COMSAE Form 113 Practice Exam Version
1 – 120 Questions Verified Answers with
Detailed Rationales | 2026 Edition
Q1. The primary motor cortex responsible for voluntary movement is located
in which of the following gyri?
A) Superior temporal gyrus
B) Precentral gyrus
C) Postcentral gyrus
D) Inferior frontal gyrus
E) Cingulate gyrus
Answer: B
Rationale: The precentral gyrus (Brodmann area 4) is the primary motor cortex,
controlling voluntary movement. Postcentral gyrus is primary somatosensory.
Superior temporal gyrus is auditory. Inferior frontal gyrus (Broca’s area) is motor
speech.
Q2. Which amino acid serves as the precursor for nitric oxide?
A) Arginine
B) Lysine
C) Glutamine
D) Tyrosine
E) Tryptophan
Answer: A
Rationale: Nitric oxide (NO) is synthesized from L-arginine by nitric oxide
synthase (NOS). Arginine is also a precursor for urea and creatine.
Q3. A 55-year-old man with chronic kidney disease has a blood pH of 7.32,
PaCO2 30 mmHg, HCO3 16 mEq/L. What is the primary acid-base disorder?
A) Metabolic acidosis with respiratory compensation
,B) Metabolic alkalosis with respiratory compensation
C) Respiratory acidosis with metabolic compensation
D) Respiratory alkalosis with metabolic compensation
E) Mixed metabolic and respiratory acidosis
Answer: A
*Rationale: Low pH (7.32) = acidosis. Low HCO3 (16) = metabolic acidosis.
PaCO2 is low (30), indicating respiratory compensation (expected PaCO2 =
1.5×HCO3 + 8 ± 2 = 32, within range). This is simple metabolic acidosis (e.g.,
from CKD).*
Q4. Which of the following enzymes is rate-limiting in glycolysis?
A) Hexokinase
B) Phosphofructokinase-1 (PFK-1)
C) Glyceraldehyde-3-phosphate dehydrogenase
D) Pyruvate kinase
E) Enolase
Answer: B
*Rationale: PFK-1 is the key rate-limiting step of glycolysis, regulated by ATP,
citrate (inhibitors), and AMP/fructose-2,6-bisphosphate (activators). Hexokinase is
also regulated but not the primary rate-limiting step.*
Q5. A patient experiences an anaphylactic reaction after eating peanuts.
Which immunologic mechanism is responsible?
A) Complement-mediated lysis
B) Antibody-dependent cellular cytotoxicity
C) Mast cell degranulation triggered by IgE cross-linking
D) Delayed T-cell mediated inflammation
E) Immune complex deposition
Answer: C
Rationale: Type I hypersensitivity (anaphylaxis) involves IgE bound to mast
cells/basophils. Cross-linking by allergen causes degranulation, releasing
histamine, leukotrienes, and other mediators.
,Q6. The inner cell mass of a blastocyst gives rise to which of the following?
A) The embryo proper (fetus)
B) The placenta
C) The umbilical cord
D) The amnion
E) The chorion
Answer: A
Rationale: The inner cell mass (embryoblast) develops into the embryo proper. The
outer cell mass (trophoblast) forms the placenta and extraembryonic membranes.
Q7. A patient with chronic alcoholism presents with confusion, ataxia, and
ophthalmoplegia. Deficiency of which vitamin is the most likely cause?
A) Vitamin B6 (Pyridoxine)
B) Vitamin B1 (Thiamine)
C) Vitamin B12 (Cobalamin)
D) Folate
E) Vitamin E
Answer: B
Rationale: Wernicke encephalopathy (confusion, ataxia, ophthalmoplegia) is
caused by thiamine (B1) deficiency, common in alcoholism. Treatment is IV
thiamine before glucose.
Q8. Which of the following structures is derived from neural crest cells?
A) Skeletal muscle
B) Dorsal root ganglia
C) Ventral horn motor neurons
D) Cerebral cortex
E) Retina
Answer: B
Rationale: Neural crest cells give rise to dorsal root ganglia (sensory neurons),
autonomic ganglia, Schwann cells, melanocytes, and craniofacial bone/cartilage.
Skeletal muscle is from mesoderm; motor neurons from neural tube.
, Q9. A 32-year-old woman with systemic lupus erythematosus has a positive
antinuclear antibody (ANA) test. Which of the following antibodies is most
specific for SLE?
A) Anti-Ro (SSA)
B) Anti-Smith (Sm)
C) Anti-Jo-1
D) Anti-Scl-70
E) Anti-centromere
Answer: B
*Rationale: Anti-Smith (Sm) is highly specific for SLE (99%), though only 20-
30% sensitive. Anti-dsDNA is also specific and associated with lupus nephritis.*
Q10. During aerobic respiration, the majority of ATP is produced by which
process?
A) Substrate-level phosphorylation in glycolysis
B) Substrate-level phosphorylation in the Krebs cycle
C) Oxidative phosphorylation in the electron transport chain
D) Beta-oxidation of fatty acids
E) Pentose phosphate pathway
Answer: C
*Rationale: Oxidative phosphorylation (chemiosmosis) generates ~34 of the ~38
ATP per glucose. Substrate-level phosphorylation yields 2 ATP in glycolysis and 2
in the Krebs cycle.*
Q11. A 45-year-old man presents with fatigue, weight gain, and cold
intolerance. Lab: TSH 25 μIU/mL, free T4 0.4 ng/dL. Which of the following
is the most likely etiology?
A) Hashimoto's thyroiditis
B) Graves' disease
C) Toxic multinodular goiter
D) Subacute thyroiditis
E) Pituitary adenoma
Answer: A
*Rationale: Elevated TSH with low free T4 indicates primary hypothyroidism.
