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Alle 15 spørgsmål i overblik

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1. 1. A person meets the same pathogen for the second time and clears it far faster than the first time. Which feature of the immune system best explains the difference?

   • A. Neutrophils now reach the site of infection sooner than they did before
   • B. The complement system was permanently strengthened by the first exposure
   • C. Memory B and T cells left by the first exposure mount a faster and larger specific response
   • D. Physical barriers such as skin and mucus have adapted to that particular pathogen
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   Svar: C. Memory B and T cells left by the first exposure mount a faster and larger specific response

   Innate defenses, meaning barriers, phagocytes and complement, respond the same way every time and keep no record of what they met. The adaptive arm does keep a record, because clonal selection during the first exposure leaves behind long lived memory B and T cells specific to that antigen. On re-exposure those cells expand quickly, so antibody appears sooner and climbs higher, which is the secondary response. That is the effect vaccines are built to produce without the first illness.

2. 2. What is the net yield of glycolysis per molecule of glucose in the cytosol?

   • A. 2 ATP, 2 NADH and 2 pyruvate
   • B. 4 ATP, 2 NADH and 2 pyruvate
   • C. 2 ATP, 2 FADH2 and 2 lactate
   • D. 36 ATP, 2 NADH and 2 pyruvate
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   Svar: A. 2 ATP, 2 NADH and 2 pyruvate

   Substrate level phosphorylation makes four ATP in the payoff phase, but two are spent priming the sugar in the investment phase, so the net is two. Glycolysis also reduces two NAD+ to NADH and ends at two pyruvate. None of it needs oxygen, which is why a cell can run glycolysis when the electron transport chain is stalled, as long as it can regenerate NAD+ some other way.

3. 3. Which of the following are true of the tertiary structure of a globular protein?

   Vælg alle, der passer.

   • A. Hydrophobic side chains tend to cluster in the interior, away from water
   • B. It is determined mainly by hydrogen bonding between backbone amide and carbonyl groups
   • C. Disulfide bridges can form between cysteine residues that are far apart in the sequence
   • D. It refers to the association of two or more separate polypeptide chains
   • E. Salt bridges between oppositely charged side chains help hold the fold together
   Vis svar og forklaring

   Svar: A. Hydrophobic side chains tend to cluster in the interior, away from water, C. Disulfide bridges can form between cysteine residues that are far apart in the sequence, E. Salt bridges between oppositely charged side chains help hold the fold together

   Tertiary structure is the three dimensional fold of one chain, and it is driven by side chain interactions: the hydrophobic effect burying nonpolar residues, disulfide bonds between cysteines, salt bridges, and hydrogen bonds between side chains. Backbone hydrogen bonding is what defines secondary structure, the helices and sheets. Two or more chains coming together is quaternary structure.

4. 4. Complete the sentence.

   In oxidative phosphorylation, electrons passed down the chain are finally handed to _____, and the proton gradient across the inner mitochondrial membrane drives _____.

   Muligheder for felt 1: carbon dioxide, oxygen, NAD+, pyruvate

   Muligheder for felt 2: ATP synthase, the citric acid cycle, glycolysis

   Vis svar og forklaring

   Svar: oxygen, ATP synthase

   Oxygen is the terminal electron acceptor and combines with protons to form water, which is why the whole chain backs up without it. The energy released as electrons fall is used to pump protons out, storing energy as an electrochemical gradient. ATP synthase then lets protons flow back down that gradient and uses the flow to phosphorylate ADP, a coupling known as chemiosmosis.

5. 5. In E. coli, glucose is plentiful and lactose is absent. What is the lac operon doing?

   • A. The repressor is inactive, so transcription runs at a high rate
   • B. cAMP is high, so CAP binds and strongly activates transcription
   • C. Lactose binds the repressor and pulls it off the operator
   • D. The repressor sits on the operator and transcription is largely off
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   Svar: D. The repressor sits on the operator and transcription is largely off

   The lac operon is under negative control by the repressor and positive control by CAP. With no lactose there is no inducer to lift the repressor, so it stays bound to the operator. Plentiful glucose also keeps cAMP low, so CAP does not bind and gives no boost. Both signals point the same way: do not build enzymes for a sugar that is not there.

6. 6. Two aqueous solutions sit either side of a membrane that lets water through but no solute. Solution A is 0.10 molar glucose and solution B is 0.10 molar sodium chloride. What happens?

   • A. Water moves toward the glucose, because glucose is the larger molecule
   • B. Water moves toward the sodium chloride, because it splits into about twice as many particles
   • C. There is no net movement, because the two molarities are equal
   • D. Water moves toward the glucose, because ionic compounds cannot generate osmotic pressure
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   Svar: B. Water moves toward the sodium chloride, because it splits into about twice as many particles

   Osmotic pressure is a colligative property, so it counts dissolved particles and ignores what those particles are. Sodium chloride dissociates into two ions per formula unit, which puts 0.10 molar NaCl near 0.20 osmolar while the glucose stays at 0.10. Water moves toward the side that is more concentrated in particle terms, so it moves toward the salt. The same counting explains freezing point depression and boiling point elevation.

