Q. 51 Acid rain with a pH of 4.0 is more acidic than the rain with a pH of 6.0 by (A) 2 times (B) 10 times (C) 100 times […]
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CSIR NET Life Science Previous Year Questions and Solution on EXTENSION OF MENDELIAN PRINCIPLES (62)
GATE Life Science 2018 Previous Year Papers with Solutions
Understanding Ecotones
Q. 50 Which of the following statements is TRUE for an ecotone? (A) An ecotone is the synonym of an ecosystem (B) An ecotone is an interface zone of two […]
GATE Life Science 2018 Previous Year Papers with Solutions
Self Incompatibility in Plants
Q. 49 Identify the CORRECT statement. (A) Receptor-like kinases play role in gametophytic self-incompatibility in Brassicaceae (B) Receptor-like kinases play role in sporophytic self-incompatibility in Solanaceae (C) Ribonucleases play role […]
GATE Life Science 2018 Previous Year Papers with Solutions
Ac and Ds Elements
Q. 48 Which of the statements is TRUE for transposable elements 𝑨𝒄 and 𝑫𝒔 ? (A) Both 𝐴𝑐 and 𝐷𝑠 are autonomous because they encode their own transposase (B) Both […]
GATE Life Science 2018 Previous Year Papers with Solutions
Plant miRNA Genes
Q. 47 The genes for microRNA (miRNA) in plants are usually transcribed by (A) RNA polymerase I (B) RNA polymerase II (C) RNA polymerase III (D) RNA polymerase IV Genes […]
GATE Life Science 2018 Previous Year Papers with Solutions
Xanthium Dimorphic Seeds
Q.46 Which of the following genera produces dimorphic seeds that help to broaden the time of germination in a variable habitat? (A) Xanthium (B) Pisum (C) Mangifera (D) Linum Xanthium […]
![Q. 45 The standard free energy (ΔG′) values of reactions catalyzed by citrate lyase and citrate synthetase are −670 cal/mol and −8192 cal/mol, respectively. Citrate lyase reaction: Citrate ⇌ Acetate + Oxaloacetate ΔG1′ = −670 cal/mol Citrate synthetase reaction: Acetyl-CoA + Oxaloacetate + H2O ⇌ Citrate + CoA ΔG2′ = −8192 cal/mol The standard free energy (in cal/mol) of acetyl-CoA hydrolysis is _____ (correct to integer number). Benzoic acid's mass spectrum shows a prominent base peak at m/z 105 due to the stable benzoyl cation. Correct Answer The base peak (100% relative abundance) in benzoic acid's electron ionization mass spectrum occurs at m/z 105. This fragment forms from the molecular ion (m/z 122) losing a hydroxyl radical (- OH, mass 17), yielding the resonance-stabilized benzoyl cation [C₆H₅CO]⁺. For Q.44, enter the integer 105. Fragmentation Pathways Benzoic acid (C₆H₅COOH, MW 122) undergoes characteristic cleavages in EI-MS. Molecular ion peak appears at m/z 122 (weak, ~10-20% abundance). Base peak at m/z 105: [M - OH]⁺, highly stable due to resonance between phenyl and carbonyl. m/z 77: C₆H₅⁺ (phenyl cation) from further loss of CO (mass 28) from m/z 105. Minor peaks: m/z 51 (C₄H₃⁺, tropylium-like), m/z 123 (M+1 from ¹³C isotope). Common Exam Options Explained Typical multiple-choice distractors test fragmentation knowledge: 105 (Correct): Most abundant due to benzoyl stability; 100% base peak. 122: Molecular ion [M]⁺- ; present but weak as aromatics fragment easily. 77: Significant (phenyl ion) but secondary (~50-70% abundance). 51 or 45: Smaller fragments (e.g., [C₆H₅COOH - COOH]⁺ or COOH⁺); low intensity. Why m/z 105 Dominates Resonance in [C₆H₅CO]⁺ delocalizes charge across oxygen and ring, enhancing survival to detector. This pattern repeats in aromatic carboxylic acids. Spectra from NIST or textbooks confirm this for benzoic acid identification.](https://www.letstalkacademy.com/wp-content/uploads/2026/01/slide_45-2.png)
GATE Life Science 2018 Previous Year Papers with Solutions
Benzoic Acid Mass Spectrum
Q. 45 The standard free energy (ΔG′) values of reactions catalyzed by citrate lyase and citrate synthetase are −670 cal/mol and −8192 cal/mol, respectively. Citrate lyase reaction: Citrate ⇌ Acetate […]
GATE Life Science 2018 Previous Year Papers with Solutions
Benzoic Acid Mass Spectrum
Q. 44 The mass spectrum of benzoic acid will generate the fragment as a base peak ( 𝟏𝟎𝟎% relative abundance) of 𝒎/𝒛 (mass to charge ratio) at ____ (correct to […]
![Q. 43 An enzyme follows Michaelis-Menten kinetics with substrate S. The fraction of the maximum velocity ( 𝑽max ) will be observed with the substrate concentration [ S ] = 𝟒𝑲𝐦 is ____ (correct to one decimal place). ( 𝑲𝐦 is Michaelis-Menten constant)](https://www.letstalkacademy.com/wp-content/uploads/2026/01/slide_43-2.png)
GATE Life Science 2018 Previous Year Papers with Solutions
Michaelis-Menten Kinetics
Q. 43 An enzyme follows Michaelis-Menten kinetics with substrate S. The fraction of the maximum velocity ( 𝑽max ) will be observed with the substrate concentration [ S ] = […]
GATE Life Science 2018 Previous Year Papers with Solutions
Percentage of α-Helix Residues
Q. 42 The secondary structure topology diagram of 400 amino acid long “Protein-X” is depicted in the figure. The start and end amino acid residue numbers of each 𝜶-helix are […]
