I believe that if I place a potato chip into a solution of higher sugar concentration than the isosmotic point the chip will shrink and become flaccid. This is because the chip has a lower concentration of sugar than in the solution, so by the process of osmosis the water will move from the chip into the sugar solution.
I also believe that the more concentrated the solution is, the more the chip will shrink; and the more dilute the solution is, the more the chip will grow.
The variable I will be investigating and therefore altering, is the solute concentration.
In order to make the experiment a fair test, there are some variables I will have to keep constant. These are: -
The amount of solution in each test tube
I will use a measuring cylinder and use the same amount every time. I will wash the measuring cylinder after each experiment.
The original concentration of the sugar solution
The sugar solution will be made up for me, I will only use the solution provided to me.
The temperature
I conducted all my experiments on the some day without opening any windows or turning on any electrical heaters. This should keep the temperature constant, at room temperature
The length of potato chip
I will cut all my chips to the same length, measured by the same ruler.
The light intensity
I will conduct all my experiments in the same room, at the same time, without shinning any lights on them or putting them in the dark. This will keep the light constant.
Equipment
8 Boiling tubes
Test Tube rack
Potato Chips
Sharp Blade
Measuring Cylinder
Sugar solution
Water
Marker Pen
Stop Watch
Sieve
Method
- Arrange 8 boiling tubes in a test tube rack.
- Cut 24 chips 50 mm using a sharp blade.
- Measure out the desired amount of sugar solution and water, and place in the boiling tube.
- Write the concentrations on the test tube rack, with a marker pen to make sure they are not forgotten.
- Place three chips in a boiling tube and start the stopwatch.
- Every two minutes place another three chips into the next boiling tube.
- After each set of chips has been in the solution for 35 minutes, take out using a sieve and measure each one using a ruler.
To make the experiment accurate, I will place three chips into each concentration and take an average change in length.
I will also use many concentrations, that way if I receive any anomalous results I will still be able to draw a good conclusion from the experiment.
The reason I will stagger the chips going into the boiling tubes is because it will give me time to measure each chip. If I did not stagger it, some chips would be out of the solution for longer than others, which might alter their lengths.
I conducted a preliminary experiment, to investigate what concentrations to use. I decided that I would base many of my concentrations around the isosmotic point. The isosmotic point is when the concentrations of both solution and the chip are the same or Isotonic; this means the chip will neither grow nor shrink.
The isosmotic point was 0.3 molar; the concentrations I decided to use are below.
My concentrations table
Results Table
These results were collected at 24ºC.
Analysis
By examining the graph I can conclude that my quantitative predictions were correct, when the concentration of the sugar solution was more than 0.27 molar (the isosmotic point), the chip shrunk and became flaccid. This process is called plasmolosys. This was because the chip had a lower concentration of sugar than in the solution, so by the process of osmosis the water moved from the chip into the sugar solution.
When the concentration was less than 0.27 molar, the chip grew and became turgid. This is because the chip had a higher concentration of sugar than in the solution, so by the process of osmosis the water moved from the sugar solution into the chip.
As you can see in the graph, as the concentration of sugar solution moved away from 0.27 molar, the more the potato chip deviated in size. 0.27 molar was the isosmotic point, meaning the solution and the chip both had a sugar solution of 0.27 molar, so the chip neither shrunk, nor grew.
The more the concentration was increased above 0.27 molar, the more the chips shrunk. When the concentration was 0.4 molar the chips average % change in length was –1.7%. When the concentration was increased to 0.8 molar, the chips average % change in length was –7.1%. This is because the chip, in the 0.4 molar solution, had a slightly lower sugar concentration than in the solution. This suggests that a small amount of water moved by the process of osmosis from the chip to the solution, meaning it did not shrink in size that much. However the chip, in the 0.8 molar solution, had a much lower sugar concentration than in the solution. This meant that a large amount of water moved by the process of osmosis from the chip to the solution, making the chip shrink considerably more.
The more the concentration was decreased from 0.27 molar, the more the chips grew. When the concentration was 0.2 molar the chips average % change in length was +1.0%. When the concentration was decreased to 0.0 molar (water), the chips average % change in length was +3.5%. This is because the chip, in the 0.2 molar solution, had a slightly higher sugar concentration than the solution. This meant that only a small amount of water moved by the process of osmosis from the solution into the chip, meaning it did not grow in size that much. However the chip in the water (0.0 molar) had a much higher sugar concentration than the solution. This meant that a large amount of water moved by the process of osmosis from the solution into the chip, making the chip grow considerably more.
Evaluation
Overall I believe that the experiment worked well because the results were consistent with each other, and as you can see in the results table, were reproducible. After plotting a line of best on the graph, I observed that five of the eight results were virtually on the line, and the other three whilst not touching were close and certainly followed the same trend. As you can see from the graph I have circled the point furthest away from the best-fit line. Possible explanations for these slight variations could be that: -
- I did not use chips from the same potato. Different potatoes would have different concentrations of sucrose. If I used a chip from a potato containing less sucrose, it would loose more water. This would make the potato chip shrink a bit more.
- I did not measure the width of the chips, I only measured the length. It is possible that the chips were getting wider as well as longer, some more so than others.
If I had to do this experiment again I would improve it in the following ways:
- I would use a burette instead of a measuring cylinder. This would make my measurements of the sugar solution and water much more accurate.
- I would conduct the experiment with a narrower range of concentrations. The burette would enable me to do this easily.
- I would get all my chips from the same potato.
- I would take the mass the chips using a balance, instead of measuring the length. This method would be quicker, much easier and more accurate.
Extension
To extend the previous enquiry, I would repeat the experiment with different types of plant cells, probably an apple or a carrot. I might also repeat using a different part of the potato plant, the stem for instance. It would also be interesting to put a potato in different concentrations of a salt solution. It would be good to repeat the experiment using plants that live underwater, for example seaweed and pondweed, and seeing how they react when placed in both salt water and fresh water.
It would be interesting to conduct this experiment with an animal cell, for instance a strip of chicken. As animal cells do not have cell walls, they do not become turgid in the same way that a plant cell does. It would be interesting to observe what would happen to an animal cell in a hypotonic solution. I expect it might explode without a cell wall. In a hypertonic solution it would shrink. I have seen a slug dehydrate and turn to mush when covered in salt. I now think that this is due to osmosis.
