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,

(a) Keep cup A empty

(b) Put one teaspoon sugar in cup B

(c) Put one teaspoon salt in cup C

(d) 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:

(i) Explain why water gathers in the hollowed portion of B and C.

(ii) Why is potato A necessary for this experiment?

(iii) Explain why water does not gather in the hollowed out portions of A and D.

(i) Water will accumulate in the hollowed portions of B and C as a result of difference in the water concentration, due to which a concentration gradient forms and thus water from higher concentration (from the trough containing water) flows to a region of lower water concentration (hollowed portion of potato cups). This is a result of osmosis of water in a hypotonic solution.

(ii) Potato cup A is essential in this experiment as it is a significant reference to compare different scenarios seen in potato cups B, C and D.

(iii) Potato cup A didn't show any change in the concentration because it is an example of isotonic solution. Potato cup D is a boiled potato which tells us that this potato has same or more water concentration than the trough containing water in which potato cup D is placed. So there is no flow of water from the trough into the hollow portion of potato cup D.