures of a plant cell to start with? So a little bit of a recall task.

You might want to discuss it with the person next to you.

I'll pause the video if you want a little bit of time.

So we have chloroplasts which are the green structures that are used for photosynthesis.

We've got vacuole which draws the cell up.

You've got a cell wall which gives the cell structure.

We got ribosomes which are used for protein synthesis.

We got mitochondria which is the site of aerobic respiration.

We've got cell membrane which controls what enters and leaves the cell, or cytoplasm where the main chemical reactions take place.

And we've got the nucleus where the genetic material, the DNA is stored.

So if you've got all those right, then well done.

So stem cells in plants are found in particular regions of the plant, which we call meristem tissue.

And we can find those in the shoots and in the stem, particularly the shoot tip and the stem and in the root tip.

Now meristem cells undergo mitosis.

Remember that means that they divide by copying their DNA and then the cell divides.

And then they can differentiate into any type of plant cell.

And this can happen throughout the whole life of the plant.

So here's an example in this image here.

So we've got mitosis at the top where we're making genetically identical copies of the cell, those meristem cells, 'cause we need a constant supply of these before they then differentiate so they change into specialised cells.

And you can see that as we are moving down through this image.

So the mitosis and differentiation of meristem allows each part of the plant to grow in heights in length and in width.

So again, you can see this image, this is down a microscope and we're looking at the cells in the tip of the root.

We've got these meristem cells that are dividing by mitosis.

And as they divide and move outwards, you get growth in both directions.

So mitosis actually only occurs in the meristem tissue.

All other growth in the plant is because the cells elongate.

And so any new cells are made in the meristem.

So we get growth as we move down through from mitosis into differentiation.

So here's an example of where you can get growth in non-meristem tissues where you have a cell and it elongates rather than making new cells.

So that's quite a difference.

So select the parts of a plant that contain meristem tissue.

So pause while you decide and then we'll come back and we'll see if you've got it right.

Okay, so we have got meristem tissue in the root tips, in the shoots, and in the stem.

So if you've got all those right then well done.

So for each of these boxes, each of these statements here, can you tick which box sort of best represents your understanding of this statement? Do you think it's correct? Or are you sure it's correct? Do you think it's incorrect? Are you sure it's incorrect? So again, pause while you decide and then we'll come back and I'll give you some feedback.

Okay, let's go through your answers then.

So plants have stem cells.

This is correct.

We've talked about that in meristem tissue.

All cells in a plant carry out mitosis.

This is incorrect because cells outside of the meristem do not.

They grow due to cell elongation.

Meristem cells differentiate into different types of plant cells.

This is correct.

And meristem tissue is only present in roots and shoots.

That is incorrect 'cause it's also present in the stem.

So if you got those right then well done.

So it's time to move on to the second part of our lesson, which is differentiation in plants.

So meristem cells can differentiate into many different types of specialised cells in a plant.

So we've got this example image of a meristem cell in the middle and we can see that it could differentiate into root hair cells, which absorb water.

We could go to palisade cells in the leaf and their main function is for photosynthesis.

You can see they're full of those green chloroplasts.

We've got guard cells in a leaf, they control whether the stoma or pore is open or not, allowing carbon dioxide to come in for photosynthesis and also to control water leaving the plant.

And then we've got xylem and phloem cells that are in the stem.

So plants have lots of different specialised cells and they have to differentiate from these meristem cells.

There's also meristem cells in the tips of shoots and they divide by mitosis and differentiate to form leaves and flowers.

And this process continues as the stem grows.

As the stem grows, you get more flowers and more leaves being produced from that meristem tissue.

There's also rings of meristem cells in the shoot.

And as it they divide and differentiate the stem, it gets wider and taller.

So let's have a little look at the stem there.

So this is looking at a cross-section down a microscope.

We can see that there's these little bundles all the way around the edge.

And these meristems form like a band.

You might be able to see that sort of dark light blue band all the way around the outside.

And as they grow and differentiate, then you're gonna get this increase in width of the stem.

Now meristem cells at the tips of roots provide a constant supply of new cells and that allows roots to grow longer and wider.

So longer down into the soil in order to reach water and wider.

The root cap, which is right at the very bottom there, that's made of older cells and that, they protect the meristem tissue behind.

So as the root pushes through the soil so that they don't get damaged.

So you've got the root cap right at the very bottom.

So you can see this sort of model image of it next to it and compare it to the microscope image there.

And then above that, we go into the meristem.

And then above that, we go into the root itself.

So the meristem cells also divide and differentiate to make tissues such as the phloem and the xylem.

