Domande di esercitazione MCAT
Le domande del test restano in inglese.
Questo è un assaggio gratuito da 15 domande scientifiche dell'MCAT, scritto dal team di StudyPDF. Ogni quesito qui è una domanda discreta, quella indipendente che arriva senza nessun brano allegato, presa da tutte e tre le sezioni scientifiche: biologia e biochimica, chimica generale e organica con fisica, e psicologia e sociologia. Rispondi a tutte e 15 le domande, poi guarda il punteggio e leggi la spiegazione di ognuna. La comprensione del testo qui non viene verificata, quella sta nella pagina CARS collegata qui sotto.
A globular protein folds in water. Which amino acid side chain is most likely to end up buried in the hydrophobic core?
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1. A globular protein folds in water. Which amino acid side chain is most likely to end up buried in the hydrophobic core?
- A. Aspartate
- B. Lysine
- C. Valine
- D. Serine
Mostra risposta e spiegazione
Risposta: C. Valine
Folding in water pushes nonpolar side chains inward and leaves charged and polar ones on the surface where they can interact with water. Valine has a branched hydrocarbon side chain with nothing to hydrogen bond, so the core is where it costs the least energy. Aspartate and lysine carry charges at physiological pH and serine has a hydroxyl group, so all three prefer the surface.
2. A competitive inhibitor is added to an enzyme assay. What happens to the apparent Km and the Vmax?
- A. Km increases and Vmax is unchanged
- B. Km decreases and Vmax is unchanged
- C. Km is unchanged and Vmax decreases
- D. Km increases and Vmax decreases
Mostra risposta e spiegazione
Risposta: A. Km increases and Vmax is unchanged
A competitive inhibitor binds the active site, so it fights substrate for the same spot. That means you need more substrate to reach half maximal velocity, which shows up as a higher apparent Km. Enough substrate still outcompetes the inhibitor completely, so Vmax is untouched. Pure noncompetitive inhibition is the mirror image: Vmax falls and Km stays put.
3. Complete the sentence.
In oxidative phosphorylation, the electron transport chain uses the energy released by electron transfer to pump protons into the _____. ATP synthase then makes ATP as those protons flow back down their gradient into the _____.
Opzioni per lo spazio 1: mitochondrial matrix, intermembrane space, cytosol
Opzioni per lo spazio 2: mitochondrial matrix, intermembrane space, cytosol
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Risposta: intermembrane space, mitochondrial matrix
The electron transport chain is a series of redox reactions, and the energy it releases is stored as a proton gradient across the inner mitochondrial membrane rather than as ATP directly. ATP synthase is the only part that turns that gradient back into chemical energy. This is why an uncoupler that lets protons leak across the membrane keeps electron transport and oxygen consumption running while ATP output collapses.
4. A buffer is made from a weak acid and its conjugate base. Its buffering capacity is greatest when:
- A. The solution pH is two units below the pKa
- B. The solution pH is two units above the pKa
- C. The solution pH equals the pKa
- D. The weak acid is present in large excess over the conjugate base
Mostra risposta e spiegazione
Risposta: C. The solution pH equals the pKa
The Henderson-Hasselbalch equation says pH equals pKa plus the log of the base to acid ratio, so pH equals pKa exactly when that ratio is one. With equal amounts of both forms the buffer has the most room to absorb either added acid or added base before one form runs out. Practically, a buffer is useful roughly one pH unit on either side of its pKa, which is why bicarbonate and phosphate cover different ranges in the body.
5. Which statements about eukaryotic gene expression are correct?
Seleziona tutte le risposte corrette.
- A. Introns are spliced out of the primary transcript before the mature mRNA leaves the nucleus
- B. The genetic code is degenerate, so several codons can specify the same amino acid
- C. RNA polymerase requires a primer to begin synthesis
- D. A missense mutation changes a codon so a different amino acid is inserted
- E. Ribosomes read the mRNA from the 3 prime end toward the 5 prime end
Mostra risposta e spiegazione
Risposta: A. Introns are spliced out of the primary transcript before the mature mRNA leaves the nucleus, B. The genetic code is degenerate, so several codons can specify the same amino acid, D. A missense mutation changes a codon so a different amino acid is inserted
Splicing, capping and polyadenylation all happen in the nucleus, and only the processed mRNA is exported. Degeneracy is why the third base of a codon often tolerates a change with no effect on the protein, which is the definition of a silent mutation, while a missense mutation swaps the amino acid and a nonsense mutation creates a stop codon. RNA polymerase can start a chain from scratch, unlike DNA polymerase, and ribosomes read mRNA 5 prime to 3 prime.
