← Biology MCQ Sets

🧬 Set 3 – 100 MCQs

100 Biology questions • 30 Clinical/Scenario-based • Tap “Answer” for explanation.

Clinical / Scenario

Q1. A child has severe recurrent pyogenic infections, absent tonsils, and profoundly reduced all immunoglobulin classes. Which defect best explains the findings?

A. Failure of B-cell maturation due to BTK dysfunctionB. Defective NADPH oxidaseC. C5 deficiencyD. AIRE mutation
Correct: A. Failure of B-cell maturation due to BTK dysfunction

Explanation: BTK signaling is required for maturation of pre-B cells; failure produces X-linked agammaglobulinaemia.

Key Concept / Clinical Relevance: B-cell development and primary immunodeficiency

Clinical / Scenario

Q2. A newborn has persistent truncus arteriosus, hypocalcaemia and recurrent viral infections. Failure of which embryologic structure is most relevant?

A. First pharyngeal archB. Third and fourth pharyngeal pouchesC. Neural tubeD. Mesonephric duct
Correct: B. Third and fourth pharyngeal pouches

Explanation: Abnormal development of the third and fourth pharyngeal pouches causes thymic and parathyroid hypoplasia in 22q11.2 deletion syndrome.

Key Concept / Clinical Relevance: Embryology links thymic development with cellular immunity

Clinical / Scenario

Q3. A woman with a mitochondrial disorder has three children. Which inheritance pattern is most characteristic?

A. Affected fathers transmit to all daughtersB. Only sons are affectedC. Affected mothers may transmit to sons and daughtersD. Transmission requires paternal imprinting
Correct: C. Affected mothers may transmit to sons and daughters

Explanation: Mitochondria in the zygote are derived predominantly from the oocyte, producing maternal inheritance.

Key Concept / Clinical Relevance: Mitochondrial inheritance

Clinical / Scenario

Q4. A patient develops haemolysis after an oxidant drug. RBCs show Heinz bodies. Which pathway is most important for protection against this injury?

A. TCA cycle generating FADH2B. Beta oxidationC. Urea cycleD. Pentose phosphate pathway generating NADPH
Correct: D. Pentose phosphate pathway generating NADPH

Explanation: RBCs require pentose-phosphate-pathway NADPH to maintain reduced glutathione against oxidative stress.

Key Concept / Clinical Relevance: RBC redox biology

Clinical / Scenario

Q5. A tumour retains one normal RB allele and one inactivated allele. A second somatic event removes the remaining functional allele. Which principle is illustrated?

A. Two-hit hypothesisB. AnticipationC. CodominanceD. Genomic imprinting
Correct: A. Two-hit hypothesis

Explanation: Tumour-suppressor genes such as RB commonly require loss of both functional alleles at the cellular level.

Key Concept / Clinical Relevance: Tumour suppressor biology

Clinical / Scenario

Q6. A patient with septic shock has warm extremities early in the course. Which vascular change most directly contributes?

A. Marked increase in systemic vascular resistanceB. Generalized arteriolar vasodilationC. Loss of capillary permeabilityD. Selective coronary vasoconstriction
Correct: B. Generalized arteriolar vasodilation

Explanation: Inflammatory mediators including nitric oxide cause systemic vasodilation and reduced vascular resistance in distributive shock.

Key Concept / Clinical Relevance: Host response and vascular physiology in sepsis

Clinical / Scenario

Q7. A climber rapidly ascends to high altitude. Which immediate change promotes oxygen unloading to tissues before longer-term acclimatization?

A. Left shift from decreased 2,3-BPGB. Loss of haemoglobin cooperativityC. Right shift from increased 2,3-BPGD. Reduced ventilation
Correct: C. Right shift from increased 2,3-BPG

Explanation: Rising erythrocyte 2,3-BPG during acclimatization shifts the oxygen dissociation curve rightward and facilitates tissue unloading.

Key Concept / Clinical Relevance: Oxygen transport and adaptation

Clinical / Scenario

Q8. A patient has metabolic acidosis and begins deep rapid breathing. Which physiological response is being used?

A. Renal bicarbonate lossB. Increased fixed-acid productionC. Reduced alveolar ventilationD. Respiratory reduction of PaCO2
Correct: D. Respiratory reduction of PaCO2

Explanation: Hyperventilation lowers PaCO2 and provides rapid respiratory compensation for metabolic acidosis.

Key Concept / Clinical Relevance: Acid-base compensation

Clinical / Scenario

Q9. A boy has recurrent Neisseria meningitidis infections. Which immune defect is most strongly associated?

A. Terminal complement C5-C9 deficiencyB. C1 inhibitor deficiencyC. Selective IgA deficiencyD. Defective IL-2 receptor
Correct: A. Terminal complement C5-C9 deficiency

Explanation: The membrane attack complex formed by C5b-C9 is particularly important in defense against Neisseria.

Key Concept / Clinical Relevance: Complement and susceptibility to infection

Clinical / Scenario

Q10. A woman has an autosomal dominant disorder but no clinical manifestations despite carrying the pathogenic variant. Which concept explains this?

A. Variable expressivityB. Incomplete penetranceC. AnticipationD. Pleiotropy
Correct: B. Incomplete penetrance

Explanation: Incomplete penetrance means a disease-associated genotype does not always produce the phenotype.

Key Concept / Clinical Relevance: Genotype-phenotype relationships

Clinical / Scenario

Q11. A newborn becomes cyanotic shortly after birth because the ductus arteriosus closes. Which fetal shunt normally connects the pulmonary artery to the aorta?

