🧬 Set 2 – 100 MCQs

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

Q1. A loss-of-function mutation in a tumour-suppressor gene most directly promotes cancer by:

A. removing a restraint on cell proliferationB. constitutively activating every receptorC. preventing all DNA replicationD. increasing antigen presentation

Correct: A. removing a restraint on cell proliferation

Explanation: removing a restraint on cell proliferation best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q2. Which event creates the greatest genetic variation during meiosis I?

A. DNA replication in S phaseB. crossing over between homologous chromosomesC. separation of sister chromatidsD. cytokinesis

Correct: B. crossing over between homologous chromosomes

Explanation: Meiosis includes two divisions after one DNA replication, reducing chromosome number and generating variation.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q3. A 22-year-old man has recurrent infections with catalase-positive organisms. A neutrophil oxidative-burst test is abnormal. Which cellular process is most likely defective?

A. antibody class switchingB. MHC-I synthesisC. generation of reactive oxygen species by NADPH oxidaseD. complement C1 activation

Correct: C. generation of reactive oxygen species by NADPH oxidase

Explanation: Haemoglobin reversibly binds oxygen, allowing efficient oxygen carriage in blood and unloading in tissues.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q4. A competitive enzyme inhibitor typically causes:

A. decreased Km and decreased VmaxB. unchanged Km with decreased VmaxC. increased Vmax with unchanged KmD. increased apparent Km with unchanged Vmax

Correct: D. increased apparent Km with unchanged Vmax

Explanation: increased apparent Km with unchanged Vmax best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q5. The Na+/K+-ATPase is electrogenic because each cycle:

A. exports 3 Na+ and imports 2 K+B. exports 2 Na+ and imports 3 K+C. moves equal positive charge in both directionsD. transports only K+

Correct: A. exports 3 Na+ and imports 2 K+

Explanation: exports 3 Na+ and imports 2 K+ best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q6. A child develops severe diarrhoea and receives a markedly hypotonic fluid. Red cells placed in a similarly hypotonic solution would initially:

A. shrink because water exitsB. swell as water enters by osmosisC. remain unchanged regardless of tonicityD. lose all membrane proteins

Correct: B. swell as water enters by osmosis

Explanation: Osmosis is water movement across a selectively permeable membrane toward higher effective solute concentration.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q7. Which junction provides the strongest mechanical linkage between adjacent epithelial cells?

A. gap junctionB. tight junction onlyC. desmosomeD. chemical synapse

Correct: C. desmosome

Explanation: desmosome best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q8. A receptor that directly alters gene transcription after ligand binding is most characteristic of:

A. catecholaminesB. peptide hormonesC. acetylcholine at nicotinic receptorsD. steroid hormones

Correct: D. steroid hormones

Explanation: Transcription uses DNA as a template to synthesize RNA.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q9. A patient with familial hypercholesterolaemia has defective LDL-receptor internalisation. Which transport process is affected?

A. receptor-mediated endocytosisB. simple diffusionC. osmosisD. gap-junction transport

Correct: A. receptor-mediated endocytosis

Explanation: receptor-mediated endocytosis best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q10. The major force favouring glomerular filtration is:

A. Bowman space hydrostatic pressureB. glomerular capillary hydrostatic pressureC. plasma oncotic pressureD. interstitial oncotic pressure

Correct: B. glomerular capillary hydrostatic pressure

Explanation: glomerular capillary hydrostatic pressure best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q11. A rightward shift of the oxyhaemoglobin dissociation curve is promoted by:

A. decreased temperatureB. decreased 2,3-BPGC. increased H+ concentrationD. fetal haemoglobin

Correct: C. increased H+ concentration

Explanation: Haemoglobin reversibly binds oxygen, allowing efficient oxygen carriage in blood and unloading in tissues.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q12. Which immunoglobulin crosses the placenta most efficiently?

A. IgMB. IgAC. IgED. IgG

Correct: D. IgG

Explanation: IgG is the immunoglobulin class efficiently transported across the placenta, providing passive fetal immunity.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q13. A woman with a mitochondrial disorder asks about transmission. Which pattern is most characteristic?

