Osmosis: Potato and Sucrose Solution

Investigation of Factors Affect Osmosis in Potatoes 

Aim 

The aim of the following experiment was to investigate the effect of  varying the concentration of sucrose solution on osmosis in a potato. 

Preliminary Experiments 

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 

* Scalpel 

* 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: 

Tube 

Start Length (cm) 

End Length (cm) 

% Change 

A (water) 

4 

4.2 

5 

B 

4 

4.1 

2.5 

C 

4 

4.3 

7.5 

D (sucrose) 

4 

3.6 

-10 

E 

4 

3.5 

-12.5 

F 

4 

3.7 

-7.5 

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. 

Prediction 

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...