Medical Tests MCAT-TEST Online Practice Questions and Exam Preparation

Medical Tests MCAT-TEST Online Questions & Answers

• Question 221:

  Which of these is NOT true about ultrasound waves?

  A. The medium (type of tissue) affects the propagation speed.
  B. If frequency increases, wavelength increases as well.
  C. The resolution of images depends on the wavelength.
  D. Propagation speed is higher through solids than through liquids.
  B. If frequency increases, wavelength increases as well.

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  Explanation/Reference:

  Actually, if an ultrasound frequency increases, its wavelength decreases. All of the other answer choices are true.

• Question 222:

  Which two elements are needed for the production of chlorophyll?

  A. Phosphorus and Sulfur
  B. Chlorine and Copper
  C. Magnesium and Iron
  D. Calcium and Phosphorus
  C. Magnesium and Iron

• Question 223:

  Four major blood types exist in the human ABO blood system: types A, B, AB, and O; and there are three alleles that code for them. The A and B alleles are codominant, and the O allele is recessive. Blood types are derived from the presence of specific polysaccharide antigens that lie on the outer surface of the red blood cell membrane. The A allele codes for the production of the A antigen; the B allele codes for the production of the B antigen; the O allele does not code for any antigen. While there are many other antigens found on red blood cell membranes, the second most important antigen is the Rh antigen. Rh is an autosomally dominant trait coded for by 2 alleles. If this antigen is present, an individual is Rh+; if it is absent, an individual is Rh-. For example, a person with type AB blood with the Rh antigen is said to be AB+.

  These antigens become most important when an individual comes into contact with foreign blood. Because of the presence of naturally occurring substances that closely mimic the A and B antigens, individuals who do not have these antigens on their red blood cells will form antibodies against them. This is inconsequential until situations such as blood transfusion, organ transplant, or pregnancy occur.

  Erythroblastosis fetalis is a condition in which the red blood cells of an Rh+ fetus are attached by antibodies produced by its Rh- mother. Unlike ABO incompatibility, in which there are naturally occurring antibodies to foreign antigens, the Rh system requires prior sensitization to the Rh antigen before antibodies are produced. This sensitization usually occurs during the delivery of an Rh+ baby. So while the first baby will not be harmed, any further Rh+ fetuses are at risk.

  The Coombs tests provide a method for determining whether a mother has mounted an immune response again her baby's blood. The tests are based on whether or not agglutination occurs when Coombs reagent is added to a sample. Coombs reagent contains antibodies against the anti-Rh antibodies produced by the mother. The indirect Coombs test takes the mother's serum, which contains her antibodies but no red blood cells, and mixes it with Rh+ red blood cells. Coombs reagent is then added. If agglutination occurs, the test is positive, and the mother must be producing anti-Rh antibodies. The direct Coombs test mixes the baby's red blood cells with Coombs reagent. If agglutination occurs, the test is positive, and the baby's red blood cells must have been attacked by its mother's anti-Rh antibodies.

  Based on information in the passage, what does the reaction below represent?

  

  A. Negative direct Coombs test
  B. Positive direct Coombs test
  C. Positive indirect Coombs test
  D. Negative indirect Coombs test
  B. Positive direct Coombs test

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  Explanation/Reference:

  As described in the passage, the Coombs tests are the screening procedures used to assess whether an Rh incompatibility reaction can or has occurred. The direct Coombs test will identify whether the baby's red blood cells have in fact been attacked by the mother's anti-Rh antibodies. The indirect Coombs test tests for the presence of anti-Rh antibodies in the mother's serum. The figure in the question shows red blood cells with anti-Rh antibodies already attached to them, being mixed with Coombs reagent. This is the test described in the fourth paragraph of the passage as being the direct Coombs tests. Therefore, choices C and D can be eliminated. The outcome shows that Coombs reagent reacted with the red blood cells; the results of this test are therefore positive; so choice A is wrong and choice B is right. In order for either a direct or indirect Coombs test to be negative, the anti-Rh antibody cannot be present. For this to have been a positive indirect Coombs test, there would have been an additional, previous step showing the mixing of the mother's serum with washed red blood cells.

• Question 224:

  The automobile airbag was designed to inflate upon impact and decrease the risk of injury to drivers and passengers. Among the challenges to its development was the need to find a reliable inflation mechanism that was sufficiently rapid, controllable, and nontoxic. Prototypes employing compressed gases failed to meet these criteria. Researchers thus turned their attention to chemical alternatives.

  The ideal inflatant requires a chemical reaction in which the reactants are stable and relatively dense in the condensed phase while the products are mostly or completely gaseous at ambient temperature and pressure. Additionally, the ideal chemical reaction would require a low activation energy and have a high kinetic rate constant, without the large exothermicity characteristic of most such reactions. Traditional explosives such as nitroglycerin, C3H5N3O9(l), were rejected almost immediately because of the extremely exothermic nature of their conversion. Benign solids such as calcium carbonate, CaCO3 , were similarly rejected, because of their large activation requirements. The desired attributes were finally found in sodium azide, NaN3, a stable, dense, ionic solid which rapidly decomposes into elemental sodium and nitrogen gas when ignited by an electrical impulse.

  

  Reaction 1

  The gas generating mixture includes excess KNO3 which reacts with the sodium metal from Reaction 1 to produce additional N2 and potassium and sodium oxides (Reactions 2 and 3). These oxides react with SiO2 to produce a non-toxic and stable alkaline silica (glass).

