Free full-length MCAT practice test — 230 questions, real timing 🇺🇸

8 original practice questions written by Myndaq in the MCAT style. They are not taken from this mock paper or from official past papers. Try each one, then open the answer.

1. Question 1Chemical and Physical Foundations of Biological SystemsOne correct answer

   A research group examined how pH affects the passage of Compound W, a weak monoprotic acid with pKa = 4.4, across an artificial lipid bilayer. The bilayer separated a donor chamber, which held W dissolved in buffer, from a receiver chamber buffered at pH 7.4. Earlier work had shown that only the uncharged form of W partitions into the bilayer to any appreciable extent.

   In Trial 1 the donor buffer was at pH 2.4; in Trial 2 it was at pH 6.4. All other conditions, including the total concentration of W in the donor chamber and the temperature, were identical. After 30 minutes the receiver chamber in Trial 1 contained many times more W than the receiver chamber in Trial 2.

   Which statement best accounts for the difference between Trial 1 and Trial 2?

   1. A. At pH 2.4 roughly 99% of W is protonated and uncharged, whereas at pH 6.4 only about 1% is, so far more W can enter the bilayer in Trial 1.
   2. B. At pH 2.4 roughly 99% of W is deprotonated, and the resulting anion is drawn across the bilayer by the higher pH of the receiver chamber.
   3. C. At pH 6.4 W is almost entirely protonated, which makes it too polar to enter the bilayer.
   4. D. The lower pH in Trial 1 makes the bilayer itself more permeable, so both forms of W cross it readily.
   Show answer and explanation

   Answer: A

   Use the Henderson–Hasselbalch equation, pH = pKa + log([A-]/[HA]).

   Trial 1: 2.4 = 4.4 + log ratio, so [A-]/[HA] = 10^-2. For every 100 molecules of HA there is 1 of A-, so about 100/101, or 99%, of W is the neutral acid. Trial 2: 6.4 - 4.4 = 2, so [A-]/[HA] = 100 and only about 1/101, or 1%, is neutral. Because only the uncharged form enters the bilayer, the donor solution in Trial 1 offers roughly 100 times more permeant W, which explains the much larger transfer.

   B reverses the protonation state (below its pKa an acid is mostly protonated) and the passage says the charged form does not partition into the membrane. C is also reversed: above the pKa the acid is mostly deprotonated, and the protonated form is the less polar one. D invokes a change in the membrane that the passage gives no evidence for; the ionization of W alone explains the result.

2. Question 2Chemical and Physical Foundations of Biological SystemsOne correct answer

   Blood flow through a short segment of an arteriole is modeled as laminar flow of a Newtonian fluid. If contraction of the vessel's smooth muscle reduces the inner radius of the segment by 20% while the pressure difference across the segment, its length and the viscosity of the blood stay the same, the volumetric flow rate becomes closest to what percentage of its original value?

   1. A. 41%
   2. B. 51%
   3. C. 64%
   4. D. 80%
   Show answer and explanation

   Answer: A

   Poiseuille's law gives Q = πΔP r^4 / (8ηL). With ΔP, η and L fixed, Q is proportional to r^4.

   The new radius is 0.8r, so the new flow is 0.8^4 = 0.8 × 0.8 × 0.8 × 0.8 = 0.64 × 0.64 = 0.4096, about 41% of the original. A modest narrowing therefore cuts flow by more than half, which is why arterioles are so effective at regulating blood flow.

   The distractors come from using the wrong power of r: 80% assumes flow is proportional to r, 64% to r², and 51% to r³.

3. Question 3Critical Analysis and Reasoning SkillsOne correct answer

   Librarians have long treated the pencilled note in a book's margin as a kind of vandalism, something to be erased before the volume returns to the shelf. The instinct is understandable. A library promises each reader a clean encounter with the text, and a stranger's exclamation marks seem to break that promise before the first page is turned.

   Yet the historian of reading has reason to regret every eraser. What survives of past readers is mostly what they chose to make public: reviews, letters meant for others, memoirs polished for posterity. The margin is different. A nineteenth-century schoolteacher who underlines a sentence praising thrift and writes 'not so' beside it is not performing for anyone; she is quarrelling with the page in private, and in doing so she records a response that no reviewer of her day would have thought worth printing. Multiply her by thousands and one begins to see how books were actually received, as opposed to how critics said they ought to be received.

