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# Osmosis investigation

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Introduction

Biology Coursework: an investigation to show how sucrose concentration effects the mass change of a potato chip by osmosis. Planning: Aim: My aim is to see how the concentration of sucrose solution affects the rate and direction of osmosis in a potato chip. I want to find the point at which there is no net movement between a sucrose solution and potato chip. This is where the concentration is the same and the particles reach equilibrium, following the idea of osmosis. I will do this by testing the change in mass of potato chips after being in a number of solutions with different concentrations. Variables: My independent variable is to be changed in order to find the point where there is no net movement between the solution and the potato chip; this is the concentration and it will be measured in Molars. My dependant variable is the percentage change in mass from the potato chip before it was placed in any solution, to the mass after it has been placed in the solution for a certain amount of time. If the percentage change is 0, then equilibrium has been reached. Because I am measuring osmosis, I will try and keep constant the other factors that affect osmosis. These are called control variables and will remain the same throughout in order to keep my test fair. I will use potato chips from the same potato, because different potatoes have different sugar levels and therefore may react differently in osmosis. I will leave my potatoes in the solutions of sucrose for the same amount of time so osmosis can happen for equal lengths of times, producing more accurate results and I will keep my method constant throughout the experiment. This means that I will cut my potatoes equally, dry them off before weighing them the same way and also weigh them the same way, recording the results to a same amount of decimal places. ...read more.

Middle

I followed this simple formula: Repeat 1 + repeat 2 + repeat 2 3 All of my results are to 2 decimal places as this allows precision when plotting a graph and also the scales were to 2 d.p. And I wanted my results to have a consistent number of decimal places. My graph is attached at the back. It shows a curve. Statement conclusion: At lower concentrations, mass was gained because the water outside the chip moves into areas of high potential- inside the potato. At higher concentration, mass is lost because there is higher water potential outside the potato so water moves out of the potato. I know that osmosis is the net movement of water across a partially permeable membrane from areas of high water potential (low concentration) to areas of low water potential (high concentration) until equilibrium is reached. I also know that at different sucrose concentrations there is a different rate and direction of osmosis, this is reflected by my results. At 0.0m when sucrose concentration increases, the percentage mass gain is very large 20.34%. This falls to an increase of only 12.12 %at the 0.2Molar concentration. At 0.4m, the mass change is only 1.04%, showing that equilibrium is nearly reached. After this point, the mass begins to decrease. At a concentration of 0.6Molar, there is a mass decrease of -11.04%, very high. The decrease continues to fall but not as rapidly as it was at the lower concentrations and at 0.8m; the mass change is -16.63%, continuing onto -18.86% at 1.0m. At 0.0Molar, there is no sucrose present because the solution is just 30ml3 of tap water. This means the water concentration is higher outside of the potato chip so water goes into the potato chips cells through the partially permeable membrane. This means mass is gained inside the chip and the cells become turgid because water makes the cell swell up and pushes against the cell wall until the cell cannot hold any more. ...read more.

Conclusion

In lower concentrations, where there was mass gain, the chips became large and affected by turgor making them swell and take up more room thus there was more surface area available and when the chip was larger, osmosis was greater. However, in the larger chips, there was more clustering in the boiling tubes and some surface area was covered which hindered osmosis as it cannot take place in covered areas. The chips in low concentrations may also have results affected by surface area. Unlike in higher concentrations, there was mass loss and so the potatoes decreased in size, which decreased the surface area for osmosis to work. If I were to redo my experiment, I would have 18 different boiling tubes with every one chip in one boiling tube so that they had the maximum surface area on display. However, in higher concentrations, the chips floated and so the surface area was limited for osmosis to work on. Not all of the chip was in contact with the water and this may have explained why in 0.8Molar and 1.0Molar there is such a small difference in mass loss between the two. If I were to redo the experiment I would try and find a way of stopping the chips from floating and making all their surface area be in contact with the water. In order to expand my knowledge and further my work I could investigate other things that affect osmosis, not just the concentration of a solution. I could investigate the time a chip is left in a solution of x Molar and then see what the relationship is between time and mass change. I could also look at temperatures because in this investigation the temperature was constantly at room temperature. Other areas I could possibly focus on are surface area of the chips because I know that the larger the surface area, the more osmosis takes place. I could also maybe use a salt solution and see its effects when the chips are put in it and then compare it to the sucrose solution. ?? ?? ?? ?? Celia Jones 10F ...read more.

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