[Music] hi and welcome back to three science lessons co uk by the end of this video you should be able to describe what's meant by osmosis you should then be able to describe the effect of osmosis on animal and plant cells in the last couple of videos we've looked at diffusion remember that diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration so in this cell we can see a higher concentration of oxygen outside the cell than inside this means that oxygen diffuses into the cell like this so in this video we're looking at osmosis I'm showing you the definition of osmosis here osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane now back inside a bit tricky so I'm going to start by going through some basic ideas I'm showing you here a dilute sugar solution so we've got sugar molecules and water molecules as you can see in dilute solutions we've got a lot of water scientists would say that dilute solutions contain a high concentration of water this shows you a concentrated sugar solution as you can see in concentrated solutions we don't have a lot of water scientists would say that concentrated solutions contain a low concentration of water here I've taken the two solutions and I've separated them using a partially permeable membrane partially permeable membranes allows some molecules to pass through but not all molecules so this membrane allows water molecules to pass through but not sugar molecules so what we've got is a higher concentration of water on the left-hand side and a lower concentration of water on the right-hand side that means that the water now diffuses from the left-hand side to the right-hand side like this so as Moses is simply the diffusion of water now as Moses can have major effect on cells so let's look at now I'm showing an animal cell here and this brings us to a key point the cytoplasm of cells is a relatively concentrated solution in other words it contains a relatively low concentration of water if we place this cell in water then osmosis will take place water will move by osmosis from outside the cell to inside the cell like this now in the case of an animal cell the water moving in will cause the cell to expand and it could even burst if we place an animal cell in a very concentrated solution then water will move out of the cell by osmosis and the cell will shrink like this I'm showing you a plant cell here if we place a plant cell in water then again water will move into the cell by osmosis and the cell will expand like this now the key point here is that the cell wall prevents the plant cell from bursting instead the cell becomes swollen and scientists call this turgid if we place the plant cell into a concentrated solution then water moves out of the plant cell by osmosis like this this causes the cell to shrink scientists say that the cell has become flaccid remember you'll find plenty of questions on osmosis in my vision workbook and you can get that by click on the link above ok so hopefully now you should be able to describe what's meant by osmosis you should then be able to describe the effect of osmosis on animal and plant cells [Music]