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Investigate the different water potentials of a fruit and a vegetable.

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Introduction

Investigate the different water potentials of a fruit and a vegetable. Objective: The objective of this experiment is to determine the water potential of both apple cells and potato cells and to see how they differ from one another. We will do this by placing the apple and potato chips in different molarity solutions for a period of time and recording the changes in mass. Hypothesis: The theory for this investigation, which is to be proved or disproved, is that as the molarity of the solution increases the average percentage difference in mass will decrease of both the apple and the potato cells. This means in a lower molarity the chips may increase in mass slightly but in a higher molarity the mass of the chips will decrease. Background information: The whole idea of the investigation revolves around the theory of osmosis. The definition of this term, is "the movement of water molecules from an area of high water potential to an area of lower water potential, through a semi permeable membrane until equal distribution is achieved" Water potential is the measure of the free kinetic energy of the water molecules in the solution and it is the term given to the tendency for water molecules to enter or leave a solution by osmosis. The highest water potential is in distilled water and is said to be 0. Solutions containing a solute therefore have lower water potentials so as the molarity increases the water potential in the solution decreases. The apple chips will contain fructose and sucrose making them more soluble than the potato chips, which contain starch, an insoluble substance. ...read more.

Middle

If they were touching osmosis levels would fall as the surface area of the chips touching would fall, once in the Petri dishes the chips will be spread out evenly to prevent this. In order to keep the temperature the same throughout the test no windows should be opened to keep the room temperature exactly the same again so osmosis is not affected. Every single chip must have identical dimensions and each chip should have its excess water removed equally before reweighing, this will mean all the chips surface areas will be the same and also equal amounts of water will be removed from each chip before reweighing to ensure some chips don't lose more water than others. Finally the chips should be taken from the same type of potato or apple for example the potato chips from a King Edward potato and the apple chips from a Golden Delicious apple. This is because different types of potato and apples could have slightly different structures and so could lose or gain water quicker. The chips should also be made from the same area of the potato or apple for example the core. Predictions: I can firstly predict by using my preliminary work and my background information that at low molarities the chips will gain in mass and in higher molarites the chips will reduce in mass, with the biggest reductions coming from the highest molarity solutions. This is because where the molarity is low there will be a higher water potential in the solution and a lower water potential in the chips. ...read more.

Conclusion

There were other factors which I felt were less significant in affecting the results. The biggest problem was with the variations in length of the chips at the beginning. If a particular chip was longer it would have a larger surface area and so during the time period more osmosis would occur as more of the chip is in contact with the solutions and so a bigger change would occur. This could be prevented if electric vernier callipers were used to cut out the lengths of the chips ensuring all the chips had exactly the same length at the beginning instead of cutting them ourselves and measuring them out with a ruler of a fairly low accuracy (1.0mm) The second biggest problem was with the dilutions and the accuracy at which we made them. When using the syringes to collect the required amount of solution it was difficult to get exactly the required amount and the readings off the syringes were left open to human error. Also the accuracy of the syringes was not particularly high and so measurements may have been slightly inaccurate here and there. If too much water was put into the petri dish the molarity would decrease and the % change in length would be affected as less water would leave the chip. In order to improve this apparatus with a higher degree of accuracy must be used to gather each solution and place it into the petri dishes, this would ensure that exactly the right amount of each solution was in each petri dish and each molarity was what it was meant to be. The third biggest problem with the procedure was the time limit the chips had in the solutions. ...read more.

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