Investigating water movement in potatoes.

Apparatus

• Test tube rack
• Measuring cylinder
• Test tubes (6)
• Different strength solutions
• Potato
• Ruler
• Weighing scales
• Scalpel
• Pipette
• Paper towel
• Tile

Method

In this experiment you will need to get all the equipment mentioned above. Once you have all the equipment you should get a Potato (one that has no skin on it) and make 6 equal sized potato pieces of the same shape, you can use a ruler to make sure that your potato pieces are the same size. You can use a scalpel to cut the potato and you can cut it on a tile if you want to. You should then get your six potato pieces and weigh them on your weighing scales, record the weight of each potato and make sure you remember which potato weighs what. You should then get your six test tubes and get each filled up with a different strength solution- 0, 0.2, 0.4, 0.6, 0.8 and 1, you must make sure you use the same amount of solution for each test tube (you can measure each solution into a measuring cylinder and you can put the solutions in with a pipette. Then get your potatoes and put one in each solution. Make a note of what time it is, as you want each potato in each solution for the same amount of time. When you have had your potatoes in the solutions for 5 minutes take them out and get rid of any surface water on the potato by wiping it on a paper towel. Then you need to weigh all your potato pieces again and make a note of each of the results. You must then repeat this until you have done the experiment 3 times.

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Fair test

To ensure that this is a fair test I need to control some things like the size of the potato pieces, each potato must be of the same shape and same size, the potato pieces should be cut from the same potato to ensure that it is not bias. If this is not possible then the potatoes should be of the same type and from the same date. The potatoes should be of a recent date so that they are fresh and can take in water. The temperature must be kept the same in the experiments as this would be another variable and we don’t want that. As mentioned in the method each different strength solution should be of the same amount. The time must be too. The same balance should also be used for the weighing of the potato before and after, as the scales may be slightly inaccurate so we want to make sure that the potatoes have been weighed with the same scales.

Safety

I will take care when I am using the scalpels. I should also take care when putting the different strength solutions in the test tubes and when taking the potato out of the water, as I do not want water on me.

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Results

Experiment 1

Experiment 2

Experiment 3

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Conclusion

My results show a trend in that they decrease; as the solution increases the average % weight change decreases. My results seem to fit my original conclusion as I thought the stronger the solution, the less the potato will weigh and as I can see from the results and especially the line graph the potatoes do weigh less as the solution gets stronger. As osmosis is the movement of water molecules through a particularly permeable membrane from a weak solution to a strong solution it is clear that osmosis has taken place.

Evaluation

I think that my experiment went quite well as most of the results seem accurate, I think that they are accurate too as we repeated the experiment, we did it 3 times, but it wasn’t all accurate as you can see from the results as there was an anomalous result; this result is most likely wrong because we probably forgot to take the surface water off. This experiment was safe as no one was injured. Although I did not find the method particularly hard it was slightly hard trying to get all the potato pieces to the same length. If I were to do this experiment again I would repeat each experiment more times and I would eliminate any anomalous results before working out the average % weight change. To further support what I have found out in this experiment I could have used different vegetables or I could have also recorded the lengths of the potato before and after putting them in the different strength solutions.