Biology · Plant Growth and Development · NEET
2,4-D is a synthetic (man-made) auxin, not a natural one. NCERT lists IAA and IBA as natural auxins isolated from plants, while NAA and 2,4-D are synthetic auxins made in a lab. NEET often tests this exact split, so remember: natural = IAA, IBA; synthetic = NAA, 2,4-D.
Lawn grass is a monocot, and 2,4-D does not affect mature monocotyledonous plants. Weeds in a lawn are mostly broad-leaf dicots, and 2,4-D kills these dicot weeds. So spraying it clears the weeds without damaging the grass. This is exactly why gardeners use it for weed-free lawns.
It kills dicotyledonous weeds. Mature monocots are not affected. This is the single most tested line: '2,4-D, widely used to kill dicotyledonous weeds, does not affect mature monocotyledonous plants.' If NEET asks which type of weed 2,4-D destroys, the answer is dicots.
All four are auxins, but their main uses differ. IAA and IBA are natural auxins used mainly for rooting and growth; NAA is a synthetic auxin used for rooting and to control fruit/leaf drop; 2,4-D is the synthetic auxin used specifically as a herbicide (weed killer). In a PYQ asking for the weed-killing hormone, only 2,4-D is correct.
NCERT notes auxin also promotes rooting in stem cuttings, prevents early fruit and leaf drop, promotes fruit growth, controls apical dominance, and controls xylem differentiation and cell division. But its herbicide role belongs only to 2,4-D. Do not mix apical dominance or rooting with the weed-killer question.
The plant hormone used to destroy weeds in a field is
Auxin is used by gardeners to prepare weed-free lawns. But no damage is caused to grass as auxin
Which of the following plant growth regulators is used as a herbicide?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
2,4-D stands for 2,4-dichlorophenoxyacetic acid. It is a synthetic auxin used mainly as a herbicide to kill dicotyledonous weeds.
No. Both are synthetic auxins, but 2,4-D is used as a herbicide, while NAA is used mainly for rooting and to prevent fruit and leaf drop. NEET expects you to keep these uses separate.
It kills dicotyledonous (broad-leaf) weeds. Mature monocotyledonous plants such as grasses are not affected.
Because it removes broad-leaf dicot weeds from a lawn without harming the monocot grass, it is used to prepare weed-free lawns.
The weed killer 2,4-D is a synthetic auxin. Natural auxins like IAA and IBA are not used as herbicides.
