question_answer

    Carry out the following osmosis experiment: Take four peeled potato halves and scoop each one out to make potato cup 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. Why is potato a necessary for this experiment? (ii) Explain why water does not gather in the hollowed out portions of; and D.    [NCER]

Answer:

                  (i) Water gathers in the hollowed portion of B and C because of the process o endosmosis (moving in of the solvent). The potato wall acts as s semipermeable membrane. As the cups B and C are filled with sugar and salt respectively and their outer part is in contact with the water, the coricentration 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 Potato A acts as a control of the experiment. It is very necessary for comparing the results of the experiment. It shows that if the concentration of water is same on both sides, there will be no movement of water. (ii) Water does not gather in the hollowed out portions of A as it does no contain hypertonic solution so there is no concentration difference am hence no movement of solvent. Water does not gather in the cup D as the cells of boiled potato are dead and the potato wall is no longer semipermeable. Hence, no osmosis occurs.