[Music] hi I'm welcome back for three science lessons co uk by the end of this video you should be able to describe how to investigate the effect of osmosis on plant tissue you should then be able to calculate percentage change this is a required practical so it's important that you learn the details in the last video we looked at osmosis we saw that osmosis is a diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane we saw that when a plants are placed in water then water will move into the cell by osmosis and the cell will expand like this however if we place a plant cell into a concentrated solution then water moves out of the plant cell by osmosis and this causes the cell to shrink so in this video we'll look at how to investigate the effect of osmosis on plant tissue the plan that we usually use is a potato but this also works well using other vegetables such as beetroot or parsnip first we peel the potato but because the potato skin can affect osmosis next we use a cork board to produce three cylinders of potato using a cork board makes all of the cylinders the same diameter we then use a scalpel to trim the cylinders to the same length around three centimeters is a good value if we use shorter cylinders then we might not be able to measure the effect of osmosis next we measure the length of each cylinder using the ruler on the mass of each cylinder using a balance we now place each cylinder into a test tube we then add 10 centimeters cubed of an 0.5 molar sugar solution to the first test tube like this we then are 10 centimeters cubed of Nohr 22 5 molar sugar solution to the second test tube and then find the 10 centimeters cubed of distilled water to the third test tube the reason that we use distilled water rather than tap water is because distilled water contains no dissolved substances and they could affect the weight of osmosis we now leave the potato simmers overnight to allow us Moses to take place next we remove the potato cylinders and we gently roll them on paper towel this removes any surface moisture it's really important at this stage not to press on the cylinders we want to remove surface water but not force water out of the cells finally we measure the length on the mass of the cylinders again this stage we need to calculate the percentage change in length and mass so we're going to look at that now to calculate percentage change we use this equation the percentage change equals the change in value divided by the original value multiplied by 100 now you're not given this equation in the exam so you need to learn it here's a sample question the potato cylinder has a starting mass of 1.5 6 grams this increases by not 0.25 grams calculate the percentage increase so pause the video now and try this yourself ok so the change in mass is not 0.25 grams and the original mass is 1.5 6 grams putting these into the equation gives us a percentage change of plus 16 point zero 3 percent to two decimal places here's another question for you to try a potato sound has a starting mass of 1 point 3 2 grams this decreases by naught point one nine grams calculate the percentage decrease pause the video and try this yourself okay so the change in mass was - naught point one nine grams um the original mass was one point three two grams putting these into the equation give us a percentage change of minus fourteen point three nine percent to two decimal places okay so now we can plot a graph of the percentage changes in mass or length against the concentration of the sugar solution we get a graph that looks like this in water the potato cylinder gains mass as water moves in by osmosis in concentrated sugar solution the cylinder loses mass as water moves out by osmosis now where the line crosses the x axis there is no change in mass that's because the concentration outside the cell is the same as the concentration inside so no overall osmosis takes place so this concentration is the approximate concentration inside the cell remember you'll find plenty of questions on this required practical in my vision workbook and you can get that by clicking on the link above okay so hopefully now you should be able to describe how to investigate the effect of osmosis on plant tissue you should then be able to calculate percentage change [Music]