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Find the water potential of potato cells.

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Introduction

GCSE Coursework investigation - Water Potential of Potato Cells Aim: to find the water potential of potato cells Introduction In my investigation, I hope to determine the water potential of potato cells. The plant material I will use in my investigation will be potato chips, which I will cut myself prior to the investigation. I hope to find the concentration of a solution where the chip stays the same mass and length, which will tell me that the water potential inside the cells is the same as the water potential outside the cells. Background Osmosis is defined as the movement of water through a semi-permeable membrane. Semi - permeable membranes are permeable to water but impermeable to certain dissolved substances. In the case of this experiment, the sucrose molecules cannot diffuse through the cell membrane because the sucrose molecules are much bigger than water molecules. The water potential of a solution is a measure how dilute the solution is, and therefore of how readily water will diffuse from this solution, through a semi-permeable membrane, into another solution. Pure distilled water has a water potential of zero: the water potential becomes more negative as more substances are dissolved in it. When two solutions are separated by a semi-permeable membrane, water moves from the side with high water potential to the side with low water potential: If we dissolve substances in water we lower the water potential of the solution:- High water potential Some water potential Low Water Potential 'Turgid' Normal 'Plasmolysed' So, in ...read more.

Middle

o Carefully measure out 100 cm3 sucrose solution using a 50ml measuring cylinder, and put into a 250ml beaker. Do the same for the other 5 solutions which include different measurements of distilled water. o Weigh each chip using the digital top-pan balance and note down which solution it will go into e.g. Red Chip 4.30g - into 80cm3 sucrose solution. o Put each chip into its correct solution at the same time. Leave for two hours. o After two hours return to experiment. Remove three chips from their solution using thread, dry them off with a paper towel, and weigh them one by one. Repeat for the remaining chips (in the correct order). Reliability of results To make results as reliable as possible, I intend to use three chips in each concentration of solution, and take the average (mean) measurements of changes in length and mass of the three. How my results will be useful In order to find the water potential of potato cells, I will need to process my results after obtaining them. I will plot a graph of change in mass or length against concentration of solution, which should reveal the concentration where the mass or length doesn't change. I will then use a table to convert this concentration into a value of the water potential of the solution. Prediction I predict that the chips in distilled water will have increased in mass and length, while the chips in 1.0M sucrose solution will decrease in mass and length. ...read more.

Conclusion

They could have been swapped the wrong way round by accident. Despite this, there are things I could have done (and not done) which might have lowered the accuracy of my results. For example, I may have unknowingly not had the right line of sight when using my measuring cylinder, or when measuring my chips with a ruler. Or, I may have not dried some of the chips well enough before measuring their mass. Many of these results can be changed quite easily just by simple human error. My experiment could have been improved by using a more sensitive balance to measure the mass, and I could have used a burette or pipette for volumes of liquids. I also could have used a sharper knife to cut the lengths of the chips. All of these things would have made my experiment more accurate. I also could have done a few more averages and repeats, to decrease the margin of error in my experiment, making my results more reliable. For further work, I would like to see if in my experiment I could actually get the result in my experiment where chip does not change at all, by putting it in the correct Molarity of sucrose solution. I would do this by putting it in different concentrations, ranging from 0.1M to 0.4M, and see what happened. I would also like to do the original experiment again, but using the improvements I listed above, and see how much of a difference there was in the results with the improvements. Paul May 11B 03/05/2007 ...read more.

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