Prediction
I predict that as the concentration of the sucrose solution increases, the length of the chip will decrease. My prediction is based on the theory of osmosis. Osmosis is the movement of water or any other molecules of solution from a region in which they are highly concentrated to a region in which they are less concentrated. This movement must take place across a partially permeable membrane such as a cell wall, which allows smaller molecules, e.g. water, to pass through but not larger molecules. The molecules will continue to diffuse until the area in which the molecules are found is equal and they are randomly distributed throughout the object, with no area having a higher or lower concentration than any other.
There is always a strong cell wall surrounding plant cells. When they absorb water by osmosis they begin to swell, but they are prevented from bursting by the cell wall. Plant cells become turgid when they are put in diluted solutions. Turgid means swollen and hard. However when plant cells are put in concentrated solutions they lose water by osmosis and they become flaccid. This is the opposite of turgid. The contents of the potato cells shrivel and move away from the cell wall. When plant cells are put in a solution which has an equal osmotic strength as they do, they are in a state between turgidity and flaccidity. This is called incipient plasmolysis. A chip in a high concentration will be similar to the diagram below.
Net Movement of Water Particles
Planning
For my preliminary work I will cut out 4 potato cylinders of different diameters, using a cork borer and making sure they are 30mm in length each time. I will then place all these chips in 50cm3 of sucrose solution and leave them for three hours. I will measure the length of each one after drying off the excess water. I will then repeat this process exactly as before but leaving the potato chips for 6 hours rather than three. Then I will calculate the percentage change in length. Below I have written the calculation that I will need to do this:
Change in length (mm) x 100 = Percentage Change in Length
Original length (mm)
I will the look at these results in order to see which factors would be most suitable for my actual experiment to be the most accurate.
Preliminary Work Results
From these results we can see that a potato cylinder of diameter 3 in sucrose solution for 6 hours will give the best range of results.
Method
- Using a cork borer I cut out 15 potato cylinders.
- Using a scalpel and a caliper I cut the cylinders down to exactly 30mm.
- I then took 5 petri dishes and labeled them :
-
50cm3 sucrose solution, 0cm3 water
-
40cm3 sucrose solution, 10cm3 water
-
30cm3 sucrose solution, 20cm3 water
-
20cm3 sucrose solution, 30cm3 water
-
10cm3 sucrose solution, 40cm3 water
- Using a measuring cylinder I measured out the correct amount of sucrose and water solution for each petri dish.
- I then placed 3 potato chips into each petri dish making sure they were completely submerged in the solution. I used three chips so that I could take an average. This would give me a better set of results and therefore more accurate graphs.
- After 6 hours I took the cylinders out of their petri dishes separately and placed them on paper towel. I then measured and recorded the change in length.
Results
All potato cylinders started at 30.0mm in length.
I have some anomalous results. This could be due to inaccurate measurement at the start or that some chips were dryer than other before they entered the solution. Due to this fact I have not plotted these results on my graph in the hope that it will be more exact without them.
Analysis
On the graph I have drawn the line of best fit for the percentage change in mass of the potato cylinders. It is a curve that slopes downwards and does not go through the origin. We can see that the percentage gain and loss in length and concentration are not directly proportional because the line is not straight and does not pass through the origin. There is a pattern however and this is that as the concentration of the solution increases, the percentage change in length decreases. The graph shows that the percentage gain and loss is inversely proportional to the concentration. The gradient does change in my graph. As the x value gets higher the gradient of the curve decreases. This is due to the potato chip becoming as flaccid as it can and so the change in length at each molar concentration is becoming closer together. I had two results that did not align with my curve. My results were therefore fairly reliable although there were anomalies. My graph supports the prediction that I made earlier.
Evaluation
In my opinion this experiment was not unsuccessful. I managed to obtain results that were not altogether accurate but did provide the information to create a graph that followed my theory. I think I took the right amount of results but taking more would of made it more accurate. The 6 hour time period was enough time to allow osmosis to occur but I could of easily gained similar results in a shorter time span. If I were to repeat the experiment I would try and find out the saturation point of the potato pieces. I had an adequate range of concentrations but creating more concentrations is a possibility if I was to repeat this experiment as I could produce a wider range of results. My results were fine even though the exact results were not persistent. This cause was probably human error, I may not have dried some potato pieces as well as other, and some would then have more excess water adding to the length at the end. If I repeat the experiment again I will look into finding some other way of drying the potatoes more thoroughly. Also my initial measurements may have been incorrect. However I think the experiment was very successful and I am pleased with the complete comparison of my results with the initial prediction I made.