Q.61 Select the CORRECT set comprising only the synthetic analogues of auxin and cytokinin
(A) IAA and Kinetin (B) 2, 4-D and Zeatin (C) IAA and Zeatin (D) 2, 4-D and Kinetin
IAA and zeatin are natural plant hormones, while 2,4-D and kinetin are synthetic analogues of auxin and cytokinin, respectively. The correct set comprising only synthetic analogues is option (D).
Correct Answer
(D) 2, 4-D and Kinetin
Plant Hormone Analogues Explained
Auxins like IAA (indole-3-acetic acid) occur naturally, promoting cell elongation and root formation; 2,4-D (2,4-dichlorophenoxyacetic acid) is a synthetic auxin herbicide mimicking IAA via TIR1/AFB receptors. Cytokinins like zeatin (from corn) drive cell division; kinetin (6-furfurylaminopurine), discovered in aged DNA, is fully synthetic with no natural source.
Option Analysis
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(A) IAA and Kinetin: Wrong. IAA is natural auxin; only kinetin synthetic.
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(B) 2, 4-D and Zeatin: Wrong. 2,4-D synthetic auxin, but zeatin natural cytokinin.
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(C) IAA and Zeatin: Wrong. Both natural (IAA auxin, zeatin cytokinin).
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(D) 2, 4-D and Kinetin: Correct. Both synthetic (2,4-D auxin analogue, kinetin cytokinin analogue).
Introduction to Synthetic Auxin Cytokinin Analogues
Synthetic auxin cytokinin analogues 2,4-D kinetin dominate GATE Life Sciences plant physiology questions like Q.61, distinguishing natural hormones (IAA, zeatin) from man-made mimics used in tissue culture and weed control. Only option (D) pairs true synthetics for cell elongation and division effects.
Natural vs Synthetic Plant Hormones
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Auxins: IAA natural; 2,4-D synthetic (stable herbicide, TIR1-binding).
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Cytokinins: Zeatin natural (tRNA-derived); kinetin synthetic (DNA extract origin).
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Synthetics resist degradation, ideal for experiments.
Q.61 Detailed Breakdown
| Option | Auxin | Cytokinin | Both Synthetic? |
|---|---|---|---|
| (A) | IAA (natural) | Kinetin (syn) | ❌ No |
| (B) | 2,4-D (syn) | Zeatin (nat) | ❌ No |
| (C) | IAA (nat) | Zeatin (nat) | ❌ No |
| (D) | 2,4-D (syn) | Kinetin (syn) | ✅ Yes |
Why 2,4-D and Kinetin for GATE?
2,4-D mimics IAA for root induction but kills broadleaf weeds via unchecked growth. Kinetin delays senescence, promotes shoot formation in culture. High-yield: Recall “IAA natural, 2,4-D fake; zeatin real, kinetin made.”
Exam Preparation Tips
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Mnemonic: “Synthetic Duo: D(2,4) and K(inetin).”
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Applications: 2,4-D herbicide; kinetin anti-aging in plants.
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PYQ pattern: Always classify IAA/zeatin natural.
Master synthetic auxin cytokinin analogues 2,4-D kinetin for GATE plant hormones success.
