Biology · Plant Growth and Development · NEET
Yes. NCERT says PGRs are also called plant growth substances, plant hormones or phytohormones. All these names mean the same chemicals. For NEET, treat these four terms as equal.
PGRs are intercellular chemical signals made inside the plant that control growth and development. They work in very small amounts. Nutrients (water, minerals, oxygen) are external factors needed in larger amounts. PGRs are intrinsic (internal) factors; light, temperature and nutrition are extrinsic (external) factors.
Yes. NCERT clearly states that any PGR has diverse physiological effects on plants. For example, auxin helps rooting, apical dominance and parthenocarpy. Also, different PGRs can show similar effects. This one-to-many and many-to-one action is a key characteristic.
No. This is the most common exam trap. PGRs can both promote AND inhibit growth. Auxins, gibberellins and cytokinins are growth promoters. Abscisic acid (ABA) is a growth inhibitor. Ethylene is a gas that can do both but is mostly an inhibitor of growth activities.
Synergistic means two PGRs work together in the same direction (their effects add up). Antagonistic means two PGRs work in opposite directions (one promotes, the other opposes). A classic pair is ABA and gibberellin in seed dormancy they act antagonistically.
No, they are of diverse chemical composition. Auxin (IAA) is an indole compound, cytokinin (kinetin) is an adenine derivative, ABA is a carotenoid derivative, gibberellin (GA3) is a terpene, and ethylene is a gas. So they differ in chemistry but all act as growth signals.
Read the following statements on plant growth and development. A. Parthenocarpy can be induced by auxins. B. Plant growth regulators can be involved in promotion as well as inhibition of growth. C. Dedifferentiation is a pre-requisite for re-differentiation. D. Abscisic acid is a plant growth promoter. E. Apical dominance promotes the growth of lateral buds. Choose the option with all correct statements.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
They are small, simple molecules of diverse chemistry, act in very low amounts, show diverse effects (one PGR many effects), can both promote and inhibit growth, and act synergistically or antagonistically.
Five main groups: auxins, gibberellins, cytokinins, abscisic acid and ethylene. The first three are growth promoters; ABA is an inhibitor; ethylene is a gas that is largely an inhibitor.
Because they are chemical signals made inside the plant (intercellular intrinsic factors). External conditions like light, temperature, water and nutrition are extrinsic factors.
Ethylene (C2H4) is the only gaseous plant growth regulator. It can fit either promoter or inhibitor group but is largely an inhibitor of growth activities.
No. PGRs often act together. Synergistic PGRs add their effects; antagonistic PGRs oppose each other (like ABA vs gibberellin in seed dormancy).
