Lesson video

Welcome to this lesson from the Unit: Cells.

The lesson title is Multicellular and Unicellular Organisms. This lesson follows directly on from the plant cells and animal cells lessons, and it's about how those cells can live by themselves or they can work together as part of a multicellular organism.

My name's Mrs. Barnard, and I'm going to be taking you through your learning today.

And by the end of today's lesson you should be able to explain the differences between multicellular and unicellular organisms. Now, as with all science lessons, there's gonna be some key words to look out for.

It's really important that we have an agreed definition of these words, even though you may have heard or used some of them before.

And the words to look out for today are unicellular, multicellular, tissue, organ, and adaptation.

So let's have a look at how we're gonna define these.

So uni meaning one, a unicellular organism is a living thing that is just one cell.

A multicellular organism are made of lots of different types of cells.

I'm sure you can think of lots of words that have multi in, like multi-pack at the supermarket, or a multi-story car park.

So multi means many.

A tissue, so that's a group of similar cells in the same place with the same job.

And then we move on to an organ, which is made up of a group of different tissues, so that's the key word above there, that work together to carry out a specific job.

So we've got tissues that are a group of cells, and then we've got organs that are a group of tissues.

And finally we have an adaptation.

So that's a feature that helps an organism to survive and function.

So our lesson today is in three sections.

Section one is unicellular and multicellular organisms. So that's the first two keywords that we were just looking at.

Following that, in the second section, we're gonna look at multicellular organisms. So that's how those larger organisms can arrange their cells into tissues and into organs.

And finally, our fifth keyword is gonna be in section three of our lesson, which is adaptations.

And it's how unicellular organisms are adapted for their surroundings.

First of all, we're gonna look at the difference between unicellular and multicellular organisms. Now, some organisms live as single cells.

Now you've covered cells in some of your previous lessons, so the structure of plant cells and animal cells.

But also you'll have heard of bacteria cells and fungi cells.

So all bacteria live as single cells, but so do some fungi, some animals and some plants.

And when they live as single cells, we call them unicellular organisms. The reason we can call them organisms, even though they're only made up of one cell, is because they survive by carrying out the common processes of living organisms. Now if you remember, those were those processes that you learned in the very first lesson of this unit, movement and reproduction and sensitivity and growth and respiration, excretion and nutrition.

It's difficult to visualise single cells as organisms because they're so small.

But you can see on this picture some bacteria that are grown on a plate and they grow in these tiny little groups together.

But each one of them is a single organism.

And when you zoom in with a very powerful microscope, you can magnify those small little groups of bacteria.

And this is what you can see.

You can see those individual cells and they are by themselves organisms because they can live by themselves because they carry out all of the processes of living organisms. So let's have a quick check.

Now, is this statement true or false? A bacterium is a unicellular living organism.

True or false? It's true.

If you got that right, well done.

So now we need to be able to explain why the answer is true.

So take your pick from the two choices below.

Is it, it is a single cell that carries out all of the common processes of living organisms? Or is it, it is made up of many cells that when joined together carry out all of the common processes of living organisms? Which explanation do you think it is? It's A.

It's true because it's a single cell that carries out all of the common processes of living organisms. So if you've got that right, well done.

Okay, let's move on.

So some organisms are made of more than one cell, and we call these multicellular organisms. Remember again, multi meaning many.

Here is an example of a plant tissue.

So this is where you've got cells together in a multicellular organism.

Now you can see that through a microscope, it's not just made of a few cells, it's made of millions of cells.

And that's how we manage to make really large organisms. 'Cause multicellular organisms are usually much larger than unicellular organisms and large multicellular organisms are made up of millions of cells.

So this picture here is just a little example of how cells working together can make part of a multicellular organism.

So let's look at this in a little bit more detail.

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

Now here are two.

We've got an animal here, a leopard, and we've got a plant.

Now, animals, as you've learned in previous lessons, are made of animal cells and plants are made of plant cells, but they are both multicellular.

Different types of cells are found in different parts of the organism.

So even though these organisms are multicellular, the cells that make them up all have their own jobs.

So if we take this leopard for example, it's skin is made of cells.

So you've got animal cells that are specifically skin cells, and then you've got blood cells.

Now these are just two examples.

