Biology : Plant Growth & Development

Explore plant growth and development from seed to tree, contrasting intrinsic and extrinsic growth, and covering seed germination, seed dormancy, growth phases, hormones, and light for flowering.

Explore seed dormancy and germination in plant growth, detailing causes—hard seed coat, impermeable water, inhibitors, immature embryos—and breaking strategies: scarification, stratification, washing, and growth regulators.

Seed germination occurs when a dormant embryo resumes metabolism in water, imbibes, activates enzymes, converts stored starch to maltose, ruptures the seed coat, and forms radical root and plumule shoot.

Explore seed germination types, hypogeal and epigeal, detailing how the epicotyl and hypocotyl elongate, cotyledons and radicle behavior, with rice, groundnut, and bean examples.

Characterize growth as the permanent, irreversible increase in size and shape. Explain it via cell division, cell elongation, and cell maturation, and the grand period of growth governs these stages.

Explore the three phases of plant growth: cell division (formative phase), cell elongation, and differentiation (maturation). See how mitosis forms daughter cells and protoplasm synthesis drives enlargement.

Explore viviparous germination, where the seed germinates inside the fruit while still attached to the parent plant; the radical elongates and lateral roots form, enabling a new plant after detachment.

Explore how plant growth follows a sigmoidal growth curve, with nonuniform growth across organs, featuring lag phase, log phase, and stationary phase driven by cell division, enlargement, and differentiation.

Discover how plant growth hormones, or plant growth regulators, control growth by promoting or inhibiting key processes like cell elongation (auxin) or stem elongation (jubelin).

Auxin, the natural plant growth hormone produced in tips of roots and shoots, promotes cell elongation and root–shoot growth; the avena curvature test shows asymmetrical auxin migration causing curvature.

Auxin promotes cell division and elongation, adventitious root formation in cuttings and tissue culture, and apical dominance that suppresses lateral buds, while preventing abscission and producing seedless fruits.

Gibberellin is a plant growth regulator that promotes stem elongation, synthesized in root tips, apical buds, and young leaves, and was discovered from rice infected by Gibberella fujikuroi.

Gibberellin promotes stem elongation and leaf expansion, increases jute fiber length and fruit size, converts dwarf plants to tall phenotypes, and breaks dormancy to enable seed germination.

Cytokinin, a plant growth regulator, drives cell division and organogenesis, delays senescence by stabilizing metabolites, and promotes root, shoot, and vascular tissue formation during secondary growth.

Ethylene, a lipid-soluble plant hormone produced in parts, acts as a ripening signal; auxin promotes its synthesis, carbon dioxide inhibits it, and it breaks dormancy and aids post harvest ripening.

Abscisic acid (ABA) is a plant growth inhibitor and anti-gibberellin stress hormone that promotes dormancy of seeds and buds, closes stomata, induces senescence, and leaf abscission.

Explore photoperiodism and how light duration governs flowering, define the critical photoperiod, and distinguish long-day, short-day, and neutral plants with practical examples.

Vernalization applies a cold or chilling treatment (0–10 degrees Celsius) to plants to stimulate flowering, converting biennial varieties to annuals and shortening the vegetative phase for earlier reproduction.