But I believe one of the most important steps 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 so that osmosis can take place in the whole of the potato slice and not just the part that is submerge.
When using the scales, we will make sure that the balance is reading zero, before we put the potato pieces on it. This is so that we do not get a false reading, with the weight of our potato with the reading it had before. And after the experiment, we will measure the potato pieces that should be dried as possible, and weigh it the same way, taking the reading to the nearest 2 decimal places.
And we will also be reading the measurements of the measuring cylinder by reading the bottom of the meniscus when measuring out the solution to make sure that the same amount of sucrose is used for every potato to make sure that it is fair.
Carrying out the experiment in a constant temperature for the whole of the experiment is important. And to avoid temperature change, which might affect our 3 different sets of results, we will take the temperature of the room into account.
Another important factor of a fair test is to start and stop the clock as quickly as possible. This meaning that we should start the clock as soon as the potato is put inside the test tube, and stop the clock as soon as 30 minutes have passed. Stopping the clock, taking them out and measuring it all in less than a minute is quite impossible because we lack the number of balances. And there are obviously too many sets to go through at such a fast time. Therefore, we will try our best to weigh the potatoes as quickly and as safely as we can.
Getting and experimenting with the exact measurements of the molarity and water is vital to this task. If the volume of one solution in a test tube is higher or lower than another, will affect the pattern of results later on.
We will also make sure that the potato is fully covered by the 6 different kinds of solutions. This is because, if the potato is not covered up by the solutions, the effect of osmosis might not occur to the fullest.
Small things such as a dirty test tube, and a slightly cracked measuring cylinder could still affect the results, and therefore we will take these into account as well.
If all of the precautions are done correctly then the experiment will be fair and so the results will be accurate and so we can get precise conclusions.
Hypothesis
Osmosis is the passage of water molecules from a weaker solution into a stronger solution, through a partially permeable membrane. In this case, the tiny holes in the membrane of the potatoes will allow the water molecules to pass through in and out of the solution and the potato, depending on the concentration gradient of the two substances. So in this case, when the water concentration is lower in the tissue, the water will go inside the tissue of the potato, and the potato will gain weight. And if there is very little different in the two water concentrations, there should not be such a big change in weight. And if there is a higher concentration of water in the potato, the water will go out of the potato.
The potato, cut up into pieces, will need some sort of element to survive, and in this experiment, it would be light and water. With both of these sources, the potato will keep on working, until it dies of either lack of water, too much water. When the concentration gradient is lower in the potato, the water will transfer from the solution to the potato. And vice versa.
In the distilled water, I believe that the sucrose is more concentrated in the potato, and therefore the water molecules should transfer from the distilled water to the potato, making the potato bigger in size, and heavier in weight. The potato tissues, being surrounded by a weak solution, will be most likely to swell up and become turgid, taking in all the water it can possibly take in.
With the potato in molar solutions of sucrose, I do not think there will be much change in the weight of the potato. This is because there is not much difference between the two substances. I believe that the weight and the size of the potato will not be altered much.
The 0.4 molar solutions of sucrose, similar to the 0.2 molar solution of sucrose, compared to the potato, both substances have very close concentration gradients. And that is why I am predicting that the weight of the potato in this experiment should be decreased by only a fraction. The 0.6 molar solution of sucrose, I think, should make a big difference now, noting that it should be a large difference between the two concentration gradients. And there fore the weight should decrease, at least noticeable for us to notice.
The difference between the water concentration in the potato and the 0.8 molar solution of sucrose is big, and the water in the potato should be transferred from the potato, through the permeable membrane, to the solution surrounding the potato. And as a result, I am sure that the weight of the potato will increase largely. And because the potato tissues are surrounded by a stronger solution, it will probably become smaller, and shrink. But because of such high molars of sucrose, the water can diffuse all the way, throughout the two substances, equalling the concentration gradient of the two substances.
My theory in this experiment is that, due to the difference in the water concentrations of the two substances, I believe that the weight of the potato will start decreasing when it is tested on 0.2 molar solutions of sucrose and greater.
Apparatus
- Stop Clock – to time our experiment
- Cutting tile – to cut the potato on
- Knife – to cut the potato
- 25cm Measuring cylinder – to measure the solutions
- Distilled water – part of the experiment
- Sucrose – part of the experiment
- Potatoes – part of the experiment
- Tissue paper – to dry the potatoes after the osmosis takes place
- Cork borer – to cut out potato cylinders
- Scales- to accurately weigh the potato before and after
Diagram
Risk assessment
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 is not handled properly. And we will also be careful that the solutions do not 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 were not any bigger matters to be cautious of.
Method
- First push the cork borer through the potato, cutting it into long cylinders with a diameter of 6mm, until you get six fairly equal sized pieces.
- Then, using a scalpel cut the skin off the potato.
- Use a ruler and make sure all the potato pieces are 5cms long
- Next, using a measuring cylinder, measure out 50cm3 of 0.2, 0.4, 0.6, 0.8, 1.0 molar solutions of sucrose solution, and of distilled water, into 6 different test tubes.
- Then weigh each potato piece, using an electronic balance, to get an accurate reading to 2 decimal places, and record these weights.
- Drop one potato piece into each of the test tubes of sucrose and start the clock watch. Note any potatoes that have floated to the top of the test tubes.
- After 30 minutes of having the potatoes completely covered in the sucrose, remove all of the potatoes.
- Dry them completely using a paper towel.
- Place each one onto the scales to get an accurate reading and record this weight.
