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Osmosis Chip Investigation

Extracts from this document...

Introduction

Osmosis investigation Aim: To determine the internal cell sap concentration of sucrose in potatoes. Apparatus: Potato chipper, Electronic Balance, Weighing boat, Potato, 5 � Beakers , 20% sugar solution,2 � 20cm3 Syringes Water, Ruler, Forceps, Scalpel, paper towels. Method: 1. The potato will be peeled so that the potato skin cannot affect the process of osmosis. 2. The potato will be cut into slices using a potato chipper which will ensure that the chips are the same height and breadth. 3. The chips length will be measured using a ruler. 4. All chips will be cut to the same length to ensure that the surface area is the same ensuring a fair test. 5. The potato chips will then be placed in a weighing boat and weighed using an electronic balance. 6. The chips will then be immersed in sugar solutions of varying concentration. Three chips will be immersed in each strength solution to provide repeat tests. Repeat tests provide accurate and reliable results. It also helps identify any anomalies. The chips will be placed in one of two containers containing sugar solutions of varying strength. One of the containers is a beaker and the other is a test tube. The container used will be determined during the preliminary experiment. The decision will be based upon practicality and on its ability to provide reliable and accurate results, meaning that the same surface area of all chips placed in the container rests upon the glass and therefore is unable to under go osmosis. Or 7. The chips will be dabbed with a paper towel to remove excess water. 8. The chips will then be re-weighed and any change in mass will be recorded. It is important to be able to identify the chips so that one can be sure that they are measuring the same chips mass before and after the experiment. For this reason paper will be put underneath the beaker with one, two and three written on it. ...read more.

Middle

Table showing the times that the chips were put in and taken out of the solution Concentration Time chip was put in the solution Time chip was taken out of the solution Total time immersed in solution (mins) 20% 9:42 10:02 20 0% 9:44 10:04 20 Preliminary Experiment Results Table of preliminary results Mass Before (g) Mass After(g) Sucrose Concentration 20% 0% 20% 0% Chip 1 2.69 2.60 2.63 2.72 Chip2 2.77 2.73 2.65 2.83 Chip3 2.85 2.83 2.83 2.92 Average 2.77 2.72 2.67 2.83 Table of the average masses and change in masses of Potato chips placed in both solutions Concentration Average Mass Before (g) Average Mass After (g) Change In Mass (g) 0% 2.72 2.83 +0.11 20% 2.77 2.67 -0.1 = Internal cell sap glucose concentration Therefore the internal cell sap glucose concentration is approximately 11%. This is a very rough estimate and the exact concentration of glucose will be determined using the results from the main experiment. It was decided during the prelim experiment that 20 minutes would be an appropriate length of time to leave the chips immersed in the solutions. This is because 20 minutes is long enough for osmosis to alter the weight significantly, if osmosis is to occur, and it is not too long a period of time for the double lessons that we are conducting the experiments in. Varying Sugar solution strength: Two different 1000 ml beakers of solutions were given one with 20% sucrose solution and one with water. Two syringes were used when making up the varying concentrations of sucrose solution, one for 20% sucrose solution and one for water. This prevented 20% sucrose solution from getting into the water solution beaker and water from getting into the 20% sucrose solution beaker. Concentrations were made up from 0% to 20% in steps of 5%. Table showing amounts of water and 20% sucrose solution in various concentrations of sugar solution: Sucrose solution concentration (%) ...read more.

Conclusion

This means the procedure had various short comings. More accurate scales could have been used and the liquids could have been measured out using syringes that were easier to make sure the volumes were exact. More accurate results would also be obtained by dabbing the chips a certain number of times per side using only the weight of the chip to put pressure on the paper towel and then laying the chip on a dry area of towel each time it is dabbed. The chips, as always, would only be handled using forceps. The fact that there was an average variation of 0.05g between results shows that the experiment is not totally reliable. When measuring a change in mass that is sometimes as small as 0.01g to collect reliable evidence the variation between results needs to be far smaller than 0.05g. This is why I do not think that the experiment is accurate enough to prove that the internal cell sap glucose concentration of the potato was exactly 8%. The results collected prove that if the potato chip is immersed in a solution with a high water potential osmosis occurs with a net flow from outside the potato chip to inside it, and when the potato chip is placed in a solution with low water potential osmosis occurs from inside the potato chip to outside it. Although the average was taken which does create a higher level of accuracy a larger number of repeats needs to be done in order to discount the variation that is larger than the result that is being measured. Therefore to prove the exact concentration of glucose in a potato I would like to do at least five repeats per concentration in the future. I would also like to do a greater number of concentrations between 0% and 20%, i.e. 0%,1%,2%,3%,4%,5%,6%,7%..etc. This would provide more points on the graph which would provide a more accurate line of best fit which would provide a more accurate internal glucose percentage. Alex Boorman Ph10 - 1 - ...read more.

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