Investigating osmosis Investigating the water potential of potato using the weighing method. INTRODUCTION When the potato is immersed in a solution where there is no change in mass, there is no net flow of water into or from the cells by osmosis, i.e. the rate at which water enters the cells = the rate at which water enters the cells. At this point, WCELL = BATHING SOLUTION Before you start work: e Read all instructions carefully. Write an equipment list from the method below Write a risk assessment and safety precautions Prepare a suitable table to record your data. Method: 1. Insert the cork borer into the peeled potato to obtain a potato cylinder. 2. Repeat step 1 to obtain six potato cylinders. 3. Use the scalpel and ruler to cut each cylinder to 5cm in length. 4. Dry off the cell sap from each cylinder with a standard procedure. 5. Record the mass of each cylinder. 6. From the 1 mole solution of sucrose, prepare 10 cm³ of each of the required solutions: 0.2, 0.4, 0.6, and 0.8 mole. Concentration of sucrose solution (M) 0 0.2 0.4 0.6 0.8 1.0 Volume of 1.0 M sucrose solution added (cm³) 0 2 4 6 8 10 Volume of distilled water added cm³) 10 8 6 4 st 2 0 7. Fill one additional test tube with 10 cm³ of distilled water. 8. Label each test tube with the solution it contains. 9. Leave the tubes in a constant temperature water bath at 30 degrees for 3 minutes. 10. Add a potato cylinder to each test tube and cover with parafilm. Note the mass of each potato cylinder in each test tube. 11. After a minimum of 15 minutes, remove the potato cylinder. 12. Dry it carefully and record its mass. 13. Plot a graph of % change in mass against solution concentration. Calculate the percentage change in mass using the formula below: % change in mass = final mass - initial mass Initial mass x 100% 14. Where there is no net gain or loss in mass, WCELL is equal to WBATHING SOLUTION. From your graph read the molarity of sucrose where the percentage mass change is zero. 15. From the table below, find the water potential of a sucrose solution of that molarity. 16. Hand in your table of results and graph to your tutor Table showing the water potential of solutions of different molarity Molarity/mol dm3 Water potential/kPa -130 0.05 -260 0.10 -410 0.15 0.20 -540 0.25 -680 0.30 -860 0.35 -970 0.40 -1120 0.45 -1280 0.50 -1450 0.55 -1620 0.60 -1800 0.65 -1980 0.70 -2180 0.75 -2370 0.80 -2580 0.85 -2790 0.90 -3000 0.95 -3250 1.00 -3500 find-initial Sucrose cone. initial final change % mass mass in (moldm3) change (g) (g) mass (g) in mass 0.0 2.51 2.74 0.23. 9.1% 0.2 2.45 2.55 0.1 4.0% 0.4 2.53 2.51 -0.02 -0.7% 0.6 2.40 2.25 0.8 2.32 2.12 2.12-0.2 1.0 2.43 2.18 -0.15 -6.2% -8.6% -0.25 -10.2% change in mass 2 G 8 10- -12- change in mass in different concentration of sucrose 4 2 10 8 24 02 4 036 08 110 Sucrose conc. (mol dm3)/n