MBBS (Bachelor of Medicine and Bachelor of Surgery) Professional Examination — Questions and Answers

Question 1: The Ziehl-Neelsen stain is used to identify organisms that are acid-fast. Which property makes mycobacteria acid-fast?

High peptidoglycan content
Thick polysaccharide capsule
Presence of teichoic acids
Presence of mycolic acids in the cell wall (Correct answer)

Correct answer: Presence of mycolic acids in the cell wall

Mycolic acids are long-chain fatty acids in the mycobacterial cell wall that retain the carbol fuchsin dye even after acid-alcohol decolorization.

Question 2: Which malaria parasite is associated with tertian fever occurring every 48 hours and can remain dormant in the liver as hypnozoites?

Plasmodium knowlesi
Plasmodium malariae
Plasmodium falciparum
Plasmodium vivax (Correct answer)

Correct answer: Plasmodium vivax

Plasmodium vivax causes benign tertian malaria with 48-hour fever cycles and forms dormant hypnozoites in the liver, responsible for relapses months to years after initial infection.

Question 3: In which organelle does the citric acid (Krebs) cycle occur?

Mitochondrial matrix (Correct answer)
Cytoplasm
Nucleus
Smooth endoplasmic reticulum

Correct answer: Mitochondrial matrix

The citric acid cycle occurs in the mitochondrial matrix, where acetyl-CoA is oxidized to CO2 with generation of NADH, FADH2, and GTP.

Question 4: Which cofactor is required for carboxylation reactions in fatty acid synthesis and gluconeogenesis?

Biotin (Correct answer)
Lipoic acid
Pyridoxal phosphate
Thiamine pyrophosphate

Correct answer: Biotin

Biotin is covalently bound to carboxylases (pyruvate carboxylase, acetyl-CoA carboxylase) and acts as a CO2 carrier in carboxylation reactions.

Question 5: Which drug is a competitive antagonist at the beta-1 adrenergic receptor used in heart failure?

Phenylephrine
Metoprolol (Correct answer)
Dobutamine
Milrinone

Correct answer: Metoprolol

Metoprolol is a cardioselective beta-1 blocker that reduces heart rate and myocardial oxygen demand, improving outcomes in heart failure with reduced ejection fraction.

Question 6: Which ion is primarily responsible for the pacemaker potential (funny current) in the SA node?

Cl-
Na+ (Correct answer)
Ca2+
K+

Correct answer: Na+

The funny current (If) in SA node pacemaker cells is mainly carried by Na+ influx through HCN channels during hyperpolarization, initiating spontaneous depolarization.

Question 7: In the complement system, which component acts as the convergence point for both the classical and alternative pathways?

C9
C1q
C5
C3 (Correct answer)

Correct answer: C3

C3 is the central convergence point; both the classical pathway (via C4b2a C3 convertase) and the alternative pathway (via C3bBb C3 convertase) cleave C3 into C3a and C3b.

Question 8: During exercise, which of the following best explains the increase in cardiac output?

Increased sympathetic activity and venous return (Correct answer)
Peripheral vasoconstriction reducing afterload
Decreased heart rate with increased stroke volume only
Increased vagal tone

Correct answer: Increased sympathetic activity and venous return

During exercise, sympathetic activation increases heart rate and contractility while increased venous return (via muscle pump) boosts stroke volume.

Question 9: What is the GFR (glomerular filtration rate) in a healthy adult?

90 mL/min
60 mL/min
180 mL/min
125 mL/min (Correct answer)

Correct answer: 125 mL/min

The normal GFR in a healthy adult is approximately 125 mL/min (180 L/day), with approximately 99% of the filtrate reabsorbed.

Question 10: Which scoring system is used to assess the severity of acute pancreatitis at 48 hours?

Child-Pugh score
Ranson's criteria (Correct answer)
APACHE II score
MELD score

Correct answer: Ranson's criteria

Ranson's criteria evaluate 5 parameters at admission and 6 more at 48 hours; a score ≥3 indicates severe pancreatitis with increased morbidity and mortality.

Question 11: A 3-year-old presents with a 'barking cough' and inspiratory stridor. Which virus is the most common cause of this condition (croup)?

Parainfluenza virus (Correct answer)
Respiratory syncytial virus
Adenovirus
Influenza A virus

Correct answer: Parainfluenza virus

Parainfluenza virus type 1 is the most common cause of croup (laryngotracheobronchitis), characterized by subglottic edema producing the classic barking cough and inspiratory stridor.

