Medical Tests MCAT-TEST Online Practice Questions and Exam Preparation

Medical Tests MCAT-TEST Online Questions & Answers

• Question 191:

  One of the most common methods that scientists use to determine the age of fossils is known as carbon dating. 14C is an unstable isotope of carbon that undergoes beta decay with a half-life of approximately 5,730 years. Beta decay occurs when a neutron in the nucleus decays to form a proton and an electron which is ejected from the nucleus. 14C is generated in the upper atmosphere when 14N, the most common isotope of nitrogen, is bombarded by neutrons. This mechanism yields a global production rate of 7.5 kg per year of 14C, which combines with oxygen in the atmosphere to produce carbon dioxide. Both the production and the decay of 14C occur simultaneously. This process continues for many half-lives of 14C, until the total amount of 14C approaches a constant. A fixed fraction of the carbon ingested by all living organisms will be 14C. Therefore, as long as an organism is alive, the ratio of 14C to 12C that it contains is constant. After the organism dies, no new 14C is ingested, and the amount of 14C contained in the organism will decrease by beta decay. The amount of 14C that must have been present in the organism when it died can be calculated from the amount of 12C present in a fossil. By comparing the amount of 14C in the fossil to the calculated amount of 14C that was present in the organism when it died, the age of the fossil can be determined.

  After a 14C nucleus decays, the electron that is emitted enters lead and is stopped. What percentage of its kinetic energy does the electron transfer to lead?

  A. 25%
  B. 33%
  C. 50%
  D. 100%
  D. 100%

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  Explanation/Reference:

  Kinetic energy, the energy of motion, is given by K.E. = (1/2)mv2 , where m is the mass of the object and v is its speed. The electron emitted when a 14C nucleus decays is emitted with some initial speed and thus has kinetic energy. After it enters lead and is stopped, the electron's speed is zero so its kinetic energy is also zero. In other words, all the electron's kinetic energy is gone. Since energy is conserved, 100% of the electron's kinetic energy must have been transferred somewhere, and in this case, it is transferred to the lead. Hence, choice D is correct.

• Question 192:

  As Alice Echols went on to claim, "Nothing seems to conjure up the 1970s quite so effectively as disco. Even at the time, critics remarked upon disco's neat encapsulation of that decade's zeitgeist. `It must be clear by now to everyone with an ear or an eye that this era,' wrote journalist Andrew Kopkind in 1979, `is already the Disco Years, whether it will be called by that name or not.' A former sixties radical, Kopkind was by turns fascinated, bemused, and appalled by the disco epoch, and he likely imagined that in years to come fellow cultural critics would share his interest. But the seventies have not loomed large in our national imagination, except perhaps as comic relief. For many Americans, these were the forgettable years.

  That forgettability owes a lot to the 1960s, the outsized decade that dwarfs all others in recent memory. The sixties will always be remembered for their audacity, whether found in the courage of civil rights protesters who put their bodies on the line or in those doomed but beautiful rock stars who tried breaking through to the other side. By contrast, the seventies seem the decade when nothing, or nothing good, happened ?an era memorable for the country's hapless presidents, declining prestige, bad fashions, ludicrous music, and such over-the-top narcissism that Tom Wolfe dubbed it the `Me Decade.' Before the decade was out, this narrative of decline had become routine. `After the poetry of the Beatles comes the monotonous bass-pedal bombardment of Donna Summer,' huffed one New York Times writer in 1979. It is a measure of the era's persistent bad press that a recent book challenging this view carries the pleading title Something Happened.

  As for the sixties, it doesn't matter how much silliness went down, we still invest those times with seismic significance. Take Joe Cocker's performance at Woodstock. His spasmodic thrashing about and his vocals, slurred to the point of incomprehensibility, are something of a joke today. Cringe-inducing though it may be, however, Cocker's performance is never made to stand in for the whole of the sixties. The sixties remain enveloped in the gauzy sentimentalism of what might have been. Yet the iconic image of John Travolta as dance-floor king Tony Manero in white polyester suit, arm thrust to the disco heavens, has come to symbolize the narcissistic imbecility and inconsequentiality of the disco years.

