Lesson video

Hello and welcome to this lesson from the unit: Stem Cells and Differentiation.

The title of today's lesson is: Specialised Cells, Unspecialized Cells and Differentiation.

So we're gonna be looking at how we manage to make up a multicellular organism, and that is through the use of specialised cells that make up different forms of tissue that have specialised jobs and how some cells start as being unspecialized and how they differentiate in order to become specialised cells.

My name is 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 describe examples of specialised cells in humans and plants and explain how unspecialized cells become specialised.

So we've got some key terms in today's lesson and our key terms are: specialised cell, unspecialized cell, multicellular, differentiation, and gene.

If you'd like to write down the definitions of those words, I'll put the slide up and you can pause it, but otherwise, we'll be going through them as we go through today's lesson.

Okay, so our lesson today is in three parts.

The first part is about specialised cells and how they make up those tissues in multicellular organisms. The second part of the lesson is about differentiation and finally, how differentiation occurs by expression of genes.

So let's get started with the first part of today's lesson, which is Specialised Cells In Multicellular Organisms. So some organisms such as bacteria, some fungi and some plants and some animals live as single cells and they are called, you might remember, unicellular organisms, so they live as single cells.

So in all cases of the different kingdoms of organisms, they can live as single cells, but bacteria always live as single cells.

And some organisms are made up of more than one cell, and these are called multicellular organisms, and they are usually much, much larger because they're made up of more than one cell and they can be made up of millions of cells like you and me.

So here's an example of a bacteria you can see magnified there.

Each of those little cells is an individual cell.

And then we've got lots of cells working together here in a tissue from a multicellular plant.

So animals, plants, and fungi can all be multicellular.

And different types of cells are found in different parts of the organism and they are specific for their function.

So for example, here we've got an animal.

So underneath that fur we've got some skin cells, so the same as your skin cells, epithelial cells.

And then we've got blood cells for example.

And then in a plant we've got those cells in the leaf.

In this example here you can see that they are palisade cells 'cause they've got chloroplasts that trap sunlight for photosynthesis.

And we've got root cells here which don't have chloroplasts because they don't trap light for photosynthesis, but they've got other functions in taking water and nutrients from the soil.

So these diagrams are models of animal and plant cells and they're structures, but not all animals and plant cells look exactly like this.

These are general models for animal and plant cells.

Now you might recall what all of the labels are on this.

So you might wanna talk to the person next to you first to see if you can remember all the different parts of an animal and plant cell, but we're gonna go through what they are now.

So here we go.

We've got the nucleus.

So that's true of an animal and a plant cell.

Cytoplasm, the jelly-like substance where the chemical reactions take place.

We've got the cell membrane that controls what substances enter and leave the cell.

We've got mitochondria, that's the site of respiration.

So where energy is released.

And then we've got ribosomes where proteins are synthesised.

So if you remembered all those, then well done.

So most cells though are actually adapted to their function, so they don't look exactly like these model cells.

They are specialised.

So multicellular organisms are often very, very complex and therefore the different functions of the organism are carried out by different organs, tissues, and cells.

And the organisation has evolved as organisms have become larger and that helps them to survive, okay? So when they're just a single cell, that single cell has to carry out all the functions.

But as they get larger, it's a bit like a big company.

Different people have different jobs on.

Different jobs, different roles, different specialisms, and that helps the company to function.

And that's the same with a living organism.

So here's some examples of specialised cells in animals, that have a very specific job.

So we've got the airway lining cell or the fancy name is the epithelial cell, ciliated epithelial cell, that lines your airway and it brushes mucus and pieces of dirt and bacteria that might be trapped.

We've got the sperm cell which carries the genetic information into the egg cell, which is there at the end, which are used in reproduction.

And then we've got the nerve cell which transmits those impulses, those electrical impulses around your body in order so that your body can move or can carry out its functions as coordinated by the brain and the spinal cord.

So animals share some common structures as we've already looked at, but some can have additional structures that make them better adapted for their role in the organism.

So they are called specialised cells and they can vary in their shape, they can vary in the number of internal structures, for example, the number of mitochondria that they might have or the number of ribosomes and also in the types of structures that they have.

So for example, some plant cells don't have chloroplasts because they're not able to trap sunlight.

So here's another couple of examples.

We've got an egg cell here, it looks very different to our intestine cell, which is a epithelial cell, which has got that very, very large surface area on that surface to absorb nutrients from the small intestine.

And we've got the egg cell which carries half of the genetic material that's going to make up the new foetus, the new zygote.

And that has got lots of mitochondria, it's also got nutrients in little vacuoles inside the cell in order to aid those first stages of growth and development.

