We will do a preliminary test to find out if there are any problems in our investigation, so we can fix or change them for the final experiment.
Prediction
In a high concentration of water the amount of sugar is low, this could be called a weak or dilute solution. In a low concentration of water the amount of sugar is high, this could be called a strong solution. When the two solutions are divided by a semi-permeable membrane the water will move from the area of high concentration to the area of low concentration, until both sides have reached equilibrium.
Knowing that osmosis will occur across a semi-permeable membrane whenever there is a difference between the water concentrations on the two sides of the membrane, and knowing that when this happens to cells they will either become turgid if water flows into them, or plasmolysed if water flows out of them, and thus change their volume, we want to test that: If the concentration of a solution into which a cube of potato is placed is greater than a certain level the cube will contract, and if the concentration is less than that level it will expand. This can be seen in living cells. The cell membrane in cells is semi-permeable and the vacuole contains a sugar/salt solution. So when a cell is placed in distilled water (high water concentration) water will move across the semi-permeable membrane into the cell (lower water concentration) by osmosis, making the cell swell.
This cell is now turgid. If done with potato cells the cells would increase in length volume and mass because of the water. If these potato cells were placed in a solution with a low water concentration, then the opposite would happen.
Water would move out of the cell into the solution. The potato cells will have decreased in length, volume and mass.
The greater the concentration of water in the external solution the greater the amount of water that enters the cell by osmosis. The smaller the concentration of water in the external solution the greater the amount of water that leaves the cell.
However, there will be a point where the concentrations of water inside and outside the potato cells are isotonic. At this point there will be no change in the length, volume and mass of the potato, as the net movement of water will be zero, no osmosis has occurred.
I think that this will happen in our potato cubes. The cubes in the stronger water solution will become turgid and the cubes in the weak water solution will become plasmolysed.
Observation
I have made the following graphs: (mass/concentration, % loss or gain/concentration and difference/amount of water or glucose)
Analysis
This graph tells me that the more water the larger the mass increase. The more glucose the more the potato chip will decrease in mass.
This graph tells me that the more glucose a potato is left in, the more mass is will loose, and the more water it is left in, the more mass it will gain.
These graphs show that the more water, the less difference in mass, and the more glucose, the larger the difference in mass.
All my graphs agreed with what I predicted. This is due to osmosis, where water passes from weak solutions to strong solutions across a semi-permeable membrane, such as a cell membrane. The potato had a lower concentration of water then the test tube when the test tube had a larger concentration of water, so the water osmosed into the potato until both the potato and the water reached equilibrium. This may not happen in certain conditions, if the temperature was very hot then the water would evaporate, and it wouldn’t have enough time to osmose properly and I would have an unreliable result.
There were no errors in my experiment and I had no anomalous results. All the apparatus was accurate enough and working properly, however, I could have used a more exact tool to cut the potato with in the first place, so they were all the exact same size. I think the way I did the experiment was accurate and fair, but it could be more accurate and fair if I started with all the potato chips the same size, and I could also maybe put the test tubes into a controlled environment so the temperature wouldn’t fluctuate.
