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In this experiment I intend to investigate the effects of osmosis on potato cells. Specifically, I intend to use my knowledge of osmosis to investigate the glucose concentration of the cell sap in potato cells.

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Introduction

Planning In this experiment I intend to investigate the effects of osmosis on potato cells. Specifically, I intend to use my knowledge of osmosis to investigate the glucose concentration of the cell sap in potato cells. Osmosis is a method by which water levels on either side of a semi permeable membrane may balance themselves. It occurs between regions of high water concentration and low water concentration. As it is a special method of diffusion exclusive to water, it also allows dilute and concentrated solutions to balance their strengths. It does this by preventing large non-water particles from passing through the semi-permeable membrane due to their size, in order that the water levels on either side may equate, regardless of the solution's other contents. Osmosis is passive, that is to say it does not require energy in order to be performed. This is because it occurs solely between regions of high and low water concentration. The direction and speed of osmosis depends on the two solutions' osmotic potential. This is the measure of the pressure by which the water molecules of a solution diffuse across a semi-permeable membrane. A solution's potential is defined by its concentration. The more soluble a solution has in it, the lower its water concentration and the lower its osmotic potential. In the example below sugar molecules represent the soluble. Cell sap is contained in the vacuole of a cell and is a part glucose, part water solution. The membrane of the cell acts as a semi-permeable membrane across which osmosis occurs (see below). In the case of osmosis into and out of the vacuole, it occurs across two membranes - the plasmalemma and the tonoplast. When osmosis occurs, water may enter or leave the vacuole according to the concentration of the substances inside and outside the potato cell. In the example below we see what would happen if a plant cell were surrounded by pure water. ...read more.

Middle

Therefore, I predict that in beaker 2 some weight gain will occur, though less this time than in beaker 1. Beaker 3: My predictions for beaker three differ very little from those for beaker 2. Once again, I predict that cell sap contains more than 20% glucose. This time however, the wight gain incurred by the potato sample will be less than that in beaker 2, as the sugar content of the solution has increased, reducing its osmotic potential. Osmosis will also occur more slowly than in beaker 2. Beaker 4: In beaker 4 I predict the water concentration of the solution and the cell sap to be closest. A glucose content of about 30% seems just about right when I consider the consistency of sap in other plants. A little osmosis may occur in either direction, as the glucose content of cell sap will not be precisely 30%. Here I expect only very little weight gain or loss in the potato sample. Beaker 5: Beaker 5 is the only beaker in which I predict that the potato sample will lose weight. This time I expect the sugar solution to have a lower concentration than the cell sap, though only marginally so. As a result I predict that some osmosis will occur, the result being that the potato sample will loose weight and may even shrivel. Obtaining Evidence I carried out my experiment as detailed in the plan. I had to take note of safety measures, especially when using the scalpel to cut the potato samples to size. Accuracy too was important. The different sugar solutions were carefully poured out into the beakers in equal amounts, and each potato sample was measured and cut with a ruler and the same potato corer each time. Finally, to ensure maximum accuracy, the weight of each potato sample, before and after the experiment, was measured to 2 decimal places. ...read more.

Conclusion

Thus it is the conclusion to the investigation. The results I finally used in my analysis were all more or less uniform, however during the investigation one set of completely anomalous results was obtained. These were left out of the averaged results. They were the first obtained results, and so the problems that caused their inaccuracies were corrected for the repeats of the experiment. When these first results were collected the time over which the samples were left appears to have been too long. When checked, the samples had grown mould or rotted, leaving them un-open to osmosis. Consequently the results were completely irregular. The main improvement that could be made to the accuracy of the experiment would be the regulation of timing. It was poor timing that caused the anomalous results in the first experiment. The more tightly controlled the timing of the experiment, the more accurate the results are likely to be. Other than this, I feel the experiment that the experiment was well conducted. Perhaps in future though, the results of other pupils' experiments could be pooled in order to obtain a wider and more precise base of evidence. There is scope for further investigation of the topic in order to obtain further evidence and draw a more accurate conclusion. For example, now the concentration of potato cell sap has been identified at about 15%, a smaller range of solution strengths could be used in an otherwise identical experiment; 5 solutions of 10% and 20% concentration for example. Alternatively, investigations could be conducted into the effects of osmosis on different vegetables or more widely plants in general. For further information on the potato, the same experiment could be conducted using samples from different parts of the plant. This would establish whether different areas of a plant have differing levels of sucrose in their cell sap. Any of these suggestions would both help to support my conclusion and extend the investigation in general further. ...read more.

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