1 – 120 Questions Verified Answers with
Detailed Rationales | 2026 Edition
Q1. The primary motor cortex responsible for voluntary movement is located
in which of the following gyri?
A) Superior temporal gyrus
B) Precentral gyrus
C) Postcentral gyrus
D) Inferior frontal gyrus
E) Cingulate gyrus
Answer: B
Rationale: The precentral gyrus (Brodmann area 4) is the primary motor cortex,
controlling voluntary movement. Postcentral gyrus is primary somatosensory.
Superior temporal gyrus is auditory. Inferior frontal gyrus (Broca’s area) is motor
speech.
Q2. Which amino acid serves as the precursor for nitric oxide?
A) Arginine
B) Lysine
C) Glutamine
D) Tyrosine
E) Tryptophan
Answer: A
Rationale: Nitric oxide (NO) is synthesized from L-arginine by nitric oxide
synthase (NOS). Arginine is also a precursor for urea and creatine.
Q3. A 55-year-old man with chronic kidney disease has a blood pH of 7.32,
PaCO2 30 mmHg, HCO3 16 mEq/L. What is the primary acid-base disorder?
A) Metabolic acidosis with respiratory compensation
,B) Metabolic alkalosis with respiratory compensation
C) Respiratory acidosis with metabolic compensation
D) Respiratory alkalosis with metabolic compensation
E) Mixed metabolic and respiratory acidosis
Answer: A
*Rationale: Low pH (7.32) = acidosis. Low HCO3 (16) = metabolic acidosis.
PaCO2 is low (30), indicating respiratory compensation (expected PaCO2 =
1.5×HCO3 + 8 ± 2 = 32, within range). This is simple metabolic acidosis (e.g.,
from CKD).*
Q4. Which of the following enzymes is rate-limiting in glycolysis?
A) Hexokinase
B) Phosphofructokinase-1 (PFK-1)
C) Glyceraldehyde-3-phosphate dehydrogenase
D) Pyruvate kinase
E) Enolase
Answer: B
*Rationale: PFK-1 is the key rate-limiting step of glycolysis, regulated by ATP,
citrate (inhibitors), and AMP/fructose-2,6-bisphosphate (activators). Hexokinase is
also regulated but not the primary rate-limiting step.*
Q5. A patient experiences an anaphylactic reaction after eating peanuts.
Which immunologic mechanism is responsible?
A) Complement-mediated lysis
B) Antibody-dependent cellular cytotoxicity
C) Mast cell degranulation triggered by IgE cross-linking
D) Delayed T-cell mediated inflammation
E) Immune complex deposition
Answer: C
Rationale: Type I hypersensitivity (anaphylaxis) involves IgE bound to mast
cells/basophils. Cross-linking by allergen causes degranulation, releasing
histamine, leukotrienes, and other mediators.
,Q6. The inner cell mass of a blastocyst gives rise to which of the following?
A) The embryo proper (fetus)
B) The placenta
C) The umbilical cord
D) The amnion
E) The chorion
Answer: A
Rationale: The inner cell mass (embryoblast) develops into the embryo proper. The
outer cell mass (trophoblast) forms the placenta and extraembryonic membranes.
Q7. A patient with chronic alcoholism presents with confusion, ataxia, and
ophthalmoplegia. Deficiency of which vitamin is the most likely cause?
A) Vitamin B6 (Pyridoxine)
B) Vitamin B1 (Thiamine)
C) Vitamin B12 (Cobalamin)
D) Folate
E) Vitamin E
Answer: B
Rationale: Wernicke encephalopathy (confusion, ataxia, ophthalmoplegia) is
caused by thiamine (B1) deficiency, common in alcoholism. Treatment is IV
thiamine before glucose.
Q8. Which of the following structures is derived from neural crest cells?
A) Skeletal muscle
B) Dorsal root ganglia
C) Ventral horn motor neurons
D) Cerebral cortex
E) Retina
Answer: B
Rationale: Neural crest cells give rise to dorsal root ganglia (sensory neurons),
autonomic ganglia, Schwann cells, melanocytes, and craniofacial bone/cartilage.
Skeletal muscle is from mesoderm; motor neurons from neural tube.
, Q9. A 32-year-old woman with systemic lupus erythematosus has a positive
antinuclear antibody (ANA) test. Which of the following antibodies is most
specific for SLE?
A) Anti-Ro (SSA)
B) Anti-Smith (Sm)
C) Anti-Jo-1
D) Anti-Scl-70
E) Anti-centromere
Answer: B
*Rationale: Anti-Smith (Sm) is highly specific for SLE (99%), though only 20-
30% sensitive. Anti-dsDNA is also specific and associated with lupus nephritis.*
Q10. During aerobic respiration, the majority of ATP is produced by which
process?
A) Substrate-level phosphorylation in glycolysis
B) Substrate-level phosphorylation in the Krebs cycle
C) Oxidative phosphorylation in the electron transport chain
D) Beta-oxidation of fatty acids
E) Pentose phosphate pathway
Answer: C
*Rationale: Oxidative phosphorylation (chemiosmosis) generates ~34 of the ~38
ATP per glucose. Substrate-level phosphorylation yields 2 ATP in glycolysis and 2
in the Krebs cycle.*
Q11. A 45-year-old man presents with fatigue, weight gain, and cold
intolerance. Lab: TSH 25 μIU/mL, free T4 0.4 ng/dL. Which of the following
is the most likely etiology?
A) Hashimoto's thyroiditis
B) Graves' disease
C) Toxic multinodular goiter
D) Subacute thyroiditis
E) Pituitary adenoma
Answer: A
*Rationale: Elevated TSH with low free T4 indicates primary hypothyroidism.
