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NDEB AFK practice questions

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Question 1Biomedical Sciences

Which cranial nerve supplies motor innervation to the muscles of mastication?

  1. Facial nerve
  2. Trigeminal nerve Correct answer.
  3. Hypoglossal nerve
  4. Glossopharyngeal nerve

Explanation

The motor root of the mandibular division of the trigeminal nerve innervates the four muscles of mastication (masseter, temporalis, and medial and lateral pterygoids), which all arise from the first pharyngeal arch.

Question 2Biomedical Sciences

The sodium-potassium ATPase pump moves ions across the cell membrane by transporting:

  1. Three sodium ions out and two potassium ions in Correct answer.
  2. Equal numbers of sodium and potassium ions in opposite directions
  3. Two sodium ions out and three potassium ions in
  4. Three sodium ions in and two potassium ions out

Explanation

For each ATP hydrolysed, the pump extrudes three sodium ions and admits two potassium ions, both against their concentration gradients, generating a net negative intracellular charge.

Question 3Biomedical Sciences

Which enzyme catalyses the rate-limiting step of glycolysis?

  1. Glucose-6-phosphatase
  2. Phosphofructokinase-1 Correct answer.
  3. Hexokinase
  4. Pyruvate kinase

Explanation

Phosphofructokinase-1 converts fructose-6-phosphate to fructose-1,6-bisphosphate and is the major regulated, flux-determining step of glycolysis, activated by AMP and inhibited by ATP and citrate.

Question 4Biomedical Sciences

Which microorganism is most strongly associated with the initiation of dental caries?

  1. Porphyromonas gingivalis
  2. Candida albicans
  3. Streptococcus mutans Correct answer.
  4. Fusobacterium nucleatum

Explanation

Streptococcus mutans adheres to the acquired pellicle, produces glucans from sucrose via glucosyltransferases, and is highly acidogenic and aciduric, making it the key organism in caries initiation.

Question 5Biomedical Sciences

Which immunoglobulin is the predominant antibody in human saliva?

  1. Pentameric IgM
  2. Secretory IgA Correct answer.
  3. Reaginic IgE
  4. Serum IgG

Explanation

Secretory IgA is produced by plasma cells in the salivary glands and is transported across the epithelium with a secretory component, making it the main mucosal antibody in saliva.

Question 6Biomedical Sciences

The muscles of mastication are derived from which pharyngeal arch?

  1. Third pharyngeal arch
  2. First pharyngeal arch Correct answer.
  3. Fourth pharyngeal arch
  4. Second pharyngeal arch

Explanation

The first (mandibular) pharyngeal arch gives rise to the muscles of mastication, the anterior digastric, mylohyoid, tensor tympani and tensor veli palatini, all innervated by the mandibular division of the trigeminal nerve.

Question 7Biomedical Sciences

The principal fibre type of the periodontal ligament is:

  1. Oxytalan fibres
  2. Reticular fibres
  3. Elastic fibres
  4. Collagen fibres Correct answer.

Explanation

The periodontal ligament consists mainly of type I collagen bundles organised into principal fibre groups that suspend the tooth in the alveolus and resist functional forces.

Question 8Biomedical Sciences

Which hormone raises serum calcium by stimulating bone resorption and renal calcium reabsorption?

  1. Aldosterone
  2. Parathyroid hormone Correct answer.
  3. Calcitonin
  4. Insulin

Explanation

Parathyroid hormone increases serum calcium through direct renal calcium reabsorption, activation of vitamin D, and osteoclast-mediated bone resorption via osteoblast signalling.

Question 9Biomedical Sciences

Which duct empties into the oral cavity at the parotid papilla opposite the maxillary second molar?

  1. Wharton duct of the submandibular gland
  2. Rivinus duct of the sublingual gland
  3. Bartholin duct of the sublingual gland
  4. Stensen duct of the parotid gland Correct answer.

Explanation

Stensen duct runs forward from the parotid gland across the masseter, pierces the buccinator, and opens at the parotid papilla adjacent to the maxillary second molar.

