The aim of the following experiment was to investigate the effect of varying the concentration of sucrose solution on osmosis in a potato.
One preliminary experiment was done before the main experiment. From the preliminary, we were trying to find out how osmosis actually occurred in potatoes, and gave us a vague idea on what the main experiment would be like.
This preliminary will aid my prediction, which is stated below. The following apparatus was used for the preliminary:
* 1 large potato (skin intact)
* 3 boiling tubes
* Set of cork borers
* Balance (accurate to 2 decimal places)
* Distilled water
* 0.5M sucrose solution
* 1.0M sucrose solution
* Dropping pipette
* Boiling tube rack
* Measuring cylinder (accurate to 1cm3)
* White tile
Take a large uncooked potato, with the skin still on, and with the cork borer, cut out three "tubes" of potato. Do this onto a white tile, so you don't cut your fingers or wreck the bench. Take a ruler and measure these tubes, and, if necessary, cut off any excess until they are all the same length. The same potato must be used; otherwise it will not be a fair test (because different potatoes may have different osmotic properties).
To ensure the experiment is as safe as possible, ensure you don't injure yourself using the cork borers. Also, we are using a sharp knife, so caution is needed there. Even though the sucrose solutions aren't poisonous, we are not 100% sure, therefore no sucrose solution will enter us.
Weigh the three tubes of potato, and record down the mass. Take the three boiling tubes, and fill 1 with 10cm3 of 1M sucrose solution, one with 10cm3 0.5M sucrose solution and one with 10cm3 of distilled water.
Label each tube clearly, then drop each potato tube into each boiling tube, one tube per boiling tube. Place the boiling tubes in a rack and leave for 24 hours.
After 24 hours, drain the solution and dry off any excess solution with paper towels from the potato. Then, reweigh the tubes, and calculate the percentage change:
These are the results from the preliminary:
Start Length (cm)
End Length (cm)
These results show clear evidence of osmosis. In tubes D-F, water was lost (hence the potato chips decreased in size) because the water potential is lower, therefore water moves down the concentration gradient into the sucrose solution. In A-C, water was gained because the water potential is higher, therefore water moves up the concentration into the potato.
Although the above results show clear evidence that osmosis has occurred, it is difficult to draw an conclusion from these results. The primary reason for this is because we didn't take any repeat results. A better preliminary would be to do 3 tests for each concentration, then take a repeat.
I alreeady know that osmosis is the net movement 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 of the sucrose solution.
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. If there is very little difference in the two water concentrations, there should not be a big change in weight. If there is a higher concentration of water in the potato, the water will go out of the potato through the membrane by osmosis.
In the distilled water, I think that the...