Chapter 1.1: Introduction to Cells and Microscopy

hello everyone welcome to a.s biology with dr demi i am dr dimiladei fayamiro and on this channel i will be sharing the chronological order of the a.s biology syllabus with you to help you revise for your exams or to simply reinforce your understanding i have taught biology for more than two years now so i am using notes from my classroom to explain some of the difficult concepts but covering all the chapters that are in the biology syllabus so if you simply want to reinforce your understanding you want to revise or you want to watch a couple of videos to see things in a different perspective then this channel is certainly for you and it would also be great if you want to interact with other students who are revising for the exams you can simply post a comment and i'm sure other students would be happy to relate with you if you have any questions you're also welcome to post them in comments and i will get back to you with explanations as soon as possible i am using notes from my classroom like i said earlier on so this is going to be a narration of all the slides that i have prepared so far in the classroom i hope you enjoy yourself i hope you have lots of fun let us get into it so to start you off i'm going to first of all tell you about the textbook that we use in my classroom this is a textbook that is accredited by cambridge and it is by mary jones richards for richard fosbre jennifer gregory and dennis taylor it's the cambridge international a s and a level biology course book the reason i love this book in particular is that the wording is very simple and easy to understand so i encourage students very often to make sure they look into the textbook and not only rely on the things that are being said in class because when you read from the textbook especially after you've attended a class or even before it helps to reinforce what you understand um for a particular topic but i've also done here and i'm just going to use a pen um to just highlight things when necessary what i've also done here is show how i split the syllabus in my classroom so for example in term one my students cover four chapters that's because time one is typically long so they have lots of time to cover these chapters and to also learn how to do their laboratory experiments in term two they cover another four well in term two it's more like three and a half but we're able to make it work and you can see there's a continuation there in term three of chapter eight and then they cover the last three chapters but by the end of the first year all students would have completed the 11 chapters of the as biology syllabus so if you're lagging behind at school or you just feel like you don't understand what's going on because you're being rushed then this channel is certainly for you because i cover every single thing that you need to know all right let us start with our very first topic so when we start a.s biology we start with the basics and that basic is that we start with the definition of what a cell is it is believed in biology that every single thing that we see on earth when dismantled to its smallest tiniest unit will be found to be made up of cells and as such we discover we define cells rather as the smallest unit of life and cells are not just round structures that you see and they look pretty around them you will see that they have membranes and so cells are not just hanging around and floating into each other they have membranes and these membranes are important because they control the substances that enter or leave the cell and you will see why this is important when we get into chapter four for example you begin to see the importance of these membranes and the role that they play in ensuring that cells are able to transport certain materials or even to communicate with each other when we start with biology something that's very important is microscopy so when we speak about cells and we say that if we strip every living thing down to its smallest unit we would find a cell what many people don't know if they are new to biology is that cells are very microscopic you can't simply look in the environment and just see a cell you would have to put it under a microscope to observe it and as such that means that when we start this chapter we often introduce students to microscopes and there are two key types of microscopes that you are expected to know there is the light microscope which is the one that you will typically find in your secondary school laboratory or your senior school laboratory and there's the electron microscope which is more likely to be found at a university the electron microscope is a lot more complicated to run compared to the light microscope and you usually have to have training to be able to run it it uses software it uses an electron beam to illuminate organisms so that they can be seen the good thing with the electron microscope is that you can see a lot more with it the light microscope on the other hand is a small desktop microscope and you can see some organelles with it when you put a cell under it but you can't see as much as an electron microscope but for your level you don't need to see that much you simply need to see the things that are important for you to know for a.s biology i'm going to explain to you how the light microscope works and so that you have an idea of it in case you haven't done this at school yet so how does the light microscope work before we even look into that i want you to take note of the different parts of the light microscope we call these parts over here and these two eye lenses we call them the eyepieces or the ocular lens and this is where you would typically look through as an observer to see whatever it is you're trying to observe we call these lenses here the objective lenses these objective lenses are for zooming in on an image or zooming out so when we say zooming in or zooming out it means that they can magnify an image and what you will find is that you have one that is 10 times which means that's 10 times magnification of the image you have one that's 40 times magnification and you have another one that is 100 times magnification something important for students to also know is that the eye pieces are always 10 times magnification so it means that when you observe a specimen and you use a 10 times objective length over here the magnification of that specimen is actually 10 times 10 which means it is a hundred because you multiply the magnification of the eyepiece length with that of the objective