Question 10Biomedical Sciences

Which gastric cells secrete intrinsic factor?

  1. Chief cells
  2. Parietal cells Correct answer.
  3. G cells
  4. Mucous neck cells

Explanation

Parietal cells secrete hydrochloric acid and intrinsic factor; the latter complexes with vitamin B12 and is required for its absorption in the terminal ileum.

Question 11Biomedical Sciences

Vitamin C is required as a cofactor for which step in collagen synthesis?

  1. Cross-linking of collagen molecules
  2. Hydroxylation of proline and lysine residues Correct answer.
  3. Cleavage of terminal propeptides
  4. Glycosylation of hydroxylysine

Explanation

Ascorbate is a cofactor for prolyl and lysyl hydroxylase, and inadequate hydroxylation reduces triple-helix stability, producing the fragile connective tissue seen in scurvy.

Question 12Biomedical Sciences

Local anaesthetics prevent nerve conduction primarily by:

  1. Opening voltage-gated potassium channels
  2. Blocking presynaptic calcium channels
  3. Inhibiting the sodium-potassium ATPase
  4. Blocking voltage-gated sodium channels from within the axon Correct answer.

Explanation

In their uncharged form, local anaesthetics cross the axonal membrane and block the inner pore of voltage-gated sodium channels, preventing depolarisation and propagation of the action potential.

Question 13Biomedical Sciences

Which class of antibiotic inhibits bacterial cell wall synthesis by binding penicillin-binding proteins?

  1. Aminoglycosides
  2. Tetracyclines
  3. Beta-lactams Correct answer.
  4. Macrolides

Explanation

Beta-lactams acylate penicillin-binding proteins, the transpeptidases that cross-link peptidoglycan, so the cell wall weakens and the bacterium lyses.

Question 14Biomedical Sciences

Which cell type is characteristically the first to arrive at a site of acute inflammation?

  1. Eosinophil
  2. Macrophage
  3. Lymphocyte
  4. Neutrophil Correct answer.

Explanation

Neutrophils marginate, adhere and emigrate within minutes to hours of injury, forming the dominant cell of early acute inflammation before monocytes arrive and mature into macrophages.

Question 15Biomedical Sciences

Endogenous antigens are presented to CD8-positive cytotoxic T cells by which molecule?

  1. MHC class II
  2. MHC class III
  3. MHC class I Correct answer.
  4. MHC class I expressed only on antigen-presenting cells

Explanation

MHC class I molecules, expressed on virtually all nucleated cells, display peptides derived from cytosolic proteins to CD8-positive T cells, allowing detection of intracellular infection.

Question 16Biomedical Sciences

The secondary palate develops from the fusion of which structures?

  1. The lateral palatal shelves Correct answer.
  2. The lateral nasal processes
  3. The maxillary and mandibular processes
  4. The medial nasal processes

Explanation

The lateral palatal shelves arise from the maxillary processes, elevate above the tongue and fuse in the midline to form the secondary palate, giving rise to the hard and soft palate posterior to the incisive foramen.

Question 17Biomedical Sciences

During the absolute refractory period of a neuron:

  1. Potassium conductance is at its lowest
  2. The membrane potential equals the resting potential
  3. No stimulus can trigger another action potential Correct answer.
  4. Only a stronger stimulus can trigger an action potential

Explanation

In the absolute refractory period, voltage-gated sodium channels are inactivated and cannot reopen, so no stimulus of any strength can generate a second action potential, which enforces unidirectional conduction.

Question 18Biomedical Sciences

Which substance is a ketone body produced by the liver?

  1. Urea
  2. Acetoacetate Correct answer.
  3. Lactate
  4. Palmitate

Explanation

During fasting, hepatic beta-oxidation generates acetyl-CoA that is converted to the ketone bodies acetoacetate, beta-hydroxybutyrate and acetone, which are exported as fuel for other tissues.

Question 19Biomedical Sciences

The maxillary artery is a terminal branch of which vessel?

