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.

This is a biology lesson and it comes under the unit called cell division, mitosis and miosis.

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

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

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

So the cell cycle is a process by which cells divide, and this involves a specific set of steps.

Most of the cells in our body are constantly going through stages of the cell cycle.

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

The nucleus is a sub-cellular structure that contains the genetic material, the DNA, and it controls the cell activities.

And the chromosome is tightly coiled strands of DNA that carry the genetic material.

If you want to pause the video now to make a note of those keywords, please do and then press play when you're ready to carry on with the rest of the lesson.

Today's lesson will be split up into two different paths.

In the first part of the lesson, we're going to be looking at stages of the cell cycle and describing what's happening in those stages.

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

So let's get going with the first part of the lesson, stages of the cell cycle.

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

Remember that multicellular organisms are organisms made up of more than one cell.

We are multicellular organisms. Cell division in multicellular organisms is important for two reasons.

The first is growth, and the second reason is repair of damaged tissue.

So in multicellular organisms, cell division is needed for growth and repair.

So here we can see an image of a plant and there's a seedling there.

Over the course of that plant's lifecycle, it will grow and you can see that in the image it's growing roots and it's growing shoots.

And in order for that plant to grow, cell division will be required.

In the same way we've got an X-ray here of a broken arm.

For that broken arm to heal, there will need to be repair of some damaged cells and that repair and replacement of damaged cells will require cell division.

It is essential that new cells are genetically identical to the original cell that is dividing.

So during cell division you have one cell and then that cell divides to produce two cells.

Now it's really important that the two cells produced are genetically identical to that original cell.

A growing and dividing cell goes through a set of specific stages called the cell cycle.

So when a cell is dividing, it goes through the stages which we're about to label called the cell cycle.

And this image here is showing you the cell cycle and it's a pie chart effectively that's got an arrow wrapped around it.

The arrow is showing you the direction in which the cell cycle happens.

So the first and largest part of the cell cycle is called cell growth.

This is stage one.

Stage one means this occurs first, and you can see from the pie chart that cell growth in stage one takes up the most time in the cell cycle.

So a cell will be in stage one for the most amount of time.

Then stage two is called mitosis, nuclear division, and this is where the nucleus divides.

And then stage three, you've got division of the cell membrane and cytoplasm.

Stage three is the point at which you will end up with two genetically identical cells.

Now we know a little bit more about the cell cycle, let's just remind ourselves about how genetic material is organised in eukaryotic cells.

In eukaryotic cells, the genetic material, the DNA is found in chromosomes inside the nucleus.

Remember, eukaryotic cells are cells that contain a nucleus.

So here we've got a eukaryotic cell and you can see within that eukaryotic cell there is a nucleus and we've enlarged that nucleus there.

And what you can see is inside of the nucleus you've got these structures which are called chromosomes.

And if you unwound a chromosome, it would be made up of highly coiled DNA, which is what you can see below that image of the chromosome.

If you unravelled it, it would be made up of coiled DNA.

With the structure of the genetic material in mind, let's have a look in more detail at the three stages of the cell cycle.

The first stage of the cell cycle is cell growth.

Here we've got the image of the cell cycle again, and the largest parts of the pie chart is stage one, which is cell growth.

So the cell spends the most amount of time in stage one cell growth.

What actually happens then during cell growth? Well, each chromosome is copied.

The sub-cellular structures such as ribosomes and mitochondria are copied and the cell grows larger.

This is really important because remember, we're trying to go from one cell to two genetically identical cells.

Now, in order for those cells to be genetically identical, we need to copy everything inside the cell before the cell splits.

So the chromosomes are copied and the sub-cellular structures such as ribosomes and mitochondria are copied and that causes the cell to grow larger.

Now, once we've got copies of everything inside of the cell, the chromosomes and the sub-cellular structures, we move on to the second stage of the cell cycle and this is nuclear division.

Now on the pie chart here we can see stage two mitosis, nuclear division.

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

It's also one part of the cell cycle.

Now this phase is much shorter than the first stage of cell growth.

Now what actually happens then during stage two? Well the chromosomes that have been copied, they line up along the middle of the cell and they are pulled apart to each end of the cell and then the nucleus begins to divide.

