Lesson video

Hi, I'm Mrs. Hudson, and today I'm going to be teaching you a lesson called Common Structures of Prokaryotic Cells.

This is a biology lesson and it comes under the unit titled: Eukaryotic and Prokaryotic Cells.

The outcome of today's lesson is: I can identify common structures of prokaryotic cells and explain their features.

So we're going to be asking ourselves what are prokaryotic cells, what do they look like and what are their features? There will be some keywords that will be very useful for today's lesson, and those words are prokaryotic, plasmid, binary fission, and eukaryotic.

So let's look at what those words mean.

Prokaryotic is a type of cell with no membrane bound nucleus; DNA is free floating in the cytoplasm.

Plasmid: a small ring of DNA found in the cytoplasm of prokaryotic cells.

Binary fission: the form of cell division that bacteria use to replicate.

And finally, eukaryotic: a type of cell that contains a membrane bound nucleus.

The DNA is usually found inside.

Today's lesson will be split up into three different parts.

Firstly, we're going to label and identify some bacterial cells, then we're going to explain why bacteria are prokaryotic, and then finally we're going to be explaining features of prokaryotic cells.

Let's get started though with labelling and identifying bacterial cells.

So let's start by looking at these three different images.

What do you think they're all showing? These are images of bacterial cells viewed under a microscope.

Bacteria come in all shapes and sizes.

Most of them though, are classified as either being round, rod or spiral shaped.

So in these images here, the first one is showing a rod-shaped bacteria.

So each individual rod shape is one bacterial cell.

The second image is showing you a spiral shaped bacteria, and then the final image is showing you some round shaped bacteria.

Now bacteria are unicellular organisms, which means they're made up of just one cell.

So each individual rod, spiral, or round shape is one unicellular organism.

This is a 2D model of a bacterial cell.

Bacteria are unicellular organisms, which we just said means that they're made up of one cell.

Most bacterial cells will contain a cell membrane, cell wall and cytoplasm, which we can see labelled here on our model of a bacterial cell.

So the cell wall is not actually the very outermost layer, but it's the second layer in, and then the third layer in is the cell membrane, and then we've also got cytoplasm, which is that jelly-like liquid that surrounds all of the subcellular structures within the cell.

There are also other features that bacteria may contain.

So as well as our three common features, the cell wall, the cell membrane, and the cytoplasm, you may also find in bacteria a capsule, kind of an outer layer, a bit like a protective coat that encapsulates the whole bacteria and protects it.

Then you have something called a plasmid, which is this circular ring inside of the bacterial cell.

And this is a small ring of DNA.

And then these little lines coming out at the end, these are called flagellum, and flagellum are mainly used for movement purposes to help bacterial cells to move.

Then we've got ribosomes, which we may have heard of before.

So ribosomes are a small subcellular structure where protein synthesis takes place.

And then finally, this big squiggly loop in the middle of the bacterial cell, this is the chromosomal loop of DNA.

So this is where the genetic material is held.

Now in our cells, in human cells, the genetic material is found inside of the nucleus.

But you'll notice from this diagram that bacterial cells do not contain a nucleus.

So therefore this chromosomal loop of DNA is found free floating within the cytoplasm.

Let's quickly check our understanding so far.

So which of these images shows a bacterial cell? A, B, or C? This is C.

A is a yeast cell, which is a type of fungi, and B is a plant cell.

Which part of the bacterial cell is the line pointing towards? A: chromosomal DNA, B: plasmid, or C: flagellum? Now this is B.

It's the plasmid.

Remember that the plasmid is the small ring of DNA.

The chromosomal DNA is the main, big, long loop of DNA that's found inside the cytoplasm.

And the flagella are those little lines that are coming out that help with movement.

Well done if got that right.

Which part of the bacterial cell is the line pointing towards? A: capsule, B: cytoplasm, or C: cell wall? Now you have to look quite carefully at this one to see where the line is.

Now, if it was the capsule, it would be pointing at the most outermost layer.

So it's not the capsule.

It is C, the cell wall.

Well done if you managed to get that right.

And then finally, which part of the bacterial cell is the line pointing towards? A: flagellum, B: ribosome, or C: cytoplasm? This is B: the ribosome.

