(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.
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.