Lesson video

Hi, I'm Mrs. Hudson.

And today I'm going to be teaching you a lesson called, "Growth in Multicellular Organisms." This is a biology lesson in science, and it comes under the unit titled "Cell Division, Mitosis and Meiosis." The outcome of today's lesson is, I can describe the role of cell division in the growth of multicellular organisms. So we're going to be asking ourselves, "What are multicellular organisms? And how is cell division involved in the growth of them?" In today's lesson, there will be some key words.

And they are growth, unicellular, multicellular and cell division.

So let's have a look at what those words mean.

Multicellular organisms grow by increasing the number of cells they have.

This involves cell division.

Unicellular is an organism that consists of only one cell.

Multicellular is an organism that is made up of many cells.

And cell division is the process by which cells replicate to produce two genetically identical cells.

If you want to pause the video to make a note of those key words, then feel free to, and then press play, ready for me to carry on with the rest of the lesson.

Today's lesson on growth in multicellular organisms is going to be split up into two different parts.

In the first part of the lesson, we'll be looking at cell structure in multicellular organisms. And then we're going to move on, in the second part of the lesson, to describing cell growth in multicellular organisms. Let's get going now, with the first part of the lesson.

Organisms can be multicellular or unicellular.

Now, we did look at those words in the keyword section at the beginning of this lesson, but you might be familiar with them.

Let's have a look at what they mean now.

Many animals and plants are multicellular.

So if we look at the word "multicellular", and break it down, "multi" means many, and "cellular" means made of cells.

So therefore the definition of multicellular is made up of many cells.

Humans are multicellular organisms. Microorganisms such as bacteria, are unicellular.

So if we have a look at the word unicellular, uni means one.

If you think of a unicycle here, a unicycle only has one wheel.

So uni is one, cellular means made of cells again, so therefore unicellular means made up of one cell.

So bacteria are only made up of one cell.

There are other types of microorganisms like yeast.

They also are just made up of one cell.

I just said that humans were multicellular.

But actually, many plants and animals are multicellular.

They are made up of many cells, organised to form tissues, organs, and organ systems. So let's have a look at what that means.

So if we start off with a cell, a cell is the smallest unit of living life, and then lots of the same type of cell form together to make a tissue.

And then lots of different tissues all work together and they form an organ, and then lots of organs work together to form an organ system.

And then all those different organ systems work together to form the whole organism.

So an example of this could be some, if we go back to the cells, heart cells all work together to form some heart tissue, and then there's different tissues in the heart work together to form the heart itself, which is the organ.

And then the heart works together with other organs to make organ systems. So in that case, it could be the circulatory system.

But then there are lots of different organ systems in the body like the digestive system, the immune system, the reproductive system.

There are more, but all of those work together to form the whole organism.

It's not just animals that are multicellular, though.

Many plants are also multicellular.

And these are some examples of different cells making tissues in plants.

So here we've got an image of a plant, and it's made up of lots of different cells.

So in the leaf of the plant, there are lots of different cells working together to form the leaf, which is actually an organ in the plant.

And we can see there, there's an image of a cross-section of a leaf, containing palisade cells and guard cells.

There were other types of cells in there as well, but they're just two specific examples you might have heard of.

So in the leaf, we've got cells that work together, to form tissues of the leaf and then make the organ, which is the leaf itself.

Then you've got the stem.

Now the vascular bundle is found in the stem, and it contains the xylem and the phloem cells, and they're very important in transporting substances up and down that plant.

And then finally in the root, you've got the root system, which contains root hair cells, but also lots of other different types of cells too.

So we can see here that plants are also multicellular because they contain lots of different cells.

Let's just look at an example again.

So we said many animals and plants are multicellular.

They're made up of many cells.

And there's an image there of a zebra, and that is a multicellular animal that contains lots of different cells.

It will also have tissues, organs, organ system, and they all work together to make that zebra, which is the overall organism.

A non example of a multicellular organism is a microorganism, such as bacteria, and they are unicellular.

They are made up of only one cell.

So in that image there, we can see a unicellular bacterium.

It's just one cell.