  Were it not for the Rubaiyat, I, too, might well regard the seventies as a lamentable and regrettable period in American history. The Rubaiyat was, yes, a disco. It was located in the heart of sixtiesland: Ann Arbor, Michigan, the home of the University of Michigan and legendary incubator of radical activism. At the height of the seventies, the town's annual Hash Bash ?a smoke-in to reform marijuana laws ?was still going strong and so were its two food co-ops-one reform, the other orthodox when it came to selling white foods (that is, rice, sugar, and flour of the white variety). Ann Arbor also had bookstores galore, including the original, wonderful Borders Bookstore, and any number of hippie-ish restaurants and bars such as the Fleetwood Diner, the Del Rio, and the Blind Pig. Musically, it prided itself on its vintage music (it hosted one of the earliest blues festivals), but at heart it was a rock town besotted with Iggy Pop and the Stooges and Sonic's Rendezvous, a band fronted by Patti Smith's future husband, Fred Smith. Its leading music store, Schoolkids' Records, stocked disco, but never played it. All of this is to say that disco-averse Ann Arbor came close to providing something of a safe haven from glitterball culture.

  The Rubaiyat was no red-velvet-rope disco where fashionista doormen determined who was sufficiently fabulous to gain entry. This would never have worked in a town where down jackets and army surplus were hardly an unusual sight. The

  club did have some pretensions to classiness, but the mismatched, sagging booths and bordello red defeated occasional efforts at upmarket sophistication. What the Rubaiyat did have were better-than-average speakers, a heterogeneous

  cliente, and a weekend cover of three dollars."

  Echols, A. (2011). Hot stuff: Disco and the Remaking of American Culture. New York: W. W. Norton.

  The passage implies that cultural commentators tend to agree on which of the following ideas about music?

  A. Popular music is typically inane because its success is determined by the narcissistic desires of the marketplace.
  B. Popular music and the social life around it are an important window into the national mood.
  C. An era is defined by whatever music becomes popular because this reflects people's desires and influences.
  D. The most talented artist of an era are "doomed" because they are not appreciated by their contemporaries.
  B. Popular music and the social life around it are an important window into the national mood.

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  Explanation/Reference:

  The Reasoning Within the Text question asks you to identify a common thread in the author's quotes and paraphrases from other cultural commentators. The author points out that "critics remarked upon disco's neat encapsulation of that decade's zeitgeist," that one journalist saw the 70s as the "Disco Years" while being "bemused...and appalled" by disco, and that the image of a dancing Tony Manero "has come to symbolize the narcissistic imbecility and inconsequentiality of the disco years." These critics all see disco as reflecting the bad qualities of an era, thus suggesting that music reflects the mindset of the time it was created.

  A. This choice is incorrect because the author suggests critics see the music of the 60s positively, therefore not all popular music is inane or determined by narcissistic trends. C. ?incorrect. The author points out that Joe Cocker's bad Woodstock performance has been overlooked, thus suggesting that critics ignore popular music if it does not fit their view of an era. Also, he starts by claiming that "Nothing seems to conjure up the 1970s quite so effectively as disco," but that "For many Americans, these were the forgettable years." This suggests that music is a good representation of the spirit of an era whether or not it is popular and appreciated or not by critics. D ?incorrect. The author suggests that some critics are fixated on doomed 60s rock stars, not that they see all talented rock stars this way.

• Question 193:

  What happens to brain waves as an organism falls asleep?

  A. The frequency increases and amplitude increases.
  B. The frequency decreases and amplitude remains constant.
  C. The frequency increases and amplitude decreases.
  D. The frequency decreases and the amplitude increases.
  D. The frequency decreases and the amplitude increases.

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  Explanation/Reference:

  As an organism loses consciousness, bodily activity slows down and brain waves become slower and bigger.

• Question 194:

  Many nutrients required by plants exist in soil as basic cations:

  

  A soil's cation-exchange capacity is a measure of its ability to adsorb these basic cations as well as exchangeable hydrogen and aluminum ions. The cation-exchange capacity of soil is derived from two sources: small clay particles called micelles consisting of alternating layers of alumina and silica crystals, and organic colloids.