A. Foramen ovaleB. Ductus venosusC. Ductus arteriosusD. Umbilical vein
Correct: C. Ductus arteriosus

Explanation: The ductus arteriosus diverts fetal right-ventricular output from the pulmonary artery into the aorta.

Key Concept / Clinical Relevance: Fetal circulation

Clinical / Scenario

Q12. A patient with severe hypoalbuminaemia develops generalized oedema. Which Starling-force change is primary?

A. Increased plasma oncotic pressureB. Reduced interstitial hydrostatic pressure onlyC. Increased lymphatic drainageD. Reduced plasma oncotic pressure
Correct: D. Reduced plasma oncotic pressure

Explanation: Loss of plasma albumin lowers capillary oncotic pressure and favors filtration into the interstitium.

Key Concept / Clinical Relevance: Capillary fluid exchange

Clinical / Scenario

Q13. An infant has failure to thrive, chronic diarrhoea and recurrent opportunistic infections with very low T- and B-cell function. Which diagnosis best fits?

A. SCIDB. Hereditary angioedemaC. Chronic granulomatous diseaseD. Selective IgA deficiency
Correct: A. SCID

Explanation: Severe combined immunodeficiency impairs both cellular and humoral adaptive immunity.

Key Concept / Clinical Relevance: Combined immunodeficiency

Clinical / Scenario

Q14. A patient receives a mismatched blood transfusion and develops rapid intravascular haemolysis. Which hypersensitivity mechanism predominates?

A. Type I IgE-mediatedB. Type II antibody-mediated cytotoxicityC. Type III immune-complexD. Type IV T-cell mediated
Correct: B. Type II antibody-mediated cytotoxicity

Explanation: Preformed antibodies bind RBC surface antigens and activate complement, a classic type II reaction.

Key Concept / Clinical Relevance: Hypersensitivity mechanisms

Clinical / Scenario

Q15. A child has a mutation that prevents lysosomal enzymes from receiving mannose-6-phosphate. Where are many of these enzymes incorrectly secreted?

A. NucleusB. Mitochondrial matrixC. Extracellular spaceD. Peroxisome
Correct: C. Extracellular space

Explanation: Without mannose-6-phosphate tagging in the Golgi, lysosomal hydrolases are misdirected and secreted outside the cell.

Key Concept / Clinical Relevance: Protein trafficking and lysosomal targeting

Clinical / Scenario

Q16. A patient has severe hypercholesterolaemia due to defective LDL receptors. Which cellular process is directly impaired?

A. Simple diffusionB. Gap-junction transportC. ExocytosisD. Receptor-mediated endocytosis
Correct: D. Receptor-mediated endocytosis

Explanation: LDL enters cells through clathrin-dependent receptor-mediated endocytosis after binding the LDL receptor.

Key Concept / Clinical Relevance: Membrane trafficking

Clinical / Scenario

Q17. A patient with carbon monoxide poisoning has normal PaO2 but severe tissue hypoxia. What best explains this?

A. CO reduces haemoglobin oxygen content and impairs unloadingB. CO lowers dissolved oxygen onlyC. CO increases haemoglobin synthesis immediatelyD. CO blocks pulmonary diffusion of nitrogen
Correct: A. CO reduces haemoglobin oxygen content and impairs unloading

Explanation: PaO2 reflects dissolved oxygen; CO reduces functional haemoglobin binding capacity and left-shifts remaining oxyhaemoglobin.

Key Concept / Clinical Relevance: Oxygen content versus partial pressure

Clinical / Scenario

Q18. A woman has recurrent miscarriages. Karyotyping shows a balanced Robertsonian translocation in her but she is phenotypically normal. Why?

A. All translocations silence every involved geneB. Balanced rearrangements can preserve overall essential genetic materialC. Robertsonian translocations occur only in mitochondrial DNAD. Balanced carriers are always mosaic
Correct: B. Balanced rearrangements can preserve overall essential genetic material

Explanation: Balanced carriers may have no major net gain or loss of essential DNA but can produce unbalanced gametes.

Key Concept / Clinical Relevance: Chromosomal rearrangements and reproductive risk

Clinical / Scenario

Q19. A patient with myasthenia gravis develops fatigable weakness. The pathogenic antibodies primarily reduce signaling at which structure?

A. Presynaptic voltage-gated calcium channel in all casesB. Muscle ryanodine receptorC. Postsynaptic nicotinic acetylcholine receptorD. Axonal sodium-potassium pump
Correct: C. Postsynaptic nicotinic acetylcholine receptor

Explanation: Most myasthenia gravis involves antibodies against postsynaptic nicotinic acetylcholine receptors, reducing neuromuscular transmission.

Key Concept / Clinical Relevance: Neuromuscular junction biology

Clinical / Scenario

Q20. A premature infant develops respiratory distress due to surfactant deficiency. Which physical consequence occurs in alveoli?

A. Reduced surface tensionB. Increased lung complianceC. Lower opening pressureD. Increased tendency of small alveoli to collapse
Correct: D. Increased tendency of small alveoli to collapse

Explanation: Surfactant lowers surface tension; deficiency increases collapsing pressure, especially in small alveoli, and reduces compliance.

Key Concept / Clinical Relevance: Laplace law and pulmonary surfactant

Clinical / Scenario

Q21. A patient with nephrogenic diabetes insipidus receives desmopressin without improvement. Which renal process remains defective?

