Study Of Osmosis By Potato Osmometer: Diagram, Experiment

Aim

To study by demonstrating the osmosis process by potato osmometer.

Theory

Osmosis forms the base of understanding the flow of water through semipermeable membranes in organisms. The paper considers the process of osmosis using a potato osmometer, an apparatus that clearly shows this particular process. In the experiment, we will see how water is moved from high to low water potential across a semipermeable membrane and how different solutions affect this process.

What Is Osmosis?

Osmosis is the flow of solvent molecules across the semipermeable membrane from areas of higher water potential to those with lower water potential and vice versa. It is a continued movement from high water potential to low until the concentration of solutes on either side of the membrane level out.

Solvent And Solute

In osmosis, the solvent refers to the liquid that crosses a semipermeable membrane, while the solute includes particles dissolved in the latter. The two of them make up a solution.

What Is The Solution?

A solution is a uniform mixture of a solute and a solvent. Its property relies on the concentration of the solute and the solvent.

Solution Types

The different types of solutions:

Hypertonic Solution

A solution with high concentrations of solutes. Now, when cells are put in a hypertonic solution, since it is hypertonic to them, because of osmosis, the water rushes out of the cells, and they shrink.

Hypotonic Solution

A solution with low concentrations of solutes. Now, if cells are put into a hypotonic solution, then, because of osmosis, water will rush into the cell and it will swell up and become turgid.

Isotonic Solution

A solution where the concentration of the solute is equal on both sides of the membrane. Cells in an isotonic solution retain their shape because there is no net movement of water.

Material Required

1. Fresh large-sized potato tuber

2. Sucrose solution of 20% concentration

3. Beaker

4. Water

5. Scalpel or blade

6. Petri dish

7. Bell pin needle marked with waterproof ink

Procedure

1. Cut the potato tuber into two halves using a scalpel or blade. Remove the skin and then cut these halves into square pieces.

2. Scoop out a small cavity from the mid-region of the potato tuber having a minimum thickness at the base. The cavity may be square or circular.

3. Fill half the cavity with freshly prepared 20% sucrose solution and put a pin into the cavity so that its mark coincides with the level of sucrose solution.

4. Place the potato osmometer in a petri dish or beaker containing water; the level is to be such that 75 % of the potato osmometer will be submerged in the water.

5. Allow to remain undisturbed for about 1 hour.

6. Observe and note the level of the sucrose solution in the osmometer at the end of the experiment.

7. Repeat the experiment with the cavity filled with water and the sucrose solution in the Petri dish or beaker.

Observation

After an appropriate length of time, the sugar solution inside the potato osmometer will rise and may also become coloured. This shows that on account of osmosis, the water moves inside the osmometer.

Conclusion

This rise in the level of sucrose solution in the osmometer is, thus, a case of endosmosis, where the water from the external beaker enters the sucrose solution within the potato. This process thus creates a water potential gradient between the external water and the osmometer. Since water can enter the sucrose solution through the selectively permeable membrane of the osmometer, separated by living potato cells, this process is explained as osmosis.

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