Incipient Point of Plasmolysis Lab
Investigation of the point of incipient plasmolysis of onion cells (Allium cepa) using NaCl (Sodium Chloride) concentrations of 0. 1M, 0. 2M, 0. 3M, 0. 4M, 0. 5M, 0. 6M Design Research Question (Aim): The aim of this lab was to determine the point of incipient plasmolysis of onion (Allium cepa) cells using Sodium Chloride (NaCl) concentrations of 0. 1M, 0. 2M, 0. 3M, 0. 4M, 0. 5M, 0. 6M. Hypothesis: When the water concentration of a solution outside the cell is lower than the concentration inside the cell, water will move from the inside to the outside of the cell due to osmosis.
As we increase the concentration of the NaCl solutions we have used (0. 1M to 0. 6M), more moles of NaCl are dissolved in the solution. Thus, the solutions increases in solute concentration but decreases in water concentration. We can therefore assume; the higher the concentration of the NaCl solution, the higher the number of plasmolysed cells as water moves outside the cell in order to dilute the NaCl concentration.
Qualitative Data:
In general, it was hard to keep an overview of the cells one has counted yet and one has not as one only counted the cells at random. To this, it was hard to determine visually whether a cell was plasmolysed or not so that one could have assumed some cells to be plasmolysed although they were not. Finally, as the results of our first trial show, we did not allow enough time for the cells to plasmolyse so that the results became inaccurate. I have calculated the average for the second and third trial only in addition to the overall average so that I can draw another graph of the averages of the second and third trial only since the results of our first trial seemed to be inaccurate. Sample Calculations:
Percentage: In order to determine the percentage of plasmolysed cells for each solute concentration, one can use the following formula; (N:T) x 100, where N stands for the numerical value (in this case the number of plasmolysed cells we have counted) and T stands for the total (in this case 30). For example, if one would want to calculate the percentage of 2 out of 30, this would result in the following formula; (2:30) x 100, since 2 is the numerical value (the number of plasmolysed cells we have counted) and 30 is the total. Average: To calculate the average, one simply adds the values and then divides it by the number of values.
One could also use the formula (? x) : n, where x are the individual values of plasmolysed cells for each trial and n is the number of values. For example, if one would want to determine the average for the number of plasmolysed cells for the concentration of 0. 6 M, one would simply add 20, 100 and 100 and then divide it by 3, since the number of plasmolysed cells is the x-values and 3 in this case is the n value. Figure 1: The average percentage of plasmolysed cells ±3. 33% of all three trials determined for each of the six NaCl concentration. The graph shows a linear trend-line in order to determine the point of incipient plasmolysis. Figure 2: The average percentage of plasmolysed cells ±3. 33% of only the second and third trial determined for each of the six NaCl concentration. The graph shows a linear trend-line in order to determine the point of incipient plasmolysis.
Conclusion & Evaluation
Conclusion: As the NaCl concentration outside is increased, more NaCl molecules are dissolved in the solution causing the solution to have a higher solute concentration but a lower water concentration. The water from the plant cell thus has a higher concentration than the outside diffuses (through osmosis) in order to dilute the NaCl concentration.
The turgor pressure that maintains the shape of the cell by pushing the plasma membrane against the cell wall is then lowered causing the cells to shrink. This is known as plasmolysis. Our hypothesis; the higher the concentration of the NaCl solution, the higher the number of plasmolysed cells as water moves outside the cell in order to dilute the NaCl concentration was therefore correct. Furthermore, we have used Figure 2 in order to determine the point of incipient plasmolysis as the results are more representable of the whole since the first trial was not included.
Figure 2 indicates that the point of incipient plasmolysis lies at approx. 0. 42M. Supporting my findings, a similar experiment was done however with saccharose solution instead of NaCl. The results show that the point of incipient plasmolysis lies of this experiment lies approx. 0. 38M which is fairly close to my results (Stadelmann, 156). In general, one can assume that the higher the concentration of the outside solution, the higher the number of plasmolysed cells as water moves outside the cell in order to dilute the outside oncentration.
Evaluation:
| Limitation | Significance | Improvement | ||
| It was hard to determine the number of | As there were generally more than 30 cells | We could have used the method of a | ||
| plasmolysed cells visually as we just counted | visible in the eye piece, it was not too hard | hemocytometer instead so that we could have | ||
| 30 visible cells at random and did not have an | to count 30 individual cells. |
However, we could counted the number of plasmolysed cells per overview of the cells we have already counted. Have still counted one cell twice and assumed square. In addition, it was hard to determine if a cell that it was two different cells. This was plasmolysed or not. limitation therefore causes an overall inaccuracy. Furthermore, we could have assumed some cells to be plasmolysed although they were not plasmolysed. We only estimated what the point of incipient. This only has a slight significance on the plasmolysis approximately would approximately exact accuracy of the point of incipient concentrations we were given and then determine be basing it on our graph (figure 1) and only plasmolysis. Where the point of incipient plasmolysis using concentrations of 0. 1M, 0. 2M, 0. 3M, 0. 4M, approximately lies.