length so that's something to just put at the back of your mind because sometimes when you do some calculations in your laboratory exam you will find that you are often asked these seemingly tricky questions and it's very easy to get the answer wrong this is called the stage over here and on the stage is where you would put your slide we call it a slide it's a piece of glass that's rectangular just like i have drawn there in red pen and your specimen is always somewhere in the center there and you're able to view your specimen by looking down at the microscope at the bottom of that you have what we call the condenser and the condenser helps to concentrate the light that's coming from the light bulb now something interesting i observe in classes with students sometimes is that they put the slide on they turn on the microscope but the condenser is not open so that the light is able to flow through and then they scream dr damie dr damia i can't see anything it would be impossible for you to see anything if you're not allowing light to flow through the condenser so the light needs to get through so that it can illuminate whatever it is you have put on the stage and then you can view it here through the eye pieces another trick that you have to know with the microscope is that you should keep both eyes open when you're looking into the microscope students tend to close one eye and if you close one eye your observations are likely to not be accurate so try to keep your eyes open um i know it can be a bit difficult this year is for focusing this knob and you will see if you are able to do this in the classroom that the more you turn either the tiny knob or the big one that your image changes in how resolute it is or in the resolution of it so it means your image either becomes really blurry or it becomes more focused so it is important for you to just spare that in mind i have put the slides here or the points here to help you know the functions of the different parts of the light microscope haven't discussed with you how the light microscope itself works so the eyepiece will focus the image from the objective so think about it this way let's think of it working from the bottom to the top you switch on the microscope here by the side this is often the power button and the light bulb comes on here that light bulb then travels upward or the rays of light travel upward and they illuminate this image here that is picked up by the objective lens the size of which the size of the image picked up is dependent on the objective lens you're using if you're using the 40 times lens the image would be bigger if you're using the 10 times less the image may be smaller but might be more focused or sharper in resolution now that is picked up by the objective lens and it goes up all the way over here to the eyepieces so that you are able to then see the image the condenser lens like i said focuses the light onto the specimen and you have the iris of the condenser which is basically used um to control the amount of light that you're getting so that's just that little pointer over there it helps you control how much light you're getting onto your specimen but if you do this in the lab i'm sure it's much more fun than what i have just explained all right the two types of cells that you are likely to observe or basically the only two types that you will observe for a.s biology are the animal cell and the plant cell usually students who are new to biology struggle to understand what the difference between these two cells are but i often start students off with a spot the difference activity what this activity simply does is to remind students first of all of the basic differences they can see by simply looking at these two cells now what can you see over here this is the animal cell on the left the animal cell here is a round shaped or a spherical shaped cell that contains all of these organelles you can see there it also has a nucleus at the center we will discuss the function of the nucleus later and this is the nucleus rather it has a nucleus within the nucleus and it has its mitochondria it has a smaller vacuole that you often would not see under the light microscope if you look at the plant cell which is labeled plant cell here you'll see that there is quite a bit of a difference just at first glance the plant cell also has a nucleus it also has a nucleolus but then it has this big wide open organelle organo and this is called the vacuole sometimes you're able to see the vacuum not sometimes most of the time you're able to see the vacuole when you observe the plant cell so it has a large vacuole and that is usually for the storage of waste material or for the storage of water or nutrients depending on what is going on within the cell we often say that the plant cell has a large central vacuole so with that said i advise you to go into your textbook and to use the power of observation simply look at the images of a plant cell and an animal cell and ask yourself what are the differences between these two when i look at them at first glance what is it that a plant cell has that an animal cell does not and what does an animal cell have that a plant cell does not have if you're able to do that even before you memorize the organelles or before you learn about their functions it would help you very well in when you're doing observations with a microscope because with the microscope you will see that the plant cells are very distinctly different or rather are just distinctly different from the animal cells so with that said then we can ask ourselves what plants and animal cells have in common first of all they have a cell membrane remember at the beginning of the chapter or at the beginning of the video i said to you that cell membranes exist to help cells regulate what goes in and what they allow to leave the cell so a cell membrane plays a very important function not just in doing that but also in communicating with other cells something that we will see when we get to chapter four they also have a nucleus in carbon if you remember the images we just looked at we saw that both cells had a nuclear and they both had nuclei which is the plural of nucleus they also have cytoplasm the cytoplasm is where all of the different organelles of the cell are floating so think of it like a stew and in this stew they're all just different pieces of vegetables or beef or chicken depending on what it is that you're into uh but that is what the cytoplasm simply is it's like a soupy mix of all the things that you need within the cell