Remember, protein synthesis takes place inside the ribosomes.

Great job.

Well done.

We are now ready to move on to our first task of the lesson.

And what you've got to do for this task is to label this bacterial cell.

So the labels have been given for you.

You just have to write what those labels are.

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

Right, I'm sure you did a really great job of that.

Let's get ready to go through those answers together.

So the outermost layer we have is the capsule.

Then the layer on next inside is the cell wall, and then we've got the cell membrane.

That ring is a small ring of DNA, which is called the plasmid.

And then the tail-like structure is the flagellum, the jelly-like liquid that surrounds all the subcellular structures is the cytoplasm.

The small circles are the ribosomes.

And then finally we've got the chromosomal loop of DNA, which again is just free floating in the cytoplasm.

Well done if you managed to get all of those right.

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

But then we'll go on to the next part of our lesson.

So now we can label and identify bacterial cells, we're going to move on to the second part of our lesson, which is to explain why bacteria are prokaryotic.

Let's get going.

Bacteria are prokaryotic organisms. So here you can see the model of our bacterial cell.

And prokaryotic organisms do not contain a membrane bound nucleus.

So here there's no nucleus inside of this bacterial cell.

Instead, there's free floating DNA.

So that chromosome or loop of DNA is just free floating in the cytoplasm.

Because there is no membrane bound nucleus, this is why the bacterial cell is prokaryotic.

So let's look at some examples of this: So first of all, we've got a bacterial cell.

There's no nucleus, and we can see that free floating DNA.

So that chromosome or loop of DNA is free floating in the cytoplasm because there is no nucleus.

A non example of a prokaryotic cell would be a plant cell and an animal cell, which you can see labelled.

They do have a nucleus, and that nucleus contains the DNA, which we can't see on this diagram, but it would be found inside of the nucleus.

Now therefore, in our example, that is a prokaryotic cell because it does not contain a membrane bound nucleus, whereas a non example, these are called eukaryotic cells because they contain a membrane bound nucleus.

The DNA in a prokaryotic cell is free floating in the cytoplasm.

It exists as one long loop of chromosomal DNA.

So here we've got our prokaryotic bacterial cell, and then that's the genetic material, which is a loop of chromosomal DNA free floating inside the cytoplasm.

Also, bacteria have something called a plasmid, which is a much smaller ring of DNA.

So there are two different places within the bacterial cell that contain DNA.

There's the long loop of chromosomal DNA, and also this much smaller ring of DNA, which is called a plasmid.

Prokaryotic cells do not contain membrane bound subcellular structures.

There are no mitochondria or chloroplasts as these on membrane bound too.

So we just spoke about how prokaryotic cells have no membrane bound nucleus, but mitochondria and chloroplasts are also membrane bound.

So therefore prokaryotic cells do not contain those either.

Let's have a look at some examples and non examples.

So an example of a prokaryotic cell is this bacterial cell here, and it just doesn't contain any membrane bound subcellular structures.

There's no nucleus, there's no mitochondria, there's no chloroplasts.

Whereas a non example would be this plant cell, which is eukaryotic, and we know it contains a membrane bound nucleus, but it also contains mitochondria and chloroplasts which are membrane bound.

So therefore, prokaryotic cells do not contain mitochondria or chloroplasts, whereas eukaryotic cells do contain mitochondria and chloroplasts.

And again, eukaryotic cells also contain a nucleus.

Let's check our understanding.

What does prokaryotic mean? A: a cell with no membrane bound nucleus, B: a cell with a membrane bound nucleus, or C: an organism made up of many cells? This is A.

Prokaryotic cells are cells with no membrane bound nucleus.

B: a cell with a membrane bound nucleus.

This would be eukaryotic, and an organism made up of many cells, that's just called multicellular.

But prokaryotic cells we said are unicellular, so it would not be C.

Which of these subcellular structures is not membrane bound? A: mitochondria, B: ribosomes or C: chloroplasts? This is B, the ribosomes.

Mitochondria and chloroplasts are both membrane bound subcellular structures, so we don't find them in prokaryotic cells.

However, ribosomes are not membrane bound, so we do find them in prokaryotic cells.

Well done if you got that right.

A true or false question now.

