hello biologists and in today's session we are going to be looking at practical investigations to do with osmosis in the previous video we had a look at the theory of osmosis and some good terminology to do with how different solutions can impact on plants and animal cells if you do want to have a recap of that and the terminology used but for today i'm going to focus on one of the main experiments that you will get in your exam which is to do with how osmosis impacts on plant material now what they normally use here is some kind of a vegetable such as a carrot parsnip or a potato now in the experiment i'm going to show you today i've used a potato in this particular example and what they would normally do is cut your vegetable in this case potato into several different pieces and they would place these different pieces of potato into different concentrations of solutes it's normally sucrose concentration that they use for this and so when i'm cutting my potato pieces it's really important that my potato pieces are the same length and ideally from the same potato so that any solute concentrations in the cells should be the same so here are some control variables that are taken from your mark scheme so once i've got my potato pieces and the cuts are the same length um what i then need to do is prepare my solution so in this particular example i've just used pure water and have used water with 40 grams of dissolved sugar in it it's really important that these are the same volumes of solutions so i've used 150 milliliters in this particular example so before i put my potato cylinders into my solutions it's really important i have to weigh my potato cylinders before i put them into my solutions so that i can see the impact that these different solutions have on the mass so mass is what i'm measuring my dependent variable now i put my potato cylinders into my different solutions and it's really important that i keep them in there for the same length of time anything in their red box on this video is taken directly from your mart schemes after my time's up in this which case i've used 40 minutes for this particular example i need to take my potato pieces out and i dry them it is really really important that i dry my potato pieces or any vegetable you've used this experiment because i have to remove the excess water because water has mass and that water that mass that the water has will impact upon my results because that is what i'm measuring my dependent variable here is mass that is what i am measuring so here you can see my potato mass before i'm a potato mass after my investigations in the different solutions on this next slide here i've just put them into a table so it makes a little bit more sense now i've also calculated here the change in mass so my change in mass here my mass after take away my mass before as you can see here my mass here is positive because my potato cylinder has increased in mass so my change in mass in grams it increased by 0.06 grams my sugar solution my potato cylinder lost mass it went from 2.85 to 2.76 so it lost mass so it's a negative number here it's also important that i calculate a percentage change in mass using this formula here so the way i interpret this is the change over the original times 100 so my change divided by my original and then i times by 100 to get 2.19 so here are my percentage changes in mass really important use percentage change in mass because it takes into consideration the starting masses potatoes here have different starting matters it's very very difficult to get your potatoes or vegetables whatever you use into the same mass so by using percentage change in mass it takes into consideration that starting mass of the potato so in sugar solution and my potato lost weight but in distilled water my potato gained weight and here are my explanations as to why now if you want in more information on this please look at the previous video which explains this in a lot more detail but this is for in a red box it's taken from me matsky now other questions that i have seen on osmosis are things like this so in this particular experiment as you can see here they've looked at the mass percentage change in mass of potato at different concentrations of sucrose concentration and what i have seen in exams is they ask you to how can i use this information to determine the water potential of the potato cells and in order to do that you would have to have a look at where this line crosses my x-axis which in this case is 0.3 what you would then do is have a look at this on a table of known potentials so in this case my water potential of my cells is here