COMSAE Phase 1 Form 113 Practice
Examination QUESTIONS WITH
CORRECT ANSWERS PLUS
RATIONALES 2026/2027 EDITION
WITH INSTANT PDF DOWNLOAD
1. A 24-year-old patient develops severe muscle weakness after
prolonged exercise. Laboratory testing demonstrates impaired
ATP production caused by a defect in the mitochondrial electron
transport chain. Which process normally generates the greatest
amount of ATP from one molecule of glucose?
A. Glycolysis
B. Citric acid cycle
C. Oxidative phosphorylation
D. Fermentation
E. Substrate-level phosphorylation
Answer: C. Oxidative phosphorylation
Rationale: Oxidative phosphorylation, consisting of the electron
transport chain and ATP synthase, produces the majority of ATP
generated from glucose. Glycolysis produces a small amount of
ATP, while the citric acid cycle primarily generates reduced
electron carriers that drive oxidative phosphorylation.
2. A researcher studies an enzyme that catalyzes the conversion
of substrate to product. Increasing substrate concentration
initially increases the reaction rate, but eventually the rate
,reaches a plateau. Which kinetic property best explains this
observation?
A. Decreased enzyme concentration
B. Enzyme saturation
C. Competitive inhibition
D. Decreased substrate affinity
E. Irreversible denaturation
Answer: B. Enzyme saturation
Rationale: As substrate concentration increases, more enzyme
active sites become occupied. Once essentially all available
active sites are occupied, the reaction approaches its maximum
velocity (Vmax), producing a plateau.
3. A child presents with severe metabolic acidosis and elevated
lactate levels after consuming a carbohydrate-rich meal. A
deficiency in pyruvate dehydrogenase is suspected. Which
molecule normally serves as the coenzyme-derived product that
enters the citric acid cycle after pyruvate metabolism?
A. Lactate
B. Acetyl-CoA
C. Oxaloacetate
D. Succinate
E. Citrate
Answer: B. Acetyl-CoA
Rationale: Pyruvate dehydrogenase converts pyruvate into acetyl-
CoA, which enters the citric acid cycle by combining with
oxaloacetate to form citrate. Deficiency of pyruvate
,dehydrogenase promotes diversion of pyruvate toward lactate
production.
4. A patient with hereditary spherocytosis undergoes
splenectomy. Which normal function of the spleen is most
directly affected?
A. Production of bile
B. Removal of aged erythrocytes
C. Production of clotting factors
D. Filtration of lymph
E. Secretion of erythropoietin
Answer: B. Removal of aged erythrocytes
Rationale: The spleen removes aged and abnormal red blood
cells through macrophage-mediated filtration. Splenectomy
therefore reduces splenic clearance of erythrocytes and
increases susceptibility to infections by certain encapsulated
organisms.
5. A patient develops jaundice due to increased destruction of red
blood cells. Which laboratory finding is most consistent with
increased hemolysis?
A. Decreased unconjugated bilirubin
B. Increased haptoglobin
C. Increased lactate dehydrogenase
D. Decreased reticulocyte count
E. Increased conjugated bilirubin only
Answer: C. Increased lactate dehydrogenase
, Rationale: Hemolysis releases intracellular enzymes, including
lactate dehydrogenase, and increases unconjugated bilirubin
production. Haptoglobin typically decreases because it binds free
hemoglobin. Reticulocytes generally increase as the bone
marrow responds to anemia.
6. A patient with chronic kidney disease develops fatigue and
pallor. The anemia is primarily caused by decreased production of
which hormone?
A. Renin
B. Aldosterone
C. Erythropoietin
D. Hepcidin
E. Thrombopoietin
Answer: C. Erythropoietin
Rationale: Renal peritubular interstitial cells produce
erythropoietin in response to tissue hypoxia. Chronic kidney
disease reduces erythropoietin production, resulting in a typically
normocytic, normochromic anemia.
7. A patient has a mutation affecting the β-globin chain of
hemoglobin, causing hemoglobin molecules to polymerize during
deoxygenation. Which condition is most likely present?
