Osmosis in a Potato

Osmosis in a Potato
Aim The aim of this experiment is to find out what concentration solution of sucrose a piece of potato can be placed in, so that no water is lost or gained by the potato cells. Prediction The solution can not be 100% sucrose concentration, because the potato will become plasmolysed or flaccid due to the lack of water. The solution can not be 100% concentration water because this will cause the potato to become turgid. I predict that the concentration will be close to 50%, more specifically, in between a concentration of 60% sucrose and 40% sucrose. In the preliminary experiments that were carried out, the potato, which was placed in the 50% concentration sucrose solution, gained water. Scientific Knowledge Osmosis is the movement of water molecules from a weaker solution, to a stronger solution, down the concentration gradient. This occurs through a partially permeable membrane. This continues until dynamic equilibrium is reached. Equilibrium is the state of both of the solutions having an equal concentration. After equilibrium is reached, water particles keep moving, however, they move very quickly, so there is no net movement.
Hypertonic solution is a strong solution in which the concentrations of the cell contents are lower than the concentration of the solution. When a plant cell is placed in a hypertonic solution, water diffuses out of the cell and the cell becomes flaccid (floppy). In the case of animal cells, the cell shrivels up. In an incredibly hypertonic solution, a plant cell would become plasmolysed (cell membrane would rip away from the cell wall). The cell is killed when it is plasmolysed. -A hypertonic solution has increased solute, and a net movement of water outside causing the cell to shrink. Hypotonic solution is a weak solution in which the concentration of the solution is lower than the concentration of the cell content. When a plant cell is placed in a hypotonic solution, the cells fill up with water, and become turgid, as the cell wall is pushed outwards due to pressure. With an animal cell, there is no cellulose cell wall, so the animal cell would burst due to the pressure. A hypotonic solution has decreased solute concentration, and a net movement of water inside the cell, causing swelling or breakage. An isotonic solution is a solution where there is no net movement of water, as the concentration of cell contents is equal to the concentration of dissolved solids. [image] If the solution is isotonic relative to the cell, then the solute concentrations are the same on both sides of the membrane and water moves equally in both directions Apparatus Used Distilled Water ? Used in the solutions, mixed with sucrose. Cardboard ? Used to ensure that the potato pieces are kept separate, therefore keeping the test fair. Petri Dish ? Used to hold the pieces of potato, without the potato pieces touching each other and affecting the experiment. Cork Borer ? In order to ensure that all the potato pieces have the same surface area/diameter. Electric Balance ? used to weigh the potato pieces as accurately as possible (to 2dp). Sucrose solution ? different concentrations of this will be added to water to gain the solution needed for each part of the experiment. Potato pieces ? Basis of the experiment, used to see what concentration of sucrose is needed to achieve the isotonic point. Syringe ? Measures the amount of sucrose added to the water to make the solution. Measuring cylinder ? Measures the amount of water added to the sucrose solution to make up the final solution. Method [image] Nine petri dishes are to be labelled with their corresponding numbers, containing 40ml of solution. In each dish, a different concentration of sucrose solution should be placed. The solutions and their respective dishes are shown below: Petri Dish One: 50% sucrose concentration (20ml sucrose ? 20ml water) Petri Dish Two: 100% sucrose concentration (40ml sucrose ? 0ml water) Petri Dish Three: 0% sucrose concentration (0ml sucrose ? 40 ml water) Petri Dish Four: 75% sucrose concentration (30 ml sucrose ? 10 ml water) Petri Dish Five: 25% sucrose concentration (10 ml sucrose ? 30 ml water) Petri Dish Six: 60% sucrose concentration (24 ml sucrose ? 16 ml water) Petri Dish Seven: 40% sucrose concentration (16 ml sucrose ? 24 ml water) Petri Dish Eight: 65% sucrose concentration (26 ml sucrose ? 14 ml water) Petri Dish Nine 35% sucrose concentration (14 ml sucrose ? 