Lesson video

Hi, I'm Mrs. Hudson, and today I'm going to be teaching you a lesson called The Size and Scale of Cells: The Basics.

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 describe numbers and sizes of cells using appropriate units.

There will be some key words in today's lesson that are really important, and they are million, billion, micrometre and magnification.

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

So a million if you're going to represent it as a number would be one followed by six zeros, and it is 1,000 thousand.

So if you times a 1,000 by a 1,000, you make a million.

A billion if you represent it as a number is one followed by nine zeros, or it's 1,000 million.

A micrometre is millionth of a metre, or it's one metre divided by 1 million.

So there are a million micrometres in a metre.

And finally, magnification is making small objects appear larger in order to see more detail.

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

In the first part of the lesson, we're going to be looking at units of microscopy, then we're going to move on to comparing sizes, and then finally we're going to have a go at some microscopy calculations.

But let's start off by looking at the units of microscopy.

Most cells are too small to see with the unaided eye.

To observe cells in detail, a microscope is necessary.

We use micrometres and nanometers when measuring cells and subcellular structures.

So here you can see an image of some E.

coli measured in micrometres, and you can actually see on the photograph itself it says one micrometre.

Why might it be better to use nanometers rather than micrometres to measure subcellular structures such as ribosomes? Ribosomes measure usually between 20 to 30 nanometers, and that number is relatively easy for us to work with.

Whereas if we kept using micrometres, we would keep having to say 20,000 or 30,000.

So we use nanometers to make numbers more manageable when we're dealing with very, very small subcellular structures.

Let's have a closer look at some of the units that we work with when we're looking at very small and larger measurements.

So on the left hand side of this table we've got the units.

So we've got metre, and then the symbol which is m, millimetre, the symbol is mm, micrometre, the symbol is that funny looking u and then an m and nanometer which has a symbol nm.

So in relationship to other units, a metre is 1/1,000 of the kilometres.

There are a 1,000 metres in a kilometre.

And how many are there in a metre? Well, there's one metre in a metre.

If we look at millimetres relationship to other units, it's 1/1,000 of a metre.

So there are 1,000 millimetres in a metre, and micrometres relationship to other units, it's 1/1,000 of a millimetre.

So that means there are 1 million micrometres in a metre and nanometer, it's 1/1,000 of a micrometre, which means that there are 1 billion nanometers in a metre.

Let's do a quick check for understanding.

What is the correct symbol for a nanometer here, a, b, c, or d.

Hopefully we recognise that this was c, nm is the correct symbol for a nanometer.

Well done if you got that right.

Let's have a go at this one now.

Starting with the largest, sort the units of measurement into decreasing size order.

a, micrometre, b, metre, c, millimetre, and d, nanometer.

Remember, you're starting with the largest.

So the order that you should have got is b, metre, c, millimetre, a, micrometre and d, nanometer.

There is a 1,000 difference between each one as we go down.

So there are a 1,000 millimetres in a metre, there are a 1,000 micrometres in a millimetre, and there are a 1,000 nanometers in a micrometre.

Let's have a look at how we convert between units.

So on this table we've got the unit and how many there are in a metre.

So in a metre you have one metre, there are a 1,000 millimetres in a metre, there are 1 million micrometres in a metre and there are 1 billion nanometers in a metre.

But if I wanted to convert from metres to millimetres, so if I had one metre, how would I know how many millimetres there are? I would times it by a 1,000 and you can see that on the table because one metre times that by a 1,000 is 1,000.

So to convert metres to millimetres, you times by a thousand.

If you wanted to convert millimetres to micrometres, you would times by a 1,000 again.

And you can see that there are a 1,000 millimetres in a metre, but times that by a 1,000 and you get a million.

So there are a million micrometres in a metre.

And to convert from micrometres to nanometers, you times by a 1,000 again.

If you want to do the opposite and go from nanometers to micrometres, rather than timesing by 1,000, you just divide by 1,000.

And again, micrometres converting to millimetres, you divide that by a 1,000 and millimetres converted to metres, you divide by a 1,000 again.

If you want to pause a video now to make a note of this, it might be useful for later parts of the lesson, then you can just press play and ready for me to continue.

Let's have a look at some examples of these conversions.

So an amoeba has a diameter of 80 micrometres, and we can see the picture of the ameba there.

What is its diameter in nanometers and what is its diameter in millimetres? So we need to convert 80 micrometres into nanometers first.

Now remember that there are a 1,000 nanometers in a micrometre, so we have to times 80 by 1,000, which gives us 80,000 nanometers.

