Question

Carry out the following osmosis experiment:

Take four peeled potato halves and scoop each one out to make potato cups. One of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water. Now,

1. Keep cup A empty
2. Put one teaspoon of sugar in cup B
3. Put one teaspoon salt in cup C
4. Put one teaspoon sugar in the boiled potato cup D.

Keep these for two hours. Then, observe the four potato cups and answer the following:

1. Explain why water gathers in the hollowed portion of B and C.
2. Why is potato A necessary for this experiment?
3. Explain why water does not gather in the hollowed-out portions of A and D.

Answer 1

1. Water gathers in the hollowed portions of set-up B and C because water enters the potato through osmosis. Since the medium surrounding the cell has a higher water concentration than the cell, the water moves inside through osmosis. Hence, water gathers in the hollowed portions of the potato cup.
2. Potato cup A is necessary for the experiment as a control to compare with situations created in potato cups B, C and D. It indicates that the potato cavity alone does not induce any movement of water.
3. Water does not collect in the hollowed-out sections of A. This can be described as follows. For osmosis, a concentration gradient must form between the two liquids on either side of a semi-permeable membrane (in this case, a potato strip). Water is only on one side of the potato cup, the convex side, while the concave side is empty. Water will only fill the concavity due to endosmosis, which occurs when a solution with a higher concentration than water is present. As a result, the hollowed-out piece of A remained vacant. Cup D cells die as a result of boiling, and the semipermeability of the membrane is eliminated, therefore no osmosis occurs.