Medical Tests MCAT-TEST Online Practice Questions and Exam Preparation

Medical Tests MCAT-TEST Online Questions & Answers

• Question 81:

  A compound, whose molecular mass is 90 grams, contains 40% carbon, 6.67% hydrogen and 53.33% oxygen. What is the true formula of the compound?

  A. CH2O4
  B. C3H6O
  C. C3HO3
  D. C2H2O4
  C. C3HO3

• Question 82:

  A pendulum of length L has a period T. If the period is doubled, the length of the pendulum is:

  A. doubled
  B. halved
  C. quadrupled
  D. increased by 2
  C. quadrupled

• Question 83:

  All of the following plants have a life history that includes alternation of generations, except:

  A. liverwort.
  B. horsetail.
  C. spirogyra.
  D. moss.
  C. spirogyra.

• Question 84:

  Hemophilia is a genetically inherited disease that causes the synthesis of an abnormal clotting factor. As a result, hemophiliacs bleed excessively from the slightest injury. The figure below is a partial pedigree for the hemophilia trait in Queen Victoria's descendants. The pedigree indicates no history of hemophilia for either parent prior to the F1 generation.

  

  According to Figure 1, which of the following assumptions about the P1 generation must be true?

  A. Albert did not have the gene for hemophilia.
  B. Queen Victoria had two X chromosomes, each with the gene for hemophilia.
  C. Neither Albert nor Queen Victorian had the gene for hemophilia.
  D. Albert was a carrier of the hemophilia gene.
  A. Albert did not have the gene for hemophilia.

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  Explanation/Reference:

  This question asks you to conclude something about the P1, or parental, generation. The easiest way to do this is to go through each statement and analyze it. Choice A states that Albert did not have the gene for hemophilia. If we look at the pedigree, we see that this in fact is true; he doesn't have the gene -- as indicated by his unshaded square. If he did have the gene then he would have been a hemophiliac, since the gene is X-linked. So choice A is the correct answer. But let's just take a look at the other choices to be sure. Choice B states that Queen Victoria had two X chromosomes, each with the hemophilia gene. Now it's true that Queen Victoria had two X chromosomes -- all normal females do. However, as indicated by the half shading on her circle in the pedigree, she was a carrier of the gene for hemophilia; that is, she only had one copy of the gene. So choice B is wrong. Choice C states that neither Albert nor Victoria had the gene for hemophilia. Well, Victoria was a carrier, so choice C is wrong too. Choice D states that Albert was a carrier. First of all, men cannot be carriers of an X-linked trait. If they have a copy of the gene in question, then they express the trait. Males cannot have two copies of a X-linked trait because they have only one X chromosome. So, choice D is also wrong.

• Question 85:

  Deoxygenated blood is received by the heart and then pumped out toward the lungs. The now-oxygenated blood is received again by the heart and pumped out toward the rest of the body. Which sequence of heart chambers correctly follows the path of blood described in the passage?

  A. right atrium - left ventricle - left atrium - right ventricle
  B. left atrium - right ventricle - right atrium - left ventricle
  C. right atrium - left atrium - left ventricle - right ventricle
  D. right atrium - right ventricle - left atrium - left ventricle
  D. right atrium - right ventricle - left atrium - left ventricle

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  Explanation/Reference:

  Deoxygenated blood is received by the right atrium via large veins called the venae cavae. It is then transferred to the right ventricle through the tricuspid valve and subsequently exits the heart through the semi lunar valve and is transferred to the pulmonary artery, where it is pumped toward the lungs for oxygenation. Oxygenated blood is received by the left atrium and transferred to the left ventricle through the mitral valve.

• Question 86:

  Sugars are carbohydrates, that is, molecules usually with the empirical formula C(H2O), and structural formulas made up of polyhydroxy aldehydes or ketones. Because of their polyfunctional nature, sugars can undergo a wide variety of

  transformations upon treatment with acids, bases, or heat, and upon reaction with other simple reagents and enzymes. While many sugars occur in nature and are thus readily available, the synthesis and modification of simple sugars is a

  necessary step in studies of enzymatic processes.

  Higher sugars can be synthesized from the simple carbohydrate D-glyceraldehyde with the following procedure:

  D-glyceraldehyde (Compound A) is reacted with HCN to produce a cyanohydrin (Compound B). Compound B is then treated with hydrogen gas and a modified palladium catalyst (similar to the Lindlar reagent) to give Compound C.

  Compound C is hydrolyzed to give the higher sugars in Mixture D. This reaction is summarized in Figure 1. Mixture D contains two compounds, which can be separated by crystallization. Two doublets near 9.5 (, ppm) are observed in the 1H

  NMR spectrum of mixture D, with each doublet corresponding to one of the two products present in the mixture. IR spectroscopy shows broad absorptions for both products around 3300 cm?.

  

  The hydroxyl groups of carbohydrates can also participate in reactions. For example, D-glyceraldehyde can react with chloromethane under basic conditions to yield a completely methylated product. This SN2 reaction is shown in Figure 2.

  

  Figure 2 Methylation of D-glyceraldehyde

  The modified palladium catalyst is used instead of platinum to:

  A. avoid reduction of the cyanohydrin to the amine.
  B. make the reaction energetically favorable.
  C. act as a Lewis acid.
  D. reduce the likelihood of attack at the carbonyl carbon.
  A. avoid reduction of the cyanohydrin to the amine.

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  Explanation/Reference:

  The cyanohydrin (compound B) is reduced to an imine (compound C). If platinum were used, reduction would proceed all the way to the amine as shown below. This must be avoided in order to produce the carbonyl group on the extended sugar.

  

  Choice B is incorrect because a catalyst will not alter the thermodynamic favorability of a reaction. A catalyst will only increase the rate of reaction by lowering the activation energy. Choice C is incorrect because a Lewis acid is an electron

  pair acceptor. The palladium catalyst acts as an activator of hydrogen.

  Platinum would function in the same way.

  Choice D is incorrect because compound B does not even have a carbonyl group (carbon double bonded to oxygen).

• Question 87:

  Aski jump is an inclined track from which a ski jumper takes off through the air. After traveling down the track, the skier takes off from a ramp at the bottom of the track. The skier lands farther down on the slope.

  Figure 1 shows a ski jump, in which the ramp at the lower end of the track makes an angle of 30?to the horizontal. The track is inclined at an angle of to the horizontal and the slope is inclined at an angle of 45?to the horizontal. A ski jumper is stationary at the top of the track. Once the skier pushes off, she accelerates down the track, and then takes off from the ramp. The vertical height difference between the top of the track and its lowest point is 50 m, and the vertical height difference between the top of the ramp and its lowest point is 10 m.

  

  Figure 1

  The distance traveled by the skier between leaving the ski jump ramp and making contact with the slope is called the jump distance. In some cases, in order to increase the jump distance a skier will jump slightly upon leaving the ramp,

  thereby increasing the vertical velocity. Unless otherwise stated, assume that friction between the skis and the slope is negligible, and ignore the effects of air resistance.

  How would the speed of a skier leaving the jump ramp change if the vertical height of the jump ramp were increased from its original height of 10 meters?

  A. increase
  B. decrease
  C. remain the same
  D. The answer depends on the incline angle of the jump ramp.
  B. decrease

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  Explanation/Reference:

  This question is testing your knowledge of the conservation of energy. When the skier is at the top of the track, she is not moving so all her energy is potential energy. At the top of the track she has potential energy. When she leaves the jump ramp, she is moving. So she has kinetic energy equal to 1/2 mv2. The difference in height between the top of the track and the point on the jump ramp where she jumps from is proportional to the amount of potential energy that gets converted to kinetic energy. Let h equal the height of the platform at the top of the track minus the height of the top of the jump ramp. The greater h is, the more potential energy gets converted to kinetic energy, and the greater the skier's speed when

  

  she jumps. Specifically, neglecting friction and air resistance, mgh = 1/2 mv2, and solving for v, we find that v = . In the question stem, we are told that the height of the ski jump ramp is increased; so h is decreased. Since v = , we see that a decrease in h corresponds to a decrease in v. Therefore, choice B is correct. You might have chosen answer choice A if you were careless and thought the track height increased.

• Question 88:

  The rich analyses of Fernand Braudel and his fellow Annales historians have made significant contributions to historical theory and research. In a departure from traditional historical approaches, the Annales historians, assume (as do Marxists) that history cannot be limited to a simple recounting of conscious human actions, but must be understood in the context of forces and material conditions that underlie human behavior. Braudel was the first Annales historian to gain widespread support of the idea that history should synthesize data from various social sciences, especially economics, in order to provide a broader view of human societies over time (although Febvre and Bloch, founders of the Annales school, had originated this approach). Braudel conceived of history as the dynamic interaction of three temporalities. The first of these, the evenementielle, involved short-lived dramatic "events," such as battles, revolutions and the actions of great men, which had preoccupied traditional historians like Carlyle. Conjonctures was Braudel's term for larger cyclical processes that might last up to half a century. The longue duree, a historical wave of great length, was for Braudel the most fascinating of the three temporalities. Here he focused on those aspects of everyday life that might remain relatively unchanged for centuries. What people ate, what they wore, their means and routes of travel -- for Braudel these things create "structures" which define the limits of potential social change for hundreds of years at a time. Braudel's concept of the longue duree extended the perspective of historical space as well as time. Until the Annales school, historians had taken the juridical political unit the nation-state, duchy, or whatever as their starting point. Yet, when such enormous timespans are considered, geographical features may well have more significance for human populations than national borders. In his doctoral thesis, a seminal work on the Mediterranean during the reign of Philip II, Braudel treated the geohistory of the entire region as a "structure" that had exerted myriad influences on human lifeways since the first settlements on the shores of the Mediterranean Sea. And so the reader is given such arcane information as the list of products that came to Spanish shores from North Africa, the seasonal routes followed by Mediterranean sheep and their shepherds, and the cities where the best ship timber could be bought. Braudel has been faulted for the imprecision of his approach. With his Rabelaisian delight in concrete detail, Braudel vastly extended the realm of relevant phenomena; but this very achievement made it difficult to delimit the boundaries of observation, a task necessary to beginning any social investigation. Further, Braudel and other Annales historians minimize the differences among the social sciences. Nevertheless, the many similarly-designed studies aimed at both professional and popular audiences indicate that Braudel asked significant questions which traditional historians had overlooked.

  The author refers to the work of Febvre and Bloch in order to:

  A. illustrate the limitations of the Annales tradition of historical interpretation.
  B. suggest the relevance of economics to historical investigation.
  C. debate the need for combining various sociological approaches.
  D. show that previous Annales historians anticipated Braudel's focus on economics.
  D. show that previous Annales historians anticipated Braudel's focus on economics.

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  Explanation/Reference:

  The reason that the author refers to Febvre and Bloch is explained in the parentheses at the end of Paragraph 1. The author states that Febvre and Bloch had anticipated Braudel by originating the historical approach that emphasized economics. Choice D is the correct answer here. Choice A is out because the limitations of the Annales approach are not discussed until the end of the passage. The relevance of economics to history has already been suggested by the time the author mentions Febvre and Bloch, so Choice B is wrong. Choice C is incorrect because the need for combining various sociological approaches is not debated in the first paragraph or anywhere else.

• Question 89:

  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

  The two products formed by the racemization reaction in Figure 3 could best be described as:

  A. enantiomers
  B. diastereomers
  C. conjugate acid and base
  D. same compound
  A. enantiomers

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  Explanation/Reference:

  The passage states that a racemic mixture is produced, indicating the presence of enantiomers in equal concentrations. Figure 3 shows the structure of the two compounds. The compounds differ in configuration at their only chiral center, indicating that they are enantiomers. Choice B is incorrect because diastereomers are not mirror images. Diastereomers may have optical rotations of different magnitudes. Thus, a solution with equal concentrations of two diastereomers may still rotate plane polarized light. In contrast, a racemic mixture does not rotate plane polarized light. Choice C is incorrect because the compounds are not conjugate acids and bases. Choice D is incorrect because meso compounds are compounds that have chiral centers but lack optical activity due to an internal plane of symmetry.

• Question 90:

  The Russian wheat aphid, Diuraphis noxia, is a small green insect discovered in southern Russia around the turn of the century. Agricultural researchers are not quite sure, but they believe the Russian aphid adapted itself to wheat about ten thousand years ago, when the crop was first domesticated by man. What is not in doubt is the insect's destructiveness. Spread by both wind and human transport, the Russian aphid has destroyed wheat fields throughout Asia, Africa, and Latin America. Until a few years ago, the United States had been free of this pest. But in the spring of 1986, a swarm of Russian aphids crossed the Mexican border and settled a few hundred miles north, in central Texas. From there, it quickly spread to other Western states, destroying wheat fields all along its path. In fact, the level of destruction has been so great over the past five years that entomologists are calling the Russian aphid the greatest threat to American agriculture since the Hessian fly, Phytophaga destructor, was inadvertently brought to the colonies on ships by German mercenary troops during the Revolutionary War. A combination of several factors have made it particularly difficult to deal with the threat posed by this aphid. First, Russian aphids reproduce asexually at a phenomenal rate. This process, known as parthenogenesis, often results in as many as twenty generations of insects in a single year. Although most generations remain in a limited geographic area because they have no wings, a few generations are born with wings, allowing the insect to spread to new areas. Second, because wheat is a crop with a very low profit margin, most American farmers do not spray it with pesticides; it simply is not economical to do so. And since the Russian aphid has only recently entered the United States, it has no natural enemies among North American insects or animals. As a result, there have been no man-made or natural obstacles to the spread of the Russian aphid in the United States.

  Agricultural researchers seeking to control the Russian aphid have looked to its place of origin for answers. In the Soviet Union, the Russian aphid has been kept in check by predators which have evolved alongside it over many thousands of years. One species of wasp seems to be particularly efficient at destroying the aphid. The pregnant females of the species search the Russian aphid's home, the interior of a wheat stalk, sting the aphid into paralysis, and then inject an egg into its body. When the egg hatches the wasp larva feeds off of the aphid, killing it in the process.

  The introduction of predators like the wasp, coupled with the breeding of new strains of insect-resistant wheat, may substantially curb the destructiveness of the Russian aphid in the future. For the time being, however, American farmers are left to their own devices when it comes to protecting their wheat crops

  According to the passage, which of the following statements is/are true of Russian wheat aphids?

  I. Most are capable of flight.

  II. They are resistant to pesticides.

  III.

  They are capable of spreading rapidly.

  A. II only
  B. III only
  C. I and II only
  D. II and III only
  I. Most are capable of flight. II. They are resistant to pesticides. III. They are capable of spreading rapidly.
  B. III only

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  Explanation/Reference:

  This is a scattered detail question in Roman numeral format. It's scattered in the sense that the reader must scan various parts of the passage in order to pinpoint the details the question requires. The fourth sentence of the third paragraph tells us that most Russian aphids are born without wings only a few generations have them), so most can't fly, making option I a false statement. Option II suggests that aphids are resistant to pesticides. We have no basis for concluding that this is true because the passage doesn't provide any information about whether or not Russian aphids are resistant to pesticides. In fact, the only piece of information the passage provides about pesticides is the fact, stated in the middle of the third paragraph, that American farmers haven't used pesticides against the Russian aphid for economic reasons. So far, then, neither options I nor II are true statements. The third sentence of the second paragraph asserts that once Russian aphids invaded the United States, they spread rapidly to different areas. Option III, therefore, is a true statement. They are capable of spreading rapidly.