Question 12: The McBurney's point, used to locate appendiceal tenderness, is located at what anatomical position?

Midpoint of a line from umbilicus to right ASIS
2/3 of the way from the umbilicus to the right ASIS
1/3 of the way from the right ASIS to the umbilicus (Correct answer)
Midpoint of the right iliac fossa

Correct answer: 1/3 of the way from the right ASIS to the umbilicus

McBurney's point is located one-third of the distance from the right anterior superior iliac spine (ASIS) to the umbilicus.

Question 13: A dental operation is being performed on a 45-year-old male who had a prosthetic aortic valve replaced five years prior. Given its better absorption, which preventive antibiotics are advised?

IV Ampicillin
Oral Vancomycin
IV penicillin
Oral amoxicillin (Correct answer)

Correct answer: Oral amoxicillin

For patients with prosthetic heart valves undergoing dental procedures, antibiotic prophylaxis is recommended to prevent infective endocarditis. Oral amoxicillin is the first-line antibiotic of choice due to its broad spectrum against common oral bacteria and its excellent oral absorption. This ensures adequate antibiotic levels are achieved to protect against bacteremia during the procedure.

Question 14: Which mechanism of antibiotic resistance involves enzymatic inactivation of aminoglycosides by modification through acetylation, adenylation, or phosphorylation?

Altered target site
Reduced outer membrane permeability
Enzymatic modification of the drug (Correct answer)
Efflux pump upregulation

Correct answer: Enzymatic modification of the drug

Aminoglycoside-modifying enzymes (acetyltransferases, adenylyltransferases, phosphotransferases) chemically modify aminoglycosides, preventing them from binding the 30S ribosomal subunit.

Question 15: What is the normal resting membrane potential of a cardiac ventricular myocyte?

-90 mV (Correct answer)
-70 mV
-110 mV
-55 mV

Correct answer: -90 mV

The resting membrane potential of ventricular myocytes is approximately -90 mV, maintained primarily by K+ leak channels.

Question 16: Alpha-1-antitrypsin deficiency causes emphysema through which mechanism?

Increased collagen deposition in lung parenchyma
Unopposed neutrophil elastase activity destroying alveolar walls (Correct answer)
Increased mucus production blocking small airways
Impaired surfactant production

Correct answer: Unopposed neutrophil elastase activity destroying alveolar walls

Alpha-1-antitrypsin normally inhibits elastase; its deficiency allows neutrophil elastase to destroy alveolar walls, causing panacinar emphysema predominantly in the lung bases.

Question 17: In the urea cycle, the final step converts arginine to urea and which other product?

Citrulline
Ornithine (Correct answer)
Fumarate
Aspartate

Correct answer: Ornithine

Arginase cleaves arginine to yield urea (excreted) and ornithine, which re-enters the cycle to accept another carbamoyl group.

Question 18: Clostridium tetani produces tetanospasmin, which causes spastic paralysis. What is its mechanism of action?

Cleaves SNARE proteins at peripheral synapses
Blocks acetylcholine release at the neuromuscular junction
Inhibits release of inhibitory neurotransmitters glycine and GABA (Correct answer)
Activates adenylyl cyclase in neurons

Correct answer: Inhibits release of inhibitory neurotransmitters glycine and GABA

Tetanospasmin cleaves synaptobrevin (a SNARE protein) in inhibitory interneurons, blocking release of glycine and GABA, resulting in unopposed motor neuron excitation and spastic paralysis.

Question 19: Which of the following best describes the role of surfactant in the lungs?

Neutralizes inhaled pathogens
Reduces surface tension to prevent alveolar collapse (Correct answer)
Facilitates oxygen diffusion across the alveolar membrane
Increases surface tension to stabilize alveoli

Correct answer: Reduces surface tension to prevent alveolar collapse

Surfactant (dipalmitoyl phosphatidylcholine) reduces alveolar surface tension, preventing collapse during expiration and reducing work of breathing.

Question 20: The Frank-Starling mechanism of the heart states that:

Stroke volume increases with increased end-diastolic volume (Correct answer)
Contractility decreases with increased stretch
Heart rate increases with increased venous return
Cardiac output is independent of preload

Correct answer: Stroke volume increases with increased end-diastolic volume

The Frank-Starling mechanism states that stroke volume increases as end-diastolic volume increases, up to a physiological limit.