  

  Replacement of + and + by other cations of lower valence creates a net negative charge within the inner layers of the micelles. This is called the soil's permanent charge. For example, replacement of an atom of aluminum by calcium within a section where the net charge was previously zero, as shown below, produces a net charge of ?, to which other cations can become adsorbed.

  

  Figure 1

  A pH-dependent charge develops when hydrogen dissociates from hydroxyl moieties on the outer surfaces of the clay micelles. This leaves negatively-charged oxygen atoms to which basic cations may adsorb. Likewise, a large pH-

  dependent charge develops when hydrogen dissociates from carboxylic acids and phenols in organic matter.

  In most clays, permanent charges brought about by substitution account for anywhere from half to nearly all of the total cation-exchange capacity. Soils very high in organic matter contain primarily pH-dependent charges. In a research study,

  three samples of soil were leached with a 1 N solution of neutral KCl, and the displaced A13+ and basic cations measured. The sample was then leached again with a buffered solution of BaCl2 and triethanolamine at pH 8.2, and the

  displaced H+ measured. Table 1 gives results for three soils tested by this method.

  Table 1

  

  Due to the buffering effect of the soil's cationexchange capacity, just measuring the soil solution's pH will not indicate how much base is needed to change the soil pH. In another experiment, measured amounts of acid and base were added to 10-gram samples of well-mixed soil that had been collected from various locations in a field. The volumes of the samples were equalized by adding water. The results were recorded in Figure 2.

  Figure 2.

  

  What percentage of the cation exchange capacity of Sample I is base-saturated?

  A. 4%
  B. 6%
  C. 29%
  D. 40%
  A. 4%

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  Explanation/Reference:

  The percentage base saturation consists of the number of milliequivalents of basic ions divided by the entire cation exchange capacity of the soil. For Sample I, that is the third column in Table 1 divided by the fifth, or 1.9 divided by 47.6. If you multiply 1.9/47.6 by 2/2, you can estimate this ratio to be approximately 4/96, which is about 4%, choice A.

• Question 195:

  Apoptosis is the process of programmed cell death that can occur in multicellular organisms. The proteins involved in apoptosis are associated with pathways for cell cycle arrest and DNA repair. These processes are mostly regulated through the interplay of various proteins involved in feedback loops including some of the ones shown in Figure 1.

  

  Figure 1: Feedback loops forming a regulatory network affecting apoptosis, cell cycle arrest and DNA repair. (Bioformatics Institute) According to Figure 1, CDK2 activity would most reasonably increase due to all of the following EXCEPT:

  A. degradation of p21.
  B. high cyclin G concentrations.
  C. a mutation in the gene that produces PTEN.
  D. high p53 concentrations.
  D. high p53 concentrations.

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  Explanation/Reference:

  Notice the key in the figure which will allow us to follow each arrow that stimulates the next protein and each symbol for negative feedback which means there will be some downregulation (amount/concentration goes down). [Notice a key step in the diagram: p21 inhibits CDK2]

  Degradation of p21 implies that the concentration of p21 in its active form goes down. The diagram shows that p21 has a negative influence on CDK2. In other words, when p21 is high, CDK2 goes low. But in our instance, p21 is low (degraded) so this allows CDK2 to rise unchecked.

  High cyclin G concentrations: From the bottom of Figure 1, we can see that high cyclin G leads to high mdm2 and low p53 (notice carefully, when we leave mdm2, there is only one place to go in the diagram because all the other symbols are pointing to mdm2 and only one symbol is pointing away). Note that we used the most direct route to get to CDK2 as the question used the words "most reasonably". Low p53 means low p21 which we established will lead to a rise in CDK2.

  A mutation in the gene that produces PTEN: The great majority of mutations will result in an ineffective gene product or none at all. Thus we have a decrease in PTEN which will lead to a rise in PIP3 (if you are unsure, think of what happens if PTEN goes up, then PIP3 must go down because of the negative feedback symbol), rise in AKT, rise in mdm2, decrease in p53 which we already established means an eventual rise in CDK2.

  High p53 concentrations: clearly we get the opposite of the above, meaning a decrease in CDK2. High p53 stimulates p21 which has a negative feedback on CDK2.

