Biology · Plant Growth and Development · NEET
Based on their function in the plant, PGRs are broadly divided into just TWO groups. Group 1 = growth promoters (auxins, gibberellins, cytokinins). Group 2 = growth inhibitors (abscisic acid, ABA). Ethylene is a special gaseous PGR that can fit either group but is mostly an inhibitor. NCERT states this two-group division clearly, so for NEET the answer is two functional types.
Promoters (they build and grow the plant): Auxins, Gibberellins, Cytokinins. They do cell division, cell enlargement, pattern formation, tropic growth, flowering, fruiting and seed formation. Inhibitor: Abscisic acid (ABA), which controls dormancy, abscission and stress responses. Simple trick: three promoters (A, G, C) and one main inhibitor (ABA).
Ethylene is a gaseous PGR that could fit either group, but NCERT says it is LARGELY an inhibitor of growth activities. It does promote some things like fruit ripening and leaf fall, but because it mostly inhibits growth, treat it as an inhibitor-type PGR for NEET unless the question says otherwise.
ABA causes growth-inhibiting actions: it promotes seed dormancy, causes abscission (falling of leaves and fruits), and helps the plant survive stress like drought (it closes stomata). Because these slow down or stop growth, ABA is grouped as a growth inhibitor. A very common NEET trap is a statement saying 'ABA is a growth promoter' — that is FALSE.
Yes, in NCERT's functional grouping auxins, gibberellins and cytokinins are the three growth promoters because their main jobs are growth-promoting: cell division, cell enlargement, flowering, fruiting and seed formation. This is the classification you must remember for NEET.
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.
Growth promoters (auxins, gibberellins, cytokinins) and growth inhibitors (abscisic acid). This is a function-based division from NCERT.
Abscisic acid (ABA) is the main growth inhibitor. It controls seed dormancy, abscission and stress responses.
No, ethylene is largely a growth inhibitor, though it can act in either group. It ripens fruit and causes leaf fall, but overall it inhibits growth.
Auxins, gibberellins and cytokinins are the three growth promoters. They cause cell division, cell enlargement, flowering, fruiting and seed formation.
NEET regularly asks which PGR is a promoter or inhibitor, and traps students with statements like 'ABA is a promoter'. Knowing the two-group classification helps you answer matching, statement and single-word questions quickly.
