Plant in equal strength solution:
(Solution equal to solution in plant cell)
H2O H2O
(Solution equal to solution outside)
In this diagram the process is balanced and so the water level is balanced in both areas because the strength of both solution are the same and this can be used to determine the cell sap strength, of the potato cell. It is this point that I will try to determine in this experiment by using potato chips as my source of plant cells and various strength sucrose solutions.
PLAN
This is how I am going to carry out my experiment:
- Cut the potato chip to wanted size (40 mm) with a scalpel to allow accurate measuring
- Label test tubes indicating the strength of the solution 0.0M, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M and my initials
- The volume of the liquid is measured at 25ml at all times.
- Measure and record the length of each chip and put chip into the test tube of the desired strength
- Leave Test tubes for three days and afterwards measure the chips are measured and compare with previous measures.
- Repeat the experiment again to get another set of results so an average can be worked out to improve the reliability of the results.
APPARATUS
- Ruler
- Scalpel
- White tile for cutting and measuring
- 12 potato chips
- 12 test tube
- 2 test tube racks
- Sugar solution: 0.0M
0.1 M
0.2 M
0.3 M
0.4 M
0.5 M
PREDICTION
What would happen when a potato chip is placed into distilled water?
The potato chip would become larger because some of the water outside would diffuse by osmosis into the potato chip.
What would happen if a potato chip were placed into a solution of equal strength to the cell sap?
If the solution were the same strength as the cell sap inside the plant cells vacuole, then water would not move in and out of the cell at equal rates, and so the potato chip would stay the same size.
What would happen if a potato chip were placed into a strong solution?
The potato chip would become smaller because the water inside would diffuse out by osmosis into the surrounding solution.
This will give a trend like the one shown in the following graph.
+
Size of
potato
chip 0
-
0.0 0.5
Water Weak Strong
Solution Solution
This graph shows what I predict the graph is going to look like when I gather the results and make a graph from it. At the point where the arrow is the strength of the cell sap is equal to the strength of the sucrose solution on the line of best fit. The experiment should allow me to determine the exact strength.
FAIR TEST
To make my experiment a fair test I must control all the factors, which could affect my experiment and give inaccurate results.
These factors are:
- Strength of the solution
- Volume of the solution
- Length of the chip
- Temperature
How I am going to control the factors:
The strength of the solution has to be controlled, as my chosen variable will be in the range of 0.0 and 0.5M.
The volume of the solution has to be kept at 25ml at all times so that it ensures accurate results. If there were a test tube containing 2ml more than the other test tubes then it would be considered as an unfair test because this variable might distort the results.
The length of the chip has to be the same (40mm&50mm) because at the end most chips would have changed in size and the only way of telling the difference is by knowing first that the chips are the same size, then measure the chips after the experiment and plot the difference on a graph.
The temperature has to be the same for all the chip. If one or more was cold then the enzymes work slower and the outcome is less reliable.
OBSERVATION
Experiment 1
Experiment 2
Average
ANALYSIS
The results show a clear trend with an increase. Also in this experiment it shows as the strength of the solution increases, the percentage difference between the original size and the new size of the potato chip has decreased.
I think that my prediction is right although my results were not close to the line of best fit; it proves if the potato chip was placed in a strong solution it would start to shrink (flaccid)
Example:
(Strong solution)
H2O
H2O
(Weak solution)
And this also shows that if a potato chip is placed in a weak solution it becomes larger (turgid)
EVALUATION
The experiment went well but my results could have been more accurate and reliable if I repeated the experiment more than twice and took the average percentage of the result tables; I could also take the results to 2 decimal places to get more accurate results and I could have improved my results and make them more accurate if I kept the lengths of the potato chip the same at both experiments.
The reason for my results to come out inaccurately is because it could have been a human error such as not reading the size of the potato chip properly, and not measuring the amount of sucrose solution added onto the potato chip.
I think my results are not reliable enough to give me a firm conclusion because the experiment was carried out on bases, which could make factors produce inaccurate results.
Therefore to improve the experiment I could repeat the experiment by making more than two people carry out the experiment, check the amount of sucrose solution added to the potato chip, take the measurement of the actual chip twice.
BIBLIOGRAPHY
I used these sources to enable me to add more information to my experiment.
- Letts biology revision guide
