Investigating osmosis You will have probably studied this in potatoes, but remember it is the same in carrot, beetroot etc….. Osmosis Osmosis is the diffusion of water molecules, from a region where the water molecules are in higher concentration, to a region where they are in lower concentration, through a partially permeable membrane. A dilute solution contains a high concentration of water molecules, while a concentrated solution contains a low concentration of water molecules. Potatoes in this section of the graph have got bigger as water moves in by osmosis You will usually be investigating the effect of sugar concentration on the mass of the potatoes. Sugar solution is the independent variable. You will measure the mass before and after putting them in the solutions. As it is hard to get the potatoes the same size you will usually calculate a percentage % so you can compare them. Where the line crosses the x axis the potatoes are at the same concentration as the solution Potatoes in this section of the graph have got smaller as water moves out by osmosis In this diagram the water particles will move from left to right by osmosis. They move from left where there is a high concentration of water molecules to the right where there is a lower concentration of water molecules. Remember the sugar molecules do not move as they are too big to fit through the semi permeable membrane.

A B C Investigating osmosis in potatoes Write a definition of osmosis: What was the independent variable? (the thing the student changed) What variables were kept the same (controlled)? Why is change in mass given as a percentage? Why did the student repeat the results 3 times? Why was it important to dry the potatoes before the mass was recorded? What was the concentration inside the potato cells? In the diagram above what direction will the water particles move? Why? Now write a plan to investigate the effect of concentration on mass of potatoes. (6 marks) _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ A B C Which cell (A,B,C): Has lost water? Is turgid (full of water) Is sitting in pure water? Is sitting in concentrated sugar solution? Will increase in mass? Water has moved out of the cell by osmosis?