so if you hear some um explosion in the background I hope it's not too loud uh but fireworks are going on right now because of the Independence Day in our country so I hope that's uh not too loud anyway this is a transmission electron micrograph of an animal cell due to the resolving power of electron microscope of 0.2 nanom when you zoom into to the cell you are able to see the cell surface membrane but even after zooming it in the best diagram that you can see over here is just like a single line which I've put in yellow it is visible but we can't see much we don't have enough information just with that diagram also if you were to look at the scanning electron micrograph of a red blood cell you can't see the inside of the cell if you remember and the part that I'm highlighting is just the cell surface membrane looked at a three-dimensional point of view and in this case even if we zoom in we can see the cell surface membrane but we can't see much detail we have a problem so the problem is what is the cell surface membrane made out of how do we describe the cell surface membrane so in 1972 two scientists by the name of Seymour Jonathan singer and goth L Nicholson proposed a particular model to describe the cell membrane and they called the model a fluid mosaic structure so what exactly is meant by the fluid mosaic structure so in an attempt to describe how the cell membrane looks like let's try to look at the first word which is Mosaic and I've highlighted that a mosaic is just basically a type of art form where tiny comp components or tiny pieces are packed very closely to create something so if you see that image there you can see tiny little tiles which are pieced together to create the image of a person to create a pattern in the middle or on the right inside some random patterns it kind of looks like an animal um on the right there the Mosaic kind of looks like I don't know a cactus in the desert I'm not too sure what do you see there now the point is a mosaic is just used to describe tiny little pieces of things grouped together to create something or an image how does the word Mosaic relate to the membrane well it's because the membrane itself is not just made up of one phospholipid molecule it is made up of many phospholipid molecules grouped together closely to create the layer known as the cell membrane more importantly as you can see there I've also drawn out some purple structures and those purple structures are basically proteins so what we know about Mosaic membrane is it is actually made out of many phospholipids and proteins randomly scattered so this is how you look at it if you're looking at from the side okay and if you look at it from the top view you are able to see the phosphate heads and just the protein molecules of course if you're looking at it from the top you will not be able to see the phospholipid tails so it's kind of like trying to see icebergs floating in the water isn't it that is how we try to describe the cell membrane so that's what the word Mosaic means and the word fluid in this case actually translates to fluidity or flexibility where the proteins and phospholipids the proteins and phospholipids are free to move around which means that they are not in a fixed position now what what I mean by that is as you can see here look at these two diagrams that I've put here now there's a membrane on the left and a membrin on the right okay and I have highlighted one of the phospholipids to have a pink polar to have a pink head another phospholipid to have a green head now notice and notice in the second diagram the pink and the green phospholipids have switched positions that means they are not in the same position anymore and the protein which was quite near them have kind of moved towards the back so what this means is phospholipids and proteins do not just remain fixed in one particular area they can move around quite fluidly because the membrane is quite a dynamic structure and not everything is tightly packed another way you can kind of Imagine This is plastic balls in a pool all right imagine if the plastic balls just represented the phospholipids and the um proteins they are not just in the fixed position they can move and switch places depending on the situation and it's the same with the phospholipids and proteins as well when the phospholipids and proteins are in the membrane they don't just remain in one place and they can switch around and move around within the membrane why is this important we will talk about that later so that is what is meant by the fluid mosaic model and now after describing the cell surface membrane using the model the fluid mosaic model let's go back to that earlier diagram so when you look at this cross-section of the cell membrane of the um animal cell the part that I've circled which is the cell surface membrane that is how the cell surface membrane is supposed to look like using the fluid mosaic model you can see the phospholipids you can see the proteins which are randomly scattered around it this is how the cell surface membrane is supposed to look like under the transmission electron micrograph and in the scanning electron micrograph if you remember we are looking at the cell surface membrane from the top so therefore in this case you are only able to see the phosphate heads and the random scattering of the protein floating in twet and the best image that we've actually been able to get for the cell surface membrane is just this diagram right here so you can see those two lines and those two lines correspond to the phosphor lipid by layer it's not much you can't see the fatty acid tails you can't see the protein but we know that they are there that is why the fluid mosaic model is useful because it helps us imagine what the cell of this membrane is supposed to be like