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My aim is to workout the different water potentials of Swede and potato cells. I will do this by looking at changes in mass when they are put into different concentrations of sucrose solution.

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A/S Biology-Comparing the Water Potential of Potato and Swede Aim: my aim is to workout the different water potentials of Swede and potato cells. I will do this by looking at changes in mass when they are put into different concentrations of sucrose solution. Introduction I will need to first understand the behaviour of water in order to fully comprehend and successfully interpret the information, which may be gained from carrying out this experiment. The water molecule is made up of one oxygen atom, which is joined by two hydrogen bonds by sharing the same electrons; this bond is called a covalent bond. Because of this the water molecule is a stable and fairly unreactive molecule. In addition to this it also has numerous unique properties. I will also need to understand water potential. Water potential is the inclination of water molecules to move from one location to another. The representation of water potential is the Greek letter psi, ?. Water potential = solute potential + pressure potential ?w = ?s + ?p Osmosis is a special case of diffusion. It is the net movement of water molecules from a region of high water molecule concentration to a region of lower water molecule concentration, across a partially permeable membrane. A hypotonic solution is, a solution, which has a lower solute concentration than the sample. A hypertonic solution is a solution, which has a higher solute concentration than the sample. Prediction I have come to two testable hypothesises after carrying out some background research. I have also used my preliminary experiment as a guide. My hypothesises are: > Potato has higher water potential than Swede. > As the concentration of the sucrose solution increases, both vegetables lose mass, however potato loses more mass than Swede. When placed in a hypotonic solution, according to my research the water potential of the cells (potato/swede) would be higher then the water potential of the external solution (sucrose solution). ...read more.


> Using the same strength of sucrose solution I need to use the same strength of sucrose solution whilst I am making different concentrations for my vegetable samples. This is because, even though I will be using different concentrations I need to use the same sucrose solution to start with. This will ensure that my results are as reliable as they can be. > Ensuring the temperature is constant throughout the experiment A change in temperature can effect the results of this experiment. As a rise in temperature would increase the collisions between the molecules. This is because the molecules in the solution would obtain more kinetic energy enabling them to move faster and therefore more successful collisions would occur. And so I will need to keep the temperatures of the sucrose solution and vegetable at a constant. > Using the same pipette to measure the solutions Making sure that the same pipette is used throughout the experiment is important, as contamination would not be a problem. This would affect the results of the experiment as the concentration of the solutions may change if contamination occurs. I will also need to make sure that I read from the bottom of the meniscus every time I use the pipette to get accurate results each time. > Using the same weighing equipment each time It is important to use the same weighing equipment each time as a change in weighing equipment could lead to inaccurate measurements. This is because one weighing scale could be taking measurements to 0.2g whereas another balance could be taking measurements to 0.1g. Although this may not seem like a major difference it could effect the final result. > The overall amount of each solution I need to keep the overall amount of each solution the same the more solution the test tube contains; the more particles there are in that particular volume. ...read more.


This shows that the pressure potential is a limiting factor. I also found that my second prediction proved to be true. My prediction was that, both swede and potato would lose mass in a high concentration of sucrose solution. In this case potato lost more mass than swede, because the potato contains a higher amount of water molecules than swede. Evaluation Looking at my graph it can be seen that I only have one slightly anomalous result. It is located on the potato results at the point of the concentration 0.4 moles/litre. Reasons for this could be lack of accuracy, or carrying out techniques inefficiently. For example; the sucrose, due to human error, may not have been read from the bottom of the meniscus. The potatoes may not have been blotted exactly the same as it is highly unlikely that the same amount of pressure was used each time. This sample of potato may not have been exactly the same size giving it a larger surface area. Other limitations I had were the fact that I could only repeat my experiment once due to lack of equipment and time. Repeating it more times or more then once would have most definitely increased the reliability of my results. This limitation of equipment and time only allowed me to have 6 samples. A large number of samples would have given me data over a larger spread and therefore in more clearer interpretation. Equipment of better quality and latest technology would have enabled me to produce more dependable results. The variables I kept constant did experiment justice and allowed it be as accurate and dependable as possible. However there are obviously the above exceptions. Improvements I could make to my experiment are to first and foremost ensure that the above limitation are invalid. I could be more accurate, and carry out more repeats. Overall, I understand that, to reach a reliable conclusion my experiment on its own is not enough. Ideally another experiment should be carried out to sustain my conclusion. Different variables or isotonic points could be considered. ...read more.

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