COMSAE Phase 1 Form ASA 103
Foundational Biomedical Sciences Exam
Practice Questions & [Verified Answers],
Plus Explained Rationales|2026 Latest
Update| Instant Download PDF
1. A 6-month-old infant presents with developmental delay,
seizures, and a musty body odor. Laboratory testing reveals
elevated phenylalanine levels. Which enzyme deficiency is
responsible for this condition?
A. Tyrosinase
B. Homogentisate oxidase
C. Phenylalanine hydroxylase
D. Branched-chain α-ketoacid dehydrogenase
Answer: C. Phenylalanine hydroxylase
Rationale: Phenylketonuria results from deficiency of phenylalanine
hydroxylase, preventing conversion of phenylalanine to tyrosine.
Accumulation causes intellectual disability, seizures, eczema, and a
musty odor if untreated.
2. A researcher administers a drug that irreversibly inhibits
cyclooxygenase activity in platelets. Which physiologic effect is
most likely?
A. Increased thromboxane A2 synthesis
B. Decreased platelet aggregation
C. Increased fibrin production
D. Increased prostacyclin synthesis
,Answer: B. Decreased platelet aggregation
Rationale: Aspirin irreversibly inhibits COX-1 in platelets, decreasing
thromboxane A2 production and impairing platelet aggregation for the
lifespan of the platelet.
3. A patient develops nephrotic syndrome. Electron microscopy
demonstrates diffuse effacement of podocyte foot processes
without immune complex deposition. What is the most likely
diagnosis?
A. Focal segmental glomerulosclerosis
B. Membranous nephropathy
C. Minimal change disease
D. Poststreptococcal glomerulonephritis
Answer: C. Minimal change disease
Rationale: Minimal change disease is characterized by podocyte foot
process effacement and selective albuminuria. It is the most common
nephrotic syndrome in children.
4. A mutation causes constitutive activation of Ras proteins. What
cellular process is most directly increased?
A. DNA repair
B. Apoptosis
C. Cell proliferation
D. Cellular differentiation
Answer: C. Cell proliferation
Rationale: Ras proteins are GTP-binding proteins involved in growth
factor signaling. Constitutive activation promotes uncontrolled cellular
proliferation and oncogenesis.
, 5. A patient experiences severe diarrhea after consuming shellfish
contaminated with Vibrio cholerae. Which intracellular messenger
is increased?
A. cGMP
B. IP3
C. cAMP
D. DAG
Answer: C. cAMP
Rationale: Cholera toxin ADP-ribosylates Gs proteins, causing persistent
adenylate cyclase activation and elevated cAMP, leading to chloride and
water secretion.
6. Which vitamin deficiency most directly impairs γ-carboxylation of
clotting factors?
A. Vitamin A
B. Vitamin D
C. Vitamin E
D. Vitamin K
Answer: D. Vitamin K
Rationale: Vitamin K is required for γ-carboxylation of factors II, VII, IX,
X, protein C, and protein S.
7. A patient has an inferior wall myocardial infarction. Which
coronary artery is most likely occluded?
A. Left anterior descending artery
B. Left circumflex artery
C. Right coronary artery
D. Diagonal artery
Answer: C. Right coronary artery
, Rationale: Inferior wall infarctions involving leads II, III, and aVF are
most commonly caused by occlusion of the right coronary artery.
8. A newborn exhibits failure to thrive and recurrent respiratory
infections. Sweat chloride testing is positive. Which protein is
defective?
A. Dystrophin
B. CFTR
C. Fibrillin
D. Spectrin
Answer: B. CFTR
Rationale: Cystic fibrosis results from mutations in the CFTR chloride
channel, leading to thick secretions in pulmonary and gastrointestinal
systems.
9. A patient develops megaloblastic anemia after gastric bypass
surgery. Which deficiency is most likely?
A. Iron
B. Folate
C. Vitamin B12
D. Copper
Answer: C. Vitamin B12
Rationale: Loss of intrinsic factor-producing parietal cells and impaired
absorption in the terminal ileum contribute to vitamin B12 deficiency.
10. Which immune cell is primarily responsible for defense
against helminths?
