Chapter 13 — Plant Growth and Development

Chapter 13 of the Class 11 Biology NCERT textbook, "Plant Growth and Development", covers this topic. Plant growth and development is the irreversible increase in size and formation of organs through division and differentiation of meristematic cells, controlled by plant growth regulators like auxins, gibberellins, cytokinins, ethylene, and abscisic acid.

• Growth as a phased, measurable process — The chapter defines growth as a permanent, quantifiable increase driven by meristems, unfolding through meristematic, elongation, and maturation phases and following arithmetic or sigmoid geometric patterns.
• Development beyond mere growth — It broadens the view from size to development, where differentiation specializes cells, and dedifferentiation and redifferentiation let mature cells regain and re-deploy division capacity, giving plants remarkable plasticity.
• Hormones as growth controllers — The chapter shows how five plant growth regulators coordinate the whole programme—governing rooting, elongation, flowering, ripening, dormancy, and stress responses—together with external factors like light, temperature, and water.

1. 01Growth is irreversible size increase measured by fresh/dry weight, length, area, volume, or cell number, driven by meristematic cell division.
2. 02Three growth phases—meristematic (active cell division), elongation (cell enlargement and vacuolation), and maturation (cell wall thickening and specialization).
3. 03Arithmetic growth shows linear increase; geometric growth shows exponential increase followed by plateau (sigmoid curve).
4. 04Plant growth regulators—auxins (rooting, flowering, apical dominance), gibberellins (elongation, ripening), cytokinins (cell division, leaf growth), ethylene (ripening, senescence), and abscisic acid (stress tolerance, dormancy)—control all developmental phases.
5. 05Differentiation specializes cells for function; dedifferentiation restores division capacity; redifferentiation specializes anew—enabling plant flexibility and tissue regeneration.
6. 06Development requires intrinsic factors (PGRs, genetics) and extrinsic factors (light, temperature, water, oxygen, nutrients, gravity).