A. ADH-dependent water permeability of collecting ductsB. Glucose filtrationC. Proximal sodium reabsorption entirelyD. Renin release from liver
Correct: A. ADH-dependent water permeability of collecting ducts

Explanation: Nephrogenic DI reflects renal resistance to ADH, so collecting-duct aquaporin-mediated water permeability fails to increase appropriately.

Key Concept / Clinical Relevance: ADH and collecting-duct physiology

Clinical / Scenario

Q22. A child has a frameshift mutation near the beginning of a coding sequence. Why is its effect often severe?

A. It affects only intronsB. It changes the reading frame for downstream codonsC. It always increases transcriptionD. It cannot introduce a stop codon
Correct: B. It changes the reading frame for downstream codons

Explanation: Insertions or deletions not divisible by three shift the reading frame and alter many downstream codons, often creating premature termination.

Key Concept / Clinical Relevance: Mutation consequences

Clinical / Scenario

Q23. A patient treated with a monoclonal antibody against a cell-surface receptor improves. What gives monoclonal antibodies their target specificity?

A. Random mixtures of immunoglobulinsB. Absence of variable regionsC. Identical antigen-binding regions recognizing a defined epitopeD. Binding only through Fc receptors
Correct: C. Identical antigen-binding regions recognizing a defined epitope

Explanation: A monoclonal antibody population derives from one clone and shares the same antigen-binding specificity.

Key Concept / Clinical Relevance: Biologic therapy and antibody structure

Clinical / Scenario

Q24. A patient with severe diarrhoea loses bicarbonate and develops metabolic acidosis. Which renal response is expected if renal function is intact?

A. Reduced ammonium excretionB. Increased urinary bicarbonate lossC. Suppression of glutamine metabolismD. Increased H+ secretion and new bicarbonate generation
Correct: D. Increased H+ secretion and new bicarbonate generation

Explanation: The kidney compensates by increasing acid excretion, including ammonium, and regenerating bicarbonate.

Key Concept / Clinical Relevance: Renal acid-base physiology

Clinical / Scenario

Q25. A child has delayed separation of the umbilical cord and recurrent bacterial infections with little pus. Which process is most likely defective?

A. Leukocyte adhesion and migrationB. Antibody class switchingC. Complement C3 synthesisD. T-cell receptor rearrangement
Correct: A. Leukocyte adhesion and migration

Explanation: Leukocyte adhesion deficiency impairs firm adhesion and transmigration of neutrophils into tissues.

Key Concept / Clinical Relevance: Leukocyte trafficking

Clinical / Scenario

Q26. A patient has macrocytic anaemia and neurologic deficits from vitamin B12 deficiency. Which biochemical process is particularly affected?

A. Glycogen phosphorylase onlyB. Methionine synthase and methylmalonyl-CoA metabolismC. Heme oxygenase onlyD. Na+/K+-ATPase
Correct: B. Methionine synthase and methylmalonyl-CoA metabolism

Explanation: Vitamin B12 is required for methionine synthase and methylmalonyl-CoA mutase reactions.

Key Concept / Clinical Relevance: Vitamin-dependent metabolism

Clinical / Scenario

Q27. A tumour biopsy shows high telomerase activity. What advantage does this provide to malignant cells?

A. Permanent arrest in G0B. Loss of DNA synthesisC. Unlimited maintenance of telomere length supporting replicative immortalityD. Immediate apoptosis
Correct: C. Unlimited maintenance of telomere length supporting replicative immortality

Explanation: Telomerase counteracts progressive telomere shortening and supports continued cell division.

Key Concept / Clinical Relevance: Hallmarks of cancer

Clinical / Scenario

Q28. A patient develops anaphylaxis minutes after a bee sting. Which event most directly causes the immediate reaction?

A. CD8 T-cell killingB. Immune-complex deposition over weeksC. Loss of central tolerance onlyD. IgE-mediated mast-cell degranulation
Correct: D. IgE-mediated mast-cell degranulation

Explanation: Allergen cross-linking of mast-cell-bound IgE rapidly triggers release of histamine and other mediators.

Key Concept / Clinical Relevance: Type I hypersensitivity

Clinical / Scenario

Q29. A fetus has an open neural tube defect. Failure of which developmental process occurred?

A. NeurulationB. Gastric rotationC. Septation of cloacaD. Implantation
Correct: A. Neurulation

Explanation: Neural tube defects result from failure of neural-fold fusion during neurulation.

Key Concept / Clinical Relevance: Embryologic mechanism of neural-tube defects

Clinical / Scenario

Q30. A patient has an inherited channelopathy in which a mutant subunit disrupts a multimeric ion channel assembled with normal subunits. Which genetic mechanism is illustrated?

A. Haploinsufficiency onlyB. Dominant-negative effectC. Genomic imprintingD. Uniparental disomy
Correct: B. Dominant-negative effect

Explanation: A dominant-negative protein interferes with the function of the normal protein, particularly in multimeric complexes.

Key Concept / Clinical Relevance: Molecular mechanisms of dominant disease

Q31. Which mechanism can produce different proteins from a single eukaryotic gene?

A. DNA replicationB. Centromere duplicationC. Alternative RNA splicingD. Telomere shortening
Correct: C. Alternative RNA splicing

Explanation: Alternative splicing combines exons in different patterns to generate multiple mRNA and protein isoforms.

Key Concept / Clinical Relevance: Post-transcriptional gene regulation

Q32. Which histone modification is most commonly associated with transcriptionally active chromatin?

