Transpiration - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

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

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.
Why cut the twig underwater?
- Answer: To prevent an air lock (embolism) in the Xylem.
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.
Analysis: Why not 100% accurate?
- Answer: Some water is used in photosynthesis or for cell turgidity, not all is transpired.
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.

Explain the imbalance.
- Answer: In the afternoon, the rate of transpiration exceeds the rate of water absorption.
Creating: Flowchart.
- Answer: High heat -> Rapid transpiration -> Cell water loss -> Loss of turgidity -> Drooping (Wilting).
Critical Thinking: Is wilting always harmful?
- Answer: No, it reduces the surface area exposed to the sun and closes stomata, preventing further water loss.
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.

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.
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.
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).
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.
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)

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

Section D: Competency & Critical Thinking

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

Section E: Advanced Competency

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

Section A: Case-Based Questions

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

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.

Why cut the twig underwater?

Answer: To prevent an air lock (embolism) in the Xylem.

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.

Analysis: Why not 100% accurate?

Answer: Some water is used in photosynthesis or for cell turgidity, not all is transpired.

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.

Explain the imbalance.

Answer: In the afternoon, the rate of transpiration exceeds the rate of water absorption.

Creating: Flowchart.

Answer: High heat -> Rapid transpiration -> Cell water loss -> Loss of turgidity -> Drooping (Wilting).

Critical Thinking: Is wilting always harmful?

Answer: No, it reduces the surface area exposed to the sun and closes stomata, preventing further water loss.

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.

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.

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.

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).

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.

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)

Designing: Cobalt Chloride paper experiment.

Answer: Clip dry paper on both sides; the paper on the lower surface turns pink faster, showing more transpiration.

Creating: Pie chart data.

Answer: [Description: Large slice for Stomata, small for Cuticle, sliver for Lenticels].

Analysis: Stomatal vs Lenticular.

Answer: Stomatal can be regulated by guard cells; Lenticular is constant (no regulation).

Designing: 24-hour graph.

Answer: Peaks at noon (highest temp/light), zero or low at night.

Visualisation: Open stoma diagram.

Answer: [Description: Kidney-shaped guard cells, open pore, chloroplasts shown].

Application: Cooling effect.

Answer: Evaporation of water from leaves absorbs latent heat from the plant and surrounding air.

Creating: Super-Arid plant modifications.

Answer: Spines instead of leaves, thick waxy cuticle, CAM photosynthesis.

Analysis: K+ ion theory.

Answer: In light, K+ ions enter guard cells -> Water enters by osmosis -> Turgidity causes opening.

Designing: Checklist.

Answer: Temperature (+), Wind (+), Light (+), Humidity (-).

Creating: Rhyme.

Answer: "From the roots to the sky, water flows when the air is dry."

Section D: Competency & Critical Thinking

Compromise.

Answer: Stomata must open for CO2 (Photosynthesis) but this inevitably lets water out (Transpiration).

Scenario: Vaseline on both surfaces.

Answer: Transpiration and Gas exchange (Photosynthesis/Respiration) will stop. Plant may die.

Critical Thinking: Needle leaves.

Answer: Reduce surface area for transpiration and prevent snow accumulation.

Application: "Bleeding".

Answer: Loss of sap from an injured part. Guttation is from intact hydathodes.

Cuticular vs Stomatal.

Answer: Cuticular: Through waxy layer. Stomatal: Through pores.

Diagram Based: Mesophyll.

Answer: Spongy mesophyll has many air spaces for easy diffusion of water vapour.

Atmospheric Pressure.

Answer: Low pressure (e.g., on mountains) increases the rate of transpiration.

Analysis: Anti-transpirants.

Answer: They reduce water loss without affecting CO2 uptake significantly, helping crops survive drought.

Competency: Cold soil.

Answer: Cold water is more viscous and root cell membranes are less permeable, slowing absorption.

Case: Water confirm test.

Answer: Cobalt Chloride paper turns blue to pink.

Creating: Stomatal frequency hypothesis.

Answer: Use nail polish impressions of the leaf surface to count stomata under a microscope.

Designing: Guttation vs Transpiration table.

Answer: [Guttation: Liquid, night/early morning, through hydathodes. Transpiration: Vapour, day, through stomata].

Application: Deforestation and rainfall.

Answer: Fewer trees means less water vapour returned to the atmosphere, leading to less cloud formation.

Critical Thinking: Forest humidifiers.

Answer: Large amounts of water vapour released by trees increase local humidity.

Analysis: Relative Humidity.

Answer: If air is already full of moisture (High RH), there is no "room" for transpired water.

Section E: Advanced Competency

Scenario: Monocot vs Dicot stomata.

Answer: Monocot: Equal on both sides. Dicot: More on the lower surface.

Designing: Cohesion-Tension model.

Answer: Pulling a wet rope through a pipe; the surface tension of water pulls the rest of the column up.

Application: Shedding leaves in autumn.

Answer: To prevent water loss during winter when soil water may be frozen and unavailable.

Creating: Guard cell diary.

Answer: "Sun's out, K+ is in! Feeling plump and open."

Case Study: Blue light receptor.

Answer: Phototropin. Blue light is the most effective for stomatal opening.

Thick Cuticle in xerophytes.

Answer: Acts as a physical barrier to prevent non-stomatal water loss.

Critical Thinking: Aquatic plants.

Answer: Submerged plants lack stomata and do not transpire. Floating plants have stomata on the upper surface.

Analysis: Windy vs Still day.

Answer: Wind removes the "layer" of humidity next to the leaf, keeping the gradient steep.

Designing: Advantages and Disadvantages.

Answer: [Advantages: Ascent of sap, Cooling, Mineral transport. Disadvantages: Energy loss, Risk of wilting].

Creating: Improved Potometer.

Answer: A digital sensor that measures the exact weight loss of the plant (Lysimeter principle).

Transpiration

Transpiration - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

Section B: Assertion-Reasoning Questions

Section C: Creating and Designing (Application & Analysis)

Section D: Competency & Critical Thinking

Section E: Advanced Competency

On this page

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Transpiration

Transpiration - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

Section B: Assertion-Reasoning Questions

Section C: Creating and Designing (Application & Analysis)

Section D: Competency & Critical Thinking

Section E: Advanced Competency

On this page