Mass of potato cylinders- the mass of the potato cylinders will be the same.
Same weighing balance- to make are results more reliable we will use the same weighing balance because there might be slight variation in sensitivity between machines.
Changing Variable
This is the variable that will be changed in each experiment. It is also the variable, which we are investigating.
Concentration of sucrose solution- this is the proportion of percentage of sucrose in the solution. The concentration of the solutions will increase by 5% in each experiment.
Uncontrollable Variables
These are the variables that cannot be controlled.
Room Temperature- the room temperature will usually stay the same but could affect the experiment slightly.
Light intensity- the light intensity has a very small affect on the experiment so will not be measured in this experiment.
Length of potato cylinder- the length of potato cylinders will be 50mm to start with. We cannot control this because we are keeping the mass constant so if one of the cylinders is overweight then we will have to cut a fraction off until it becomes that mass.
Measurements
To make this experiment a fair test we will keep all values we are not investigating the same. To decide on the values of variables we will keep the same we have carried out trial experiments.
The variable we were investigating in our trial experiment was length and to test the range of concentration and to use in the experiment. These experiments were important to carry out because we could decide on suitable time intervals to use. This could also make sure that osmosis did not take place too slowly to give us a small range of results.
For this experiment we used two solutions, distilled water and 20% sucrose solution.
Our results are shown underneath.
Trial Experiment:
- 10ml of Distilled water
- 10ml of 20% Sucrose solution
- 50mm of potato cylinders
- We took results after 3 hours
Looking at these results we decided that mass was more a more important factor than length. This is because the length went down which means that the width could have been affected. I have decided to keep the mass constant for each potato cylinder. In the real experiment we are going to use 10ml of sucrose solution and take results every hour for five hours. I will also add another result, which will be recorded 22 hours after the experiment fist took place. We are going to repeat this experiment twice so we can take averages of our results.
Apparatus:
- Stop Clock – to time our experiment
- Cutting tile – to cut the potato on
- Knife – to cut the potato
- Measuring cylinder – to measure the solutions-should be at least 10ml
- Distilled water – part of the experiment
- 5, 10, 15, 20, 25, 30 and 35% of sucrose solution – part of the experiment
- Large Potato – part of the experiment
- Tissue paper – to dry the potatoes after the osmosis takes place
- Balance – to weigh the potatoes-should be go to 2 decimal places
- Cork borer – to cut out potato cylinders
- 16 test tubes- to keep the potatoes and solution in
- Test tube holder- to hold the test tubes while osmosis is taking places.
- Pencil to extract the potato cylinders from the cork borer
Method:
This is the instruction you need to do the experiment:
- Push a Cork Borer into a large potato.
- Push the potato tissue out of the cork borer using a pencil.
- Prepare a number of potato cylinders in this way. Cut them down until they reach the same weight (In this experiment we are using 3.28 grams).
- Label the test to know what solution is in each.
- Measure 25ml of each solution.
- Put the potato cylinders in each test tube.
- Now pour each solution into the rightly labelled test tubes.
- Leave the tubes for an hour.
- After this time, remove cylinder and wipe with a tissue to get rid of any excess liquid.
- Record mass.
- Repeat this for the other test tubes and the other hours.
Observation
While working, all safety procedures were followed very carefully like the use of safety goggles and putting the bags under the table. The measurements I feel were fairly accurate as the results were what were expected. We repeated the experiment two times so we could find averages and get more accurate results. The results were measured in grams to 2 decimal places because this was the maximum accuracy of the weight balances. The results show the values we got for each experiment.
Results:
Here is a table of results, which shows the masses of the potatoes in grams at different hourly intervals.
* These are anomalous results (the results I think do not fit in the pattern and do not match my predictions). I will talk about this in more detail in my Evaluation.
Looking at the previous results I am going to create a series of tables, which shows this information in more detail. Each table will show the results, which only apply to a certain hour. I will show the mass before and after and the difference in mass. I will also show the percentage changes in mass. The calculation I need to do this will also be displayed.
To work out the difference in masses I will use this formula;
Difference in mass=Mass after-Mass before
I am going to calculate the percentage change in masses with the formula;
Percentage change in mass=Difference in mass ÷ Mass before×100
Results: 1 hour after
Results: 2 hours after
Results: 3 hours after
Results: 4 hours after
Results: 22 hours after
In this second series of results I am going to calculates averages to make my results more reliable.
Average results: 1 hour after
Average results: 2 hours after
Average results: 3 hours after
Average results: 4 hours after
Average results: 22 hours after
Graph of results:
I am going to do several graphs to show the results so it is easier to interpret the information. I will do all my graphs by hand. In all my graphs I am going to use the information from the average tables because the results are more reliable.
Analysis and Conclusion
All the graphs basically show that as the percentage of sucrose solution increases, first (0%- distilled water) the percentage change in mass decreases. The potato after 22hours graph shows that at 0% the percentage change in mass is 15%. This decreases rapidly to 5% at 5% sucrose solution. The change in mass slows down and does not decrease as rapidly. When it reaches 10% sucrose solution the change in mass is 0%. The change in mass then decreases rapidly once again to 15% at 15% sucrose solution. It carries on rapidly decreasing to 30% at 20% sucrose solution. This rapid decrease slows down and at 25% sucrose solution it is 38%. After this the percentage change in mass seems to increase and at 30% sucrose solution it reaches 35%. This increase starts to level of and at 35% sucrose solution it is 34%.