Oh, those are labelled on there.

So nutrient stores for growth, and then we've got a jelly layer for protection.

And then we've got the folded membranes to increase the surface area.

So adaptions make cells specialised for their functions.

So here's another two examples.

We've got a muscle cell, so it's got lots of mitochondria and that allows it to carry out muscle contraction.

So to release the energy required for the muscles to contract.

And we've got a fat cell here, they do have fewer mitochondria because their job is not to release as much energy, but they do have a storage, a structure that stores fats inside them.

So those fats can be used later, in either respiration to release energy or for insulation or warmth.

Plants are also multicellular and their specialised cells also have to be adapted for their function.

So some of them might contain chloroplasts and some of them mightn't.

It depends on if their function involves photosynthesizing.

So in these two examples, they're not involved in photosynthesis, so they don't have chloroplasts.

This is a phloem cell, it's got no nucleus, but this provides extra space for moving sugars through the plant.

So we can see there that the sugars would move down through the cell.

These cells actually stack on top of each other and those gaps in the wall would join with the gaps in another wall.

And then that allows the sugars to flow through the plant.

And this cell here is on the surface of a leaf and it's got this waxy layer for protection.

So it makes it waterproof.

It's also transparent.

It means that light can pass through and it can get to the cells underneath that do have the chloroplasts.

So time for a quick check.

Which of the following organisms can be multicellular? So choose from those four, pause the video and then we'll see if you've got it right.

Okay, let's see, which of the following organisms can be multicellular? So fungi, yes, bacteria, no, animals, yes, and plants, yes.

So if you chose those three, then well done.

Okay, now another check.

So all plants cells have the same structure and shape.

Now do you think that's true or false? So there's a picture there to help you.

And once you've decided whether it's true or false, which of the statements underneath best justifies your choice? So pause the video while you decide and then we'll get back to you.

Okay, so the answer is false And the reason is because most plant cells have common structures, but they have adaptations to suit their different functions.

So if you got that right, then well done.

So time for a practise task here.

So we've got a confidence grid.

So what I'd like you to do for each statement is I'd like you to tick which box best describes how you feel about your answer.

So are you sure that it's correct, the statement or do you think it's correct? Do you think it's incorrect or are you sure it's incorrect? So pause the video while you decide and you can have maybe a little bit of a discussion and then we'll get back and we'll see how you've got on.

Okay, let's see how you got with this one then.

So all organisms are multicellular.

This one is incorrect, okay, because as we already know, bacteria are always unicellular.

All plant cells are the same.

This is also incorrect because some of them are specialised for their functions, so will have different structures, different numbers of internal structures.

Only animals have specialised cells.

This again, is false because we saw some examples of plant cells there that are specialised for their roles.

For example, the phloem.

And specialised cells are adapted for their function.

This is correct.

So hopefully you got all of those right.

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

So in a multicellular organism, a group of specialised cells with the same structure and processes can work together to carry out the same function.

This is called a tissue.

And cells can divide to form cells of the same type by mitosis.

Now hopefully you have learned about mitosis before.

It's a process of cell division where new copies of cells are made that are identical to the parent cell.

So for example, we have a smooth muscle cell and when that copies by mitosis, it undergo cell division, then we get lots of smooth muscle cells that are all the same type.

And this was what forms a tissue.

So as I already said, mitosis is a type of cell division.

It produces two identical daughter cells and therefore when the cell divides, each new cell produced has the same genetic information.

So here's an image to show you how it does this.

So new specialised cells can be formed by mitosis to make tissues.

We've got the original cell here and we can see the chromosomes there.

Obviously that's not all of the chromosomes, but as you know from all of the model images that we use, we have to use a small number of chromosomes so that we can see them.

The DNA copies itself and forms those chromosomes that look like Xs.

Often people think that that's what chromosomes look like all the time, but it's only after the DNA is copied, and that's actually when we can see them down a microscope.

Those chromosomes then line up and the cell divides, and then we end up with cells that look identical to that very original cell at the start there.

So two identical cells.

So if that's the specialised cell that we start with with our original cell, then the cells that we make, the daughter cells, are going to be exactly the same as that original cell.

So unspecialized cells are those that have no specific function, and therefore have not developed particular structures or processes that make them specialised for any job or function.

So unspecialized cells have the capability to turn into lots of different types of cells in a process we call differentiation.

Now, the way I remember this is it's making it different.

So different and so differentiation.

So here we go, we've got an unspecialized animal cell here, and then it can undergo differentiation.

And these are two different types of cells it might form.

