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Q9(iii):
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: (iii) Explain why water does not gather in the hollowed out portions of A and D.
Solution :
Step 1: Theoretical Foundation of Osmosis
Osmosis is the net movement of water molecules from a region of higher water potential (hypotonic solution) to a region of lower water potential (hypertonic solution) through a selectively permeable membrane [Per the principle of Osmotic Diffusion]. For water to gather in the potato cups, there must be a persistent concentration gradient established by a solute (sugar or salt) within the hollowed portion, and the cells of the potato must be alive and functional to serve as an effective semi-permeable barrier.
Step 2: Analysis of Cup A (The Empty Control)
In Cup A, the hollow portion is empty. The potato is placed in a trough of pure water. While the external water potential is high, there is no solute concentration gradient established inside the hollow cavity to draw the water across the potato cells [By the laws of thermodynamics, net water movement requires a chemical potential gradient]. Because the water potential inside the cup is equal to or higher than the external water potential, there is no osmotic pressure driving water accumulation.
Step 3: Analysis of Cup D (The Boiled Potato)
Cup D consists of a boiled potato. Boiling causes the denaturation of membrane proteins and the destruction of the plasma membrane's structural integrity [Per the principles of Cell Biology]. A functional plasma membrane is essential for osmosis because it regulates the selective permeability required for osmosis to occur. Once the potato is boiled, the cells become dead and their membranes lose the ability to act as a selectively permeable barrier. Consequently, the solutes (sugar) cannot maintain a localized hypertonic environment, and the structural "pumps" are rendered non-functional.
Step 4: Comparative Data Summary
| Cup | Condition | Presence of Osmosis | Reason |
|---|---|---|---|
| A | Empty | No | Lack of concentration gradient ($\Psi_s = 0$) |
| D | Boiled | No | Membrane permeability lost; cell death |
Final Solution: Water does not gather in Cup A because there is no solute concentration gradient to induce osmosis, and it does not gather in Cup D because the boiling process has destroyed the selectively permeable nature of the potato cell membranes, rendering the tissue incapable of facilitating osmotic transport.
More Questions from Class 9 Science The Fundamental Unit of Life Exercises
- Q1: Make a comparison and write down ways in which plant cells are different from animal cells.
- Q2: How is a prokaryotic cell different from a eukaryotic cell?
- Q3: What would happen if the plasma membrane ruptures or breaks down?
- Q4: What would happen to the life of a cell if there was no Golgi apparatus?
- Q5: Which organelle is known as the powerhouse of the cell? Why?
- Q6: Where do the lipids and proteins constituting the cell membrane get synthesised?
- Q7: How does an Amoeba obtain its food?
- Q8: What is osmosis?
- Q9(i): 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 of B and C.
- Q9(ii): 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: (ii) Why is potato A necessary for this experiment?
- Q10: Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?
CBSE Solutions for Class 9 Science The Fundamental Unit of Life
Chapters in CBSE - Class 9 Science
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