A. Global histone deacetylationB. Centromeric condensationC. DNA depurinationD. Histone acetylation
Correct: D. Histone acetylation

Explanation: Histone acetylation generally loosens chromatin by reducing histone-DNA interaction and favors transcription.

Key Concept / Clinical Relevance: Epigenetic regulation

Q33. The wobble phenomenon primarily explains why:

A. one tRNA can recognize more than one synonymous codonB. one codon encodes several unrelated amino acidsC. DNA uses uracilD. translation occurs in the nucleus
Correct: A. one tRNA can recognize more than one synonymous codon

Explanation: Flexible pairing at the third codon position permits some tRNAs to recognize multiple synonymous codons.

Key Concept / Clinical Relevance: Genetic code and translation

Q34. Which DNA repair pathway corrects bulky helix-distorting lesions such as UV-induced pyrimidine dimers?

A. Mismatch repair onlyB. Nucleotide excision repairC. Nonhomologous end joining onlyD. Base excision of uracil only
Correct: B. Nucleotide excision repair

Explanation: Nucleotide excision repair removes oligonucleotide segments containing bulky DNA lesions.

Key Concept / Clinical Relevance: DNA repair pathways

Q35. During meiosis I, homologous chromosomes separate during:

A. Anaphase IIB. Metaphase IIC. Anaphase ID. Prophase II
Correct: C. Anaphase I

Explanation: Anaphase I separates homologous chromosomes; sister chromatids remain joined until anaphase II.

Key Concept / Clinical Relevance: Meiotic chromosome segregation

Q36. Which event is a major source of loss of heterozygosity in tumour cells?

A. Translation initiationB. mRNA cappingC. Ribosomal translocationD. Deletion or mitotic recombination affecting the remaining normal allele
Correct: D. Deletion or mitotic recombination affecting the remaining normal allele

Explanation: Loss of heterozygosity can remove a remaining functional tumour-suppressor allele.

Key Concept / Clinical Relevance: Cancer genetics

Q37. Which receptor class commonly signals through intrinsic tyrosine kinase activity?

A. Insulin receptorB. Nicotinic acetylcholine receptorC. GABA-A receptorD. Glucocorticoid receptor
Correct: A. Insulin receptor

Explanation: The insulin receptor is a receptor tyrosine kinase that autophosphorylates after ligand binding.

Key Concept / Clinical Relevance: Cell signaling

Q38. Activation of a Gs-coupled receptor most directly increases:

A. phospholipase C inhibitionB. adenylyl cyclase activity and cAMPC. nuclear DNA replicationD. chloride diffusion through CFTR directly
Correct: B. adenylyl cyclase activity and cAMP

Explanation: Gs activates adenylyl cyclase, raising intracellular cAMP and activating protein kinase A.

Key Concept / Clinical Relevance: Second-messenger signaling

Q39. Which organelle imports most of its proteins after translation in the cytosol?

A. NucleolusB. Golgi cisterna onlyC. MitochondrionD. Lysosomal lumen directly from nucleus
Correct: C. Mitochondrion

Explanation: Most mitochondrial proteins are nuclear encoded, synthesized on cytosolic ribosomes and imported through translocases.

Key Concept / Clinical Relevance: Organelle biogenesis

Q40. Ubiquitination most commonly targets short-lived intracellular proteins for degradation by the:

A. lysosomal acid pumpB. Golgi apparatusC. peroxisomal catalaseD. proteasome
Correct: D. proteasome

Explanation: Polyubiquitin chains commonly direct proteins to the 26S proteasome for ATP-dependent degradation.

Key Concept / Clinical Relevance: Protein quality control

Q41. Which extracellular-matrix protein provides high tensile strength to connective tissue?

A. CollagenB. Elastin onlyC. Laminin onlyD. Hyaluronan only
Correct: A. Collagen

Explanation: Collagen fibrils are the principal tensile-strength elements of many connective tissues.

Key Concept / Clinical Relevance: Extracellular matrix biology

Q42. Integrins primarily connect:

A. DNA to histonesB. extracellular matrix to the cytoskeletonC. ribosomes to lysosomesD. mitochondria to Golgi
Correct: B. extracellular matrix to the cytoskeleton

Explanation: Integrins are transmembrane adhesion receptors linking extracellular matrix proteins to cytoskeletal structures.

Key Concept / Clinical Relevance: Cell-matrix adhesion

Q43. Which epithelial junction creates the strongest seal against paracellular diffusion?

A. Gap junctionB. DesmosomeC. Tight junctionD. Hemidesmosome
Correct: C. Tight junction

Explanation: Tight junctions form occluding barriers regulating paracellular movement.

Key Concept / Clinical Relevance: Epithelial barrier function

Q44. Which collagen type is a major component of basement membranes?

A. Type IB. Type IIC. Type III onlyD. Type IV
Correct: D. Type IV

Explanation: Type IV collagen forms sheet-like networks characteristic of basement membranes.

Key Concept / Clinical Relevance: Histology and matrix

Q45. The Frank-Starling mechanism depends primarily on the relationship between:

A. initial myocardial fibre length and force of contractionB. heart rate and AV nodal delayC. arterial oxygen and ventilationD. plasma sodium and aldosterone
Correct: A. initial myocardial fibre length and force of contraction

Explanation: Within physiological limits, increased ventricular filling stretches sarcomeres and increases contraction force.

Key Concept / Clinical Relevance: Cardiac mechanics

Q46. Most filtered bicarbonate is reabsorbed in the:

A. thin descending limbB. proximal tubuleC. collecting duct onlyD. renal pelvis
Correct: B. proximal tubule

Explanation: The proximal tubule reabsorbs the majority of filtered bicarbonate through carbonic-anhydrase-dependent processes.

