The Effect of Osmosis on Potato Cells

The Effect of Osmosis on Potato Cells
The Effect of Osmosis on Potato Cells Introduction Osmosis is the movement of water molecules from an area of low concentration (lots of water) to an area of high concentration (little water) through a semi permeable membrane. A semi permeable membrane is a membrane that only lets selected molecules to pass through it. In a plant water is taken into the roots by the process of Osmosis. This is because the cells inside the roots have a higher concentration than the soil outside the roots. So the water from the soil moves into the cells by osmosis. When a large volume of water enters the cell, it swells causing the membrane to push against the cell wall. We say that the cell is fully turgid. When the water moves out of the cell, the membrane shrinks away from the cell wall and becomes a flaccid cell. This causes the plant to wilt, as the cells can no longer provide support for the leaves. Equipment 3 test tubes Top pan balance Test tube rack Tile 10mls of weak sugar solution Labels 10mls of water Scalpel 10mls of Strong sugar solution Ruler Measuring cylinder Potato Core borer Label Diagram
Water Variables Below is a list of all the variables I can consider to use in my experiment: ? Have several different concentrated solutions. ? Use different lengths and weights of potatoes ? Have the solution at different temperatures. ? Different volumes of solutions. ? Several potato chips in one solution Fair Test To make sure my experiment is fair I am going to: ? Make sure I use the same volume of solution in each test tube ? Have roughly the same size and weight of potato chips ? Same size test tube ? Leave the potato in the test tube for the same length of time Safety To make sure my experiment is safe I will wear goggles at all times and take care when using the equipment, especially when cutting the potatoes using the scalpel. Prediction ? preliminary plan I predict that the size of the potato chip placed in the weakest solution will increase because all the water will move into the potato cells by osmosis. The concentration in the cells is much higher than the concentration on the solution. The size of the potato chip in the water will remain the same because both the concentration in the cell and in the solution will be the same. The size of the potato in the strongest solution will decrease because the concentration in the cells will be lower than the concentration in the solution. Therefore the water will move out of the cell. Method ? Preliminary plan 1. Collect all equipment. 2. Write out 3 labels, one saying weak solution, one saying distill solution and one saying strong solution. 3. Place each label on to a test tube. 4. Using the measuring cylinder, measure out 10 mls of each solution and pour each solution into its correct test tube. 5. Cut out 6 potato chips using a core borer. 6. Weigh each potato chip and make sure all six are 10g, using the scalpel to help you cut. 7. Place 2 potato chips in the test tube labeled ?weak solution? and start the stopwatch. 8. Time for 10 minutes and then stop the stopwatch. 9. Carefully take the potato chips out and weigh them, recording your results. 10. Repeat steps 7, 8 and 9 but this time using the distilled solution and then the strong solution. 11. In my actual investigation I will follow the above method but instead used the solutions listed below; Test tube Volume of Stock (ml) Volume of Water (ml) A B C D E F G H I J K 10 9 8 7 6 5 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 10 Results Results of Preliminary Test Liquid in Test Tube Original length of chip (cm) Final length of chip (cm) Change in length of chip (-/+ cm) Weak sugar solution Water Strong sugar solution 2 2 2 2.3 1.9 1.8 +0.3 -0.1 -0.2 Results for the 1cm potato chips Test Tube Start mass (g) Final mass (g) Change in mass (g) A B C D E F G H I J K 1.2 1.5 1.4 1.4 1.2 1.4 1.5 1.6 1.3 1.2 1.4 0.8 0.8 0.8 0.7 0.8 1.0 1.0 1.1 1.2 1.3 1.4 -0.4 -0.5 -0.6 -0.7 -0.4 -0.4 -0.5 -0.5 -0.1 0.1 0 Results for the 2cm potato chips Test Tube Start mass (g) Final mass (g) Change in mass (g) A B C D E F G H I J K 2.9 2.6 2.6 2.4 2.6 2.6 2.4 2.7 2.3 2.4 2.3 1.9 1.5 1.5 1.5 1.6 1.8 1.8 1.9 2.2 2.6 2.6 -1.0 -1.1 -1.1 -0.9 -1.0 -0.8 -0.6 -0.8 -0.1 -0.2 0.3 Average of change in mass Test Tube Change of Mass (g) for 1cm potato chip Change of Mass (g) for 2cm potato chip Average A B C D E F G H I J K -0.4 -0.5 -0.6 -0.7 -0.4 -0.4 -0.5 -0.5 -0.1 0.1 0 -1.0 -1.1 -1.1 -0.9 -1.0 -0.8 -0.6 -0.8 -0.1 -0.2 0.3 -0.7 -0.8 -0.85 -0.8 -0.7 -0.6 -0.55 -0.65 -0.1 0.05 0.15 Analysis Looking at the results of my preliminary test I had found what I had originally expected. I predicted that the potato chip in the weak sugar solution was going to increase in size because the concentration in the potato cell was much higher than the concentration in the solution. Therefore the water will move out of the potato cells by osmosis. In my results the potato in the weak sugar solution did actually increase in size from 2cm to 2.3cm. There was an increase of 0.3cm. For the potato chip in water, I predicted that the potato chip was going to stay the same because the concentration in the cell would be the same as the concentration of the water. I found that the potato chip actually decreased in size but only slightly. It decreased from 2cm to 1.9cm. I was not surprised to find this, as the concentrations can not always be exactly the same. The concentration in the cells must have been slightly lower than the solutions concentration. I finally predicted that the size of the potato in the strong sugar solution would decrease because the concentration in the cells would be lower than the concentration of the solution. Therefore the water would move out of the cell. The original size of the chip was 2cm, the size decreased to 1.8 ? a change of 0.2cm. So I had predicted correctly. In my actual investigation I found that the more sugar in the solution (stock), the smaller the potato chip was. So if there was a lot of sugar in the solution then the potato chip decreased in mass. If there was only a little sugar in the solution the potato chip