What is 80 micrometres then in millimetres? Well, this time there are a 1,000 micrometres in a millimetre, so we have to divide by a 1,000.

So 80 divided by a 1,000 is equal to 0.

08 millimetres.

Your turn to have a go at this now.

So an E.

coli bacterium has a diameter of 2.

2 micrometres.

What is its diameter in nanometers and what is its diameter in millimetres? You have a go.

So hopefully for the first one in nanometers we have to times 2.

2 by a 1,000, which gives us 2,200 nanometers.

And in the second example, we have to divide 2.

2 by a 1,000, which gives us 0.

0022 millimetres.

Really great job if you manage to get both of those right? We're now ready to move on to our first task of the lesson.

And in the first part, number one, you're going to convert the following to complete the table.

So you've got metres, millimetres, micrometres and nanometers, and you've got three numbers that have been placed in.

So you need to convert those numbers either by times by a 1,000 or divided by a 1,000 to work out each unit value.

Then number two, a human egg cell has a diameter of 118 micrometres.

What is its diameter in nanometers? What is its diameter in millimetres? And then number three, an adult fruit fly has a length of three millimetres.

What is its length in nanometers and what is its length in micrometres? There's slightly different units there.

I'm sure you're gonna do a wonderful job of this.

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 we're starting the table.

So 0.

28 metres, if we want to convert to millimetres, we have to times by a 1,000, So that's 280, we times by a 1,000 again for micrometres, So 280,000 and times by a 1,000 again for nanometers, which is 218 million.

So check the number of zeros there, make sure it's correct.

Now this time we've been given 6.

4 millimetres, so if we want to work out metres, we have to divide by a 1,000 which is 0.

0064, and then to convert millimetres to micrometres we times by a 1,000, so 6,400, and times by a 1,000 again to get nanometers.

So 6,400,000.

This time we've been given 15 micrometres.

So in metres we would divide by a 1,000 and then divide by a 1,000 again.

So this is 0.

000015.

So make sure you check you've got the right number of noughts after the decimal point there.

15 divided by a 1,000 will give us our millimetres, so 0.

015, and then to convert micrometres to nanometers, we times by a 1,000 which is 15,000.

Brilliant job if you've got those right.

Let's move on to number two.

So we've got to human egg cell with diameter of 118 micrometres.

So 118 micrometres is equal to 118,000 nanometers, we times by a 1,000 and to get to millimetres, we would have to divide 118 by a 1,000, so 0.

118 millimetres.

And then number three, we've got a fruit fly with a length of three millimetres.

What is its length in nanometers and what is its length in micrometres? So three millimetres, if we wanted to get that to nanometers, we would times by a 1,000 and then times by a 1,000 again, so that would be 3 million nanometers.

And for micrometres we would just times by a 1,000 which is 3,000.

Really brilliant job if you managed to get all of those correct, well done.

Fantastic job, so we've now done the first part of our lesson units of microscopy.

Let's move on now to look at comparing sizes.

So we can use this scale here to help us to compare organisms on earth.

And you can see the scale kind of slides up.

So if we start at the very left, we've got 0.

1 nanometers and then it goes up into micrometres then millimetres, centimetres and then metres.

Now the organisms kind of up to one millimetre in size, probably a little bit less than one millimetre, but definitely a 100 micrometres.

They would be microscopic in size, which means that we would need a microscope in order to be able to see them.

So that would be unicellular organisms and also subcellular structures like the chloroplast that you can see on there and then going right back into the size of an atom, 0.

1 nanometers which is unbelievably small.

So we would need microscopes to be able to see them.

Whereas if you look at the frog cell, which is the size is just slightly above that at one millimetre all the way up to the blue whale, those are eukaryotic organisms where they're visible with the human eye.

So we don't need a microscope to see them.

And we can see how the different units of measurement are used on this scale.

So we've got nanometers, which are the very smallest objects that we can see.

Micrometres, so we've got chloroplast there up to the human egg cell.

And remember for nanometers and micrometres, we would need a microscope in order to be able to see those.

And then going up for millimetres, centimetres and then metres to measure some of the larger organisms such as humans and the blue whale.

Let's do another check for understanding.

How many cells make up a unicellular organism? a, one, b, thousands, c millions or d billions.

A unicellular organism is made up of, a, just one cell.

Let's have a look at comparing some sizes of organisms then.

