Change in mass/Initial mass * 100
To make this experiment fair, I will take many precautions;
- I will keep the potato chips in the same environment, therefore if in different temperatures particle movement may vary
- I will keep the volume of the solutions the same – 15ml
- I will use potato chips, that are from the same potato, due to older potatoes having more starch in them
- I will use the same size potato borer, therefore having the potatoes the same size. As if one potato was longer than another, the surface area would be bigger and there would be more space for osmosis to occur
To make the experiment accurate;
- I will use the same apparatus
- I will keep the potatoes in the same environment, therefore keeping them at room temperature
- I will use the same volume for each test
- I will use the same borer, therefore keeping the surface area the same
To make the experiment reliable;
- I will use the same scale to measure the mass of the potatoes, as some scales can be faulty or measure differently from other scales
- I will use the same measuring cylinder, as markings can vary from each cylinder
There isn’t much need of safety precautions in this experiment, due to no toxins or open flames being used, but I would do the necessary precautions of tying your hair back, and wearing overalls to protect clothing from spillages. Take care with cutting and make sure glassware is away from the edge of the desk, to prevent accidents.
Results:
(Graph attached)
Analysis: Looking at the graph you will notice that the graph shows a positive
correlation. My results agree with my prediction in the sense that they are
showing the same thing that I had predicted. Which was, that the potato chip
would increase in mass when it was put into pure water and would decrease in
mass when put into pure sucrose solution. The steepness of the graph refers to how quickly the potato lost and gained weight. From 0-0.2, there is hardly a curve showing that it lost weight quickly, although the rest of the graph shows more of a curve, showing us that the weight decreased a lot faster as the concentration of the sucrose became higher. The line on the graph crosses the x axis at 0.24, showing us that at this point of concentration; the concentration of solution is the same inside the potato chip as well as out.
Splitting the graph in two from where the line hits the x axis, the mass gain differs. Before it hits the line, the mass gain decreases, whereas after it hits the line, the mass gain increases. Therefore contradicting my hypothesis; saying that as the sucrose concentration increases, not only does the mass gain decrease but it also increases. Via osmosis this shows us how the sucrose solution decreases the mass of the potato chip as less water molecules are occupied within the cells.
Conclusions: To conclude this experiment, I can say that the movement of water through a selectively permeable membrane is affected by concentration of sucrose solution, or by any other solution. The higher the concentration of sucrose solution, the more the potato chip will lose its weight, width and length.
Because water molecules have kinetic energy, they are constantly moving around in gaseous or liquid form, moving randomly from one place or another. The greater the concentration of water molecules in a system or solution, the greater the total kinetic energy, and the higher its water potential. This means, that as the concentration of sucrose increases in a solution, the concentration of water decreases, lessening the solution’s water potential, and lessening its ability to move between solutions by osmosis. Relating this to the potato chips; basically, as the concentration of sucrose in each solution increases, the water in that solution is less able to move to the potato, causing water from the potato to move to the solution, decreasing its length, weight and width.
In the living cell, both the cell wall and plasma membrane determine the permeability of the cell, but the latter of the two is the less permeable. The ability of a substance to pass through these barriers is known as the permeation of the substance. Since not all substances may pass into or out of the cell, the cell surface is known as selectively permeable or as a semi permeable membrane. The semi permeability varies from cell to cell and under certain conditions. Water molecules alone permeate freely, but ions do so more slowly, many large molecules and no electrolytes, such as sugars, do not move at all. This indicates that temperature could also affect osmosis. A solution in which the concentration of salt is greater than that inside the cell is called a hypertonic solution and will cause a cell to become plasmolyzed. An example of this in my results is the test at 0.8 molar. In other words, it becomes dehydrated and loses water through plasmolysis, which is the separation of the plasma membrane from the cell wall in a plant cell. If the concentration of the salt solution (in our case Glucose solution) outside the cell is less than that inside the cell, this means that the solution is Hypotonic to the cells of the potato chip. The water will diffuse into the cells, making it turgid. This would explain why potato chips put into a solution of 0 molar seemed very firm compared to the potato chip used for 0.8 molar, this was because the cells of the potato had lost their turgor, and had become flaccid.
Evaluation: The method I used was reliable. There were not any anomalous results; this can be seen on the graph as all the points on the graph correlate well (shown also by the line of best fit). If I could do this investigation again, I would have repeated the investigation five times because if you do an experiment several times you get a better average. I could have investigated a wider range of variables (i.e. 1, ½, ¼, 1/8, 1/16, 1/32) this would show better the relationship between sugar solution concentration and the amount of osmosis occurring.
We weighed the potatoes accurately, resetting the scales to zero every time we had finished, and taking done results with 2 d.p. Measuring the amount of solution being put into the syringes, we used a measuring cylinder. If I were to do this experiment again I would consider using a syringe to measure the volume, to receive a more accurate measurement.
The results shown in the table are varied i.e. not having recurring numbers or amounts more than 2g apart. The results are reliable due to this, as we have don’t have any results that vary incredibly, but are close together. With this our mean can be more reliable.
The points plotted on the graph are the percentage change, showing the difference from the initial and final mass. The formula for this is shown earlier on.
If able to hypothesise what would happen in this experiment again, I wouldn’t change anything, due to the obvious trend shown on the graph, supporting my hypothesis. Although, there is always the possibility to find out the affects of osmosis in related situations, not using a potato. We could do this with a variety of plant cells, due to their expandable cell wall, for example, celery. By putting food dye into the water they feed off of, we can see how it affects the leaves. Using Carnations as an example is also a god way of showing the affects of osmosis.