Key Concept / Clinical Relevance: Renal physiology

Q47. Which nephron segment is classically impermeable to water while actively reabsorbing Na+, K+ and Cl−?

A. Thin descending limbB. Proximal tubuleC. Thick ascending limbD. Inner medullary collecting duct with ADH
Correct: C. Thick ascending limb

Explanation: The thick ascending limb dilutes tubular fluid and contributes to the medullary concentration gradient while remaining water-impermeable.

Key Concept / Clinical Relevance: Countercurrent physiology

Q48. The Bohr effect describes decreased haemoglobin oxygen affinity caused by:

A. decreased temperature onlyB. decreased 2,3-BPGC. carbon monoxide removalD. increased H+ and CO2
Correct: D. increased H+ and CO2

Explanation: Higher CO2 and H+ stabilize deoxygenated haemoglobin and facilitate oxygen unloading.

Key Concept / Clinical Relevance: Oxygen dissociation physiology

Q49. Pulmonary surfactant stabilizes differently sized alveoli mainly by:

A. reducing surface tension, especially as alveoli become smallerB. raising pleural pressureC. increasing airway resistanceD. eliminating elastic recoil
Correct: A. reducing surface tension, especially as alveoli become smaller

Explanation: Surfactant molecules become more concentrated as alveoli shrink, lowering surface tension and reducing collapse tendency.

Key Concept / Clinical Relevance: Alveolar stability

Q50. Which coagulation factor is not synthesized in the liver?

A. FibrinogenB. von Willebrand factor predominantly from endothelium and megakaryocytesC. ProthrombinD. Factor X
Correct: B. von Willebrand factor predominantly from endothelium and megakaryocytes

Explanation: vWF is produced mainly by endothelial cells and megakaryocytes, unlike most coagulation factors synthesized hepatically.

Key Concept / Clinical Relevance: Haemostasis biology

Q51. Class switching of an activated B cell changes primarily the:

A. antigen-binding specificity of variable regionsB. light-chain variable sequence entirelyC. heavy-chain constant region and effector functionD. somatic chromosome number
Correct: C. heavy-chain constant region and effector function

Explanation: Class switching replaces the immunoglobulin heavy-chain constant region while retaining antigen specificity.

Key Concept / Clinical Relevance: Humoral immunity

Q52. Somatic hypermutation occurs primarily in:

A. T-cell receptor genes of mature erythrocytesB. mitochondrial rRNA onlyC. MHC genes in hepatocytesD. immunoglobulin variable-region genes of activated B cells
Correct: D. immunoglobulin variable-region genes of activated B cells

Explanation: Activated germinal-center B cells mutate immunoglobulin variable regions to permit affinity maturation.

Key Concept / Clinical Relevance: Affinity maturation

Q53. MHC class I molecules normally present peptides mainly to:

A. CD8+ T cellsB. CD4+ T cellsC. B cells through IgMD. neutrophils through Fc receptors
Correct: A. CD8+ T cells

Explanation: MHC I presents endogenous peptides to CD8+ cytotoxic T lymphocytes.

Key Concept / Clinical Relevance: Antigen presentation

Q54. MHC class II molecules normally present peptides mainly to:

A. CD8+ T cellsB. CD4+ T cellsC. erythrocytesD. platelets
Correct: B. CD4+ T cells

Explanation: Professional antigen-presenting cells use MHC II to present exogenous peptides to CD4+ helper T cells.

Key Concept / Clinical Relevance: Antigen presentation

Q55. Which immunoglobulin is transported across the placenta most efficiently?

A. IgMB. IgAC. IgGD. IgE
Correct: C. IgG

Explanation: FcRn-mediated transport allows maternal IgG to cross the placenta and provide passive neonatal immunity.

Key Concept / Clinical Relevance: Maternal-fetal immunity

Q56. A superantigen activates many T cells by cross-linking MHC II with the:

A. CD8 molecule onlyB. B-cell receptor Fc regionC. complement C9D. Vβ region of the T-cell receptor outside the peptide-binding groove
Correct: D. Vβ region of the T-cell receptor outside the peptide-binding groove

Explanation: Superantigens bypass conventional peptide specificity and activate large T-cell populations through MHC II and TCR Vβ binding.

Key Concept / Clinical Relevance: Microbial immune activation

Q57. Endotoxin from Gram-negative bacteria is principally associated with:

A. lipid A of lipopolysaccharideB. peptidoglycan tetrapeptideC. teichoic acidD. capsular polysaccharide only
Correct: A. lipid A of lipopolysaccharide

Explanation: Lipid A is the toxic component of LPS and potently activates innate inflammatory pathways.

Key Concept / Clinical Relevance: Bacterial pathogenesis

Q58. Horizontal transfer of bacterial DNA by a bacteriophage is called:

A. transformationB. transductionC. conjugationD. transposition
Correct: B. transduction

Explanation: Transduction is bacteriophage-mediated transfer of bacterial genetic material.

Key Concept / Clinical Relevance: Bacterial genetics

Q59. Compared with non-enveloped virions, disruption of which feature makes enveloped viruses especially vulnerable to detergents?

A. their capsid symmetryB. their viral polymeraseC. their lipid envelopeD. their genome segmentation
Correct: C. their lipid envelope

Explanation: Disruption of the lipid envelope by detergents or solvents can abolish viral infectivity.

