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The Concentration inside Potato Cells

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Introduction

The Concentration inside Potato Cells Aim To find the concentration of the inside of potato cells. Prediction and Background Knowledge It is hard to make a prediction about what the concentration of the potato cells will be until I have completed my preliminary experiment. By looking at my background knowledge I can see a general idea what will happen during the experiment. Theory of osmosis: Osmosis is the process by which water molecules move from an area of a low solute concentration to an area of high solute concentration through a semi-permeable membrane to balance out a concentration gradient. When the concentration gradient has been balanced out this is called an equilibrium. Encarta 98 says that osmosis is "the flow of one constituent of a solution through a semi-permeable membrane while the other constituents are blocked and unable to pass through the membrane". In my experiment the particles that will pass through the semi-permeable membrane of the potato cells are water particles and the particles that are blocked from passing through the semi-permeable membrane are the sodium chloride particles. Osmosis can work both ways and water is being lost from the potato but the net movement happens with water going into the potato, as shown in the diagram above. When osmosis occurs in the potato cells the potato gains water and therefore its mass increases as does its length. The potato cells become turgid and swollen which causes in increase in length and mass, as shown in the diagram: When turgid, the cells no longer take on water by osmosis as they are full. This is the normal state for cells to be in. ...read more.

Middle

I took a normal raisin and sketched a rough drawing of it. I then placed it in a dish of water and left it for 24 hours. I then took it out and drew the raisin with its new look. Here is the raisin before, and after: Osmosis has taken place here because the sugar concentration inside the raisin is very high so water is taken on by osmosis to balance out the concentration gradient. The cell walls around the raisin cells prevent the raisin from bursting although it is very swollen. Prediction: From looking at my preliminary results I predict the concentration of the potato cells to be between 0.00M and 0.2M. Real Experiment Apparatus * 1 large potato * 8 boiling tubes * 2 test tube racks * 20cm� of 0.00M sodium chloride (distilled water) * 20cm� of 0.05M sodium chloride * 20cm� of 0.10M sodium chloride * 20cm� of 0.15M sodium chloride * 20cm� of 0.20M sodium chloride * 20cm� of 0.40M sodium chloride * 20cm� of 0.60M sodium chloride * 20cm� of 0.80M sodium chloride * 30cm ruler * knife * top pan balance (reads to 2dp) * tissue paper * corer (5mm) * plastic forceps * 25cm� measuring cylinder * tile * stopwatch Diagram Sodium chloride solutions containing potato cores: 0.00M 0.05M 0.10M 0.15M 0.20M 0.40M 0.60M Method I will set up the apparatus as shown in the diagram. Using a 5mm corer I will cut six cores of potato from the same potato. I will weigh the cores on a pan balance and measure them with a ruler. I will cut them to be the same mass and length if they need it using the knife. ...read more.

Conclusion

Two points are slightly away from my line of best fit and one result is anomalous in my table showing the 1st set of results (however this didn't affect percentage changes). I may have these anomalous results because there was a difference in the surface area of the potato that was uncovered. This was because some potato cores had to be cut down to make their mass the same. A higher surface area would mean more osmosis could take place in a shorter time. Another reason to explain my anomalous results is that the accuracy in the concentrations of the sodium chloride may have differed on the days I did the experiment. The solution may have been made up wrongly before I started to use it. My results are good enough to make a firm conclusion about the experiment because I did all I could to lessen the effects of factors such as mass and surface area on my results. I made sure that the mass wasn't affected by excess sodium chloride solution by drying it with a piece of tissue before weighing it. To improve my results I could take the temperature of the sodium chloride solution and take all my results on the same day so mistakes in the concentration of the sodium chloride are constant. To extend this investigation further I could use more concentrations between 0.15M and 0.20M to check my result and be even more accurate. I could use different types of potato to see how their concentrations compare or I could use a different sized corer to cut the potato. 1 Ami Broughton 11K ...read more.

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