Transpiration - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

Case Study 1: A student sets up a Ganong's Potometer.

1. What is the principle behind using a Potometer?
   • Answer: It measures the rate of water uptake, which is almost equal to the rate of transpiration.
2. Why cut the twig underwater?
   • Answer: To prevent an air lock (embolism) in the Xylem.
3. Designing: Predict the effect of a fan.
   • Answer: The bubble will move faster because the fan removes the humid air around the leaf, increasing the diffusion gradient.
4. Analysis: Why not 100% accurate?
   • Answer: Some water is used in photosynthesis or for cell turgidity, not all is transpired.
5. Resetting the air bubble.
   • Answer: Open the stopcock of the reservoir to let water push the bubble back.

Case Study 2: Balsam plant wilting in afternoon, recovering in evening. 6. Identify the phenomenon.

• Answer: Temporary wilting.

7. Explain the imbalance.
   • Answer: In the afternoon, the rate of transpiration exceeds the rate of water absorption.
8. Creating: Flowchart.
   • Answer: High heat -> Rapid transpiration -> Cell water loss -> Loss of turgidity -> Drooping (Wilting).
9. Critical Thinking: Is wilting always harmful?
   • Answer: No, it reduces the surface area exposed to the sun and closes stomata, preventing further water loss.
10. Temporary vs Permanent Wilting.
    • Answer: Temporary: Recovers with water/time. Permanent: Damage is irreversible, plant dies.

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): Transpiration creates a suction force. Reason (R): This force helps in the ascent of sap.
    • Answer: (a) Both A and R are true and R is the correct explanation.
12. Assertion (A): Stomata close at night in most plants. Reason (R): Closure prevents water loss when photosynthesis isn't occurring.
    • Answer: (a) Both A and R are true and R is the correct explanation.
13. Assertion (A): High humidity increases the rate of transpiration. Reason (R): The diffusion gradient is reduced.
    • Answer: (d) A is false but R is true. (Humidity decreases transpiration).
14. Assertion (A): Some desert plants have sunken stomata. Reason (R): They reduce transpiration by creating a pocket of humid air.
    • Answer: (a) Both A and R are true and R is the correct explanation.
15. Assertion (A): Transpiration is a "necessary evil". Reason (R): It leads to water loss but is essential for cooling and transport.
    • Answer: (a) Both A and R are true and R is the correct explanation.

Section C: Creating and Designing (Application & Analysis)

16. Designing: Cobalt Chloride paper experiment.
    • Answer: Clip dry paper on both sides; the paper on the lower surface turns pink faster, showing more transpiration.
17. Creating: Pie chart data.
    • Answer: [Description: Large slice for Stomata, small for Cuticle, sliver for Lenticels].
18. Analysis: Stomatal vs Lenticular.
    • Answer: Stomatal can be regulated by guard cells; Lenticular is constant (no regulation).
19. Designing: 24-hour graph.
    • Answer: Peaks at noon (highest temp/light), zero or low at night.
20. Visualisation: Open stoma diagram.
    • Answer: [Description: Kidney-shaped guard cells, open pore, chloroplasts shown].
21. Application: Cooling effect.
    • Answer: Evaporation of water from leaves absorbs latent heat from the plant and surrounding air.
22. Creating: Super-Arid plant modifications.
    • Answer: Spines instead of leaves, thick waxy cuticle, CAM photosynthesis.
23. Analysis: K+ ion theory.
    • Answer: In light, K+ ions enter guard cells -> Water enters by osmosis -> Turgidity causes opening.
24. Designing: Checklist.
    • Answer: Temperature (+), Wind (+), Light (+), Humidity (-).
25. Creating: Rhyme.
    • Answer: "From the roots to the sky, water flows when the air is dry."

Section D: Competency & Critical Thinking

26. Compromise.
    • Answer: Stomata must open for CO2 (Photosynthesis) but this inevitably lets water out (Transpiration).
27. Scenario: Vaseline on both surfaces.
    • Answer: Transpiration and Gas exchange (Photosynthesis/Respiration) will stop. Plant may die.
28. Critical Thinking: Needle leaves.
    • Answer: Reduce surface area for transpiration and prevent snow accumulation.
29. Application: "Bleeding".
    • Answer: Loss of sap from an injured part. Guttation is from intact hydathodes.
30. Cuticular vs Stomatal.
    • Answer: Cuticular: Through waxy layer. Stomatal: Through pores.
31. Diagram Based: Mesophyll.
    • Answer: Spongy mesophyll has many air spaces for easy diffusion of water vapour.
32. Atmospheric Pressure.
    • Answer: Low pressure (e.g., on mountains) increases the rate of transpiration.
33. Analysis: Anti-transpirants.
    • Answer: They reduce water loss without affecting CO2 uptake significantly, helping crops survive drought.
34. Competency: Cold soil.
    • Answer: Cold water is more viscous and root cell membranes are less permeable, slowing absorption.
35. Case: Water confirm test.
    • Answer: Cobalt Chloride paper turns blue to pink.
36. Creating: Stomatal frequency hypothesis.
    • Answer: Use nail polish impressions of the leaf surface to count stomata under a microscope.
37. Designing: Guttation vs Transpiration table.
    • Answer: [Guttation: Liquid, night/early morning, through hydathodes. Transpiration: Vapour, day, through stomata].
38. Application: Deforestation and rainfall.
    • Answer: Fewer trees means less water vapour returned to the atmosphere, leading to less cloud formation.
39. Critical Thinking: Forest humidifiers.
    • Answer: Large amounts of water vapour released by trees increase local humidity.
40. Analysis: Relative Humidity.
    • Answer: If air is already full of moisture (High RH), there is no "room" for transpired water.

Section E: Advanced Competency

41. Scenario: Monocot vs Dicot stomata.
    • Answer: Monocot: Equal on both sides. Dicot: More on the lower surface.
42. Designing: Cohesion-Tension model.
    • Answer: Pulling a wet rope through a pipe; the surface tension of water pulls the rest of the column up.
43. Application: Shedding leaves in autumn.
    • Answer: To prevent water loss during winter when soil water may be frozen and unavailable.
44. Creating: Guard cell diary.
    • Answer: "Sun's out, K+ is in! Feeling plump and open."
45. Case Study: Blue light receptor.
    • Answer: Phototropin. Blue light is the most effective for stomatal opening.
46. Thick Cuticle in xerophytes.
    • Answer: Acts as a physical barrier to prevent non-stomatal water loss.
47. Critical Thinking: Aquatic plants.
    • Answer: Submerged plants lack stomata and do not transpire. Floating plants have stomata on the upper surface.
48. Analysis: Windy vs Still day.
    • Answer: Wind removes the "layer" of humidity next to the leaf, keeping the gradient steep.
49. Designing: Advantages and Disadvantages.
    • Answer: [Advantages: Ascent of sap, Cooling, Mineral transport. Disadvantages: Energy loss, Risk of wilting].
50. Creating: Improved Potometer.
    • Answer: A digital sensor that measures the exact weight loss of the plant (Lysimeter principle).