PLANT GROWTH AND DEVELOPMENT · Comparison Tables

1. Growth vs Development

Feature	Growth	Development
Meaning	Irreversible, permanent increase in size of an organ, its parts or an individual cell.	All changes an organism undergoes during its life cycle, from seed germination to senescence.
Major basis	Increase in protoplasmic material, measurable as fresh/dry weight, length, area, volume or cell number.	Sum of growth and differentiation.
Control	Requires water, oxygen, nutrients and optimum environmental conditions.	Controlled by intrinsic factors (genes, PGRs) and extrinsic factors (light, temperature, water, oxygen and nutrition).
Plant character	Usually open and indeterminate because meristems keep adding new cells.	Flexible; plants can adopt different pathways in response to environment or life stage.

2. Primary Growth vs Secondary Growth

Feature	Primary growth	Secondary growth
Meristem responsible	Root apical meristem, shoot apical meristem and, where present, intercalary meristem.	Lateral meristems: vascular cambium and cork cambium.
Main result	Elongation of the plant axis.	Increase in girth of organs.
Occurrence	Occurs from apical regions during growth.	Appears later in life in dicotyledonous plants and gymnosperms.
Growth form	Continued meristematic activity adds cells throughout life, producing the open form of plant growth.

Recall A meristem that ceases to divide cannot maintain the indeterminate growth characteristic of plants.

3. Meristematic vs Elongation vs Maturation Phase

Feature	Meristematic phase	Elongation phase	Maturation phase
Position	At root and shoot apices.	Just proximal to, or away from, the meristematic zone.	Further proximal to the elongation zone.
Cell activity	Cells divide continuously.	Cells enlarge and elongate.	Cells attain final size and specialised form.
Cell features	Dense protoplasm, large nuclei, thin primary cellulosic wall and many plasmodesmata.	Increased vacuolation, cell enlargement and new cell-wall deposition.	Wall thickening and protoplasmic modifications.
Outcome	New cells are produced.	Length/size increases.	Most tissues and cell types acquire mature characteristics.

4. Arithmetic vs Geometrical vs Sigmoid Growth

Feature	Arithmetic growth	Geometrical growth	Sigmoid growth
Daughter-cell fate	Only one daughter cell continues to divide; the other differentiates and matures.	Both daughter cells retain capacity to divide.	Geometrical growth that slows under limiting nutrient supply.
Rate pattern	Constant rate, such as root elongation.	Slow lag phase followed by rapid exponential/log phase.	Lag -> log/exponential -> stationary phase.
Graph	Linear curve.	Exponential curve under ideal conditions.	S-shaped curve; characteristic of cells, tissues and organs growing naturally.
Expression	L_t = L₀ + rt	W₁ = W₀e^rt	No separate equation; represents the complete natural growth sequence.

5. Absolute Growth Rate vs Relative Growth Rate

Feature	Absolute growth rate	Relative growth rate
Definition	Total growth per unit time.	Growth per unit time expressed on a common basis, such as per unit initial parameter.
What it compares	Actual increase in a parameter such as area, weight or length.	Efficiency of growth relative to the initial size.
Example	Two leaves can each add 5 cm² in the same time.	The smaller initial leaf has the greater relative growth rate when both add 5 cm².
Related term	Describes amount gained.	In geometric growth, r is a relative growth rate and efficiency index for producing new plant material.

6. Differentiation vs Dedifferentiation vs Redifferentiation

Process	What happens	NCERT example
Differentiation	Meristem-derived cells mature to perform a specific function; they undergo structural changes in wall and protoplasm.	A tracheary element loses protoplasm and develops strong lignocellulosic secondary walls to conduct water.
Dedifferentiation	Living differentiated cells that lost the capacity to divide regain it under certain conditions.	Fully differentiated parenchyma forms interfascicular cambium or cork cambium.
Redifferentiation	Cells formed from a dedifferentiated meristem lose the capacity to divide and mature again for specialised functions.	New cells produced by those cambia mature into specialised tissues.
Plasticity	Ability to form different structures in response to environment or phase of life.	Heterophylly: juvenile and mature leaves differ in cotton, coriander and larkspur; aerial and aquatic leaves differ in buttercup.

7. Five Major Plant Growth Regulators

PGR	Nature / example	Predominant grouping	High-yield role
Auxins	Indole compounds; IAA, IBA; synthetic NAA and 2,4-D.	Growth promoter.	Cell enlargement, rooting, apical dominance and parthenocarpy.
Gibberellins	Terpenes; GA₃ is the best studied.	Growth promoter.	Axis elongation, bolting, delayed senescence.
Cytokinins	Adenine derivatives; kinetin, zeatin.	Growth promoter.	Cytokinesis, lateral-bud growth and delayed senescence.
Ethylene	Simple gas, C₂H₄.	Largely growth-inhibitory but has diverse effects.	Fruit ripening, abscission and dormancy breaking.
Abscisic acid	Carotenoid derivative; ABA.	Growth inhibitor / stress-response regulator.	Stomatal closure, dormancy and stress tolerance.

8. Key PGR Effects and Applications

PGR	Physiological effect	Agricultural / horticultural application
Auxin	Promotes rooting and flowering; apical bud inhibits lateral buds; can induce parthenocarpy.	Rooting of stem cuttings; decapitation in tea plantations and hedges promotes lateral branches; 2,4-D kills dicot weeds.
Gibberellin	Elongates axis, fruits and stalks; promotes bolting; delays senescence.	Improves apple shape, lengthens grape stalks, speeds malting, and increases sugarcane yield.
Cytokinin	Promotes cell division, new leaves, chloroplast formation, lateral shoots and nutrient mobilisation.	Delays leaf senescence and helps overcome apical dominance.
Ethylene	Promotes ripening, respiratory climacteric, senescence, abscission, root hairs and flowering in specific plants.	Ethephon hastens fruit ripening; ethylene synchronises pineapple fruit-set and promotes female flowers in cucumber.
ABA	Inhibits germination and metabolism; closes stomata; promotes seed maturation and dormancy.	Called stress hormone; dormancy helps seeds survive desiccation and unfavourable conditions.

One-line answers Induce rooting: auxin. Ripen fruit: ethylene. Delay leaf senescence: cytokinin. Bolt rosette plant: gibberellin. Immediate stomatal closure: ABA.