Osmosis: Potato and Sucrose Solution

Investigation of Factors Affect Osmosis in Potatoes Aim The aim of the following experiment was to investigate the effect of  varying the concentration of sucrose solution on osmosis in a potato. Preliminary Experiments One preliminary experiment was done before the main experiment. From  the preliminary, we were trying to find out how osmosis actually  occurred in potatoes, and gave us a vague idea on what the main  experiment would be like. This preliminary will aid my prediction, which is stated below.

The  following apparatus was used for the preliminary: 1 large potato (skin intact) * 3 boiling tubes * Set of cork borers * Scalpel * Balance (accurate to 2 decimal places) * Distilled water * 0. 5M sucrose solution * 1. 0M sucrose solution * Dropping pipette * Boiling tube rack * Measuring cylinder (accurate to 1cm3) * White tile Take a large uncooked potato, with the skin still on, and with the  cork borer, cut out three "tubes" of potato. Do this onto a white  tile, so you don't cut your fingers or wreck the bench.

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Take a ruler  and measure these tubes, and, if necessary, cut off any excess until  they are all the same length.

The same potato must be used; otherwise  it will not be a fair test (because different potatoes may have  different osmotic properties). To ensure the experiment is as safe as possible, ensure you don't  injure yourself using the cork borers. Also, we are using a sharp  knife, so caution is needed there. Even though the sucrose solutions  aren't poisonous, we are not 100% sure, therefore no sucrose solution  will enter us.

Weigh the three tubes of potato, and record down the mass. Take the  three boiling tubes, and fill 1 with 10cm3 of 1M sucrose solution, one  with 10cm3 0. M sucrose solution and one with 10cm3 of distilled  water. Label each tube clearly, then drop each potato tube into each boiling  tube, one tube per boiling tube. Place the boiling tubes in a rack and  leave for 24 hours. After 24 hours, drain the solution and dry off any excess solution  with paper towels from the potato. Then, reweigh the tubes, and  calculate the percentage change: These are the results from the preliminary: Tube Start Length (cm) End Length (cm) % Change A (water) 4 4. 2 5 B 4 4. 1 2. 5 C 4 4. 3 7. 5 D (sucrose) 4 3. 6 -10 E 4 3. 5 -12. 5 F 4 3. 7 -7. These results show clear evidence of osmosis. In tubes D-F, water was  lost (hence the potato chips decreased in size) because the water  potential is lower, therefore water moves down the concentration  gradient into the sucrose solution. In A-C, water was gained because  the water potential is higher, therefore water moves up the  concentration into the potato. Although the above results show clear evidence that osmosis has  occurred, it is difficult to draw an conclusion from these results. The primary reason for this is because we didn't take any repeat  results.

A better preliminary would be to do 3 tests for each  concentration, then take a repeat. Prediction I alreeady know that osmosis is the net movement of water molecules  from a weaker solution into a stronger solution, through a partially  permeable membrane. In this case, the tiny holes in the membrane of  the potatoes will allow the water molecules to pass through in and out  of the solution and the potato, depending on the concentration of the  sucrose solution. When the water concentration is lower in the tissue, the water will go  inside the tissue of the potato, and the potato will gain weight.

If  there is very little difference in the two water concentrations, there  should not be a big change in weight. If there is a higher  concentration of water in the potato, the water will go out of the  potato through the membrane by osmosis. In the distilled water, I think that the water is more concentrated in  the potato, and therefore the water should transfer from the water to  the potato, making the potato bigger in size, and heavier in weight. With the potato in molar solutions of sucrose, I do not think there  will be much change in the weight of the potato. This is because there  is not much difference between the two substances.

I believe that the  weight and the size of the potato will not be altered much. The 1. 0M solutions of sucrose, similar to the 0. 5M solution of sucrose  should produce similar results. The 1. 25M solution of sucrose, I  think, should make a big difference now, noting that it should be a  large difference between the two concentration gradients. The weight  should decrease. The difference between the water concentration in the potato and the  2M solution of sucrose is big, so the water in the potato should be  transferred from the potato, through the permeable membrane, to the  solution surrounding the potato by osmosis.

Therefore, the weight of  the potato will increase greatly. The potato tissues are surrounded by  a stronger solution, therefore it will probably shrink. However,  because of such high concentrations of sucrose, the water can diffuse  all the way, throughout the two substances, equalling the concentration gradient of the two substances. I think that in this experiment, the weight of the potato will start  decreasing when it is tested on 0. 5M solutions of sucrose and greater  due to the difference in the water concentrations of the two  substances. Equipment List 18 standard test-tubes to hold the sucrose solution plus the potato. * 5cm3 syringe (accurate to 0. 5cm3) - to accuratly measure the sucrose  solution. * Distilled water - for the 0M test, and to make up other concentrations. * A standard potato - to provide the chips. * Cork borers - to bore chips out of the potato. * Test tube racks - to hold the test tubes. * 1M sucrose solution - for the 1M test. * Beaker - to stand test-tubes in that won't fit into the rack. * Scalpal - to cut the potato. * Sticky labels - to label the tubes so you can distinguish which tube  holds which concentration. White tile - to cut the potato onto. * Forceps (broad point) - to pick up the chips of potato off the table  and drop them into the beaker. * Ruler (accurate to 1mm) - to measure the chips. Safety Safety is a primary factor in this experiment. We are using a scalpel,  which has the potential to harm people. Therefore, we will take great  care with the scalpel, and always cut onto a white tile. This avoids  cutting your fingers, and it also avoids wrecking the bench. Cork  borers can cut skin as well, so we must take care with these as well. We will always cut onto a white tile.