So if it was in the part of the body that stores fat, fat cells, and if it was in the muscle, it would form muscle cells.

So time for a quick check.

Select two ways in which specialised cells can be formed.

So choose from that list of four.

So pause while you decide and then we will check back.

Okay, let's see if we've got that right then.

So we can form them through differentiation, which is from a unspecialized cell differentiating into a specialised cell or through mitosis where a specialised cell that's already there might divide and make a genetically identical copy of itself, and therefore that's mitosis.

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

So different tissues are made up of the same type of specialised cell.

So for example, epithelial cells.

So those are the ones on the surface of our skin, can make up the tissue in animals that forms the top layer of skin.

So these are animal cells here.

These are actually cheek cells, this example here.

So from inside your mouth.

And then we've got palisade cells.

So they're the ones that make up part of the leaf.

So they've got lots of chloroplasts in them.

So they'll be in the leaf in order to trap the sunlight.

And then we've got, here we've got hyphae cells.

So they make up the fungi.

So they form strands so that the fungi can spread and you can see those very, very long, thin cells.

So all of these images are taken down a optical microscope, a light microscope.

So a group of different tissues that work together to perform a particular job is called an organ.

You might recall learning about this before.

So for example, we've got a stomach.

So its main job is mechanical and chemical digestion.

But if we look at it closely, it's made up of different tissues.

So we've got the epithelial tissue again, which is the lining tissue, and that gives a protective barrier 'cause there's lots of acid inside that stomach.

So we need to protect the cells underneath from that.

Then we've got muscle tissue.

So that's what contracts, so that's the thing that churns up your food when your stomach is contracting and moving, relaxing, churning up that food.

And then we've got nerve tissue.

So that's gonna receive electrical signals from the brain and that's gonna control digestion.

There are other layers of tissue in the stomach, but those are three of the main ones.

So let's look at an example from a plant.

So an organ from a plant for example, is a leaf and its job is to carry out photosynthesis.

But if we look really closely at that leaf, we can see it's made up of tissues.

And here's a cross section of that.

So we've got that waxy tissue layer that's on the surface.

It protects the leaf, possibly from parasites, but also it's waterproof.

The palisade tissue layer underneath, that's all with lots of cells in that are this, they're sort of turned on their side.

So they're sort of long and thin, and they've got lots of chloroplasts, which means that the light has to pass through lots of chloroplasts on way through the leaf.

And then finally we've got the epidermis there at the bottom and it's got these guard cells in it which control the gases that move in and out.

So carbon dioxide moving in for photosynthesis, but also water vapour leaving the plant as well, which fuels the movement of water through the plant.

Okay, so let's move on now.

So in a multicellular organism, these organs all have different functions and the organs work together within an organ system.

So again, for example, hopefully one you've come across before, we've got the digestive system and these are the different organs of the digestive system that are working together.

So we've got the oesophagus, the stomach, the small intestine, and the large intestine.

We've also got other organs that are involved there like the liver and the pancreas.

So the organs of the digestive system work together to digest and absorb nutrients from food into the blood.

So in summary, large multicellular organisms are organised as follows: We start with the specialised cell, then through mitosis that cell is going to divide to give us a tissue, and then we move on to an organ and then onto an organ system.

And then finally a whole organism.

Now that's also true of other organisms as well.

We've just used a plant as an example here.

So let's do a check.

So starting with the smallest, put these structures of multicellular organisms in the correct order.

So remember we're starting with the smallest.

So pause while you decide and then we'll come back and we'll see how you've got on.

Okay, let's see if you've got this right then.

So the smallest one is a specialised cell, then we move into tissue, then we move into organ, and then finally into organ system.

And then once we put all the systems together, we could go to a whole organism.

So if you got those right, then well done.

Let's move on to a practise task now.

So Izzy and Aisha are discussing the role of mitosis and differentiation, and Izzy says "Mitosis is making new cells." And Aisha says "Differentiation is making different cells." Now they both have a correct understanding, which is good.

So explain in detail the role of both mitosis and differentiation in making tissues and organs.

So I want you to add more detail to what they're saying.

So if somebody was saying to you, mitosis is making new cells, what does that mean? That's what I would like you to write in your explanation.

Okay, so pause while you do this extended writing and then we'll come back and we'll give you some feedback.

So let's see how we got on with explaining these then.

So first of all, mitosis is the process of making identical copies of specialised cells to form a tissue that then carries out a particular function.

And the tissue will work with other different tissues as part of an organ.

But differentiation is the process of making specialised cells from an unspecialized cells.

These cells will develop the structures and processes that help them to carry out their functions.

