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USMLE Step 1-style Mock Test
A timed 25-question mock for the USMLE Step 1-style basic science practice covering biology, chemistry. Answer, submit and review every question with its explanation; set negative marking to match your exam’s current scheme.
USMLE Step 1-style mock test
25 questions · 1 mark each · the timer starts with your first answer and the test submits itself when time runs out.
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Q1.BiologyWhich blood vessels carry blood away from the heart?
Answer: D — Arteries
Arteries carry blood away from the heart.
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Q2.ChemistryWhich gas is responsible for most of the greenhouse effect from human activity?
Answer: A — Carbon dioxide
CO₂ from burning fossil fuels is the largest human-caused contributor.
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Q3.BiologyWhich part of the brain controls balance and coordination?
Answer: D — Cerebellum
The cerebellum coordinates movement and balance.
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Q4.Chemistry90 g of KCl (molar mass 74.5) is dissolved to make 1000 mL of solution. Find the molarity.
Answer: C — 1.208 M
Moles = 90/74.5 = 1.208; molarity = moles ÷ litres = 1.208 ÷ 1 = 1.208 M.
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Q5.BiologyThe father of genetics is:
Answer: C — Gregor Mendel
Mendel’s pea plant experiments established the laws of inheritance.
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Q6.ChemistryWater has a maximum density at about:
Answer: A — 4 °C
Water is densest at about 4 °C.
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Q7.BiologyBile is produced by the:
Answer: B — Liver
Bile is made in the liver and stored in the gall bladder.
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Q8.Chemistry36.5 g of KCl (molar mass 74.5) is dissolved to make 2000 mL of solution. Find the molarity.
Answer: B — 0.245 M
Moles = 36.5/74.5 = 0.49; molarity = moles ÷ litres = 0.49 ÷ 2 = 0.245 M.
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Q9.BiologyThe basic unit of heredity is the:
Answer: B — Gene
Genes are segments of DNA that carry hereditary information.
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Q10.ChemistryWhich is the most electronegative element?
Answer: C — Fluorine
Fluorine has the highest electronegativity (3.98 on the Pauling scale).
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Q11.BiologyPhotosynthesis takes place in the:
Answer: B — Chloroplasts
Chloroplasts contain chlorophyll that captures light energy.
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Q12.ChemistryWhat is the pH of a solution with [H⁺] = 10⁻¹ mol/L?
Answer: C — 1
pH = −log[H⁺] = −log(10⁻¹) = 1.
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Q13.BiologyWhich vitamin deficiency causes scurvy?
Answer: C — Vitamin C
Scurvy results from a lack of vitamin C (ascorbic acid).
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Q14.ChemistryAn oxidation reaction involves:
Answer: B — Loss of electrons
Oxidation is loss of electrons (OIL RIG).
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Q15.BiologyNormal human body temperature is approximately:
Answer: B — 37 °C
About 37 °C (98.6 °F).
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Q16.ChemistryWhat is the pH of a solution with [OH⁻] = 10⁻³ mol/L at 25 °C?
Answer: C — 11
[OH⁻] = 10⁻³ → pOH = 3; pH = 14 − 3 = 11 (at 25 °C).
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Q17.BiologyThe green pigment in plants is:
Answer: B — Chlorophyll
Chlorophyll absorbs red and blue light for photosynthesis.
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Q18.ChemistryThe hardest naturally occurring substance is:
Answer: D — Diamond
Diamond, a carbon allotrope, is the hardest natural material.
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Q19.BiologyHaemoglobin contains which metal?
Answer: C — Iron
Iron in the haem group binds oxygen.
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Q20.ChemistryWhat is the pH of a solution with [OH⁻] = 10⁻⁶ mol/L at 25 °C?
Answer: D — 8
[OH⁻] = 10⁻⁶ → pOH = 6; pH = 14 − 6 = 8 (at 25 °C).
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Q21.BiologyThe number of chromosomes in a normal human body cell is:
Answer: D — 46
Humans have 46 chromosomes (23 pairs).
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Q22.ChemistryA solution with pH 3 is:
Answer: D — Acidic
pH below 7 is acidic.
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Q23.BiologyThe universal blood donor group is:
Answer: C — O−
O negative red cells lack A, B and Rh antigens.
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Q24.BiologyGas exchange in the lungs takes place in the:
Answer: D — Alveoli
Thin-walled alveoli allow oxygen and CO₂ to diffuse.
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Q25.ChemistryAvogadro’s number is approximately:
Answer: B — 6.022 × 10²³
One mole contains 6.022 × 10²³ particles.
How the mock test works
- The timer starts with your first answer; the test submits itself when time runs out.
- Choose the negative marking that matches your exam (this test has no negative marking by default — check the official notification).
- After submitting you get your score, accuracy, time taken and a topic-wise breakdown, then every explanation.
- “New mock test” builds another paper — calculation questions get new numbers.
About USMLE Step 1-style
USMLE Step 1-style basic science practice — conducted by Practice in the style of the USMLE (FSMB & NBME); not affiliated. Foundational biomedical science practice for medical students preparing for licensing exams.
Original practice questions written for this site in the style and difficulty of each exam’s syllabus. They are not past papers and the site is not affiliated with any exam body. Exam patterns, marking schemes and syllabi change — always check the latest official notification.
USMLE Step 1-style practice topics
| Topic | Section | Question source |
|---|---|---|
| Biology | Science | Question bank |
| Chemistry | Science | Calculated + question bank |