• Question 196:

  Alleles are created when a single gene undergoes several distinct mutations. These alleles may have different dominance relationships with one another; for example, there are three alleles coding for the human blood groups, the IA, IB, and i alleles. Both the IA and IB alleles are dominant to the i allele, but IA and IB are codominant to each other.

  A multiple-allele system has recently been discovered in the determination of hair coloring in a species of wild rat. The rats are found to have one of three colors: brown, red, or white. Let B = the gene for brown hair; b = the gene for red hair; and w = the gene for white hair. The results from nine experimental crosses are shown below. The males and females in Crosses 1, 2, and 3 are all homozygous for hair color.

  

  Based on the experimental results, what is the genotype of the female in Cross 5?

  A. Bb
  B. BB or Bb
  C. BB or Bw
  D. BB, Bb, or Bw
  D. BB, Bb, or Bw

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  Explanation/Reference:

  In Cross 5, a brown male is mated with a brown female, and we're told that 100% of their offspring are brown. Since we know that the big B allele is dominant to the little b and w alleles, there are three types of genotypically distinct crosses between two brown parents that result in all brown progeny; again, you might want to write these down to avoid confusion: (1) big B, big B ?big B, big B; (2) big B, big B ?big B, w; and (3) big B, big B ?big B, little b. From this we see that at least one of the parents must be big B, big B. If the female is big B, big B, then the male can be big B, big B; big B, little b; or big B, w. Likewise, if the male is b B, big B, then the female can be big B, big B; big B, little b; or big B, w.

• Question 197:

  Mg(OH)2 is slowly dissolved in 500 mL of 25oC water until the solution becomes fully saturated. Which of the following occurs when 10.0 mL of 0.1 M HCl is added?

  A. MgCl2 precipitates.
  B. Mg(OH)2 precipitates.
  C. Ksp for Mg(OH)2 increases.
  D. [H2O] increases.
  D. [H2O] increases.

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  Explanation/Reference:

  This question is testing your understanding of solution chemistry, equilibrium, and solubility rules. In a saturated solution of Mg(OH)2, the maximum concentrations of Mg2+(aq) and OH-(aq) ions have been reached and are in equilibrium with

  the solubility product, as follows:

  Mg(OH)2(s) ?Mg2+(aq) + 2OH-(aq)

  When HCl is added to the solution, the pH of the solution decreases. The additional H+ ions react with the dissolved OH- ions forming water. Thus, D is the correct answer.

  Magnesium chloride is soluble in water, eliminating choice A.

  When HCl is added, the hydroxide concentration decreases shifting the equilibrium to the right, making choice B false.

  The solubility product, Ksp, is a constant that varies only with temperature, making choice C incorrect.

• Question 198:

  Although nihilism is commonly defined as a form of extremist political thought, the term has a broader meaning. Nihilism is in fact a complex intellectual stance with venerable roots in the history of ideas, which forms the theoretical basis for many positive assertions of modern thought. Its essence is the systematic negation of all perceptual orders and assumptions. A complete view must account for the influence of two historical crosscurrents: philosophical skepticism about the ultimacy of any truth, and the mystical quest for that same pure truth. These are united by their categorical rejection of the "known". The outstanding representative of the former current, David Hume (1711?776), maintained that external reality is unknowable, since sense impressions are actually part of the contents of the mind. Their presumed correspondence to external "things" cannot be verified, since it can be checked only by other sense impressions. Hume further asserts that all abstract conceptions turn out, on examination, to be generalizations from sense impressions. He concludes that even such an apparently objective phenomenon as a cause-and-effect relationship between events may be no more than a subjective fabrication of the observer. Stanley Rosen notes: "Hume terminates in skepticism because he finds nothing within the subject but individual impressions and ideas". For mystics of every faith, the "experience of nothingness" is the goal of spiritual practice. Buddhist meditation techniques involve the systematic negation of all spiritual and intellectual constructs to make way for the apprehension of pure truth. St. John of the Cross similarly rejected every physical and mental symbolization of God as illusory. St. John's spiritual legacy is, as Michael Novak puts it, "the constant return to inner solitude, an unbroken awareness of the emptiness at the heart of consciousness. It is a harsh refusal to allow idols to be placed in the sanctuary. It requires also a scorching gaze upon all the bureaucracies, institutions, manipulators, and hucksters who employ technology and its supposed realities to bewitch and bedazzle the psyche". Novak's interpretation points to the way these philosophical and mystical traditions prepared the ground for the political nihilism of the nineteenth and twentieth centuries. The rejection of existing social institutions and their claims to authority is in the most basic sense made possible by Humean skepticism. The political nihilism of the Russian intelligentsia combined this radical skepticism with a near mystical faith in the power of a new beginning. Hence, their desire to destroy becomes a revolutionary affirmation; in the words of Stanley Rosen, "Nihilism is an attempt to overcome or repudiate the past on behalf of an unknown and unknowable, yet hoped-for, future." This fusion of skepticism and mystical re-creation can be traced in contemporary thought, for example as an element in the counterculture of the 1960s.

