9. 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 o
B and C.
(ii) Why is potato A necessary for this experiment?
(iii) Explain why water does not gather in the hollowed or
portions of A and D.
Answers
Explanation:
(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.
(i) Since sugar and salt was present in B and C respectively, water from the trough gathered in the hollowed portions of potato in B and C by the process of osmosis.
(ii) Potato A is necessary for carrying out this experiment because it acts as a control experiment. Control helps us to check what changes occurred during the course of the experiment and helps us to compare the results.
(iii) Water does not gather in the hollowed portion of potato A as it was empty. Water also does not gather in the cup D because the potato used was boiled which makes it inactive as after boiling its protein structure were denatured, resulting in the disruption of the cell membrane.
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