Calcium Requirement in Legumes: Leguminous crops (Fabaceae) have a significantly higher physiological calcium ($Ca^{2+}$) requirement than graminaceous cereals and grasses.
Physiological Roles: Calcium is indispensable for root hair curling, infection thread formation, and nodulation by Rhizobium bacteria, as well as synthesizing calcium pectate in the middle lamella of rapidly expanding root and pod tissues (e.g., preventing "pops" in groundnut).
Cation Exchange Capacity (CEC): Legume roots possess high root CEC (~40–60 cmol/kg) with strong affinity for divalent cations like $Ca^{2+}$, whereas cereal roots have much lower root CEC (~10–25 cmol/kg). (Correct answer: Option 2)
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Q.47
Soil Science- ICAR JRF/SRF 2024
MCQ (Single Correct)+4−1
Nicotine is found in tobacco plant and it is used as insecticide. Itis a
Nicotine Nature & Classification: Nicotine [3-(1-methylpyrrolidin-2-yl)pyridine] is a natural heterocyclic pyridine-pyrrolidine alkaloid synthesized in the roots of Nicotiana tabacum and Nicotiana rustica and translocated to the foliage.
Insecticidal Mode of Action: Acts as an agonist on nicotinic acetylcholine receptors (nAChRs) in insect nervous systems, inducing synaptic block and paralysis; historically formulated as nicotine sulfate (40%) contact insecticide.
Other Classes: Limonoids and terpenoids are isoprene-derived bitter compounds (e.g., azadirachtin); carotenoids are tetraterpenoid pigments. (Correct answer: Option 4)
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Bordeaux Mixture Composition: A protective contact fungicide discovered by Pierre-Marie-Alexis Millardet in France (1885) to control downy mildew (Plasmopara viticola) in grapes.
Chemical Formulation: Prepared by reacting copper sulfate ($CuSO_4 \cdot 5H_2O$) with quicklime ($CaO$) or hydrated slaked lime [$Ca(OH)_2$] in water, typically in a 5:5:50 (or 1%) ratio, precipitating insoluble basic copper sulfates. (Correct answer: Option 3)
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Imazethapyr Classification: A selective, broad-spectrum systemic herbicide belonging to the imidazolinone chemical family.
Mode of Action: Inhibits the enzyme acetolactate synthase (ALS / AHAS), blocking the biosynthesis of branched-chain essential amino acids (valine, leucine, and isoleucine).
Crop Usage: Extensively recommended for selective control of both grassy weeds and broadleaf weeds in major legume crops like soybean, groundnut, and blackgram when applied as pre-emergence or early post-emergence. (Correct answer: Option 1)
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Q.50
Soil Science- ICAR JRF/SRF 2024
MCQ (Single Correct)+4−1
Ideal range of absorbance for accepting data from spectrophotometer is
Photometric Accuracy & Beer-Lambert Law: In UV-Vis spectrophotometry, photometric accuracy and reproducibility depend on maintaining transmission within the optimal linear dynamic range where the relative error in concentration measurement is minimized.
Ideal Absorbance Range: The optimal absorbance range for analytical measurement is 0.2 to 0.8 (corresponding to ~15% to 65% transmittance), where spectrophotometric detector noise and stray light errors are minimal. (Correct answer: Option 4)
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