Conclusion
The overall trend of the graph is that as the molarity increases, the percentage change of mass decreases, thus the potato chips mass decreases as they are put in concentrated sucrose solutions.
The graph shows that in the 0.0M and 0.2M concentrations, there is higher water potential in the distilled water and 0.25M solutions than in the potato, which has a high concentration of solutes. This is why the water diffuses by osmosis down the concentration gradient from a higher water potential (high concentration) of water molecules, to lower water potential (low concentration) of water molecules, resulting in the potato gaining mass.
The opposite occurs in the solutions where the molarity is higher 0.4M and 0.5M, the potato in these concentrations looses some mass, because there is a water potential (higher concentration) of water inside the potato than in the solutions, therefore the water diffused out of the potatoes by osmosis because now the sucrose solution has a lower water potential, down the concentration gradient and into the solutions outside, this resulted in the loss of mass.
So as the molarity increases, the potato chip suffers from more mass loss (becomes plasmolysed). And as molarity decreases, the potato chip gains mass (becomes turgid). This shows that osmosis is proportional, net movement of water only occurs when there isn't equilibrium. This process is proven in the scientific knowledge.
As water molecules diffuse into the potato chip, more pressure is applied to its cell wall, this adds to water potential, as the pressure potential is increased the cells become turgid.
Another important fact is that the graph makes a curved shape (if a line of best fit is drawn) that will result in the potato not being able to take in any more water.
Discussion
Water moves from an area of high water potential to an area of lower water potential through a partially permeable membrane. This movement is called osmosis.
A less negative water potential is a higher water potential (nearer to zero) than a more negative, so we can always say that water moves from a less water potential to one with a more negative water potential. This is proven by my results as distilled water 0.0 is a less negative (nearer to zero) and it moves into the potato cells which have a more negative water potential. When the potato cell has the higher negative water potential than the sucrose solution the net flow of water moves into the sucrose solution.
Osmosis and diffusion are passive processes needing only the kinetic energy of particles themselves (they need no (ATP) from respiration).
Evaluation
Sources of error:-
- Equal surface areas of potato discs – the potato discs didn’t have equal surface area. So therefore there wasn’t exactly same amount of potato in each container, which means that we can’t compare concordantly as the surface areas were different.
- Equally sliced discs – the potato discs aren’t equal so therefore the experiment is not consistent as the exact same materials (and dimensions) as they are from the same source but are not identical.
- All the sucrose may have not been removed from the potato discs so the sucrose solution (which may still be on the discs has been weighed as well as the potato discs.
Limitations:-
- The weighing scales – were not accurate as we were handling small numbers so we need a weighing scale which is more precise e.g. that could measure to 0.01g
- Blade- the blade didn’t promise concordant discs of potatoes because you were not able to accurately cut it and then the surface area, length, width were not exactly the same for each disc.
Anomalies:-
I have one known anomaly which is result 4 (0.3 molar solution) because it was the same as it had a very high value compared to other results (and because it was identical to the last result taken). I believe that the anomaly was due to human error which was dude to my colleague for not removing the oil efficiently or it could also be that my colleague wasn’t able to cut the potato discs inaccurately giving them a bigger surface area.
Improvements:-
- A better weighing scale is needed one that measures to a greater degree of accuracy e.g. a weighing scale that measures to 0.001 grams
- Abetter blade or slicer/cutter will help give the experiment a more accurate surface area, length, width etc which will improve the results significantly.
- A more efficient method for removing the oil as this will also improve the results.
