Study of Osmosis

Materials Required

Real Lab Procedure

  1. Place the peeled potato on the tile and using the knife, cut both ends of the potato to make it flat.
  2. Use the knife to make a cavity at the centre of the potato from one of the flat sides almost up to the bottom.
  3. Pour distilled water into the Petri dish until it is half full.
  4. Now, place the potato in the Petri dish.
  5. Fill half the cavity made in the potato with 20% sugar solution.
  6. Mark the level of sugar solution in the cavity using a pin.
  7. The potato now functions as an osmometer.
  8. Leave the osmometer undisturbed for about two hours.
  9. Mark the rise in the level of the sugar solution in the cavity with another pin.

Simulator Procedure (as performed through the Online Labs)

  1. To increase or decrease the concentration of the sugar solution in the Petri dish, choose the concentration of sugar from the 'In Petri dish: Select the sugar concentration’ drop down list.
  2. To increase or decrease the concentration of the sugar solution in the potato, choose the concentration of sugar from the ‘In potato: Select the sugar concentration’ drop down list.
  3. Click on the Check box ‘Cross sectional view’ to view the cross section of the potato, that helps view the water level inside potato.
  4. Drag a pin to mark the initial level of the sugar solution in the cavity.
  5. Click on the start button to start the experiment.
  6. A timer is shown and you need to wait till the timer stops.
  7. Drag another pin and mark the rise in level of the sugar solution in the cavity.
  8. Click on the information icon to see the inference.
  9. You can redo the experiment by clicking on the ‘Reset’ button.

Observation

The level of sugar solution in the potato cavity rises after some time due to the entry of water into the sugar solution through the selectively permeable membrane of the cells of the potato.

Conclusion

The movement of water from the Petri dish to the potato cavity occurs because of the difference in the concentration of solvent molecules in the two regions: sugar solution in the potato cavity and pure water in the Petri dish.

Precautions

  • The cavity should be deep enough to keep only a thin layer of tissues at the base of the potato.
  • The sugar solution should be of sufficiently high osmotic concentration as compared to the cell sap of potato cells.

 

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