26 ml water) Potatoes are to be cut into 27 identical cylinders with the cork borer. These cylinders should be weighed accurately with a balance, and the relative information recorded into a result table. Three pieces of potato (A, B and C) should be placed evenly spaced, into each petri dish. Red pigment cardboard is to be used to separate the potato pieces into their own sections, which is labelled on the dish with a marker, so that each potato piece can be identified at the end of the experiment. Clingfilm should placed over the petri dishes, preventing the evaporation of the sucrose solution, and effect from other outside factors. This is done so that the concentration of the solution does not change, and so that all nine petri dishes are in an identical environment to keep the experiment fair. The petri dishes should then be left overnight. In an idyllic situation, the mass of the potato cylinders would be checked hourly, but as this is not possible, the mass should be checked after 24 hours. These masses are to be recorded in the table below. Fair Testing ==== The concentration gradient effects osmosis more than anything. If there is a large concentration gradient, there will be a large net movement of water. If there is a small concentration gradient, there will be a smaller net movement of water. The rate of osmosis is faster with a larger gradient, and slower with smaller gradient. The concentration can be varied in order to achieve the concentration gradient where there is no net movement (for an isotonic solution). ============== This experiment has a single factor, solution concentration. All other factors are to be kept constant, such as the solution volume, type of water (distilled), surface area and size of potato before the experiment, variety of potato and temperature. A cork borer is used to ensure that every potato piece is the same size. A top pan balance is the most accurate form of weighing available to me. Cling film is placed over the petri dishes to ensure that no outside factors affect osmosis, and no evaporation occurs. The potato pieces are placed on a paper towel for sixty seconds each, to ensure that all pieces receive an equal amount of time for excess water to drain. To ensure that there are no anomalous results, three potato pieces are used for one concentration, and then an average is taken. Factors to control: ? Temperature ? Size of potato cylinders ? Amount of solution used ? Use only one variety of potatoes ? The same type of water must be used (distilled water) Planned Results Table Sucrose concentration of the solution (%) Potato Piece Mass (g) Change in Mass (g) % Change in Mass 1 d.p. Average % Change in Mass 1 d.p. Before experiment (Initial) After experiment (Final) 0 A B C 25 A B C 35 A B C 40 A B C 50 A B C 60 A B C 65 A B C 75 A B C 100 A B C Preliminary experiment A preliminary experiment was carried out with one petri dish. This dish contained 10ml water and 10ml sucrose. 3 pieces of potato cylinders were placed in the dish. These were weighed before the experiment and after 24 hours, they were reweigh to see if any change in weight had occurred. The results are shown in the table below. Results table Potato cylinder Weight before experiment /g Weight after experiment/g Mass increase/decrease (g) Percentage change A 0.66 0.68 +0.02 +3.030% B 0.66 0.72 +0.06 +9.090% C 0.66 0.67 +0.01 +1.1.51% The results show that 50% water and 50% sucrose made the solution weak. More sugar solution is needed in the main experiment. Calculations Change in Mass = Mass After Experiment ? Mass Before Experiment % Change in mass = Change in mass X 100 [image] Initial Mass Average % change in mass = % Change in mass for potato A = Change in mass for Potato B = % Change in mass for Potato C Predicted Graph === Where the line of best fit is horizontal, it shows that no more water can diffuse in or out of the cell. Remembering that this is only a prediction, where the line of best fit is above the x-axis, the cells gain water, and mass. Therefore, where the line of best fit is below the x-axis, cells lose water and mass. The line crosses the x-axis at the isotonic point. At the isotonic point, and straight parts of the curve, no net diffusion occurred. Planned results table Sucrose concentration of the solution (%) Potato Piece Mass (g) Change in Mass (g) % Change in Mass 1 d.p. Average % Change in Mass 1 d.p. Before experiment (Initial) After experiment (Final) 0 A B C 25 A B C 35 A B C 40 A B C 50 A B C 60 A B C 65 A B C 75 A B C 100 A B C Results Sucrose Potato Piece Mass (g) Change in % Change in Average % Change concentration (%) Initial Final Mass (g) Mass 1 d.p in Mass 1 d.p 0 A 0.64 0.84 0.2 31.3 25.7 B 0.6 0.84 0.24 40 C 0.7 0.74 0.04 5.7 25 A 0.7 0.7 0 0 0.9 B 0.82 0.83 0.01 1.2 C 0.66 0.67 0.01 1.5 35 A 0.69 0.58 -0.11 -15.5 -40.5 B 0.64 0.56 -0.08 -12.5 C 0.64 0.56 -0.08 -12.5 40 A 0.77 0.6 -0.17 -22.1 -22 B 0.64 0.5 -0.14 -21.9 C 0.68 0.53 -0.15 -22.1 50 A 0.65 0.49 -0.16 -24.6 -24.2 B 0.61 0.45 -0.16 -26.2 C 0.73 0.57 -0.16 -21.9 60 A 0.74 0.46 -0.28 -37.8 35.8 B 0.63 0.41 -0.22 -34.9 C 0.75 0.49 -0.26 -34.7 65 A 0.65 0.39 -0.26 -40 -40.7 B 0.72 0.42 -0.3 -41.7 C 0.72 0.43 -0.29 -40.3 75 A 0.76 0.33 -0.43 -56.6 -42.9 B 0.62 0.44 -0.18 -29 C 0.74 0.42 -0.32 -43.2 100 A 0.65 0.33 -0.32 -49.2 -47.1 B 0.62 0.29 -0.33 -53.2 C 0.59 0.36 -0.23 -39 Graph (See graph paper) Analysis The graph showing the results from the experiment has a curved line of best fit, meaning that osmosis reduces. At the lower concentrations, there is osmosis occurring in the potato cells, but there is less as we approach the isotonic point. As concentrations increase, osmosis occurs, and water leaves the potato cells, and mass falls. Towards