Key Concept / Clinical Relevance: Viral structure and environmental stability

Q60. Which mechanism most directly explains antigenic shift in influenza A?

A. single point mutation onlyB. host DNA integrationC. ribosomal frameshifting onlyD. Reassortment of segmented viral genomes
Correct: D. Reassortment of segmented viral genomes

Explanation: Coinfection can allow reassortment of influenza A genome segments, producing abrupt major antigenic change.

Key Concept / Clinical Relevance: Viral evolution

Q61. Biofilm formation commonly increases bacterial persistence because the biofilm:

A. creates a protected community with altered physiology and reduced antimicrobial penetrationB. forces all cells into rapid divisionC. eliminates extracellular matrixD. prevents horizontal gene transfer
Correct: A. creates a protected community with altered physiology and reduced antimicrobial penetration

Explanation: Biofilms combine extracellular matrix, altered metabolic states and community behavior that enhance persistence.

Key Concept / Clinical Relevance: Microbial persistence

Q62. Which mechanism maintains central T-cell tolerance?

A. class switching in bone marrowB. Deletion of strongly self-reactive thymocytesC. neutrophil respiratory burstD. complement activation
Correct: B. Deletion of strongly self-reactive thymocytes

Explanation: Negative selection in the thymus removes many T cells that bind self antigens too strongly.

Key Concept / Clinical Relevance: Immune tolerance

Q63. Regulatory T cells characteristically help maintain peripheral tolerance through:

A. production of haemoglobinB. activation of complement membrane attack complexC. suppression of autoreactive immune responsesD. generation of bacterial capsules
Correct: C. suppression of autoreactive immune responses

Explanation: Tregs restrain immune activation through contact-dependent mechanisms and inhibitory cytokines such as IL-10 and TGF-beta.

Key Concept / Clinical Relevance: Peripheral tolerance

Q64. The primitive streak is most directly associated with:

A. neural crest migration onlyB. placental separationC. closure of ductus arteriosusD. gastrulation and germ-layer formation
Correct: D. gastrulation and germ-layer formation

Explanation: Cells migrate through the primitive streak during gastrulation to establish the three germ layers.

Key Concept / Clinical Relevance: Early embryogenesis

Q65. Neural crest cells contribute to all of the following EXCEPT:

A. hepatocytesB. melanocytesC. adrenal medullaD. peripheral ganglia
Correct: A. hepatocytes

Explanation: Hepatocytes are endoderm-derived; melanocytes, adrenal medulla and much of the peripheral nervous system have neural-crest origins.

Key Concept / Clinical Relevance: Embryologic derivatives

Q66. The fetal vessel carrying the highest oxygen content from placenta toward fetus is the:

A. umbilical arteryB. umbilical veinC. pulmonary arteryD. superior vena cava
Correct: B. umbilical vein

Explanation: The umbilical vein carries oxygenated placental blood to the fetus.

Key Concept / Clinical Relevance: Fetal circulation

Q67. The principal stimulus for ovulation is the:

A. FSH nadirB. progesterone withdrawal at midcycleC. LH surgeD. prolactin surge
Correct: C. LH surge

Explanation: Sustained high estradiol produces positive feedback leading to the midcycle LH surge and ovulation.

Key Concept / Clinical Relevance: Reproductive endocrinology

Q68. Which placental hormone helps maintain the corpus luteum in early pregnancy?

A. hPL onlyB. oxytocinC. FSHD. hCG
Correct: D. hCG

Explanation: hCG from syncytiotrophoblast rescues the corpus luteum and supports progesterone production early in pregnancy.

Key Concept / Clinical Relevance: Placental endocrinology

Q69. Hardy-Weinberg equilibrium requires all EXCEPT:

A. strong natural selectionB. random matingC. very large populationD. absence of migration
Correct: A. strong natural selection

Explanation: Hardy-Weinberg equilibrium assumes no selection, mutation or migration, random mating and a very large population.

Key Concept / Clinical Relevance: Population genetics

Q70. A population bottleneck can change allele frequencies primarily through:

A. directed mutationB. genetic driftC. meiotic drive in every survivorD. horizontal gene transfer
Correct: B. genetic drift

Explanation: A severe reduction in population size amplifies random sampling effects and genetic drift.

Key Concept / Clinical Relevance: Population genetics

Q71. The basic reproductive number R0 is best interpreted as the average number of secondary infections generated by:

A. all cases after herd immunityB. one vaccinated personC. one typical infectious case in a wholly susceptible populationD. one vector regardless of pathogen
Correct: C. one typical infectious case in a wholly susceptible population

Explanation: R0 describes transmission potential under specified conditions in a fully susceptible population.

Key Concept / Clinical Relevance: Infectious-disease ecology

Q72. Which ecological interaction benefits one species while harming the other?

A. MutualismB. CommensalismC. NeutralismD. Parasitism
Correct: D. Parasitism

Explanation: In parasitism, the parasite benefits at the expense of the host.

Key Concept / Clinical Relevance: Species interactions

Q73. Which process explains why a persistent contaminant may reach its highest concentration in a top predator?

A. increasing concentration of a persistent substance at higher trophic levelsB. rapid biodegradation in soilC. decreasing toxin concentration up a food chainD. movement of nitrogen into plants
Correct: A. increasing concentration of a persistent substance at higher trophic levels

Explanation: Persistent contaminants can accumulate and become more concentrated in organisms at successive trophic levels.

Key Concept / Clinical Relevance: Environmental biology

Q74. Which molecular technique amplifies a defined DNA sequence through repeated cycles of denaturation, annealing and extension?

