Apparatus:
Notes:
- Test Tube rack so I can watch an keep the experiments steady and safe the results will be more accurate.
- The cutting tile prevents the surface from getting damaged and a ruler can be used to cut the potato strips for more accuracy.
Method:
1) Cut out 3 strips of potato (from the same potato to ensure a fair test).
2) Cut the 3 strips to equal length (4cm), and measure and record.
3) Place the 3 test tubes in the test tube rack and measure out the three measurements of hydrogen peroxide of 5ml.
4) For heating, boil water and add it to the following:
200ml of heated water, with 5ml of solution.
150ml of heated water and 5ml of solution.
100ml of heated water and 5ml of solution.
Use the same measurements but for cooling used cold water, instead.
For room temperature don’t add any water just place in rack.
6) Now place the test tube with the hydrogen peroxide in the beaker of water or leave the test tube in rack depending, which test your doing and add the thermometer an record then add the potato chip an start the stop watch.
7) When it stops frothing record how much it has and stop the timer and record your results.
Results:
Room Temp:
Heating:
Freezing:
Just Ice:
Graph
Conclusion:
These results show that at a point between concentrations 0.25 and 0.5 there is a point at which the potato tissue neither gains in mass or decreases in mass, i.e. it supports the idea that there is an equilibrium reached, so that there is no net movement of water because the water potential will be the same in one region as it is in the other. It also shows that potato tissue will gain in mass when it is in a surrounding solution which has a higher water potential than itself (weak sucrose solution), and conversely it will decrease in mass when in a surrounding solution which has a lower water potential than itself (stronger sucrose solution). This supports the belief that water moves across a concentration gradient, i.e. move from areas of high water potential to areas of low water potential.
Evaluation:
The results of this experiment support the basic beliefs about osmosis in plant cells, i.e. Water moves from an area of high water potential to an area of low water potential, and once the water potential in both regions is the same, the cell will reach equilibrium, i.e. There will be no net movement of water through a partially permeable membrane. The main fault with the data is that I did not test the potato tissue with enough sucrose solutions, so my results were not accurate enough. From my results I can state that the point of equilibrium in the potato occurs in a concentration some where in between 0.25 and 0.50 but the exact point is just an estimate and I could make the results more accurate by testing a larger variety of sucrose solutions.
The graphs shows that the data which I have collected supports the general beliefs about osmosis in plant cells, so therefore I do not feel the need to change factors such as the size of the potato or the volume of solution used because they have proved to me effective. I think that it would increase the accuracy of the main investigation to use a larger variety of sucrose concentrations.