- Repeat the experiment three times so that you can make sure that all of the results are similar, and so that you will be able to take the average of the 3 experiments. This makes sure that you get accurate results. 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.
OBTAINING EVIDENCE
After the experiment, I had to dry the potatoes first, so that the water outside the tissue of the potatoes will not alter the weight of what it is supposed to be. I quickly took all of them out, and put them onto a piece of tissue paper, into their own groups.
When obtaining my results it was all done in room temperature, 25, so that this did not affect the rate of the osmotic activity.
Table of results
In the table below, it shows the ‘solution´ column, which are the 6 different types of solutions. The weight before and after the experiment represents the 3 sets of results and the average taken out of the three. The increase/decrease of the weight is calculated by taking the weight after, minus the weight before. The percentage increase/decrease of the weight of the potato is calculated by taking the weight increase/decrease divided by the original weight multiplied by a hundred. This should help us lead to a more accurate result, and the average percentage will be used to present the graph.
Analysis
On the graphs shown below, I have made the ‘different solutions´ as my independent variable, since it won’t be changing on any event. And I have made the ‘Average percentage change´ as my dependent variable. I have decided to make a bar graph and a line graph as they both clearly show the decrease in the average percentage change. I have taken the average result of the 6 different solutions and put it on the graph to be more accurate.
EVALUATION AND CONCLUSION
Conclusion
In this experiment, I believe that I have collected enough data to support my hypothesis. This investigation was, I think, successful. Successful meaning my results collaborated my predictions.
This experiment shows the osmosis theory as the potato cells, working to stay alive, take in, or give out water, depending on the concentration of the tissue, and the concentration of the solution it is surrounded in. The potato took up water by osmosis and it began to swell and became turgid when it was put in the more diluted solutions such as the sucrose solution with the molartiy of 0.4 to 0.0.
However, when the potato was placed in higher concentrated sugar solutions (molarity 0.6 to 1.0), it lost water by osmosis and they become flaccid. This is because osmosis is the passage of water molecules from a weaker solution into a stronger solution, through the partially permeable membrane. In this case, the tiny holes in the membrane of the potatoes allow the water molecules to pass through in and out of the solution and the potato, depending on the concentration gradient of the two substances.
Looking at my results
Looking at the results I can see that my investigation was fully accomplished, and was an achievement. I can tell this because my results coincide with my hypothesis that the average percentage weight changes of the potato will decrease as the molarity increases. I think that my results have been fairly accurate due to my careful precautions I took, to make sure that a fair test took place.
In the table above, the percentage shows a steady decrease, telling us that the percentage of the difference decreases as the water concentration decreases.
The graphs and the results show that:
- Osmosis actually took place in the experiment.
- As the molarity increased, the percentage of the weight difference decreased.
- That there was an anomalous result.
Anomalous results
In my experiment I found one anomalous results, which can be easily seen on my graph. This was the average percentage change in the weight of the potato for the sucrose molarity of 1.0, as it has increased slightly from the average percentage change in the sucrose with the molarity of 0.8. This breaks the pattern seen in all the other results, which is the higher the concentration, i.e. the higher the molarity of the sucrose is, the lower the average change in weight is. This anomalous result may be due to inaccurate results from weighing out the potato, inaccurately measuring out the sucrose solution or inaccurately recording the results down. Also, in test tube 1.0, in all three results, the potato floated to the top of the test tube so this might have meant less solution was covering it and therefore less osmotic activity may have taken place.
Evaluation
I followed the plan correctly; I believe I gained accurate and sufficient enough results to conclude the experiment, and to prove my hypothesis. My final results were fairly reliable, due to the precautions I took to make this a fair test.
Problems and Improvements
Even thought I tried to keep my experiment fair as possible, there were problems in the experiment. These include that some potatoes had more time in the sucrose solution, as there was there was a time delay in putting all of the potatoes into the different test tubes and when I had to move the potatoes from the test tube to the balance. This means that more osmosis could of taken place in the potatoes that went in the test tubes first or came out last. This could have been the reason for the anomalous result as it leads to inaccuracy. To improve this, I believe that I could have done one test at a time, so that I can reduce the time difference, therefore, I would be able to concentrate more on one of the sets, instead of trying to finish all of them as quickly as I can.
Other changes I could of done to make my experiment more accurate include:
- Using more types of molarity sucrose solutions would have helped me obtain better results, and more accurate results, so that I can make sure the results are totally correct. This is because I will have a wider range of results so I will be able to see if the osmosis theory works for wide range of molarities.
- Experimenting with one set for a longer period of time, for each set, would lead us to better results, because the osmosis action would reach its maximum capability, and therefore tell me how much water could be transferred for each solution.
- By repeating the experiments more than three times so that I get a more accurate average result.
But overall, given the apparatus that I got to carry out the test, I think this experiment turned out to be very successful, and I´m very please with my results
Future experiments
To investigate osmosis even further I could do additional experiments such as the following experiment.
Diagram
Method
- Set up apparatus as shown above.
- As soon as the visking tubing enters the sugar solution, record the height of the liquid in the glass tube and start the stop clock
- Every 5 minutes record the height of the liquid.
- After 30 minutes, remove the visking tubing
- Record you results in a graph
Results
Conclusion
From looking at the graph I can see that in this experiment, the results have the same pattern as the results in my potato experiment. Therefore I accept the osmosis theory that lower concentrated solution of sucrose passes through the permeable membrane to the higher concentrated solution.