The whole organism is that one cell, and therefore it is unicellular.

Let's see how much of that we have understood so far.

So a few questions for you to have a go at.

The first question.

"What is the best description of a multicellular organism?" A, made up of many cells.

B, made of only one cell.

Or C, an organism with only one function.

This is A, a multicellular organism is made up of many cells.

Great job if you got that right.

Let's look at the next true or false question now.

"Bacteria are multicellular organisms. True or false? And then justify your answer." A, bacteria are made up of many different cells.

Or B, bacteria are made up of only one cell.

Bacteria are unicellular organisms, so this is false.

They are not multicellular.

And to justify your answer, you should have written B, bacteria are made up of only one cell.

Brilliant job if you got those right.

We know the definitions now of multicellular and unicellular.

Let's have a look at some animal and plant cells, which would be multicellular organisms. The animal and plant cells share some common features called sub-cellular structures.

And we can see here we've got a model animal cell, and a model plant cell image.

So let's have a look at the common sub-cellular structures that the animal and plant cells share.

So first of all, we've got the nucleus.

Then you've got the cytoplasm, which looks like empty space, but actually it's a jelly-like substance that surrounds all of the other sub-cellular structures.

Got the smallest sub-cellular structure, which is the ribosomes.

And then the cell membrane and the animal cell is the outermost layer, whereas in the plant cell, it's the second layer in.

And then finally we've got the mitochondria, which is very important, is where aerobic respiration takes place.

Now there are three sub-cellular structures that animal cells don't have, but plant cells do have.

So again, to have a look at those now.

The first one is the chloroplast.

Chloroplasts are where photosynthesis takes place.

Now, plants photosynthesize to make glucose, but animals do not need to photosynthesize, which is why their cells don't have chloroplasts.

Then you've got the permanent vacuole.

The permanent vacuole stores nutrients and cell sap in the plant.

And then the final structure is the cell wall, which is the outermost layer of that plant cell.

So the three sub-cellular structures that are different, the chloroplast, permanent vacuole, and cell wall.

And the sub-cellular structures that are common are the nucleus, cytoplasm, ribosomes, cell membrane, and mitochondria.

Now today we're gonna be talking in detail about something called DNA.

The genetic material, also known as the DNA, is found inside the nucleus in plant and animal cells.

So again here, we can see our animal and plant cell model.

And just a reminder, could you label the nucleus on these two cells? Hopefully you pointed to this structure here.

So we've got the nucleus, which contains the DNA.

The nucleus controls the activities of the cell.

Most animal and plant cells need a nucleus in order for that cell to function.

Now, there are other organisms, which we call prokaryotic cells, like bacteria, where there is still genetic material, but it's not enclosed within a nucleus.

It's just free floating in the cytoplasm.

But for now, we're just looking at eukaryotic cells, which do contain a nucleus.

Let's see if we can remember what we've just said.

So which sub-cellular structure is the line pointing towards here? A, the mitochondria.

B, the nucleus.

Or C, the ribosomes? Hopefully we can remember this.

We've just covered it.

This is B, the nucleus.

And the next question.

"Which sub-cellular structure is the line pointing towards here?" A, the mitochondria, B, the cytoplasm, or C, the ribosome? This is A, the mitochondria.

And remember, aerobic respiration happens inside the mitochondria.

And then the next question.

"What is the function of the nucleus?" A, controls what enters and exits the cell.

B, contains nutrients and cell sap.

Or C, contains DNA and controls cell activities.

This is C, contains DNA and controls the cell activities.

A, controls what enters and exits the cell, that is the function of the cell membrane.

And B, contains nutrients and cell sap, that is the function of the vacuole in the plant cell.

Well done if you managed to get those right.

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

So the first part of task A, number one, is to identify each organism as multicellular or unicellular.

And there's a rose bush, human and bacterium.

So you just need to write in there, multicellular or unicellular.

And then number two, describe the difference between a multicellular and a unicellular organism.

Now think here what the definitions are.

That will help you.

And then finally, part three, complete the missing label on the plant and animal cell, and describe the function of this sub-cellular structure.

