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.

1. Identify the tropic movements.
   • Answer: Stem: Negative Geotropism. Root: Positive Geotropism.
2. 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.
3. Designing: Clinostat.
   • Answer: Rotate the plant slowly. Gravity acts on all sides equally, so the plant grows straight.
4. 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.
5. Differential growth name.
   • Answer: Tropism.

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

• Answer: Gibberellins.

7. Synthetic hormone as weedicide?
   • Answer: 2,4-D (2,4-Dichlorophenoxyacetic acid).
8. Creating: Schedule.
   • Answer: Apply 2,4-D in early spring to kill young weeds; apply Gibberellins when plant size is sufficient for flowering.
9. 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).
10. 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.

11. 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.
12. 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.
13. 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.
14. 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.
15. 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)

16. Designing: Hydrotropism experiment.
    • Answer: Use a perforated container with moist sawdust; seeds germinate, and roots grow towards the moisture source despite gravity.
17. Creating: Mnemonic.
    • Answer: All Good Cells Eat Apples (Auxin, Gibberellin, Cytokinin, Ethylene, ABA).
18. Analysis: Tropic vs Nastic.
    • Answer: Tropic: Directional (growth-related). Nastic: Non-directional (usually turgor-related).
19. Designing: Cytokinins table.
    • Answer: [Promotes cell division, delays senescence, breaks seed dormancy, promotes lateral growth].
20. Visualisation: Phototropism diagram.
    • Answer: [Description: Auxin on shaded side makes cells longer, bending shoot to light].
21. Application: Ripening bananas.
    • Answer: Ripe bananas release Ethylene gas, which speeds up ripening of other fruits.
22. Creating: Lacking Gibberellins.
    • Answer: The plant would be extremely short (dwarf) with very small internodes.
23. Analysis: Chemotropism in fertilization.
    • Answer: The pollen tube grows towards the chemicals (sugars) secreted by the synergids in the ovule.
24. Designing: "Bushy" rose.
    • Answer: Remove the apical buds (Pruning) to stop apical dominance and allow lateral buds to grow.
25. 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

26. Parthenocarpy.
    • Answer: Development of fruit without fertilization. Induced by Auxins and Gibberellins.
27. Scenario: Transporting bananas.
    • Answer: Keep them in a cold, well-ventilated area with low Oxygen or use Ethylene absorbers (KMnO4).
28. 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).
29. Application: "Bolting".
    • Answer: Sudden elongation of internodes just before flowering, caused by Gibberellins.
30. Phototropism vs Photonasty.
    • Answer: Phototropism: Stem grows to light. Photonasty: Flower opens/closes depending on light intensity (regardless of direction).
31. Diagram Based: Tendril coiling.
    • Answer: Contact with support reduces auxin on the touch side, causing the outer side to grow faster and coil.
32. Ethylene effects.
    • Answer: Promotes abscission of leaves and flowers.
33. Analysis: ABA vs Gibberellins.
    • Answer: ABA promotes dormancy and inhibits growth; Gibberellins break dormancy and promote growth.
34. Competency: Mimosa mechanism.
    • Answer: Electrical stimulus causes K+ and water to leave pulvinus cells, causing sudden loss of turgidity and drooping.
35. Case: Rapid cell division chemical.
    • Answer: Cytokinin.
36. Creating: Sensitivity hypothesis.
    • Answer: Roots respond to much lower concentrations of stimuli than shoots.
37. Designing: Apical Dominance aid.
    • Answer: [Sketch showing tall plant with inhibited side buds vs decapitated plant with growing side buds].
38. Application: Rooting of cuttings.
    • Answer: Dipping the base of a stem cutting in Auxin solution induces rapid root formation.
39. Critical Thinking: No nervous system.
    • Answer: Plants coordinate via chemical signals (Hormones) which are slower but effective.
40. Analysis: Senescence.
    • Answer: Biological aging of plant parts. Delayed by Cytokinins.

Section E: Advanced Competency

41. Scenario: Covered tip.
    • Answer: No bending. The tip is where light is perceived and auxin is produced.
42. Designing: Phytohormone poster.
    • Answer: [Visuals of different hormones and their "jobs"].
43. 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.
44. Creating: Tissue culture recipe.
    • Answer: High Auxin + Low Cytokinin = Roots. Low Auxin + High Cytokinin = Shoots.
45. Case Study: Hormone in drought.
    • Answer: Abscisic Acid (ABA). Closes stomata.
46. Biological Clock.
    • Answer: Circadian rhythms like sleep movements of leaves.
47. Critical Thinking: Response without division.
    • Answer: Yes, via turgor changes (e.g., stomata, Mimosa).
48. Analysis: Speed of response.
    • Answer: Nastic (Turgor) is much faster than Tropic (Growth).
49. Designing: Coleoptile growth graph.
    • Answer: Bell-shaped; growth increases with auxin to an optimum, then decreases due to toxicity/ethylene induction.
50. Creating: "Gigantin".
    • Answer: Would likely be a variant of Gibberellin that causes extreme cell elongation.