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How does the concentration of sucrose affect the weight of pieces of potato after osmosis has taken place?

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Introduction

Biology SC1: How does the concentration of sucrose affect the weight of pieces of potato after osmosis has taken place? Aim The aim of this is experiment is to investigate how much sucrose is in a potato. We are going to investigate the effect of different concentrations of sucrose on the weights of pieces of potato after osmosis has taken place. Prediction I predict that the less concentrated the solution of sucrose is, the greater the weight of the potato will be. I predict this because osmosis is the movement of water from a region of high water concentration to a region of low water concentration through a semi-permeable membrane i.e. the cell wall of the potato. If the concentration of water inside the potato is high then the water will pass out through the cell wall, decreasing the weight of the potato. If the concentration of water outside of the potato is high then the water from outside of the potato will pass through the cell wall into the potato, thus increasing the weight of the potato. A low concentration of sucrose will have a greater ratio of water to sucrose, so more water will pass thorough into the potato in an attempt to even up the amounts of water and sucrose on both sides. If the concentration of sucrose outside of the potato is high then there will be less water to pass through into the potato and the potato will therefore lose water from inside in an attempt to even up the concentrations of sucrose and water on both sides. If the cell has lost water then it will not weigh as much as a cell full of water as the cell will be flaccid. If the cell has gained water then it will be turgid and will weigh more. The higher the concentration of the sugar solution, the faster osmosis will take place. ...read more.

Middle

test tubes to ensure an accurate test that we can draw a firm conclusion from and that will fit in with the background information. To make this experiment safe we will act sensibly in the laboratory and we will not run around. The test tubes will not be placed near the end of the bench in case they fall off and break and cause any injuries. They will be placed in the test tubes racks so that they will not roll of the end of the bench or will not tip over and spill everywhere. The results graph will be plotted using the average change in mass after the experiment. We will need to have a suitable number and range of observations so that there are enough values in the important region that we will need to be investigating in i.e. the range of concentrations that we obtained from out preliminary work. It is essential that we obtain enough results so that we can plot a graph and achieve a firm conclusion from them. To make it a fair test only one variable can be changed, this is the concentration of the sugar solution. Other factors that may affect the experiment: Temperature- if the temperature is high then this may affect the experiment and may speed up osmosis. To control this we can make sure that the test tubes aren't left near any open windows or near any heaters. Surface area of the potato- we will need to ensure that the surface area of each potato that we will cut out will have the same surface area. We will therefore need to take care and be as accurate as we can whilst measuring each potato and make sure that each piece of potato is the same length (2cm). We will also need to use the same potato borer each time as some will produce thicker pieces of potato and if we use different sizes of potato each time then the experiment will not be fair. ...read more.

Conclusion

Cutting the ends of the pieces of potato may have affected the weight of the potato if we cut too much off. Therefore this may have had an effect on the weights of some of the pieces of potato, making this a slightly unfair test. To improve our experiment if we were to do it again, we could take more care measuring out the solutions using the measuring cylinder and we did not have enough time to rinse out the measuring cylinder after measuring out each molar solution. This may have had an affect on our results, due to some excess sucrose left in the measuring cylinder after use. Next time we could also make sure that we rinse out the measuring cylinder after each use so that we will not have any excess sucrose solution left in that will affect the next measurement. Our results were also left by a window, so the temperature could have been affected if the window was open or the weather outside was hot. To improve this experiment next time we can also make sure that we leave the test tubes in the test tube racks nowhere near anything that will affect the temperature i.e. a heater or a window. The conclusion may only be valid only within a certain range, if we were to use even more precise concentrations of sucrose solution then we can eventually find out the precise concentration that provides the correct answer. The concentrations used were slightly too vague as I had to say that the answer must lie between two amounts. However, if we were to improve the experiment by narrowing down the concentrations we will use even more then this will be time-consuming and very tedious. Therefore, it will not be a good idea to try and improve the experiment in this way. To extend this investigation we can also experiment changing the following variables: ==> Temperature of the experiment ==> Surface area of the pieces of potato ==> Weight of the potato ==> How long the experiment is left for. ...read more.

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