So in between the lines, you need to write what that sub-cellular structure is that the lines are pointing towards.

And then above it, can you write down what the function of that sub-cellular structure is? As much information as possible.

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

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

Let's see how we did then.

So first of all, question one.

We've got the table.

A rose bush, that is multicellular.

It's made up of lots of different cells.

Remember the slide where we had the picture of the plant, and we pointed towards three different organs? The leaf, the stem, and the root.

There are lots of different cells that make up the tissues within those organs, so they're multicellular.

A human, again, is multicellular.

And bacterium is a unicellular organism.

So well done if you've got those right.

Question two, a little bit harder, this one.

Describe the difference between a multicellular and unicellular organism.

Now you might not have exactly the same word-for-word answer as what I'm about to put up, but maybe pause the video and just check that you've got all the information within this answer in your answer.

The multicellular organisms are made up of many cells, whereas unicellular organisms are made up of only one cell.

Fantastic job if you managed to get that right.

Let's have a look at question three now.

So that missing label, first of all, is the nucleus.

And then the function of that nucleus is that the nucleus contains the genetic material, which we said was also known as DNA, and it controls the activities of the cell.

And then you might have also written, most animal and plant cells need a nucleus in order to function correctly.

Brilliant job if you managed to answer all of those questions and get everything right.

If you need to pause the video to add anything into your answers, then please do, and then press play, ready to carry on with the rest of the lesson.

Great start to this lesson.

We've done the first learning point, which was the cell structure and multicellular organisms. And now we're going to move on to describing cell growth in multicellular organisms. So let's get going.

Multicellular organisms need to grow as part of their lifecycle.

So what we can see below are two images.

First of all, we've got an image which is roughly representing the growth of a human.

So you start with a baby, and then we'll grow into a toddler, and then a young person, a teenager, and then eventually, an adult.

So that person is going through a phase of growth.

And then you can also see on the right hand side, we've got an image which is representing the growth of a plant seed.

And we can see that that seedling has grown roots coming outta the bottom, but also the stem and the leaves have also started to grow too.

Growth occurs due to the number of cells in that organism increasing.

And this involves cell division.

So really important concept is the idea that as part of a life cycle, multicellular organisms will grow, and that growth is due to the number of cells increasing.

And the way that the number of cells increase is through a process called cell division.

Multicellular organisms also need to repair damaged tissue as part of their lifecycle.

In order to repair damaged tissue, new cells need to be generated, and this occurs by cell division.

So we can see here an image of an X-ray of a broken arm.

So that bone has broken.

And for that bone to heal, there will need to be some repair and regeneration of new cells in order to heal that bone.

Another example could be, if you fall over and break your skin, and there's a scab there, the development of that scab, and the process of the skin healing involves new tissues and new cells being made.

And this all happens by the process of cell division.

It's not just those two examples.

There are lots of examples in lots of multicellular organisms, where damaged tissues and cells need to be replaced.

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

So an example, multicellular organisms usually undergo cell division for two purposes.

We've spoken about those.

They are growth and repair of damaged tissue.

A non-example though would be, unicellular organisms undergo cell division to reproduce.

So here there's an image of a bacterium, and cell division in that unicellular organism is not used for growth and repair, it's used for them to reproduce.

Let's check our understanding of that.

So first question.

"What is the purpose of cell division in multicellular organisms?" A, growth and reproduction.

B, growth and repair.

Or C, reproduction and repair? Now, there's a few words here that have been put into throw you off, but hopefully you got B, growth and repair.

Next question.

"How does growth occur in multicellular organisms?" A, the number of cells decreases.

B, the number of cells increases.

Or C, the size of the cells increases.

So hopefully here, we went with B.

We said that growth occurs in multicellular organisms because the number of cells increases.

Great job if you remember that.

Okay, so let's move on to the next part of the lesson.

In multicellular organisms, most cells are produced from other cells by the process of cell division.

Cell division occurs when one cell divides to produce two genetically identical cells.

So if a multicellular organism is growing, or it's wanting to create new cells for repair, then the cell will have to divide.

And that process of cell division is when you get one cell, and it divides to produce two genetically identical cells.

