Chemical Coordination in Plants - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

Case Study 1: Potted plant placed horizontally. Stem bends up, roots bend down.

Identify the tropic movements.
- Answer: Stem: Negative Geotropism. Root: Positive Geotropism.
Explain role of Auxin in stem.
- Answer: Auxin accumulates on the lower side due to gravity. In stems, higher auxin concentration stimulates growth, causing the lower side to grow faster and bend the stem upwards.
Designing: Clinostat.
- Answer: Rotate the plant slowly. Gravity acts on all sides equally, so the plant grows straight.
Analysis: Stem vs Root auxin.
- Answer: Stems have a higher optimal concentration for growth than roots. The same concentration that stimulates a stem inhibits a root.
Differential growth name.
- Answer: Tropism.

Case Study 2: Gardener wants flowers out of season and to kill weeds. 6. Hormone for flowering?

Answer: Gibberellins.

Synthetic hormone as weedicide?
- Answer: 2,4-D (2,4-Dichlorophenoxyacetic acid).
Creating: Schedule.
- Answer: Apply 2,4-D in early spring to kill young weeds; apply Gibberellins when plant size is sufficient for flowering.
Critical Thinking: Why specific to broad-leaved?
- Answer: Broad-leaved plants (dicots) have a higher absorption rate and different metabolic sensitivity to 2,4-D compared to narrow-leaved grasses (monocots).
Delay ripening?
- Answer: Avoid Ethylene.

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): Decapitation promotes lateral growth. Reason (R): Apical dominance is caused by Auxins.
- Answer: (a) Both A and R are true and R is the correct explanation.
Assertion (A): ABA is "Stress Hormone". Reason (R): It stimulates closure of stomata.
- Answer: (a) Both A and R are true and R is the correct explanation.
Assertion (A): Ethylene is unique. Reason (R): It is a gaseous hormone.
- Answer: (a) Both A and R are true and R is the correct explanation.
Assertion (A): Roots show positive phototropism. Reason (R): Roots grow towards light.
- Answer: (d) A is false but R is true (in its definition, but roots actually show negative phototropism). Actually, A is false and R is false as a fact. Let's fix: (d) A is false. Roots are negatively phototropic.
Assertion (A): Thigmotropism in tendrils. Reason (R): It is response to touch.
- Answer: (a) Both A and R are true and R is the correct explanation.

Section C: Creating and Designing (Application & Analysis)

Designing: Hydrotropism experiment.
- Answer: Use a perforated container with moist sawdust; seeds germinate, and roots grow towards the moisture source despite gravity.
Creating: Mnemonic.
- Answer: All Good Cells Eat Apples (Auxin, Gibberellin, Cytokinin, Ethylene, ABA).
Analysis: Tropic vs Nastic.
- Answer: Tropic: Directional (growth-related). Nastic: Non-directional (usually turgor-related).
Designing: Cytokinins table.
- Answer: [Promotes cell division, delays senescence, breaks seed dormancy, promotes lateral growth].
Visualisation: Phototropism diagram.
- Answer: [Description: Auxin on shaded side makes cells longer, bending shoot to light].
Application: Ripening bananas.
- Answer: Ripe bananas release Ethylene gas, which speeds up ripening of other fruits.
Creating: Lacking Gibberellins.
- Answer: The plant would be extremely short (dwarf) with very small internodes.
Analysis: Chemotropism in fertilization.
- Answer: The pollen tube grows towards the chemicals (sugars) secreted by the synergids in the ovule.
Designing: "Bushy" rose.
- Answer: Remove the apical buds (Pruning) to stop apical dominance and allow lateral buds to grow.
Creating: Mimosa story.
- Answer: "A finger touched me! Quick, pull the water out of my leaf base (pulvinus) so I can fold up and hide."

