Lesson video

Hi, I'm Mrs. Hudson, and today I'm going to be teaching you a lesson called The Cell Cycle and Cell Division: Mitosis including PMAT.

This is a biology lesson and it comes under the unit titled Cell Division: Mitosis And Meiosis.

The outcome of today's lesson is I can describe the phases of the cell cycle including mitosis.

So we're going to be looking at the cell cycle and saying what is the cell cycle? And then we're going to specifically look at something called mitosis and be able to identify and describe the stages of mitosis.

In today's lesson, there will be some key words and they are cell cycle, mitosis, nucleus, and chromosomes.

Let's have a look at what those words mean.

The cell cycle is the process by which cells divide.

This involves a specific set of phases.

Mitosis is a type of cell division that produces genetically identical cells.

It's a part of the cell cycle.

Nucleus is a subcellular structure that contains the genetic material, the DNA, and it controls the cell activities and chromosomes are tightly coiled strands of DNA that carry the genetic material.

If you want to pause the video to make a note of those keywords, then please do and then press play when you're ready to continue.

Today's lesson is going to be split up into two parts.

In the first part of the lesson, we're going to be describing the cell cycle.

And then in the second part of the lesson we're going to be describing the phases of mitosis.

Let's get going with the first part of the lesson, describing the cell cycle.

Most multicellular organisms need to grow as part of their lifecycle.

Multicellular organisms are organisms made up of more than one cell.

We humans are multicellular organisms and most multicellular organisms will have to grow as part of their lifecycle.

Cell division in multicellular organisms is important for two reasons.

The first reason is for growth and then the second reason is for repair of damaged tissue, which means that new cells need to be made.

So this image here is showing you a seedling which is going to grow to form a plant, and you can see that as part of that plant's lifecycle, it has to grow.

So it's growing roots out from underneath into the soil and also growing chutes, which is making the stem and the leaves.

And then this picture is showing us an X-ray of a broken arm and you can see that that arm is broken and in order to repair that broken bone, new cells will need to be made to repair that broken bone.

What we need to take from this slide is the cell division in multicellular organisms is needed for growth and repair.

Unicellular organisms typically reproduce asexually, they use cell division to do this.

So unicellular organisms are made up of only one cell.

A yeast is an example of a unicellular organism.

Now, yeast cells, they use cell division to reproduce.

So what we can see here is that we've got our parent yeast cell and then cell division is used for that yeast cell to reproduce asexually.

And then you end up with two genetically identical yeast cells.

So in the previous slide we said that multicellular organisms use cell division for growth and repair, whereas some unicellular organisms such as yeast cells, they use cell division to reproduce asexually.

And the resulting cells are daughter yeast cells that are genetically identical with the same chromosomes as the parent cell.

Let's quickly check our understanding so far.

So there's a few questions here for you to have a go at.

The first question, in multicellular organisms, cell division is important for which two processes? A, reproduction, b, growth, and c, repair.

Remember, you're picking two answers from this one.

So you should have got for this question b and c.

In multicellular organisms, cell division is important for growth and repair but it is not involved in reproduction.

The next question, why is cell division important for unicellular organisms? A, for growth, b, for asexual reproduction, or c, for sexual reproduction? This is b for asexual reproduction.

Remember we use the example of a yeast cell and yeast cells reproduce asexually.

Let's look now a little bit more about the cell cycle.

The cell cycle is a series of phases a cell undergoes in order to divide.

Mitosis is a part of the cell cycle.

It is a type of cell division that creates genetically identical cells.

And then underneath we've got this image of the cell cycle.

Effectively, that image looks a bit like a pie chart, which is broken up into six parts and then around it is an arrow.

That arrow is showing you the direction in which the cell cycle always takes place.

So let's look at the different phases.

The first phase is called interphase and this is where cell growth occurs.

Chromosomes and subcellular structures are copied in interphase.

What you can also see is that the section of the pie chart that represents interphase is the largest section.

What this means is that a cell spends most of its life in the interface phase of the cell cycle.

And then if we look, we've got five smaller sections of the pie chart and all of this is mitosis.

