Investigate the effects of different water potential sucrose solutions, on the size and weight of potato cylinders over the period of 48hours.

When water is lost, cells shrink in size and lose weigh due to lose of water, so this means that potato cylinder will decrease in size and weight from its original state.

But when the potato cylinder is placed in pure water which has the highest water potential of zero or any other solution which has higher water potential than the potato cells, the potato cells will swell up, therefore their size and weight increases. This is again due to osmosis but in the opposite direction. Now the solute has higher water potential, the water molecules enter the potato cells through the freely permeable cell wall and the partially permeable plasma membrane and enter the protoplast. This increases the volume of the cell, the protoplast (the living part of the cell inside the cell wall) starts to push against the cell wall and pressure starts to build up rapidly. This is the pressure potential and it increases the water potential of the cell until water potential inside the cell equals the water potential outside the cell, and equilibrium is reached. The inelastic and tough cell wall prevents the cell from bursting. When the potato cell is fully inflated with water, it is described as turgid. So the potato cylinder is now larger in size and has increased weight due to the extra water in its cells.

Apparatus:

1. Measuring Cylinder (25ml)
2. Syringe (5ml)
3. 5 Test tubes
4. Distilled water (25ml)
5. Sucrose solution 1 molar Concentration (25ml)
6. Beaker (50ml)
7. 5 potato cylinders (30mm width)
8. Scalpel
9. Electronic balancer
10. Accurate ruler for measurement (in mm)
11. Foil and tissue paper

Method:

• First stage is to cute the 5 potato cylinders accurately to width of 30mm using ruler and scalpel
• We then measure the potato cylinders weight by placing each on the electronic balancer and recording the data
• Second stage is to create the 5 different concentration solutes to pour into each test tubes by using the information on the table below:

• After creating the solutions (10ml each), then we add each potato cylinders to each test tubes containing sucrose solution in order which I recorded their weight by
• Then Secure each test tube by raping the end by aluminium foils
• The test tubes are placed in a test tube holder and left for period of 48hours
• After 48hours take out each potato cylinder in order and measure their size and weight and record them on the results table and calculate the differences in weight and size in mm and grams.

Results:

The table above are my recorder results and according to them I have produced two graphs which show the pattern of changes in weight and size of the potato cylinders to help me in my conclusion.

Conclusion:

My results have proven that my predictions were correct. Looking at the graph for difference in size and the table section of difference in size, we can see that 1 molar sucrose solution which has the lowest water potential and highest concentration has decreased the size of the potato cylinder by -5 mm and also -0.49g decrease in weight. This means that the potato cells have been plasmolysed and shrunk due to lose of water through its permeable membrane by osmosis, and you can see a general pattern in the graph which shows that as concentration of the sucrose solution decreases, there is a less decrease in size and weight of the potato cylinders.
The graph also proves my second prediction, which was an explanation of increase in size and weight due to inflation of water in potato cells. Looking at both graphs, the 0 concentration solution which is basically distilled pure water which has highest water potential; there is an increase in weight (+0.21g) and size(+3mm). This means that cells have taken in water by osmosis and are inflated fully with water and are turgid. They now have higher volume. This issue is fully explained in my prediction.

Evaluation:

• Although my prediction seems to be generally correct by looking at my graphs and results table, but there is an inaccurate result which seems to be an outlier and a mistake which does not make sense.  Looking at my 0.5molar sucrose solution results, we can see a +0.1 g increase in weight, but looking at difference in size, there is a -1 mm decrease in size. This can be simple mistake in measurement using apparatus such as ruler and electronic balancer. Therefore to provide more accurate results and fair test, much more attention and concentration is required.
• Using ruler to cut each potato cylinder is not very accurate since we have to rely on accuracy of human eyes which is simply not enough. In order to have exact equal size potato cylinders, mechanical machine cutters can be used.
• Other factor which may have affected my results is the electronics balancer. The electronic balancer needs to be on a fully flat surface before use, because if it is moved to a different place, different results maybe given since the flatness of different surfaces are differ.
• To produce different concentration solutions of sucrose, we again have to rely on our sight accuracy when using measuring cylinders to mix distilled water with sucrose (1molar). Simple inaccuracy may have effects on our results so to make this a fair test; more accurate apparatus which have much more accurate measurement can be used.