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The aim of this experiment is to work out if potatoes lose or gain mass in different sugar solutions due to osmosis and to solve where the water concentration outside the cell is equal to the concentration inside the cell;

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Introduction

The Aim: The aim of this experiment is to work out if potatoes lose or gain mass in different sugar solutions due to osmosis and to solve where the water concentration outside the cell is equal to the concentration inside the cell; this is known as the isotonic point. In the investigation I would have to be as precise and accurate as I possibly can in order to have a reliable set of results for a good conclusion. Introduction: I am going to perform an investigation on osmosis in potato cells. Osmosis is the movement of water molecules through a semi permeable membrane, separating solutions of different concentrations. The water molecules pass from a region of high concentration to a region of low concentration. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than any other. Many cell membranes behave as semi permeable membranes, and osmosis is a vital mechanism in the transport of fluids in living organisms, for example, in the transport of water from the soil to the roots in plants. If a cell is in contact with a solution of lower water concentration than its own contents, then water leaves the cell by osmosis, through the cell membrane. ...read more.

Middle

Fig. 1 Volume of distilled water (cm3) Volume of 1Molar sugar solution (cm3) Concentration of sugar solution (M) 10 0 0.0 6 4 0.4 2 8 0.8 0 10 1.0 I chose these certain concentrations because I wanted there to be a distance between the concentrations in order to get a wider set of results and a smother curve on my graph. If I chose concentrations that were close together I would not be able to see much difference between the concentrations and it would affect the graph because it would not be clear to see changes between concentrations. So in other words doing so makes my results more reliable because of the wide range. Precautions: During this investigation the measurements for the solutions had to be precise as to not change the outcome of the experiment. I had to ensure that I took care cutting the potatoes because I could have easily cut myself by accident. I also had to ensure that every time I handled the potatoes my hands were clean and dry. This was to stop any kind of contamination and made sure that I did not pass on any extra water onto the potato which would alter the tables of results for all concentrations. How I kept it a fair test? : To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable is changed. ...read more.

Conclusion

So I believe that the reliability of my investigation is sufficient to back up my conclusion. I have several proposals for further experiments to provide additional evidence for my conclusion. I would like to undertake another experiment with sucrose concentrations at 0.05 intervals from 0 to 1. I would like to do this as I feel it would provide a better and more reliable set of results and a more justified conclusion. When there are more concentrations the shape of the curve shape can be seen more clearly, I suspect that at the lower concentrations of sucrose the graph falls more steeply, flattening off at higher concentrations. I would also like to conduct an investigation, in conjunction with this experiment, to calculate the concentration of sap within the vacuole. To do this, I would find between which parameters the curve crosses the x-axis of sucrose concentration and retest at every 1% between these two parameters until I have found the concentration which contains a core that neither gains nor loses mass. This osmotic concentration would be the equivalent of the sap in the vacuole (isotonic point). As an extension to this investigation, I would run two experiments in parallel. All cores would be from the same potato, but one would run for an hour, as this one did and for the other the cores would be left in the solutions for longer, perhaps 24 hours, to establish if one hour is the end point of the osmotic diffusion. ...read more.

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