7. 7. Two identical 10 ohm resistors are connected in parallel across a battery. What is the resistance of the pair, and how does it compare with one resistor on its own?

   • A. 20 ohms, which is larger than either resistor alone
   • B. 10 ohms, the same as either resistor alone
   • C. 5 ohms, which is smaller than either resistor alone
   • D. 0 ohms, because parallel paths cancel each other
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   Svar: C. 5 ohms, which is smaller than either resistor alone

   Parallel resistors add as reciprocals, so one over the total equals one tenth plus one tenth, and the total is 5 ohms. Adding a parallel path always lowers total resistance, because current gains another route to take. Series resistors do the opposite and simply add. The same reasoning is why opening more parallel vascular beds lowers total peripheral resistance.

8. 8. Which statements about a galvanic cell, also called a voltaic cell, are correct?

   Vælg alle, der passer.

   • A. The standard free energy change of the cell reaction is positive
   • B. Oxidation happens at the anode and reduction happens at the cathode
   • C. An external power supply is needed to drive the reaction forward
   • D. The standard cell potential is positive
   • E. The salt bridge keeps each half cell electrically neutral as the reaction runs
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   Svar: B. Oxidation happens at the anode and reduction happens at the cathode, D. The standard cell potential is positive, E. The salt bridge keeps each half cell electrically neutral as the reaction runs

   A galvanic cell runs a redox reaction that is already favorable, so its standard cell potential is positive and its standard free energy change is negative, the two tied together by delta G naught equals minus n F E naught. Oxidation at the anode and reduction at the cathode holds in every electrochemical cell, so that pairing is not what separates the two types. Direction is what separates them, since an electrolytic cell needs an outside supply to push an unfavorable reaction uphill. The salt bridge moves ions between the half cells to cancel the charge buildup that would otherwise halt the reaction within seconds.

9. 9. Complete the sentence.

   A reaction whose enthalpy change is negative and whose entropy change is positive is _____.

   Muligheder for felt 1: never spontaneous, spontaneous only at high temperature, spontaneous at every temperature, spontaneous only at low temperature

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   Svar: spontaneous at every temperature

   Gibbs free energy change equals enthalpy change minus temperature times entropy change. A negative enthalpy term and a positive entropy term both push that value negative, and absolute temperature is always positive, so the sign never flips. Spontaneous says nothing about speed, though. A reaction can be thermodynamically favorable and still sit untouched for years behind a large activation barrier.

10. 10. Students are told a hard test measures ability in an area where their group is stereotyped as weaker. They score lower than an otherwise identical group told the same test is a problem-solving exercise. This result is usually explained as:

    • A. social loafing
    • B. the bystander effect
    • C. deindividuation
    • D. stereotype threat
    Vis svar og forklaring

    Svar: D. stereotype threat

    Stereotype threat is the drop in performance that appears when someone is reminded of a negative stereotype about a group they belong to, because the resulting worry and self-monitoring consume the working memory the task needs. Nothing about ability changed between the two groups here, only the framing of the task, which is why the instructions alone moved the scores. Social loafing, the bystander effect and deindividuation are all effects of being in a group, and none of them turn on how a task is described to an individual.

11. 11. Which of the following are true of classical conditioning?

    Vælg alle, der passer.

    • A. A previously neutral stimulus comes to produce a response on its own
    • B. The response is voluntary and is shaped by the consequences that follow it
    • C. Presenting the conditioned stimulus repeatedly without the unconditioned stimulus leads to extinction
    • D. After extinction, the conditioned response can reappear later with no new training
    • E. Learning requires the learner to watch a model being rewarded
    Vis svar og forklaring

    Svar: A. A previously neutral stimulus comes to produce a response on its own, C. Presenting the conditioned stimulus repeatedly without the unconditioned stimulus leads to extinction, D. After extinction, the conditioned response can reappear later with no new training

    Classical conditioning pairs a neutral stimulus with one that already produces a reflexive response until the neutral stimulus produces it alone. Break the pairing and the response fades, which is extinction, and it can come back on its own later, which is spontaneous recovery. Behavior shaped by its consequences is operant conditioning, and learning by watching a model is observational learning.

12. 12. Complete the sentence.

    The system that holds a few items for a matter of seconds while you actively work on them is _____. Recalling a fact more easily in the room where you first learned it is an example of _____.