This is where the chromosomes move to either end of the cell and the cell divides.

So the two main parts of the cell cycle are interface and mitosis.

Let's just see how much of that we can remember.

So we're going to start with a true or false question.

Chromosomes and subcellular structures are copied in mitosis.

True or false? And then justify your answer, a, chromosomes and subcellular structures are copied in interface or b, chromosomes and subcellular structures are copied in every stage of the cell cycle.

This is false, chromosomes and subcellular structures are not copied in mitosis.

And then to justify the answer, you should have a, chromosomes and subcellular structures are copied in interphase which is the first stage of the cell cycle.

Really well done if you manage to get those right.

We're ready now to do the first task of the lesson.

In the first part of the task, you need to describe what multicellular organisms use cell division for and then in the second part, annotate the diagram to show how unicellular organisms use cell division.

Then for the third part of task A, label the image of the cell cycle to show the phases and describe what happens at each phase.

I'm sure you're gonna do a really fantastic job.

Pause the video now and then press play when you're ready for me to go through the answers.

Let's have a look at how we did.

So question one, describe what multicellular organisms use cell division for.

Multicellular organisms use cell division to grow in size and repair damaged cells and tissues.

And then number two, annotating this diagram to show how unicellular organisms use cell division.

So we should have that one individual cell labelled as a yeast cell and it's the parent cell, and then that line is representing cell division.

And then the daughter yeast cells that are genetically identical with the same chromosomes as the parent cell.

Amazing job if you remembered all of that information.

Let's have a look at question three.

We had to label this cell cycle and then describe what's happening at each phase.

So, the largest part of that pie chart is the first stage, which was called interphase and cell growth occurs here.

Chromosomes and subcellular structures are copied during interface and then the remaining five sections are all mitosis, and this is where chromosomes are moved to either end of the cell and the nucleus divides.

Fantastic job if you manage to get all of that down.

If you need to pause the video to add any detail into your answer, then please do, and then we're gonna carry on with the second part of our lesson.

Great job.

We've managed to get through the first part of our lesson.

Let's have a look now at the second part, which is describing the phases of mitosis.

Mitosis is a type of cell division that produces genetically identical cells.

The phases of the cell cycle are interphase, which was the first stage, followed by mitosis.

And mitosis is made up of the following stages: prophase, metaphase, anaphase, telophase, and cytokinesis.

And we can see that there's a diagram below and this is showing us the different phases of the cell cycle.

So let's have a look at labelling this image.

The first cell that we can see is interphase and that was the first stage that we've just spoken about in the cell cycle, the cell spends the most amount of time in interphase, and this is where the DNA and the subcellular structures are copied.

Then we've got a phase called prophase, then metaphase, then anaphase, then telophase.

And the final phase that we need to know about in mitosis is cytokinesis.

So this diagram links to what we've just learned about with the cell cycle.

Interphase we had labelled in that pie chart and then prophase, metaphase, anaphase, telophase, and cytokinesis are all stages that happen as part of mitosis.

A mnemonic can be used to remember the different phases of mitosis.

It can be really difficult for you to remember the names of those different phases and what order they occur in.

So a really useful way of trying to remember this is by using a mnemonic.

And here is an example.

So the mnemonic that I use is I Push My Amazing Trolley Carefully, and the beginning of each word starts with the same letter as the letter that starts the phase of mitosis.

So I is interphase, Push is prophase, My metaphase, Amazing anaphase, Trolley telophase, and Carefully cytokinesis.

I Push My Amazing Trolley Carefully.

Can you think of your own mnemonic for the different phases of mitosis? You might have come up with your own mnemonic or you can just use my mnemonic of I Push My Amazing Trolley Carefully.

And then we can use that mnemonic to help us put the stages of mitosis into order then let's check for understanding now.

Put the phases of the cell cycle of mitosis into the correct order.

So you've got the phase there and the order.

You have a go.

Okay, so if we use the mnemonic, I, so interphase is first, Push, prophase is second, My, metaphase is third.

Amazing, anaphase is fourth.

