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, - Keep cup A empty
- Put one teaspoon sugar in cup B
- Put one teaspoon salt in cup C
- 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:
- Explain why water gathers in the hollowed portion of B and C.
- Why is potato A necessary for this experiment?
- Explain why water does not gather in the hollowed-out portions of A and D.
- Keep cup A empty
- Put one teaspoon sugar in cup B
- Put one teaspoon salt in cup C
- 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:
- Explain why water gathers in the hollowed portion of B and C.
- Why is potato A necessary for this experiment?
- Explain why water does not gather in the hollowed-out portions of A and D.
Solution and Explanation
(i) Osmosis is the process responsible for the gathering of water in the hollowed portion of B and C. Since, the concentration of solute (sugar in cup Band salt in cup C) is higher inside the cup as compared to the water, which is outside the cup. Hence, water from its higher concentration (outside the cup) will move towards the lower concentration (inside the cup). This process of osmosis (moving in of solvent) is called endosmosis.
(ii) Potato A acts as a control for the experiment. This is required for comparing the results of the experiment.
(iii) Water does not gather in the hollowed-out portions of A and D because of the following reasons:
• The hollowed portion of potato A is empty. So, because of no concentration difference, no osmosis can occur.
• The hollowed portion of potato D contains sugar in it, but it is boiled.
So, osmosis cannot occur as its semipermeable membrane is destroyed by boiling.
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Concepts Used:
Osmosis
Osmosis is a passive process and happens without any expenditure of energy. It involves the movement of molecules from a region of higher concentration to lower concentration until the concentrations become equal on either side of the membrane.
There are three different types of solutions:
- Isotonic Solution is one that has the same concentration of solutes both inside and outside the cell.
- Hypertonic solution is one that has a higher solute concentration outside the cell than inside.
- Hypotonic solution is one that has a higher solute concentration inside the cell than outside.