    Muligheder for felt 1: working memory, sensory memory, procedural memory

    Muligheder for felt 2: proactive interference, the serial position effect, context dependent retrieval

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    Svar: working memory, context dependent retrieval

    Sensory memory holds a raw impression for well under a second, working memory holds a small handful of items while you manipulate them, and long term memory has no known practical ceiling. Retrieval is a separate problem from storage, since a memory can be stored perfectly well and still be hard to reach without the right cue. Context dependent retrieval is one of those cues, where the surroundings present at encoding are reinstated at recall, and state dependent retrieval does the same with internal state.

13. 13. Read the excerpt, then answer the question. The catalogue is the quiet argument of a museum. Curators speak of hanging a room, of letting one canvas answer another, and visitors read the sequence as though it were natural. It is not. Every wall states a claim about what belongs beside what, and about which century explains which. A visitor who walks the rooms in order absorbs a thesis she was never asked to accept, and rarely notices that a thesis was offered at all. Which of the following best states the main idea of the passage?

    • A. Museums ought to display their collections in strict chronological order
    • B. The arrangement of a museum makes an argument that most visitors take as given
    • C. Curators disagree sharply with one another about which paintings matter most
    • D. Visitors would learn more from reading a catalogue than from walking the galleries
    Vis svar og forklaring

    Svar: B. The arrangement of a museum makes an argument that most visitors take as given

    The passage says every wall states a claim and that visitors absorb the resulting thesis without noticing it, which is the one idea that covers the whole excerpt. Main idea questions reward the choice that spans the passage, not a detail lifted from one line. The option about chronological order and the one about catalogues both recommend something the author never recommends, and the option about curators disagreeing introduces a conflict the passage never mentions.

14. 14. Read the excerpt, then answer the question. Economists once treated household labor as a residual, a thing done in the hours left over after real work. The convention was convenient. Unpaid hours resisted measurement, and what resists measurement tends to fall out of the model. When time use surveys finally arrived, they did not so much discover housework as make it countable, and the finding was greeted less as news than as an accounting problem. The hours had always been there. Only the ledger had changed. The author's remark that the surveys did not so much discover housework as make it countable most nearly implies that:

    • A. the work in question was new to the period the surveys covered
    • B. economists had deliberately concealed the existence of unpaid labor
    • C. the surveys changed what could be measured rather than what was happening
    • D. time use surveys were less accurate than the methods that came before them
    Vis svar og forklaring

    Svar: C. the surveys changed what could be measured rather than what was happening

    The last two sentences say the hours had always been there and only the ledger changed, so the shift was in measurement and not in behavior. Reasoning questions want the smallest step past what the text supports. Deliberate concealment is far stronger than anything the author claims, since he calls the old convention convenient rather than dishonest, and the passage never compares the accuracy of one method with another.

15. 15. Read the excerpt, then answer the question. Defenders of the classics rarely argue that old books are useful. They argue instead that usefulness is the wrong test, and that a culture which asks only what a thing is for will end by keeping nothing it cannot spend. The claim has force, and it also has a convenient shape, since any objection can be dismissed as proof of the very narrowness complained of. An argument that cannot lose is not thereby strong. It has only stopped being an argument. Which best describes the author's attitude toward the defense he describes?

    • A. Sympathetic but critical, since he grants the defense force and then objects to its shape
    • B. Full agreement, since he says outright that the claim has force
    • C. Dismissive, since he holds that old books have no practical use
    • D. Neutral, since he only reports what defenders of the classics say
    Vis svar og forklaring

    Svar: A. Sympathetic but critical, since he grants the defense force and then objects to its shape

    The author concedes that the claim has force, which rules out dismissal, and then complains that a defense treating every objection as evidence for itself has stopped being an argument. That is criticism of the reasoning, not of old books, so he never takes the dismissive position either. Attitude questions on this section usually land on a mixed answer whenever a passage contains both a concession and a complaint.

Hvad MCAT er, og hvordan den bedømmes

MCAT skrives og afholdes af Association of American Medical Colleges. Den har fire dele, der tæller med i scoren: Chemical and Physical Foundations of Biological Systems, Critical Analysis and Reasoning Skills, Biological and Biochemical Foundations of Living Systems og Psychological, Social, and Biological Foundations of Behavior. Hver del bedømmes på en skala fra 118 til 132, så totalen løber fra 472 til 528, og 500 ligger på skalaens midtpunkt. Der er ingen beståelsesgrænse. AAMC offentliggør percentiler for hver score, og hvert medicinstudie afgør selv, hvad det vil se, så den eneste brugbare målestok er scoreprofilen for de studier, du planlægger at søge ind på.

