Carry out the following osmosis experiment: Take four peeled potato halves and scoos 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 n

Explanation

(i) When unboiled potato cups B and C were put into a through containing water, the cells of potatoes gained water by endosmosis. When a teaspoon of sugar and salt were added later in the hollowed portion of B and C cups respectively water movement occurred through the plasma membranes of the cells from within the cells of potato into the hollowed portiono f both B and C cups because of exosmosis (i.e., exit of water molecules through permeable plasma membranes from within the cells of unboiled potatoes into the hollowed portions having hypertonic sugar and salt, respectively).
(ii) Potato cup A is necessary in the experiment as a control for providing comparison with situations created in potato cups, B, C and D. It indicates that the potato actity alone does not induce movement of water.
(iii) Water does not gather in the hollowed portion of potato cup A because it doen not possess highre osmotic concentration that the cells of potato.
Potato cup D is boiled potato cup. On boiling, potato cells lost their permeability. As a result, when teaspoon of sugar is added into the hollowed portion of boiled potato cup D, water does not come out form within the potato cells into the hollowed portion.