In order to prevent this from happening salt is sometimes added to the pure water in the saucepan creating a solution that is equal to or greater than the solute concentration in the potato.
This will prevent water from entering the potato.
Osmosis occurring in Cells
1. In Plants
Plants are able to take up water by osmosis from a solute solution that is less concentrated then their cell sap. It becomes swollen with water. This is called turgid. The plant cells cell wall stops any more water from entering.
If a plant cell is placed in a high solute solution, it looses its water. It becomes plasmolysed and then flaccid. If this happened to the whole of a plant, it would die.
2. In animals
In animals, if the red blood cells are placed in a high solvent solution they take in much water and burst. This occurs, as there is no cell wall to resist the water as there is in plant cells.
If animal cells are placed in a high solute solution, they lose water and become water.
Experiments showing osmosis
Not all membranes are permeable. Most membranes allow either all or none solutions to pass through – only a few are selective.
In order to determine where and when osmosis takes place experiments are necessary. Experiments show which membranes are partially or selectively permeable.
In a common experiment used to prove osmosis, a vertical visking tube containing a solute solution is placed in a beaker of water. The level of solution in the visking tube evidently rises.
Another experiment used to show how osmosis works is when a visking tube is filled with pure water with a coloured dye. A beaker is filled with a solution that has both a solute and a solvent. As the water from the visking tube travels through the tube, it takes the dye with it so that it can be visibly seen.
Hypothesis
The Weaker the Sugar solution is the heavier the potato chips will become.
Apparatus
1. Measuring Cylinder
2. Five Test tubes
3. Test tube rack
4. Carving Knife
5. Weighing Scales
6. Tile
7. Five Beakers
Method
The potato chips were first cut up into 15 pieces. Each piece was weighed and measured and then recorded. 20 ml of each of the following were put in separate test tubes: 0.2, 0.27, 0.3, 0.4g sugar solutions and distilled water. Three potato pieces were placed in each test tube – each numbered in order to keep an accurate account of how much weight each potato piece had lost or gained. The potato chips were then left in the test tubes for 24 hours. They were then dried and weighed. The results were recorded. The only thing that was changed was the concentration of sugar in each of the solutions. This was done to ensure that it was a fair test. Three potatoes were used in each test tube in order to get a mean mass change in order to get a more accurate result.
Prediction
I predict that the weaker the sugar solution is the heavier the potato chips will become. This is because the cells in the potato are partially permeable. The water goes from an area of low solute concentration to an area of high solute concentration.
Conclusion
I proved that my prediction was correct. The three potato chips that were left in the Distilled water and 0.2g solutions for twenty-four hours had a higher mass then they had before. Incidentally, the potato chips that had been left in the 0.3 and 0.4g sugar solutions had lost mass. The potato chips that were in the 0.27g sugar solution had relatively the same mass.
According to my graph the isotonic point, (the point where the solute concentration of the solution in the test tube is equal to the solute concentration of the potato,) is reached at approximately 0.24g sugar solution.
The experiment also proves that osmosis is the net movement of water from an area of high water concentration to an area of low water concentration. It also shows that the membrane of plant cells in the skin of the potato is partially permeable.
Evaluation
In order to ensure that it was a fair test I made sure that I kept the following factors the same:-
* The Volume of solution in each test tube
* The length of the potato chips
* The Width of the potato chips
* The amount of potato chips in each test tube
In order to get a more precise result I could have used five potato chips in each test tube. This would have enabled me to get a better mean for the mass change of the potatoes in each solution.
In order to get a more varied result I could have used several more different sugar concentration solutions. If I had I would have been able to find the exact isotonic point.
None of my results were completely unexpected but a few were slightly further from the line of best fit. This was mainly caused by human errors. One example is when the potatoes were dried – some were dried too much and perhaps even squeezed where as others were not dried enough so there was still too much water that would have made the mass seem higher then it actually was.
Overall I believe that the investigation went fairly well. My graph made sense and showed an expected set of results.
