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Investigation on the effect of osmosis in plant tissue.

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Introduction

INVESTIGATION ON THE EFFECT OF OSMOSIS IN PLANT TISSUE AIM: To investigate the effect of osmosis in potato tissue through turgor and plasmolysis. APPARATUS: 18 test tubes, 2 test tube racks, 3 potatoes, 5mm cork borer, electronic weighing scales, stopwatch, measuring cylinder, scalpel, thermometer, cutting board, 200ml of molar sugar solution and 500ml of distilled water. METHOD: 1) Place one of the potatoes on a cutting board and insert the cork borer into it, whilst keeping it steady. After the borer has been pushed about 5cm into the potato, remove it and extract the tissue using a pencil. Repeat this procedure a further 17 times to obtain 18 potato tissue cylinders. You may require the other two potatoes. 2) Weigh the potato tissue cylinders on an electronic scale and cut them if necessary, using a scalpel, until their masses are equal or similar. 3) Take three of the test tubes and label them 'A'. Then fill them with 20ml of water and place them in the test tube rack. Next label the other three test tubes 'B' and fill them with 20ml of a 0.2 molar concentration sugar solution. To do this, simply add 16ml of distilled water and 4ml of the molar sugar solution to the test tubes. Place these in the test tube rack. 4) Follow the basic procedure mentioned in 3) labelling another four sets of three test tubes 'C', 'D', 'E' and 'F'. Fill these with sugar solutions of concentration 0.4 molar, 0.6 molar, 0.8 molar and molar. 5) Clean the measuring cylinder with distilled water before and after placing the sugar solution into the test tubes for better accuracy. ...read more.

Middle

Thus these cells would lose water by osmosis. This results in the cylinder feeling flabby due to the lack of water causing a low turgor pressure (the cells become flaccid). The potato tissue cylinder would also become lighter at the end of the experiment because of the water loss through osmosis. Therefore from this prediction it is possible to assume that the more concentrated the sugar solution is, the more mass the potato tissue cylinder loses. For example, if the mass lost by the potato tissue cylinder is 2% for a concentration of 0.4 molar sugar solution, you can predict that a greater loss of mass, say 7%, would occur in a more concentrated sugar solution of 1.0 molar. Although it is impossible to link a mathematical theory with the mass loss of the potato tissue cylinder and the sugar solution concentration, it is however feasible to predict it by the formation of a graph, which would produce a curve as seen below: As the graph shows, the loss of mass is gradual at first for the weaker sugar solutions. This is because their concentrations are almost equal to or not much greater than the concentration of the potato cell sap itself; meaning that any weight loss would be small. During the central stage of the graph the increase is fairly steep as the concentration of the sugar solution far exceeds the concentration of the potato cell sap, meaning a large mass loss. Once the sugar solution concentrations reach a maximum towards the end of the graph, little mass is lost, as the potato cells have become completely flaccid with barely any cell sap available to lose. ...read more.

Conclusion

Due to these inaccuracies my investigation was less efficient than it should have been. In this experiment I do not feel that there were any major anomalous results that I had not predicted, although some were rather surprising. These could have been due to the tissue cylinders being taken from a less turgid potato, as opposed to the others. To overcome this, all the cores should have been soaked in a beaker containing distilled water prior to the investigation and then gently dried in filter paper immediately before each individual experiment. The investigation could have been further improved if I had managed my time more efficiently to begin with, preventing hurried measuring and weighing of the potato tissue cylinders. If I would have left each cylinder in the solution for a longer period of time, for example 24 hours, more accurate and definite results could have been achieved. A wider range of solutions, including 0.1 molar, 0.3 molar, 0.5 molar, 0.7 molar and 0.9 molar would also help to produce a more precise graph. I am satisfied that stronger solutions will take water from weaker solutions until their concentrations are equal. The evidence that I have obtained is sufficient to support my conclusion, although I did refer to other information sources to confirm and reinforce each theory. In order to extend the investigation I could test other plant tissues. It could prove interesting to see their viability in cases of drought. For example, I could propose the question 'do plants living in high drought areas have more concentrated sugar solutions than plants living in wetland areas, such as cacti and watercress?' I could also involve marine plants that live in a salty environment and examine what would happen to them in terms of osmosis. ...read more.

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