Title: Osmosis and water potential Aim of the experiment: Finding the water potential of potato. Biological principles: Independent variable: concentration of the solution. Dependent variable: percentage changed in weight of the potato strips. Controlled variable: size of the potato strips, it can be controlled by cutting the length of the strips. Procedure: Table 1. Concentration of sucrose solution table Concentration/ M| Sucrose Solution/ ml| Distilled Water/ ml| 0 (Water)| 0| 10| . 2| 2| 8| 0. 4| 4| 6| 0. 6| 6| 4| 0. 8| 8| 2| 1| 10| 0| 1. Prepared 6 solutions. 0. 2M, 0. 4M, 0. 6M, 0. 8M, 1M sucrose solution and water. (Table 1) 2. Filled six boiling tubes with 5 cm3 of the solutions and labeled the boiling tubes. 3. The potato should be cut into 6 strips by cork borer and should be cut with the same length of 5 cm. 4. The potato strips should be dried. 5. The initial reading of the mass should be recorded. (Table 2) 6. Each boiling tube should be immersed one strip. 7.
Strips should be taken from the solutions by the forceps after 30mins. 8. The potato strips should be dried. 9. The second reading of the mass should be recorded. (Table 2) 10. Calculate the percentage changed in mass. Table 2. Initial and final reading of mass and percentage changed in mass | 1 M| 0. 8 M| 0. 6 M| 0. 4 M| 0. 2 M| Water(0M)| Initial mass (g)| 1. 01| 1. 02| 1. 04| 1. 01| 0. 98| 1. 02| Final mass (g)| 0. 78| 0. 83| 0. 89| 1. 01| 1. 08| 1. 21| Percentage change* (%)| -22. 8| -18. 6| -14. 4| 0| 10. | 18. 6| *percentage changed: [(final – initial)/initial] x100% Fig 1. Procedure graph P. 1 Result: From the graph, 0M (water) and 0. 2M sucrose solution have higher water potential than the cell sap. Water molecules entered the cell by osmosis. Because of it, the cell became heavier, turgid and swelled. As a result, the solutions are hypotonic to the cell. 0. 4M sucrose solution is isotonic to the cell sap. Because of it, there is no net water movement.
Also, the mass of the strip and the touching of it remain the same. 0. 6M, 0. 8M and 1M sucrose solutions have lower water potential than the cell. Water molecules left the cell by osmosis. As the cell lost water, it became flaccid, plasmolysed and decreased in mass. As a result, the solutions are hypertonic to the cell. Discussion: Error: Measurement: The sensitivity of the balance may affect the mass that we measured. Individual variation: The concentration of the solution may not be accurate.
The boiling tubes should be covered with food wrap, otherwise, water may evaporated and affecting the concentration. Conclusion: The water potential of the potato that we used is 0. 4M. It’s because there is no change in the mass of the strip at 0. 4M sucrose solution. A solution that water potential is lower than 0. 4M, it is hypotonic to the potato. Water move into it by osmosis and it becomes turgid and swell. As for solution that water potential is higher than 0. 4M, it is hypertonic to the potato. Water leaves the potato cell and it becomes flaccid and plasmolysed. P. 2