hi everyone and welcome to chapter one cell structure this is part one of this chapter and just to give you an overview there are three parts number one is microscopy which is all about microscopes number two is more about calculation uh specifically magnification and basically how we are using microscopes to measure cells and Ma tree there is cell structure and function and this part you should be a little bit familiar with because you have learned some basics in igcs or all levels but right now you will be discovering more of these things in much more detail so let's start with the first part that is microscopy now in microscopy there are three main microscopes that you are going to be learning number one is the light microscope number two is the electron microscope and there are two types of electron microscopes here transmission and scanning that I'll be hearing about soon now before we go into the specifics for each microscope we must first look at uh some terms now first you must understand that electromagnetic radiation would be involved here there is a electromagnetic spectrum which means that there is a range of different wavelengths uh that can be involved in making microscopes and in the case of the microscopes we learn about that will be light microscope which uses light visible light as a source of electromagnetic radiation and that's electron microscopes which uses electrons and how it reflects off different specimens to a visualize the image of a particular specimen under the microscope now other than this concept set right here we also need to establish magnification and resolution because this is a common misconception that a lot of students have okay they think that magnification and resolution is the same thing but it is not now let's look at the definitions number one magnification is the number of times an image is enlarged compared to the actual size of the object so if you say that a object is 10 times enlarged this means that the image is 10 times the size of the actual object right so that's magnification and usually an X sign or time sign is placed in front of a number to show how many times it is enlarged so so under microscope in the lab uh which the standard one uh in in Cambridge centers exam centers that would be times 10 that would be times 40 that's on the microscope okay so that's magnification how about resolution resolution is the ability to distinguish between two points clearly and separate this is quite interesting what it's saying really is uh basically that hey when there is two points pardon me uh when there's two points perhaps like between this and this right to distinguish these two points would be the resolution if there is a high resolution you would be able to see these two points as separate from the background and as separate from uh each other now if there is a lower resolution image right maybe there are two points but you cannot distinguish them from one another because they are so so close together and it's not clear enough an image to be able to see the difference between two points uh if there's an even lower resolution you might not be able to distinguish this point from the background so that's why it's defined this way ability to distinguish between two points clearly separate we usually Express the units of resolution in nanometers and this is something we'll look at in a moment uh we'll look at it right after we clarify this magnification and resolution thing now an increase in magnification does not equal to an increase in resolution let let's look at this image for example right this is magnification increasing in each image that looks quite far away but you enlarge your picture you know maybe using a camera it seems nearer but it's in fact the image has just been enlarged up to 20 times now if you use a phone camera you be quite familiar with this concept because as you zoom in maybe the image becomes more blurry so basically you have increased the magnification but the resolution of the image the same right it did not improve as you magnify the image the image is not clear especially if you magnify it a lot correct let's take another picture as an example this is an image under a microscope of high resolving power and you can see a lot of detail you can see there like little spots here and here you don't need to know what it is just need to know that hey I can see more detail uh you can even see this vague spot here as separate from the background however if you look at this picture which is from a microscope with a lower resolving power same specimen same magnification but it does seem to blur and you can you can barely see this point that's supposed to be here as separate from the background therefore we say that this image right here has a higher magnific oh sorry higher resolution therefore the ability to distinguish two points is separate is much higher whereas this picture here on the right has a lower resolving power all right it's under microscope of lower resolving power it has a lower resolution uh and we cannot distinguish this point as separate as different from the background per se so yeah that's magnification and resolution now what determines resolution and I kind of give you a spoiler just now basically it's the electrom Spectrum it's what wavelength you choose to use in your microscope the short the wavelength used will give you a higher resolving power now wavelength of visible light is longer than of an electron and because the wave length is longer this would be uh a lower resolving power okay so visible light longer wavelength therefore light microscope would have a lower res resolving power because the ability to distinguish between two points is lower so even if you magnify it by a lot the resolution will not improve the image will look blur when you zoom in a lot yeah now how do we describe resolution as we sit just now the units are in nanometers right the max resolution by the way is the shortest distance between two separate points and the max resolution is half the wavelength use okay so the longer the wavelength AK visible like longer wavelength means larger