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Determining the water potential of potato tuber cells.

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Introduction

Determining the water potential of potato tuber cells I will carry out an investigation that will enable me to determine the water potential of the tested potato tuber cells. Water Potential is the measurement of the tendency of water molecules to move from one place to another. (Ridge 1991) Water always moves down the water potential gradient, therefore moving from an area of higher water potential to an area of lower water potential. Equilibrium is reached when the water potential in one region is equal to the water potential in another region. For example, if a plant cell (like the potato tuber cells) is in equilibrium with an external solution of such a concentration that there is no net gain or loss of water then the water potential of the external solution will be equal to the water potential of the cell. (Roberts 1991) By convention, the water potential of pure water is set at zero. Knowing that solutes make the water potential of solutions lower, solutes make solutions negative. Solute potential is the amount that the solutes lower the water potential of a solution. Pressure potential is especially important in plant cells. If a plant, for example the potato tuber cells, is placed in pure water (or a dilute solution), the water (or solution) has a higher water potential than the plant cell. This causes the movement of water to the cell due to the higher water potential in the cell. Water enters a cell through the partially (semi) permeable membrane by osmosis. Osmosis is the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. The diagram below shows the water potential changes in a plant cell in a solution of different water potentials (Cambridge 2000) The different changes shown in the diagrams are caused because all plant cells, unlike animal cells, have a cell wall. ...read more.

Middle

8. I will then plot a graph to show my results and enable myself to compare the change in mass to the molarity of the sucrose solution. Before and whilst carrying out my investigation I must consider safety. The most obvious danger in this investigation is the knife needed to cut the potato tuber cell to the necessary shape. I must take great care when handling the knife and ensure it is put away when not in use. The knife is not the only safety aspect I need to consider. Although there are no other immediate safety hazards, like the knife, I will wear safety goggles at all times during the course of the experiments just to be sure that the either solution or the water being dealt with do not enter my eye and cause unnecessary irritation. I also need to clear any obstacles from the laboratory, for example objects that I could trip on - like a stool. Here are the results from my investigation. CONCENTRATION OF SUCROSE SOLUTION (M) AVERAGE INITIAL WEIGHT OF POTATO (g) AVERAGE FINAL WEIGHT OF POTATO (g) AVERAGE CHANGE IN WEIGHT (g) AVERAGE PERCENTAGE CHANGE IN WEIGHT (%,g) 1 4.38 2.12 - 2.26 - 52 0.8 3.97 1.86 - 2.11 - 53 0.6 3.93 2.25 - 1.68 - 43 0.4 4.30 3.12 - 1.18 - 27 0.2 4.57 4.55 - 0.02 - 0.44 0 4.37 4.76 + 0.39 + 8.94 The results table above shows the total weight of the three potato samples before and after the samples were placed in the different concentrations of sucrose solution. I have then calculated the average change in weight for all the potato samples and the average percentage change in weight. This allows me to easily compare my results obtained while carrying out the experiment. During the experiment I looked out for any unexpected activities or observations and I noted these down. ...read more.

Conclusion

Another less significant limitation during the preparation of the samples was the fact that the sample could have unintentionally been placed on a drop of water or a wet paper towel, while weighing it. This extra water may have caused the sample to have less solute in it than the solution, making it less dense. This extra water also had an effect on the results due to the fact that more water would have been lost by osmosis. My results are accurate and reliable. Nevertheless there were several aspects of my investigation that I would definitely change if I ever was to re-do this investigation in the future. My accuracy of observations and noting down any other significant information down efficiently during the experiments could be improved. I did not record the actual type of potato I used in my investigation, this was important as there are hundreds of types of white potatoes. Also, most importantly, I would ensure that I recorded the individual weights of each individual potato sample before and after the experiments take place. I only recorded the average weight of all three experiments with the same concentrations of sucrose solution. If I had recorded this information it would have significantly improved the accuracy of my results and made it much easier for me to identify any anomalous results or errors. Due to the fact that there were several sources of error in my investigation there are uncertainties in my results and therefore also uncertainties in the validity of my conclusions. However despite the possible improvements my results justify my prediction which was based on scientific knowledge. Before carrying out the investigation I predicted that the water potential of the potato tuber cells would be within the range of minus 1200 kPa and minus 200 kPa. My prediction was correct and my results justify this despite the accuracy factors that could be improved. This shows that the uncertainties in the evidence I collected are not a significant problem, in fact they did not effect the validity of my results at all. ...read more.

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