A. an affected mother may transmit the mutation to sons and daughtersB. an affected father transmits it to all sonsC. only daughters can inherit mitochondrial DNAD. paternal transmission is obligatory

Correct: A. an affected mother may transmit the mutation to sons and daughters

Explanation: Mitochondria generate most aerobic ATP through the TCA cycle and oxidative phosphorylation.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q14. MHC class I molecules normally present endogenous peptides to:

A. CD4+ T lymphocytesB. CD8+ T lymphocytesC. B lymphocytes onlyD. neutrophils

Correct: B. CD8+ T lymphocytes

Explanation: CD8+ T lymphocytes best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q15. The classical complement pathway is most directly initiated by:

A. mannose residues aloneB. spontaneous C3 hydrolysisC. antigen-antibody complexesD. TLR4 activation

Correct: C. antigen-antibody complexes

Explanation: B lymphocytes can differentiate into plasma cells that secrete antibodies.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q16. A couple are both carriers of the same autosomal recessive disorder. What is the probability that each pregnancy will produce an affected child?

A. 0%B. 50%C. 75%D. 25%

Correct: D. 25%

Explanation: 25% best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q17. Type IV hypersensitivity is primarily mediated by:

A. T lymphocytesB. IgE and mast cellsC. IgG against cell surfacesD. circulating immune complexes

Correct: A. T lymphocytes

Explanation: T lymphocytes best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q18. Which bacterial mechanism can transfer plasmids through direct cell-to-cell contact?

A. transductionB. conjugationC. transformation onlyD. binary fission

Correct: B. conjugation

Explanation: T lymphocytes are central to cell-mediated immunity; CD8 cells kill infected cells and CD4 cells coordinate immune responses.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q19. A boy has haemophilia A, while his father is unaffected. The inheritance pattern is most consistent with:

A. Y-linked inheritanceB. mitochondrial inheritanceC. X-linked recessive inheritanceD. autosomal dominant inheritance

Correct: C. X-linked recessive inheritance

Explanation: X-linked recessive inheritance best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q20. An enveloped virus is generally more susceptible than a non-enveloped virus to:

A. ribosomal inhibitorsB. beta-lactam antibioticsC. folate antagonistsD. detergents and lipid solvents

Correct: D. detergents and lipid solvents

Explanation: detergents and lipid solvents best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q21. The normal microbiome can protect the host mainly through:

A. colonisation resistance and metabolic competitionB. eliminating all innate immunityC. preventing antibody formationD. blocking epithelial turnover

Correct: A. colonisation resistance and metabolic competition

Explanation: colonisation resistance and metabolic competition best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q22. Hardy-Weinberg equilibrium assumes:

A. strong selection and small population sizeB. random mating in a large population without major evolutionary forcesC. continuous migration and mutationD. assortative mating

Correct: B. random mating in a large population without major evolutionary forces

Explanation: Hardy–Weinberg equilibrium relates allele and genotype frequencies in an ideal non-evolving population.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q23. A patient has trisomy 21 caused by meiotic nondisjunction. Nondisjunction means failure of:

A. DNA to contain thymineB. mRNA to leave the nucleusC. chromosomes or chromatids to segregate normallyD. ribosomes to bind tRNA

Correct: C. chromosomes or chromatids to segregate normally

Explanation: chromosomes or chromatids to segregate normally best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q24. Genetic drift has the greatest effect in:

A. very large randomly mating populationsB. populations with no allele variationC. only polyploid organismsD. small populations

Correct: D. small populations

Explanation: small populations best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q25. Mitochondrial inheritance typically shows transmission from:

A. affected mothers to sons and daughtersB. affected fathers to all sonsC. affected fathers to all daughtersD. males only

Correct: A. affected mothers to sons and daughters

Explanation: Mitochondria generate most aerobic ATP through the TCA cycle and oxidative phosphorylation.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q26. A tumour biopsy shows loss of both functional RB alleles. The immediate biological consequence is impaired control of the:

A. lysosomal pHB. G1-to-S cell-cycle checkpointC. Golgi glycosylation onlyD. mitochondrial genetic code

Correct: B. G1-to-S cell-cycle checkpoint

Explanation: G1-to-S cell-cycle checkpoint best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q27. Genomic imprinting refers to gene expression that depends on:

A. the chromosome size onlyB. the number of ribosomesC. the parent of origin of an alleleD. the cell membrane potential

Correct: C. the parent of origin of an allele

Explanation: the parent of origin of an allele best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q28. A nonsense mutation results in:

A. replacement of one amino acid onlyB. addition of a whole chromosomeC. failure of DNA replication initiationD. premature termination of translation