And then finally we've got the third stage of the cell cycle, and this is where the cell membrane and cytoplasm divide.

So stage three, division of the cell membrane and cytoplasm.

And effectively what's happening here is the chromosomes have gone to either end of the cell, but now we need to create two different cells.

So for that to happen, the cell membrane and cytoplasm need to divide to create those two separate cells.

So the cytoplasm and cell membrane divide and two genetically identical cells are produced.

Let's see how much of that we can remember with some checks for understanding.

So in the first question, match each stage of the cell cycle to the correct description of what happens.

We've got nuclear division, cell growth, cell membrane and cytoplasm division, and stage one, stage two, stage three.

So you match those up now.

Okay, so hopefully we remembered this, nuclear division happens in stage two, cell growth happens in stage one and cell membrane and cytoplasm division happens in stage three.

Really good job if you managed to get those right.

Let's look at the second check for understanding.

Which two occur during cell growth? A, chromosomes split in half, B, chromosomes are copied, or C, sub-cellular structures are copied.

You should have got B and C.

So cell growth is the first stage of the cell cycle and the chromosomes are copied and the sub-cellular structures are also copied.

Remember we said two examples were the mitochondria and the ribosomes.

A is incorrect.

The chromosomes do not split in half.

The chromosomes are copied during cell growth.

It's really important that the chromosomes are copied to make sure that when the cell splits, each new cell has got the full amount of DNA that the original cell had.

And the final check for understanding.

Which stage of the cell cycle takes the most time? A, copying of chromosomes and sub-cellular structures.

B, nuclear division or C, cell membrane and cytoplasm divide.

This is A, copying of chromosomes and sub-cellular structures.

That happens during stage one, cell growth.

And remember when we looked at the pie chart, that was the largest section of the pie chart.

The cell spends the most amount of time in cell growth.

Brilliant job if you managed to get those questions right.

We're ready now to move on to the first task in our lesson.

So the first part of task A, can you label this diagram to show how genetic information is stored in a eukaryotic cell? And then question two, label the image of the cell cycle to show the stages and describe what happens at each stage.

So you want to have stage one, stage two, stage three, but then actually say what is happening at those specific stages.

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

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

Right, let's see how we did.

So in this first question we had to label this diagram to show how the genetic information is stored in a eukaryotic cell.

So let's start on the left hand side.

That image there is showing you a eukaryotic cell.

It's eukaryotic because it contains a nucleus, which we could label there.

So the nucleus is that kind of red structure, and then we've kind of magnified that so that it looks bigger.

And then inside of the nucleus you've got the chromosomes.

And the chromosomes are effectively highly coiled DNA.

So if you need to pause the video to add anything in, please do, but well done if you managed to get all of those labels correct.

Now moving on to the second part of the task.

So this was an image of the cell cycle and you needed to label the stages and describe what's happening.

So let's start with the first stage, which was the largest part of the pie chart.

That is cell growth.

During cell growth, the chromosomes are copied, the sub-cellular structures are copied.

You might have written, for example, ribosomes and mitochondria, and then finally the cell grows larger.

Then the second part of the cell cycle is stage two mitosis, nuclear division.

And what happens here is the chromosomes line up along the middle of the cell and the nucleus divides.

You may have also written that the chromosomes line up along the middle of the cell and are pulled apart.

That's excellent if you've written that, added more detail.

And then stage three, division of cell membrane and cytoplasm.

So what happens in stage three is the cell membrane and cytoplasm divide to produce two genetically identical cells.

There's a lot of information on this page, so if you need to pause the video to fully check your answers and make sure you've not missed anything out, then please do and then press play ready for me to go through to the second part of our lesson.

A brilliant start to today's lesson, well done.

We now know the stages of the cell cycle.

So let's have a look at describing mitosis.

Mitosis is a process used to produce new cells for growth and repair.

The new cells made are genetically identical to the parent cell.

So we spoke about that earlier on in the lesson.

Mitosis is a type of cell division used for growth and repair in multicellular organisms and it produces two genetically identical cells.

And here we've got an image of some dividing cells and we can see there we've got one cell and then this shows two genetically identical cells produced from a single cell that's undergone one division by mitosis.

So we've gone from one cell to two cells and that's happened through the process of mitosis.