DNA is found inside the nucleus in prokaryotic cells.

True or false? And then justify your answer.

A: prokaryotic cells have no nucleus and their DNA is free floating in the cytoplasm, or B: prokaryotic cells have a nucleus and the DNA is found inside.

This is false.

So DNA is not found inside the nucleus in prokaryotic cells.

And the reason why is A, because prokaryotic cells have no nucleus and their DNA is free floating in the cytoplasm.

Great job if you've got both of those correct.

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

So what you need to do for this one, first of all, is annotate the diagram to show where the DNA is found in a prokaryotic cell.

Remember, there were two places where we could find DNA, and then secondly, why are bacteria considered prokaryotic organisms? And then three, Jacob is describing prokaryotic cells, what is correct and what is incorrect about what Jacob has said? Correct the incorrect statements.

And this is what Jacob has said.

"Prokaryotic cells have no membrane bound subcellular structures, therefore they don't have a nucleus.

They do contain ribosomes, mitochondria, and chloroplasts, and their DNA is held within the ribosomes." So what is correct, what is incorrect? And correct the incorrect statements.

I'm sure you're going to do a really great job of this.

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

Right, let's have a look at how we did.

So annotate the diagram.

First of all, we've got that long loop of chromosomal DNA and it's free floating in the cytoplasm.

And then the second part is the plasmid, which is a ring of DNA.

So hopefully we got both of those.

And then number two, why are bacteria prokaryotic organisms? Bacteria are prokaryotic organisms as they have no membrane bound subcellular structures.

A nucleus is membrane bound, so they do not have this.

Instead, their DNA is free floating in the cytoplasm.

Bacteria do not contain mitochondria or chloroplasts as these are also membrane bound subcellular structures.

Now you might not have all of that information in exactly the same order, so I'd recommend that you pause the video now and check your answer against this answer and then press play when you're ready for me to go through the next part.

So onto part three now.

What is correct and incorrect about what Jacob has said? So Jacob is correct saying prokaryotic cells contain no membrane bound nucleus.

Jacob is correct saying prokaryotic cells contain ribosomes.

Jacob is incorrect saying prokaryotic cells contain mitochondria and chloroplasts.

These are membrane bound subcellular structures and are not found in a prokaryotic cell.

And then Jacob is incorrect saying the DNA in prokaryotic cells is contained within the ribosomes.

It is free floating in the cytoplasm.

Again, if you need to pause the video to check your answer against this because it's in a different order, please do.

But well done on completing that task.

Let's move on to the final part of our lesson.

You've done a really great job so far.

So finally, as part of this lesson, we're going to be explaining features of prokaryotic cells.

So let's have a look.

The first feature we're going to look at is size and complexity.

So prokaryotic cells are usually smaller in size compared to eukaryotic cells.

If we look here at the two pictures of the cells, we've got a prokaryotic bacterial cell at the top and then a eukaryotic animal cell at the bottom.

Now the prokaryotic cell is usually between one to five micrometres in size, whereas the eukaryotic animal cell could be between five to a hundred micrometres in size, but usually larger than the prokaryotic cell.

That little funny U with a little squiggly line coming down from it.

That is the sign for micrometres.

There are a thousand micrometres in a millimetre.

Prokaryotic cells do not contain membrane bound subcellular structures and therefore usually have a simpler structure.

But if we look at that eukaryotic animal cell, again, we've got a nucleus and mitochondrion, which are both membrane bound subcellular structures.

And because they contain these membrane bound structures, they're usually more complex than prokaryotic cells.

So prokaryotic cells are smaller and generally have a simpler structure.

Prokaryotic cells contain a cell wall usually made of peptidoglycan.

So if that's our prokaryotic cell there, the cell wall is a second layer in and it's made from peptidoglycan.

The cell wall provides structure and gives the cell its shape.

And interestingly as well, some antibiotics work by targeting the cell wall of bacteria.

So they try to break down that cell wall to distort the bacteria and kill the bacteria.

That's why the capsule is very important 'cause it can inhibit those sorts of things from happening to the cell.

Prokaryotic cells divide by a process called binary fission.

So here we have one bacterial cell.

Bacterial cells will replicate, and what happens is they split up to produce two bacterial cells, and that process is called binary fission.

