 On your screen is an animal cell and eukaryotic animal cell and by eukaryotic I mean that it will have membrane-bound cell organelles, cell organelles. Now we know what an organ is but what are these organelles now? Well organelles simply means tiny organs, tiny organs and why do we call them tiny organs? Well just like lungs, kidney, heart, all different organs in your body perform different functions in order to keep you alive. Similarly these tiny compartments or these tiny organelles inside a cell all perform different functions and keep a cell functioning or keep a cell alive. So in this video we are going to learn about few of the organelles inside an eukaryotic cell. So the first organelle we are going to talk about are these orange tube-like structures that you see near the nucleus. These are called the endoplasmic reticulum. Then we will discuss about another organelle which is called the Golgi apparatus or the Golgi body. Next we will talk about these sphere kind of thing lying in the cytoplasm which are called lysosomes. And the last organelle we will talk about in this video are the vacuoles. Let's make one vacuole here. So we will talk about vacuoles. Alright now let's make some space and bring each organelle out and discuss their function. So the first organelle is the endoplasmic reticulum or we simply call it the ER. Here endoplasmic means the endoplasm or the cytoplasm inside the cell and reticulum means network or mesh. And this structure that you see is a network or a mesh-like thing that lies in the endoplasm or the cytoplasm and therefore it is called the endoplasmic reticulum. Alright now let's talk about the membrane of the ER, the membrane that makes up this whole new organelle. This membrane is very similar to the plasma membrane or the nuclear membrane. Now can you guess why? Well the simple answer is that this ER is nothing but the continuation of this nuclear membrane. This nuclear membrane it extends and it folds in order to form this network kind of structure. Forming these long tubules or oblong shaped vesicles. Again another very prominent thing that you will notice is the presence of this tiny white dots on the surface of the ER. And then again there are 13 ERs down here which do not have this tiny dots on their surface. So first of all what are these tiny white dots? These are nothing but the ribosomes. So the ER which are close to the nucleus has a lot of ribosomes attached to its surface or attached to its membrane which gives it a bumpy rough appearance. Therefore we call this ER as the rough endoplasmic reticulum or the RER. And the one which is further from the nucleus which do not have these white dots or ribosomes on its surface, we call it the smooth endoplasmic reticulum or the SER. Now this RER and SER differ not just in appearance but also in their function. So how about we separate them and discuss about them separately. First let's talk about the RER. The RER has ribosomes attached to its membrane and these ribosomes are the protein manufacturers of a cell. So let's say this white long protein chain is the one made by the ribosome and it is released inside the lumen or in the long tubules of the ER or RER. Now the job of the RER is to fold this long protein chain into a functional protein. It also does certain required modifications and sends it down this tubular network until it reaches the vesicles that is formed from the membrane of the RER. So RER forms a bud-like structure in which it stores the modified protein and then that bud pinches out from this ER and moves towards another organelle, the organelle which is just below the ER which is the Golgi body. So basically all it does inside a cell is protein production. So any part of your body demanding more protein will have cells with more RER in them. For example if we talk about the digestive enzyme producing cells in your stomach that releases enzyme to digest your food, it will have a lot of RER in them because enzymes are mostly proteins. And not just enzymes, most hormones are also proteins. For example insulin that regulates your blood sugar is also a protein. So the cells in the pancreas that will secrete insulin will also have a lot of RER in them. Alright now let's move on to the smooth ER. The smooth ER are responsible for producing fats or lipids. Now before you consider them to be the culprit for all the excess fat you have in your body, let me tell you that fats and lipids are actually very essential for our body. We make up one of the most vital component of a cell that is the cell membrane. The cell membrane is a lipid bilayer. It obviously has other constituents in it but the main component of a cell membrane are lipids. And the process of building cell membrane from lipid is called membrane biogenesis. And not just that, the smooth ER are also responsible for detoxification of drugs or poisons and this detoxification happens in the liver cells. So the liver cells will have a lot of smooth ER in them. And these smooth ER they biochemically change the toxins or the drugs into what a soluble form so that it goes out of the body through urine and that is how they detoxify the body. So this was all about the endoplasmic reticulum that roughened the smooth. Now let's move on to another