HypothesisI predict that the percentage of plasmolysed cells will increase as the concentration of the NaCl is increased. This is because the high concentration of salt in the soloution will cause more water to diffuse out of the cell by osmosis, as the concentration gradient will increase. VariablesDependent; % of cells plasmolysed as a result of the change in solution concentration. Independent; Concentration of the solution in M Control; number of cells used for the percentage, size of the sample of onion, same onion used in every test Apparatus
Method
ResultsGraph showing percentage of cells plasmolysed against concentration of solution in ConclusionThe results show here that the increase in the concentration of the soloution will indeed cause the % of cells that show plasmolysis to increase as well. This is proven as an increase in the concentration of the surrounding soloution will mean that there is a lower concentration of water molecules outside the cell than in. The concentration gradient will increase as the concentration of water outside the cell decreases and so more water will diffuse out by osmosis and so will cause the cell membranes to retract from the cell wall as the cell now no longer is turgid and has a lower turgor pressure creating more cells that display plasmolysis Its also worthy to note that as the water potential of the surrounding soloution decreases as the concentration increases meaning more water will be drawn out of the cell. When we get to the point where 50% of the cells are plasmolysed we get something called incipient plasmolysis. This is where the concentration of the water both in and out of our cell is the same. For us this point seems to lie just over the 0.6 mol dm-3 so we can deduce that the point of incipient plasmolysis will be at 0.64 mol dm-3 EvalutationThis experiment could have been a lot more reliable when producing our results. Unfortunately we were very much constrained for time so we had no time to do repeats for our experiments so the results are just from one round of trials. However I feel like the accuracy of the equipment was more than adequate for the experiment. The error on the ruler (± 1mm), the timer (± 0.5 ms) and the syringe (± 0.5 ml) are adequate enough to provide very accurate results. I thought that the variable intervals we a bit too large, IO think that they could have been brought down to 0.05 per interval but this would have taken up too much time. However it would have allowed us to see a little bit more clearly where the jump in % plasmolysed starts between 0.5 and 0.6 mol dm-3 Finally I think we could have maybe introduced another control variable in the form of temperature. We could have done this by placing our sample and soloution into test tubes in a set temperature water bath ResearchResearch
Plasmolysis can also have an industrial effect as it helps the in vitro embryogenesis to be more successful An article from PCTOC ( Plant Cell Tissue and Organ Culture ) states: "Adventive embryogenesis in vitro-grown somatic cells of Daucus carota L. was increased three-fold by a 45 min plasmolysis pre-treatment using 1M sucrose solutions. A high degree of synchronous development also resulted from this treatment. The enhancement of embryogenesis is interpreted as an increase in the regeneration of cells which have become physiologically somewhat isolated from the tissue of their origin by the plasmolysis-caused rupture of plasmodesmata."[1] [1] Wetherell, D.F., 1984. Enhanced adventive embryogenesis resulting from plasmolysis of cultured wild carrot cells. Plant cell, tissue and organ culture, 3(3), pp.221-227.
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