USMLE STEP 1 – MOCK EXAM 100 QUESTIONS AND
CORRECT DETAILED ANSWERS FOR GUARANTEED
SUCCESS / NEWEST 2025/2026 GRADED
A+||BRAND NEW VERSION!!
1. A 25-year-old man presents with fatigue and pallor. Lab results show
microcytic anemia and low ferritin. Which mechanism is most directly
responsible?
A. Decreased erythropoietin secretion
B. Impaired heme synthesis
C. Increased hemolysis
D. Bone marrow aplasia
Correct Answer: B
Iron deficiency leads to impaired heme synthesis, resulting in microcytic anemia.
2. Which vitamin deficiency is most likely to cause night blindness?
A. Vitamin D
B. Vitamin E
C. Vitamin A
D. Vitamin K
Vitamin A is essential for retinal phototransduction.
3. A drug that increases GABA-A receptor activity would most likely cause
which effect?
A. Increased neuronal firing
, B. Decreased chloride influx
C. Hyperpolarization of neurons
D. Increased glutamate release
GABA-A activation increases chloride influx, hyperpolarizing neurons.
4. Which embryologic structure gives rise to the adrenal cortex?
A. Neural crest
B. Mesoderm
C. Endoderm
D. Intermediate mesoderm
The adrenal cortex originates from mesoderm; medulla from neural crest.
5. A patient with chronic pancreatitis is at greatest risk for deficiency of which
vitamin?
A. Vitamin B12
B. Vitamin D
C. Vitamin C
D. Folate
Fat malabsorption leads to deficiency of fat-soluble vitamins.
6. Which immunoglobulin is most abundant in mucosal secretions?
A. IgG
B. IgM
C. IgA
D. IgE
IgA protects mucosal surfaces.
, 7. A decrease in which variable will shift the oxygen-hemoglobin dissociation
curve to the left?
A. Temperature
B. 2,3-BPG
C. CO₂
D. Hydrogen ion concentration
Decreased H⁺ increases hemoglobin’s oxygen affinity.
8. Which enzyme is deficient in classic galactosemia?
A. Galactokinase
B. Galactose-1-phosphate uridyltransferase
C. Lactase
D. Aldolase B
This deficiency leads to liver failure, cataracts, and E. coli sepsis.
9. A patient with myasthenia gravis has antibodies against which receptor?
A. Muscarinic
B. Dopamine
C. Nicotinic acetylcholine
D. GABA
Autoantibodies impair neuromuscular transmission.
10.Which hormone is secreted in response to hypocalcemia?
A. Calcitonin
B. Vitamin D
C. Parathyroid hormone
D. Aldosterone
PTH increases serum calcium.
CORRECT DETAILED ANSWERS FOR GUARANTEED
SUCCESS / NEWEST 2025/2026 GRADED
A+||BRAND NEW VERSION!!
1. A 25-year-old man presents with fatigue and pallor. Lab results show
microcytic anemia and low ferritin. Which mechanism is most directly
responsible?
A. Decreased erythropoietin secretion
B. Impaired heme synthesis
C. Increased hemolysis
D. Bone marrow aplasia
Correct Answer: B
Iron deficiency leads to impaired heme synthesis, resulting in microcytic anemia.
2. Which vitamin deficiency is most likely to cause night blindness?
A. Vitamin D
B. Vitamin E
C. Vitamin A
D. Vitamin K
Vitamin A is essential for retinal phototransduction.
3. A drug that increases GABA-A receptor activity would most likely cause
which effect?
A. Increased neuronal firing
, B. Decreased chloride influx
C. Hyperpolarization of neurons
D. Increased glutamate release
GABA-A activation increases chloride influx, hyperpolarizing neurons.
4. Which embryologic structure gives rise to the adrenal cortex?
A. Neural crest
B. Mesoderm
C. Endoderm
D. Intermediate mesoderm
The adrenal cortex originates from mesoderm; medulla from neural crest.
5. A patient with chronic pancreatitis is at greatest risk for deficiency of which
vitamin?
A. Vitamin B12
B. Vitamin D
C. Vitamin C
D. Folate
Fat malabsorption leads to deficiency of fat-soluble vitamins.
6. Which immunoglobulin is most abundant in mucosal secretions?
A. IgG
B. IgM
C. IgA
D. IgE
IgA protects mucosal surfaces.
, 7. A decrease in which variable will shift the oxygen-hemoglobin dissociation
curve to the left?
A. Temperature
B. 2,3-BPG
C. CO₂
D. Hydrogen ion concentration
Decreased H⁺ increases hemoglobin’s oxygen affinity.
8. Which enzyme is deficient in classic galactosemia?
A. Galactokinase
B. Galactose-1-phosphate uridyltransferase
C. Lactase
D. Aldolase B
This deficiency leads to liver failure, cataracts, and E. coli sepsis.
9. A patient with myasthenia gravis has antibodies against which receptor?
A. Muscarinic
B. Dopamine
C. Nicotinic acetylcholine
D. GABA
Autoantibodies impair neuromuscular transmission.
10.Which hormone is secreted in response to hypocalcemia?
A. Calcitonin
B. Vitamin D
C. Parathyroid hormone
D. Aldosterone
PTH increases serum calcium.