   None of this means that every scribble deserves a vault. Most annotations are dull, and some are merely rude. But the decision about which ones are worth keeping cannot be made at the circulation desk by someone paid to restore blankness. It calls for the same judgment we already apply to letters and diaries, documents that were also, when they were written, thought to be of no interest to anyone but their authors.

   The author's central purpose in the passage is to:

   1. A. argue that readers' notes in library books can be valuable historical evidence and should not be erased as a matter of routine.
   2. B. urge libraries to preserve every annotation, whatever its content, as part of the historical record.
   3. C. condemn nineteenth-century readers for defacing books that belonged to the public.
   4. D. show that published reviews are a more trustworthy guide to past readers' opinions than private notes.
   Show answer and explanation

   Answer: A

   The passage grants the librarians' concern, then argues that margins preserve private reactions found nowhere else, and closes by saying the choice of what to keep needs expert judgment rather than automatic erasure. That is exactly A.

   B goes too far: the third paragraph says outright that not every scribble deserves a vault. C misreads the tone; the schoolteacher is presented sympathetically as a valuable witness, not as a vandal. D reverses the argument, since the author says margins reveal how books were actually received, as opposed to what critics said.

4. Question 4Critical Analysis and Reasoning SkillsOne correct answer

   Librarians have long treated the pencilled note in a book's margin as a kind of vandalism, something to be erased before the volume returns to the shelf. The instinct is understandable. A library promises each reader a clean encounter with the text, and a stranger's exclamation marks seem to break that promise before the first page is turned.

   Yet the historian of reading has reason to regret every eraser. What survives of past readers is mostly what they chose to make public: reviews, letters meant for others, memoirs polished for posterity. The margin is different. A nineteenth-century schoolteacher who underlines a sentence praising thrift and writes 'not so' beside it is not performing for anyone; she is quarrelling with the page in private, and in doing so she records a response that no reviewer of her day would have thought worth printing. Multiply her by thousands and one begins to see how books were actually received, as opposed to how critics said they ought to be received.

   None of this means that every scribble deserves a vault. Most annotations are dull, and some are merely rude. But the decision about which ones are worth keeping cannot be made at the circulation desk by someone paid to restore blankness. It calls for the same judgment we already apply to letters and diaries, documents that were also, when they were written, thought to be of no interest to anyone but their authors.

   Based on the passage, the author would most likely agree with which statement?

   1. A. A library's wish to offer readers an unmarked text is not a reasonable concern.
   2. B. Letters and diaries generally reveal less about past readers than marginal notes do.
   3. C. That a document's writer considered it private and unimportant is not, by itself, a good reason to discard it.
   4. D. Decisions about which annotations to keep are best left to circulation staff, who handle the books every day.
   Show answer and explanation

   Answer: C

   The final sentence compares annotations to letters and diaries, which were also thought to matter only to their authors when written, yet are now preserved after careful judgment. The author's reasoning therefore depends on the principle in C: a document's apparent privacy and unimportance at the time does not justify throwing it away.

   A contradicts the first paragraph, where the author calls the librarians' instinct understandable. B is never claimed; letters and diaries are used as a parallel case, not ranked against marginalia. D is the opposite of the author's view that the decision cannot be made at the circulation desk.

5. Question 5Biological and Biochemical Foundations of Living SystemsOne correct answer

   Investigators studying Enzyme K, a kinase from a soil bacterium, measured initial reaction velocities over a range of substrate concentrations with and without Compound Q. Fitting the data to the Michaelis–Menten equation gave the following values.

   Without Q: Km = 0.40 mM and Vmax = 90 μmol/min.

   With 5 μM Q: Km = 0.40 mM and Vmax = 45 μmol/min.

   In a separate test, raising the substrate concentration to 50 times the Km did not restore the velocity in the presence of Q to the uninhibited Vmax.

   Which type of inhibition by Compound Q is most consistent with these results?

   1. A. Competitive inhibition
   2. B. Uncompetitive inhibition
   3. C. Pure noncompetitive inhibition
   4. D. Mixed inhibition in which Q binds the free enzyme more tightly than the enzyme–substrate complex
   Show answer and explanation

   Answer: C

   Q halves Vmax but leaves Km unchanged, and excess substrate cannot overcome it. That pattern fits pure noncompetitive inhibition: the inhibitor binds the free enzyme and the enzyme–substrate complex with equal affinity at a site other than the active site. It lowers the amount of functional enzyme without changing how well the remaining enzyme binds substrate. On a Lineweaver–Burk plot the two lines would cross at the same x-intercept (-1/Km), and the inhibited line would have the higher y-intercept.