And then here we've got four genetically identical cells produced from a single cell that's undergone two divisions by mitosis.

The three stages of the cell cycle can be seen in the diagram below.

And this diagram is showing you what happens during mitosis.

So the first stage is cell growth and what we can see in cell growth is that we've got that parent cell and that the chromosomes have been copied and then nuclear division occurs and we can see there that the chromosomes have lined up along the middle and they've been pulled apart to either end of the cell and their nucleus has begun to divide.

And then the final stage, we've got division of the cell membrane and cytoplasm.

And the end result is that we have two genetically identical daughter cells.

So overall we start with one parent cell and in mitosis you end up with two genetically identical daughter cells.

So now we're going to look at cell division and mitosis by using some diagrams to help us understand the cell cycle even more.

A growing and dividing cell goes through a series of stages called the cell cycle.

In the first stage, the chromosomes and sub-cellular structures are copied.

So this was stage one in the cell cycle.

So here we've got our parent cell and the chromosomes are copied.

So we can see in that second cell, the chromosomes and sub-cellular structures are replicated, which means copied and the cell has got twice the amount of DNA, there's double the number of chromosomes in that second cell, and this is stage one of the cell cycle, cell growth.

This ensures that the daughter cells have the full set of chromosomes once the cell has divided.

So here again, we've got our image of mitosis.

And in the first part of mitosis you've got cell growth.

Once the chromosomes have been replicated, they line up along the middle and are then pulled to either end of the cell.

So on this image here, we can see that cell growth has occurred before.

And we're looking at the second part now of the cell cycle, which is where the chromosomes line up along the middle and are pulled to either end of the cell.

The nucleus then begins to divide stage two of the cell cycle.

So the chromosomes line up along the middle, which we can see here, and then the pairs of chromosomes are pulled to each end of the cell and the nucleus begins to divide.

We can see from this image here how we've gone from having double the amount of chromosomes to the final part of the image looking like we'll end up with two separate genetically identical cells.

So now we've looked at cell growth and we've looked at nuclear division, stage one and stage two.

Let's look at the third and final stage of the cell cycle.

So in the final stage of cell division, the cytoplasm and cell membrane divide to form two genetically identical daughter cells.

Each daughter cell has the same chromosomes as the parent cell.

So here in the final stage there's the division of the cell membrane and the cytoplasm, the cytoplasm and cell membrane divide.

And then two genetically identical cells form.

Each cell has the same chromosomes as the parent cell.

And we can see that in the image.

You end up with two of exactly the same cell that you started with and they've got exactly the same chromosomes within them.

Now the really important part of that process is that during cell growth, the chromosomes have to be replicated so that at the end both cells have the full amount of DNA.

Let's have a look at all the stages of cell division together.

So we can see on this diagram here, all the stages of cell division can be seen in the diagram below.

And we've got the three different stages underneath the diagram.

So cell growth, then nuclear division, and then finally division of the cell membrane and cytoplasm.

So let's have a look at the first part, cell growth.

We start off with our parent cell and the chromosomes are copied.

So we can see in the first cell we've got four different chromosomes.

And then in the second cell you've got eight chromosomes where you've got pairs of each one.

And then in stage two nuclear division, the chromosomes line up in the middle and then chromosomes are pulled apart and the nucleus begins to divide.

And then stage three, the final part, the cytoplasm and membrane split to form two genetically identical cells.

And one of the key things here is the idea that the chromosomes have to be copied and that has to happen so that each daughter cell has got the same chromosomes as the original parent cell.

Let's check our understanding.

So true or false question to begin with.

True or false, mitosis produces cells with half the number of chromosomes.

And then justify your answer.

A, mitosis produces genetically identical cells or B, mitosis produces cells with variation.

So this is false.

Mitosis doesn't produce cells with half the number of chromosomes and the justification is A, mitosis produces genetically identical cells.

So for them to be genetically identical, the daughter cells have to have exactly the same chromosomes as the parent cell.

And for that to happen, the chromosomes are copied during cell growth.

Really great job if you managed to get that right.

Second question, which of the following shows the first stage in the cell cycle? Image A, image B or image C? This is image B, and we know that because we've got the parent cell to begin with and you can see that the chromosomes have been copied.

So therefore this must be the first stage of the cell cycle, cell growth.

