Osmosis is the passage of water from a region of high water concentration through a partially permeable membrane to a region of low water concentration. The definition contains three important statements:
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Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
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Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
Fair Test Fair testing should play a big part in this experiment. If this experiment isn’t a fair test, we will be obtaining the wrong results, which could lead us to the wrong conclusions.
First of all, and most importantly, we will have to get the measurements and the weights of the solutions and the potatoes as exact, and as accurate as possible. We will try and get the measurements of the potatoes as accurate as possible for every single potato, evenly cutting the potato pieces, and making a record of the length to the nearest millimetre. And we will be using a very sensitive balance so that we can get the best readings possible.
But I believe one of the most important step in the fair testing is to make sure that the potato is fully covered by the solution. This is because the potato should fully submerge, by having total contact with the solution. When using the balance, we will make sure that the balance is reading zero, before we put the potatoes on it. This is so that we don’t get a false reading, with the weight of our potato with the reading it had before. And after the experiment, we will measure the potatoes that should be dried as possible, and weigh it the same way, taking the reading to the nearest 2 decimal places.
Method There won’t be any control for this experiment, because the weight would vary depending on the potato pieces. And therefore, it might affect the results, which we are going to take in after the experiment.
First I will have to get the pieces of potatoes ready. I will push the cork borer through the potato, cutting it into long cylinders with a diameter of 6mm. And then I will cut the potatoes into cylinders of 40mm. I will have 6 sets because we will have to test the potatoes in 6 different types of solutions; 0.2, 0.4, 0.6, 0.8, 1.0 molar solutions of salt and distilled water. I will weigh each set and have them ready for us to put into the test tube. Then we will put the 6 sets potatoes in the 6 test tubes at the same time and start the clock running for 10 minutes.
After 10 minutes, we will take all of the potatoes out of the test tube, so that the actual osmosis action stops, and we will put the potatoes onto one piece of dry towel, in their own groups. We will dry them with the tissue paper, and weigh and measure the potatoes taking in the average reading of the potato pieces.
We will repeat the experiment three times so that we can make sure that all our results are accurate, and so that we will be able to take the average of the 3 experiments. Repeating the experiments are important, because we will be able to receive valid results, and look for any anomalous results. Not to mention that we will take the fair testing into account.
Safety Safety is an important aspect in every experiment, even if the experiment seems to be very harmless. And that is why we take this into consideration, no matter what.
We will be using a very sharp knife, which could injure someone if it’s not handled properly. And we will also be careful that the solutions don’t get into our bodies internally, just in case, because we are not fully aware of the damage it could do to us.
But other than that, there aren’t any bigger matters to be cautious of.
Results
Tube number Average length of cylinders before (cm) Average length of cylinders after (cm) % change in length 1 (Analysis The results show that, in accordance with our hypothesis, the cylinders will expand when external solute concentration is low (high water concentration), and contract in strong solutions (low water concentration). This is due to osmosis, where water passes from weak solutions to strong solutions across a semi-permeable membrane, such as a cell membrane. The graphs of % change against solution strength show that the results tend to form a curve, crossing the x axis (where there is no change in length), at approximately 0.2 molar concentration.
Evaluation
In my opinion the experiment went well. I gained a good set of results and altogether I am pleased with the investigation. The graph obtained from the results has a strong resemblance to the one in the prediction. This suggests that the experiment was fairly accurate. Although 3 repetitions of each concentration are sufficient, there was a possible anomalous result (circled on graph). This part of the investigation would need to be repeated. A possible factor affecting my results is that although the cylinders were taken from the same potato there is no guaranteeing that the density remains the same throughout the potato. Another factor is that the potato from which the cylinders are taken could be abnormal - this could be prevented by amalgamating sets of results, for example of a whole class, where each experimenter used a different potato. I think that three sets of results was a good number. However, I think that in order to improve my results, the last concentration (1 molar) needs to be retaken, as it is an anomalous result. Further work could be carried out to include concentrations that increased in 0.1 M rather than 0.2M. This would increase the accuracy and improve the graph. Other investigations could include using different varieties of potato or different plant tissues e.g. carrot.