During binary fission, the chromosomal loop of DNA replicates and the cell splits into two genetically identical cells.

So in order for that cell to replicate, it needs to replicate its chromosomal loop of DNA.

But then what happens is you end up with the cell splitting and two genetically identical cells will be produced.

So the way that prokaryotic cells divide is through binary fission.

Prokaryotic cells can contain small rings of DNA called plasmids.

So we spoke about plasmids, that's what they look like on our model of a bacterial cell.

And plasmids carry genes and can be transferred between bacterial cells, which can give rise to variation amongst bacteria.

Now, some people believe that bacteria can evolve really quickly because they are able to transfer plasmids rapidly, which contain genes potentially that have got the code for antibiotic resistance.

Let's just quickly check our understanding.

Which substance usually makes up the bacterial cell wall? A: cellulose, B: peptidoglycan, or C: capsule? This is B: Peptidoglycan.

Cellulose is a substance that usually makes up plant cell walls, and the capsule is just the outermost layer, which is not part of the cell wall.

What is the name of the small ring of DNA found in a prokaryotic cell? A: flagellum, B: plasmid, or C: capsule? This is B: the plasmid.

Remember the flagellum is the tail-like structure and also the capsule we just spoke about is the outermost layer of the bacterial cell.

And finally, what is the function of the cell wall? A: it provides structure and gives shape, B: it allows plasmids to be transferred, or C: it allows substances to enter and exit the cell.

This is A: the cell wall provides structure and gives the bacterial cell its shape.

Amazing job if you manage to get all of those questions right.

We're now ready to move on to the final task of this lesson.

So the first part is that you are going to annotate the diagram to show how the labelled feature gives rise to variation in bacteria.

Then number two: annotate the diagram to describe the process by which bacteria replicate.

Use the labels there to try and help you.

Then number three: describe the prokaryotic cell wall and its function.

And four: describe the differences in size and complexity between prokaryotic and eukaryotic cells.

Pause the video now.

I'm sure you're gonna do a great job, 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 annotating this first picture, so important it was saying here how that feature gives rise to variation.

So this feature: prokaryotic cells can have rings of DNA called plasmids.

Plasmids carry genes and can be transferred between bacterial cells giving rise to variation.

Number two: annotating this diagram to describe the process by which bacteria replicate.

So first of all, we should have identified that the process by which bacteria replicate is called binary fission.

And as part of binary fission, the DNA loop replicates and then the cell splits it to form two genetically identical cells.

If you need to pause the video to add anything into your answers, please do and then press play when you're ready for me to continue.

So number three: describe the prokaryotic cell wall and its function.

The prokaryotic cell wall is usually made from peptidoglycan.

The cell wall provides structure to the cell and also gives the prokaryotic cell its shape.

So well done if you've got both of those parts.

And then number four: describe the differences in size and complexity between prokaryotic and eukaryotic cells.

So prokaryotic cells are usually smaller than eukaryotic cells.

You could have the opposite of that as well.

So eukaryotic cells are usually larger than prokaryotic cells.

Prokaryotic cells are usually between one to five micrometres in length.

You might also have written the length of eukaryotic cells.

Prokaryotic cells are usually simpler cells and they do not contain membrane bound subcellular structures such as nucleus, mitochondria and chloroplasts.

You've done an absolutely brilliant job today.

Well done.

If you need to pause the video to add anything into your answers to make them really great, please do.

But I'm going to move on now to summarising what we've learned in this lesson.

So today we've learned a lot of information and we have said that bacteria are prokaryotic cells.

They have no membrane bound subcellular structures.

Prokaryotic cells contain no membrane bound nucleus, and their DNA is free floating in the cytoplasm.

They also do not contain mitochondria or chloroplasts.

Prokaryotic cells can contain plasmids, which are small rings of DNA that can be transferred, giving rise to variation.

Prokaryotic cells divide by a process called binary fission.

Prokaryotic cells have a cell wall, which is usually made from peptidoglycan.

And finally, prokaryotic cells are usually smaller than eukaryotic cells, with lengths between one to five micrometres.

You've done an amazing job in today's lesson.

I hope you've enjoyed it, I know I have, and I really look forward to seeing you next time.