Determination of Plant Tissue Water Potentila by Measuring Changes in Dimension
... whether taking potatoes out of the solution, drying them with a paper towel and weighing them so many times would effect the osmosis. I, therefore, decided to carry out a second experiment in which I put the potatoes into the test tubes containing sucrose solutions and did not handle them until the final reading 30 minutes later. I have found out that handling the potatoes several times during the experiment did effect the final results slightly. I think that this was mainly due to the way the potatoes were dried before each weighing. I have drawn a graph plotting the results of the first experiment joining them with a line X. Results of my second experiment form line Y. I have then taken the results from the first and second experiment and counted the average results, which are plotted on the graph under line Z. The graph shows that the potato in the 0.0M solution and in the 0.25M is hyperosmotic. This means that there is higher water potential in the distilled water and 0.25M sucrose solution than in the potato. Therefore, this is why the water diffuses by osmosis down the concentration gradient from high concentration to low concentration, resulting in the potato gaining mass. The opposite occurs in the solutions where the molarity is higher i.e. 0.5M, 0.75 and 1.0M. The potato in these solutions is hypo-osmotic because there is higher concentration of water inside the potato than in the solutions, therefore the water diffused out of the potatoes through the partially permeable membrane by osmosis down the concentration gradient and into the solutions outside. This resulted in the loss of mass. On my graph I marked the point where the graph line (of average results = line Z) crosses the place on the axis where the potato neither loses mass nor gains mass. This happens at approximately 0.4M, which means that 0.4M of sucrose would be the isotonic solution for the tested potato. I have found out that each potato has to be in the solution for at least 10 minutes in order for us to notice that osmosis is actually taking place i.e. any difference in the weigh of the potato. In my first experiment, where I weight the potatoes after only 5 minutes, there was a slight increase in weight in all of the potatoes, which I think only confirmed the inaccuracy caused by the way the potatoes were dried before weighing. Obviously, I would have had to allow more time for each experiment in order to find the potato saturation point (when the potato can no longer take in any more water) and the dehydration point (when the potato cannot lose any more water). Evaluation of practical work In this experiment, I believe that I have collected enough data to support the theory of osmosis. The results were fine and by looking at the weights measured before the expe...