Lesson video

This lesson is called plant roots are adapted to absorb water and mineral ions and is from the unit transport and exchange surfaces in plants.

Hi there, my name's Mrs. McCready and I'm here to guide you through today's lesson.

So thank you very much for joining me today.

In our lesson today, we're going to explain how water and mineral ions are absorbed into a plant via specialised root hair cells that are adapted to maximise absorption.

So in our lesson today, we're gonna come across a good number of keywords and they're shown up here on the screen for you.

Now you may wish to pause the video to make a note of them, but I will introduce them to you as we come across them.

Now in our lesson today, we're gonna first of all have a look at why water is so essential for plants.

And then we're gonna have a look at why mineral ions are essential for plants.

Before we consider how roots are adapted for absorption of water and mineral ions.

So are you ready to go? I am.

Let's get started.

Plants need water to survive, just like animals do.

And this is because water is an essential reactant for the reactions of photosynthesis which is how plants make their own food.

In photosynthesis, water is combined with carbon dioxide to make glucose, the plant's food and oxygen.

So you can see how water is critical to the success of this chemical reaction.

Water is also required because as with all organisms, it is essential for cellular processes to be carried out within.

So water makes up the vast majority of every cell.

In particular the cytoplasm.

Most of the cytoplasm is made of water.

And this is essential because water acts as a solute where substances and products are dissolved in water.

And water enables chemical reactions, therefore to take place.

So water being present within the cytoplasm is essential for chemical reactions to take place.

Water is also essential for maintaining the structural integrity of a plant, and this is because plants don't have bones.

So if you think about that, what do our bones do in our body? Well, they help to provide us with structure.

So if plants don't have bones, how do they have structure? Well, one of the ways they achieve that is by filling their cells up with water.

And what that does is make their cells nice and turgid, nice and fully filled, and strong, and therefore gives them structure.

And you can see this when you have a wilted plant.

If you then give it a good water, it will absorb all of that water into its structure and stand back upright again.

So water is acting in part as a structural support mechanism for plants as well as being an essential component for photosynthesis and also our solute for many, many chemical reactions to take place within.

So water is essential for plants.

So let's just check our understanding of that.

Water is essential in a plant for which reasons? A, for maintaining its structural integrity by making a plant flaccid.

B, converting carbon to carbohydrates using photosynthesis.

And C, providing a solvent in which reactions and products are dissolved in cells.

But which ones are correct? I'll give you five seconds to think about it.

Okay.

Have you decided? Well, you should have decided that both B and C are correct.

Now we can make A correct by turning the word flaccid to turgid.

And then that is a correct statement as well.

Did you get all of those? Well done if you did.

Now how does water get into a plant? Well, water enters a plant at its roots and once it's entered the plant, it can then travel up through the plant via the stem, and it can leave the plant via pores in the leaves called stomata.

So water is entering a plant at the roots.

Now plant roots are made of cells just like the whole of the rest of the plant.

And water enters the cells by a process called osmosis.

So just to remind you of what osmosis is, osmosis is the net movement of water molecules through a selectively-permeable membrane from a region of high water concentration to a region of low water concentration.

And you can see that in the diagram where there is more water in the left side than in the right and therefore a higher concentration of water in the left than the right.

So water is moving down the concentration gradient from high to low and therefore moving from left to right within the diagram through the selectively-permeable membrane.

And that is the process of osmosis.

So water enters the plant by osmosis at the roots.

So let's quickly check our understanding of this.

Can you change the last word of each sentence to be correct? So A says, water enters the plant via the leaves.

B says, it moves up through the petals.

And C says, it can leave the plant via pores called osmosis.

But what is the correct last word of each sentence? I'll give you five seconds to decide.

Okay, let's see what the correct word of each sentence is.

So for A, the word leaves should have been corrected to roots.

For B, petals should have been stem.

And C, osmosis should have been stomata.

Did you get all of those right? Well done if you did.