  1. Internal carotid artery
  2. Superficial temporal artery
  3. External carotid artery Correct answer.
  4. Facial artery

Explanation

The external carotid artery terminates by dividing into the maxillary artery and the superficial temporal artery, with the maxillary artery supplying deep facial structures including the teeth and palate.

Question 20Biomedical Sciences

Which feature best distinguishes a malignant neoplasm from a benign one?

  1. Close resemblance to the tissue of origin
  2. Presence of a fibrous capsule
  3. Slow rate of growth
  4. Metastasis to distant sites Correct answer.

Explanation

Metastasis, the spread of tumour cells to distant sites, is the definitive feature of malignancy; benign tumours remain localized and do not metastasize.

Question 21Biomedical Sciences

A patient with metabolic alkalosis from prolonged vomiting is expected to show which respiratory compensation?

  1. Hyperventilation, which raises oxygen saturation
  2. Hyperventilation, which lowers carbon dioxide
  3. Hypoventilation, which retains carbon dioxide Correct answer.
  4. No change in the rate or depth of ventilation

Explanation

In metabolic alkalosis the hydrogen ion concentration is low, so the respiratory centre is depressed; hypoventilation raises arterial carbon dioxide and restores the bicarbonate-to-carbonic acid ratio toward normal.

Question 22Biomedical Sciences

Epinephrine is included in a local anaesthetic solution mainly to:

  1. Raise the pH of the cartridge
  2. Speed hepatic breakdown of the anaesthetic
  3. Constrict local vessels and prolong anaesthesia Correct answer.
  4. Prevent allergic reactions to the anaesthetic

Explanation

Vasoconstriction reduces local blood flow, slowing systemic absorption of the anaesthetic; this prolongs the block, deepens anaesthesia and lowers the risk of systemic toxicity.

Question 23Biomedical Sciences

A disorder caused by a mutation in mitochondrial DNA is inherited:

  1. In an autosomal dominant pattern
  2. Essentially from the mother alone Correct answer.
  3. In an X-linked recessive pattern
  4. Equally from either parent

Explanation

Because the zygote receives its mitochondria almost entirely from the oocyte, mitochondrial DNA mutations are transmitted maternally, and affected mothers pass the mutation to all their children.

Question 24Biomedical Sciences

A patient develops urticaria and bronchospasm within minutes of a penicillin injection. The reaction is mediated by:

  1. Complement activation by IgM
  2. Direct T-cell cytotoxicity
  3. IgG-containing immune complexes
  4. IgE bound to mast cells Correct answer.

Explanation

This is a type I immediate hypersensitivity reaction in which penicillin-specific IgE cross-links on mast cells, triggering degranulation and release of histamine and other mediators.

Question 25Biomedical Sciences

Which statement correctly describes competitive inhibition of an enzyme?

  1. It raises the apparent Km without changing Vmax Correct answer.
  2. It binds irreversibly at the active site
  3. Its effect is intensified by raising the substrate concentration
  4. It lowers Vmax without changing Km

Explanation

A competitive inhibitor competes with substrate for the active site, so more substrate is needed to reach half-maximal velocity (raised apparent Km), but sufficiently high substrate displaces it and Vmax is unchanged.

Question 26Biomedical Sciences

The epithelium covering the hard palate and attached gingiva is best described as:

  1. Pseudostratified ciliated columnar
  2. Keratinized stratified squamous Correct answer.
  3. Non-keratinized stratified squamous
  4. Simple columnar with goblet cells

Explanation

Masticatory mucosa, which covers the hard palate and attached gingiva, is subjected to heavy frictional forces and is therefore orthokeratinized or parakeratinized. The surface keratin layer provides this mechanical protection.

Question 27Biomedical Sciences

At a chemical synapse, the immediate trigger for fusion of synaptic vesicles with the presynaptic membrane is:

  1. Sodium influx
  2. Calcium influx Correct answer.
  3. Chloride influx
  4. Potassium efflux

Explanation

Depolarization of the presynaptic terminal opens voltage-gated calcium channels, and the resulting calcium entry is the direct trigger for vesicle fusion and transmitter release. Sodium entry generates the action potential but does not itself cause exocytosis.

