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Determination of molarity of cell sap in potato tubers.

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Introduction

Biology Coursework Determination of molarity of cell sap in potato tubers Planning Plant and animal cells are made up of a cell membrane. The plant cells have the cell membrane line in the inside of the cell wall. The cell wall provides the turgidity to the cell. The cell wall is dead and allows all substances to pass freely through it whereas the cell membrane is alive and selective. This is the case also for the cell membrane of the animal cells. The only difference is however that the cell membrane is the only layer around the cell unlike the cell wall that is part of the plant cells. The cell membrane is alive and selective as we know. This means that it is semi-permeable. This is called a semi permeable membrane. Semi permeable means that it is a layer or a surface that allows only certain particles to pass through but not any others. A completely permeable membrane means that it is a membrane that allows any particles to pass through like is the case for the dead cell wall. This cell membrane is a thin layer of cytoplasm and allows the cell to control the products that come through and go out. For example the cell membrane allows only substances like water, glucose and water are allowed to enter and waste products are removed. However the other way round is not possible because the membrane does not allow the wastes to enter and the vital particles to exit. The membrane is very important to organisms. The movement of gas molecules is called diffusion. The diffusion of other substances such as liquids across a semi permeable membrane is called osmosis. The process of osmosis will be studied in detail here. There is another type of movement and it is called active transport. To understand both of these it is important to know what the concentration gradient is. ...read more.

Middle

Here we will be using varying concentrations of solutions. From the concentrations that are being used, I think that the potato cylinders placed in solution with the highest concentration will lose mass because it has a dilute solution compared to the solution in dish and the one that is placed in distilled water will become thick and gain mass. The other concentrations will also be affected the same way because the potato cylinders have more dilute solution than them and so this will be used to check for it. The more concentrated the solution the more the loss in mass and the more flaccid the potato tubers will become. Fairness of the experiment/ Precautions The experiment has to be a fair test. This means that the experiment has to be correctly done without ignoring minute details that may affect it and we cannot ignore them. They are some of the precautions that have to be taken for the experiment to be used to test osmosis. The first thing is that all the test tubes have to be cleaned out with distilled water. Each test tube has to be cleaned with each its respective solutions. For example Tube A will hold 1 M solution and so we will have to clean it out with 1M solution and not any other one as the final result may differ. Care should also be taken to see that the flask is not broken or cracked neither are the test tubes. The potatoes that are taken have to be from the same farm or from the same plantation or the same size, preferably. This is because different potatoes have different concentrations of solutions in them and this can vary in the experiments and so we will not get accurate reading and thus there can be no conclusion. The potato tubers have to be cut accordingly and according to that the length should be not more than 5 cm. ...read more.

Conclusion

No. Initial Length Average Final Length Average Change Percentage Change 1 5 cm 5 cm 4.6 cm 4.6 cm -0.4 cm -8 % 2 5 cm 4.7 cm 3 5 cm 4.6 cm 4 5 cm 4.6 cm 5 5 cm 4.5 cm Petri Dish C S. No. Initial Length Average Final Length Average Change Percentage Change 1 5 cm 5 cm 5 cm 4.9 cm -0.1 cm - 2 % 2 5 cm 4.9 cm 3 5 cm 4.9 cm 4 5 cm 4.8 cm 5 5 cm 4.9 cm Petri Dish D S. No. Initial Length Average Final Length Average Change Percentage Change 1 5 cm 5 cm 6 cm 6 cm 1 cm 20 % 2 5 cm 6.1 cm 3 5 cm 5.8 cm 4 5 cm 6 cm 5 5 cm 6.1 cm Mass Petri Dish A S. No. Initial Mass Average Final Mass Average Change Percentage Change 1 2.49 g 2.488 g 2.2 g 2.16 g -0.328 g -13.18% 2 2.49 g 2.12 g 3 2.46 g 2.17 g 4 2.48 g 2.21 g 5 2.52 g 2.1 g Petri Dish B S. No. Initial Mass Average Final Mass Average Change Percentage Change 1 2.4 g 2.408 g 1.82 g 1.83 g -0.578 g -24 % 2 2.41 g 1.87 g 3 2.43 g 1.88 g 4 2.4 g 1.72 g 5 2.4 g 1.86 g Petri Dish C S. No. Initial Mass Average Final Mass Average Change Percentage Change 1 2.35 g 2.356 g 2.27 g 2.256 g -0.1 g -4.24 % 2 2.34 g 2.29 g 3 2.36 g 2.22 g 4 2.37 g 2.29 g 5 2.36 g 2.21 g Petri Dish D S. No. Initial Mass Average Final Mass Average Change Percentage Change 1 2.39 g 2.378 g 3.13 g 3.098 g 0.72 g 30.27 % 2 2.41 g 3.09 g 3 2.36 g 3.07 g 4 2.39 g 3.1 g 5 2.34 g 3.1 g These are the results that are obtained from the experiment. The graph for the isotonic point is shown on the next page. ...read more.

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