Correct: D. premature termination of translation

Explanation: Translation occurs on ribosomes, where mRNA directs amino-acid sequence.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q29. A patient receives a drug that competitively inhibits an enzyme. Increasing substrate concentration restores near-normal reaction velocity. This is because competitive inhibition:

A. can be overcome by sufficiently high substrate concentrationB. irreversibly destroys the enzymeC. always lowers VmaxD. removes the active site permanently

Correct: A. can be overcome by sufficiently high substrate concentration

Explanation: can be overcome by sufficiently high substrate concentration best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q30. Telomerase activity is characteristically increased in many:

A. mature erythrocytesB. malignant cellsC. terminally differentiated skeletal muscle fibres onlyD. platelets

Correct: B. malignant cells

Explanation: T lymphocytes are central to cell-mediated immunity; CD8 cells kill infected cells and CD4 cells coordinate immune responses.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q31. PCR requires a thermostable DNA polymerase primarily because:

A. RNA must be translated during each cycleB. primers are proteinsC. repeated high-temperature denaturation would inactivate ordinary polymerasesD. DNA cannot melt below 100°C

Correct: C. repeated high-temperature denaturation would inactivate ordinary polymerases

Explanation: PCR amplifies a selected nucleic-acid target through repeated cycles of denaturation, primer annealing and extension.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q32. Reverse-transcription PCR begins by converting:

A. protein into RNAB. DNA into lipidC. RNA directly into proteinD. RNA into complementary DNA

Correct: D. RNA into complementary DNA

Explanation: Transcription uses DNA as a template to synthesize RNA.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q33. A patient with severe metabolic acidosis hyperventilates. The respiratory response helps compensate by:

A. lowering arterial CO2B. raising arterial CO2C. retaining volatile acidD. stopping bicarbonate buffering

Correct: A. lowering arterial CO2

Explanation: lowering arterial CO2 best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q34. CRISPR-Cas9 target specificity is principally directed by:

A. antibody bindingB. guide RNA base pairingC. ribosomal RNA methylationD. ATP concentration alone

Correct: B. guide RNA base pairing

Explanation: CRISPR systems use guide RNA to direct a nuclease to a complementary nucleic-acid sequence for targeted editing.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q35. Apoptosis differs from necrosis because apoptosis usually:

A. causes marked early cell swelling and ruptureB. always triggers intense inflammationC. occurs with membrane integrity preserved until late stagesD. is caused only by infection

Correct: C. occurs with membrane integrity preserved until late stages

Explanation: Apoptosis is regulated cell death with cell shrinkage and fragmentation, usually without the inflammatory leakage typical of necrosis.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q36. A climber rapidly ascends to high altitude. The earliest major stimulus increasing ventilation is:

A. increased CSF bicarbonateB. high arterial PO2C. suppression of carotid bodiesD. reduced arterial PO2 sensed by peripheral chemoreceptors

Correct: D. reduced arterial PO2 sensed by peripheral chemoreceptors

Explanation: reduced arterial PO2 sensed by peripheral chemoreceptors best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q37. A cell undergoing hypertrophy shows:

A. increased cell sizeB. increased cell number onlyC. conversion to another mature cell typeD. irreversible nuclear fragmentation

Correct: A. increased cell size

Explanation: increased cell size best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q38. Metaplasia is best defined as:

A. uncontrolled malignant invasionB. replacement of one differentiated cell type by anotherC. increase in cell sizeD. programmed cell death

Correct: B. replacement of one differentiated cell type by another

Explanation: replacement of one differentiated cell type by another best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q39. A patient with pulmonary fibrosis has impaired oxygen transfer despite ventilation. Which property is most directly reduced?

A. haemoglobin synthesis in marrowB. SA-node automaticityC. diffusing capacity across the alveolar-capillary membraneD. glomerular filtration fraction

Correct: C. diffusing capacity across the alveolar-capillary membrane

Explanation: Alveoli provide a very large, thin surface for diffusion of respiratory gases between air and pulmonary capillary blood.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q40. The principal extracellular protein providing tensile strength in connective tissue is:

A. glycogenB. actinC. haemoglobinD. collagen

Correct: D. collagen

Explanation: collagen best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q41. Osteoclasts primarily function to:

A. resorb boneB. synthesize osteoidC. produce antibodiesD. form myelin

Correct: A. resorb bone

Explanation: resorb bone best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q42. Cardiac muscle cells are electrically coupled mainly through:

A. tight junctions onlyB. gap junctions in intercalated discsC. myelin sheathsD. basement membrane pores

Correct: B. gap junctions in intercalated discs

Explanation: gap junctions in intercalated discs best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q43. A premature infant develops respiratory distress because of surfactant deficiency. The major physical consequence is:

A. decreased elastic recoil to zeroB. excessive haemoglobin affinityC. increased alveolar surface tension and tendency to collapseD. increased renal filtration

Correct: C. increased alveolar surface tension and tendency to collapse

Explanation: Alveoli provide a very large, thin surface for diffusion of respiratory gases between air and pulmonary capillary blood.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q44. The rapid depolarisation phase of a typical neuronal action potential is mainly due to:

A. K+ influxB. Cl− effluxC. Ca2+ extrusionD. Na+ influx

Correct: D. Na+ influx

Explanation: Na+ influx best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q45. Saltatory conduction occurs because action potentials are regenerated mainly at:

A. nodes of RanvierB. Schwann-cell nucleiC. dendritic spinesD. neuromuscular end plates

Correct: A. nodes of Ranvier

Explanation: nodes of Ranvier best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q46. A dehydrated patient has increased plasma osmolality. Which hormone rises to conserve free water?

A. ANPB. ADHC. insulinD. calcitonin

Correct: B. ADH

Explanation: ADH best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q47. At the skeletal neuromuscular junction, the neurotransmitter is:

A. dopamineB. GABAC. acetylcholineD. serotonin

Correct: C. acetylcholine

Explanation: acetylcholine best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q48. The Frank-Starling mechanism states that, within physiological limits, increased ventricular filling:

A. always decreases stroke volumeB. stops sympathetic activityC. reduces myocardial fibre lengthD. increases force of contraction

Correct: D. increases force of contraction

Explanation: increases force of contraction best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q49. A patient with primary adrenal insufficiency has reduced aldosterone activity. Which electrolyte pattern is biologically expected?

A. tendency to hyperkalaemiaB. tendency to hypokalaemia from excess K+ secretionC. isolated hypercalcaemia onlyD. severe hyperphosphataemia in every case

Correct: A. tendency to hyperkalaemia

Explanation: tendency to hyperkalaemia best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q50. The dominant pacemaker of the normal heart is the:

A. atrioventricular nodeB. sinoatrial nodeC. Purkinje networkD. bundle of His

Correct: B. sinoatrial node

Explanation: sinoatrial node best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q51. Most carbon dioxide in blood is transported as:

A. dissolved CO2 onlyB. carbaminohaemoglobin onlyC. bicarbonateD. carbonic acid only

Correct: C. bicarbonate

Explanation: bicarbonate best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q52. Pulmonary surfactant primarily:

A. increases airway resistanceB. raises pleural pressureC. prevents oxygen diffusionD. reduces alveolar surface tension

Correct: D. reduces alveolar surface tension

Explanation: Alveoli provide a very large, thin surface for diffusion of respiratory gases between air and pulmonary capillary blood.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q53. A patient with vomiting develops metabolic alkalosis. Which renal process helps maintain the alkalosis when volume depleted?

A. increased sodium reabsorption coupled to H+ secretionB. complete suppression of aldosteroneC. obligatory bicarbonate excretion regardless of volumeD. loss of all proximal sodium transport

Correct: A. increased sodium reabsorption coupled to H+ secretion

Explanation: increased sodium reabsorption coupled to H+ secretion best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q54. ADH increases water reabsorption primarily in the:

A. proximal tubule onlyB. collecting ductsC. thin ascending limbD. glomerulus

Correct: B. collecting ducts

Explanation: collecting ducts best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q55. Aldosterone promotes:

A. Na+ excretion and K+ retentionB. glucose secretionC. Na+ reabsorption and K+ secretionD. bicarbonate loss only

Correct: C. Na+ reabsorption and K+ secretion

Explanation: Na+ reabsorption and K+ secretion best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q56. A patient has macrocytic anaemia after terminal ileal resection. Deficiency of which absorbed nutrient is most likely?

