so now that we have introduced osmosis as a concept what we're going to do is we're going to be talking a little bit about how osmosis can have an effect on animal cells you see if I were to just draw out the animal cell here I'm not going to draw out the the nucleus Golgi apparatus ER and such you can just see the cell surface membrane and the purple color highlight is just the cytoplasm of the cell it is very important to know that the cytoplasm contains dissolved substances you see yes the cytoplasm is made up of water but it will also contain solutes within itself as well such as glucose salts amino acids and so on so the water potential of the cytoplasm cannot be zero kilopascals because if you remember a water potential of zero kilopascal is only possible with distilled water because it does not have any solutes in there and the cytoplasm is not just made out of distilled water it contains water and dissolved substances so the water potential of the cytoplasm is probably going to be a negative value because as I've mentioned before the more solutes there are inside the solution the water potential will decrease so for the sake of today's video I am going to say that the water potential of the animal cell is negative 300 kilopascals you do not need to memorize this because different types of animal cells will have different water potential I am just choosing negative 300 for the sake of this video so what will happen if we were to immerse the animal cells in three different types of solution if we immerse the animal cell in distilled water with the water potential of zero kilopascals dilute salt solution for example water potential of negative 300 kilopascal and concentrated salt solution in water potential of negative 700 kilopascals so again I don't need you to memorize all these values these are just values that I am choosing except distal water because distilled water does have a water potential of zero kilopascals because it doesn't have any dissolved substances in it so if you were to immerse the animal cell into these three different types of solution will anything happen to the animal cell the answer is yes a lot of things can actually happen to the animal cell in fact sometimes it can cause harm to the cells so what do I mean by that let's look at the first one in the first one if I were to immerse the animal cell in distilled water remember the animal cell has a water potential of negative 300 kilopascals and the distal water which is surrounding the cell has a water potential of zero kilopascals so the first thing that you have to do is you have to determine which area has a more negative water potential and less negative water potential so the cytoplasms water potential is more negative and the distal water has a less negative water potential osmosis is what happens when water molecules move from an area of less negative to more negative water potential or a higher to lower water potential and when water rushes into the cell the water molecules are trying to equilibrate the water potential inside and outside the cell but the problem is when too much water rushes into the cell pressure within the cell increases and the cell fills up like a balloon and what will actually happen is it may burst and if it bursts the cell is dead that is why distilled water can be quite dangerous if we were to inject it directly into our veins because it may cause the cells in our body to swell and burst it's not a good idea to give dehydrated patients just distilled water through an intravenous infusion of course some students will ask can I drink distilled water well you can bring distilled water but most of the time even if you were to drink a lot of distilled water your body will control how much water is absorbed and most of the time you will urinate the excess water out the danger is what happens if in the hospital they were to inject distilled water directly into your veins because the water can actually directly cause the cells to burst and we don't want that to happen in the next diagram we would see what happens if you put the cell in a concentrated salt solution so the cell again it has negative 300 kilopascals in its water potential but the solution outside the cell is negative 700 kilopascals in this case the cytoplasms water potential is less negative and the concentrated Salt Solutions water potential is more negative again osmosis is net movement of water from a less negative water potential to a more negative water potential in this case water rushes out of the cell and if water rushes out of the cell the cell loses the volume of its cytoplasm in the cell May shrink why is this dangerous because the cells are losing water we I mean you know for the fact that we need water to survive so if our cells are deprived of water the cell will die of course some students will ask why does the cell die if it has a lack of water well you see a lot of chemical reactions that happen in your cell require water as a reacted for example hydrolysis of proteins hypolysis of carbohydrates or of lipids they require water to break down the covalent bonds so if there's no water important chemical reactions such as this may not be able to happen and if that's the case the cell may die if you were to immerse the cell in let's say a dilute salt solution notice that here the water potential inside the cell and the water potential outside the cell which is the salt solution are equal so in this case will osmosis happen osmosis will not happen because there won't be a net movement of water either into the cell or out of the cell it is very important to know that water is still moving in and out of the cell but at an equal rate which means the amount of water going into the cell and the amount of water going out of the cell is the same therefore will the cell expand or Shrink it will neither shrink nor expand because there is no net change in the volume of the cytoplasm so in this situation over here it's very important to know that osmosis is no longer taking place imagine if you're the doctor and a patient comes to the hospital and they are extremely dehydrated they can be dehydrated due to you know they were lost in the jungle and they did not have enough water or they had food poisoning and they had very bad diarrhea or they can also have an infectious disease known as cholera which we will see in chapter 10 by the way and in cholera it may cause the person to have such severe diarrhea that they do not have enough water in their body in that case as a doctor the most important thing is you will have to rehydrate the patient using something called intravenous therapy IV or intravenous therapy is what happens when you poke a needle into the patient's vein connected to a bag of liquid and the liquid flows directly into the vein and rehydrates the patient but of course if the patient is dehydrated where they have a lack of water what kind of liquid should be inside the bag it cannot be pure water or distilled water of course then students will go wait the patient is dehydrated they don't have enough water so I should give them pure water no if you give them pure water or distal water you might kill them because remember when you give this to water distilled water has a water potential of zero kilopascals it may go directly into the cells of the patient and may cause the cells to swell or burst what we do in hospitals usually is we give something called 0.9 sodium chloride solution don't need to memorize this but it's just good to know also referred to as a normal saline solution the normal saline solution is interesting because the normal saline solution has a water potential equal to the cell cytoplasm so even if you were to inject normal saline solution into the patient osmosis will not damage the cell either causing it to shrink or causing it to burst neither will happen so you are able to rehydrate the patient without causing any severe damage to the patient's cells that is why in dehydrated patients it is important not to just give pure water but also add about 0.9 percent sodium chloride inside to prevent osmosis from damaging the cells