A. Western blotB. PCRC. ELISAD. Flow cytometry
Correct: B. PCR

Explanation: PCR exponentially amplifies a target DNA region using primers and a thermostable DNA polymerase.

Key Concept / Clinical Relevance: Molecular diagnostics

Q75. Reverse-transcription PCR differs from conventional DNA PCR because it begins with:

A. protein converted to RNAB. lipid converted to DNAC. RNA converted to complementary DNAD. antibody converted to cDNA
Correct: C. RNA converted to complementary DNA

Explanation: Reverse transcriptase first generates cDNA from an RNA template before amplification.

Key Concept / Clinical Relevance: RNA detection

Q76. In quantitative PCR, a lower threshold cycle generally indicates:

A. less starting target in all assaysB. complete absence of amplificationC. lower primer specificity necessarilyD. more starting target nucleic acid
Correct: D. more starting target nucleic acid

Explanation: When assay efficiency is comparable, abundant starting template reaches the fluorescence threshold in fewer cycles.

Key Concept / Clinical Relevance: qPCR interpretation

Q77. Next-generation sequencing differs from traditional Sanger sequencing chiefly by enabling:

A. massively parallel sequencing of many DNA fragmentsB. protein sequencing without nucleic acidsC. direct microscopy of chromosomes onlyD. PCR without primers
Correct: A. massively parallel sequencing of many DNA fragments

Explanation: NGS platforms sequence very large numbers of fragments in parallel, increasing throughput.

Key Concept / Clinical Relevance: Genomic technology

Q78. CRISPR-Cas9 target specificity is primarily directed by:

A. random histone acetylationB. guide RNA base pairing with target DNA adjacent to an appropriate PAMC. ribosomal RNAD. antibody Fc binding
Correct: B. guide RNA base pairing with target DNA adjacent to an appropriate PAM

Explanation: The guide RNA directs Cas9 to complementary DNA, while PAM recognition is also required for cleavage.

Key Concept / Clinical Relevance: Genome editing

Q79. A loss-of-function variant introduced by CRISPR is often generated through error-prone repair by:

A. homologous recombination in every cellB. RNA splicingC. nonhomologous end joiningD. base excision only
Correct: C. nonhomologous end joining

Explanation: Double-strand breaks repaired by NHEJ often acquire small insertions/deletions that disrupt coding sequence.

Key Concept / Clinical Relevance: Genome editing repair

Q80. RNA interference reduces gene expression primarily through:

A. irreversible deletion of chromosomesB. translation of intronsC. activation of telomeraseD. sequence-specific targeting of mRNA
Correct: D. sequence-specific targeting of mRNA

Explanation: Small RNAs guide silencing complexes to complementary transcripts, causing degradation or translational repression.

Key Concept / Clinical Relevance: Post-transcriptional gene silencing

Q81. A liquid biopsy most commonly seeks tumour-derived material such as:

A. circulating tumour DNAB. bone collagen onlyC. alveolar surfactantD. CSF myelin only
Correct: A. circulating tumour DNA

Explanation: Circulating tumour DNA can provide molecular information about a cancer through a blood sample.

Key Concept / Clinical Relevance: Molecular oncology

Q82. A predictive biomarker is most useful for estimating:

A. anatomic location aloneB. likelihood of response to a particular therapyC. patient ageD. laboratory reference range
Correct: B. likelihood of response to a particular therapy

Explanation: Predictive biomarkers help identify patients more likely to benefit from a specific treatment.

Key Concept / Clinical Relevance: Precision medicine

Q83. Single-cell RNA sequencing is especially useful because it can reveal:

A. only average expression across an entire tissueB. protein structure without RNAC. gene-expression heterogeneity among individual cellsD. chromosome number without sequencing
Correct: C. gene-expression heterogeneity among individual cells

Explanation: Single-cell RNA-seq resolves transcriptional differences that bulk tissue measurements can obscure.

Key Concept / Clinical Relevance: Single-cell biology

Q84. Organoids are best described as:

A. fully formed transplanted human organsB. single purified proteinsC. bacterial colonies onlyD. three-dimensional cell-derived structures that reproduce selected features of an organ
Correct: D. three-dimensional cell-derived structures that reproduce selected features of an organ

Explanation: Organoids self-organize in 3D and model aspects of tissue architecture and function.

Key Concept / Clinical Relevance: Regenerative and translational biology

Q85. A major advantage of induced pluripotent stem cells is that differentiated somatic cells can be:

A. reprogrammed toward a pluripotent stateB. converted directly into bacteriaC. made genetically identical to every personD. prevented from expressing any genes
Correct: A. reprogrammed toward a pluripotent state

Explanation: Defined reprogramming factors can return differentiated cells to a pluripotent-like state.

Key Concept / Clinical Relevance: Stem-cell biology

Q86. Which feature distinguishes apoptosis from necrotic cell death most reliably?

A. universal membrane rupture at onsetB. caspase-mediated controlled dismantling with limited inflammationC. always severe surrounding inflammationD. ATP-independent swelling only
Correct: B. caspase-mediated controlled dismantling with limited inflammation

Explanation: Classical apoptosis is an organized, caspase-driven process with membrane integrity maintained until late stages.

Key Concept / Clinical Relevance: Programmed cell death

Q87. The intrinsic apoptotic pathway is closely regulated by proteins of the:

A. collagen familyB. globin familyC. BCL-2 familyD. integrin alpha-only family
Correct: C. BCL-2 family

Explanation: Pro- and anti-apoptotic BCL-2 family proteins regulate mitochondrial outer-membrane permeabilization.

