Expected Results:
I expect that the blocks of potato with a bigger surface area will have a bigger mass at the end of the experiment then the blocks of potato with a smaller surface area. The blocks of potato in the sucrose solution will have a smaller mass then the blocks in the water because to balance the concentration of water in the two beakers between the potato cells and the liquid surrounding the potato there would have to be less water entering the cells when the potato is in the sucrose solution, but more water entering when the potato is in the water. The mass difference of the potato pieces with a surface area of 48cm2 will be double the mass to that of 24cm2 pieces of potato because the surface area is doubled. The experiment carried out with water acted as a pilot study to control the results I obtained when I carried out the experiment in sucrose solution. The results I expect to obtain are shown in a graph (see next page).
Variables:
The independent variable in my experiment was the surface area of the pieces of potato. The dependant variable in this experiment was the mass of the potato after the experiment. Other variables in this experiment include the time that the potatoes were left in the water, the time that they were put into the beakers was synchronised, therefore each different surface area had the same amount of time for osmosis to take place. The volume of liquid was another variable, I measured the volume by using a pipette and lowering my eyes to the level that the beaker was at to get a more accurate reading. Another variable also includes the conditions the beakers are left in, such as temperature. The temperature was all the same for both experiments as I did them in room temperature in the same room, therefore the temperature was not too high as too much heat will denature the cells therefore not allowing osmosis to take place.
Apparatus List:
- 12 small beakers
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150cm3 Water
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150cm3 1molar sucrose solution
- 12 pieces of potato
- Stopwatch
- 2 measuring cylinders
- Knife
- Scales
- Dry cloth
- Chopping tile
Procedure:
The first experiment that I did acted as a pilot study; this helped me to conclude whether the results I got for the second experiment were correct and also helped me to
The pieces of potato that I will be using will be cut in to pieces similar to these, with the same measurements so that the surface area will be exact.
- Cut 6 pieces of potato into blocks like the ones shown above.
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Fill 6 of the beakers with 25cm3 of water each
- Cut the other 6 pieces of potato into blocks like the ones above
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Fill the other 6 beakers with 25cm3 of 1molar sucrose solution each
- Weigh all the blocks and record the weight in the table
- Put all the blocks in the beakers, making sure to separate the water solutions and the sucrose solutions by leaving them on separate trays, one labelled water and the other sucrose, leave for 90mins
- Weigh all the pieces of potato after they have been drained of excess liquid by means of patting dry with an absorbent towel, being careful to keep the pieces separate from each solution to avoid confusion, record the results.
- Find out the mass change of the pieces of potato by subtracting the mass afterwards from the mass beforehand. Record the results.
Measurements:
- I will measure the surface area by using an accurate ruler when cutting the pieces of potato.
- I will measure the mass of the potato by weighing it after the potato has been left in the solution for 90 mins.
- I will measure the time the potatoes are left in the beakers by using a stopwatch, once the time has got to 90 mins, I will take the potatoes out of the beakers and dry them before weighing them.
Fairness Precautions:
- Make sure the amount of liquid in each of the beakers are exact so that a piece of potato doesn’t have more water to transfer into the cell, therefore making the mass heavier and the results wrong.
- Make sure the blocks of potato are cut with the precise measurements to let the surface area be exact otherwise either more or less water can be transferred at the one time depending on the actual measurements of the pieces.
- Be sure to time the experiment accurately and take the potato out after exactly 1hr so that one piece of potato doesn’t get more time for the water to transfer into or out of the cells otherwise the mass expected may be wrong.
- Be sure to leave the potato on the scales until the weight has settled before recording the results in case of recording the wrong results.
Safety:
- Be careful with the knife when cutting the potatoes, be sure to cut away from the body when and use a chopping board to cut on, when the knife is not in use have a protective covering over it.
Data Recording:
I will record the results in a table like the one below-
Data Presentation:
I will record my data in the form of a table (like the one above) then convert those results into a scatter graph with a best fit line (as shown below) so that I am able to view them more easily to be able to find a pattern in them and be able to determine whether my hypothesis was correct and to make a suitable conclusion and evaluation.
Results:
I carried out the experiment in 2 lessons. The first lesson I obtained the results for the potatoes in water which was a pilot study, and in the second lesson I obtained the results for the potatoes in the sucrose solution which was the real experiment. The results I obtained were good, although I had to repeat the experiment in water for the surface area of 40cm2 because I was not sure of the reading I got the first time so I repeated that experiment in the second lesson along with the other sucrose solutions.
I transferred the results I obtained into a graph (see next page). The graph shows that when a plant cell is put into a beaker with 100% pure water the mass will increase, but if it is put into a beaker with 1molar sucrose solution (about 34% sucrose and 66% water) the mass will decrease.
Conclusion:
These results fit in well with the results I expected to get. Some of the points are not exactly on the best-fit line shown on the graph below but still follow the basic pattern the line sets. By looking at the graph we can see that the larger the surface area, the larger the mass difference in the potato pieces at the end of the experiment. I also found that it takes a longer amount of time for water to diffuse out of the cells then it takes for water to diffuse into the cells because the amount of water diffused out of the cells in the sucrose solution according to the mass change was less then the amount of water diffused into the cells as the mass change was much larger in water then that of the potato in sucrose.
I expected the mass difference in the potato pieces in water to increase more then it did, but my results make sense. Cells have a concentration of 90% water and around it was 100% water, therefore not much diffusion was needed to balance to concentrations of the water in the cells and around the cells.
These results support my hypothesis very well. The pieces of potato with the larger surface area did have a larger mass difference at the end of the experiment and also the mass of the potato pieces left in the sucrose solution did decrease in mass, and the pieces left in water increased in mass.
Evaluation:
The results I obtained when carrying out this experiment were very good although there were a couple of points on the graph that didn’t fit into the pattern the best fit line set as well as the other points. This was probably due to insufficient drying of the potato pieces before weighing when the experiment was finished because the mass difference was larger then I had expected and the excess water would have added more weight to the reading. I noticed this on both experiments when I weighed the potato with a surface area of 36cm2. The results I recorded were accurate to two decimal places and the readings on the scales were correct because I waited for the reading to settle before recording it on the table. I collected six sets of data, which was an adequate amount to show a pattern on the graph I produced. Although I would have expected the pieces of potato with a surface area of 48cm2 to have a mass difference double to that of 24cm2 because it is double the surface area, but my results did not show that. This may have been because they were not left for an adequate amount of time to let the rate of diffusion settle.
To make the experiment even more accurate I could have suspended the potato pieces in the solution to make it certain that all of the surfaces were exposed to the liquid without excluding the base. This would have given me better results because the surface area played a main part in the experiment and the sides that were excluded would have made a difference in the results I obtained. I could have also used more surface areas to make the experiment even more accurate. For example, I could have cut more pieces of potato to give surface areas of 26cm2, 26cm2, 30cm2, 38cm2, 42cm2, 44cm2 and 46cm2 to fill the gaps on the graph which hopefully would have given more of a pattern to the graph.
To extend this work I would try different concentrations of sucrose with different surface areas to look at any patterns which might emerge there, I would also repeat the experiment and measure the amount of liquid left in the beakers at the end of the experiment. I also think it would have been useful to repeat the experiment another time and make more replicates to try and get the average results instead of only having one set of results to follow. It is possible that my results were wrong because of a fault in my method or the apparatus I used, but it is unlikely as the results I collected were close to the results I predicted.