So if we look at those little bundles around the outside of this cross section of the stem closely, we can see we can divide it up.

So the phloem in there is on the outside those darker cells.

Remember the phloem are the vessels that transport sugars through the plant shown in this image here in yellow.

And then in the middle we've got the meristem and again shown in this image in blue.

And those are the cells that will differentiate into either phloem or xylem.

And then the xylem are in the middle.

Now the xylem vessels transport water and these are hollow tubes.

So we can see as you look in the microscope that they look like hollow tubes, like a straw that you're looking down.

They haven't stained at all 'cause there's nothing inside them.

So meristem cells between the xylem and phloem increase the width and height of the plant.

Now you can see the growth of the meristem leading to more xylem and phloem in the rings in the cross section of trunks.

Have you ever thought about that? So when you look at the cross section of a trunk, of a tree, you can see these circles.

And that's produced because of growth.

They're often called growth rings, aren't they? And that is because you've got new vessels that have divided out from the meristem at that point.

So time for a quick check.

Identify the specialised cells in a leaf.

So pause the video while you decide and then we'll check if you've got it right.

Okay, so the correct answer is A.

Now the reason that we can tell that is because these are green, they've got chloroplast in them and chloroplast traps sunlight and that is the main function of the leaf organ.

So these are specialised cells from a leaf.

And now time for a practise test for you.

So meristem cells differentiate into many different types of cells which allow a plant to grow.

So the first thing that I would like you to do is add labels to a diagram of a plant to show where specialised cells are found in different parts of the plant.

And then, indicate which meristem tissue each type of specialised cell has differentiated from.

Remember, there are only three types of meristem that you need to recall.

So here's an example of one that's been done for you.

So an image of a guard cell on a leaf.

For the guard cells control the stomata pore.

And it says guard cells in the leaf are differentiated from shoot meristem, 'cause the leaves come from shoot meristem.

So it'll take you a little bit of time to this diagram.

Do it really nice and big, this diagram, so that you can get all of your images around the outside with descriptions.

So pause while you do this and then we will come back and I'll give you some feedback.

Okay, so let's have a look at how you got on with this.

Hopefully you took some time to draw it really big with lots of big pictures.

So here's my example.

So we've got a plant through the middle and then we've got that example that was to start with, which was the guard cells in the leaf.

Now these are some examples you might have done different cells and that's perfectly fine.

So we've also got palisade cells which are in the leaf.

And they are differentiated from shoot meristem.

Palisade cells, what their main function is photosynthesis.

They got lots of chloroplast in there and they are long and thin for light to pass through.

And then we have got root hair cells.

So they've got those long projections out the side that give them an increased surface areas for water absorption and they are differentiated from root meristem.

Then we have got phloem and xylem cells with an image here on the side.

And you can see that the xylem ones are completely hollow, whereas the phloem ones, most of the contents of the cell has been pushed to the outside for sugars to pass through.

And they are differentiated from stem meristem.

If you've got some other examples on there, then that's absolutely great.

But hopefully you've got all of the different meristem indicated on your drawing.

Okay, then it is time to move on to the third part of our lesson today.

And the third part of our lesson is uses of meristem in agriculture and conservation.

So stem cells from meristem tissue enable clones of plants to be grown quickly and economically from cuttings.

The clones are genetically identical to a parent plant.

So you might have heard this word clone before.

So a clone is when something is genetically identical to another organism.

So for example, we have a parent plant and we select it and we usually select the parent plant because it's got all of the characteristics, the phenotypes that we want in the plant for commercial reasons.

So it might be that it grows well in certain conditions or it may be produces flowers or leaves that we use in foods or it's got a certain taste or texture.

So we're gonna select the plant that we want the features of.

Then what we're gonna do is take a cutting of it.

Now you might have had a chance to do an example of this before, but you can take a cutting of it.

Not all plants grow well from cuttings, but some of them do so.

The cutting has to contain meristem tissue in order that it can divide and differentiate into other cells because we'll need this plant to reroot.

Often at this point they might add some chemicals to help the plant reroot, but then these cuttings are taken and those meristem cells are going to differentiate to form all of the tissues needed to grow plants from cuttings.

Now obviously we can do this with plants because of meristem tissues.

We couldn't do this with sort of humans for example, okay, because that's not how our organisms are made up.

So we take each of these cuttings, we plant them.

This means that the plant is already a certain size, so therefore it's not gonna take as long to get to full size before that we can use it for whatever it's being used for in commerce.

So producing plants this way is quicker than by traditional reproduction, which would be to pollinate, then collect the seeds, and then plant them.