Next question.

Which of the following shows the second stage in the cell cycle? Image A, image B or image C? This is image A, and we can see here that the chromosomes have lined up along the middle of the cell and then they are being pulled apart to either end and the nucleus is dividing.

So this is the second stage of the cell cycle.

Great job if you recognised that.

We're now ready to move on to task B.

So in the first part of task B, you need to annotate the labels on this diagram to show what happens during mitosis.

So in the brackets underneath the image, you're going to write what the stage is and what's happening, and then you're going to write in a little bit more detail using the labels, what is happening at each stage.

And then in question two in task B, explain why it is important for chromosomes to be copied during cell growth.

And number three, during cell growth, the chromosomes are copied.

What else is copied during this process? And then finally, question four, Lucas is talking about the cell cycle and mitosis.

There are some errors in his statements.

Correct the errors so that the sentences are correct.

And this is what Lucas has said.

The cell cycle consists of two stages, cell growth and cell division.

During cell growth, the sub-cellular structures are copied and the chromosome split in half.

During nuclear division, the chromosomes line up along the middle of the cell and are pulled apart.

In cell division, the nucleus, cytoplasm, and cell membrane divide to form two daughter cells with half the genetic material.

So what is incorrect about what is written and can you correct those sentences? I'm sure you're gonna do a fantastic job.

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

Let's see how we did.

So first of all, we needed to label this diagram of cell division and mitosis.

So the first stage is showing cell growth and we've got a parent cell there.

And we can see during cell growth that chromosomes are copied.

You might have also written in there that sub-cellular structures are copied as well, but that line is pointing towards a chromosome.

And then the second stage is nuclear division, and the first line is showing you chromosomes line up along the middle of the cell.

And then secondly, the chromosomes are pulled apart and the nucleus begins to divide.

And then in the final stage we've got division of cell membrane and cytoplasm.

You'll have written there something along the lines of cytoplasm and cell membrane split to form two genetically identical cells.

Fantastic job if you managed to get all of that information down.

If you need to pause the video to check anything, please do and then press play ready for me to carry on.

So for question two, why is it important for chromosomes to be copied during cell growth? Mitosis is a type of cell division that produces two genetically identical daughter cells.

This means that the chromosomes have to be copied to make sure the daughter cells have a full set of chromosomes.

So you might have got something similar written, maybe not word for word the same, but it's the idea that if you're going to create two genetically identical cells, you have to double the number of chromosomes in order for them to be equal at the end.

Otherwise you would end up with half the number of chromosomes in your copied cells.

And then question three, what else is copied other than the chromosomes? It's during cell growth, the chromosomes and sub-cellular structures are copied.

For example, the ribosomes and mitochondria.

Well done if you remembered that.

And then finally for question four, we were correcting what Lucas had said.

So let's have a look at the answers.

The words in bold are highlighting the bits that were wrong.

So the cell cycle consists of three stages, cell growth, nuclear division, and cell membrane and cytoplasm division.

During cell growth, the sub-cellular structures are copied and the chromosomes are copied.

During nuclear division, the chromosomes line up along the middle of the cell and are pulled apart.

Then the nucleus begins to divide.

And then in the final stage, the cell membrane and cytoplasm divide to form two daughter cells that are genetically identical with a full set of chromosomes.

Great job if you recognised those errors.

If you need to pause the video now to check your answers and add any detail in, then please do.

And I'm gonna summarise everything that we've learned in the lesson so far.

So today we've been looking at the cell cycle and cell division, mitosis, and we have learned that unicellular organisms use cell division to grow and repair damaged tissue.

A growing and dividing cell goes through a set of specific stages called the cell cycle, and those stages are cell growth, mitosis, nuclear division, and cell membrane and cytoplasm division.

Stage one is called cell growth and this is where the chromosomes and sub-cellular structures are copied.

And then in stage two, which is called nuclear division, this is where the chromosomes line up along the middle of the cell and are pulled apart and then the nucleus begins to divide.

And stage three is where the cell membrane and cytoplasm divide.

And then finally, mitosis produces two genetically identical daughter cells.

I hope you have enjoyed today's lesson.

You've done some absolutely brilliant learning.

Well done.

I really enjoyed it and I look forward to seeing you next time.