The Effect of Different Sugar Concentrations on Potatoes

The Effect of Different Sugar Concentrations on Potatoes
Aim: To investigate the effect of different sugar concentrations on potatoes. Osmosis is defined as the net movement of water molecules from a region in which they are highly concentrated to a region in which they are less concentrated. This movement must take place across a partially permeable membrane such as a cell wall, which lets smaller molecules such as water through but does not allow bigger molecules to pass through. The diffusion of water molecules will continue until it reaches equilibrium. This means that the molecules are randomly distributed throughout, leaving no area of lower or higher concentration. Plant cells always have a strong cell wall surrounding the cell membrane. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become ?turgid? when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. On the other hand, when plant cells are placed in concentrated sugar solutions, they lose water by osmosis and become ?flaccid.?
This is exact opposite of ?turgid?. The contents of the potato cells shrink and pulls away from the cell wall. These cells are said to be ?plasmolysed?. In my experiment, I will analyse the effect of various concentrations of sugar solution on the potato slices and will use the following equipment: Equipment and Materials: ? Dried potatoes. ? Kitchen knife. ? Ruler. ? Test tube rack. ? Test tubes. ? Concentrated solutions. ? Measuring cylinder. ? Water. ? Balance scales. ? Stopwatch. ? Clean tile. ? Marker. ? Paper towels. To create a fair test conditions, certain aspects of the experiment will have to be kept the same whilst one key variable is changed. I chose to vary the concentration of sugar solution. This will give me a varied set of results from which I hope to make a positive conclusion. If any of the non-variables are not kept constant it would mean that it is not a fair test. For instance if one of the potato slices was 1cm longer, the surface area of the potato slice would be larger and there would be more space for osmosis to occur. Moreover, I will perform all tests at room temperature. The mass of the potato is a dependent variable, and this means that it will be measured throughout the experiment. I will measure the mass in grams. The potato slice will be measured before it is put in the solution, and after. This will allow me to see whether osmosis has taken place. The volume of the solution that the potato slices are kept in must be sufficient. They must be totally covered in the solution, and the amount of solution will be kept the same because all the potato slices are the same size. I am also going to use the same balance to weigh my potato slices. This is because the measurements may slightly vary between scales. While performing this experiment, I have to take a few precautions: 1. I have to keep all of the different non-variables the same. 2. Whilst cutting the potato, extreme care and precision has to be taken with the knife as it is very sharp and could easily cause a serious injury. 3. The measurement for the solutions has to be perfect as not to change the out come of the experiment. 4. I have to ensure that every time I handle the potatoes my hands are clean and dry. This stops any kind of contamination and ensures that I do not pass on any extra water onto the potatoes. For this investigation, I presume that the lower concentration of sugar solution will result in larger mass of the potato. This is because the water molecules pass from a high water concentration to a low concentration, into the potato slice. Therefore, the potato in higher water concentrations will have a larger mass than the potatoes in lower water concentrations. Before the actual experiment, I performed a preliminary test to get an idea of the results of actual and more accurate experiment. These preliminary results give me an overall idea on the potato mass gained or lost. Table 1 showing preliminary results. Concentration of solution Mass before(grams) Mass after(grams) % mass change 0.0m 1.66 1.74 4.81 0.25m 1.70 1.62 -4.70 0.50m 1.69 1.62 -4.14 0.75m 1.76 1.60 -9.09 1.0m 1.74 1.59 -8.62 The following is the average of the above results. Table 2 showing average % mass change of preliminary results. Concentration of solution Average % mass change 0.0m 4.94 0.25m -2.11 0.50m -5.16 0.75m -8.93 1.0m -9.66 [image] These results clearly show that as the concentration of the solution is increased, the percentage mass change decreases because of movement of water from areas of high concentration to lower concentration. I believe that my actual experiment results will look familiar to these ones. Method: ? I took two average sized healthy potatoes. ? Using a standard kitchen knife I peeled the potatoes and cut each one into an even block on a white tile. ? With a knife and ruler I cut the potato into slices which were 3 cm long. I had to be very careful whilst cutting the potato as the knife is exceptionally sharp. After slicing the potato I had 15 pieces. ? In a test tube rack I placed 5 test tubes and then labeled them different concentrations 0M, 0.25M, 0.5M, 0.75M and 1M. (Where M stands for concentration). ? After measuring out different amounts of sugar solution and water, I poured them into the test tubes in percentage strengths showing various concentrations. ? Then I weighed every potato slice on an electronic balance and recorded the mass. ? I placed 3 potato slices into each test tube and then started my stopwatch. Three slices were used to create an average which gave me a better set of results and more accurate graphs. ? Whilst waiting, I set out some paper towels for drying the slices and also drew up a basic table for my results. ? After 30 minutes I drained out the solutions in the sink and placed all the slices on the paper towel in the order I had put them in the test tubes as not to mix them up. ? I dried each slice with the paper towel. ? I recorded the final mass of the potato slices on the scales. ? To obtain reliable results, I repeated the whole experiment following identical steps. Results: Table 3 showing results at Concentration: 0.0M Mass before(grams) Mass after(grams) Change in mass(grams) %change