organelles are basically defined as structures inside the cell that have a specific function and organelles are divided into two types membrane-bound organelles and non-membrane-bound organelles basically membrane-bound organelles just means that the specific structures inside the cell have their own membrane if you remember we were talking about compartmentalization in the earlier video where the cell creates a subdivision or the room so that it can carry out specific functions so some organelles require a membrane so that they can carry out separate functions some organelles don't the organelles that do not need membranes are called non-membrane-bound organelles as a student you must be able to draw out the organelles especially if they do ask you that in paper two of biology in paper one and sometimes also paper two you are also required to identify these organelles especially when viewed under light and electron microscope and of course you can't run away from it you have to know the basic structure of each organelles and also their functions so important things to know about the nucleus will be the fact that it is a double membrane organelle it has nuclear pores nucleolus and chromatin chromatin is just basically linear dna wrapped around histone proteins if you are wondering what histone proteins is do not worry about that we will be addressing that in chapter five and when we are doing chapter 5 i will send a reminder i will remind you of this term clomatin now as i zoom into the nucleus you can see those two lines where the arrows pointing that is just basically pointing to the membrane and you can see there are two layers two lines you can see there are two lines over there and those two lines correspond to the double membrane of the nucleus the tiny little holes interspersing the membrane is referred to as the nuclear pole there's a reason why this paw or this hole exists and we will see that in chapter six also inside the nucleus they have this condensed structure made out of dna grouped together and that structure is known as the nucleolus now some students think oh is the dna only found in the nucleolus no of course not there are also chromatin floating around within this room and i'm just highlighting it with the grayish colors over there you might be wondering oh why can't i see the double helix well you just can't because double helix is too small to be seen using light or electron microscopes for that matter over here you're looking at two images of the nuclei look observed under the microscope just a bit of revision which picture is taken using the light microscope and which one is taken using the electron microscope yes the one on the left is taken using the light microscope and the one on the right is taken using the electron microscope because if you remember light microscope produces images with color electron microscopes will always produce black and white images the nucleus will observe under the light microscope does not give you much of a clear image you can kind of see that dark area over there but it doesn't tell you much you might be able to see the nucleolus when you're viewing it under the light microscope however when we zoom in into the image under the electron microscope we can see this beautiful detailed image we can see this beautiful detailed image because if you remember electron microscopes have a resolution of 0.5 nanometers it can pick out extremely tiny detailed structures for example that two arrows over there they are pointing towards the double membrane organelle they are pointing towards double membrane organelle of the nucleus you can also see the nucleolus the darkening area and the hazy structure surrounding the nucleolus is the clomatin so when you're viewing and uh when you're viewing a nucleus under the electron microscope you just basically get a detailed image light microscope will not yield you much you might you will still be able to see the nucleus but you are you're not able to put you're not able to get a detailed image out of it and of course last but not least we also have to know the function of the nucleus in the igcsc it was sufficient to say that the nucleus was the brain of the cell and it controls cell activities for a levels sadly that won't be sufficient what you have to know is let's talk about it so the nucleus is like a room and the room contains genetic information which is chromatin you can put that in the exam it is also the site of transcription which is for protein synthesis i will not elaborate on this yet because we are going to be looking at this in chapter six so do not worry about that and last but not least you also have the nucleolus within the nucleus and the nucleolus is responsible for producing the ribosomes that the cell requires for number two we are going to be doing two organelles at the same time the rough and smooth endoplasmic reticulum also known as rough and smooth er we have to know the general structure as usual and they are single membrane organelles and what do i mean by single pimpline organelles you can actually see that the membrane itself has a fluid filled space and the entire thing is just basically known as a system a i'm highlighting the fluid fill space over that and you can see that it's a single membrane organelle because if imagine if you wanted to enter the space within the endoplasmic reticulum you will just have to cross one membrane that is why it's called a single membrane organelle simple as that now the single membrane over here forms an extremely weird shape called the network also known as the reticulum you can kind of imagine it to be like a branching of a single membrane to form this odd structure now there are two types of endoplasmic reticulum the smooth and the rough one both smooth and above endoplasmic reticulum have the same general structure however the rough endoplasmic reticulum has two different features number one it is studded with ats ribosomes on the surface of the membrane ats ribosomes are just a specific type of ribosome that are only found in eukaryotic cells and the rough endoplasmic reticulum may be directly connected to the nuclear membrane it's not a fixed thing that oh it will definitely be connected to the nuclear membrane most of the time you can find a lot of rough endoplasmic reticulum directly next to the nuclear membrane and as you can see over here the smooth between the smooth endoplasmic and rough endoplasmic reticulum the smooth endoplasmic reticulum has a well it has a smoother surface and the rough endoplasmic reticulum has a rougher surface it's in the name the reason why it has a bumpy surface on the rough