increased in mass. This follows the same prediction as the one I made for the preliminary test. low concentration high concentration [image] The diagram above can help explain what is actually happening within the test tube. One side can be the solution and one side can be the potato cell. The semi permeable membrane, in this case, would be the cell membrane of the potato cell. When the potato chip is put into a solution of high concentration, for example solution A (contains a lot of sugar but little water), the water within the potato cell will move out of the cell and into the solution. This will cause the potato to decrease in mass. For example, the potato chip placed in solution A had an original mass of 1.2g. It had then decreased to 0.8g (refer to results table for the 1cm potato chips) Looking at the graphs I found that between solution C and D was where the potato chip began to increase in mass. I know this because the line of best fit first slopes downwards but soon as it reaches Solution C it changes direction and goes upwards. This could be the point of equal concentration. There was a rough trend running through all three graphs. As soon as the line reached solution C it began to increase upward. This happened in all of the graphs. The potato chip placed in solution K had the highest change in mass. This is probably because it only had water in it so the water had move into the potato chip. The concentration in the potato cell must have been lower than the water solution. Plants rely a lot on osmosis to support and hold particular organs, like leaves, upright. Inside the vacuole is a very strong cell sap solution made up of mainly water containing various dissolved sugars, salts and chemicals. This is where the water enters during osmosis. When the cell is placed in a low concentration solution, the water moves into the cell by osmosis. The cell becomes blown up like a balloon but is prevented from bursting by the cell wall. We say the cell is fully turgid. Turgid cells hold the plant upright. A fully turgid cell [image] [image] [image] If the cell is placed in a solution that is of a higher concentration than the cell sap, water will move out of the cell by osmosis. Therefore the cell wall can no longer provide support for the plant. We say that the cell is flaccid. A plant begins to wilt when its cells are flaccid. [image] A fully flaccid cell Connecting this theory with my actual investigation, I found that the before I put the potato chip into the solution it was hard and firm. This is because the cells were fully turgid, giving the potato support and strength. When I took the potato chip out of the solution it felt very soft and limp. This because the potato cells were fully flaccid, not giving the potato chip any support at all. Evaluation Generally, I think my results obtained were fairly accurate. From my preliminary test I learnt that the three solution was not enough, so I decided to have 11 solutions instead. I think my decision really helped because I obtained more varied results, giving me suitable graphs. This would make the graphs more clear and easier to notice any trends or patterns. I used the same method I wrote for the preliminary test for the actual test. During my preliminary test I also found that leaving the potato chip in the test tube for 10 minutes was not long enough. So for my actual investigation I decided to keep them in for a whole night. This would have given us a bigger range between each result recorded. If I was to do the experiment again then I think I would choose one of the solutions and dilute in further. For example: Test tube Volume of Stock (ml) Volume of Water (ml) H H1 H2 H3 H4 H5 3 2.9 2.8 2.7 2.6 2.5 7 7.1 7.2 7.3 7.4 7.5 By doing this, it will help me find the cell concentration of the cell sap solution. It also me give far more accurate results and a more general idea of what was happening. During my investigation I found it very difficult to get all the potato chips exactly the same sizes and mass. I first cut 11 potato chips to 1cm and the cut the remaining 11 to 2cm. After weighing them on the top pan balance I found that each chip was slightly bigger or smaller than the other was (in mass). I did not have time to cut them further to get them all exactly the same mass. This made the investigation slightly inaccurate but the differences were not great enough to cause any major problems. I do not think it was very fair using two different surface areas of potato chips (1cm and 2cm). I chose two different sizes so that I knew which potato chip I was measuring and it also saved time. However, if I did have time then I think it would have been much fairer if I had 22 test tubes, with only one potato chip inside it. If we had time then to make the investigation very accurate it would have been recommendable to find the surface area of the potato chips. But this involves a lot of time and care and it is very difficult considering how small the chips are. I would have used the formula, pr²h, which is the formula to find the surface area of a cylinder. Looking at my graphs I noticed several anomalous results (circled in blue on graphs). For example if you look at the graph showing the average change in mass, you will notice that one result (circled in blue) looked very odd. This could be due to the inaccurate measuring of the chips original size. This may have also been the explanation for all the other anomalous results. To extend my investigation further it would be interesting to also investigate what would be the best temperature for osmosis to occur or whether temperature does or does not effect osmosis. Instead of using several different solutions, in this investigation you would use only one, varying the temperature for each one. Using a Bunsen burner, the solution can be boiled to maybe 15ºC, 30ºC, 45ºC, 60ºC, 75ºC, and left for about 10 minutes. I know that osmosis does occur after 10 minutes because it occurred after 10 minutes in my preliminary test. By doing this investigation we would be able to understand what the best conditions are, if any, for osmosis.

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