6. In the proximal tubule of the nephron, glucose crosses the apical membrane into the cell against its own concentration gradient by moving together with sodium. This is best described as:
- A. Simple diffusion
- B. Facilitated diffusion
- C. Primary active transport
- D. Secondary active transport
Mostra risposta e spiegazione
Risposta: D. Secondary active transport
Secondary active transport means the carrier itself burns no ATP. It rides an ion gradient that some other pump paid for. Here the sodium potassium ATPase on the basolateral side spends ATP to keep intracellular sodium low, and the sodium glucose cotransporter uses that inward sodium gradient to drag glucose uphill. Block the ATPase and the sodium gradient collapses, and glucose reabsorption stops even though the cotransporter is untouched.
7. Complete the sentence.
In an infrared spectrum, a broad absorption centered near 3300 reciprocal centimeters points to an _____ bond, while a strong sharp band near 1700 reciprocal centimeters points to a _____.
Opzioni per lo spazio 1: O to H, C to H, C to C double
Opzioni per lo spazio 2: carbon carbon double bond, carbonyl group, nitrile group
Mostra risposta e spiegazione
Risposta: O to H, carbonyl group
Infrared spectroscopy reports bond vibrations, and the two most useful signals for a first pass are the broad hydroxyl stretch and the sharp carbonyl stretch. The hydroxyl band is broad because hydrogen bonding gives the bond a range of strengths across the sample. Seeing both a broad hydroxyl band and a carbonyl band in one spectrum is the classic hint that you are looking at a carboxylic acid.
8. Which carboxylic acid derivative is most reactive toward nucleophilic acyl substitution?
- A. An acyl chloride
- B. An ester
- C. An amide
- D. A carboxylate ion
Mostra risposta e spiegazione
Risposta: A. An acyl chloride
Reactivity in this family tracks two things: how good the leaving group is and how much the attached atom donates electron density into the carbonyl. Chloride is a weak base and a good leaving group, and it donates very little, so the acyl chloride sits at the top. Nitrogen donates strongly, which makes amides the most stable of the neutral derivatives, and a carboxylate is already deprotonated and negatively charged, so a nucleophile has little reason to attack it.
9. A reaction has a negative delta G under the given conditions. Which statements are correct?
Seleziona tutte le risposte corrette.
- A. The reaction must proceed quickly
- B. The reaction is spontaneous as written under those conditions
- C. The reaction must be exothermic
- D. An enzyme could speed it up without changing the value of delta G
- E. Under standard conditions, a negative standard delta G means the equilibrium constant is greater than one
Mostra risposta e spiegazione
Risposta: B. The reaction is spontaneous as written under those conditions, D. An enzyme could speed it up without changing the value of delta G, E. Under standard conditions, a negative standard delta G means the equilibrium constant is greater than one
Delta G is about thermodynamics, not speed. A spontaneous reaction can take years if the activation energy is high, and a catalyst lowers that barrier without touching the free energy difference between reactants and products. Spontaneity also does not require heat release, since a positive entropy change at high enough temperature can make delta G negative for an endothermic reaction. Standard delta G is related to the equilibrium constant by delta G naught equals minus RT ln K, so a negative value puts K above one.
10. Circulating thyroid hormone rises because the thyroid gland itself is overproducing. In an intact feedback loop, what happens to TSH released by the anterior pituitary?
- A. It rises, because hormone levels and TSH move together
- B. It falls, because the high hormone level suppresses the pituitary and the hypothalamus
- C. It stays the same, because TSH is regulated only by the hypothalamus
- D. It rises first and then stays permanently elevated
Mostra risposta e spiegazione
Risposta: B. It falls, because the high hormone level suppresses the pituitary and the hypothalamus
The hypothalamus releases TRH, the anterior pituitary releases TSH, and the thyroid releases its hormones, which then feed back to shut down the two levels above. When the gland at the end of the chain is the source of the excess, the feedback signal is strong and TSH goes down. That inverse pattern is the point of a negative feedback loop, and the same logic runs the hypothalamus, pituitary and adrenal axis with cortisol.