organelle which is called the Golgi body. The Golgi body or the Golgi apparatus is named after its discoverer, Camilo Golgi. And this organelle is composed of a parallely stacked flattened sac-like structures. These sacs are also called cisternae or a singular it is called cisterna. Now any product from the ER whether rough or smooth has to go through the Golgi body. Why is that? Is Golgi the boss of the cell? Well the answer is the cisterna of Golgi has the potential to modify and properly pack the products coming from the ER. So the Golgi stores the proteins and lipids and according to the need of the body it modifies it and packs it into vesicles and sends it wherever it is required. So if it is an enzyme that needs to be secreted out of the cell the vesicles will move near the cell membrane, it will fuse with the cell membrane and secrete the product outside. So in short Golgi acts like the dispatch unit of a factory that stores that has the potential to modify if there is a need from the customer and it properly tags and packs the product before it is dispatched out of the factory. But sometimes certain packages do not leave the factory or I should say 13 vesicles never leave the cell. Instead they remain suspended in the cytoplasm forming a whole different organelle on its own. And if these vesicles are filled with powerful digestive enzymes capable of breaking down organic material we call it the lysosome. But if the vesicles are comparatively void or empty we call it the vacuoles. Now let's first talk about the lysosome's role inside the cell. What do they do with all these digesting enzymes inside of it? Well their main role is to keep the cell safe or I should say maintain the cell health. For example let's say there is this very nasty bacteria near the cell. So what the cell does is encurse the bacteria and allow these lysosomes to go and release its digesting enzymes and kill the bacteria. So this way it saved the cell from foreign invader. Or if any of the cell organelle let's say a mitochondria is not functioning inside the cell. So then it is the lysosome that will go and fuse with the non-functioning mitochondria and will kill that cell organelle. And again when it is time when the cell is old enough to die it is the lysosome that bursts inside the cell. A lot of lysosome together it bursts in order to kill the cell. Now since the lysosome has the capacity to kill its own cell it is also called the suicidal bag of the cell. Now if you are wondering why would this lysosome kill the cell? Then let me tell you if a cell do not die it will continue to grow and that is how cancerous tissues are formed. So whenever the time is right, whenever the cell is old enough the lysosome bursts and the cell dies. So this is a very normal process. Now let's move on to the fourth organelle which is the vacuole which is again formed by the Golgi body. Vacuole simply means an empty space in a cell. Now the empty vesicles formed from the Golgi body they don't remain empty for very long because the vacuoles are used as pantry or storage unit by the plant cells. Anything that the cell has an excess it is sent to the vacuole. Excess of amino acid send it to the vacuole. Excess of water, sugar, organic acid, proteins, no worries. The plant has enough storage space in their vacuoles. And the vacuoles in plant cells holds a lot of water in it that maintains the turgidity of a plant cell. And therefore the vacuoles in plant cells are huge. They occupy roughly 50 to 90% of the cell volume and are called the central vacuole. Now apart from vacuoles in plants animals also have vacuoles in them. For example the single cellular organism amoeba has food vacuole and these vacuoles are temporary and it forms only when the food is ingested. So this orange dot you see is food and this is an amoeba. So whenever it comes in contact with the food it extends its arms or its membrane and gulfing the food. So as you can see here it has engulfed the food completely forming a food vacuole. And this vacuole pinches off from the cell membrane and moves towards the center of the body. It is then digested and absorbed and whatever waste remains is again excreted out of the body this way. So this is a food vacuole. Now there is another type of vacuole which again is seen in single cellular organisms like amoeba and it is used to excrete excess of water out of the body. So whatever excess water gets inside the body is stored in this vacuole and when this vacuole is filled it slowly moves towards the cell membrane and then excretes out the excess water. This is how water balance is maintained and this is how different vacuoles serves different purposes in living cells. Now the thing that fascinates me so much about these four organelles is that the membrane of one organelle interacts so well with the with the membrane of the other organelle and the membrane sometimes end up producing new organelles altogether like the lysosomes or the vacuoles in case of plant cells which are formed from the colgy and because of this property of these four organelles because their membrane interacts and coordinates so well inside the cell in order to accomplish a particular goal these four organelles are together placed under the endome membrane system.