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Life Sciences (XL) PYQs Feb 2021

This collection gathers the Life Sciences (XL) previous year questions that appeared in the February 2021 exam. It includes the original questions and detailed solutions, helping students revise key concepts and practice exam-style problems.

99 questions

Physiology Ecology and Evolution

Dry air is fed into a tray dryer. The percentage relative humidity of the air leaving the dryer is 60% at 70°C and 101.3

Biologically, verbal and logical reasoning operates via grammar, vocabulary and inference determine correct usage. Thus Option NAT is appropriate since it meets linguistic and logical standards, reinforcing core concepts taught in general aptitude.

Ref: Wren and Martin, High School English Grammar and Composition, Revised Edition, Chapter 12, Vocabulary and Usage, discusses synonyms, antonyms, spelling rules, sentence completion and comprehension providing guidance for verbal aptitude.

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Physiology Ecology and Evolution

A cross is made between two animals of genotypes AaBb x AaBb, where loci A and loci B assort independently. The progeny

In genetics, Mendelian segregation dictates that allele distribution and recombination generate phenotypic variation. Therefore Option NAT is correct as it follows segregation and linkage principles, supported by mechanistic studies and conserved across related systems.

Ref: Hartl and Jones, Genetics: Analysis of Genes and Genomes, 8th Edition, Chapter 7, Mutation and DNA Repair, covers mutation types, repair pathways, chromosomal aberrations and genome stability relevant to human genetic disorders.

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Physiology Ecology and Evolution

An enzyme catalyzes the conversion of 30 micro M of a substrate to product at reaction velocity of 9.0microM s ⁻¹ When [

Mechanistically, enzyme kinetics involves substrate binding and catalytic efficiency determine reaction rates. This validates Option NAT because it reflects active-site specificity and regulation, a pattern repeatedly demonstrated in biochemistry research.

Ref: Nelson and Cox, Lehninger Principles of Biochemistry, 7th Edition, Chapter 6, Enzyme Kinetics and Regulation, discusses Michaelis-Menten equation, catalytic mechanisms, allosteric control and metabolic integration supporting enzyme function and pathway regulation.

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Microbiology Immunology and Biotechnology

In the structure of a polypeptide, one a.-helix (3.6 ₁₃ helix) contains 32 intrachain hydrogen bonds. The number of turn

This outcome reflects molecular bonding, where hybridization and orbital overlap dictate geometry and reactivity. Option NAT captures this correctly because it satisfies bonding and stability criteria, consistent with textbook descriptions and experimental observations in chemistry.

Ref: Atkins and de Paula, Physical Chemistry, 11th Edition, Chapter 14, Molecular Structure and Bonding, discusses VSEPR, hybridization, molecular orbitals, dipole moments and spectroscopic properties explaining chemical bonding and reactivity.

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Microbiology Immunology and Biotechnology

A population of snakes in an isolated island is in Hardy-Weinberg equilibrium for a gene with only two alleles (A and a)

This outcome reflects Mendelian segregation, where allele distribution and recombination generate phenotypic variation. Option NAT captures this correctly because it follows segregation and linkage principles, consistent with textbook descriptions and experimental observations in genetics.

Ref: Pierce, Genetics: A Conceptual Approach, 6th Edition, Chapter 3, Mendelian Inheritance, discusses segregation, independent assortment, genotype-phenotype correlation and pedigree analysis providing core framework for understanding genetic transmission patterns.

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Microbiology Immunology and Biotechnology

A man, whose mother and father had blood groups A and 0 respectively, marries a woman with blood group AB. If the man ha

Understanding homeostatic regulation reveals hormonal feedback and ion transport maintain balance. Therefore Option NAT is correct because it sustains physiological integration, which underpins key processes in physiology. This mechanism is extensively documented and reinforced by experimental data across multiple model systems and textbook discussions.

Ref: Guyton and Hall, Textbook of Medical Physiology, 14th Edition, Chapter 75, Endocrine Regulation, explains hormone synthesis, secretion, feedback mechanisms and metabolic control relevant to physiological homeostasis and integration.