There's lots of different types of cells within animals and all multicellular organisms, these are two examples for you, skin cells and blood cells.

So let's look at a plant, now.

A plant has leaf cells.

So you can see those ones there.

You might remember those from a previous lesson.

They've got lots of chloroplast in them for trapping sunlight.

And then we've got root cells.

And those root cells don't have any chloroplast in them.

They're quite different from each other.

So all the cells have different jobs, but together they make up multicellular organisms. So let's have a little check.

So a multicellular organism is made up of lots of the same type of cell.

Now, do you think that's true or false? And I want you to justify your answer with one of the explanations below.

Is it A, it's made up of lots of the same cell working together or is it made of lots of different cells that have different jobs? What do you think? Okay, it's false.

A multicellular organism is not made up of lots of the same type of cell.

And the reason for this is because it's made of a lots of different cells that have different jobs.

Okay, it's time to have a practise of what you've learned so far.

So we've got two friends, Sam and Laura, and they're talking about what they think a human is.

And Sam says, "I think a human is unicellular because we're made of cells that are united together." And Laura says, "Humans are multicellular because we're made of hundreds of cells." Now, Sam and Laura are actually both wrong.

So what I'd like you to do is explain the correct ideas.

Now, you probably want to pause the video at this point to give yourself a little bit of time to write some sentences, but come back when you are ready.

So how did you do with that? Hopefully you got some answers there and you worked out where they were both wrong.

So let's have a look.

So Sam was wrong because unicellular doesn't mean united.

The uni means single, single cell and humans are actually multicellular.

And what's about Laura? Why was Laura wrong? Laura was wrong because she said humans are made of hundreds of cells when in fact they are made of millions of cells.

Hope you found those two mistakes and now it's time to move on.

It's time to move on to the next section of our lesson, which is multicellular organisation.

In a multicellular organism, a group of cells with the same structure work together to carry out the same job.

This is called a tissue.

And here's an example.

We've got a smooth muscle cell, which is an animal cell like those that you've learned about in a previous lesson.

And when those smooth muscle cells, which have a very particular structure work together, they make smooth muscle tissue.

Now, you might find a tissue like this in an organ such as the small intestines, for example, to help move your food along your tubes.

So here are some examples of tissues.

We've got skin cells.

So these are the cells that make up the tissue in animals that form the top layer of your skin.

So that includes the skin on the outside of your body and the skin that lines things on the inside of your body, like inside of your mouth, for example.

Here is a tissue from plants.

So those cells make up a tissue in a plant leaf that traps sunlight.

Now again, you've come across these cells before in the previous lesson on plant cells where you looked at the structures of the chloroplasts that were inside those cells.

And finally here we've got some fungi cells.

You see, they're very, very long and thin, and those cells make up a tissue in a fungi that form strands so the fungi can spread.

It's how they reproduce.

Okay, it's time for a quick keyword check.

So I'd like you to complete this sentence.

So a something is a group of similar cells in the same place with the same job.

What is the missing word? And the word is tissue.

A tissue is a group of similar cells in the same place with the same job.

Well done if you got that right.

So what happens if we get lots of tissues together? So a group of different tissues that work together to perform a particular job are called an organ.

How many organs can you name? I bet you came up with quite a lot.

These will be organs that you talk about in everyday life and maybe some that you've learned in science before.

Did you come up with any of these examples? The heart, the lungs, the stomach.

All of these are examples of organs.

And when we think of that example of tissue that we looked at earlier with the smooth muscle cells, that smooth muscle tissue, you would also find in the lungs and the stomach along with lots of other different types of tissues that have different jobs.

So let's have a look at this example from the animal.

Let's have a look at the stomach.

So the stomach, its job is to digest food.

So the organ is the stomach and its job is to digest food, but it's made of tissues that all have a different role in this job.

There they are, divided up.

And we've got one layer here, which is the lining tissue.

So that's the bit on the inside and that releases the chemicals that help to break down food.

And we've got the next layer down, which is that smooth muscle.

So it's muscle tissue, and it squeezes and it churns up the food and helps to break it down into smaller particles.

Sometimes you can feel your stomach doing that when you're really hungry and your stomach starts to rumble.

And finally we've got nerve tissue.

So nerve tissue, that's how the information gets from your brain to the stomach and back again.