minimum distance two points need to be further apart to be viewed as separate therefore this is deemed as a lower resolution overall okay what am I talking about let's look at an example in like number ter right so mation again is the shortest distance between two separate points uh to be seen as separate now if max resolution equals to half the wavelength used and the wavelength of visible light is around 400 to 700 meters that's a range there then the max resolution of a light microscope will be half of that because of this uh formula here right so it's max resolution will be 200 nanometers what does this mean this means if this point and this point right to be seen as separate it must be at least 200 nanometers and above to be seen as two separate points um actually in real life um to be seen as separate from the background the object needs to be kind of larger than 200 nanometers and if the object is closer or smaller than 200 nanometers then these points cannot be distinguished and separate in fact it will not be visible at all as separate from the background so for example a ribosome right ribosome is 25 Nomas it is the smallest organ of the cell you do need to remember that number by the way ribosomes are 25 Nomas so when you look down a microscope will you be able to see it and the answer is a no because 25 nomers is way smaller than 200 Nom and it cannot be distinguished from the background and therefore it is not seen now a nucleus however is around 1 micrometer that's 1,000 nanometers and therefore it can definitely be seen under a light microscope so yeah I hope you get the idea a resolution now okay now that we have established what magnification is and what resolution is we can talk about the details what is a light microscope what does it use source of electromagnetic radiation would be visible light this is how a standard microscope looks like in the lab I hope you would have a chance to use it if you go to a proper school right if you don't I think there are facilities out there for you to be able to rent Labs you need to get your hands on one in order to practice anyways the wavelength of electromagnetic radiation here is approximately 400 to 700 MERS and it has much lower energy okay much longer wave lengths than the electrons and the light is mostly focused using mirrors and glass lenses to direct it uh in this case the light is directed upwards and into the lens uh and into your eyes now these this results in a picture that you see through the eyepiece which is here now the highest magnification it can go is 1,500 times however the one that use the microscope usually during the exam would be would have only 10 times and times 40 now at such a high magnification you will be able to see chlorop plus you will be able to see nucle and uh chromosomes when the cells are dividing uh sometimes you'll be able to see a glimpse of mitochondria but not very often honestly mostly chloroplast uh and yeah that's that's high enough information to do that the mix resolution is 200 nanometers which is rather low this is half again half the the wavelength so minimum is 400 ma resolution would be 200 N you want the mix resolution to have a small as a value as possible to be considered high and that's why we take 200 nanometers and not 350 nanometers smaller the higher resolution smaller the value the higher the resolution this is considered quite a large value so it's a low resolution compared to the electron microscope now what is the advantage okay even though it's not very high reification uh high enough but not very high uh even though the resolution is not that great the advantage is live specimens can be viewed okay you can put live cells under microscope and you'll be able to see them and if you stain the cells as in color the image can be seen as colored okay or if the chloroplast are green you are able to visualize green chloroplast and green cells under the microscope and if it's live specimen you can even observe uh the cell dividing under the microscope definitely possible um yeah and of course it's not here it's not in the M scheme but of course there's also the other advantage of it being cheap easily accessible you can buy it on shoppy and uh other online websites like Amazon okay it's very easily accessible and it can fit on the table okay so that's that's a huge Advantage there again not in Mark scheme they want to hear lives speci image that can be colored uh and by the way uh if you're viewing structures on a microscope you usually would present the actual size of the organisms in micrometer that makes sense microscope light microscope micrometer now let's at electron microscope the source of electromagnetic radiation here is three electrons the wavelength contrary to the previous microscope is approximately 1 nanometer that is incredibly short very high energy however it's an electron and it's not visible light so you can't you know reflect it using mirrors and stuff it must be uh using magnets okay so electrons they are negatively charged right so you can use magnets uh positively charge negative charge to kind of focus it and also because it has such high energy you would want it to be in a vacuum environment vacuum environment in order for the electron to travel in straight lines what happens when when it is not a vacuum environment these electrons are focused and they are um the speed is kind of fast so if there is air it's going to uh create a lot of heat and that will not be not good for a microscope not good so yeah uh those that's the source of electromagnetic radiation free electrons good part about this is that it has a very high magnification the highest would be 250 ,000 times the size honestly the ones on the market probably better know but this is in your textbook okay now the mix resolution of electron microscope is around half the wavelength of the three electrons which is approximately one Nom so M resolution would be 0.5 nomers which is very high the smaller the value the higher the resolution because what is this value again this value is the shortest distance the min minimum the minimum distance two points need to