A. vitamin CB. vitamin K onlyC. sodiumD. vitamin B12

Correct: D. vitamin B12

Explanation: vitamin B12 best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q57. The major extracellular buffer system is:

A. bicarbonate-carbonic acidB. DNA-phosphate onlyC. creatine-phosphocreatineD. bilirubin-albumin

Correct: A. bicarbonate-carbonic acid

Explanation: bicarbonate-carbonic acid best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q58. Most nutrient absorption occurs in the:

A. oesophagusB. small intestineC. stomachD. colon

Correct: B. small intestine

Explanation: small intestine best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q59. A patient develops urticaria and wheeze minutes after a drug injection. The mechanism most consistent with this rapid reaction is:

A. CD8-mediated cytotoxicity developing over daysB. immune-complex deposition onlyC. IgE-mediated mast-cell degranulationD. delayed macrophage activation

Correct: C. IgE-mediated mast-cell degranulation

Explanation: IgE-mediated mast-cell degranulation best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q60. Intrinsic factor is required for intestinal absorption of:

A. vitamin CB. iron in all formsC. folateD. vitamin B12

Correct: D. vitamin B12

Explanation: vitamin B12 best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q61. Insulin lowers plasma glucose partly by promoting:

A. GLUT4 translocation in skeletal muscle and adipose tissueB. hepatic glycogenolysisC. adipose lipolysisD. renal gluconeogenesis

Correct: A. GLUT4 translocation in skeletal muscle and adipose tissue

Explanation: Insulin promotes glucose uptake and storage and suppresses hepatic glucose production, lowering plasma glucose.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q62. Parathyroid hormone tends to:

A. decrease serum calciumB. increase serum calciumC. decrease renal calcium reabsorptionD. block vitamin D activation

Correct: B. increase serum calcium

Explanation: increase serum calcium best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q63. A patient develops haemolysis after antibodies bind directly to red-cell surface antigens. This is an example of:

A. type I hypersensitivityB. type III hypersensitivityC. type II hypersensitivityD. type IV hypersensitivity

Correct: C. type II hypersensitivity

Explanation: type II hypersensitivity best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q64. The LH surge directly triggers:

A. implantationB. menstruationC. spermatogenesisD. ovulation

Correct: D. ovulation

Explanation: IgG is the immunoglobulin class efficiently transported across the placenta, providing passive fetal immunity.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q65. The trophoblast contributes directly to formation of the:

A. placentaB. neural tubeC. somitesD. notochord only

Correct: A. placenta

Explanation: IgG is the immunoglobulin class efficiently transported across the placenta, providing passive fetal immunity.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q66. A tuberculin skin test becomes indurated 48–72 hours after injection. The response is mainly mediated by:

A. IgE and eosinophils within minutesB. sensitised T lymphocytes and macrophagesC. preformed IgM onlyD. mast-cell histamine alone

Correct: B. sensitised T lymphocytes and macrophages

Explanation: sensitised T lymphocytes and macrophages best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q67. The neural tube gives rise primarily to the:

A. skeletal muscleB. intestinal epitheliumC. central nervous systemD. adrenal cortex

Correct: C. central nervous system

Explanation: central nervous system best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q68. Fetal haemoglobin has higher oxygen affinity than adult haemoglobin partly because it:

A. contains iron in ferric formB. cannot bind carbon dioxideC. has no globin chainsD. binds 2,3-BPG less avidly

Correct: D. binds 2,3-BPG less avidly

Explanation: Haemoglobin reversibly binds oxygen, allowing efficient oxygen carriage in blood and unloading in tissues.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q69. An unvaccinated child recovers from measles and is protected on re-exposure years later. The key biological basis is:

A. long-lived memory lymphocytesB. persistent feverC. permanent neutrophiliaD. loss of antigen specificity

Correct: A. long-lived memory lymphocytes

Explanation: long-lived memory lymphocytes best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q70. Which is a major function of the placenta?

A. direct mixing of maternal and fetal bloodB. maternal-fetal exchange and endocrine supportC. production of fetal neuronsD. formation of maternal erythrocytes

Correct: B. maternal-fetal exchange and endocrine support

Explanation: IgG is the immunoglobulin class efficiently transported across the placenta, providing passive fetal immunity.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q71. An autosomal recessive disorder is more likely to appear in children of:

A. an affected father and unrelated non-carrier mother onlyB. a carrier father with no maternal mutant alleleC. two heterozygous carriersD. two individuals with only wild-type alleles

Correct: C. two heterozygous carriers

Explanation: two heterozygous carriers best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q72. X-linked recessive disorders classically affect males more often because males are:

A. homozygous for all X-linked genesB. unable to inherit maternal X chromosomesC. diploid for the Y chromosomeD. hemizygous for X-linked genes

Correct: D. hemizygous for X-linked genes

Explanation: hemizygous for X-linked genes best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q73. A septic patient has profound vasodilation after Gram-negative bacteraemia. Which microbial component can strongly activate innate immunity?