the end of the best-fit line, osmosis slows down once again. The isotonic point is where the line of best fit meets the x-axis. In the petri dish one, the average percentage change in mass was 25.7% increase. The solution is hypotonic, water will move from the solution and into the potato cells. In petri dish two, the average percentage change in mass was a 0.9% increase. The solution is hypotonic, water is moving from the solution, into the cell. In petri dish three, the average percentage change in mass of a 13.5% decrease. The solution is hypertonic, water is moving from the potato cells and into the solution. In petri dish four, the average percentage change in mass of a 22% decrease. The solution is hypertonic, water is moving from the potato cells and into the solution. In petri dish five, the average percentage change in mass was a 24.2% decrease. The solution is a hypertonic solution, water moves from the potato cells into the solution. In petri dish six, there is an average percentage change in mass of a 35.8% decrease. This is a hypertonic solution, water is moving from the potato into the solution. In petri dish seven the average percentage change in mass was a 40.7% decrease. The solution is hypertonic, water is moving into the solution. In petri dish eight, average percentage change in mass was a 42.9% decrease. The solution is hypertonic, water is moving from the potato cells into solution. In petri dish nine, the average percentage change in mass turned out to be a 47.1% decrease. The solution is hypertonic, water moved through the potato and into the solution. Conclusion == From the above, I can conclude that the isotonic point is between 35% sucrose concentration, and 25% sucrose concentration. This is not the range that was concluded from the preliminary experiment. The range predicted in the preliminary is from 60% ? 40%. I think that the main reason for this is due to the difference in accuracy of the two experiments. Only one piece of potato was used per solution concentration, and three different concentrations were used in the preliminary experiment. This is opposed to the three pieces of potato per solution concentration, for nine different concentrations, and then, an average per concentration was taken. This makes the actual experiment much more accurate than the initial experiment. Using the graph, the isotonic point is 26% sucrose concentration. However, this may not be as accurate as possible, due to the human error involved in drawing a line of best fit. Evaluation == I think that my final experiment was reliable. It was as accurate as possible, when conducted with the available facilities. Most of the variables were controlled. However, the temperature was not kept constant. This is an important factor, and although the petri dishes were kept in the same place for 24 hours, the temperature at night in a lab is not the same as during the day. However, considering that all the petri dishes were kept together, this should have not affected the experiment too much, as all the dishes were subjected to whatever temperature change occurred. The temperature does affects the rate of osmosis, so the experiment would have been more accurate if it was conducted in controlled environments. This means that the results of this experiment can not be compared to the results of the same experiment conducted at a different time in the year, under different temperature circumstances. Human error could have affected the experiment more than any factor. All anomalous looking results have been highlighted in red in the main result table. These probably occurred due to inaccurate recording, or other human error. The potatoes may have been slightly different, or the solution concentration could have differed. To ensure that all osmosis had occurred, ideally, the potatoes? masses should have been recorded every two hours. When there is no difference between the previously recorded result and the current result, osmosis has stopped occurring. To make the experiment more accurate, more frequent readings and more potato pieces per solution concentration are a good idea. Extension ===== For an extension experiment, the focus could be the isotonic point in different types of potatoes. You could explore the isotonic point in Boiling Potatoes such as Round White or the Round Red and Baking Potatoes such as the Russet (see www.potatoes.com): The method would remain exactly as before, and the nine petri dishes could be prepared for Round Red potatoes. At the same time, nine petri dishes could be prepared for Russet potatoes. The rest of the experiment would be exactly the same down to each and every detail. A result table (like the following) could be filled out for the Russet, and one for Round Reds. Sucrose concentration of the solution (%) Potato Piece Mass (g) Change in Mass (g) % Change in Mass 1 d.p. Average % Change in Mass 1 d.p. Before experiment (Initial) After experiment (Final) 0 A B C 25 A B C 35 A B C 40 A B C 50 A B C 60 A B C 65 A B C 75 A B C 100 A B C

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