A. Neutrophils
B. Basophils
Foundational Biomedical Sciences Exam
Practice Questions & [Verified Answers],
Plus Explained Rationales|2026 Latest
Update| Instant Download PDF
1. A 6-month-old infant presents with developmental delay,
seizures, and a musty body odor. Laboratory testing reveals
elevated phenylalanine levels. Which enzyme deficiency is
responsible for this condition?
A. Tyrosinase
B. Homogentisate oxidase
C. Phenylalanine hydroxylase
D. Branched-chain α-ketoacid dehydrogenase
Answer: C. Phenylalanine hydroxylase
Rationale: Phenylketonuria results from deficiency of phenylalanine
hydroxylase, preventing conversion of phenylalanine to tyrosine.
Accumulation causes intellectual disability, seizures, eczema, and a
musty odor if untreated.
2. A researcher administers a drug that irreversibly inhibits
cyclooxygenase activity in platelets. Which physiologic effect is
most likely?
A. Increased thromboxane A2 synthesis
B. Decreased platelet aggregation
C. Increased fibrin production
D. Increased prostacyclin synthesis
,Answer: B. Decreased platelet aggregation
Rationale: Aspirin irreversibly inhibits COX-1 in platelets, decreasing
thromboxane A2 production and impairing platelet aggregation for the
lifespan of the platelet.
3. A patient develops nephrotic syndrome. Electron microscopy
demonstrates diffuse effacement of podocyte foot processes
without immune complex deposition. What is the most likely
diagnosis?
A. Focal segmental glomerulosclerosis
B. Membranous nephropathy
C. Minimal change disease
D. Poststreptococcal glomerulonephritis
Answer: C. Minimal change disease
Rationale: Minimal change disease is characterized by podocyte foot
process effacement and selective albuminuria. It is the most common
nephrotic syndrome in children.
4. A mutation causes constitutive activation of Ras proteins. What
cellular process is most directly increased?
A. DNA repair
B. Apoptosis
C. Cell proliferation
D. Cellular differentiation
Answer: C. Cell proliferation
Rationale: Ras proteins are GTP-binding proteins involved in growth
factor signaling. Constitutive activation promotes uncontrolled cellular
proliferation and oncogenesis.
, 5. A patient experiences severe diarrhea after consuming shellfish
contaminated with Vibrio cholerae. Which intracellular messenger
is increased?
A. cGMP
B. IP3
C. cAMP
D. DAG
Answer: C. cAMP
Rationale: Cholera toxin ADP-ribosylates Gs proteins, causing persistent
adenylate cyclase activation and elevated cAMP, leading to chloride and
water secretion.
6. Which vitamin deficiency most directly impairs γ-carboxylation of
clotting factors?
A. Vitamin A
B. Vitamin D
C. Vitamin E
D. Vitamin K
Answer: D. Vitamin K
Rationale: Vitamin K is required for γ-carboxylation of factors II, VII, IX,
X, protein C, and protein S.
7. A patient has an inferior wall myocardial infarction. Which
coronary artery is most likely occluded?
A. Left anterior descending artery
B. Left circumflex artery
C. Right coronary artery
D. Diagonal artery
Answer: C. Right coronary artery
, Rationale: Inferior wall infarctions involving leads II, III, and aVF are
most commonly caused by occlusion of the right coronary artery.
8. A newborn exhibits failure to thrive and recurrent respiratory
infections. Sweat chloride testing is positive. Which protein is
defective?
A. Dystrophin
B. CFTR
C. Fibrillin
D. Spectrin
Answer: B. CFTR
Rationale: Cystic fibrosis results from mutations in the CFTR chloride
channel, leading to thick secretions in pulmonary and gastrointestinal
systems.
9. A patient develops megaloblastic anemia after gastric bypass
surgery. Which deficiency is most likely?
A. Iron
B. Folate
C. Vitamin B12
D. Copper
Answer: C. Vitamin B12
Rationale: Loss of intrinsic factor-producing parietal cells and impaired
absorption in the terminal ileum contribute to vitamin B12 deficiency.
10. Which immune cell is primarily responsible for defense
against helminths?
A. Neutrophils
B. Basophils