So we've got an ant here which has a length of nine millimetres and amoeba with a length of 90 micrometres, a red blood cell with a diameter of nine micrometres, bacterium which have a length of one micrometre and a virus with a diameter of a 100 nanometers.

Now you can see that they've got different units representing them.

So if we were going to compare the size, it's quite difficult to that without making sure that we're using a consistent unit, the same unit, but the length of an amoeba is 10 times the diameter of a red blood cell.

And if we were gonna look at that, we would say 90 micrometres divided by nine micrometres is equal to 10.

So when comparing size, it's important to work with the same units.

And we can see here that that's kind of easy to do for the amoeba and the red blood cell because they have the same unit, but it would be difficult to do that for say the ant and the ameba because the unit are given here slightly different.

So let's now look at the ant and the amoeba.

What is the length of the ant compared to the length of the amoeba? So the length of the ant is nine millimetres.

The length of the ameba is 90 micrometres.

So the first thing we need to do is convert the nine millimetres into micrometres, and to do that we would have to times by 1,000.

The nine times by a 1,000 is 9,000 micrometres.

So the length of the ant is 9,000 micrometres.

And now we've got the units the same, we can compare them more accurately.

So we would do 90,000 divided by 90.

So we've taken the larger number divided by the smaller number, which gives us a 100.

So the ant is 100 times longer than the ameba.

Your turn to have a go now.

What is the length of the bacterium compared to the diameter of the virus? So the bacterium, the length is one micrometre and the virus diameter is a 100 nanometers.

Then remember we need to make those units the same.

So you have a go at that.

Okay, so let's convert the micrometres into nanometers.

So to do that we have to times by a 1,000.

So one times by a 1,000 is a 1,000 nanometers, so the length of the bacterium is a 1,000 nanometers.

And then we divide the larger number by the smaller number.

So a 1,000 divided by a 100 is 10, the bacterium is 10 times longer than the diameter of the virus.

Well done if you managed to get that right.

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

So there are three questions here and in each question you've been given two different cells and their sizes, and you have to work out how those two different cells compare in size with each other.

It's exactly the same method that we just used in our practise examples.

So we need to make sure the units are the same to begin with, and then divide the bigger unit by the smaller to work out which one is bigger.

Press pause and then when you're ready for me to go through the answers, press play.

Let's see how we did.

So for the first example, we're working with the same units already, so we don't need to convert anything, we just need to take the bigger number and divide it by the smaller number, which is 120 divided by 1.

5.

So the human egg cell is 80 times larger than the diameter of the E.

coli cell.

For the second part, again, we've got the same units, we're working in micrometres, but this time the palisade cells diameter is bigger than the TB cells diameter, so we do 70 divided by 0.

35.

So it's the palisade cell is 200 times larger than the TB cell.

And then finally again we've got the same units, so we don't need to convert, but we do 475 divided by nine.

So therefore the large amoeba is 52.

78 times larger than the human red blood cell.

We've written that number to two decimal places there.

So if you round it slightly differently, your answer might be a little bit different to that, but you know roughly if you've got it right.

If you've written for example, 52.

8, then that is also absolutely fine.

Well done if you got those answers right.

Brilliant job.

We are now ready to move on to the final part of our lesson, which is microscopy calculations.

Let's get going.

Magnification is a measurement of how many times an object has been enlarged.

We can calculate magnification using the real size and the image size of a magnified image using the following equation.

Magnification equals the size of the image divided by the size of the real object.

Now if you're wondering what image size is, image is the the size of the image that is produced underneath the microscope or the drawing of that cell, whereas the size of the real cell is the actual size of that cell.

We can also rearrange the magnification equation to calculate the size of an image or the size of a real object.

So it's the same equation, but we've just changed the subject.

So for the size of the image, it's magnification times by the size of the real object.

And for size of the real object, it is size of the image divided by the size of magnification.

You might want to pause a video now and make a note of those equations because we will be using them later on in the lesson.

So let's put those equations into practise.

Calculate the magnification of an amoeba with a diameter of 90 micrometres and an image measuring 18 millimetres.

So if we just focus on that part of the question first, we've been given the diameter of 90 micrometres.

That is the the real size of the cell, and the image is measuring 18 millimetres, that is the image size.

Now, for us to be able to input those values into our equation, we have to make sure that the units are the same.

So therefore we have to convert 18 millimetres into micrometres, so we times 18 by a 1,000 which you can see underneath the picture of the amoeba is 18,000 micrometres.

So therefore the real size of the cell is 90 micrometres and the image size is 18,000 micrometres.