Trolley, so telophase is fifth, and Carefully is cytokinesis so that is sixth.

Great job if you manage to put those into order correctly.

The mnemonic is really useful to help with this.

Now we can remember the phases and put them into the correct order, let's apply this to the diagram that shows mitosis.

So another quick check for understanding.

The diagram below shows mitosis.

What are the names of each phase? So hopefully we used our mnemonic again.

I Push My Amazing Trolley Carefully.

So interphase, prophase, metaphase, anaphase, telophase, and cytokinesis.

Amazing job if you got that right.

Now we know what the phases of the cell cycle are, let's look at each phase in more detail.

So let's start with interphase.

So on each of these slides, we're gonna have the name of the phase and then the same diagram, which is showing you all the phases of mitosis.

But we're going to look specifically at one phase, which in this case is interphase.

The cell spends most of its life in this phase.

DNA is replicated resulting in two copies of each chromosome.

And the subcellular structures are replicated.

So on this diagram here, the first cell over to the left is showing interphase, and that is called the parent cell.

The original cell that you start with is the parent cell.

And during interface, the DNA replicates to make two copies of each chromosome.

So you can see in the second cell over that now we've got visible chromosomes and there's two copies of the same chromosome.

This is because the DNA has replicated during interphase.

Then the next phase of mitosis is prophase.

In prophase, the nuclear membrane breaks down so there's no longer a nuclear membrane surrounding the genetic material.

And then the chromosomes condense to become more visible.

So what we can see here on that cell, that dotted line, is representing the nuclear membrane breaking down.

So during interface, the genetic material is surrounded by a nuclear membrane, but during prophase, that nuclear membrane breaks down.

And you can see during interphase that these long chromosome chains, and they are not very visible under a microscope.

But during prophase, the DNA condenses to form chromosomes, which are much more visible using a light microscope.

And then the next phase is metaphase.

During metaphase, the chromosomes line up along the equator of the cell.

The equator of the cell is the very middle part of the cell and you can see that that is represented in the diagram as this dotted line.

So during metaphase, those condensed chromosomes line up along the equator of the cell.

The next stage is anaphase.

And during anaphase, the chromosomes split into two identical chromatids and the chromatids are pulled to either ends of the cell.

So we can see on our diagram here that we've got the chromosomes, which we said were in the previous phase, which was metaphase.

And those chromosomes have got two molecules of DNA and they've lined up along the equator of the cell.

And then what happens during anaphase is that the chromosomes split to just be one molecule of DNA and these are called chromatids.

And those chromatids are pulled to either end of the cell.

So each end of the cell will end up with the same chromatids.

And then the next phase is telophase.

During telophase, the chromatids decondense to become strands of DNA and again, that would mean they become slightly less visible and the nuclear membrane reforms around each end of the cell.

So during telophase, you've got the nuclear membrane reforming which again we can see is being represented by that dotted line.

So at this point of mitosis in telophase, the nuclear membrane starts to reform and it reforms at each end of the cell around the chromatids that have been pulled apart.

The final phase of mitosis is cytokinesis and this is where the cytoplasm and cell membrane divide to form two genetically identical cells.

Remember the whole point of mitosis is that it's a type of cell division that produces two genetically identical cells, though the final phase of mitosis is when the cell membrane and cytoplasm divide to form those two genetically identical cells.

So here the cell membrane and cytoplasm divide and you end up with two genetically identical cells.

Let's check our understanding of those phases.

So question one, what happens during interphase? A, DNA is copied, b, chromosomes line up at the equator of the cell, or c, the nuclear envelope breaks down.

This is a, during interface the DNA is copied.

Next question.

Image B shows the nuclear membrane breaking down.

What phase of mitosis does this happen in? A, interphase, b, prophase, or c, metaphase.

This happens during b, prophase.

So during prophase, the nuclear membrane breaks down and the DNA condenses to form visible chromosomes.

Next question.

The image shows interphase, prophase, and metaphase.

Anaphase is the next phase.

