Chapter 25 · Class 11-12 & NEET

Plant Growth & Development

18 topics in 17 parts

Key ideas

Biological Parameter	Primary / Normal Condition	Alternative / Specialized Variant
Morphological Feature	Conserved anatomical architecture	Adapted/Modified structure for specialized function
Energetic / Metabolic State	Basal physiological activity	Induced / Stress-responsive activation
Regulatory Control	Endocrine & enzymatic feedback	Autonomous / Environmental signaling
Evolutionary Fitness Impact	Essential for organismal survival	Enhances reproductive efficiency & niche adaptation

Key Scientific Principles, Pathways & Diagnostic Points

// NCERT Histological Signatures & Classifications
1. Root Endodermis : Casparian Strip (Suberin waxy deposition, forces symplastic transit)
2. Guard Cells      : Dicot = Kidney-shaped; Monocot (Grasses) = Dumbbell-shaped
3. Xylem Polarity   : Stem = Endarch (Protoxylem inside); Root = Exarch (Protoxylem outside)
4. Vascular Bundles: 
   - Dicot Stem    : Conjoint, Collateral, Open (Cambium present), Arranged in Ring
   - Monocot Stem  : Conjoint, Collateral, Closed (No Cambium), Scattered in Ground Tissue
   - Dicot Root    : Radial (2 to 4 Xylem/Phloem patches), Diarch to Tetrarch
   - Monocot Root  : Radial, Polyarch (> 6 Xylem bundles), Large well-developed Pith

Plant Growth & Development

Diagnostic Histological Comparison Matrix

Anatomical Feature	Dicot Stem	Monocot Stem	Dicot / Monocot Root
Vascular Bundle Arrangement	Arranged in a regular ring; open	Scattered throughout ground tissue; closed	Radial arrangement (Xylem & Phloem on alternate radii)
Cambium & Secondary Growth	Intrafascicular cambium present; secondary growth occurs	Cambium absent; secondary growth absent	Vascular cambium originates secondarily during growth
Xylem Polarity	Endarch (Protoxylem towards center)	Endarch with Y-shaped vessel pattern	Exarch (Protoxylem towards periphery)
Pith Characteristics	Central parenchymatous pith well-developed	Pith not demarcated (undifferentiated ground tissue)	Dicot: small/inconspicuous; Monocot: large & prominent

High-Yield NEET Exam Question (Direct NCERT Extract)

NEET Problem: A transverse section of a plant organ shows conjoint, collateral, open vascular bundles arranged in a ring with endarch protoxylem and well-developed pith. Identify the organ. Step-by-step Solution: 1. "Conjoint and collateral" means xylem and phloem lie on the same radius → Characteristic of stem (rules out root, where bundles are radial). 2. "Open vascular bundle" means cambium is present between xylem and phloem → Characteristic of dicots (monocots are closed). 3. "Arranged in a ring with large pith and endarch xylem" confirms Dicot Stem (Anatomy of Dicotyledonous Stem). Correct Option: Dicotyledonous Stem (e.g., Sunflower stem).

Checkpoint

1. Which of the following structures in plant anatomy is composed of dead cells at functional maturity and possesses heavily lignified secondary cell walls?

All 18 topics in Plant Growth & Development

Plant Growth Regulators
- Plant Growth Regulators
Auxin
- Herbicidal Use
- Avena Curvature Bioassay
Gibberellins
- Gibberellins
Ethylene
- Ethylene
Cytokinins
- Cytokinins
Growth Phases
- Growth Phases
Abscisic Acid
- Abscisic Acid
Differentiation
- Tissue Culture
Growth Measurement
- Growth Measurement
Developmental Plasticity
- Developmental Plasticity
Apical Dominance
- Apical Dominance
Arithmetic Growth
- Arithmetic Growth
Meristems
- Meristems
Exponential Growth
- Sigmoid Growth Curve
Photoperiodism
- Photoperiodism
Seed Dormancy & Germination
- Seed Dormancy & Germination
Vernalization
- Vernalization