A. lipopolysaccharideB. human collagenC. viral envelope cholesterol onlyD. host haemoglobin

Correct: A. lipopolysaccharide

Explanation: lipopolysaccharide best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q74. A Barr body represents:

A. a condensed Y chromosomeB. an inactivated X chromosomeC. mitochondrial DNAD. a nucleolus

Correct: B. an inactivated X chromosome

Explanation: an inactivated X chromosome best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q75. Anticipation in some genetic disorders is commonly associated with:

A. loss of all intronsB. mitochondrial fissionC. expansion of nucleotide repeatsD. chromosome condensation during mitosis

Correct: C. expansion of nucleotide repeats

Explanation: expansion of nucleotide repeats best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q76. A patient receiving broad-spectrum antibiotics develops an opportunistic intestinal infection. One contributing mechanism is loss of:

A. mitochondrial inheritanceB. erythrocyte glycolysisC. meiotic recombinationD. normal microbiome colonisation resistance

Correct: D. normal microbiome colonisation resistance

Explanation: normal microbiome colonisation resistance best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q77. Which process generates mature mRNA from eukaryotic pre-mRNA?

A. splicing with capping and polyadenylationB. DNA replicationC. translationD. glycolysis

Correct: A. splicing with capping and polyadenylation

Explanation: splicing with capping and polyadenylation best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q78. A promoter is a DNA region that primarily:

A. terminates protein foldingB. helps initiate transcriptionC. anchors lysosomesD. forms spindle fibres

Correct: B. helps initiate transcription

Explanation: Transcription uses DNA as a template to synthesize RNA.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q79. A pregnant patient is exposed to a teratogen during early organogenesis. The fetus is at greatest risk of:

A. only postnatal behavioural change with no structural riskB. no developmental effect because placenta blocks all chemicalsC. major structural malformationsD. chromosome doubling in every cell

Correct: C. major structural malformations

Explanation: major structural malformations best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q80. MicroRNAs commonly regulate gene expression by:

A. increasing chromosome numberB. forming peptide bondsC. replicating mitochondrial DNAD. reducing translation or promoting degradation of target mRNA

Correct: D. reducing translation or promoting degradation of target mRNA

Explanation: Translation occurs on ribosomes, where mRNA directs amino-acid sequence.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q81. A monoclonal antibody preparation consists of antibodies that:

A. recognise the same epitopeB. are produced by every B-cell cloneC. have no antigen specificityD. contain only IgM

Correct: A. recognise the same epitope

Explanation: B lymphocytes can differentiate into plasma cells that secrete antibodies.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q82. The principle of vaccination is to generate:

A. permanent innate inflammationB. immunological memoryC. loss of lymphocytesD. antigen-independent antibodies

Correct: B. immunological memory

Explanation: immunological memory best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q83. A newborn fails to close the ductus arteriosus. In fetal life, this vessel normally connects the:

A. right atrium to left atriumB. umbilical vein to inferior vena cavaC. pulmonary artery to the aortaD. portal vein to hepatic vein

Correct: C. pulmonary artery to the aorta

Explanation: pulmonary artery to the aorta best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q84. Clonal selection predicts that antigen exposure causes:

A. random conversion of neutrophils into B cellsB. loss of receptor specificityC. all T cells to make antibodyD. expansion of lymphocytes with matching receptors

Correct: D. expansion of lymphocytes with matching receptors

Explanation: expansion of lymphocytes with matching receptors best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q85. A primary immune response generally differs from a secondary response by having:

A. a longer lag and lower initial antibody titreB. a shorter lag and higher affinity immediatelyC. no IgM productionD. no memory-cell formation

Correct: A. a longer lag and lower initial antibody titre

Explanation: B lymphocytes can differentiate into plasma cells that secrete antibodies.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q86. A woman undergoing IVF asks why multiple early embryos can be genetically tested before transfer. The relevant technology analyses:

A. maternal red-cell nuclei onlyB. DNA from sampled embryonic cellsC. seminal plasma proteins onlyD. placental blood after birth

Correct: B. DNA from sampled embryonic cells

Explanation: DNA from sampled embryonic cells best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q87. Biofilm formation can make bacteria harder to eradicate because it:

A. removes bacterial adhesionB. prevents horizontal gene transferC. creates a protected community with altered physiologyD. makes every cell metabolically hyperactive

Correct: C. creates a protected community with altered physiology

Explanation: creates a protected community with altered physiology best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q88. Endotoxin is primarily associated with:

A. peptidoglycan of all bacteriaB. fungal ergosterolC. viral capsid proteinD. lipopolysaccharide of Gram-negative bacteria

Correct: D. lipopolysaccharide of Gram-negative bacteria

Explanation: lipopolysaccharide of Gram-negative bacteria best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q89. A patient with chronic myeloid leukaemia has a recurrent chromosomal translocation producing an abnormal kinase. This illustrates how cancer can result from:

A. a genomic rearrangement creating an oncogenic driverB. loss of all cellular RNAC. failure of osmosisD. absence of ribosomes

Correct: A. a genomic rearrangement creating an oncogenic driver

Explanation: a genomic rearrangement creating an oncogenic driver best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q90. Prions are infectious agents composed primarily of:

A. DNA enclosed in lipidB. misfolded proteinC. RNA with reverse transcriptaseD. bacterial spores

Correct: B. misfolded protein

Explanation: misfolded protein best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q91. Natural selection acts directly on:

A. future mutations chosen by needB. acquired traits regardless of heredityC. phenotypic variation affecting reproductive successD. individual desire to adapt

Correct: C. phenotypic variation affecting reproductive success

Explanation: Natural selection changes population allele frequencies when heritable traits influence reproductive success.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q92. In an ecosystem, energy flow is:

A. perfectly recycledB. independent of primary producersC. increased at each trophic levelD. unidirectional with loss as heat

Correct: D. unidirectional with loss as heat

Explanation: unidirectional with loss as heat best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q93. A patient’s tumour is sequenced to identify a mutation predicting response to a targeted drug. This is an example of:

A. precision medicine using molecular biomarkersB. classical taxonomyC. ecological successionD. passive immunisation only

Correct: A. precision medicine using molecular biomarkers

Explanation: precision medicine using molecular biomarkers best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q94. Biomagnification refers to:

A. rapid decomposition of toxinsB. increasing concentration of some persistent substances at higher trophic levelsC. movement of water through soilD. increase in biodiversity

Correct: B. increasing concentration of some persistent substances at higher trophic levels

Explanation: increasing concentration of some persistent substances at higher trophic levels best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q95. One Health emphasizes the interconnection of:

A. only hospital infection controlB. only human geneticsC. human, animal and environmental healthD. only veterinary vaccination

Correct: C. human, animal and environmental health

Explanation: human, animal and environmental health best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q96. A bacterial isolate becomes resistant after receiving a plasmid from another bacterium through a pilus. The mechanism is:

A. translationB. binary fissionC. sporulationD. conjugation

Correct: D. conjugation

Explanation: conjugation best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q97. Pharmacogenomics studies how:

A. genetic variation influences drug responseB. drugs change chromosome number in every patientC. microbes synthesize all medicinesD. diet alone determines pharmacokinetics

Correct: A. genetic variation influences drug response

Explanation: genetic variation influences drug response best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Q98. A liquid biopsy may detect tumour-derived:

A. bone mineral onlyB. circulating DNA or cellsC. bile salts onlyD. mature erythrocyte nuclei

Correct: B. circulating DNA or cells

Explanation: circulating DNA or cells best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.

Clinical / Scenario

Q99. After repeated antibiotic exposure, resistant bacteria become increasingly common in a ward. The best evolutionary explanation is:

A. antibiotics intentionally create useful mutations in every bacteriumB. all susceptible bacteria transform into resistant cells by needC. selection favours pre-existing or acquired resistant variantsD. resistance occurs without heritable variation

Correct: C. selection favours pre-existing or acquired resistant variants

Explanation: selection favours pre-existing or acquired resistant variants best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Clinical integration: Apply the core mechanism rather than relying on isolated recall.

Q100. Single-cell sequencing is particularly useful because it can reveal:

A. only average signals from millions of cellsB. bone density directlyC. blood pressure continuouslyD. cell-to-cell heterogeneity within a tissue

Correct: D. cell-to-cell heterogeneity within a tissue

Explanation: cell-to-cell heterogeneity within a tissue best fits the biological mechanism or definition being tested here; the alternatives describe different structures, processes, or consequences.

Key Concept / Clinical Relevance: Apply the core mechanism rather than relying on isolated recall.