Question 21: Which chamber of the heart forms the majority of the anterior surface?

Left ventricle
Right atrium
Right ventricle (Correct answer)
Left atrium

Correct answer: Right ventricle

The right ventricle forms the majority of the anterior (sternocostal) surface of the heart.

Question 22: Which segment of the nephron is impermeable to water under all conditions?

Thick ascending loop of Henle (Correct answer)
Thin descending loop of Henle
Proximal convoluted tubule
Collecting duct

Correct answer: Thick ascending loop of Henle

The thick ascending limb of the loop of Henle is always impermeable to water but actively transports NaCl, creating the medullary concentration gradient.

Question 23: Which cell type is the primary effector in granuloma formation?

Epithelioid macrophages and giant cells (Correct answer)
Plasma cells
Neutrophils
NK cells

Correct answer: Epithelioid macrophages and giant cells

Granulomas consist primarily of activated epithelioid macrophages and multinucleated giant cells, organized to wall off persistent antigens.

Question 24: Prions are infectious agents associated with transmissible spongiform encephalopathies. What is the defining characteristic of prion proteins?

They contain RNA but no protein
They are lipid-coated viral particles
They replicate using reverse transcriptase
They are misfolded proteins that induce normal proteins to misfold (Correct answer)

Correct answer: They are misfolded proteins that induce normal proteins to misfold

Prions are abnormally folded PrP^Sc proteins that act as templates to convert normal cellular PrP^C into the pathological conformation, propagating without any nucleic acid.

Question 25: The femoral triangle is bounded superiorly by which structure?

Sartorius muscle
Inguinal ligament (Correct answer)
Adductor longus muscle
Poupart's ligament

Correct answer: Inguinal ligament

The inguinal ligament forms the superior boundary of the femoral triangle.

Question 26: Which hormone causes water reabsorption in the collecting duct by inserting aquaporin-2 channels?

Aldosterone
Antidiuretic hormone (ADH) (Correct answer)
Atrial natriuretic peptide
Parathyroid hormone

Correct answer: Antidiuretic hormone (ADH)

ADH (vasopressin) binds V2 receptors in the collecting duct, triggering aquaporin-2 insertion and increasing water reabsorption.

Question 27: What pulmonary function test is the most effective at predicting postoperative performance when lobectomy is being considered?

Gas exchange functions, such as DLCO (diffusion of carbon monoxide in the lung)
Plain chest roentgenogram
Quantitative radionucleotide perfusion scanning
Predicted postoperative forced expiratory volume (FEV) in 1 second (FEV1) (Correct answer)

Correct answer: Predicted postoperative forced expiratory volume (FEV) in 1 second (FEV1)

When considering a lobectomy, accurately predicting the patient's postoperative pulmonary function is critical for assessing surgical candidacy and minimizing complications. The predicted postoperative forced expiratory volume in 1 second (ppoFEV1) is the most effective and widely accepted pulmonary function test for this purpose. It provides a reliable estimate of the remaining lung function after resection, guiding surgical decisions.

Question 28: Which antibiotic acts by inhibiting bacterial cell wall synthesis by binding to the D-Ala-D-Ala terminus of peptidoglycan precursors?

Rifampin
Penicillin
Vancomycin (Correct answer)
Ciprofloxacin

Correct answer: Vancomycin

Vancomycin binds to the D-Ala-D-Ala terminus of peptidoglycan precursors, preventing transglycosylation and transpeptidation, thereby inhibiting cell wall synthesis.

Question 29: Which antiepileptic drug acts by prolonging the inactivation state of voltage-gated sodium channels?

Phenytoin (Correct answer)
Ethosuximide
Valproate
Clonazepam

Correct answer: Phenytoin

Phenytoin stabilizes the inactive state of voltage-gated Na+ channels, preventing rapid repetitive neuronal firing without affecting normal neural function.

MBBS (Bachelor of Medicine and Bachelor of Surgery) Professional Examination

The MBBS Professional Examinations assess medical students' knowledge across pre-clinical and para-clinical subjects including Physiology, Pharmacology, and Microbiology, aligned with India's National Medical Commission (NMC) CBME curriculum standards.

Questions

35 min

Time Limit

50%

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