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An experiment to investigate osmosis in plant tissue.

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Introduction

GCSE BIOLOGY INVESTIGATION An experiment to investigate osmosis in plant tissue Aim: To conduct an investigation to compare the osmotic behavior of two types of plant tissue in varying concentrations of sucrose solution. To find the point at which there is no change in mass or length of a specific plant tissue in a certain sucrose solution, the point of equilibrium, where sucrose and water contents are both equal in the solution and the tissue. Introduction: When a plant cell is placed in a sucrose solution there may be a change in mass and length depending on the sucrose solution and tissue itself. A tissue is a group of similar cells that perform the same task or function. Therefore the whole tissue will react because it is just a huge cluster of cells. These changes occur because of osmosis. Osmosis is the movement of water molecules from a dilute solution (has a High Water Potential) to a more concentrated solution (has a Low Water Potential) through a selectively permeable membrane in order to achieve equilibrium. A membrane that allows water to pass through, but not solute molecules. Osmosis is a biological process If equilibrium is ever achieved then water molecules will move back and forth between the substances. If a surrounding sucrose solution has a lower water potential than the plant tissue in the solution, then, through osmosis water will move from the tissue into the surrounding solution, the tissue will lose mass and length as a result and will be flaccid. Water will be lost from the tissue and depending on the amount lost the weight and length will decrease accordingly. If a surrounding sucrose solution has a higher water potential than the tissue then water will move by osmosis from the solution into the tissue. The tissue would gain in mass and length and will become turgid. If plant tissue has a higher water potential than the solution it is put into and the solution was highly concentrated then enough water ...read more.

Middle

xx. Measure lengths of every potato and radish chip and record results. xxi. Clear up apparatus. xxii. Collect results in a clear table and create graphs to illustrate them. Predictions and hypothesis I believe that as the concentration of the solution that the chips were placed in increases that the length and weight will decrease from the first solution, 0.0M. I say this because distilled water has the highest water potential of all, therefore anything placed in it that contains any sucrose at all, will take on water through osmosis as it will have a lower water potential. It will gain weight and grow in length because of this. At the next molarity of 0.25M I expect that their will be very little increase or decrease in length and an even smaller increase or decrease in its weight as I have done a previous experiment similar to this one which gave me those results. At 0.50M I expect a decrease in both length and weight from the original results. A concentration of sucrose solution with 0.50M has fairly high concentration of sucrose molecules and therefore has quite a low water potential. I wouldn't expect a potato or radish chip to have a water potential that low so I would expect a fair amount water to move through osmosis into the surrounding solution and leave the tissue lighter and shorter because of this. At 0.75M I would expect the same process to occur as at 0.50M but with the tissue losing more water and becoming lighter and shorter as a result. At 1.0M there is a very large amount of sucrose molecules thus having a very low water potential, I would expect an even further drop in mass and length than at 0.75M. Prediction Graphs The graphs are just rough predictions as to what the results graphs will look like. They are based upon a similar experiment's results that were obtained prior to this experiment. ...read more.

Conclusion

It was a standard investigation into osmosis and to find the point of equilibrium for two different types of plant tissue. The method let me do this effectively and let me illustrate my results well. However the method was not perfect if one wanted an almost 100% accurate investigation as there are uncontrollable factors in the method. Accuracy of Observations The accuracy of some of the measurements were very good, especially for the mass results. The length measurements were not very accurate because we only measured one dimension of the 2cm and 4cm chips allowing a wide range of surface areas on chips that were supposed to be equal lengths. This would explain some of the results being a lot different to the predicted results or the results of a different tissue type of the same length. Reliability of the Evidence The evidence that suggest that the cell sap sucrose solution is 0.30M is very reliable. It was the average result for 2cm and 4cm chips of both potato and radish tissue types. It was obtained from the mass results I would believe that the actual cell sap sucrose concentration is very close to this. The mass results are far more accurate than the length results which are not very reliable. The mass results were recorded to 2 decimal places, using an electronic balance rather than a simple mm ruler. The mass results are very reliable, the length results are not though. Improvements for further work If repeating this experiment then I would do the following to increase accuracy overall and specifically to find the point of equilibrium: i. Allow more time to exaggerate results. ii. Measure length, width, and height of each chip. iii. Repeat the whole experiment then average both sets of results. iv. Use more specific molarities closer to the possible range of the point of equilibrium. v. Conduct the experiment in a room in which the temperature could be constant at all times and the same in all parts of the room. vi. Use more chips at different lengths for comparison. Sonya Shah Biology cousework ...read more.

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