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Factors Affecting Osmosis.

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FACTORS AFFECTING OSMOSIS AIM The aim of this experiment is to investigate the factors affecting osmosis. I have chosen to investigate the effect varying concentration of sucrose solution has on the amount of osmotic activity between the sucrose solution and a plant cell. The plant cell I have chosen to use is a potato tuber from which I plan to cut potato chips of equal length which I will place in test tubes filled with varying concentrations at equal volumes of sucrose solution. After a set amount of time I will remove the potato chips and record the change in length. BACKGORUND KNOWLEDGE High water potential is a solution which has a high concentration of water and a low concentration of solute (e.g. sugar, sucrose or salt) or no solute at all. Therefore it can either be a very dilute solution of something like sucrose or pure water, however in each case there is a lot of water. Whereas low water potential is the opposite of high water potential being a solution of low concentration of water and high concentration of solute (sugar, sucrose or salt). Hence it can be a concentrated solution of something like sucrose, however in this case there is much less water. When to solutions one of high water potential and one of low water potential are divided by a semi-permeable membrane water molecules will move from the solution of high water potential through the partially permeable membrane to the solution of low water potential. This will continue until both sides have reached a state of equilibrium or isotonic point, which is when both solutions wither side of the partially permeable membrane have equal water potential neither having higher or lower potential, they are said to be isotonic. When this occurs there is no net movement of water across the membrane only random diffusion of particles. What I have discussed in the previous paragraph is the process of osmosis, however in short osmosis is defined as the net movement of water molecules from a high water potential through a partially permeable membrane to a low water potential. ...read more.


no extra light must be shone on the experiment. This is because light is heat which would increase the temperature around the test tubes, causing the temperature to increase, which in turn would cause the molecules to gain more kinetic energy, meaning that they would move faster and there would be more collisions so the rate of osmosis will be faster. 7. The same top pan balance (accurate to 2 decimal places) must be used to measure all the potato chips because the measurements may slightly vary between scales. I will control this variable by always using the same top pan balance to measure the mass of my potato chips before and after the experiment. When using the top pan balance I must make sure that the balance is reading zero before I begin to weigh each potato cylinder so that I do not get an inaccurate reading. MAIN INVESTIGATION For my main investigation I will use the same concentrations of sucrose solution as for my pilot. There will be a range of 5 concentrations at intervals of 0.5M. The concentrations of sucrose solutions will be 0.0M (which is distilled water); 0.5 M; 1.0M; 1.5M; and 2.0M. I will repeat the experiment three times so that I obtain 3 sets of precise and reliable results for each sucrose solution, which I will then average. In doing this I hope that any anomalous results will have a chance to show. It is important to repeat any experiments more than once because if they were conducted only once, then an anomalous result might be gained, and I wouldn't even know because I wouldn't have any data to compare it with. Anomalous result need to be repeated because they are inaccurate results and therefore cause any graphs and further calculations also to be inaccurate which in turn cause that a precise conclusion cannot be made. If I get any anomalous results, which are inaccurate results that don't fit in with the pattern of the rest of the results I will repeat the procedure again until I get an accurate reliable set of results. ...read more.


not to 0.00g but to 0.0000g. The one variable which was not controlled successfully was temperature. Temperature was not kept constant for all the experiments because the experiment was carried out during the summer term over two lessons all of which were on different days and at different times of the day. Thus the temperature in the room varied from each lessons because one day could have been warmer or colder than the other and mornings were colder than afternoons, which in summer were hot. Therefore I can conclude that in some sets of experiments the rate of osmosis either decreased or increased depending whether it was colder or warmer. This would have an effect on the accuracy of my results. This investigation can be extended further in the following ways: * Using different plant cells i.e. different vegetable, perhaps celery or cucumber and investigating whether osmosis occurs at the same speed and in the same way in all plant cells. * The experiment could be carried out using an animal cell, so that osmosis in plant and animal can be compared and differences observed. * The experiment could be carried out not only using sucrose solution but also using other solutions for example salt solution to see if the solution affects the rate of osmosis and how much osmosis takes place. * I could extend the range of the independent variable to see at what concentration the limiting factor would apply. * The potatoes could be left in the sucrose solution longer, enabling me to find the saturation point and dehydration point. The saturation point is when the potato can no longer take in any more water and the dehydration point is when the potato cannot lose any more water. * I could extend the experiment to a more exact level by looking at the potato cylinders under a microscope, then I would be able to see the cells in greater detail and draw some observational results. Resources used: - Encarta DVD - Britannica - Biology - Mary Jones and Geoff Jones - Biology (Key Science) - David Applin 4 ...read more.

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