they also have mitochondria mitochondria play a very important role in providing energy for the cell the mitochondria plays this role because it is called the powerhouse of the cell and as you go deeper in biology and that is beyond the scope of the as syllabus so this is at a level at the advanced level you will learn the processes that the mitochondria goes through in order to make atp which is the energy currency of the cell they also have golgi apparatus golgi apparatus are very important in the transportation of proteins and the folding of the proteins that are made by the cell and again all of these will become more and more interesting as you learn more about biology so don't stress so much if it feels like oh my goodness this is just a lot you will gain understanding as we go along so here can you tell the difference usually when i give students this it is to help them see that sometimes in your question papers the cells are not easily drawn for you to be able to see they are not presented in color where you can simply look and say oh look at that it's a beautiful animal cell sometimes they come out in micrographs that look like this and so i used this to familiarize students with how the animal cell would look or how the plant cell would look if it was in a micrograph always pay attention first of all to the shapes of the cell when you see a spherical shape it means you are dylan or something that looks like a spherical shape it means you are dealing with an animal cell and when you see a cell shape that kind of looks like a rectangle but not quite one then you know that you are dealing with a plant cell in other words the plant cell has edges sort of compared to the animal cell the animal cells tend to be continuous spherical um images or structures when you view them under the microscope now something big that you have to know and this is important for the next video is what we call magnification versus resolution now if you take your phone camera today you can probably zoom five times and everything would still be clear especially if you use a very good phone with some phones however the moment you start to zoom what do you notice that whatever it is you're focusing on becomes blurry it is not as clear or as crisp as you would like it to be this is why we say magnification versus resolution as opposed to magnification and resolution magnification is the number of times by which an image is bigger than the actual object so if for example you start to zoom in on a dog that is far away that dog as you zoom in the resolution might be compromised but you have made the image bigger by zooming in it's definitely bigger than the dog that you're looking at so that is what magnification is resolution on the other hand is the ability to distinguish between two objects which are very close together so this image of this dog over here this is a very clear image of the dog but as you can see here this is not a so clear distinct image what has happened here is that the resolution has been affected so you can't tell the distinct features of this dog by looking at it anymore you can't see its eyes or its nose which means that it you've sort of lost your resolution or your crispness of this image as opposed to the previous um image on the left so can we measure cells since we talk about magnification and these things that are bigger or smaller or more resolute then the question becomes well how do we know when something has been magnified and how can we tell by how much it has been magnified also how do we just measure cells generally speaking the formula for magnification is that you divide the act of the observed size by the actual size or most times we like to write it as i over a where i is image size um and a is actual size of the of the um the image or the objects rather that you're looking at also something that you must learn here is the conversions or the units with which we measure so there are three units that you are likely to come in contact with as you go through the syllabus you are likely to come in contact with millimeters micrometers and nanometers now when you want to go from millimeters to micrometers all you have to do um it's taking a while here to write this down because i'm using a mouse if you go from millimeters to micrometers all you have to do here is multiply by 1000 because from millimeters to micrometers you take in an additional three series if you're going from micrometers to nanometers that is times another 1000 over there so what this tells you then is that if you want to go from meters to millimeters to micrometers and to nanometers then um this is nanometers it's just going to write this as an n so it's just going to erase that so you you're able to see better so that's an n so meters to millimeters would be times one thousand okay millimeters to micrometers would be times another one thousand so i'm just going to write it as 10 to the power of 3 micrometers to nanometers is times another 10 to the power of 3. so if you're going from meters to micrometers it means that you're going to do 10 to the power of 3 twice so that's going to be times 10 to the power of 6. i hope that makes sense if you're going from meters to nanometers it would be 10 to the power of 9 because you're doing 10 to the power of 3 3 times and it's important that i show you that because on the next slide i have an activity for you to do that you can do just to practice your conversions of these units because they become important once you start to do your microscopy experiment so this here is an activity i often give my students to wrestle with um just to help them practice how to convert from different units so you can see here that i have put different numbers on the different units and what i would like for you to do is to convert them into the other units so for example 0.5 meters what would that be in millimeters in micrometers and in nanometers and you can do that for all the different numbers that are here so it's just something nice to help you practice and to get familiar with conversions because when you start to do the microscopy experiments these become very important as a matter of fact if you don't use the correct unit in a calculation you are likely to get the answer wrong and that means you lose marks for something that is such a simple thing so i don't want you to overlook this activity try to give um some thought to it and to walk through it and i will see you in the next video where we look at this activity again and i show you the answers until then have a good time