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The aim of the experiment is to investigate the movement of water particles into and out of potato cells by osmosis and to compare the water potential of old and new potatoes.

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Introduction

An investigation to compare the water Potential of old and new potatoes Aim The aim of the experiment is to investigate the movement of water particles into and out of potato cells by osmosis and to compare the water potential of old and new potatoes. From this experiment we should be able to draw conclusions by looking at the change in mass to whether potatoes marketed, as 'new' potatoes really are newly grown or just smaller sized old potatoes. Background Information and Terminology New Potatoes apart from obviously being smaller in size than old ones have a more distinctive sweeter taste. This is because they are still growing so all their energy is stored as glucose, whereas old potatoes have finished growing and their energy is converted into storage polysaccharides such as starch because it is insoluble. The water potential (?) of pure water is zero, when substances are dissolved in water the solutes make the water potential lower so the value becomes more negative. Any substance dissolved in water is called a solute; A solvent is a liquid that is able to dissolve another substance (i.e. A solute) This forms a solution. The water potential of a solution is the term given to the tendency for water molecules to enter and leave the solution by osmosis. Osmosis is the flow of water molecules by diffusion through a partially permeable membrane, from areas of high water potential (low solute concentration) to regions of low water potential (high solute concentration) ...read more.

Middle

* The same old and new potato will be used for samples * All potatoes will be left in the solution for the duration of 48 hours, they must have the same exposure for osmosis to take place. Risk Assessment * Care must be taken when using the scalpel * Care should be taken when using any chemical in the laboratory * Care should be used with glassware * Hands should be washed before and after lab-work * Use the ceramic tile when cutting the potato. Results * New Potato This table shows the results of the experiment involving the new potato. Concentration (mol dm ) Original Mass (g) Final Mass (g) Change in Mass % Change in mass Distilled Water 1.23 1.38 +0.15 + 15% 0.2 1.42 1.50 +0.08 + 8% 0.4 1.48 1.30 -0.18 - 18% 0.7 1.52 1.09 -0.43 - 43% 0.9 1.55 1.24 -0.31 - 31% 1.0 1.46 1.24 -0.22 - 22% * Old Potato This table shows the results of the experiment involving the old potato Concentration (mol dm ) Original Mass (g) Final Mass (g) Change in Mass % Change in mass Distilled Water 1.37 1.45 +0.08 + 8% 0.2 1.57 1.49 -0.08 - 8% 0.4 1.53 1.39 -0.14 - 14% 0.7 1.41 1.06 -0.35 - 35% 0.9 1.49 1.22 -0.27 - 27% 1.0 1.52 1.25 -0.27 - 27% Using the graphs plotted overleaf, the water potential of both the old and new potato can be calculated. By reading of the isotonic points of both varieties of potato, (this is when there is no change in mass) ...read more.

Conclusion

new potatoes have a higher water potential than old because of their composition consisting of higher concentration of glucose energy stores rather than starch. It also supports the claim that yes potatoes sold as 'new' potatoes are actually newly grown potatoes and not smaller sized previously grown potatoes. Evaluation Overall the experiment was carried out efficiently and successfully, no real problems occurred. The results obtained were as accurate as could be expected because there are some limitations of accuracy with this experiment. For example the experiment has limited accuracy due to human error and also due to the equipment, measuring the glucose using a measuring cylinder or cutting the potato to size using a ruler has a limited accuracy of ? 0.1mm. Also it is impossible to tell how much each individual potato piece was dried with paper towel, if some weren't dried as thoroughly as other this would increase their final weight and could lead to inaccurate misleading results. However no obvious anomalous results were obtained that could not be fitted into the pattern in some way. Improvements * To make the experiment as accurate as possible it needs to be repeated more times, (3 for example) for each concentration. This makes any anomalous results obvious and also for an average to be calculated. * A greater range of molarities could be investigated, ideally over smaller increments. This would allow for a more precise graph curve to be drawn, * Ideally all samples should be taken from the same part of the potato to avoid any differences in cell texture and composition. ...read more.

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