Question 28Biomedical Sciences

The rate-limiting enzyme of glycolysis is:

  1. Phosphofructokinase-1 Correct answer.
  2. Glucose 6-phosphatase
  3. Hexokinase
  4. Pyruvate kinase

Explanation

Phosphofructokinase-1 catalyses the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate, the slowest and most heavily regulated step of glycolysis. It is activated by AMP and fructose-2,6-bisphosphate and inhibited by ATP and citrate.

Question 29Biomedical Sciences

Which microorganism is most strongly implicated as the principal aetiological agent of smooth-surface dental caries?

  1. Veillonella parvula
  2. Streptococcus mutans Correct answer.
  3. Lactobacillus acidophilus
  4. Actinomyces viscosus

Explanation

Streptococcus mutans adheres to the acquired pellicle, synthesizes glucans from sucrose via glucosyltransferases, and is both strongly acidogenic and aciduric, making it the principal initiator of smooth-surface caries. Lactobacilli are associated more with established cavitated lesions.

Question 30Biomedical Sciences

Taste sensation from the posterior third of the tongue is carried by which nerve?

  1. Facial (VII)
  2. Mandibular division of trigeminal (V3)
  3. Hypoglossal (XII)
  4. Glossopharyngeal (IX) Correct answer.

Explanation

Taste from the posterior third of the tongue travels via the lingual branches of the glossopharyngeal nerve to the nucleus solitarius. The facial nerve serves the anterior two thirds through the chorda tympani.

Question 31Biomedical Sciences

Non-steroidal anti-inflammatory drugs such as ibuprofen produce their analgesic and anti-inflammatory effects mainly by:

  1. Blocking voltage-gated sodium channels
  2. Inhibiting phospholipase A2
  3. Activating opioid receptors
  4. Inhibiting cyclooxygenase Correct answer.

Explanation

NSAIDs inhibit cyclooxygenase-1 and cyclooxygenase-2, reducing conversion of arachidonic acid to prostaglandins, which are mediators of pain and inflammation. They do not act on sodium channels or opioid receptors.

Question 32Biomedical Sciences

DNA replication occurs during which phase of the cell cycle?

  1. G1
  2. M
  3. S Correct answer.
  4. G2

Explanation

DNA synthesis occurs in S phase, which lies between G1 and G2. G1 is the growth phase preceding replication and G2 follows it, while chromosome segregation and division occur in M phase.

Question 33Biomedical Sciences

Which immunoglobulin is transferred across the placenta and provides passive immunity to the newborn?

  1. IgA
  2. IgM
  3. IgG Correct answer.
  4. IgE

Explanation

IgG is the only immunoglobulin actively transported across the human placenta, via the neonatal Fc receptor, conferring passive humoral immunity on the fetus and newborn. IgM is too large to cross, and IgA is instead transferred in colostrum.

Question 34Biomedical Sciences

Which change shifts the oxyhaemoglobin dissociation curve to the right, favouring oxygen unloading in tissues?

  1. Decreased temperature
  2. Increased PCO2 Correct answer.
  3. Decreased 2,3-BPG
  4. Increased blood pH

Explanation

The Bohr effect describes the rightward shift produced by a rise in carbon dioxide tension and the accompanying fall in pH, which reduces haemoglobin affinity and improves oxygen delivery to active tissues. Increased pH, lower temperature and lower 2,3-BPG all shift the curve left.

Question 35Biomedical Sciences

An infarct in the cerebral cortex undergoes which type of necrosis?

  1. Caseous necrosis
  2. Coagulative necrosis
  3. Liquefactive necrosis Correct answer.
  4. Fibrinoid necrosis

Explanation

Brain infarcts produce liquefactive necrosis because the tissue is rich in hydrolytic enzymes and poor in supporting stroma, so dead tissue is digested into a cystic cavity. Coagulative necrosis is instead typical of infarcts in heart, kidney and spleen.