  Which of the following provides the best continuation for the final paragraph of the passage?

  A. Thus, the negative effects of nihilism are still being felt.
  B. Classical nihilism has thus been superseded by a new and unrelated type.
  C. The revolutionaries of that time did, after all, reject society and hope for something better.
  D. The study of nihilism, then, belongs to the past rather than to the present.
  C. The revolutionaries of that time did, after all, reject society and hope for something better.

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  Explanation/Reference:

  For the final question of this passage, you have to pick the choice that would best continue the passage's final paragraph. On this type of question, you are looking for a choice that follows logically from the flow of the author's argument. So you can bet that the right answer will somehow refer to the counterculture movement of the 1960s that is mentioned in the passage's final sentence.

  Choice A suggests that the negative effects of nihilism are still being felt, but the author never hints that any form of nihilism had a negative effect on anything, so A should be tossed out. The nihilistic element of the counterculture movement is not new and different from classical nihilism, so B is wrong. Choice C would conclude the passage by commenting further on the nihilism of the 1960s revolutionaries -- this is more like what you're looking for. A quick look at Choice D confirms that Choice C is the best answer. Since the author has obviously been studying nihilism, he isn't going to say that the study of nihilism belongs to the past but not the present.

• Question 199:

  What is the normality of a solution containing 49 g of H3PO4(MW=98 g/mol) in 2,000 mL of solution?

  A. 0.25
  B. 0.50
  C. 0.75
  D. 1.50
  C. 0.75

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  Explanation/Reference:

  Normality is defined as the number of equivalents of solute per liter of solution. An equivalent of an acid is the amount of acid required to give one mole of H+. Phosphoric acid, which contains three moles of protons per mole of acid, therefore contains three equivalents per mole. A one molar solution of phosphoric acid is said to be 3 normal. The solution in question contains 49 grams of phosphoric acid, and the molar mass of phosphoric acid is 98. Since 49 is half of 98, the amount of phosphoric acid in this sample is half of the 3 equivalents in each mole of the acid. So there are 1.5 equivalents of phosphoric acid in this solution. Now, the total volume of the solution is 2000 milliliters, or 2 liters. So this solution contains 1.5 equivalents of acid per 2 liters. This comes to 0.75 equivalents per liter, which is a 0.75 N solution.

• Question 200:

  Which of the following is NOT an intermolecular force?

  A. Dispersion forces
  B. Resonance
  C. Hydrogen bonding
  D. Dipole interactions
  B. Resonance

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  Explanation/Reference:

  All intermolecular attractions involve some kind of electrostatic interaction. Hydrogen bonding is a strong dipole interaction between a positive hydrogen dipole in one molecule and another negative dipole. This definitely is an intermolecular attraction, so choice C isn't the answer. Dispersion forces, choice A, are slight momentary dipole interactions that occur between molecules as the electron clouds around them go through random variations, so this too is incorrect. Dipole interactions characterize the attractions between molecules that have permanent variations in electron density around the molecule, so choice D is also wrong. However, resonance, choice B, is something else entirely; it is the distribution of electrons among atoms within a molecule in more than one possible pattern. Resonance is not a form of intermolecular attraction because it only involves the effects the electron density has on the single molecule. It is an intramolecular phenomenon, so choice B is the correct answer.