32. The plant hormone gibberellins (GA) are a group of
(1) Monoterpenes (C10)    (2) Diterpenes (C20),
(3) Triterpenes (C30)                 (4) Sequiterpenes (C15)

Correct answer: (2) Diterpenes (C20)

Explanation:

• Gibberellins (GAs) are classified as diterpenes, which are terpenoids made up of 20 carbon atoms. These are biosynthesized from four isoprene units (C5 units).

• Other terpene classes:

  • Monoterpenes (C10) consist of two isoprene units.

  • Sesquiterpenes (C15) have three isoprene units.

  • Triterpenes (C30) are made of six isoprene units.

• GA molecules share a tetracyclic diterpenoid acid structure derived via the terpenoid biosynthesis pathway.

Explanation of options:

• (1) Monoterpenes (C10) – not gibberellins.

• (2) Diterpenes (C20) – correct classification of gibberellins.

• (3) Triterpenes (C30) – larger terpenes, e.g., sterols, not GAs.

• (4) Sesquiterpenes (C15) – a distinct class, not GAs.

  Gibberellins are diterpene plant hormones that play essential roles in regulating growth and development processes such as stem elongation, seed germination, and flowering by modulating cellular activities at the molecular level.