Before Osmosis
A partially permeable membrane separates two solutions. The solute molecules are too big to pass through the pores in the membrane, but the eater molecules are small enough.
Picture a
A B
After Osmosis
The two solutions are of equal solution concentration, as the arrow shows from picture a more molecules of water moved from A to B, so the net movement of water was from A to B, raising the level of solution in B and lowering it in A.
Picture b
A B
Plant cells have a strong cell wall surrounding them. When taking up water by osmosis the cell begins to swell, but the cell wall prevents it from bursting. Plant cells become ‘turgid’ when they let extra water into the cell. Turgid means that the potato chip for example will swell up and go hard.
When plant cells lose water by osmosis they become ‘flaccid’. This is the exact opposite of "turgid". The contents of the potato cells would shrink and pull away from the cell wall, these cells are said to be ‘plasmolysed’.
Potato chip swells Potato chip normal Potato chip shrinks
0m 0.2m 0.6m
= Net movement of water
A diagram supporting my prediction from Biology 1, suggesting that the solution with the same or closest solution concentration to the red blood cell, is the best.
Diagram:
Potato chip Yogurt Pot Salt Solution
O O.2 O.4 O.6 O.8 1
Apparatus:
Fairtest:
- The potato chips must all be in the salt solutions for the same amount of time.
- Label all the yogurt pots.
- Potato chips must be all the same size.
- Pat all chips dry in the same way.
- Only the difference in the concentration of the salt solution.
- The experiment will be done at room temperature.
- We will use the same potato from which to cut out the potato chips.
- I will make sure that the amount of salt solution is the same in every yogurt pot.
Safety:
- Knife put somewhere safe when not being used.
- Goggles should be worn when cutting the potato.
- Dispose of all potato peeling to stop the risk of accidents.
- Wipe up any salt solution spilt to stop any accidents.
Method:
- Peel potato of the chopping board.
- Cut the potato into 6 exactly the same size potato chips (4cm x 1cm x 1cm).
- Put the left over potato peelings in the bin.
- Pat all chips dry equally and in the same way, to make it a fair test.
- Weigh the potato chips.
- Record potato chip weights.
- Put chips in yogurt pots with 1OOml of salt solution.
- Leave potato chips in the salt solutions for 24hrs.
- After 24hrs take potato chips out of salt solutions at the (same time so is a fair test.)
- Pat the chips dry, again for the same amount of time to keep it a fair test.
- Weigh the chips again.
- Record results.
- I repeated the experiment under exactly the same conditions. This gave me a secondary set of results, which gave me a more accurate view on which salt solution is the best one.
- The experiment should be done three times to get a fair test and precise answer.
Conclusion:
Evaluation:
In my opinion the experiment was very successful. I obtained a large quantity of very accurate results from which I was able to create an informative averages graph, and I didn’t have any anomalous results.
I think I recorded enough results for the amount of concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I might well increase the time of the result to allow more osmosis tooccur. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have more varied results, i.e. 0.10m, 1.15m, 1.20m, and so on. The cutting of the potatoes was the most difficult part of the experiment, it could well have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would have possibly found a machine to cut the potato, as it would ensure that all potatoes would be the same weight and dimensions. As well as the potato I could have found a more accurate way to measure out the solutions. This would ensure that I have an accurate amount of fluid in each test tube. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.0000g. There were not any out of the ordinary results, but some were not as close to the line as others. This may have been caused by human error. When the potato chips were removed from the yogurt pots and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. However I think that the experiment was a success and I was very pleased that my prediction matched the end result that O.2m is the best salt solution to store potato chips in.