The characteristics observed of the different potato samples after 35 minutes in solution are shown below:
Results:
The following table shows the results from the data collected regarding the weight of the potatoes before and after they undergo the process of osmosis and showing this relationship clearly in the last columns, where the percentage change is calculated:
The graph below portrays the results of the last columns of the graph (the percentage change from the original weight) in all solution concentrations and a best fit line:
The following graph shows all sucrose concentration data with the purpose of finding a best fit line according to its sucrose concentration and thus a clear relationship between the two variants presented:
We can appreciate that, as the concentration of sucrose increases the percentage change in weight of the potato decreases from an increase of 9% in weight, in a distilled water or 0M sucrose concentration solution, to a decrease in weight of 20% in the beaker containing a solution of 0.9 M sucrose concentration. This is more clearly shown in the best fit line (in black) as opposed to the actual data line (in blue). This means that these two variables (the percentage change in weight and the solution concentration) are inversely proportional or share a negative correlation.
Discussion
Conclusions:
As we can appreciate from out results, the amount of sucrose concentration in solution greatly affects the weight of the potato sample. As the amount of sucrose concentration increased, the weight of the potato decreased. This clearly proves how osmosis took place.
In a 0M sucrose or distilled water solution, the concentration of water molecules was greater outside and cells will travel across the ppm of the potato cell to try to balance this difference in concentrations, increasing the amount of water inside the cells. This is why the potato samples up to a 0.2 M sucrose concentration were found to be bigger and heavier, more turgid. This means that the solution is hypotonic and that, up to that point, the concentration of sucrose was greater inside the cells than in the solution. In the last graph shown a dot marks the point in the best fit line where the weight change is 0 (approximately at 2.2M sucrose concentration). This point would represent when the solution in the beaker is isotonic, meaning the concentration inside and outside the potato cells is the same, so the water molecules do not need to travel across the ppm.
Conversely, the samples of a 0.3 M sucrose concentration and above show a decrease in weight as well as a loss in firmness (flaccid) and start to wilt. The sucrose concentration in the solution is higher than that found inside the potato cells (hypertonic) and water molecules will flow outside the ppm causing cells to shrink, wilt (in plant cells) and eventually die.
The differences in concentration are shown in the following diagram:
Effects of the sucrose concentration in a potato cell
We also appreciated that sucrose density varied with its concentration when some potato samples floated in the 0.6M and 0.9M solution concentration, those of highest concentration. Consequently, this is prove that a potato’s density remains the same and hinted this particular samples density must have been under the density of the 0.6M sucrose sample.
The two samples which were placed in a starch solution, though experiencing an increase in weight, failed to show a significant difference between each other, due to their concentrations. This means that starch has no effect on osmosis as the increase in weight was also similar to that in distilled water. The difference between the effects of sucrose and starch, both carbohydrates, is due to their structure. Sucrose is, as it is known, a disaccharide consisting of a molecule of glucose and one of fructose. Its small structure makes it easier to dissolve in solution. On the other hand, starch is polysaccharide of a large structure. This means it is more difficult to dissolve it and when tried to do so in water there will we spaces between the polymer chains containing water molecules, unlike sucrose where all the spaces in the water solution will contain this disaccharides molecules.
This means that the gradient or water concentration of starch remains unaffected and thus water molecules do not have the need to cross the ppm as the strength of water between starch molecules remains; in those gaps there is only pure water molecules (if distilled water is used).The properties of these two carbohydrates can be shown in several processes performed in organisms of both animals and plants.
When plant cells store glucose, water which will assumedly have a lower concentration will travel across the gradient, entering the cells and limiting storage capacity. However, if they store starch, a gradient is not created so storage capacity is increased.
This is also shown in the liver when our organisms store starch when storing carbohydrates. Since animal cells do not own a cell wall, they have the risk of bursting if they store much sucrose because water molecules would enter the cell to level the water concentrations and it volume would increase.
Marielle Alvino