Plant growth regulators (PGRs), also called phytohormones or plant hormones, are small, simple chemical molecules made by the plant itself that control growth, differentiation, and development. NCERT places them in five groups: auxins, gibberellins, cytokinins, abscisic acid, and ethylene. Memory hook: "PGR = the plant's own chemical message" — remember they can both promote AND slow down growth, so they are called "regulators", not just "promoters".
PGRs are plant-made chemical molecules split into two functional groups: promoters (auxins, gibberellins, cytokinins) and inhibitors (abscisic acid, ethylene). This "both promote and inhibit" split is the reason they are called regulators, and it is the single most tested NEET point.
Your doubts, answered
Is a phytohormone the same thing as a plant growth regulator?
Yes, for NEET they mean the same. NCERT says PGRs are 'variously described as plant growth substances, plant hormones or phytohormones'. So plant growth regulator, plant hormone, phytohormone, and plant growth substance are all the same thing. Do not treat them as different in an exam.
Do plant growth regulators only make plants grow more?
No. This is the most tested point. PGRs are divided into TWO groups: growth promoters (auxins, gibberellins, cytokinins) that increase cell division and enlargement, and growth inhibitors (abscisic acid, and ethylene in many roles) that slow growth or cause dormancy and stress response. Because they do both, they are called 'regulators'.
Are these hormones made by the plant or sprayed from outside?
Natural PGRs are made by the plant itself in one part and often act in another part. Some, like 2,4-D or synthetic auxins, are man-made and sprayed on crops. NEET asks about natural PGRs (five groups), but also tests their synthetic uses in agriculture.
Why do we call them 'regulators' instead of just 'hormones'?
Because they control (regulate) growth in both directions — speeding it up and slowing it down. A single PGR can also have many different effects, and different PGRs can give the same effect. They may act together (synergistically) or against each other (antagonistically), so 'regulator' fits their role better.
What are the five groups I must remember?
Auxins, Gibberellins, Cytokinins, Abscisic acid (ABA), and Ethylene. First three = growth promoters. ABA = growth inhibitor (stress hormone). Ethylene = gaseous PGR, mostly inhibitory but promotes ripening and root hair growth.
⚠️ The NEET trap ✗ Plant growth regulators are only substances that promote plant growth. ✓ PGRs both promote AND inhibit growth — auxins, gibberellins, and cytokinins promote, while abscisic acid inhibits (dormancy, stress). That is why they are called regulators. 🧠 NEET 2025 tested exactly this: 'PGRs can be involved in promotion as well as inhibition of growth' was a CORRECT statement, while 'ABA is a plant growth promoter' was WRONG.
Real NEET questions
NEET 2025
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.
A · A, D, E only
B · B, D, E only
C · A, B, C only ✓
D · A, C, E only
Solution: A is correct: auxins induce parthenocarpy (seedless fruits). B is correct: PGRs both promote and inhibit growth — this is the core definition. C is correct: dedifferentiation precedes redifferentiation. D is WRONG: ABA is an inhibitor/stress hormone, not a promoter. E is WRONG: apical dominance suppresses lateral buds. So only A, B, C are correct.
ReNEET 2026
Which of the following plant growth regulators is used as a herbicide?
A · 2,4-D ✓
B · Kinetin
C · Abscisic acid
D · Gibberellin
Solution: 2,4-D (2,4-dichlorophenoxyacetic acid) is a synthetic auxin used to kill dicot weeds, so it acts as a herbicide. Kinetin is a cytokinin, ABA is a growth inhibitor, and gibberellin promotes elongation — none of these are herbicides.
Solved Plant Growth and Development NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What is the simple definition of plant growth regulators?
They are small, simple chemical molecules made by a plant that control its growth, differentiation, and development. Also called phytohormones or plant hormones.
How many groups of plant growth regulators are there?
Five natural groups: auxins, gibberellins, cytokinins, abscisic acid, and ethylene.
Which PGRs are growth promoters and which are inhibitors?
Promoters: auxins, gibberellins, cytokinins. Inhibitor: abscisic acid. Ethylene is mostly inhibitory but promotes fruit ripening and root hair formation.
What is the chemical nature of each PGR?
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.
Can two PGRs act together?
Yes. PGRs may act synergistically (helping each other) or antagonistically (opposing each other). One PGR can have many effects, and many PGRs can give a similar effect.