Question 36Biomedical Sciences

The predominant immunoglobulin in saliva and other mucosal secretions is:

  1. Secretory IgA Correct answer.
  2. Pentameric IgM
  3. Monomeric IgG
  4. Monomeric IgE

Explanation

Secretory IgA is a dimer joined by J chain and coated with secretory component, which protects it from proteolysis so that it can neutralize pathogens at mucosal surfaces. IgG predominates in serum and IgM in the early primary response.

Question 37Biomedical Sciences

Vitamin K is required as a cofactor for which reaction in the synthesis of clotting factors?

  1. Cleavage of the signal peptide
  2. Formation of disulphide bonds
  3. Hydroxylation of proline residues
  4. Gamma-carboxylation of glutamate Correct answer.

Explanation

Vitamin K is the cofactor for gamma-glutamyl carboxylase, which converts glutamate residues of factors II, VII, IX, X and proteins C and S to gamma-carboxyglutamate, permitting calcium-dependent binding to phospholipid membranes. Warfarin acts by blocking this cycle.

Question 38Biomedical Sciences

Atropine is given preoperatively to dry airway and salivary secretions. This action results from:

  1. Competitive muscarinic blockade Correct answer.
  2. Sympathetic nerve stimulation
  3. Acetylcholinesterase inhibition
  4. Ganglionic nicotinic blockade

Explanation

Atropine is a competitive antagonist at muscarinic acetylcholine receptors, so it blocks parasympathetic drive to salivary and airway glands and reduces secretion. Its effect is surmountable by raising acetylcholine concentration at the receptor.

Question 39Biomedical Sciences

Which pharyngeal arch gives rise to the stapes?

  1. Second Correct answer.
  2. Third
  3. Fourth
  4. First

Explanation

The second (hyoid) arch gives rise to the stapes, styloid process, stylohyoid ligament and the muscles of facial expression, all supplied by the facial nerve. The first arch forms the malleus and incus.

Question 40Biomedical Sciences

During surgical removal of a mandibular third molar, which nerve is most at risk from a bur penetrating the lingual cortical plate?

  1. Lingual nerve Correct answer.
  2. Inferior alveolar nerve
  3. Chorda tympani
  4. Mylohyoid nerve

Explanation

The lingual nerve lies close to the lingual cortical plate below the third molar region, so lingual perforation can injure it, causing loss of sensation and taste on the anterior tongue. The inferior alveolar nerve is at risk within the mandibular canal rather than at the cortex.

Question 41Biomedical Sciences

Antidiuretic hormone increases water reabsorption by collecting duct principal cells through which mechanism?

  1. Stimulating aldosterone release
  2. Increasing sodium reabsorption in the ascending limb
  3. Raising medullary blood flow
  4. Inserting aquaporin-2 channels apically Correct answer.

Explanation

ADH binds V2 receptors on principal cells, raises cyclic AMP and promotes insertion of aquaporin-2 water channels into the apical membrane, so water moves down the medullary osmotic gradient and urine is concentrated. Sodium handling in the thick ascending limb is not its target.

Question 42Biomedical Sciences

Which organism is a Gram-negative, black-pigmenting obligate anaerobe strongly associated with chronic periodontitis?

  1. Aggregatibacter actinomycetemcomitans
  2. Streptococcus sanguinis
  3. Porphyromonas gingivalis Correct answer.
  4. Lactobacillus casei

Explanation

Porphyromonas gingivalis is a Gram-negative, black-pigmenting anaerobe that expresses gingipains and other virulence factors and is strongly associated with chronic periodontitis. The other listed organisms are early plaque colonizers, a capnophilic species, or caries-associated acidogens.

Question 43Biomedical Sciences

In a healing surgical wound, which cell is the principal source of newly synthesized collagen in granulation tissue?

  1. Neutrophil
  2. Endothelial cell
  3. Fibroblast Correct answer.
  4. Macrophage

Explanation

Fibroblasts are the principal collagen-producing cells of granulation tissue, depositing the type I and type III collagen that forms the mature scar. Inflammatory cells contribute cytokines and debridement but not the collagen matrix.

