What is apical dominance and which hormone controls it?

Apical dominance is the suppression of lateral (axillary) bud growth by the apical bud. It is controlled by auxin secreted from the shoot apex. Removing the apex (decapitation) allows lateral buds to grow.

What is the difference between short-day and long-day plants?

Short-day plants (e.g., rice) flower when the night period exceeds a critical length. Long-day plants (e.g., wheat) flower when the night period is shorter than a critical length. Both respond to night length, not day length.

Why is ethylene used commercially to ripen fruits?

Ethylene is a natural plant hormone that triggers fruit ripening by activating enzymes that break down starch to sugars, soften cell walls, and produce volatile compounds for flavour and aroma. Commercially, ethylene gas is applied to unripe fruits in enclosed chambers.

Plant Growth Regulators

Plant Growth and Development • Class 11 Biology • NCERT • CBSE

Plant growth regulators: Auxins (cell elongation), Gibberellins (stem elongation, seed germination), Cytokinins (cell division), ABA (dormancy, stress response), Ethylene (fruit ripening). Seed germination: imbibition → enzyme activation → radicle emergence.

Key Formulas

Arithmetic growth: L_t = L₀ + rt
Geometric growth: W_t = W₀ × e^(rt)

Frequently Asked Questions

What is apical dominance and which hormone controls it?: Apical dominance is the suppression of lateral (axillary) bud growth by the apical bud. It is controlled by auxin secreted from the shoot apex. Removing the apex (decapitation) allows lateral buds to grow.
What is the difference between short-day and long-day plants?: Short-day plants (e.g., rice) flower when the night period exceeds a critical length. Long-day plants (e.g., wheat) flower when the night period is shorter than a critical length. Both respond to night length, not day length.
Why is ethylene used commercially to ripen fruits?: Ethylene is a natural plant hormone that triggers fruit ripening by activating enzymes that break down starch to sugars, soften cell walls, and produce volatile compounds for flavour and aroma. Commercially, ethylene gas is applied to unripe fruits in enclosed chambers.

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