Equipment:
- 15 test tubes in total to contain the potato cylinders in the different solutions for each test. I have chosen test tubes rather than say, beakers because they are most practical and economical by ensuring the potato cylinder is completely immersed in the solution, not having to waste any solution as may be the case with beakers.
- 2 potatoes to collect the 15 potato cylinders from.
- 1 cork borer to create the cylindrical shape of the potato to go in the test tube.
- 1 sharp knife the cut the potato cylinders to identical lengths.
- 1 white tile to cut the potatoes on.
- 1 test tube rack to hold all the test tubes.
- 1 stop watch to time how long the potato cylinders are in the solutions for.
- 1 ruler to measure the changes in length of the potato cylinders.
- 1 measuring cylinder/pipette to measure out 10cm of the solution each time.
- 30ml of each concentration of the 5 different sucrose solutions.
Possible Variables:
These are the possible factors that I could change, which would affect the results of the experiment:
Time: the longer the potato cylinders are left in the solutions, the more or less they could decrease/increase in size dependent on the solution they are in.
Temperature: is known to affect the rate of reactions and it would also affect the results in this experiment because if the temperature is hotter, osmosis would happen more quickly because the particles would have more energy to move around; meaning the potato cylinder would increase more in size.
Solution volume: Obviously if there is more of one solution, there is more water in this case to travel through the semi-permeable membrane of the potato, so it would increase in size more.
The potato cylinders: If the sizes of the cylinders are different, the surface area of the potato membranes would be different so some could absorb through osmosis more or less of the solution.
Concentration of solution: the more sucrose in a solution, the less water there is to be absorbed, so in my prediction, the less increase in size.
The only factor I will be changing is the solution concentration. Therefore it is vital that all the other possible variables are kept the same.
Results:
See final page for graph of results.
Conclusion:
I can see that my prediction was in fact correct; the potato in distilled water increased the most in size and became the most turgid for the reasons explained in my prediction – if there is more water which can pass through the potato’s semi-permeable membrane; the potato will consequently increase more in size than a potato cylinder in a stronger concentrated sucrose solution because in such a solution there are more molecules which cannot pass through the semi-permeable membrane and less water.
Evaluation:
I am very happy with the way my experiment turned out, the results were typical of my prediction and there were no significant anomalies.
I kept to my method and did as much as I could within my control to keep the variables (time, temperature – as far as I could control it; solution volume and potato cylinder size) the same. I was as exact as possible with the timing and made sure I removed all the potato chips after 30 minutes; I measured all the solutions exactly as well as the potato cylinders.
Other than temperature, the one factor I think could have been more exact was timing, because after the 30 minutes, it was difficult to remove all 5 potato chips at the exact same time – the last chip I removed would obviously have been in the solution for a bit longer than the first I removed. However this would have only been a very slight difference in time and is unlikely to have affected the results significantly.
If I was to do the experiment again, I think I would use potato cylinders of 3cm in length, not 2 and leave them immersed in the solutions for a bit longer, possibly 35 minutes. This would allow more time for osmosis to take place and hopefully produce more differentiated results, because the differences in this experiment’s results were only very slight – about 0.1cm
Kelly Nash 10P