The reason for these changes in masses is osmosis, and the rate of osmosis is different at varying concentrations. When the percentage of sucrose is 0% (distilled water) the water concentration is higher outside the potato chip (and its cells). This concentration gradient causes water molecules to osmose down the concentration gradient, across selectively permeable membrane and into the plant cells (potato tissue). This was the case at concentrations of 25, 30 and 35% sucrose solution, where mass was gained by the potatoes. This causes the cells to become turgid.
At a concentration of 9% sucrose solution, the concentration of water inside the potatoes (and its cells) and outside are the same because net movement of water is 0.0, and no mass is gained or lost by the chip. The potato has reached a state of incipient plasmolysis.
At concentrations of 10% and higher, mass is lost by the potatoes, I think this is because the concentration of water inside the cell is greater than that of outside the cell, therefore water osmoses out of the cell. At the concentration of 10 to 35% mass is lost because of this, and the cells had lost water.
In my graph I have already explained, firstly mass is gained, then the mass decreases until, it continues to rapidly deceased and at the end increases a little. Basically as the concentration of sucrose increase the mass of the potato decreases.
So in conclusion this experiment was basically a success. I believe that I have collected enough data to support my hypothesis. This investigation was successful because my results mostly collaborated my predictions.
The potato cells, working to stay alive, took in, or gave out the water depending on the concentration of the tissue, and the concentration of the solution it is surrounded in.
As the weights before the experiment was 3.28g, this tells us that the potato pieces were cut well, and I believe accurate enough.
The graphs and the results show that:
1) Osmosis actually took place in the experiment.
2) As the molars increased, the percentage of the weight difference decreased.
Evaluation
We followed the plan correctly; although there were anomalous results I still believe we gained accurate and sufficient enough results to conclude the experiment, and to prove our hypothesis.
When I first did my experiment the results that I obtained was completely useless because the starting weight for each piece of potato cylinder were not equal. This was due to human error but did not become apparent until during the experiment. However this was corrected and I obtained reliable and informative results.
There were some anomalous results in my experiment. These are listed in the first main table of my results. There are many theories I have to why this happened. One of the reasons could simply be because of human error. May be some potatoes were not dried as much as others or were left to dry longer than other potato cylinders. Another reasons could be due to the room temperature, which could not be controlled. The window might have been opened and depending on the time of day the humidity in the room could alter the amount of osmosis taking place. I think another reason was because of light intensity in the room, which also could not be controlled. Light has is known to have an affect on plants and plant cells. Because we took results over a long period of time the potato were subjected to different light intensities throughout the experiment. This could have had an adverse effect on the experiment.
Although there were some anomalous results I still think my final results were fairly reliable, due to the precautions I took to make this a fair test.
To make this experiment better, I believe that we could have done one test at a time, so that we can reduce the time difference, when we have to move the potato from the test tube to the balance. Between this, we have to dry the potatoes just enough, and then put it on the balance. When we are doing this for one set, writing down the results at the same time, while the other 5 sets are on the tissue paper, the water outside the potato tissue is going to vary for all. Therefore, we would be able to concentrate more on one of the sets, instead of trying to finish all of them as quickly as we can.
We also could have got more people to do the experiment with us, so that we can organize the tasks, and we would be able to divide the tasks.
Using more types of molar sucrose solutions would have helped us obtain better results, and more accurate results, so that we can make sure the results are totally correct.
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 tells us how much water could be transferred for each solution.
Further work could be carried out to include concentrations that increased in 1.5 M rather than 5%. 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, apple.
Other variables in the experiment could be changed for example instead of changing the mass of the potato the species of the potato could be changed. For example I could use a new potato and a really old potato.
Also the shape and size could be changed. However this would not affect the results much. This is because the variable would only change the rate of osmosis because of a different weight and size.
Using more types of molar sucrose solutions would have helped us obtain better results, and more accurate results, so that we can make sure the results are totally correct.
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 us how much water could be transferred for each solution.
Temperature could also be changed for example the samples could be placed in different water baths and brought up to different temperatures to see if temperature played its part in the osmosis of potatoes. 5 sets of 5 potatoes could be placed in water baths at 10ºC, 20ºC, 30ºC, 50ºC and 60ºC. Then leave them for 24 hours making sure all the variables in the first experiment still apply however just using one molar solution. Then after 24 hours re-weigh the samples and record the result. I would expect that at high temperatures the potato samples would osmosis the most. This is because at high temperatures the solutions with water molecules would move faster and therefore equal the concentration faster. A preliminary experiment could be set up beforehand to find out how long the experiment should be kept going because if the concentration of the potatoes equalises then the weight of the potatoes will be almost exactly the same.
The cutting of the potatoes was the most difficult part of the experiment as although I was recording my results by mass, 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. Perhaps I could have used a burette. 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 0.000g.
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 errors. When the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. This also may have caused the potato to lose water but it also caused there to be less and less solution in the test tube when it was put back in. This meant the test would not be completely fair. 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. I could also improve the experiment by extending the length of time. The original plan was to test the tubes every hour for 5 hours and then again, 22 hours later but because of the mistakes made when weighing the potato I did not have enough time to do the 5th hour. So I should add a 5th hour and maybe a few more hours to obtain perfect results. So this his how I would improve my experiment.
However with all this said I think that the experiment was truly successful and I was very pleased with the complete comparison of my results with my initial prediction.
