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.
Also draw the set-up for the experiment.
Answers
Answer:
(i) Water gathers in the hollowed portion of B and C because of the process of endosmosis (moving in of the solvent). A potato is made up of several cells, and the cell membranes are selectively permeable. As the cups B and C are filled with sugar and salt respectively and their outer part is in contact with the water, the concentration of water outside the cups is higher than inside the cups, so water moves from its higher concentration towards the lower concentration, i.e., inside the cup.
(ii) Potato A acts as a control of the experiment. It is very necessary for comparing the results of the experiment and shows that if the conc. of water is same on both sides, there will be no movement of water.
(iii) Water does not gather in the hollowed out portions of A as it does not contain hypertonic solution so there is no concentration difference. Water does not gather in the cup D as the cells of boiled potato are dead and hence no osmosis occurs.
Explanation:
