Medical Tests MCAT-TEST Online Practice Questions and Exam Preparation

Medical Tests MCAT-TEST Online Questions & Answers

• Question 451:

  A fireman of mass m slides down a vertical pole with an average acceleration a. If the acceleration due to gravity is g, what is the average frictional force exerted by the fireman?

  A. mg
  B. m(g + a)
  C. m(g – a)
  D. ma
  C. m(g – a)

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  Explanation/Reference:

• Question 452:

  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. The method of carbon dating used to determine age depends upon the assumption that:

  A. the half-life of 14C changes when it is ingested.
  B. all ingested 14C is incorporated into the body.
  C. the half-life of 14C depends on the type of molecule in which it resides.
  D. the half-life of 14C does not depend upon conditions external to the 14C nucleus.
  D. the half-life of 14C does not depend upon conditions external to the 14C nucleus.

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  Explanation/Reference:

  Carbon dating uses the fact that 14C is unstable and decays over time, while 12C is stable and does not decay. Let's say the ratio of 14C to 12C in an organism is known at the moment of death. By measuring the ratio of 14C to 12C in a fossil, the age of the fossil can be determined because the 14C in the dead organism decays over time in a quantifiable way. Although it is not explicitly stated in the passage, choice D is an assumption of carbon dating. It correctly states that the half-life of 14C does not depend upon conditions external to the 14C nucleus. This means that the half-life does not depend on the weather, the amount of 14C present, etc. Because the half-life is a constant with respect to conditions external to the nucleus, it can be used to measure elapsed time accurately. Since measuring time is the goal of carbon dating, choice D is a necessary assumption. Choice A is wrong because ingestion is an event that is external to the nucleus. Choice C is wrong because the type of molecule in which 14C is incorporated is also a condition external to the nucleus. Choice B is wrong because we know from biology that some carbon leaves the body as waste. This does not affect carbon dating, however, because what matters is the ratio of 14C to 12C left in the body, not the specific amount of 14C left in the body.

• Question 453:

  

  For a particular plant, straight leaves result from a dominant gene (L) and wrinkled leaves result from a recessive gene (l), and tall height results from a dominant gene (T) while short height results from a recessive gene (t). A dihybrid cross is performed with plants heterozygous for both traits. What is the expected ratio of short, straight-leaved plants to tall, straight-leaved plants?

  A. 1:1
  B. 1:2
  C. 1:3
  D. 3:1
  C. 1:3

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  Explanation/Reference:

  In a dihybrid cross, the genes for two traits are crossed in a Punnett square. For two heterozygotes crossed in a Punnett square, the expected ratio of recessive/recessive, dominant/recessive, recessive/ dominant, to dominant is 1:3:3:9. In this particular question, the ratio of both recessive/dominant to dominant/dominant is 1:3.

• Question 454:

  The hydrogens of alkanes have pKa values that are over 30 or 40. In contrast, the -hydrogens of aldehydes and ketones have pKa values that range from 19 to 21. These fairly acidic -hydrogens can be removed by strong bases to form anions called enolates. The enolate ions are strongly stabilized by resonance. Protonation of the enolate at oxygen produces an enol. Interconversion between the keto and enol forms is called tautomerization and is illustrated in Figure 1. The keto form is usually highly favored.

  

  Figure 1

  Keto-enol tautomerization has some interesting consequences. For example, if a ketone is treated with acid or base in a solvent of D2O (heavy water), all of the - hydrogens will be exchanged for deuterium. This reaction is shown in Figure 2.

  

  Figure 2

  Another consequence of keto-enol tautomerization is the racemization of chiral -carbons. In the enol form, the -carbon adopts a planar configuration and is no longer chiral. Tautomerization back to the ketone produces a racemic mixture of products. This is shown in Figure 3.

  

  Figure 3

  A scientist attempts to follow the progress of the -deuteration shown in Figure 2 using proton NMR. Which of the following would be the best indicator that the reaction has proceeded to completion?

  A. Singlet at 9.8 ppm
  B. Quadruplet between 1.0 and 2.0 ppm
  C. Doublet between 3.0 and 4.0
  D. No signal
  D. No signal

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  Explanation/Reference:

  Proton NMR is used to identify the number and environments of 1H nuclei. Therefore, deuterium, 2H, will not appear on the NMR and as the alpha hydrogens are replaced with deuterium, the signals will disappear. Choice A is incorrect because a peak at 9.8 ppm, which, by the way, is rarely a singlet, indicates an aldehyde proton. No aldehydes are present here. Choice B is incorrect because a quadruplet in the alkane range (1.0?.0) indicates hydrogens with 3 neighboring hydrogens, leading to splitting. Choice C is incorrect because a peak between 3.0?.0 may indicate an alcohol. A doublet indicates splitting by a single neighboring hydrogen.

• Question 455:

  Millenialism is, generally speaking, the religious belief that salvation and material benefits will be conferred upon a society in the near future as the result of some apocalyptic event. The term derives from the Latin word for 1,000; in early Christian theology, believers held that Christ would return and establish his kingdom on earth for a period of a thousand years.

  Millenialist movements, Christian and non-Christian, have arisen at various points throughout history, usually in times of great crisis or social upheaval. In "nativistic" millenialist movements, a people threatened with cultural disintegration attempts to earn its salvation by rejecting foreign customs and values and returning to the "old ways." One such movement involving the Ghost Dance cults, named after the ceremonial dance which cult members performed in hope of salvation, flourished in the late 19th century among Indians of the western United States.

  By the middle of the 19th century, western expansion and settlement by whites was seriously threatening Native American cultures. Mining, agriculture and ranching encroached on and destroyed many Indian land and food sources. Indian resistance led to a series of wars and massacres, culminating in the U.S. Government's policy of resettlement of Indians onto reservations which constituted a fraction of their former territorial base. Under these dire circumstances, a series of millenialist movements began among western tribes.

  The first Ghost Dance cult arose in western Nevada around 1870. A Native American prophet named Wodziwob, a member of a Northern Paiute tribe, received the revelation of an imminent apocalypse which would destroy the white man, restore all dead Indians to life, and return to the Indians their lands, food supplies (such as the vanishing buffalo), and old way of life. The apocalypse was to be brought about with the help of a ceremonial dance and songs, and by strict adherence to a moral code which, oddly enough, strongly resembled Christian teaching. In the early 1870s, Wodziwob's Ghost Dance cult spread to several tribes in California and Oregon, but soon died out or was absorbed into other cults.

  A second Ghost Dance cult, founded in January 1889, evolved as the result of a similar revelation. This time Wovoka -- another Northern Paiute Indian, whose father had been a disciple of Wodziwob -- received a vision during a solar eclipse in which he died, spoke to God, and was assigned the task of teaching the dance and the millennial message. With white civilization having pushed western tribes ever closer to the brink of cultural disintegration during the previous twenty years, the Ghost Dance movement spread rapidly this time, catching on among tribes from the Canadian border to Texas, and from the Missouri River to the Sierra Nevadas -- an area approximately one-third the size of the continental United States.

  Wovoka's Ghost Dance doctrine forbade Indian violence against whites or other Indians; it also involved the wearing of "ghost shirts," which supposedly rendered the wearers invulnerable to the white man's bullets. In 1890, when the Ghost Dance spread to the Sioux Indians, both the ghost shirts and the movement itself were put to the test. Violent resistance to white domination had all but ended among the Sioux by the late 1880s, when government- ordered reductions in the size of their reservations infuriated the Sioux, and made them particularly responsive to the millenialist message of the Ghost Dance. As the Sioux organized themselves in the cult of the dance, an alarmed federal government resorted to armed intervention which ultimately led to the massacre of some 200 Sioux men, women and children at Wounded Knee, South Dakota in December of 1890. The ghost shirts had been worn to no avail, and Wounded Knee marked the end of the second Ghost Dance cult.

  The author answers all of the following questions EXCEPT:

  A. What was the magical property attributed to the "ghost shirts"?
  B. Was there any connection between the prophets of the two Ghost Dance cults?
  C. What distinguishes "nativistic" millenialist movements from other millenialist movements?
  D. What caused the first Ghost Dance cult to die out?
  D. What caused the first Ghost Dance cult to die out?

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  Explanation/Reference:

  This seeks the answer choice that asks a question which the author didn't address in the passage. Quickly scan the choices, looking for one that leaps out immediately. If this dies not reveal the correct answer, carefully check the choices one by one. Choice (A) asks about the magical powers of the “ghost shirts.” This refers back to the first sentence of paragraph 5, where the author says that the shirts “supposedly rendered the wearers invulnerable to the white man's bullets.” Thus, choice (A) will not be the answer to question 43. Choice (B) asks if there was a connection between the prophets of the two Ghost Dance cults. This is answered in the second sentence of paragraph 4, where the author states that the father of the second prophet, Wovoka, “had been a disciple of Wodziwob,” prophet of the first cult. There was a connection, so choice (B) is also eliminated. Choice (C) inquires whether the passage describes the difference between “nativistic” and other millenialist movements. That question is answered in the third and fourth sentences of the first paragraph, where the author says that millenialist movements are brought on by crises and social upheavals, while nativistic millenialist movements arise out of the specific threat of cultural disintegration. In addition, believers in nativistic millenialist movements are said to have a specific recipe, as it were, for being saved: they try to earn salvation by “rejecting foreign customs” and “returning to the ‘old ways.’” No such plan of attack is mentioned for non-nativistic millenialist movements, so choice (C) is eliminated, and choice (D) is left as the correct answer.And indeed, the author never says why the first Ghost Dance cult died out. He only notes, at the very end of the third paragraph, that it “soon died out or was absorbed into other cults,” without explanation.

• Question 456:

  A researcher investigated the equilibrium between CO2, C, and CO as a function of temperature. The equation is given below:

  

  CO2(g) + C(s) 2 CO(g) Carbon dioxide, at 298 K and 1 atm, and an excess of powdered carbon were introduced into a furnace, which was then sealed so that pressure would increase as the temperature rose. The furnace was heated to, and held constant at, a predetermined temperature. The pressure within the furnace chamber was recorded after it had remained unchanged for one hour. The table below shows the pressures recorded for a series of temperatures together with the pressures expected if no reaction had taken place. Table 1

  

  If 0.6 g of elemental carbon are consumed during a trial, how many grams of CO are produced?

  A. 0.8
  B. 1.4
  C. 1.6
  D. 2.8
  D. 2.8

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  Explanation/Reference:

  Since carbon has a molar mass of 12 grams, a tenth of a mole would be 1.2 grams, and the 0.6 grams stated in the question is one twentieth of a mole. The equation given in the passage shows that for every one mole of carbon consumed, two moles of CO are produced. So, if one twentieth of a mole of carbon is consumed, two twentieths, or one tenth, of a mole of CO will be produced. One tenth of the molar mass of CO, 28 grams, is 2.8 grams. Therefore, choice D is the correct response.

• Question 457:

  In the figure below, aqueous solutions A and B are separated by a semipermeable membrane. Which of the following will occur?

  

  A. Glucose molecules will move from side B to side A.
  B. Glucose molecules will move from side A to side B.
  C. Both water and glucose molecules will move from side A to side B.
  D. Water molecules will move from side B to side A.
  D. Water molecules will move from side B to side A.

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  Explanation/Reference:

  A semipermeable membrane allows the movement of solvent molecules, but not solute molecules. This means that water molecules can move through the semipermeable membrane and that glucose molecules cannot. Choice A, choice B, and choice C can all be eliminated, leaving choice D as the correct response. You should be aware that osmosis is the net movement of solvent molecules through a semipermeable membrane from a pure solvent or a dilute solution to a more concentrated solution. In this case, solution A, which is 5% glucose, is more concentrated than solution B, which is only 1% glucose. So, there will be a movement from the more dilute solution, solution B, to one of higher concentration, which is solution A.

• Question 458:

  Which of the following best accounts for the negative slope of the liquid-solid equilibrium line in the phase diagram for water?

  A. H2O(s) has a greater density than H2O(l), which causes the solid to form liquid under high pressure conditions.
  B. H2O(s) has a greater density than H2O(l), which results from the hydrogen bonds formed between water molecules.
  C. H2O(s) has a lower density than H2O(l) which results from the crystalline framework that forms due to hydrogen bonds.
  D. H2O(s) has a lower density than H2O(l) which causes the solid to form liquid under low pressure conditions.
  C. H2O(s) has a lower density than H2O(l) which results from the crystalline framework that forms due to hydrogen bonds.

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  Explanation/Reference:

  This question asks the examinee to identify the correct explanation for the negatively sloped phase diagram for water. During the crystallization of water, each molecule forms four hydrogen bonds with adjacent water molecules resulting in three-dimensional hexagonal lattice structure. Thus, the density of solid water is less than the density of liquid water eliminating choices A and B. The negatively sloped liquid-solid equilibrium line in the phase diagram means that an increase in pressure at a constant temperature can cause water to change phases from solid to liquid. The increase in pressure causes water to convert to the more compact liquid phase in order to relieve the increased pressure. Therefore, answer choice C is the best answer.

• Question 459:

  When the temperature of an iron bar is raised, its length expands. If the temperature of a second iron bar, which is initially twice as long as the first bar, is raised by twice as much, what is the ratio of the change in length of the first bar to the change in length of the second bar?

  A. 1:1
  B. 1:2
  C. 1:4
  D. 2:1
  C. 1:4

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  Explanation/Reference:

  To answer the question, apply the formula for the thermal expansion of a solid. This formula is given by L = LT, where L is the change in length, L is the original length, T is the change in temperature, and is some constant which depends on the type of material. This formula makes sense intuitively: as the length increases, there is more material available to expand, and as the temperature increases, the more vigorously the material expands.

  

  Compared with the first iron bar, the second iron bar is twice as long, so L2 = 2L1 , and is raised twice as much in temperature, so . Note that is the same for both bars because they are made of the same material. Therefore, the ratio of the first bar's length change to the second bar's length change is

  

  so choice C is correct.

• Question 460:

  ...Until last year many people -- but not most economists -- thought that the economic data told a simple tale. On one side, productivity--the average output of an average worker -- was rising. And although the rate of productivity increase was very slow during the 1970's and early 1980's, the official numbers said that it had accelerated significantly in the 1990's. By 1994 an average worker was producing about 20 percent more than his or her counterpart in 1978. On the other hand, other statistics said that real, inflation- adjusted wages had not been rising at anything like the same rate. In fact, some of the most commonly cited numbers showed real wages actually falling over the last 25 years. Those who did their homework knew that the gloomiest numbers overstated the case....Still, even the most optimistic measure, the total hourly compensation of the average worker, rose only 3 percent between 1978 and 1994.... ...But now the experts are telling us that the whole thing may have been a figment of our statistical imaginations.... a blue-ribbon panel of economists headed by Michael Boskin of Stanford declared that the Consumer Price Index [C.P.I.] had been systematically overstating inflation, probably by more than 1 percent per year for the last two decades, mainly failing to take account of changes in the patterns of consumption and improvements in product quality.... ...The Boskin report, in particular, is not an official document -- it will be quite a while before the Government actually issues a revised C.P.I., and the eventual revision may be smaller than Boskin and his colleagues propose. Still, the general outline of the resolution is pretty clear. When all the revisions are taken into account, productivity growth will probably look somewhat higher than it did before, because some of the revisions being proposed to the way we measure consumer prices will also affect the way we calculate growth. But the rate of growth of real wages will look much higher -- and so it will now be roughly in line with productivity, which will therefore reconcile numbers on productivity and wages with data that show a roughly unchanged distribution of income between capital and labor. In other words, the whole story about workers not sharing in productivity gains will turn out to have been based on a statistical illusion. It is important not to go overboard on this point. There are real problems in America, and our previous concerns were by no means pure hypochondria. For one thing, it remains true that the rate of economic progress over the past 25 years has been much slower than it was in the previous 25. Even if Boskin's numbers are right, the income of the median family -- which officially has experienced virtually no gain since 1973--has risen by only about 35 percent over the past 25 years, compared with 100 percent over the previous 25. Furthermore, it is quite likely that if we "Boskinized" the old data -- that is, if we tried to adjust the C.P.I. for the 50's and 60's to take account of changing consumption patterns and rising product quality--we would find that official numbers understated the rate of progress just as much if not more than they did in recent decades.... ...Moreover, while workers as a group have shared fully in national productivity gains, they have not done so equally. The overwhelming evidence of a huge increase in income inequality in America has nothing to do with price indexes and is therefore unaffected by recent statistical revelations. It is still true that families in the bottom fifth, who had 5.4 percent of total income in 1970, had only 4.2 percent in 1994; and that over the same period the share of the top 5 percent went from 15.6 to 20.1. And it is still true that corporate C.E.O.'s, who used to make about 35 times as much as their employees, now make 120 times as much or more.... ...While these are real and serious problems, however, one thing is now clear: the truth about what is happening in America is more subtle than the simplistic morality play about greedy capitalists and oppressed workers that so many would- be sophisticates accepted only a few months ago. There was little excuse for buying into that simplistic view then; there is no excuse now....

  The Boskin report does all of the following EXCEPT:

  A. Reveals that the C.P.I. was inaccurate.
  B. Reconciles the present disparity between productivity levels, wage levels, and the percentage of labor's share in national income.
  C. Reveals the reasons for the increasing disparity between the highest and lowest income earners.
  D. Helps clarify economic progress in the 1950s and 1960s.
  C. Reveals the reasons for the increasing disparity between the highest and lowest income earners.

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  Explanation/Reference:

  Paragraph six of the passage indicates, "[t]he overwhelming evidence of a huge increase in income inequality in America has nothing to do with price indexes and is therefore unaffected by recent statistical revelations." As Boskin's report is concerned with price indexes and led to recent statistical revelations, it follows that his report has no connection to the increasing disparity between highest and lowest wage earners. Choice A is incorrect as the primary revelation of the Boskin report was that the C.P.I. has been inaccurate. That Boskin's report addresses CPI inaccuracy can be inferred from paragraph two of the passage, in which it is noted that Boskin and his colleagues have proposed that the C.P.I. be revised. Choice B is incorrect. One of the primary results of the Boskin report was that it reconciled the previously perceived disparity between productivity levels, wage levels, and labor's share in the national income. As the second paragraph of the passage notes, once the C.P.I. has been revised (as Boskin and his colleagues recommend), "...the rate of growth of real wages will look much higher -- and so it will now be roughly in line with productivity, which will therefore reconcile numbers on productivity and wages with data that show a roughly unchanged distribution of income between capital and labor." Choice D is incorrect. Paragraph three of the passage reveals the clarifying effect of Boskin's report on understanding 50s and 60s economic progress. The author notes that "...if we `Boskinized' the old data -- that is, if we tried to adjust the C.P.I. for the 50s and 60s to take account of changing consumption patterns and rising product quality -we would find that official numbers understated the rate of progress just as much if not more than they did in recent decades."