(A), (B), (D), (E) only Gibberellins (GAs) are key plant hormones with specific structural and biosynthetic traits; statements (A), (B), and (C) are correct, while (D) and (E) are not.
Correct Answer
(A), (B), (C) only.
Statement Analysis
(A) All GAs possess a tetracyclic ent-gibberellane skeleton: True. Bioactive GAs and precursors share this conserved four-ring ent-gibberellane structure derived from geranylgeranyl diphosphate.
(B) GA biosynthesis inhibitors (Cycocel) help reducing plant stem length and lodging: True. Cycocel (chlormequat chloride) inhibits ent-kaurene oxidase in GA biosynthesis, shortening stems, promoting sturdiness, and preventing lodging in cereals.
(C) GAs are diterpenoids: True. GAs derive from the C20 diterpenoid pathway via GGPP, distinguishing them from sesquiterpenoid or triterpenoid hormones.
(D) GA biosynthesis occurs in cytoplasm: False. Early steps (terpenoid backbone) occur in plastids; later oxidation in endoplasmic reticulum and cytosol.
(E) GA is synthesised in the aleurone layer of embryo: False. In seeds, aleurone synthesizes alpha-amylase in response to GA from the embryo, but GA biosynthesis is primarily in young, growing tissues like apical meristems, not aleurone.
Option Breakdown
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(A), (B), (C) only: Correct; matches verified true statements.
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(A), (B), (C), (D) only: Incorrect; adds false (D).
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(A), (B), (C), (E) only: Incorrect; adds false (E).
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(A), (B), (D), (E) only: Incorrect; includes two falses.
Gibberellins biosynthesis inhibitors Cycocel target GA pathway to control stem elongation and lodging in agriculture.
Structural Features
All GAs possess a tetracyclic ent-gibberellane skeleton, ent-kaurene being key intermediate.
Biosynthesis and Inhibitors
GAs are diterpenoids synthesized plastid-to-cytosol; Cycocel blocks early steps, reducing GA levels for compact growth.
Site of Action
Not in cytoplasm alone or aleurone; active in meristems, with seed roles in signaling not synthesis.
| Statement | Correct? |
| (A) Tetracyclic skeleton | Yes |
| (B) Cycocel reduces length/lodging | Yes |
| (C) Diterpenoids | Yes |
| (D) Cytoplasm biosynthesis | No |
| (E) Aleurone synthesis | No |