Okay, what I'd like you to do now is to add labels and arrows to the diagram of a plant to show where water enters the plant and the name of the process by which this occurs, to show where water moves through the plant, and to show where water can leave the plant, and the name of the structures through which this occurs.

Then once you've finished labelling the diagram, I would like you to describe why water is essential for plants' survival.

So pause the video and come back to me when you're ready.

Okay, let's see how you got on them.

So firstly, I asked you to add labels and arrows to the diagram.

So you should have added that water enters the plant at the roots via the process of osmosis.

That water travels up through the plant via the stem.

And that water can leave the plant via pores in the leaves called stomata.

Did you get all of those correct parts labelled and the processes by which they are occurring as well? Well done if you did.

Then I asked you to describe why water is essential for plants' survival.

So you should have included that water is essential to maintain the structural integrity of the plant by making it turgid.

Therefore it fills up the cells, which helps the plant to keep its structure and shape.

You should also have included the fact that water is an essential reactant in the process of photosynthesis.

And in this process, water is combined with carbon dioxide to make glucose, which is the plant's food and oxygen.

You should also have said that the cell cytoplasm is mainly water.

And this is essential because the water is a solvent in which reactants and products are dissolved.

Now just check over your work.

Did you get those three key reasons why water is essential for plant survival? Add anything in that you missed and well done indeed.

Okay, let's move on to see why mineral ions are so important to plants.

So we've already seen how water is essential, but plants also need mineral ions in order to grow and survive.

Nitrogen is an essential ion because it is required to make amino acids, which when put together form proteins.

Magnesium is an essential ion because it forms part of chlorophyll in chloroplasts and is therefore essential for photosynthesis.

And phosphates are essential because they make up part of the structure of nucleotides which when you stack lots of those together, makes DNA.

So we have three key mineral ions.

Nitrogen, magnesium, and phosphates.

All of which are essential for different parts of why plants can grow and survive.

So which ion is required for making proteins? A magnesium, B nitrogen, or C phosphates? I'll give you five seconds to decide.

So the ion required to make proteins is nitrogen.

Did you get that? Well done.

Now nitrogen is abundant in the atmosphere.

More than 70% of the atmosphere is made of nitrogen.

Unfortunately, plants cannot absorb this nitrogen.

Instead, they obtain nitrogen via nitrates found in the soil.

So they are absorbing nitrogen in a form called nitrates via their roots in the soil.

Now nitrogen is stored as these nitrate ions, NO3-, and these are made after decomposition of dead organisms and waste material.

So all of that waste material, all of those dead organisms ultimately get broken down by decomposers and detritivores and broken down into their respective mineral ions including nitrates.

So nitrate ions in the soil are absorbed into the plant via the roots.

And then they are transported up through the stem along with the water to the various different parts of the plant.

So nitrates are entering the plant at the roots from the soil.

And that is one of the reasons why soil is so essential to life.

Now nitrates are at a much higher concentration inside the root cells than they are in the soil.

So therefore they should diffuse out of the cell into the soil.

Now obviously that's going to be really unhelpful for the plants for them to lose nitrogen to the soil rather than extract nitrogen from the soil into their body.

So that means that there needs to be a process to counteract that and plants can extract nitrates from the soil by using a process called active transport.

Now active transport is the net movement of particles against a concentration gradient, and this requires energy.

So we can see in the diagram there that there are very few ions in the soil outside of the cell, and there are many more inside the cell.

But active transport is used to transport those ions against the concentration gradient from a low concentration outside of the cell to a much higher concentration inside the cell.

And this is essential for moving nitrates into the plant rather than losing them into the soil.

So active transport happens because it uses a carrier protein in order to move the ions from the position of low concentration to the place of higher concentration.

And these carrier proteins are found within the cell membrane.

You can see that there within the diagram, the carrier protein embedded within the cell membrane.

So the nitrate ion binds to the carrier protein.

And using energy, the carrier protein changes shape.

