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Investigate what factors would have most effect on osmosis in plant cells.

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OSMOSIS INVESTIGATION Introduction Osmosis is the diffusion of water molecules across a partially permeable membrane, from a region of high concentration to a region of low concentration. The partially permeable membrane contains a series of small holes, allowing only water molecules to pass through, as shown in the diagram below. The glucose molecules (represented by red circles) are too big to fit through the membrane. As there are a greater number of water molecules (represented by blue circles) on the left side, there is a steady net flow into the right side with fewer water molecules, i.e. into the stronger solution. Water moves into and out of plant cells by osmosis, depending on the concentration of the surrounding solutions. When water moves into a plant cell, the vacuole increases in size, pushing the cell membrane against the cell wall. The cell wall makes sure that too much water doesn't enter, which would cause the cell to burst. The cell becomes turgid or firm when the cell membrane pushes against the cell wall. It gives the cell support and keeps the plant upright. Plant cells which do not receive enough water cannot stay turgid and so wilting occurs. Cells which are not turgid are described as flaccid. ...read more.


being able to show whether the mass of the plug has increased or decreased. Identifying variables (a) Independent variable. The independent variable is the factor that needs to be changed to experiment. In this case, the independent variable is the sucrose concentration of the water. (b) Dependent variable. The dependent variable is what is measured in the experiment, and here it is the change in mass of the potato plug. (c) Control variables. The control variables are factors that need to be kept the same in order to make it a fair test. There are many control variables in this experiment, including volume of water, atmospheric temperature, shape of container, time elapsed, initial mass of potato plug, same potato used, same scales used, etc. It is also important to repeat the test a number of times and get the average results, in order to make my results as precise as possible. Instead of doing the test again myself a number of times, I will get the results from other groups doing the experiment. Safety factors In order to keep my experiment safe, I will: do all cutting on a white tile; be careful not to spill any sucrose solution or distilled water; have paper towels near at hand to clean up any spillages which may occur; take care while using the scalpel. ...read more.


I think the time that I used for the experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I might well increase the length of time to allow more osmosis to happen and possibly find out the saturation point of the chips. The range of concentrations was adequate, but if I were to do the experiment again I would possibly create more concentrations so that I would have more varied results. This way would have allowed me to also find out the isotonic point far more accurately as the one that I estimated (page 5) is rather approximate. I could have also made the results more accurate, i.e. to records my results to more than only two decimal places. There were not many out of the ordinary results, but some were not as close to the line as others. When the potato chips were removed from the test tubes and dried some groups may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. However with all this said I think that the experiment was quite successful and I was very pleased with the complete comparison of my results with my initial prediction. - Page 1 - ...read more.

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