So that tissue is really important in communication.

So you can see you've got three different tissues here that all have the same job overall, which is to digest food, but within that they play their own role.

Let's have a look at plants now.

So in a plant, a leaf is an organ.

Now you might not have known that a leaf was an organ, but it is and its job is to absorb light.

So let's have a look at what the tissues inside the leaf are.

Now I know a leaf looks really thin, but it is actually made of layers of tissues and you can see the cells there that it's made up of.

You see it down a microscope.

And the tissue's here.

So we've got this top layer here, which is a waxy tissue, and that stops bacteria and other microorganisms getting into the leaf and causing it harm.

It also makes the leaf waterproof.

Now the next layer down here, so this has got a tricky word, the palisade tissue, but palisade is a word that you'll come across in future units.

So don't worry about it too much at the moment, but it's that layer of cells, the tissue that traps sunlight to be used to make food.

So you saw some of those cells in a previous lesson.

And finally we've got this epidermis tissue.

Again, another word here, you may not have come across before, but it appears in future units, but it's the layer on the bottom of the leaf and that allows gases to move in and out of the leaf.

So carbon dioxide to move in and oxygen and water to move out.

So it's a gas exchange surface.

So different organs have different jobs.

They also work together in organ systems. Here's an example of an organ system that you will be quite familiar with.

So you've got this long tube that goes from your mouth all the way to your stomach called the oesophagus, and food passes down this tube into the stomach and it's moved along by muscles.

And then in the stomach we've already discussed, it's got all of those layers of tissues with inside that organ, which allows it to digest food.

And then that food moves from the stomach into the small intestine in order for the food, those very small food particles to be absorbed into the blood.

And anything that isn't then absorbed into the blood moves then into the large intestine where water is absorbed.

So you can see each of those four organs have a different function that then works together to form the digestive system.

So the organs of the digestive system work together to break down food into tiny particles that can be absorbed into the blood.

So let's take a look at a plant systems now.

So plants actually have two organ systems. They have the shoot system and they have the root system, and you can see those on that picture there.

So the shoot system involves organs that are to do with reproduction and also organs that are to do with absorbing light in order to make food.

So you can see there's different organs there and they make up a system.

So in summary, large multicellular organisms are organised as follows: So we start with a cell, a single cell, and then a group of those cells with a similar structure working together is called a tissue.

And if we get different tissues together, they all have a role in helping the organ to carry out its specific job.

Then lots of organs together form an organ system.

And finally, those systems come together to form a large multicellular organism.

So let's have a quick check now.

So starting with the smallest, put these structures in order of size.

So you can pause the video now while you do that.

Okay, how did you find that? So the smallest should be a cell, so we could give that number one.

And then the next one would be tissue, so we'd give that number two.

And the next one would be organ.

And then finally organ system.

So well done if got that right.

So let's move on.

We're going to practise your understanding now.

If you cut through a blood vessel from the circulatory system, this is what it would look like.

Got some labels here for you.

So we've got an outer layer here that's made of elastic and it allows the blood vessels to stretch and spring back as the blood flows.

Then we've got a lining layer of cells here, and that's smooth so the blood can flow easily.

And we've got some muscle cells that control the size of the blood vessel.

So, Andeep here, he thinks that this blood vessel could be called an organ.

So using your knowledge of cells, tissues, and organs, can you explain why this blood vessel could be called an organ? It'll take you a few minutes to write some sentences, so pause the video.

Okay, here we go.

Let's see what you got.

So explain why this blood vessel could be called an organ.

So it could be called an organ because it's got more than one type of tissue.

And those tissues all have different jobs or roles.

And the tissues work together to carry out a particular function, in this case, it's transporting blood.

So if you've got any of those right, it shows that you have a really good understanding of the definition of an organ.

So well done.

We now move on to the third section of our lesson, which is adaptations of unicellular organisms. So there are many different types of unicellular organisms. Remember unicellular means single cell, but it doesn't tell you what type of cell that it is.

So examples of these cells include an amoeba, and that lives in water.

A yeast, and a yeast is a type of fungus.

And finally a bacteria.

Now bacteria are found in all natural environments including inside animals, which includes you.

So all unicellular organisms are made of just one cell like you can see in these three images below.

But they do have some structures in common.

