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Free MCAT practice questions with answers.
Choose your answer before opening the explanation. Then inspect why each alternative fails and name one idea to apply on your next question. These examples are also used in our quick diagnostic, so use fresh questions when checking your progress later.
C/P · Original practice question
1. Parallel Circuit Power
A 4.0 Ω resistor and a 12 Ω resistor are connected in parallel across an ideal 12 V battery. What total power does the battery deliver?
- A.48 W
- B.12 W
- C.36 W
- D.9.0 W
Show answer and explanation
Answer: A. 48 W
Equivalent resistance: 1/R_eq = 1/4.0 + 1/12 = 3/12 + 1/12 = 4/12, so R_eq = 3.0 Ω. Total power P = V²/R_eq = (12 V)²/(3.0 Ω) = 144/3.0 = 48 W. Check by summing branches: P(4.0 Ω) = 144/4.0 = 36 W and P(12 Ω) = 144/12 = 12 W, and 36 + 12 = 48 W. Units: V²/Ω = (J/C)²·(A/V) = J/s = W.
- Why not B?
- 12 W is the power dissipated by the 12 Ω branch alone.
- Why not C?
- 36 W is the power dissipated by the 4.0 Ω branch alone.
- Why not D?
- 9.0 W comes from adding the resistances as if in series (16 Ω): 144/16 = 9.0 W.
Takeaway: For parallel resistors at fixed voltage, use P = V²/R and remember the lowest-resistance branch draws the most power.
B/B · Original practice question
2. Quaternary Structure Interactions
A newly purified enzyme elutes from a size-exclusion column under nondenaturing conditions with an apparent mass of 100 kDa. On SDS-PAGE it migrates as a single 50 kDa band regardless of whether a thiol reducing agent is included in the sample buffer. Which conclusion about the enzyme's structure is best supported?
- A.It is a dimer of 50 kDa subunits held together by noncovalent interactions such as hydrophobic contacts, hydrogen bonds, and salt bridges.
- B.It is a dimer of 50 kDa subunits covalently linked by an interchain disulfide bond.
- C.It is a single 100 kDa polypeptide whose compact tertiary fold causes it to migrate anomalously fast in SDS-PAGE.
- D.It is a single 50 kDa polypeptide whose two intrachain disulfide bonds double its apparent mass in solution.
Show answer and explanation
Answer: A. It is a dimer of 50 kDa subunits held together by noncovalent interactions such as hydrophobic contacts, hydrogen bonds, and salt bridges.
Size-exclusion chromatography under native conditions reports the mass of the intact assembly, here 100 kDa. SDS coats polypeptides and disrupts the hydrophobic interactions, hydrogen bonds, and salt bridges that stabilize tertiary and noncovalent quaternary structure, but it does not break covalent bonds. Because the protein splits into 50 kDa pieces in SDS even without a reducing agent, the two halves cannot be linked by a disulfide bond, which would require a thiol reductant to cleave. Therefore the native 100 kDa species is a dimer of two 50 kDa chains associated purely through noncovalent interactions. The primary structure (peptide bonds) of each chain is intact, which is why each subunit appears as a discrete 50 kDa band.
- Why not B?
- An interchain disulfide would survive SDS treatment and yield a 100 kDa band unless a reducing agent were added; the observed reductant-independent 50 kDa band rules this out.
- Why not C?
- SDS unfolds tertiary structure and imposes a roughly uniform charge-to-mass ratio, so a 100 kDa chain would not migrate at 50 kDa because of its fold.
- Why not D?
- Intrachain disulfides link cysteines within one chain and cannot double the mass of a monomer; they affect compactness, not molecular weight.
Takeaway: Compare native and denaturing masses, then ask whether a reducing agent changed the result to distinguish noncovalent from disulfide-linked quaternary structure.
P/S · Original practice question
3. Proactive Interference
After using the same four-digit door code for five years, an employee is assigned a new code. For several days, she often enters the old code when trying to recall the new one. Which process best explains these errors?
- A.Retroactive interference, because the new code disrupts retrieval of the old code
- B.Decay, because both code memories weaken solely with the passage of time
- C.Proactive interference, because the old code disrupts retrieval of the new code
- D.Source amnesia, because she remembers a code but not where she learned it
Show answer and explanation
Answer: C. Proactive interference, because the old code disrupts retrieval of the new code
The well-practiced old code is the earlier memory, and it intrudes specifically when the employee tries to retrieve the later code. That old-to-new direction identifies proactive interference rather than retroactive interference.
- Why not A?
- This describes new learning impairing an older memory, but the observed errors show the older code intruding on recall of the newer code.
- Why not B?
- The errors are systematic intrusions of a competing code, not nonspecific forgetting attributable only to elapsed time.
- Why not D?
- She knows which code is old and which is new, so the problem is not loss of contextual information about a memory's source.
Takeaway: Track the direction of interference: identify which memory came first and which memory the person is trying to retrieve.
These standalone examples cover the science and behavioral sections. For passage-based practice including CARS, try the free MCAT diagnostic. These are original 528 Academy questions, not AAMC exam items.
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A productive practice block has four parts: answer under a clearly chosen timing condition, analyze the first point where your reasoning diverged, repair the smallest underlying gap, and retest that lesson in a new context. This keeps practice from becoming a cycle of completing sets without changing your method.
1. Practice
2. Analyze
3. Target
4. Adapt
Timing
Use timed and untimed work for different jobs.
Untimed practice is for making a method visible. It gives you room to identify the task, find the relevant evidence, predict, eliminate, and notice exactly where the process breaks. It should still be closed-book and deliberate.
Timed practice is for testing whether that method remains reliable under constraint. Begin with short blocks, review where the time went, and increase set length gradually. A timer is useful evidence; it is not a substitute for understanding.
For a deeper progression from accuracy to pace, read our guide to timed versus untimed MCAT practice.
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Review
Review the reasoning, not only the answer key.
Before reading an explanation, state why you chose your answer. Then locate the first faulty step. That record is more useful than a note that says only “content” or “careless.” It tells you whether to learn a fact, change how you read evidence, tighten an inference, or adjust your timing behavior.
- Explain why your chosen option felt plausible
- Name the exact detail that eliminates it
- State the smallest durable rule to remember
- Retest the rule away from the original wording
- Track recurring patterns across multiple sets
- Remove priorities when later evidence shows improvement
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MCAT practice FAQ
Where can I try free MCAT practice questions?
Try the three original questions and explanations on this page without an account. A free 528 Academy account includes 40 selected questions across all four sections. The free diagnostic also includes passage-based practice; it is not a full-length exam or an official score prediction.
How many MCAT practice questions should I do each day?
Choose a number you can review completely. For many students, 10 to 30 carefully reviewed questions teach more than a large set that receives only answer-key review. Increase volume after your review process is repeatable.
Should MCAT practice be timed or untimed?
Use untimed practice to build or repair a reasoning method, then use short timed sets to make that method efficient. Full timed sections are best for checking pacing and endurance after the underlying process is stable.
When should I start doing MCAT practice questions?
Start early enough that questions can guide content review. You do not need to finish every chapter first. A question exposes whether you can retrieve and apply a concept, which passive review alone cannot show.
Can third-party questions replace official AAMC practice?
No. Original third-party questions are useful for building volume, repairing concepts, and practicing a method. Official AAMC material remains essential for calibrating to the exam maker's wording and for final-stage simulation.