Root Apex — Longitudinal Section
Maturation Zone
(root hairs)
Elongation Zone
(cell growth)
Meristematic Zone
(cell division)
Root Cap
(protection)
Key:
Maturation
Elongation
Meristematic
Root Cap
Cues (Left Column)
- What is growth?
- Three phases of growth?
- Where does growth occur?
- Sigmoid curve phases?
Notes (Right Column)
Definition: Plant growth = irreversible, permanent increase in size. Involves:
- Cell division (at meristems)
- Cell enlargement (vacuoles enlarge)
- Cell differentiation (specialization)
Three Phases of Growth:
| Phase | Location | Key Event |
|---|---|---|
| Meristematic | Root/shoot apices | Active cell division |
| Elongation | Just behind meristem | Vacuole enlargement, cell size increases |
| Maturation | Further from apex | Differentiation into permanent tissues |
Sigmoid Growth Curve — Three Phases:
| Phase | Graph shape | Biology |
|---|---|---|
| Lag | Flat/shallow | Cells prepare machinery; slow growth |
| Log | Steep rise | Exponential growth; = eʳᵗ |
| Stationary | Flat plateau | Limiting factors; growth ≈ 0 |
Growth occurs at meristems:
- Shoot apical meristem (SAM)
- Root apical meristem (RAM)
- Lateral meristems (vascular cambium, cork cambium) — secondary growth
Summary (Bottom)
Growth = irreversible permanent increase. Three phases: M-E-M (Meristematic, Elongation, Maturation). Sigmoid curve: Lag → Log → Stationary. Growth occurs at meristematic regions (apices).