Section D: Competency & Critical Thinking

Parthenocarpy.
- Answer: Development of fruit without fertilization. Induced by Auxins and Gibberellins.
Scenario: Transporting bananas.
- Answer: Keep them in a cold, well-ventilated area with low Oxygen or use Ethylene absorbers (KMnO4).
Critical Thinking: Sunflower movement.
- Answer: It is not a growth movement in the short term; it's due to turgor changes in the pulvinus-like region of the stem (Heliotropism).
Application: "Bolting".
- Answer: Sudden elongation of internodes just before flowering, caused by Gibberellins.
Phototropism vs Photonasty.
- Answer: Phototropism: Stem grows to light. Photonasty: Flower opens/closes depending on light intensity (regardless of direction).
Diagram Based: Tendril coiling.
- Answer: Contact with support reduces auxin on the touch side, causing the outer side to grow faster and coil.
Ethylene effects.
- Answer: Promotes abscission of leaves and flowers.
Analysis: ABA vs Gibberellins.
- Answer: ABA promotes dormancy and inhibits growth; Gibberellins break dormancy and promote growth.
Competency: Mimosa mechanism.
- Answer: Electrical stimulus causes K+ and water to leave pulvinus cells, causing sudden loss of turgidity and drooping.
Case: Rapid cell division chemical.
- Answer: Cytokinin.
Creating: Sensitivity hypothesis.
- Answer: Roots respond to much lower concentrations of stimuli than shoots.
Designing: Apical Dominance aid.
- Answer: [Sketch showing tall plant with inhibited side buds vs decapitated plant with growing side buds].
Application: Rooting of cuttings.
- Answer: Dipping the base of a stem cutting in Auxin solution induces rapid root formation.
Critical Thinking: No nervous system.
- Answer: Plants coordinate via chemical signals (Hormones) which are slower but effective.
Analysis: Senescence.
- Answer: Biological aging of plant parts. Delayed by Cytokinins.

Section E: Advanced Competency

Scenario: Covered tip.
- Answer: No bending. The tip is where light is perceived and auxin is produced.
Designing: Phytohormone poster.
- Answer: [Visuals of different hormones and their "jobs"].
Application: 2,4-D safety in wheat.
- Answer: Wheat (monocot) metabolizes or sequesters the chemical differently, making it resistant to the dose that kills weeds.
Creating: Tissue culture recipe.
- Answer: High Auxin + Low Cytokinin = Roots. Low Auxin + High Cytokinin = Shoots.
Case Study: Hormone in drought.
- Answer: Abscisic Acid (ABA). Closes stomata.
Biological Clock.
- Answer: Circadian rhythms like sleep movements of leaves.
Critical Thinking: Response without division.
- Answer: Yes, via turgor changes (e.g., stomata, Mimosa).
Analysis: Speed of response.
- Answer: Nastic (Turgor) is much faster than Tropic (Growth).
Designing: Coleoptile growth graph.
- Answer: Bell-shaped; growth increases with auxin to an optimum, then decreases due to toxicity/ethylene induction.
Creating: "Gigantin".
- Answer: Would likely be a variant of Gibberellin that causes extreme cell elongation.

Section A: Case-Based Questions

Case Study 1: Potted plant placed horizontally. Stem bends up, roots bend down.

Identify the tropic movements.

Answer: Stem: Negative Geotropism. Root: Positive Geotropism.

Explain role of Auxin in stem.

Answer: Auxin accumulates on the lower side due to gravity. In stems, higher auxin concentration stimulates growth, causing the lower side to grow faster and bend the stem upwards.

Designing: Clinostat.

Answer: Rotate the plant slowly. Gravity acts on all sides equally, so the plant grows straight.

Analysis: Stem vs Root auxin.

Answer: Stems have a higher optimal concentration for growth than roots. The same concentration that stimulates a stem inhibits a root.

Differential growth name.

Answer: Tropism.

Case Study 2: Gardener wants flowers out of season and to kill weeds. 6. Hormone for flowering?

Answer: Gibberellins.

Synthetic hormone as weedicide?

Answer: 2,4-D (2,4-Dichlorophenoxyacetic acid).

Creating: Schedule.

Answer: Apply 2,4-D in early spring to kill young weeds; apply Gibberellins when plant size is sufficient for flowering.

Critical Thinking: Why specific to broad-leaved?

Answer: Broad-leaved plants (dicots) have a higher absorption rate and different metabolic sensitivity to 2,4-D compared to narrow-leaved grasses (monocots).

Delay ripening?

Answer: Avoid Ethylene.

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): Decapitation promotes lateral growth. Reason (R): Apical dominance is caused by Auxins.

Answer: (a) Both A and R are true and R is the correct explanation.

Assertion (A): ABA is "Stress Hormone". Reason (R): It stimulates closure of stomata.

Answer: (a) Both A and R are true and R is the correct explanation.

Assertion (A): Ethylene is unique. Reason (R): It is a gaseous hormone.

Answer: (a) Both A and R are true and R is the correct explanation.

Assertion (A): Roots show positive phototropism. Reason (R): Roots grow towards light.

Answer: (d) A is false but R is true (in its definition, but roots actually show negative phototropism). Actually, A is false and R is false as a fact. Let's fix: (d) A is false. Roots are negatively phototropic.

Assertion (A): Thigmotropism in tendrils. Reason (R): It is response to touch.

Answer: (a) Both A and R are true and R is the correct explanation.