So now we can put those values into our equation.

So magnification equals image size divided by real size.

So 18,000 divided by 90, which gives us a magnification of 200.

Let's see if you can have a go at a similar sort of question.

So your job here is to calculate the magnification of an E.

coli cell with a length of 1.

7 micrometres and an image measuring 10.

2 millimetres.

And the equation is written there for you, so magnification equals image size divided by real size.

And remember, the first thing we need to do is make sure that the units are the same.

So first thing I would like you to do is to convert the image size into micrometres.

Now, hopefully we've recognised here that we need to times by 1,000.

So 10.

2 millimetres is equal to 10,200 micrometres.

Now we know the two values.

So the second part of this that I would like you to do is to input those values into the equation to work out the magnification.

Okay, so hopefully what you've done here is 10,200 divided by 1.

7 which gives a magnification of 6,000.

Amazing job if you manage to get that right, well done.

We're now ready to move on to the final task of today's lesson, and this is where we use everything that we've learned so far.

So the conversion of units and also the equations that we just learned to calculate some magnification.

So there are three questions here for you to have a go at.

Remember, we need to make sure first of all that the units that we're working with are the same, and then we need to plug those values into the equation.

And then the fourth example is to complete the table.

So you've been given the size of the real object, the size of the image in micrometres and the size of the image in millimetres, and then a magnification.

And you've been given various different pieces of information in each one.

So you need to use the equation to fill in the gaps on the table.

I'm sure you're gonna do a really great job.

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

Okay, let's see how we did.

So in the first example our units are not the same, so we have to convert the image size into micrometres.

So 14 times by a 1,000 is 14,000 micrometres, and then we do image size divided by real size which is 14,000 divided by 0.

7, so the magnification is 20,000.

For the second example, we need to convert here centimetres into millimetres.

So 17.

5 times by 10 is equal to 175 millimetres.

And then again we do image size divided by the real length, which is 175 divided by 1.

4, which is a magnification of 125.

And then for number three, we need to again convert centimetres to millimetres.

So two times 10 is 20, and then we do image size divided by the real size which is 20 divided by 9.

5.

So the magnification is times by 40.

Brilliant job if you manage to get all of those correct.

Well done.

Let's move on to our table now.

So in the first example, you've been given the real size and the magnification.

So you're trying to work out image size.

And remember, image size is real size times by magnification.

So therefore, in micrometres we would get an answer of 425,000 because that's 500 times by 850.

But if we wanted to convert that into millimetres, we would then have to divide by a 1,000 which would give us 425.

For the second example, we've got the size of the real object of 200 nanometers and the size of the image in micrometres.

So the first and most obvious thing to do is calculate the size of the image in millimetres, which would be five we would divide by a 1,000.

So working out the magnification is a little bit more tricky in this example because the units are not the same.

So we would have to convert the 5,000 micrometres into nanometers.

So we would times that by a 1,000 which gives us 5 million, and then divide 5 million by 200 which gives us an answer of 25,000 as a magnification.

For the third example, we have got the magnification and we've got the size of the real object.

So therefore, to work out the size of the image, we would do the real size times by the magnification, which gives 37,500, and then to convert that into millimetres, we divide by a 1,000 which gives 37.

5.

And then in the final example, we've been given the real size of the object in metres and the size of the image in micrometres.

First thing to do is convert that micrometres into millimetres by dividing by a 1,000, so there's 10 millimetres as the size of the image.

And then to work out the magnification, we need to make sure that the units are the same.

So probably the easiest way of doing this is, if the size of the image is 10 millimetres, let's convert that into metres.

So 10 divided by a 1,000 is 0.

01 and then you do point 0.

01 divided by 0.

005 which gives you a magnification of times 20.

That is absolutely brilliant if you've managed to complete all of those and get your head around it and fit in that table.

We're working with lots of different units and you've done such a brilliant job.

Well done.

I think we're ready now to summarise everything that we've learned this lesson.

So most animals and plants are made up of millions or billions of cells.

Cells are too small to see with the unaided eye.

We need a microscope in order to see them.

We can compare the sizes of eukaryotic and prokaryotic cells and the subcellular structures using the same units.

We can calculate magnification using the real size and the image size of a magnified image using the following equation.

Magnification equals size of the image divided by the real size of the object.

And remember, one of the most important things we need to do in those equations is make sure that we've converted units so that they are the same.

You've done an absolutely fantastic job of today's lesson.

Well done, I'm really looking forward to seeing you next time.