Question 44Biomedical Sciences

Classic galactosaemia results from deficiency of which enzyme activity?

  1. Glucokinase
  2. Fructose-1-phosphate aldolase
  3. Galactokinase
  4. Uridyl transferase Correct answer.

Explanation

Classic galactosaemia is caused by deficiency of galactose-1-phosphate uridyltransferase, leading to accumulation of galactose-1-phosphate which is toxic to liver, brain and lens. Galactokinase deficiency produces a milder disorder, usually with cataracts only.

Question 45Biomedical Sciences

The bulk of filtered glucose is reabsorbed in which segment of the nephron?

  1. Distal convoluted tubule
  2. Collecting duct
  3. Proximal convoluted tubule Correct answer.
  4. Descending limb of the loop of Henle

Explanation

About ninety per cent of filtered glucose is reabsorbed in the proximal convoluted tubule by SGLT2 and SGLT1 cotransporters, with the remainder handled in the straight proximal tubule. More distal segments have little glucose transport capacity.

Question 46Biomedical Sciences

A patient has a serum sodium of 140 mmol/L, chloride of 100 mmol/L and bicarbonate of 14 mmol/L, with normal albumin and potassium. The calculated anion gap is:

  1. 18 mmol/L
  2. 26 mmol/L Correct answer.
  3. 40 mmol/L
  4. 12 mmol/L

Explanation

The anion gap is sodium minus the sum of chloride and bicarbonate: 140 − (100 + 14) = 26 mmol/L, which is raised and indicates an acidosis caused by unmeasured anions such as ketones or lactate. The normal range is approximately 8 to 12 mmol/L.

Question 47Biomedical Sciences

A condition affects only males, affected men have unaffected parents with carrier mothers, and no affected father ever transmits the condition to his sons. This pattern indicates:

  1. Autosomal dominant inheritance
  2. Autosomal recessive inheritance
  3. X-linked recessive inheritance Correct answer.
  4. Mitochondrial inheritance

Explanation

In X-linked recessive inheritance males are hemizygous and therefore affected, carrier mothers are usually unaffected, and an affected father cannot transmit the allele to his sons because he passes only a Y chromosome to them. Autosomal dominant disease would affect both sexes and show male-to-male transmission.

Question 48Biomedical Sciences

Phenytoin at therapeutic doses shows zero-order (saturation) kinetics. The clinical consequence of this is that:

  1. Renal clearance becomes the rate-limiting elimination step
  2. Half-life falls as the dose rises
  3. Steady-state level rises disproportionately with dose Correct answer.
  4. A constant fraction is eliminated per unit time

Explanation

Zero-order kinetics means the metabolizing enzymes are saturated, so a constant amount of drug is eliminated per unit time rather than a constant fraction. A small increase in dose can therefore cause a disproportionately large rise in plasma concentration and toxicity.

Question 49Biomedical Sciences

The p53 protein protects the genome primarily by:

  1. Halting the cycle or triggering apoptosis Correct answer.
  2. Repairing double-strand breaks directly
  3. Promoting new vessel growth in ischaemic tissue
  4. Activating telomerase in stem cells

Explanation

p53 is a transcription factor that senses DNA damage and either arrests the cell cycle at G1 to permit repair or drives apoptosis when damage is irreparable, which is why it is called the guardian of the genome. Loss of its function predisposes to many cancers.

Question 50Biomedical Sciences

C3b generated during complement activation contributes to host defence mainly by:

  1. Acting as a chemotaxin for neutrophils
  2. Neutralizing histamine released by mast cells
  3. Opsonizing microbes for phagocytosis Correct answer.
  4. Forming a membrane attack complex pore

Explanation

C3b binds covalently to microbial surfaces and is recognized by complement receptor 1 on phagocytes, greatly enhancing phagocytosis. The membrane attack complex is formed by C5b to C9, and neutrophil chemotaxis is mediated chiefly by C5a.