be at so if an object is like 05 nanometer big all right anything above 0.5 nanometers this object will be able to be seen under the electron microscope the smallest organ the cell again it's ribosomes and it's 25 nomers right so it would be definitely very visible under the electron microscope now what's the disadvantage though even though it has a very high magnification and very uh high resolution the disadvantage is because it needs to be in a vacuum environment only dead material can be examined and because it's not using visible light where you know light can bounce off and there's a spectrum like a rainbow color right but because it's using electrons and the reflections of the electrons are read by computers the computers interpret this Imes as black and white only and um but we can use software to kind of color it in to uh view the image better but um when the computer initial initially processes it it would be in black and white also there is a big disadvantage that's again not part of the MK scheme very much so but it's a real life thing this electron microscope usually takes up an entire room or at least an entire like bench space and again it's a very sensitive piece of equipment because it needs to be in a vacuum environment not to mention that is incredibly expensive to obtain one you can Google the market rates for an electron microscope yourself anyways because of the high resolution um okay my Google just activated anyways what I was saying is since it has such high magnification and high resolution when we look at electron microscope images we usually measure them Express their measurements in nanometers just FYI now as mentioned just now there are two types of electron microscopes uh there is transmission electron microscopes and there is scanning electron microscopes right now transmission electron microscopes you can see here it's looking at the internal structure of something right usually the specimens have to be like laser cut tin in order for uh the electrons to pass through the specimen in order to be red okay the the equipment kind of looks like this there is a filament that can discharge electrons and they focus using this magnetic lenses and they have to pass through the specimens and then the Imaging plate at the bottom kind of reads uh collects the data um I think it kind of measures the speed of the electrons hitting the plate and therefore um the computer is able to process an image okay something like that but anyways the point is you need for a transmission electr microscope you need to have these specimens to be cut laser tin in order for the electrons to pass through now scanning electron microscope by the way are built differently okay they are built in a way that has a slightly lower modification resolution but to visualize the outside surface of object so like this is blood cells this is jophil jopa fruit flies eyes a fli eye and these are pollen grains not like powdery as you thought it's kind of spiky good for clinging to stuff anyway yeah and these are different this is how you describe them as I mentioned has the pass through the specimen if it's a transmission electron microscope it gives a 2d appearance because when you're cutting laser tin um and you're looking it from upwards up like it's like a from the up side on the surf you know what I'm saying and you are able to see details inside C this is a chloroplast look how crazy it looks just now the light microscope uh image or we call it light micrograph you could see like little Car Plus like kind of like in a circle circle kind of floating around and it look cute and stuff this is the interal structure guys look at it it's like stacks of uh these are called gr these are tyo stacks and look at how amazing that looks it up close right these are details these are internal structures uh transm Mission electron microscopes have such high resolution you can even look at the membranes within those internal structures here these are tiny tin membranes that is crazy anyways the transmission what scanning electr microscopes this is a dite I think on flea this is uh definitely lower resolution however it's pretty cool to it gives you a 3D appearance it scans the surface of speci ments so you get really cool images like this but again it's in black and white and usually if you see like colors on these images they are all CGI they all computer generated and they are all like colored in by softwares but yeah those are the light transmission electron microscopes and scanning electron microscopes all right before we end um just because you're new to the this course this is a common question by the way in the exam especially in paper Tre they often ask you to list the differences between light microscope and electron microscope now if they do this in paper 3 especially you should always present your answer as a table the first row okay row I emphasize not column right the first row usually has marks uh you have to label features okay and and then whatever you're comparing and the other one so A and B okay that that first row has one Mark usually and then uh in the table you have to be specific in your features use comparative language and um don't take across you know write present absent bigger smaller right they want to see words now usually yeah is one mon for the first row but if there are four marks I do encourage students to write four points just in case okay just in case the first Tre are wrong at least uh there is one Mark at the end so yeah I'll let you feel that in yourself I think it should be quite obvious uh magnification is one point uh source of that truma radiation there's resolution you can figure this out I believe in you here's other answers if you want to um yeah and you can check it once you're done but yes this table kind of summarizes our entire lesson today this are the differences between light electron microscopes uh they do sometimes ask you the differences between transmission and scanning as well so make sure you know that and of course make sure you never confuse between magnification and resolution that's it for now see you next video bye-bye