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GCSE Biology What effects the rate of Osmosis

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Introduction

Factors affecting osmosis Possible independent variables - these are the factors that could be changed: - Surface area: volume of potato - Temperature - Time: How long the potato piece is left in - Concentration of solution - Mass of potato piece All of these factors would have some kind of effect on osmosis: We would expect that if the temperature was increased, then osmosis would occur quicker as the water molecules would be moving faster. We would also expect that there would be a greater rate of osmosis if the surface area: volume had increased. How long the chip was left in the solution would also affect the experiment, as we would expect that with a longer duration, there would be more time for osmosis to occur. I do believe that mass wouldn't be a good independent variable as it would be hard to increase the mass of the chip without increasing the volume. Therefore I believe mass would be better suited as the dependent variable. Chosen independent variable - this is the factor (input) that I will change: - concentration of solution I hope to use this variable as it would give me a wide variety of results and will give me an interesting conclusion. Controlled variables - These are the variables that I will keep the same so they make no disparity to the overall experiment: - Volume of water - Surface area: volume of potato - Time: How long the potato chip is left in - Temperature of solution and surroundings I will have to keep these the same so to keep the whole experiment as fair as possible. As any of these variables would have an unwanted affect, e.g. if the surface area was different for each chip, we would assume that osmosis would occur more in the chip with the larger surface area, resulting in the whole experiment becoming inequitable. ...read more.

Middle

At 0.00 Molars, the change in mass is not at 0% but at 4.908%, with the information that the line does not pass through the origin and knowing that the line is not entirely straight; we can deduce that the concentration of salt and the mass of the potato are not proportional to each other. Although we do see a distinct pattern on the graph between the 2 variables. As the independent variable (concentration of solution) increases, the dependent variable (mass of chip) decreases. I can also conclude that the rate of osmosis was high up to 0.75 Molars where it then rapidly slowed down and would seem to eventually stop, or continue to slow down onto an inadequate and unnecessary rate. The gradient remains reasonably constant up to 0.75 Molars; where it rapidly decreases. It then decreases until the gradient is near to a 0% representation in mass change. This makes the line essentially parallel to the X axis. The line may be in this form because at the point where the gradient becomes close to 0, the chip must have become fully plasmolysed as at the lower concentration the chip had a constant mass. If we look carefully at my line graph with the inclusion of the line of best fit, you can clearly see the consistent pattern. As the concentration increases on the x- axis you can clearly see the percentage mass decreases at the same time as shown by the y-axis. This proves that my initial prediction is correct. "As the concentration of the solution increases, the mass of the chip will decrease". As earlier stated, osmosis is the diffusion of water molecules from a hypotonic solution to a hypertonic solution through a selectively permeable membrane. This is also typical with this experiment, as the hypotonic solution is in the chip and the hypertonic solution is in the actual solution. ...read more.

Conclusion

It would also be extremely useful to have more group members so there would be awareness of what is actually happening to the chip and more attention to specific concentrations. I furthermore had to rely on one large measuring cylinder which meant we had to rinse and dry the measuring cylinder after each reading was taken with it. It would be useful next time to have the freedom of having more measuring cylinders. Having previously cut the potato chips out or to have a machine cut the potatoes out more accurately would've definitely increased the consistency. Even leaving the potato chips in the solution even longer would have increased the reliability of our results. Finally it would be beneficial to have an alternative method of drying the chip so to minimise the risk of absorbing water from the chip or leaving water on the surface of the chip. If I wanted to extend my investigation there are a number of elements I could change such as using temperature as a variable that would be changed to see how hot or cold concentrations affect the rate of osmosis. Or we could use the size (surface area to volume ratio) as a changeable variable to see how that affects osmosis. One other factor that would be interesting to test would be how a different substance that is soluble to the solution affects the rate of osmosis, we would presume that it would be extremely similar to that of the experiment held in this investigation, although there may be other factors involved. The experiment overall was extremely successful in that the practical was completed in time and I had acquired reliable and accurate results which is proved on my line graph. I took all the necessary precautions outlined in the risk assessment of my plan. Overall I can again succeeding outline that through the experiment I have accomplished my aim and fulfilled the entire investigation. Osmosis Coursework 1 ...read more.

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