Although the sucrose solutions are harmless, we will ensure that no  liquid enters our bodies internally, as there may be other chemicals  in the solution. The solution has been prepared in a scientific  environment, not a sterile one. Method Take 18 clean test tubes and label them. Use any suitable labelling  method, but label them with the concentration and the test tube  name/number. Take a potato, and, using the cork borer, cut out 18  tubes of potato and place them in a beaker of water, ensuring that  they don't dry up during the preperation time. Prepare the sucrose solutions. I am testing 6 different oncentrations, O, O. 25, 0. 5, 0. 75, 1 and 1. 25M. The 0M is just  distilled water. To prepare the different concentrations of solutions,  just mix up sucrose solution and water in different ratios. In each  test tube, there should be 5cm3 of solution. Make sure all the potato chips are all a universal size. Measure them  out on a ruler and cut off any excess using the scalpel. Fill each  test tube with the solution (there should be 18 test tubes, with 3  test tubes of the same solution - this allows an average). Take the potatoes out of the water and dry them off using a paper  towel.

Weigh each potato tube, and write this result down in a table. Leave the potato tubes for 24 hours, in a place where it cannot be  disturbed, then, re-weigh the potato tubes and record the results down  in a table. Width (mm) Length (mm) Mass (g) Concentration Before After Before After Before After 0M 5 8 33 36 0. 57 0. 48 0. 25M 5 8 33 35 0. 72 0. 91 0. 5M 5 7 33 35 0. 64 0. 71 0. 75M 5 6 33 32 0. 73 0. 81 1M 5 4 33 34 0. 65 0. 68 1. 25M 5 4 33 30 0. 68 0. 85 Concentration Average change in Width (mm) Average change in Length (mm) Average change in Weight (g) 0M 3 3 0. 09 0. 25M 3 2 . 19 0. 5M 2 2 0. 07 0. 75M 1 1 0. 08 1M 1 1 0. 03 1. 25M 1 3 0. 17 Concentration Percentage Change In Mass (%) 0M -9 0. 25M +19 0. 5M +7 0. 75M +8 1M +3 1. 25M +17 Analysis This graph shown on the previous page gives the line of best fit for  the percentage change in mass of the potato chips over the course of  the 24-hour experiment. The graph is a curve that slopes downwards and  does not go through the origin. Because the line is not straight and  does not pass through the origin, it means that the percentage gain  and loss in mass and concentration are not directly proportional.

However, there is a pattern on my graph, and this is, as the  concentration of the solution increases, the percentage change in mass  decreases. The graph shows that the percentage gain and loss in  inversely proportional to the concentration. The gradient does change  in my graph. It gets less steep as X axis gets bigger. From the line  of best fit that has been added in, it can be seen that some of my  points were very close to creating a perfectly smooth curve (there are  a few anomilies, which are circled). This shows that my results are  fairly reliable, but 100% accurate.

It shows that the potato cells increase in mass in solutions with a  high water concentration and decrease in mass in solutions with a low  water concentration. My results also match with my initial  predictions. This graph of the change in mass helps prove the point of complete  plasmolysis, whereby the potato cannot expand and take in any more  water. As you can see as the molar concentration increases the change  in mass decreases. From right to left the first two points on the  graph are very spread out indicating that there was a large change in  the mass.

This decreases throughout the increasing molar concentration  until the change is minuscule (about 0. 02g). This graph above shows a clear indication that there was an overall  decrease in mass during the experiment. At the point 0. 00 M the line  for after the experiment is above the line for before the experiment  unlike any of the others. This is because the water potential of the  sugar solution is higher than that of the potato chip. Evaluation The experiment was very successful in my opinion. I obtained a large  quantity of very accurate results from which I was able to create an  informative graph.

I think I took easily enough results for the amount  of concentrations that I was using, and the time that I used for the  experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I might well increase the  time of the result to allow more osmosis to happen and possibly find  out the saturation point of the chips. The range of concentrations was  adequate but I would possibly create more concentrations if I repeated  the experiment so that I would have more varied results, i. e. 0. 0m,  1. 15m, 1. 20m, and so on. The cutting of the potatoes was the most difficult part of the  experiment as although I was recording my results by mass, it could  well have affected the surface area and so the overall rate of  osmosis. If I were to repeat the experiment I would have possibly  found a machine to cut the potato as it would ensure that all potatoes  would be the same weight and dimensions. As well as the potato I could  have found a more accurate way to measure out the solutions and to  determine the molar concentrations.

Perhaps I could have used a  burette. This would ensure that I have an accurate amount of fluid in  each test tube. I could also weigh each chip on a more accurate scale,  e. g. not to 2 decimal places but to 3 decimal places. There were not any out of the ordinary results, but some were not as  close to the line as others. This may have been caused by human error. With all this said I think that the experiment was truly successful  and I was very pleased with the complete comparison of my results with  my initial prediction.