The aim of this experiment was to determine the different affect that distilled water (DW) and sodium chloride (NaCl) have on plasmolysis in potato cells. Plasmolysis is the contraction of the protoplasm in a living cell when water is removed by osmosis, resulting in the contraction of the cytoplasm away from the cell walls, in other words the cell becomes dehydrated (Lawrence, E. 1995). Substances are held within a cell with biological tissue such as the plasma membrane, the membrane controls the cells homeostatic status directing movement of substances into and out of the cell. For this particular experiment water moves passively across membranes by osmosis from a higher free energy level to a lower free energy level (Knox, Ladiges, Evans & Saint. 2010).
Materials used included three 50ml beakers, scales, tweezers, 12 cylinders of potato cuts, 30ml DW and 1.5M of NaCl. In order to determine the affect of each solution on plasmolysis in potato cells we cut 12 cylinders of potato into 1cm lengths, weighed them and then immersed them in a beaker of either DW, 0.5M of NaCl or 1M of NaCl, with four cylinders of potato in each beaker to determine an average score for each solution. We then weighed each cylinder of potato at staggered five minute intervals, ensuring correct measurement, for a total of thirty minutes (Kemp, A. 2012). We sectioned the base of each beaker into quarters in order to distinguish and keep track of each potato cylinder, dabbing each cylinder on paper towel before weighing. Once we had completed weighing all the cylinders from each beaker after the thirty minute mark we placed one slice of one cylinder from the 1.0M NaCl, which we thought would show the greatest amount of plasmolysis, onto a microscope slide at 100X magnification, examining the cells and then drawing what we could see, shown in results section.
All results obtained from Mudra, C. (2012). Figure1: Average weights (grams) of potato cylinders over thirty minutes
As seen in Figure 1 the weight of the potato cylinders in each different solution increased and reduced over the time period. The weight of the potato that was placed in the distilled water experienced an increase by roughly 50 milligrams over the 30 minutes with the greatest increase in the first five minutes. The potato placed in the 0.5M NaCl solution saw a decrease in the mass of the potato with a relatively steady decline over the half an hour, overall the weight decreased by 90 milligrams. Figure 2 shows the progressive change in mass over the 30 minutes and clearly illustrates the decrease in mass that the potato placed in the 0.5M NaCl solution experiences. The pattern of weight gain/loss for the potato placed in the 1M NaCl solution is not particularly recognisable, it remains fairly steady with a particularly large increase in the last five minutes (as seen in Figure 2). The rate of change for the potato placed in the 0.5M NaCl solution was the most significant at 3mg/minute, while the potato in the distilled water experienced a rate of change of 1.7mg/min. The potato placed in the hypertonic solution; 1M NaCl was expected to experience plasmolysis although the results do not show this particularly well.
Table 2: Average rate of water flux Overall Difference In mass (mg) Rate of water gain/loss per minute (mg/min)
Distilled water 50 1.7
0.5M NaCl 90 3
1M NaCl 10 0.3
Discussion: The aim of this experiment was to determine the different affect that DW and NaCl have on plasmolysis in potato cells. It was clear that NaCl had an affect on the weight of the potato cylinders over the thirty-minute period as both the 0.5M and 1.0M solutions showed a decrease in weight of 0.5grams and 0.1grams respectively. Knox, Ladiges, Evans, and Saint (2010) stated that water travels passively across membranes from a higher free energy level to a lower free energy level. From the experiment we can see…