Section C: Creating and Designing (Application & Analysis)

Designing: Hydrotropism experiment.

Answer: Use a perforated container with moist sawdust; seeds germinate, and roots grow towards the moisture source despite gravity.

Creating: Mnemonic.

Answer: All Good Cells Eat Apples (Auxin, Gibberellin, Cytokinin, Ethylene, ABA).

Analysis: Tropic vs Nastic.

Answer: Tropic: Directional (growth-related). Nastic: Non-directional (usually turgor-related).

Designing: Cytokinins table.

Answer: [Promotes cell division, delays senescence, breaks seed dormancy, promotes lateral growth].

Visualisation: Phototropism diagram.

Answer: [Description: Auxin on shaded side makes cells longer, bending shoot to light].

Application: Ripening bananas.

Answer: Ripe bananas release Ethylene gas, which speeds up ripening of other fruits.

Creating: Lacking Gibberellins.

Answer: The plant would be extremely short (dwarf) with very small internodes.

Analysis: Chemotropism in fertilization.

Answer: The pollen tube grows towards the chemicals (sugars) secreted by the synergids in the ovule.

Designing: "Bushy" rose.

Answer: Remove the apical buds (Pruning) to stop apical dominance and allow lateral buds to grow.

Creating: Mimosa story.

Answer: "A finger touched me! Quick, pull the water out of my leaf base (pulvinus) so I can fold up and hide."

Section D: Competency & Critical Thinking

Parthenocarpy.

Answer: Development of fruit without fertilization. Induced by Auxins and Gibberellins.

Scenario: Transporting bananas.

Answer: Keep them in a cold, well-ventilated area with low Oxygen or use Ethylene absorbers (KMnO4).

Critical Thinking: Sunflower movement.

Answer: It is not a growth movement in the short term; it's due to turgor changes in the pulvinus-like region of the stem (Heliotropism).

Application: "Bolting".

Answer: Sudden elongation of internodes just before flowering, caused by Gibberellins.

Phototropism vs Photonasty.

Answer: Phototropism: Stem grows to light. Photonasty: Flower opens/closes depending on light intensity (regardless of direction).

Diagram Based: Tendril coiling.

Answer: Contact with support reduces auxin on the touch side, causing the outer side to grow faster and coil.

Ethylene effects.

Answer: Promotes abscission of leaves and flowers.

Analysis: ABA vs Gibberellins.

Answer: ABA promotes dormancy and inhibits growth; Gibberellins break dormancy and promote growth.

Competency: Mimosa mechanism.

Answer: Electrical stimulus causes K+ and water to leave pulvinus cells, causing sudden loss of turgidity and drooping.

Case: Rapid cell division chemical.

Answer: Cytokinin.

Creating: Sensitivity hypothesis.

Answer: Roots respond to much lower concentrations of stimuli than shoots.

Designing: Apical Dominance aid.

Answer: [Sketch showing tall plant with inhibited side buds vs decapitated plant with growing side buds].

Application: Rooting of cuttings.

Answer: Dipping the base of a stem cutting in Auxin solution induces rapid root formation.

Critical Thinking: No nervous system.

Answer: Plants coordinate via chemical signals (Hormones) which are slower but effective.

Analysis: Senescence.

Answer: Biological aging of plant parts. Delayed by Cytokinins.

Section E: Advanced Competency

Scenario: Covered tip.

Answer: No bending. The tip is where light is perceived and auxin is produced.

Designing: Phytohormone poster.

Answer: [Visuals of different hormones and their "jobs"].

Application: 2,4-D safety in wheat.

Answer: Wheat (monocot) metabolizes or sequesters the chemical differently, making it resistant to the dose that kills weeds.

Creating: Tissue culture recipe.

Answer: High Auxin + Low Cytokinin = Roots. Low Auxin + High Cytokinin = Shoots.

Case Study: Hormone in drought.

Answer: Abscisic Acid (ABA). Closes stomata.

Biological Clock.

Answer: Circadian rhythms like sleep movements of leaves.

Critical Thinking: Response without division.

Answer: Yes, via turgor changes (e.g., stomata, Mimosa).

Analysis: Speed of response.

Answer: Nastic (Turgor) is much faster than Tropic (Growth).

Designing: Coleoptile growth graph.

Answer: Bell-shaped; growth increases with auxin to an optimum, then decreases due to toxicity/ethylene induction.

Creating: "Gigantin".

Answer: Would likely be a variant of Gibberellin that causes extreme cell elongation.

Chemical Coordination in Plants

Chemical Coordination in Plants - 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

BioBot

Chemical Coordination in Plants

Chemical Coordination in Plants - 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