This means that the nitrate iron can be moved from the outside to the inside and released into the cytoplasm, but it does, as I say, require energy which is why it's called active transport.

Because it's an active process, it requires energy in order to happen.

So let's quickly check our understanding of that.

True or false? Nitrogen is found in the soil at a higher concentration than inside the cell.

So you should have said that that is false.

But why? So you should have explained that nitrogen is found in lower concentrations in the soil which is why it is actively transported into the root cells.

So what I'd like you to do now is to describe using diagrams to help how nitrate ions are moved into a root cell using active transport.

Then I'd like you to explain why active transport is required to transport nitrate ions into a root cell.

Then finally I'd like you to consider this.

One of the most important crops to grow are legumes.

That's peas and beans.

Runner beans, French beans, that sort of thing.

And this is because they have bacteria in their roots that can take nitrogen out of the atmosphere and they add nitrates to the soil as the plants decompose.

So can you explain why these plants are important for keeping the soil healthy? So pause the video and come back to me when you're ready.

Okay, let's see how you got on.

So firstly, I asked you to use diagrams to describe how nitrate ions are moved into a root cell using active transport.

So you should have shown firstly, the nitrate ion outside the cell, a carrier protein within the cell membrane, and the fact that the nitrate ion binds to the carrier protein.

Then you should have shown how energy is used to change the shape of the carrier protein, moving the nitrate ion inside the cell membrane, and releasing it out into the cytoplasm.

So check your work over, make sure you've got all of those key parts.

The fact that the nitrate ion is binding to the carrier protein.

Energy is required to change the carrier protein's shape.

And that releases the nitrate ion into the cytoplasm.

Then I asked you to explain why active transport is required to transport nitrate ions into a root cell.

So you should have said that the concentration of nitrate ions is lower outside the cell or in the soil than inside the cell.

And because of this, nitrate ions need to be transported against the concentration gradient into the cells.

And this requires carrier proteins.

And because it requires carrier proteins and because we're going against the concentration gradient, it requires energy and is therefore called active transport.

Then I asked you to consider why legumes, so peas and beans are essential plants for keeping soil healthy.

So you should have included that crops such as peas and beans have bacteria in their roots.

And these take nitrogen from the atmosphere and essentially are adding nitrates into the soil as the plants decompose.

And what this does is increases the concentration of nitrates in the soil.

What this means is this will ensure that there is a healthy amount of nitrogen in the soil for future crops to use to make the proteins that they need.

So just check over your work, make sure you've got that idea that legumes are using the bacteria in their roots to replenish the nitrates in the soil, which is good both for the legumes growing in the field at the time, but also for future plants that will grow in the soil later on.

So let's move on to the last part of our lesson, which is a looking at the adaptations of plant roots in order to absorb water and mineral ions.

Now if we zoom into plant's roots, we will see that the outermost part of the root has these specialised cells called root hair cells, and you can see them labelled there in the diagram and in the microscope image.

Now root hair cells are where the water and mineral ions are absorbed.

And these are highly specialised cells which are very specifically adapted in order to perform this absorption function efficiently.

Now you can see in the photograph there how the roots appear fuzzy, and that's because of the root hair cells.

So let's take a bit more of a detailed look.

So a root hair cell is absorbing water by the process of osmosis.

Osmosis moves water from the soil into the cytoplasm and the vacuole, and then water can continue its pathway through the plant.

Roots also absorb mineral ions including nitrates into the root hair cells by this process of active transport.

And in order to do that, they require energy.

So root hair cells have a lot of mitochondria and through the process of cellular respiration, mitochondria transfer the energy required for active transport to take place.

Now osmosis and active transport both occur via the cell membrane.

Water is moving, remember from high to low concentration by the process of osmosis and active transport is moving mineral ions from low to high concentration into the cytoplasm as well.

And you can see that in the diagram there on the screen.