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Microbiology Immunology and Biotechnology

The generation time of E. coli is 30 minutes. For an exponentially growing culture, the initial number of bacteria requi

Evidence for microbial physiology indicates growth regulation and phage life cycles follow molecular programs. Option NAT aligns with this, as it corresponds to prokaryotic replication strategies, reflecting standard interpretations in microbiology.

Ref: Prescott et al., Microbiology, Chapter 16, Microbial Genetics and Horizontal Transfer, covers plasmids, conjugation, transformation, transduction and antibiotic resistance mechanisms supporting microbial evolution concepts.

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Microbiology Immunology and Biotechnology

The decimal reduction time (D) for reducing 10 ¹² spores of Clostridium botulinum to 1 spore at 111°C will be min (in in

Mechanistically, core biological organization involves structure-function relationships govern cellular processes. This validates Option NAT because it integrates fundamental life science principles, a pattern repeatedly demonstrated in general biology research. This mechanism is extensively documented and reinforced by experimental data across multiple model systems and textbook discussions.

Ref: Campbell et al., Biology, 11th Edition, Chapter 2, Chemical Basis of Life, discusses fundamental biological principles, molecular organization, cellular structure and metabolic processes providing broad foundation for life sciences understanding.

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Microbiology Immunology and Biotechnology

Suppose the mRNAs in a newly discovered bacteria are composed of only two distinct nucleotides (as opposed to four found

This outcome reflects DNA replication fidelity, where polymerase proofreading and origin firing ensure accurate duplication. Option NAT captures this correctly because it matches high-fidelity synthesis mechanisms, consistent with textbook descriptions and experimental observations in molecular biology.

Ref: Alberts et al., Molecular Biology of the Cell, 6th Edition, Chapter 5, DNA Replication and Repair, discusses origin recognition, helicase activity, replication fork dynamics and leading-lagging strand synthesis ensuring high fidelity genome duplication.

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Microbiology Immunology and Biotechnology

The genome of a bacterium encodes for 10 different surface antigens, whose expression can be turned 'ON' or 'OFF' random

Understanding immune recognition reveals antigen presentation and clonal selection drive specificity. Therefore Option NAT is correct because it demonstrates adaptive immune activation, which underpins key processes in immunology. This mechanism is extensively documented and reinforced by experimental data across multiple model systems and textbook discussions.

Ref: Abbas, Lichtman and Pillai, Cellular and Molecular Immunology, 9th Edition, Chapter 4, Innate Immunity, explains pattern recognition receptors, complement activation, inflammation and innate defense mechanisms bridging innate and adaptive immunity.

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Cell Biology and Genetics

One mole of a circular bacterial plasmid was digested with a high-fidelity restriction enzyme. The plasmid has five rest

Evidence for enzyme kinetics indicates substrate binding and catalytic efficiency determine reaction rates. Option NAT aligns with this, as it reflects active-site specificity and regulation, reflecting standard interpretations in biochemistry.

Ref: Lehninger Principles of Biochemistry, 7th Edition, Chapter 15, Metabolic Regulation, explains hormonal control, allosteric regulation, feedback inhibition and pathway coordination essential for understanding intermediary metabolism and homeostasis.

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Cell Biology and Genetics

In a population of a diploid plant species obeying Hardy-Weinberg equilibrium, a locus regulating flower color has two a

Understanding Mendelian segregation reveals allele distribution and recombination generate phenotypic variation. Therefore Option NAT is correct because it follows segregation and linkage principles, which underpins key processes in genetics. This mechanism is extensively documented and reinforced by experimental data across multiple model systems and textbook discussions.

Ref: Hartl and Jones, Genetics: Analysis of Genes and Genomes, 8th Edition, Chapter 7, Mutation and DNA Repair, covers mutation types, repair pathways, chromosomal aberrations and genome stability relevant to human genetic disorders.

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