in mass 1 1.46 1.52 0.06 4.10 2 1.64 1.75 0.11 6.70 3 1.72 1.85 0.13 7.55 R1 1.64 1.89 0.25 15.24 R2 1.63 1.85 0.22 13.49 R3 1.75 1.95 0.20 11.42 Av 1.64 1.80 0.16 9.75 R= repeat results Av= average Table 4 showing results at Concentration: 0.25M Mass before(grams) Mass after(grams) Change in mass(grams) %change in mass 1 1.56 1.46 -0.10 -6.41 2 1.66 1.64 -0.02 -1.20 3 1.60 1.61 0.01 0.62 R1 1.51 1.15 -0.36 -5.48 R2 1.63 1.68 0.05 3.06 R3 1.34 1.39 0.05 3.73 Av 1.55 1.48 -0.06 -2.41 R= repeat results Av= average Table 5 showing results at Concentration: 0.50M Mass before(grams) Mass after(grams) Change in mass(grams) %change in mass 1 1.65 1.45 -0.20 -12.12 2 1.66 1.52 -0.14 -8.43 3 1.88 1.71 -0.17 -9.04 R1 1.42 1.36 -0.06 -4.22 R2 1.66 1.51 -0.15 -9.03 R3 1.60 1.52 -0.08 -5.0 Av 1.64 1.51 -0.13 -7.97 R= repeat results Av= average Table 6 showing results at Concentration: 0.75M Mass before(grams) Mass after(grams) Change in mass(grams) %change in mass 1 1.64 1.36 -0.28 -17.07 2 1.49 1.34 -0.15 -10.06 3 1.87 1.74 -0.13 -6.95 R1 1.39 1.26 -0.13 -9.35 R2 1.80 1.63 -0.17 -9.44 R3 1.38 1.18 -0.20 -14.49 Av 1.59 1.41 -0.17 -11.23 R= repeat results Av= average Table 7 showing results at Concentration: 1.0 M Mass before(grams) Mass after(grams) Change in mass(grams) %change in mass 1 1.52 1.19 -0.33 -21.71 2 1.64 1.39 -0.25 -15.24 3 1.66 1.49 -0.17 -10.24 R1 1.61 1.46 -0.15 -9.31 R2 1.66 1.49 -0.17 -10.24 R3 1.56 1.42 -0.14 -8.97 Av 1.60 1.40 -0.20 -12.62 R= repeat results Av= average The table below shows averages of the results above in all concentrations. My graph will be plotted using this information. Table 8 showing average % mass change of final results. Concentration of solution Average % mass change 0.0m 9.75 0.25m -4.00 0.50m -7.97 0.75m -11.23 1.0m -12.62 [image] Analysis Point A demonstrates movement of water from area of high water concentration to a low water concentration (i.e. from solution to potato). Point B again shows movement of water from higher concentration to lower but in this case in the opposite direction (i.e. from potato to solution). The reason for this shift is lower concentration of water in the solution at point B. The change from point C to D is less significant because the cell is almost ?plasmolysed? and no more water can leave the cell. At point E there is an ?equilibrium? with no gain or loss of mass. At this point no more water can move in or out but it is equal on both sides of the cell. This graph shown above gives the line of best fit for the percentage change in mass of the potato slices over the course of the thirty minute experiment. The graph is a curve that slopes downwards and does not go through the origin because the line is not straight. It means that the percentage gain and loss in mass and concentration are not directly proportional. The gradient does change in my graph. It gets less steep as X axis values get bigger. There is a pattern on my graph, and this is, as the concentration of the solution increases, the percentage change in mass decreases. From the line of best fit that has been added in, it can be seen that all of my points were very close. This shows consistency in my results. This graph also closely follows my preliminary results and graph. The graph above shows a clear indication that there was an overall decrease in mass during the experiment. Looking at the first table of results, my repeat experiment has a large range of % mass increased. This may have been an inaccuracy of cutting the potato exactly perfect. Due to the inaccuracy, there may have been more osmosis occurred. At 0.0m all of the results follow the trend and fit the prediction. The results at 0.25m start to fall towards negative. This is a sign that osmosis is starting. At 0.5m all of the results are in negative. Majority of the results follow the prediction. At 0.75m all of the results follow the pattern. This is because of the extra precautions I took with cutting of the potato slices. At 0.75 the graph begins to become flat and there is not much steepness. This links back to the definition mentioned in the plan on how the water moves in different sugar solutions. Evaluation In my opinion the experiment is a success and confirms the aim of my investigation. Overall, I had only 3 out of 30 (10 %) anomalous findings. Ninety percent (27 out of 30) of the outcome are reliable. Therefore, the evidence is sufficient to draw the conclusion that ?increasing sugar concentration caused decreased average mass of the potato slices due to osmotic effect?. The 3 results which were not consistent are: Table 3- R1, Table 3 R2 and Table 4 R1. Although I am not certain about the exact reasons behind these anomalies, they may be due to slight variation in potato size or exact recording of mass. These might due to human error. Moreover, when the potato slices were removed from the test tubes and dried I may have dried some potatoes more thoroughly than others and so some would have excessive water, which would add to the mass. The experiment was a success in my opinion. I obtained a large quantity of accurate results from which I was able to create informative graphs. I believe that time that I spent for the experiment was enough to allow sufficient osmosis to occur. However, allowance of bit more time would have possibly found a point of saturation. In addition, I would possibly create more concentrations so that I could have more varied results, i.e. 0.10M, 1.15M, 1.20M, and so on. This procedure would have helped me to obtain a more accurate reading of the equilibrium point. If I get the opportunity to re-do the whole set of tests, certain improvements can be made. For example, I would possibly find a machine to cut the potato as it would ensure that all potatoes would be of same weight and dimensions. I would try to measure more accurately and I would also take great care to get a solution of specific concentrations. I could also weigh each slice on a more accurate scale, e.g. not to 0.00g but to 0.000g. I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. I think that the experiment was successful and I was very pleased with the complete comparison of my results with my initial prediction.

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