 In our previous video, we discussed about endoplasmic reticulum and the Golgi body which are two organelles of the endomembrane system. In this video, we are going to talk about the remaining two which is the lysosome and the vacuoles. So let's begin quickly with lysosomes. What are they? These are the tiny vesicles that you see scattered in the cytoplasm. And what do they do? Well, from the name we can guess that lyso comes from a Greek word which means to digest. And soma simply means the body. So it is a body that has the potential to digest something. Now what does it digest? Well, it can pretty much digest anything that is not good for the cell. For example, if a foreign invader like a bacteria enters the cell, this lysosome will come and digest it. Or let's say any of the cell organelle got damaged and it needs to be removed. It is our lysosome that will go and digest it. Or even sometimes if a cell is old enough to die, it is the lysosome that digest the entire cell. Yes. And therefore, maybe it is very correctly called as the killer or the suicidal bag of the cell. But where do they get this superpower from? If you can recall, we discussed that vesicles bud out from the Golgi body and they remain scattered in the cytoplasm to form lysosomes. So these are normal vesicles that budded out from the Golgi body. Now Golgi body do not have any of these properties. So where did the lysosome get them from? Well, the secret behind this superpower is this fluid which is filled inside the lysosome. This fluid is hydrolytic in nature. We call it the hydrolytic enzyme that has an acidic pH. So that means it has the protease, lipase, carboxylase, phosphatase and so many other digesting enzymes inside this vesicle. And that makes them capable of digesting whatever they want to. Now imagine the glass jar in your chemistry lab that has concentrated acid in it. Now if you touch the glass jar, nothing will happen. But if this jar happens to break and the acid flows out and you happen to touch it, then your hand will burn. Same is the case with the lysosome. The concentrated acids are carefully packed in these vesicles and until and unless this vesicle breaks or bursts, nothing will happen. Now let's see how this lysosome works. Let us take the example of a macrophage which is roaming around in search of any invader. And look what he found, a bacteria. Now as soon as this macrophage comes in contact with an invader, it extends its arms. Like the pseudopodias of amoeba. And as soon as this bacteria is pulled inside the body, the lysosomal membrane will fuse with it. It will release its hydrolytic enzymes which is acidic that will kill the bacteria. Now apart from killing foreign invaders, the other job of lysosome is to maintain cell health. By this I mean if any of the organelle inside the cell is old or it is not working properly, the cell sends a signal to the lysosome to go and destroy that organelle. For example, let's imagine that one of the mitochondria is not functional. The lysosome will go and fuse with the membrane of mitochondria. It will release its lytic enzymes and destroy the entire organelle. And not just that, sometimes if a cell is heavily infected by foreign invaders, infected to an extent that it cannot be recovered or sometimes if a cell is old enough to die, then it is the lysosomes that breaks and kills the entire cell. And this different course of actions of lysosomes are given different names. For example, digesting one's own organelles are called autophagy. Digesting the entire cell which is called the programmed cell death or apoptosis. And digesting a foreign substance is called heterophagy. So this was all about the killer organelle or the suicidal bag which is the lysosome. Now let's move on to the last organelle of the endomembrane system which is the vacuole. Now on your screen is a plant cell and the big blue thing that you see inside is the vacuole. Now I want you to imagine this vacuole as a balloon. And what do you think will happen if I ask you to fill in more air in this balloon? Well the size of the balloon will increase and that will exert pressure on the walls of the cell, right? And if that happens, the cell size will increase, right? So this is exactly what the vacuole does inside the cell. Its main job is to maintain the cell shape. And again do you know that vacuole means empty but don't get fooled by its name because these vacuoles are nowhere near to empty because it is filled with a lot of stuff. The major portion of this vacuole is occupied by water. There is a huge amount of water inside this vacuole which we call the cell sap. Now the more water stored in this vacuole, the bigger the vacuole will be and the bigger will be the size of the cell. So as the vacuole grows, the cell grows, right? And apart from water, the cell stores almost anything it has in excess in this vacuoles. It acts both like a storage unit or like a dustbin. So the other major components that are seen in the vacuoles are a lot of ions. And apart from that, a lot of water soluble pigments like anthocyanin which gives the flower the purple color is seen stored in this vacuoles. And apart from that, all other waste products is stored in this vacuole because here, the more the merrier, the more stuff inside the vacuole, the larger the size will be and that will increase the size of the cell, right? Now all this stuff stored in the vacuole exerts a lot of pressure on the wall of the vacuole and the wall of the vacuole is called the tonoplast. Tono comes from the word tension. The tension that is always exerted by the stored substances in the vacuole. So here we saw that the vacuole acts like a storage unit. It provides structural support and also acts like a recycle bin. Now anything stored in this large vacuole which is also called the central vacuole in plants is utilized by the plant cell whenever there is stress or whenever there is unfavorable condition and there is not enough resources for the cells to grow. And also just like lysosomes, this central vacuole is also originated from the Golgi body. The vesicles that detach from the Golgi did not leave the cell and grow this big when it comes to plant cell and we call them the central vacuole. Now again this is not the only kind of vacuole that we get to see in living cells. There are other different kinds and one of them is called the food vacuole which we see in single cellular organisms and to explain it to you I have taken the help of amoeba. Now every time amoeba encounters food it extends its cell membrane around the food forming pseudopodias. So these are false food or pseudopodias that engulfs the food forming a food vacuole. So this vesicle kind of thing that has the food inside we call it the food vacuole. Now the food inside will be digested and whatever is required for the body will diffuse into the body and whatever is left is the waste product that needs to be excreted and for that the vacuole slowly moves towards the cell membrane fuses its membrane with the cell membrane and excretes the waste out. So this is what food vacuole is and it is very temporary as you saw it is formed only when the food is ingested. Alright so this was food vacuole. Now let's move on to another kind of vacuole which is called the contractile vacuole and we get to see them in single cellular organisms like amoeba and perimation. Now why do they need them? Well the single cellular organism do not have specific organs inside to ingest food and water. So the water moves inside the body through osmosis from the surrounding. So who controls how much water should go inside the cell? Because it is a living cell its concentration will be much higher than its surrounding right? So the water will tend to get inside the cell. But who regulates how much water should get inside? Well there is no proper regulatory system. The water keeps coming in but it has to be sent out. So as to maintain the fluid balance or we can call it the homeostasis inside the cell and that is done by vacuoles that are present inside the cell. So this tiny vacuole sucks up the excess water inside them. It swells up and gradually moves towards the cell membrane and just like how excess of food was excreted in food vacuole it excretes out or squeezes out excess of water from the cell. And then again contracts back to its original small size and that is why we call it the contractile vacuole. So the contractile vacuoles are nothing but the osmo regulators. Because it is this contractile vacuole that maintains a constant osmotic pressure and balances the salt and iron concentration inside the cell keeping it alive. So these are the different type of vacuoles that we see in living cell which is a part of the endomembrane system. So with this we have come to the end of the endomembrane system. So these are the four organelles that we discussed under the endomembrane system. They work in a coordinated fashion in order to help the cell perform and survive. These are the endoplasmic reticulum, the Golgi body, lysosome and the vacuoles.