11. A vessel behaves as a rigid tube with steady laminar flow. If its radius drops to half while the pressure difference across it stays the same, the flow rate becomes about:
- A. One half of the original
- B. One quarter of the original
- C. One eighth of the original
- D. One sixteenth of the original
Mostra risposta e spiegazione
Risposta: D. One sixteenth of the original
Poiseuille's law says flow rate is proportional to the fourth power of the radius for a given pressure difference, viscosity and length. Halving the radius therefore divides flow by two to the fourth, which is sixteen. That fourth power dependence is why radius changes dominate resistance in the circulation, and why small changes in vessel diameter matter far more than changes in length or viscosity.
12. A student has a headache, takes a painkiller, and the headache goes away. She now reaches for the painkiller sooner whenever a headache starts. In operant terms this is:
- A. Positive reinforcement
- B. Negative reinforcement
- C. Positive punishment
- D. Classical conditioning
Mostra risposta e spiegazione
Risposta: B. Negative reinforcement
In operant conditioning, reinforcement means the behavior becomes more frequent and punishment means it becomes less frequent. Positive and negative describe whether something was added or taken away, not whether it felt good. Here an unpleasant stimulus was removed and the behavior increased, which is negative reinforcement by definition. Classical conditioning would involve pairing two stimuli to produce an involuntary response, not strengthening a voluntary action by its consequence.
13. The smallest change in a stimulus that a person can detect half of the time is called the:
- A. Absolute threshold
- B. Signal detection criterion
- C. Difference threshold
- D. Point of sensory adaptation
Mostra risposta e spiegazione
Risposta: C. Difference threshold
The difference threshold, also called the just noticeable difference, is about telling two stimuli apart, while the absolute threshold is the smallest stimulus that can be detected at all half the time. Weber's law adds that the difference threshold is a constant proportion of the original stimulus rather than a fixed amount, so a heavier weight needs a bigger change before you notice it. The signal detection criterion is a separate idea about how willing someone is to say yes when they are unsure.
14. Researchers record the diets of 2,000 healthy adults, then follow the same people for 20 years and record who develops heart disease. Which statements about this study are correct?
Seleziona tutte le risposte corrette.
- A. It is a prospective cohort study
- B. Participants were randomly assigned to a diet
- C. Participants dropping out over the 20 years can bias the result
- D. It can measure how many new cases of heart disease appear in each diet group
- E. It shows that diet causes heart disease
Mostra risposta e spiegazione
Risposta: A. It is a prospective cohort study, C. Participants dropping out over the 20 years can bias the result, D. It can measure how many new cases of heart disease appear in each diet group
The exposure was measured before the outcome appeared and the group was followed forward, which makes this a prospective cohort study. That design can measure incidence, meaning new cases over time, which case control studies cannot do directly. What it cannot do is establish causation, because nobody assigned the exposure and people who eat differently may differ in many other ways. Attrition matters because the people who leave a long study are often not a random sample of those who stay.
15. Complete the sentence.
Blaming a stranger's rudeness on their personality while ignoring what is going on around them is the _____. Explaining your own good grade by your ability but your own bad grade by an unfair test is the _____.
Opzioni per lo spazio 1: fundamental attribution error, self-serving bias, just world hypothesis
Opzioni per lo spazio 2: actor observer bias, self-serving bias, halo effect
Mostra risposta e spiegazione
Risposta: fundamental attribution error, self-serving bias
Attribution questions turn on two axes: whether the cause is placed inside the person or in the situation, and whether the person being judged is you or somebody else. The fundamental attribution error is over-weighting personality when explaining other people. The self-serving bias protects your own self-image by taking internal credit for success and external blame for failure. Both are on the MCAT because they shape how patients and clinicians read each other.
Cosa chiedono davvero le tre sezioni scientifiche
L'MCAT ha quattro sezioni. Tre sono scientifiche: Chemical and Physical Foundations of Biological Systems, Biological and Biochemical Foundations of Living Systems e Psychological, Social, and Biological Foundations of Behavior. La quarta è Critical Analysis and Reasoning Skills, che è pura lettura e ha una pagina tutta sua. Ogni sezione scientifica al momento conta 59 domande in 95 minuti, e circa 15 di quelle 59 sono domande discrete che stanno in piedi da sole, senza brano. I punteggi di sezione vanno da 118 a 132, e le quattro sezioni sommate danno un totale tra 472 e 528, con 500 al centro della scala. L'AAMC può cambiare il formato, quindi verifica i numeri aggiornati su aamc.org prima di costruirci sopra un programma.
