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The plant hormone used to destroy weeds in a field is:
The synthetic auxin 2,4-dichlorophenoxyacetic acid (2, 4-D) is widely used to kill broad-leaved dicotyledonous weeds while having zero detrimental effect on mature monocotyledonous plants (cereal crops and lawns)! Match Option (3)!
Auxins include both naturally occurring phytohormones and synthetic chemical analogues:
At elevated concentrations, 2, 4-D acts as a systemic hormonal herbicide. It induces uncontrolled, aberrant cell division and vascular crushing in broad-leaved (dicotyledonous) weeds, leading to their rapid death. Monocotyledonous plants (such as wheat, rice, corn, and turf grasses) rapidly metabolize and conjugate 2, 4-D, remaining unharmed. Hence, it is universally applied to maintain weed-free lawns and cereal fields.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
IAA (Indole-3-acetic acid) is an endogenous plant growth promoter that induces cell elongation, apical dominance, and rooting, not a commercial weedicide.
NAA (Naphthalene acetic acid) is used to induce rooting in stem cuttings and prevent pre-harvest fruit drop in apples, not as a weedicide.
2, 4-D (2,4-dichlorophenoxyacetic acid) is the canonical synthetic auxin employed globally to destroy dicot weeds in agricultural fields.
IBA (Indole-3-butyric acid) is primarily utilized as a root-inducing hormone in vegetative propagation cuttings.
IAA, NAA, 2, 4-D, and IBA are all auxins! Students must remember the exact agricultural application assigned to each in NCERT.
"2, 4-D, widely used to kill dicotyledonous weeds, does not affect mature monocotyledonous plants. It is used to prepare weed-free lawns by gardeners."
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