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How are Potatoes CellsAffected by Osmosis?

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How are Potatoes Cells Affected by Osmosis? Biology Coursework Osmosis in Plant Cells Aim: The aim of this experiment is to investigate the process of osmosis in plant cells taken from potatoes and to observe what changes which take place in the potato when left in varying glucose solutions. Background: The porous nature of the cell membrane means that only those molecules that are small enough will diffuse through it unimpeded. Larger molecules penetrate either slowly or not at all. Thus, the cell membrane is considered to be semi-permeable. In the diagram shown below, the cell has a higher concentration of glucose on the right-hand side compared to the left-hand side, as there are more glucose molecules per water molecules. Osmosis involves the passage of water molecules from a region of high water concentration (the left-hand side) to a region of lower water concentration (the right-hand side), through a semi-permeable membrane. This is why the water molecules will diffuse from the left-hand side, through the semi-permeable membrane and into the right-hand side. However, there will be no diffusion of glucose molecules across the semi-permeable membrane from the right to the left, as the glucose molecules are too large to pass. A solution consists of the molecules or ions of one substance (the solute) dissolved in another (the solvent). If a cell is surrounded by pure water, or a solution whose solute concentration is lower than that of the cell's contents, water flows into the cell by osmosis, and the cell swells up. In this case, the concentration of glucose in the left-hand side is lower than that of the right-hand side, and accordingly the solution is said to be hypotonic to the right-hand side. On the other hand, the right-hand side is said to be hypertonic to the left-hand side as the concentration of glucose is higher than the left. The following diagram further illustrates the act of osmosis and its effects on fluid levels in a beaker of solutions separated by a semi-permeable membrane. ...read more.


With this experiment, a knife was used to cut the potatoes. Care needs to be taken not to cut one's fingers during this step of the experiment. Actual Method: First, the 6 different 50 cm3 solutions were made consisting of 100% glucose, 80% glucose, 60% glucose 40% glucose, 20% glucose and 0% glucose (distilled water). The glucose solutions were made using the following table. ? The measuring cylinder was used to obtain the correct volume and therefore percentages of water and glucose for each glucose solution. The pipette was used to add water or glucose with precise accuracy, as required. Next, the solutions were poured into six labelled Petri dishes. 18 potato chips were cut out using the cork borer. Care was taken not to bore into the hole left by other samples which were taken from the potato. Every chip was full in diameter for the entire length of its cylindrical shape. The tile was used as a base for cutting the potatoes. All the chips were cut to exactly 50 mm using a ruler and a knife. The ends of every single chip were removed of its skin so that it would not affect the effects of osmosis. Three potato chips were placed into each of the six solutions and left for a period of twenty-four hours. Every Petri dish was covered and placed in way so that they all received the same amount of light (natural or un-natural), which might have affected the temperature of the Petri dish. Glucose Solution Length of Potato Chips Before Soaking (mm) x Length After Soaking # 1 (mm) # 2 (mm) # 3 (mm) Average Length [(#1)+(#2)+(#3)] 3 (mm) y Average Difference (mm) Percentage Change of Original 100(y - x) x 0% 50 55 54 55 54.7 4.7 9.3% 20% 50 50 53 53 52.0 2.0 4.0% 40% 50 49 49 49 49.0 -1.0 -2.0% 60% 50 46 46 45 45.7 -4.3 -8.7% 80% 50 45 45 46 45.3 -4.7 -9.3% 100% 50 44 43 ...read more.


Having taken so much care in setting up the experiment and keeping the variable to an absolute minimum, I feel that a fair test was give and that the accuracy of my results can be fully relied upon. Having used three potato chips for each solution, I increased the repetition of my experiment. Taking the average of the repeats would rule out any anomalous results that might have occurred due to any natural imperfections or irregularities in the potato chips themselves. If I had more time, I would have liked to do the experiment again so that I could record a wider range of data. I would have liked to record the mass of each potato chip before and after soaking in the solution. If I had performed the experiment at different temperatures, I could have observed how osmosis is affected by temperature. I would have also liked to use smaller intervals between the glucose solution concentrations, possibly 10% increments of concentrations of the solutions. I could have also used four or five potato chips per solution. This would have produced a much wider range of data and allowed me to have a stronger conclusion. Using different types of cells from various different sources would have provided an accurate account of how the effects of osmosis affect different types of organisms. When researching secondary sources, I came across an experiment in which osmosis was observed in human cells. Human red blood cells were placed in hypertonic, 1.2% salt solution and they were found to shrink perceptibly. If the cell was placed in a weaker (hypotonic) solution, they would swell and burst, a phenomenon known as haemolysis. Had I have had access to the proper equipment and facilities, I would have been especially interested to observe just how important it is to have an isotonic environment for living creatures. Overall, I am pleased with how the experiment turned out and I feel that I have gained a sound understanding of how osmosis occurs. ?? ?? ?? ?? - 1 - ...read more.

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