Il contenuto viene dalle categorie di contenuto che l'AAMC pubblica. La sorpresa per la maggior parte delle persone è quanta biochimica compaia, e che compaia in due sezioni diverse. Amminoacidi, cinetica enzimatica e metabolismo possono essere chiesti nella sezione di biologia e di nuovo in quella di chimica e fisica. La fisica è ristretta e applicata, soprattutto fluidi e pressione, termodinamica, ottica e circuiti, ed è quasi sempre inquadrata dentro un sistema vivente invece che in un blocco che scivola lungo un piano inclinato.
La sezione di psicologia e sociologia è una vera sezione di contenuto con un suo lessico, non una sezione di buon senso, e questo coglie le persone impreparate. Condizionamento, sistemi di memoria, soglie percettive, teoria dell'attribuzione e disegno della ricerca hanno tutti definizioni precise, e le domande girano su quelle definizioni. In tutte e tre le sezioni la maggior parte dei quesiti non è semplice memoria. Ti mettono davanti uno scenario, un grafico o una serie di risultati e ti chiedono cosa ne consegue, quindi conoscere un termine è solo metà di quello che ti serve.
Come usare questo assaggio
Ogni domanda qui sotto è una domanda discreta di proposito. Le discrete sono la prova più pulita di quanto conosci davvero il contenuto, perché non c'è nessun brano accanto alla domanda che ti passa il contesto in silenzio. Se rispondi alle discrete a freddo, i brani diventano molto più facili. Se non ci riesci, esercitarti sui brani nasconde la lacuna invece di chiuderla. I due quiz gemelli qui sotto coprono lo stile misto con i brani e la sezione di lettura, quindi falli tutti e tre e confronta dove perdi punti.
Fallo tutto d'un fiato senza appunti, a circa 90 secondi per domanda, poi leggi la spiegazione di ogni quesito comprese quelle a cui hai risposto giusto. Indovinare e sapere non sono la stessa cosa, e solo una delle due sopravvive al giorno d'esame. Considera ogni errore un argomento e non un dettaglio. Se hai sbagliato la domanda sui tamponi e quella sulla termodinamica, ripassa acido base ed equilibrio insieme, perché sono lo stesso ragionamento applicato a due grandezze diverse.
Una nota su cosa sono queste domande. Il team di StudyPDF le ha scritte tutte e 15 partendo dalle categorie di contenuto che l'AAMC pubblica. Non sono quesiti dell'AAMC, non sono copiati da nessuna banca dati o manuale di preparazione, e StudyPDF non è affiliata all'AAMC. Sono esercitazione per l'esame, non indicazioni mediche, e niente in questa pagina va usato per prendere una decisione su un paziente reale.
Come StudyPDF crea test completi dai tuoi materiali
Quindici domande possono mostrarti quale categoria di contenuto è debole. Non possono reggere un intero piano di preparazione all'MCAT, e una banca dati generica raramente corrisponde a ciò su cui insistono i manuali di ripasso e gli appunti di lezione su cui stai davvero studiando.
StudyPDF parte invece dal tuo materiale. Carichi il capitolo del tuo manuale di preparazione, le slide delle lezioni di biochimica o lo schema di una via metabolica che hai costruito tu, e Bo, l'agente di studio, scrive test completi da quelle pagine esatte. Ogni domanda nasce dal tuo materiale e ogni spiegazione indica da dove viene la risposta, così quando qualcosa non ti torna puoi andare subito alla fonte e controllare. Puoi generare test nuovi quante volte vuoi, restringerli a un'area sola come la cinetica enzimatica o il disegno della ricerca, e tenere traccia dei concetti che continui a sbagliare.
Per iniziare non serve un file. Se non hai niente da caricare, nomina invece un argomento, per esempio il ciclo dell'acido citrico o il condizionamento operante, e Bo ci scrive sopra una serie di esercizi. Inizi gratis.
Scritto dal team di StudyPDF. Ultimo aggiornamento 2026-08-19.