StudyPDF er ikke tilknyttet AAMC, og intet på denne side er et officielt AAMC-produkt. Hvert spørgsmål og hver forklaring her er skrevet af StudyPDF-teamet ud fra de indholdskategorier, AAMC offentliggør, og tekstuddragene i de sidste tre spørgsmål har vi også skrevet selv. Der er ikke gengivet et eneste spørgsmål fra AAMC eller fra nogen anden testudbyder nogen steder på denne side. Det skærer begge veje. Fordi spørgsmålene er vores egne, kan de kun nærme sig den rigtige vare, så brug dem til at finde huller, og brug officielt AAMC-øvemateriale, når du vil have et pålideligt billede af, hvor din score faktisk ligger.

Formatet er langt. Hver af de tre naturvidenskabelige dele giver dig 59 spørgsmål på 95 minutter, og ræsonnementsdelen giver dig 53 spørgsmål på 90 minutter, hvilket lægger den samlede tid i stolen på cirka syv en halv time, når pauser og indtjekning tælles med. De fleste spørgsmål hænger på en tekst, med en mindre gruppe fritstående enkeltspørgsmål, som kun findes i de naturvidenskabelige dele. Der trækkes ikke fra for et forkert svar, så et blankt felt er altid værre end et gæt. Regler på prøvedagen, pausestruktur, tilmelding og økonomisk støtte til gebyret ændrer sig, så bekræft de aktuelle detaljer på students-residents.aamc.org frem for at stole på et tal, du har læst i et forum.

Sådan bruger du smagsprøven

De 15 spørgsmål herunder følger eksamens egen balance i miniature. Fem kommer fra de biologiske og biokemiske grundlag, fire fra de kemiske og fysiske grundlag, tre fra de psykologiske og sociale grundlag for adfærd, og tre er spørgsmål i kritisk analyse og ræsonnement. Hvert ræsonnementsspørgsmål har sit eget korte tekstuddrag, skrevet af os i det toneleje, den del bruger, så du kan træne færdigheden uden først at skulle lede efter en tekst. Den rigtige eksamen bruger kun multiple choice med ét rigtigt svar, så vælg alle der passer og udfyld det tomme felt er et studieredskab her frem for et varsel om formatet. De er med i blandingen, fordi det at binde sig til hver del af et svar afslører huller, som fire pæne svarmuligheder kan skjule. Ingen af dem er rigtige eksamensspørgsmål, og ingen af dem er medicinsk vejledning. Det her er eksamenstræning, ikke andet.

Tag den i ét stræk uden noter, og læs så forklaringen til hvert spørgsmål, også dem du svarede rigtigt på. På MCAT ser et heldigt gæt og et gennemtænkt svar ens ud på scorerapporten og helt forskellige ud inde i hovedet på dig, så gennemgangen er der, hvor læringen sker. Behandl et forkert svar som et emne frem for som et faktum. Missede du spørgsmålet om osmotisk tryk og spørgsmålet om termodynamik, er problemet formentlig, at du lærer formler udenad i stedet for at læse, hvad hver variabel egentlig står for.

Bagefter fordeler du din læsetid ærligt. Repetition af stof lukker huller, men scoren flytter sig som regel af fuldlange prøver på tid og af at gennemgå dem langsomt. Ræsonnementsdelen er undtagelsen, for den belønner rolig daglig læsning af tung argumenterende tekst mere end nogen indholdsliste. Timing er en færdighed for sig. 95 minutter til 59 spørgsmål giver dig lidt over halvandet minut per spørgsmål, og de fleste taber point i slutningen af en del frem for i starten, så når stoffet sidder, øver du på tid i stedet for uden ur. De to søskendequizzer herunder går dybere ned i de naturvidenskabelige dele og i ræsonnement, så kør alle tre, og se hvilken der gør ondt.

Sådan bygger StudyPDF fulde øveprøver ud fra dit materiale

Femten spørgsmål kan vise dig, hvor du er svag. De kan ikke gøre dig klar alene, og en generisk spørgsmålsbank rammer sjældent det, som netop den repetitionsbog, det kursus eller de forelæsningsnoter, du faktisk arbejder dig igennem, lægger vægt på.

StudyPDF arbejder ud fra dit materiale i stedet. Du uploader dine MCAT-repetitionsbøger, dine slides fra biokemi eller psykologi, eller de kapitelresuméer du selv har skrevet, og Bo, studieagenten, bygger fuldlange øveprøver ud fra præcis de sider. Hvert spørgsmål bygger på dit materiale, og hver forklaring henviser til, hvor svaret kommer fra, så når noget ser forkert ud, kan du gå direkte til kilden og tjekke det. Du kan lave nye prøver så tit du vil, holde dem på ét område som aminosyrer, elektriske kredsløb eller forskningsmetode, og følge med i hvilke begreber du bliver ved med at ramme forkert.

Du behøver ikke uploade noget for at komme i gang. Har du ingen fil ved hånden, så nævn et emne i stedet, for eksempel syre-base-kemi, muskelfysiologi eller social lagdeling, så skriver Bo en øveprøve ud fra det. Gratis at komme i gang.