Investigation into factors that affect Osmosis in potatoes.

Investigation into factors that affect Osmosis in potatoes

I will investigate how different concentrations of sucrose affect potato in terms of turgidity. The sucrose will be in varying concentrations compared to water.

I hypothesise that the higher the concentration of sucrose around the potato, the more mass the potato will lose. I believe that this will happen as the potato will try to lose water to equalise the concentration of the sucrose compared to water, this is the process of osmosis. This happens through the pores on the selectively permeable membrane on the potato, which allows water through it but not sucrose.

To measure the effect of osmosis with sucrose on potatoes, I will measure percentage change in both length and mass, using balances and measuring implements. I will measure weight to 2 decimal places, and length to the nearest millimetre. I will follow normal laboratory procedure, and will take special precautions when using scalpels and borers.

I will cut the cylindrical pieces of potato to the same diameter which is 5mm, by using a cork borer and to the same length (4cm), by using a scalpel. I will put the piece of potato into a boiling tube, and I will put varying concentrations of sucrose in with it. I will put 10ml of sucrose with 0ml of water, then 8ml Sucrose and 2ml water, then 6ml sucrose with 4ml water, then 4ml sucrose with 6ml water, then 2ml sucrose with 8ml of water and 0ml sucrose with 10ml of water. I will leave the boiling tubes overnight, and will then remove, measure length and weigh each piece of potato. I will take the percentage change of each piece of potato by:

Change in length x100

Original length

Change in mass x100

Original mass

Although if the pieces of potato do not have enough time in the boiling tubes to complete the process of osmosis, the results will not be accurate. In my preliminary experiment I found that the potato did have enough time to complete the process, so the results should be accurate.

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Change in length x100

Original length

Change in mass x100

Original mass

Variables involved are: length and diameter of pieces (this will be kept the same), amount of solution (same), temperature (room temperature), Time (this will be kept the same), type of potato (same), size of potato (same) and concentration of glucose (this is the only variable to change). I am most of these variables constant to ensure that the experiment is fair, and so that the results are accurate. I will control these by repeating the experiments exactly every time; this is the only way to ensure exact repetition. I will use the same equipment and the same methods each time. I will repeat the experiment 3 times to ensure that the results are accurate, and so that any anomalous results can be spotted easily.

I will bung the boiling tubes to prevent exposure to the air, due to the fact that high concentrations of sucrose absorb moisture, and will change concentration. This would invalidate the results. The pieces of potato will be blotted before use, as any surface water would change the concentration and invalidate the results. Before the pieces are weighed, they will be blotted again so that it is not the solution being weighed as well.

When I get the results I will put them in a table and draw a graph to illustrate the results.

Equipment list:

Scalpel – cut the potato to size

Boiling tubes (x6) – to put the solution and potato in

Borer (5mm) – to cut the pieces out of a potato

White tile – to prevent damage to the bench

Boiling tube rack – to hold the boiling tubes

Sucrose (1 molar) – for the solutions

Distilled water – to vary the concentration of sucrose

Bungs – to stop air getting in the boiling tubes

100cm3 Beaker – to keep the sucrose in

Pipette – to transfer the sucrose to the boiling tubes

Ruler – To measure pieces

Scales – To weigh pieces

Blotting paper – to take away surface water from pieces

Obtaining Evidence

I used the equipment listed in the plan, and it all worked properly. To measure the length, I just lined up the pieces against the ruler and measured them. I did the same thing with the set up of the experiment, where I measured a 4cm strip of potato and cut it with a scalpel. I believe that the results I have obtained are both reliable and accurate, as I carried out my plan correctly and exactly and repeated the experiment three times.

I believe that I have taken enough observations, as I have three sets of data. I believe this is enough to enable me to observe correct trends in the data.

I believe I have covered the whole range of data that I intended to collect – that is the change in length and mass.

Below are tables and graphs of the averaged data – along with all the other tables of data.

The patterns that the graphs show are that with higher concentrations of sucrose, the potatoes lose mass and length. And with just water, the potatoes gain length and mass. The greatest changes in length and mass occur with low concentrations of sucrose, with higher concentrations of sucrose the rate of change between two concentrations is much less. There seems to be a relationship between length and mass in the way that they both have the same downward trend.

Conclusion

When there were high concentrations of sucrose around the potato, it lost the most mass and length. When there was no sucrose around the potato, it gained mass and length. This happens as if there is a sucrose solution around the potato, it tries to lose water to equalise the concentration of sucrose compared to water – this is the process of osmosis. Osmosis is defined as the movement of water from an area of high pressure/concentration to one of lower concentration across a selectively permeable membrane. Only water molecules can move because the membrane allows the passage of small molecules but prevents the movement of large molecules. When there is just pure water around the potato, it gains length and mass due to water potential. Water potential relates to the amount of water in a solution. The greater the water content the higher the water potential. Pure water has the highest water potential. In osmosis water moves from a higher water potential to a lower water potential.

This result is what I predicted would happen in my hypothesis. Most of my results support my conclusion, but there is just one anomalous result for change in length, but this is ironed out in the best-fit line. I think my conclusion will be the same in most similar situations, as it follows the scientific theory.

Evaluation

I believe that this was a successful experiment, due to the fact that the results follow the scientific theory. Most of my results fit the prediction, but there are some that don’t – but this is to be expected due to experimental uncertainty or uncontrollable circumstances. I believe that the experimental uncertainties are within acceptable limits. I can and have used scientific theory to support my results, and I believe that my evidence is sufficient to support my decision. I feel that three sets of data is enough to make a valid conclusion and I have proved this.

I believe that it was a fair test, due to the fact that I repeated the experiment exactly each time. My results should be reliable and reproducible, as they follow the theory about osmosis.

If I had to repeat the work, then I would not really change anything. I might leave some samples for longer time periods, to see what would happen. I would use the same equipment as it all worked as I wished it to, but I may use more accurate equipment – like scales to 3 decimal places. I would choose the same variables, but I might experiment with one more, maybe temperature.

If I had more time to do the experiment then I would investigate all the variables, and would experiment with different sizes and types of potato. I would also take more readings for example 1/9, 3/7 and 5/5 concentrations of sucrose to water. These would make the results and conclusion more accurate and reliable. I would use additional evidence, by maybe using completely different techniques and equipment to see if those results are comparable to my own.