By genetically identical, we mean that they contain the same DNA as the original cell.

So here, we have an animal cell, what will happen is that cell will divide to produce two genetically identical cells.

And the nucleus in the original animal cell will contain exactly the same DNA as the two cells that are produced through cell division.

During cell division, the genetic material, the DNA, must be copied before the cell can divide into two genetically identical cells.

So we just said that the nucleus of each cell that's produced has exactly the same DNA as the original cell.

Now for this to happen, the original cell must copy its DNA to begin with so that each resulting cell has the same amount of DNA.

So here we can see a diagram which is representing cell division, and you've got the genetic material, the DNA, held inside that original cell.

Then that genetic material is copied, and you can see that the second cell has got twice the amount of DNA.

And then what happens is that that copied DNA will split up equally, and be pulled to either end of the cell, and the cell splits into two genetically identical cells.

Many types of cell are undergoing almost continuous renewal in multicellular organisms. So I gave you two examples earlier of breaking a bone, or if you fell over and broke the barrier of your skin, and had a graze, then you would need new cells to be produced.

But actually, inside of our body, all the time without us knowing, there's almost continuous renewal of cells.

And that's because remember, our cells form tissues, which then form organs, and organs work together in the organ systems. So we need to make sure that all of the organ systems are working correctly, in order for the organism to be able to survive.

And this is a highly regulated process in order to keep all the different tissues of the body working together correctly.

So I don't want you to think that there's only two uses of cells being replaced.

This is a constant process that's happening all the time to keep us alive.

Let's check our understanding with a true or false question.

"During cell division, the genetic material is halved.

True or false? And then justify your answer." A, genetic material is replicated to create two genetically identical cells.

Or B, genetic material is halved to create two cells with half the DNA.

This is false.

During cell division, the genetic material is not halved.

And the justification is A, genetic material is replicated to create two genetically identical cells.

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

So the first part of task B is that cell division is usually used for two purposes in multicellular organisms. What are they? And then the second question, "How does growth in a multicellular organism occur?" And then question three, "Laura is talking about cell division.

Identify what Laura has said that is correct and incorrect.

Correct the incorrect statements." And Laura has said, "Multicellular organisms usually use cell division to reproduce and grow.

Unicellular organisms use cell division for repair." And then the final part, four.

"Annotate the diagram to show how cell division occurs in multicellular organisms." I'm sure you're gonna do a really great job of this.

Give it your absolute best go, press pause, and then play when you're ready for me to feedback the answers.

Let's see how we did.

So in the first question, what were the two purposes of cell division in multicellular organisms? Cell division in multicellular organisms is usually used for growth and repair.

The second question, "How does growth in a multicellular organism occur?" Multicellular organisms grow by increasing the number of cells within the organism.

The number of cells increases because of cell division.

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

Question three, what have Laura said that was correct and incorrect, and then correct the incorrect statements.

So multicellular organisms usually use cell division for growth and repair.

Unicellular organisms use cell division for reproduction, not for repair.

Multicellular organisms only use cell division for reproduction in specialised organs.

And number four, annotate the diagram to show how cell division occurs in multicellular organisms. So we've got the diagram there, and you want to label the genetic material as the DNA.

And then firstly, the genetic material is copied, and then finally the cell splits into two genetically identical cells.

And this whole process is called cell division.

Really fantastic job if you managed to get those right.

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

We're going to summarise everything that we've learned in the lesson next.

So in summary, for our lesson called "Growth in Multicellular Organisms," we said that multicellular organisms are made up of many cells.

Humans, and lots of different animals, and plants are multicellular.

They're made up of lots of different cells working together, which is the next point.

So multicellular organisms rely on lots of different types of cells working together, and then they will form tissues, which then different tissues work together to form organs and different organs form organ systems, which all together form the organism.

Cell division is usually used in multicellular organisms for growth and repair.

And then finally, we said during cell division, the genetic material, the DNA, is replicated, and then the cell splits to form two genetically identical cells.

I hope that you've enjoyed today's lesson.

I've really enjoyed teaching it.

And I look forward to seeing you next time.