Key Concept / Clinical Relevance: Apoptosis regulation

Q88. p53 activation after severe DNA damage can promote:

A. unrestricted S-phase entryB. telomerase activation in all cellsC. loss of checkpointsD. cell-cycle arrest, DNA repair or apoptosis
Correct: D. cell-cycle arrest, DNA repair or apoptosis

Explanation: p53 coordinates stress responses that prevent propagation of damaged genomes.

Key Concept / Clinical Relevance: Genome integrity

Q89. Which hallmark enables malignant cells to continue dividing despite progressive telomere shortening?

A. replicative immortalityB. contact inhibitionC. terminal differentiationD. senescence
Correct: A. replicative immortality

Explanation: Cancer cells often maintain telomeres, commonly through telomerase, enabling sustained proliferation.

Key Concept / Clinical Relevance: Cancer cell biology

Q90. Epithelial-mesenchymal transition can facilitate cancer progression by increasing:

A. tight-junction stability onlyB. cell motility and invasive behaviorC. terminal keratinizationD. antigen specificity
Correct: B. cell motility and invasive behavior

Explanation: EMT-like programs reduce epithelial adhesion and increase migratory/invasive properties.

Key Concept / Clinical Relevance: Invasion and metastasis

Q91. Angiogenesis in growing tumours is strongly promoted by:

A. erythropoietin onlyB. insulin in all tumoursC. VEGFD. C3 convertase
Correct: C. VEGF

Explanation: Hypoxia and oncogenic signaling can increase VEGF, promoting formation of tumour-associated blood vessels.

Key Concept / Clinical Relevance: Tumour microenvironment

Q92. The Warburg effect describes the tendency of many cancer cells to favor:

A. fatty-acid oxidation exclusivelyB. urea synthesisC. absence of glucose uptakeD. aerobic glycolysis despite available oxygen
Correct: D. aerobic glycolysis despite available oxygen

Explanation: Many cancers exhibit high glucose uptake and lactate production even under oxygenated conditions.

Key Concept / Clinical Relevance: Cancer metabolism

Q93. Which omics field studies the complete set of RNA transcripts in a cell or tissue?

A. TranscriptomicsB. ProteomicsC. MetabolomicsD. Epigenetics only
Correct: A. Transcriptomics

Explanation: Transcriptomics characterizes RNA expression profiles across genes.

Key Concept / Clinical Relevance: Omics terminology

Q94. Proteomics is particularly complicated by the fact that:

A. proteins contain only four basesB. one gene can yield multiple protein isoforms and post-translational modificationsC. all proteins have identical abundanceD. proteins cannot be modified
Correct: B. one gene can yield multiple protein isoforms and post-translational modifications

Explanation: Alternative splicing and post-translational modification expand proteomic complexity beyond gene count.

Key Concept / Clinical Relevance: Proteome complexity

Q95. Metabolomics most directly examines:

A. chromosome bandingB. antibody gene rearrangement onlyC. small-molecule metabolites in biological systemsD. tissue anatomy
Correct: C. small-molecule metabolites in biological systems

Explanation: Metabolomics profiles small molecules that reflect ongoing biochemical activity.

Key Concept / Clinical Relevance: Systems biology

Q96. Pharmacogenomics aims primarily to relate:

A. blood group to climateB. microbiome to chromosome count onlyC. histology to bone lengthD. genetic variation to drug response
Correct: D. genetic variation to drug response

Explanation: Pharmacogenomics studies how genomic variation influences efficacy, dosing and adverse drug reactions.

Key Concept / Clinical Relevance: Precision therapeutics

Q97. A theranostic strategy combines:

A. diagnostic targeting information with a matched therapeutic approachB. two unrelated screening testsC. surgery and histology onlyD. vaccination and sanitation
Correct: A. diagnostic targeting information with a matched therapeutic approach

Explanation: Theranostics links molecular diagnosis or targeting with a corresponding therapy, often using related ligands or targets.

Key Concept / Clinical Relevance: Precision medicine

Q98. CAR-T cells are engineered primarily to:

A. produce antibioticsB. recognize selected surface antigens on target cells through a synthetic receptorC. replace erythrocytesD. synthesize complement in the liver
Correct: B. recognize selected surface antigens on target cells through a synthetic receptor

Explanation: Chimeric antigen receptors redirect T cells toward specified cell-surface antigens without conventional MHC recognition.

Key Concept / Clinical Relevance: Cellular immunotherapy

Q99. An antibody-drug conjugate is designed to:

A. increase nonspecific drug distributionB. remove all Fc functions necessarilyC. deliver a cytotoxic payload preferentially to antigen-expressing cellsD. replace DNA repair
Correct: C. deliver a cytotoxic payload preferentially to antigen-expressing cells

Explanation: The antibody provides target recognition while the linked payload delivers cytotoxic activity to selected cells.

Key Concept / Clinical Relevance: Targeted biologic therapy

Q100. Which feature most strongly supports a causal role for natural selection in antibiotic resistance?

A. bacteria mutate because they need resistanceB. all exposed bacteria acquire identical mutationsC. antibiotics direct specific adaptive DNA changesD. pre-existing heritable variants become enriched under antibiotic pressure
Correct: D. pre-existing heritable variants become enriched under antibiotic pressure

Explanation: Selection changes the frequency of heritable resistance variants; it does not purposefully create mutations in response to need.

Key Concept / Clinical Relevance: Evolution of antimicrobial resistance