endoplasmic reticulum is because of the ats ribosomes on their membranes now endoplasmic reticulum and ribosomes are not visible under light microscope they cannot be picked up by the light microscope because number one their structure is too small number two it's extremely thin so the thickness of the membranes are lesser than 200 nanometers it will not be picked up by the light microscopes limitation in resolution they are only visible under electron microscope this over here is an image of the endoplasmic reticulum using the transmission electron microscope that's what i mean by tem over there the orange color line that you can see is the nuclear membrane and remember i told you rough endoplasmic reticulum are usually found directly connected to the nuclear membrane so those green color lines that i'm drawing over there are the rough endoplasmic reticulum and as you can see on their surface they seem a little bit grainy you can see those kind of grainy material and those grainy material over there are those grainy uh kind of substances are the ribosomes too small to be seen using the light microscope this one over here is another beautiful image captured using the transmission electron microscope and as you can see the networks over there those are the above endoplasmic reticulum and i'm just drawing one out to show you the membrane the system a and also the grainy ribosomes on its surface so that's how you recognize the rough er under electron microscopes functions are going to be quite simple the smooth endoplasmic reticulum function is for the synthesis and transport of lipids and steroids what this just basically means is the smooth endoplasmic reticulum has the capability of producing certain types of fats such as triglycerides in our body examples of steroids that the smooth endoplasmic reticulum can produce will be hormones such as oestrogen because these are lipid-based hormones above endoplasmic reticulum because it has those ats ribosomes on its surface they have the capability of synthesizing and transporting proteins now some students will ask the question hey wait a second you said that the ribosome synthesizes protein now you're saying that the rough endoplasmic reticulum synthesizes protein which one is it the ribosomes on the rough endoplasmic reticulum are the ones that are synthesizing the protein what the rough er can do is because it has membranes it can do something unique where it can transport the proteins as you can see those orange colored dots imagine those to be the proteins inside the space of the rough endoplasmic reticulum what will actually happen is the rough endoplasmic reticulum will form a kind of bubble as you can see in that diagram and the proteins will enter this so-called bubble and the bubble pops out of the endoplasmic reticulum and the proteins are now transported within this bubble and that bubble by the way is not is known as the vesicle and if you remember vesicles are just basically small vacuoles that travel within the cell and that's how the above endoplasmic reticulum transports proteins within the cell so the third organelle that we're going to be looking at is the golgi apparatus some books will refer to this organelle as the golgi complex or also the golgi body means the same thing so do not get alarmed when you say the word when you see other variant or other other variations of the names to this organelle again when we are looking at uh the structure of the golgi apparatus just like the endoplasmic reticulum it is a single membrane organelle with a fluid filled space this is the name the membranes will be arranged in stacks and they are surrounded by vesicles now one of the biggest issues over here is students get confused when they look at the golgi appellatus and the endoplasmic reticulum because they kind of look similar to each other i've drawn one out there for you an endoplasmic reticulum at the top just for you to compare it between the golgi pilots and the endoplasmic reticulum what you notice is number one the endoplasmic reticulum forms a network whereas and when i say it forms a network the membranes are interconnected with each other it forms like a branching whereas for the golgi paratest it forms a stack kind of like a pancake basically and more importantly it is you should also be aware that the membranes of the golgi apparatus the sistane are curved they have a kind of curved uh they have a curved appearance some some of my students will refer to them as the wi-fi signal and they're not completely wrong actually it does look a little bit like the wi-fi signal and of course golgi abilities would have um a fair bit of vesicles surrounding them this is a picture of a golgi apparatus taken under the transmission electron microscope and of course we cannot view the golgi apparatus under the light microscope for the very same reasons as the endoplasmic reticulum because the size of the membranes the stack of membranes are too thin to be resolved under light microscope you can see over here that the membrane the cysteine are curved they form a stack of membranes and you can also see vesicles surrounding them the functions of golgi apparatus include number one they produce things known as lysosomes we are going to cover lysosomes for number four so you don't have to worry about that the golgi apparatus is also the organelle in our cells that package and modify proteins now sometimes now students will be wondering what does protein modification means modifying proteins just basically means changing the structure of the protein for for various reasons by the way so as we are talking about later chapters we are going to see some examples of this protein modification but if you want to know an example of it is the golgi appellate test will have the capability of taking carbohydrates and proteins and they will be able to combine these two molecules together to become something known as glycoproteins examples of glycoproteins will include antibodies and mucus do you have to memorize them right now no because we will be looking at antibodies and mucus in later chapters so you see in a levels this chapter is just an introduction for better or worse things to come because sometimes this scares students in a way you don't have to worry so much because when we are doing the chapters in the future i will be referring back to chapter one as a way to link all these chapters in biology together and as you can see over there as well the hydrolytic enzymes are just basically and special types of enzymes in the cells they will enter the golgi apparatus and they'll be packaged or put into small little vesicles known as lysosomes