And it also allows you to make many genetically identical copies of a plant that donated meristem has been used from.

So for example, tea plants and grapes in vineyards are both grown by cuttings.

So you could have fields and fields of plants that all come from the same parent plant originally, so they are genetically identical.

Now that's not necessarily good if the environment changes, but if the environment doesn't change and these plants are well adapted to their environment, it's useful commercially because it means it preserves the characteristics that you want in your plants.

Such as, in terms of tea, flavour.

Sexual reproduction would introduce variation, which again as we said might be useful if the environment is changing, but it might not be desirable if you are just trying to maintain a certain characteristic of your plant.

So time for a quick check.

Why does growing plants from cuttings help to preserve characteristics such as flavour? So pause while you decide and then we'll see how you've got them.

Okay, so the correct answer is the plants are all genetically identical.

So if you selected that one then well done.

So some plants such as ornamental orchids, so you might have seen these orchids, you can get them quite often from flower shops, you give them as presents, they are prized for their appearance.

They don't actually grow very well from cuttings In this case, instead of taking a cutting, stem cells from the meristem tissue samples can be used to produce genetically identical clones via a tissue culture.

So instead of taking a whole cutting, you just take a sample of the tissue.

So again, a parent plant is selected.

And then instead of taking a whole cutting, you just take a tissue sample.

And then you grow the tissue sample in agar, in a petri dish.

You give it nutrients and growth hormones and then eventually roots and leaves and stem cells will be formed from the differentiation of those meristem cells.

You see, they grow there into little plantlets.

And then these plantlets will be planted into a compost to allow them to grow further.

So meristem tissue samples can also be taken to produce clones of rare and endangered species.

So this helps us to protect them from extinction, so it's an important technique.

Here's an example of one that's been done recently.

So the Hill's thistle is quite a rare plant that's found in North America and it is threatened with extinction.

Now lots of attempts were made in order to try to to save this plant, to get it to reproduce.

Lots of seeds were taken and they were planted in various sites and it wasn't as successful as they hoped, because the seeds didn't germinate well.

And not many of the seeds actually became plants.

So what they did instead is they used lab-based cloning from meristem cells.

They made lots and lots and lots of little plantlets and then they planted and they were far more successful at being transplanted into the wild.

So it is a really good technique in order that we save endangered species.

So time for a quick check.

So put these steps in the correct order for making a clone from meristem tissues via tissue culture.

So pause the video while you do this and then we'll come back and we'll see if you've got them in the right order.

Okay, let's see them.

So number one, the first thing you would do is take a sample of meristem tissue from a parent plant.

And then D is number two, to place the meristem cells on agar with nutrients and growth hormones.

And then three, allow the meristem cells to grow into plantlets.

And then four, plant the plantlets in compost.

Okay, so time for a practise task now.

So crop plants can be cultivated from meristem tissue samples as we've already described.

So use these images to explain how crop plants such as tea can be produced from meristem from a single parent plant.

And then I would like you to explain the advantages of this method.

So again, pause while you do this and then we'll come back and we'll see how you've got on.

Okay, so you might have done this in different ways.

You might have done some images and annotated them or you might have written it out.

But either way, this is a sort of a model answer that we would be looking for.

So a cutting is taken from the shoot of a parent plant.

And you might have said why that you chose that parent plant for particular characteristics.

The cutting contains a shoot meristem tissue.

The meristem cells can differentiate into any type of cell.

Root, stem, and leaves developed to form plants.

And the new plants are all genetically identical to the parent plant that was selected for its desirable characteristics.

The plantlets are planted and grow into adult plants.

So if you've included the key ideas from that in some order or in a diagram, then well done.

So the second part of the question was to look at the advantages of this, and it's because it's a quicker way of producing lots of crop plants that have the desired characteristics such as flavour.

So if you've got those right, then well done.

So now that brings us to the end of our lesson.

So plants have unspecialized cells called meristem cells.

And meristem cells at the tips of plant roots and shoots divide by mitosis and differentiate to enable roots and shoots to grow longer.

Rings of meristem in roots and shoots divide and differentiate to enable roots and shoots to grow wider.

Plant growth in other areas of the plant is by cell elongation.

Meristem cells in shoots also divide and differentiate to make leaves and flowers.

Meristem cells in bundles in the cell and root, sorry in the stem and roots, divide and differentiate to make tissues such as xylem and phloem.

And meristem tissue can be used to clone plants for crops or to protect endangered species.

It is a quicker process than relying on reproduction alone.

So well done for your work in today's lesson and we will see you soon.