What happens during anaphase? A, the nuclear membrane reforms, b, the cytoplasm and cell membrane divide, or c, chromosomes split to form chromatids and are pulled to either end of the cell.

Hopefully the pictures here have helped you.

So we've got interphase, prophase, and metaphase in those pictures.

And metaphase, you've got the chromosomes lining up at the equator of the cell.

So the next phase, anaphase, is going to be c, where the chromosomes split to form chromatids and are pulled to either end of the cell.

Amazing job if you managed to get that right.

Well done.

We're now ready to move on to the second task of the lesson, task B.

In the first part of task B, you have a diagram which shows a phase in mitosis.

Name the phases and use the diagrams to help explain what is happening at each phase.

So you need to use the images and the labels to help you identify the phase that's taking place and then describe in detail what is happening.

And for question two, we've got two more phases of mitosis and you have to the same thing.

So use the images and the labels to help identify the phase and explain what is happening at each of those phases.

And then for three, we're doing the same thing.

We've got some images and you need to say which phase is taking place and explain what is happening at each of those phases.

Sure, you're gonna do a fantastic job of this.

Pause a video, give it your best go, and then press play ready for me to go through the answers.

Let's see how we did.

So in the first image, you've got the parent cell and then the DNA.

And this is showing interphase, the first stage of the cell cycle.

And you might have written something along the lines of the cell spends most of its life in this phase.

DNA is replicated resulting in two copies of each chromosome.

The subcellular structures are also copied.

And then the second image is showing you the nuclear membrane and then you've also got the chromosomes labelled.

This is showing prophase and here the nuclear membrane breaks down and the chromosomes condense to become more visible.

Amazing job if you manage to remember that.

Moving on to the second part.

So the first image, you've got the equator, and then the chromosomes labelled.

This is showing metaphase and the chromosomes line up along the equator of the cell during metaphase.

And then the next image, you've got the chromatids labelled.

This is anaphase.

The chromosome split to form identical chromatids.

And then these are pulled to either ends of the cell.

And then number three, in the first image, you've got the nuclear membrane labelled again.

This is telophase and you should have that the chromatids decondense to become strands of DNA and the nuclear membrane reforms at each end of the cell.

And then in the final image, this is labelling the cell membrane.

This is cytokinesis.

The cell membrane and cytoplasm split to form two genetically identical cells.

Absolutely fantastic job if you remembered all of those stages and explained what was happening at each stage using the diagram.

If you need to pause the video to go back and add anything into your answers, then please do.

And I'm gonna go through and summarise everything that we've learned this lesson.

So in today's lesson, we were looking at the cell cycle and cell division, mitosis.

In the first part of the lesson, we said that multicellular organisms use cell division to grow and repair damaged tissue.

We also said that some unicellular organisms such as yeast, they use cell division for asexual reproduction.

During the cell cycle, a cell grows during interphase and divides by mitosis.

Mitosis has different phases: prophase, metaphase, anaphase, telophase, and cytokinesis.

And we said a really great way of remembering those phases was with a mnemonic.

So if we included interphase as well, you could use the mnemonic I Push My Amazing Trolley Carefully.

Then we talked about how mitosis results in two cells with identical copies of chromosomes in each nucleus.

And then the diagram at the bottom is showing you the diagram that we looked at to represent the cell cycle and we've got interface to begin with, prophase, metaphase, anaphase, telophase, and cytokinesis.

During interface, the DNA is copied and the subcellular structures are copied.

Then in prophase, the nuclear membrane breaks down and the DNA condenses to become visible chromosomes.

Then in metaphase, those chromosomes line up along the equator of the cell, and then in anaphase, those chromosomes split to form identical chromatids, and those identical chromatids are pulled to either end of the cell.

Then in telophase, the chromosomes start to decondense again into DNA and the nuclear membrane starts to reform at each end of the cell around that DNA.

And then finally, cytokinesis.

This is where the cell membrane and cytoplasm divide to form two genetically identical cells.

We've covered a lot of material in today's lesson and you've done such an amazing job.

I hope you've enjoyed it.

I have and I really look forward to seeing you next time.