Now because these absorptions, because these processes are happening across the cell membrane, the root hair cells need to have a high surface area and therefore they have a large protrusion from the surface of the cell called the hair.

Now it's referred to as a hair, but it isn't actually made of hair.

It's an extension of the cell cytoplasm and the cell membrane.

And this massively increases the surface area of the root hair cell and that means that absorption of water and mineral ions can happen efficiently because there is a huge surface over which those exchanges can occur.

So let's quickly check our understanding then.

Whose explanation of the shape of the root hair cell is correct? So Lucas says, "The hair of the cell can wriggle which lets it move through the soil to find water." Andeep says, "The root hair cell has a long section which can reach further into the soil to look for water and mineral ions." And Sofia says, "The long extension increases the cell's surface area, so more water and mineral ions can be absorbed." But who is correct? I'll give you five seconds to think about it.

Okay, so you should have decided that Sofia is correct.

Root has do not wiggle and they cannot search for water.

So be clear about the function of a root hair cell.

So what I'd like you to do finally in this lesson is to firstly draw a diagram of a root hair cell and then add labels to the hair part, the cell membrane, the cytoplasm, and the vacuole.

Then I would like you to explain why the shape of a root hair cell is a helpful adaptation for a plant to have.

Before finally considering this scenario, that a rather enthusiastic gardener has moved a plant into a new pot, but he's cleaned the roots with a rough cloth before replanting.

So what I'd like you to do is to suggest how this might damage the root cells and why the plant might struggle to absorb enough water and nitrates afterwards.

So pause the video and come back to me when you're ready.

Okay, let's check our work then.

So firstly, I asked you to draw and label the diagram of a root hair cell.

So firstly, you should have drawn a diagram of the root hair cell, then labelled the hair part, the protrusion, the cell membrane, the cytoplasm, and the vacuole.

You might also have added labels to mitochondria as well.

Well done if you did that extra bit.

Then I asked you to explain why the shape of the root hair cell is a helpful adaptation and you should have said that the hair of the root hair cell greatly increases the surface area of the cell.

And what this does is increase the surface over which diffusion osmosis and the active transport can take place.

And therefore this greatly increases how much water and mineral ions can be absorbed by the plant.

And this in turn increases its chance of survival.

So well done if you got all of those correct.

Then finally, I asked you to consider this over enthusiastic gardener and what damage to the root cells he might have caused and why the plant may struggle to absorb water and nitrates now.

So you should have said that the gardener might have damaged the root hair cells by breaking off the hairs or the extensions of the cytoplasm and the membrane.

And what he's done by doing that is massively reduce the surface area of the root hair cells.

This will in turn reduce the amount of water and mineral ions that the plant can absorb because the surface area is much reduced.

This is likely to lead to the plant wilting because of lack of water 'cause it can't absorb the water as effectively as it had been able to.

And it's also gonna struggle to absorb other nutrients, mineral ions required to make proteins, chlorophyll and DNA, for instance, and therefore will a struggle to grow and maintain its general health as well.

So by cleaning the roots, the gardener has really done quite a disservice to the poor plant.

So well done if you got all of those ideas down and well done for your work today.

So we've come to the end of our lesson today.

Well done indeed.

Now in our lesson today, we have seen that plants need water for photosynthesis.

It's a solvent in the cytoplasm for chemical reactions.

And it's also used to provide support for the cells and the plant structure itself.

We've also seen how water is absorbed into the plant by osmosis via the root hair cells.

This is a net movement of water down a concentration gradient.

We've also seen how plants require nitrate ions, and these are essential to provide nitrogen, which is required to make proteins.

Now nitrate ions are absorbed into a plant via the roots against the concentration gradient via a process called active transport, also via the root hair cells.

And in order to absorb water by osmosis and nitrate ions by active transport, root hair cells are adapted to increase their surface area so that osmosis and active transport can take place effectively.

So thank you very much for joining me today.

I hope you've enjoyed today's lesson and I hope to see you again soon.

Bye.