To find the isotonic level of a potato.

 

  For this particular investigation I think that the lower the concentration of the sugar solution in the test tube the larger the mass of the potato will be. This is because the water molecules pass from a high concentration, i.e. in the water itself, to a low concentration, i.e. in the potato. Therefore, the potatoes in higher water concentrations will have a larger mass and then decrease. In higher sugar concentrations it will increase in mass.

Fair Testing:

In this experiment on osmosis there should only be two changing variables:

1: Different concentrations of sugar solution,

2: Change in mass of the potato samples.

To keep these two variables the only variables in the experiment I must:

1: Keep the potato samples the same length (7mm). This is because if one potato sample is 7mm long and one is 1cm long then the 1cm long sample will have a larger surface area and will osmosis much more quickly. So we controlled the surface area using a cork borer.

2: Use the same type of potato. This is because many factors due to the potato may affect the experiment. For example the age and sizes might be different, which means one potato might have more water in them then another.

3: Stop the evaporation of any of the sugar solution. This is because if the sugar solution evaporates past the level of the potato, then the potato sample will have less surface area in the solution so this would make osmosis happen much slower. To stop any solution evaporating a cork lid can be placed on top of the test tube.

4: Accurate amount of sugar solution: More Bathing solution may affect the rate of solution. To make the amount of solution placed in the test tube as accurate as possible a syringe will be used to measure out the exact amount needed.

5: Contamination: As each test tube is filled up with the different sugar solutions the syringe which would measure the amount of solution placed in the test tube may become contaminated with different substances. To stop his from happening, the beaker and syringe must be washed every time they are used.

6: Average: To make the experiment as accurate as possible an average will be taken out of the 3 sets of results taken. We made up 3 test tubes of the same sugar solution, which is how we obtained 3 sets of results for an average.

7:Temperature: The temperature may affect the reliability of the experiment for example at extreme temperatures the cells of the potato may die and at less extreme temperatures the experiment may be speeded up. To keep this from happening, all the test tubes will be kept in the same place and at the same time of the half-hour experiment.

Apparatus I will need:

· Cork Borer,

· Water,

⋅ Sugar,

· Forceps,

· Timer,

· Measuring cylinder,

· Tile,

· Potato,

· Weighing balance,

· Stirring rod,

· Test tubes,

· Test tubes rack,

· Paper towels,

· Sticky labels,

· Ruler,

⋅ Cork lid,

⋅ Burette,

⋅ Volumetric Flask.

Method:

  I plan to carry out this experiment by using all the safety issues and fair testing procedures to give me the most reliable and most accurate set of results.

  I plan to have a range of sugar solutions prepared with concentrations from 0% sugar to 25% sugar, in intervals of 5%, (I will be using three sections of potato with each sugar solution, as this should be more than enough to explain the effects of the potato on osmosis). Then sections of potato will be cut using a cork borer and scalpel to equal lengths keeping the surface area constant. I will then measure each tissue of potato using an electric balance, which indicates weight in grams. I will then fill three test tubes to the top with 0% sugar solution. Then to each test tube a cut piece of potato will be added and its concentration added to the label. These will be left for 30 minutes. We left the potato in the sugar solution for 30 minutes because when we carried out the visking tubing experiment in the preliminary work, we found that 30 minuets was enough time for osmosis to take place. Then the potato pieces will be removed from the test tubes, and surface solution on the potato will be removed using paper towels. I will then measure the potatoes again, recording its change in mass by weighing them. A repetition of the experiment will be carried out using each sugar solution. The results will be taken and an average will be calculated from each concentration (shown below) to make a graph.

  0.59 + 0.60 + 0.59 = 1.78 ÷ 3 = 0.593

  After looking at my preliminary work it suggested that there was enough concentrations of sugar to compare each result to each other (the experiment could have been repeated with more concentrated solutions but this is not necessary). The timing of the potatoes weren't left for enough time in the experiment, as the results didn't have much change, therefore it would be much more accurate to leave them for an hour instead of half an hour to give a greater mass change. I will also be measuring the mass change as a percentage as it will be more appropriate so that reasonable results could be obtained. The graph below shows the possible outcome of the experiment.

 

Conclusion:

  I feel that the experiment worked well in terms that it proved my hypothesis to be correct and we achieved what we set out to complete. I wrote my hypothesis out of my scientific knowledge for what would happen, the potato didn’t taste very sweet so in this I knew the sugar content would be at a low rate. We found the isotonic value of a potato as accurately as possible by collecting an accurate set of results and finding the average. I also feel that I carried out the experiment with as much precaution / safety and fairness as possible.