Carry out the following experiment: Take four peeled potato halves and scoop. Class 9

Carry out the following experiment: Take four peeled potato halves and scoop. Class 9

Question 1.

Carry out the following 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. Place each of the potato cups in a beaker containing water (Fig.). Now, set up the experiment as follows: Class 9

(a) Keep Cup A empty.

(b) Add one teaspoon sugar in Cup B.

(c) Add one teaspoon salt in Cup C.

(d) Add one teaspoon sugar in the boiled potato in Cup D.

Observe the four potato cups at least two hours and answer the following questions:

(i) Explain why water gathers in the hollowed portion of Cup B and Cup C.

Answer:

The sugar solution in Cup B and salt solution in Cup C create a hypertonic environment inside the potato cup relative to the water in the surrounding beaker. Since the potato walls are made of cells with a selectively permeable membrane, water from outside moves into the hollowed portion by osmosis - from the region of lower solute concentration (surrounding water) to higher solute concentration (inside the cup). This is why water gathers inside Cups B and C.

(ii) Why is Cup A necessary for this experiment?

Answer:

Cup A is the control in the experiment. It has no solute added to it, so no osmosis should occur. If water is also observed gathering in Cup A, it means the results in B and C may not be due to osmosis alone (perhaps due to some leakage or other reason). Cup A lets us confirm that the water gathering in Cups B and C is specifically because of the solute concentration difference - not because of some unrelated factor.

(iii) Explain why water does not gather in the hollowed portions of Cups A and D.

Answer:

Cup A (empty): There is no solute concentration difference between the inside of Cup A and the surrounding water. So no osmosis occurs and no water gathers.

Cup D (sugar in boiled potato): The potato used to make Cup D has been boiled. Boiling kills the cells and destroys the cell membrane. A dead, damaged membrane is no longer selectively permeable - it cannot control the passage of water. Without a functional selectively permeable membrane, osmosis cannot occur. So even though sugar is present, water does not gather because the membrane is non-functional.