So if you wrote something like that with words to those effect, then well done.

And let's move on to the next part of our lesson.

And the next part of our lesson today is differentiation and genes.

So we're gonna be looking at how is it that that unspecialized cell suddenly becomes a specialised cell? So during sexual reproduction in humans, fertilisation produces a single cell, a zygote, and this cell is unspecialized.

So you might remember this from previous units of work when you've done reproduction.

So we have the sperm and the egg come together and when they come together we form the zygote.

And the zygote is unspecialized so it can become any type of cell.

The zygote will then undergo mitosis, which forms an embryo.

And now all of the cells are copies of that original zygote 'cause it's got that full set of chromosomes where it's got half from the sperm and half from the egg.

But all of those original cells of that embryo are also unspecialized.

They don't have a particular function.

The zygote, after it undergoes mitosis to form the embryo, it will then undergo differentiation.

So when we get to a certain stage past the eight cell stage, then that embryo, those cells of that embryo are then gonna start to become specialised.

And here's some examples of the specialised cells it might form.

So for example, a neuron which is a nerve cell, a fat cell, a muscle cell or an epithelial cell.

There's lots of different cells.

These are just some examples of different cells with different shapes and structures.

Now how does it do that? So a little bit of a reminder about DNA and genes now.

So genes are short sections of DNA, that code for proteins, but not all proteins are needed by all cells.

So a specialised cell will only make the proteins that it needs to survive and to carry out its function.

So here we go.

We've got an example of DNA here, you might remember this, it's a bit of model of the genome and the genome is made up of genes and non-coding DNA.

The genes are a code for proteins and those proteins are what give the phenotype of the organism.

So an example here, the genes here are making proteins.

Now not all cells will make all of the proteins that are coded for in genes and that's what will make them different from one another.

So if a protein is not needed by a cell, then the gene, the codes for it will be turned off.

Therefore, different specialised cells can produce different proteins.

So even though that that gene is still there, there'll be chemical signals that ensure that that gene is turned off in a particular specialised cell.

So it'll only make the proteins that it needs to carry out its specific function.

So which genes are turned on and which genes are turned off in each specialised cell controls, what structures it has, what shape it has and what processes it carries out.

So that allows lots and lots of different tissues and organs to form and that aids the survival of a multicellular organism.

So again, a reminder here, we've got our multicellular organisms that are made up of these different cells and in each of these different cells they will have different genes that are turned off and on, and that's what makes them different from each other.

So time for a quick check.

What are the missing words here? Now there's two missing words in this sentence.

So something can be turned off and on to control what? So pause while you decide.

Okay, so the correct answer is genes can be turned off and on to control differentiation.

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

So time for a quick practise task now then.

So pupils are discussing the differentiation of cells.

We've got lots of different comments here to read through.

So Lucas says, "All cells can make all proteins as they have the same genes." And Alex says, "All cells begin life as specialised cells depending on their function." And Sam says, "Mitosis is the process of differentiating cells." And Sofia says, "Specialised cells form organs with a specific function." Now in all of these examples, the pupils have some incorrect ideas.

So what I would like you to do is take each statement and correct it for me, please.

And then once you've corrected it, can you put them in an order that forms a description of differentiation and its purpose.

So take some time to decide how you would correct them first and then put them in an order and write it out.

Okay, so pause the video while you do that, and then when you come back, we'll give you some feedback.

Okay, then let's look at how you got on.

So we're correcting these pupil's statements.

So the first one, Alex, "All cells begin life as specialised cells." We need to correct that to "All cells begin life as unspecialized cells." And then for Sam, we need to correct that one to, "Mitosis is the process of making copies of the same cell." And then for Lucas, we need to correct his to, "Specialised cells make proteins using the code from the genes that are switched on, this is differentiation." And for Sofia, we need to say that "Specialised cells form tissues with a specific function that then work together to form organisms." And then we've got them in the correct order there, 'cause we've started with our unspecialized cells and then we've got our mitosis making copies, and then we've got specialised cells making proteins depending on which genes are turned on and off.

And then finally we've got those specialised cells working together to form tissues and organs.

So if you got that correct, then well done.

And that brings us to the end of today's lesson.

So here is our summary.

So plant and animals and fungi can be multicellular and most of their cells are specialised.

They have structures and processes that are adapted for their functions.

Multicellular organisms grow, make new cells by mitosis and develop by making specialised cells to form tissues and then organs.

Unspecialized cells become specialised through a process called differentiation.

And during differentiation, particular genes in the cell's genome are switched off or on.

And specialised cells only use particular genes, so only make the proteins needed for the function that they are actually adapted to do.

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