A. Hereditary spherocytosis
B. Sickle cell disease
C. G6PD deficiency
D. Thalassemia minor
E. Hereditary elliptocytosis
Examination QUESTIONS WITH
CORRECT ANSWERS PLUS
RATIONALES 2026/2027 EDITION
WITH INSTANT PDF DOWNLOAD
1. A 24-year-old patient develops severe muscle weakness after
prolonged exercise. Laboratory testing demonstrates impaired
ATP production caused by a defect in the mitochondrial electron
transport chain. Which process normally generates the greatest
amount of ATP from one molecule of glucose?
A. Glycolysis
B. Citric acid cycle
C. Oxidative phosphorylation
D. Fermentation
E. Substrate-level phosphorylation
Answer: C. Oxidative phosphorylation
Rationale: Oxidative phosphorylation, consisting of the electron
transport chain and ATP synthase, produces the majority of ATP
generated from glucose. Glycolysis produces a small amount of
ATP, while the citric acid cycle primarily generates reduced
electron carriers that drive oxidative phosphorylation.
2. A researcher studies an enzyme that catalyzes the conversion
of substrate to product. Increasing substrate concentration
initially increases the reaction rate, but eventually the rate
,reaches a plateau. Which kinetic property best explains this
observation?
A. Decreased enzyme concentration
B. Enzyme saturation
C. Competitive inhibition
D. Decreased substrate affinity
E. Irreversible denaturation
Answer: B. Enzyme saturation
Rationale: As substrate concentration increases, more enzyme
active sites become occupied. Once essentially all available
active sites are occupied, the reaction approaches its maximum
velocity (Vmax), producing a plateau.
3. A child presents with severe metabolic acidosis and elevated
lactate levels after consuming a carbohydrate-rich meal. A
deficiency in pyruvate dehydrogenase is suspected. Which
molecule normally serves as the coenzyme-derived product that
enters the citric acid cycle after pyruvate metabolism?
A. Lactate
B. Acetyl-CoA
C. Oxaloacetate
D. Succinate
E. Citrate
Answer: B. Acetyl-CoA
Rationale: Pyruvate dehydrogenase converts pyruvate into acetyl-
CoA, which enters the citric acid cycle by combining with
oxaloacetate to form citrate. Deficiency of pyruvate
,dehydrogenase promotes diversion of pyruvate toward lactate
production.
4. A patient with hereditary spherocytosis undergoes
splenectomy. Which normal function of the spleen is most
directly affected?
A. Production of bile
B. Removal of aged erythrocytes
C. Production of clotting factors
D. Filtration of lymph
E. Secretion of erythropoietin
Answer: B. Removal of aged erythrocytes
Rationale: The spleen removes aged and abnormal red blood
cells through macrophage-mediated filtration. Splenectomy
therefore reduces splenic clearance of erythrocytes and
increases susceptibility to infections by certain encapsulated
organisms.
5. A patient develops jaundice due to increased destruction of red
blood cells. Which laboratory finding is most consistent with
increased hemolysis?
A. Decreased unconjugated bilirubin
B. Increased haptoglobin
C. Increased lactate dehydrogenase
D. Decreased reticulocyte count
E. Increased conjugated bilirubin only
Answer: C. Increased lactate dehydrogenase
, Rationale: Hemolysis releases intracellular enzymes, including
lactate dehydrogenase, and increases unconjugated bilirubin
production. Haptoglobin typically decreases because it binds free
hemoglobin. Reticulocytes generally increase as the bone
marrow responds to anemia.
6. A patient with chronic kidney disease develops fatigue and
pallor. The anemia is primarily caused by decreased production of
which hormone?
A. Renin
B. Aldosterone
C. Erythropoietin
D. Hepcidin
E. Thrombopoietin
Answer: C. Erythropoietin
Rationale: Renal peritubular interstitial cells produce
erythropoietin in response to tissue hypoxia. Chronic kidney
disease reduces erythropoietin production, resulting in a typically
normocytic, normochromic anemia.
7. A patient has a mutation affecting the β-globin chain of
hemoglobin, causing hemoglobin molecules to polymerize during
deoxygenation. Which condition is most likely present?
A. Hereditary spherocytosis
B. Sickle cell disease
C. G6PD deficiency
D. Thalassemia minor
E. Hereditary elliptocytosis
