How NEET Tests 'Plant Growth & Development' - High-Yield Traps

This chapter rewards precise recall of discoveries, hormone roles and photoperiod logic. Master these rank-splitters:

  • Arithmetic vs geometric: arithmetic = one daughter keeps dividing, linear plot, Lt = L0 + rt; geometric = both daughters divide, exponential, W = W0 e^rt; the natural curve is sigmoid (lag -> log -> stationary). Be ready to calculate Lt from L0, r and t.
  • Differentiation terms: differentiation = mature to a function (tracheary element loses protoplasm, gains lignified wall); dedifferentiation = mature cells REGAIN division (interfascicular & cork cambium); redifferentiation = they lose it again (secondary xylem/phloem/cork). A plant cell's fate is set by its position.
  • Development = growth + differentiation (germination -> senescence); plasticity/heterophylly (cotton, coriander, larkspur; aquatic vs land buttercup); totipotency = whole plant from one cell. Maize does NOT show plasticity/heterophylly.
  • Hormone discovery pairings: coleoptile phototropism/tip = Darwin -> auxin (Went, Avena); bakanae disease of rice (Gibberella fujikuroi) = gibberellin; kinetin from herring-sperm DNA / zeatin from corn & coconut milk = cytokinin.
  • Natural vs synthetic auxins: natural = IAA, IBA; synthetic = NAA, 2,4-D. 2,4-D = herbicide (kills dicot weeds, spares mature monocot grasses).
  • Signature roles: apical dominance & rooting & 2,4-D = auxin; bolting, malting/brewing, grape size, sugarcane & conifer maturity = gibberellin; cytokinesis, overcome apical dominance, delay senescence by nutrient mobilisation = cytokinin; ripening, abscission, triple response, root-hair, mango/pineapple flowering = ethylene (gaseous); stomatal closure, seed dormancy, stress, anti-GA = ABA.
  • Photoperiodism: SDP need a long continuous dark period (a night-break flash of light stops SDP flowering - the dark period is decisive); the leaf perceives the photoperiod; florigen is the hypothetical flowering hormone; phytochrome is the photoreceptor.
  • Vernalisation: low temperature promotes flowering (winter wheat/rye, biennials like sugar beet & cabbage) - do not confuse with photoperiodism.

Below are challenging assertion-reason, match-the-column, multi-statement and sequence questions built on exactly these distinctions.