   Competitive inhibition raises the apparent Km, leaves Vmax unchanged and is overcome by high substrate, so the data rule it out. An uncompetitive inhibitor binds only the ES complex and lowers Km and Vmax by the same factor, so Km would have fallen to 0.20 mM. Mixed inhibition that favours the free enzyme would raise the apparent Km as well as lowering Vmax.

6. Question 6Biological and Biochemical Foundations of Living SystemsOne correct answer

   A woman who does not have a certain X-linked recessive trait has a father who does have it; her mother is not a carrier and has no family history of the trait. She and a man who does not have the trait plan to have children. What is the probability that their first child will be a son who has the trait?

   1. A. 0
   2. B. 1/8
   3. C. 1/4
   4. D. 1/2
   Show answer and explanation

   Answer: C

   A father passes his only X chromosome to every daughter, so the woman must have received the recessive allele from him. Her mother gave her a normal allele, which makes her an obligate carrier (X^A X^a). Her partner is X^A Y.

   For the first child to be an affected son, two independent events must happen: the child must be male (probability 1/2) and must receive the mother's X^a (probability 1/2). The combined probability is 1/2 × 1/2 = 1/4. No daughter would have the trait, because every daughter receives the father's normal X.

   1/2 is the probability that a child already known to be a son is affected, not the probability for a child of unknown sex. 1/8 wrongly adds a further factor of 1/2 for the woman being a carrier, which is certain here. 0 would be correct only if an unaffected woman could not pass the allele on.

7. Question 7Psychological, Social, and Biological Foundations of BehaviorOne correct answer

   In a memory study, 60 undergraduates listened to lists of 15 unrelated concrete nouns read aloud at a rate of one word every 2 seconds. After each list, half of the participants (Group I) immediately wrote down as many words as they could remember, in any order. The other half (Group D) first spent 30 seconds counting backward by sevens from a three-digit number shown on a screen and then wrote down the words.

   Group I recalled the first few and the last few words of each list better than the words in the middle. Group D recalled the first few words about as well as Group I did, but their recall of the last few words fell to roughly the level of the middle words.

   Which explanation best accounts for the change in recall of the final words in Group D?

   1. A. The counting task displaced the final words from short-term memory before they could be rehearsed and encoded into long-term memory.
   2. B. Proactive interference from the earlier words erased the final words from long-term memory.
   3. C. The delay gave participants extra time to consolidate the first words, which pushed the final words out of long-term memory.
   4. D. Counting backward reinstated the context in which the first words were encoded, so only those words benefited from context-dependent retrieval.
   Show answer and explanation

   Answer: A

   The serial position curve has two parts. The primacy effect comes from early words that were rehearsed more often and reached long-term memory. The recency effect comes from the last words, which are still held in short-term (working) memory at the moment of recall. Short-term memory has limited capacity and loses unrehearsed items within seconds. The counting task both fills working memory and blocks rehearsal, so the last words are lost, while the early words, already in long-term memory, are unaffected. That matches the data: Group D kept the primacy effect and lost the recency effect.

   B cannot explain a difference between the groups, because both heard the same earlier words; besides, interference does not erase items that were never stored in long-term memory. C is wrong because long-term memory is not a small store that consolidation fills up, and Group D's recall of the first words did not improve. D is unsupported: counting digits does not reinstate the setting in which the list was learned, and the finding to explain is a loss of the last words, not a gain for the first ones.

8. Question 8Psychological, Social, and Biological Foundations of BehaviorOne correct answer

   Priya is the first person in her family to attend university. She notices that several classmates whose parents hold graduate degrees already seem to know the unwritten academic norms: how to word an email asking for a deadline extension, what to say during office hours and which study habits instructors expect. None of these classmates has any personal connection to the faculty. The advantage these classmates have is best described as:

   1. A. cultural capital.
   2. B. social capital.
   3. C. role strain.
   4. D. anomie.
   Show answer and explanation

   Answer: A

   Cultural capital, a concept associated with Pierre Bourdieu, refers to non-financial assets such as knowledge, skills, tastes and ways of interacting. These are usually learned in the family and rewarded by institutions such as schools. Knowing the unwritten rules of academic communication is a clear example, and it gives these students an advantage over first-generation students like Priya.

   Social capital means the resources a person can reach through a network of relationships, and the stem rules this out by saying the classmates have no personal connection to the faculty. Role strain is tension between competing demands within a single role, such as a student juggling several assignments. Anomie, in Durkheim's sense, is a breakdown or absence of shared norms, which is almost the opposite of what the classmates show.