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Q8(a):
Which one of the plant growth regulators would you use if you are asked to:
(a) induce rooting in a twig
Solution :
Identification of the Plant Growth Regulator
To induce rooting in a cut twig (stem cutting), the plant growth regulator of choice is Auxin, specifically Indole-3-butyric acid (IBA) or 1-Naphthaleneacetic acid (NAA).
Step 1: Theoretical Basis of Root Initiation
Rooting in vegetative propagules (cuttings) is a physiological process known as adventitious root formation. [Per the hormonal theory of organogenesis, the balance of internal auxins and cytokinins dictates cell differentiation]. When a twig is detached, the high concentration of endogenous auxins synthesized in the apical meristems is disrupted. The application of exogenous auxins artificially stimulates the pericycle cells or vascular cambium cells to undergo dedifferentiation and subsequently develop into root primordia.
Step 2: Role of Indole-3-Butyric Acid (IBA)
IBA is the synthetic or naturally occurring auxin most favored in horticultural practices for the following reasons:
- High Physiological Activity: It exhibits strong translocation properties and higher stability than Indole-3-acetic acid (IAA).
- Cell Differentiation Induction: It promotes the transformation of unspecialized parenchyma cells into organized root apical meristems.
- Polar Transport: Auxins move in a polar fashion (basipetal transport), ensuring the accumulation of the hormone at the basal cut end, which triggers the emergence of roots [By the Cholodny-Went Theory of phototropism and growth distribution].
Step 3: Schematic Visualization of Root Induction
Step 4: Comparative Analysis of Regulatory Effectiveness
| Regulator | Primary Function | Suitability for Rooting |
|---|---|---|
| Auxins (IBA/NAA) | Root initiation | High (Standard Choice) |
| Gibberellins | Stem elongation | Low (Can inhibit rooting) |
| Cytokinins | Cell division/Shoot formation | Low (Promotes shoots over roots) |
Final Solution: The plant growth regulator to be used is an Auxin, specifically Indole-3-butyric acid (IBA), as it effectively triggers the dedifferentiation of cells at the basal end of the twig to form adventitious roots.
More Questions from Class 11 Biology Plant Growth and Development EXERCISES
- Q1: Define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate.
- Q2: Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?
- Q3(a): Describe briefly: (a) Arithmetic growth
- Q3(b): Describe briefly: (b) Geometric growth
- Q3(c): Describe briefly: (c) Sigmoid growth curve
- Q3(d): Describe briefly: (d) Absolute and relative growth rates
- Q4: List five main groups of natural plant growth regulators. Write a note on discovery, physiological functions and agricultural/horticultural applications of any one of them.
- Q5: Why is abscisic acid also known as stress hormone?
- Q6: ‘Both growth and differentiation in higher plants are open’. Comment.
- Q7: ‘Both a short day plant and a long day plant can produce can flower simultaneously in a given place’. Explain.
- Q8(b): Which one of the plant growth regulators would you use if you are asked to: (b) quickly ripen a fruit
- Q8(c): Which one of the plant growth regulators would you use if you are asked to: (c) delay leaf senescence
- Q8(d): Which one of the plant growth regulators would you use if you are asked to: (d) induce growth in axillary buds
- Q8(e): Which one of the plant growth regulators would you use if you are asked to: (e) ‘bolt’ a rosette plant
- Q8(f): Which one of the plant growth regulators would you use if you are asked to: (f) induce immediate stomatal closure in leaves.
- Q9: Would a defoliated plant respond to photoperiodic cycle? Why?
- Q10(a): What would be expected to happen if: (a) $GA_3$ is applied to rice seedlings
- Q10(b): What would be expected to happen if: (b) dividing cells stop differentiating
- Q10(c): What would be expected to happen if: (c) a rotten fruit gets mixed with unripe fruits
- Q10(d): What would be expected to happen if: (d) you forget to add cytokinin to the culture medium.
CBSE Solutions for Class 11 Biology Plant Growth and Development
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Cell Cycle and Division
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Digestion and Absorption
- Breathing and Exchange of Gases
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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