Now, you all have heard about these in previous lessons that you've done on cells.

So first of all, we've got the cell membrane.

So remember, the role of the cell membrane is to control what enters and leaves the cell, and they've all got cytoplasm.

That's where all the main chemical reactions of the cells take place.

So they absorb all the nutrients that they need through their cell membrane, and then they use it in the chemical reactions within their cytoplasm.

So there are some similarities and there are some differences between different unicellular organisms. So all unicellular organisms have DNA because DNA has the instructions which helps to control the cell, but bacteria don't store it in a nucleus.

You'll remember from the animal and plant cells lesson, that there is a nucleus in those cells and it stores the DNA.

So in these two, you can see that DNA is stored in the nucleus in the amoeba and in the yeast.

But in the bacteria, it's a loop of DNA that floats within the cytoplasm.

So some unicellular organisms have different shapes and structures, and these are the adaptations that help them to stay alive.

So adaptations are differences between the cells that allows them to survive in their surroundings.

So some of them have a cell wall and that protects them and it also helps to give them structure.

And amoeba doesn't have a cell wall, it's a bit more similar to an animal cell.

It's just got a cell membrane around the outside, but this allows it to be flexible.

It allows it to change shape, to take in nutrients, and also to move.

Some unicellular organisms have extra structures on their surface that help them to move around.

For example, you can see in the bacteria, it's got a tail like structure on the back there, and that's called a flagella.

Time for a quick check.

So we've got a true or a false question, and the statement is, unicellular organisms all have the same cells structures.

So is that true or false? And then if you can choose an explanation below to justify your answer.

Is it because they're all living cells and must all have the same structures? Or is it they're all living cells but have different structures to survive in their surroundings? Pause the video.

So how did you get on? Let's have a look.

So unicellular organisms all have the same cell structures.

This is false.

And the reason for this is because they are all living cells, but they have different structures to survive in their surroundings, that's adaptations.

So let's have a go at some practise.

You've got three images here, and for each one, I would like you to decide whether it is unicellular or multicellular.

Does it belong to a unicellular or a multicellular organism? And once you've decided that, then I'd like you to explain your answers using the features that you can see in the images.

So you need to write a few sentences so you can pause the video.

Okay, let's see how you got on.

So for each one, we decided whether it was unicellular or multicellular.

So for the first one, example, A was a unicellular organism, and you could tell because it was a single cell and it had hairs around it to help it move, those were special adaptations.

And example B is from a multicellular organism because it's got more than one cell, and each of those cells look different from each other.

And the answer is the same for example C, it's also a multicellular organism as it has more than one cell and the cells look different from one another.

If we knew more about those images, we might be able to write more, but it was only based on what you could see.

So let's move on to another task.

So Jacob talks about this bacterial cell, and you can see there's an image of a bacteria cell there.

And he says, "This is not a living organism, it's just one cell and it doesn't have a nucleus." Now Jacob is incorrect.

So what I would like you to do is to write a detailed explanation to help Jacob understand why this bacteria cell is a living organism.

You need to include the structures that it has.

Remember, those are the adaptations that it has to help it to survive.

Okay, time to pause the video again.

Okay, let's see how we got on.

So did you manage to write a few sentences? It'd be good to have a longer answer for this particular task.

So it is a living unicellular organism.

It's adapted to survive as a single cell.

So just because it's one cell doesn't mean it's not an organism.

It has DNA, but it's not stored in a nucleus, but it still does have DNA, which are the instructions.

It has structures on its surface to help it move.

Now what's it going to move to do? Perhaps to find some food or to find an environment where the conditions are slightly better for it.

And it has a cell wall to help protect it and to support it.

So if you've got any of those answers there, you've got a clear understanding of what a unicellular organism is and how it adapts to survive in its surroundings.

Now we come to our summary.

Unicellular organisms are made of a single living cell.

Multicellular organisms are made of more than one cell, sometimes millions, as the is the case with with humans, and different cells take on different jobs.

In multicellular organisms, cells join together to form tissues with specific jobs.

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

And a group of organs that work together are called an organ system.

Unicellular organisms have different structures that have adaptations to help them function and stay alive.

Well done.

We've now come to the end of our lesson and we have completed our work on multicellular and unicellular organisms..