Absorption by Roots - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

Case Study 1: A student sets up a potato osmoscope using strong sugar solution and water.

1. Identify the process responsible for the rise in the sugar solution level.
   • Answer: Endosmosis.
2. What acts as the semi-permeable membrane in this setup?
   • Answer: The living cytoplasmic lining of the potato cells.
3. Designing: What would happen if the potato was boiled?
   • Answer: No rise in level. Boiling kills the cells, destroying the semi-permeable nature of the membrane, making it freely permeable.
4. Analysis: Direction of water movement.
   • Answer: From Hypotonic (water in beaker) to Hypertonic (sugar solution in cavity).
5. If the beaker and cavity have the same concentration?
   • Answer: No net movement; level stays the same (Isotonic).

Case Study 2: A farmer applies excessive chemical fertilizer and plants wilt. 6. Identify the condition.

• Answer: Plasmolysis.

7. Explain "Hypertonic solution" in this context.
   • Answer: The high concentration of fertilizer in the soil makes the soil water hypertonic compared to the cell sap of the root hairs.
8. Creating: Visual representation.
   • Answer: [Description: Plasmolysed cell shows shrunken protoplasm away from the cell wall].
9. Critical Thinking: How to reverse it?
   • Answer: Deplasmolysis by adding plenty of water to the soil to make it hypotonic.
10. Define "Exosmosis" and relate to wilting.
    • Answer: Exosmosis is the outward movement of water from the cell. Loss of turgidity leads to wilting.

Section B: Assertion-Reasoning Questions

Directions: (a) Both A/R true, R explains A; (b) Both true, R doesn't explain A; (c) A true, R false; (d) A false, R true.

11. Assertion (A): Roots absorb water by osmosis. Reason (R): Cell sap has higher concentration than soil water.
    • Answer: (a) Both A and R are true and R is the correct explanation.
12. Assertion (A): Active transport requires energy (ATP). Reason (R): It moves ions against concentration gradient.
    • Answer: (a) Both A and R are true and R is the correct explanation.
13. Assertion (A): A plant cell bursts if placed in distilled water. Reason (R): Wall pressure counteracts turgor pressure.
    • Answer: (d) A is false but R is true. (Plant cells don't burst due to cell wall).
14. Assertion (A): Salt is a preservative. Reason (R): Salt causes plasmolysis in bacteria.
    • Answer: (a) Both A and R are true and R is the correct explanation.
15. Assertion (A): Wooden doors swell in rainy season. Reason (R): This is due to Imbibition.
    • Answer: (a) Both A and R are true and R is the correct explanation.

Section C: Creating and Designing (Application & Analysis)

16. Designing: Root Pressure experiment.
    • Answer: Cut the stem of a potted plant near the base; attach a glass tube with a rubber connection. Water rises in the tube due to root pressure.
17. Creating: Metaphor for Semi-permeable membrane.
    • Answer: Like a sieve that allows water through but stops the noodles (solute).
18. Analysis: Diffusion vs Osmosis.
    • Answer: Osmosis is diffusion of solvent through a semi-permeable membrane.
19. Designing: Table TP vs WP.
    • Answer: TP (Turgor Pressure) is exerted by the cell contents against the wall. WP (Wall Pressure) is exerted by the wall against the contents. In turgid cell, TP = WP.
20. Visualisation: Root hair diagram.
    • Answer: [Description: Long extension of epiblema cell with large vacuole and thin wall]. Wall is freely permeable because it's cellulose.
21. Application: Saltwater gargle.
    • Answer: Hypertonic salt water causes exosmosis from the swollen tissues/bacteria, reducing inflammation.
22. Creating: Journey of a water molecule.
    • Answer: Soil -> Root Hair -> Cortex -> Endodermis -> Pericycle -> Xylem.
23. Analysis: Surface Area of root hairs.
    • Answer: Thousands of root hairs vastly increase the surface area available for absorption.
24. Designing: Test if tissue is alive.
    • Answer: Place in sugar solution; if it plasmolyses, it's alive.
25. Creating: Why plants "drink".
    • Answer: Plants use water to stand tall (turgidity) and to cook their food (photosynthesis).

Section D: Competency & Critical Thinking

26. DPD (Diffusion Pressure Deficit).
    • Answer: The thirst of a cell for water. DPD = OP - TP.
27. Scenario: Force at night.
    • Answer: Root Pressure.
28. Critical Thinking: Distilled water in IV?
    • Answer: No. It would cause RBCs to swell and burst (Haemolysis) because it's hypotonic to blood.
29. Application: Guttation.
    • Answer: Loss of liquid water from hydathodes. Dew is atmospheric condensation.
30. Apoplast vs Symplast.
    • Answer: Apoplast: Through cell walls. Symplast: Through cytoplasm/plasmodesmata.
31. Diagram Based: Turgid cell arrows.
    • Answer: TP outwards, WP inwards.
32. Cohesion and Adhesion.
    • Answer: Cohesion: Water-water attraction. Adhesion: Water-Xylem wall attraction.
33. Analysis: Fish osmoregulation.
    • Answer: Freshwater fish are hypertonic to water, so water enters by osmosis; they don't need to drink.
34. Competency: Endodermis checkpost.
    • Answer: Casparian strip forces water/minerals through the cell membrane (Symplast), allowing the cell to regulate entry.
35. Case: Cutting stem underwater.
    • Answer: Prevents air bubbles from entering the Xylem, which would break the water column.
36. Creating: Temp hypothesis.
    • Answer: Rate of absorption increases with temperature up to a certain point due to kinetic energy.
37. Designing: Passive vs Active Absorption.
    • Answer: Passive: Driven by transpiration pull (No ATP). Active: Driven by roots using energy (ATP).
38. Application: Killing weeds with salt.
    • Answer: Causes exosmosis from roots, leading to physiological drought and death.
39. Critical Thinking: Fully turgid absorption.
    • Answer: No more water can enter when Water Potential is zero (TP = OP).
40. Analysis: Hydrotropism movement.
    • Answer: Differential cell elongation on the side with more water.

Section E: Advanced Competency

41. Scenario: Water flow direction (DPD).
    • Answer: Cell A (DPD=4), Cell B (DPD=5). Water flows from lower DPD to higher DPD (A to B).
42. Designing: Imbibition model.
    • Answer: Soak dry seeds in a graduated cylinder. Measure the increase in volume.
43. Application: Importance of Turgidity.
    • Answer: Provides mechanical support to herbaceous plants and drives movements like stomatal opening.
44. Creating: Ascent of Sap graphic.
    • Answer: [Loop showing Root Pressure (push), Capillarity (minor), Transpiration Pull (main pull)].
45. Case Study: Transplanted plant death.
    • Answer: Loss of delicate root hairs means the plant cannot absorb enough water to replace what is transpired.
46. Isotonic Solution.
    • Answer: Solution with same concentration as cell sap; no net movement of water.
47. Critical Thinking: Fertilizer and soil OP.
    • Answer: More solutes increase the Osmotic Pressure of soil, making it harder for roots to absorb water.
48. Analysis: Plasmolysis vs Flaccidity.
    • Answer: Plasmolysis: Protoplasm shrunken. Flaccidity: Cell is not turgid but protoplasm still touches the wall.
49. Designing: Rate vs Soil Temp graph.
    • Answer: Rate is low at 0°C (viscous water), increases with temp, then drops at very high temp (membrane damage).
50. Creating: "Super Root".
    • Answer: Deep taproot, high concentration of solutes in sap, and thick mucilage coating.