Plant growth can be artificially stimulated by the addition of

Step 1: Analyze the question The question asks which substance can be added to artificially stimulate plant growth. We need the option that is a growth-promoting plant hormone (or growth regulator).

Step 2: Explain the concepts (plant hormones)

• Gibberellin: Promotes stem elongation, seed germination, breaking of dormancy, and fruit growth. It is widely used commercially to stimulate growth (e.g. making dwarf plants grow taller and producing larger seedless grapes).
• Kinin (cytokinin): Promotes cell division and delays leaf senescence. It also stimulates growth, but it is more associated with cell division and delaying ageing.
• Abscisic acid: A growth inhibitor. It causes dormancy, stomatal closure, and leaf fall.
• Ethylene: Promotes fruit ripening and leaf abscission. It generally inhibits stem elongation.

Step 3: Eliminate the options

• C (abscisic acid) is out because it inhibits growth.
• D (ethylene) is out because it is mainly for ripening and senescence.
• This leaves A (gibberellin) and B (kinin). Both promote growth, but gibberellin is the classic hormone for stimulating overall plant growth (stem and shoot elongation). It is the one commonly applied artificially (e.g. sprayed on crops), which is why the question points to it.

Step 4: Answer The correct option is A. gibberellin.

Tip: Remember the hormones by their main jobs:

• Gibberellin = Growth (elongation)
• Kinin = Kell division (cell division)
• ABA = Appose growth (stress and dormancy)
• Ethylene = Eripening (ripening)