  

  Reaction 2

  

  Reaction 3

  

  All of the following are resonance structures of N3- EXCEPT:

  

  A. Option A
  B. Option B
  C. Option C
  D. Option D
  D. Option D

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  Explanation/Reference:

  The formal charges are assigned incorrectly: their values should be as indicated in choice B. Resonance structures vary only in their arrangement of electrons. The connectivity of nuclei is preserved. The other resonance structures for N3are valid and contribute to the resonance hybrid structure that is more stable than any of the individual resonance structures alone.

• Question 225:

  Which of the following is called DIOL?

  A. Glycerol
  B. Glycol
  C. Methanol
  D. Ethanol
  B. Glycol

• Question 226:

  The endosymbiosis theory proposes that mitochondria originated through the engulfing of aerobic prokaryotes by anaerobic host prokaryotes. Many of the enzymes required for aerobic respiration are located on the inner membrane of the mitochondria. Where would these enzymes, or their precursors, most likely have been found three billion years ago (prior to endosymbiosis)?

  A. In the cytoplasm of the anaerobic prokaryotic host cells
  B. On the plasma membrane of the anaerobic prokaryotic host cells
  C. On the plasma membrane of the aerobic prokaryotic engulfed cells
  D. In the cytoplasm of the prokaryotic aerobic cells
  C. On the plasma membrane of the aerobic prokaryotic engulfed cells

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  Explanation/Reference:

  As the host cell engulfs a prokaryotic aerobic cell, the host cell membrane forms a vesicle about the aerobic cell, giving a double membrane structure. The inner membrane is formed bythe plasma membrane of the aerobic cell.

  Choice A is incorrect because enzymes in the cytoplasm of the anaerobic host cell would remain in the cytoplasm.

  Choice B is incorrect because enzymes on the plasma membrane of the anaerobic host cell would befound on the outer membrane of the mitochondria formed by endosymbiosis. Choice D is incorrect because enzymes in the cytoplasm of

  the aerobic cell would be within the matrix of the mitochondria formed by endosymbiosis.

• Question 227:

  ...[TV Guide's] immediate concern was the television quiz show scandal, which had reached its climax two weeks earlier when Charles Van Doren, the appealing young man who'd taught viewers the value of learning while winning big on MCA's Twenty-one, stood before a House committee and admitted he was a fraud. But the issue went well beyond rigged quiz shows. The charge was that through their stranglehold on talent, MCA and William Morris monopolized the medium to the detriment of their clients, the industry, and the public at large. This was why the Justice Department had launched a secret investigation of both agencies more than two years before. The Morris Agency had started the quiz show vogue in 1955, when it packaged The $64,000 Question for Revlon and sold it to CBS. While the show won praise for its "educational" nature, the real source of its appeal was in its crapshoot format -- the idea that once contestants' winnings hit the $32,000 mark, they had to decide whether to go double or nothing on the final, $64,000 question, or play it safe and go home. The response was tremendous. Within weeks, the show knocked I Love Lucy out of the number-one slot in the ratings. Casinos in Vegas emptied out when it went on the air. Bookies took odds on whether the first contestant to go for the big one -- a marine captain whose specialty was cooking -- would get the answer right. (He did.) Revlon sold so much Living Lipstick that its factory was unable to meet the demand. The $64,000 Question quickly inspired imitators, among them an MCA package called Twenty-one. Based on the card game, more or less, Twenty-one was a dismal failure at first. "Do whatever you have to do," the sponsor ordered angrily, so the producers put the fix in. In December 1956, when Charles Van Doren, a boyishly attractive English instructor at Columbia University, beat Herb Stempel, a short, squat, nerdy grad at City College, Van Doren became the first intellectual hero of the television age. Honors and acclaim poured in -- the covers of Time, letters by the hundreds, offers of movie roles and tenured professorships and a regular guest spot on The Today Show. But Herb Stempel didn't like being told to lose, especially to some Ivy League snot. He went to the press. The DA's office started to investigate. The walls began to close in. Meanwhile, the show's producers agreed to sell the rights to NBC for $2 million. One of them started to feel queasy about selling the show without letting the network know the score, so he went to Sonny Werblin, MCA's top man in New York, and asked his advice. Werblin, the man behind such hits as The Ed Sullivan Show and The Jackie Gleason Show, ran the television department as if it were a football team coached by Attila the Hun. "Dan," he asked the producer, "have I ever asked you whether the show was rigged?" No, he hadn't. "And has NBC ever asked you whether the show is rigged?" No, they hadn't either. "Well," Werblin concluded, "the reason that none of us has asked is because we don't want to know." And with good reason. Not only was Twenty-one an MCA package and Van Doren himself an MCA client; Werblin had a special relationship with NBC's president, Robert Kintner. Kintner had been president of ABC until...ABC's chairman forced him out in his determination to move the network out of third place. MCA used its influence to place him at NBC, where he proved an extremely pliant customer. In the spring of 1957, when the networks were putting together their schedules for the next season, Werblin went to a meeting of NBC programming executives led by Kintner and his boss, RCA chairman Robert Sarnoff. "Sonny, look at the schedule for next season," Kintner said when he walked in, "here are the empty slots, you fill them."

  The author's description of Kintner as "an extremely pliant customer" (line 64):

  A. reinforces his description of Werblin as an exacting taskmaster.
  B. supports his contention that NBC lacked strong leadership.
  C. indicates the degree of MCA's influence over the network.
  D. contradicts the implication that NBC knew their quiz show was rigged.
  C. indicates the degree of MCA's influence over the network.

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  Explanation/Reference:

  The description is used by the author to describe the level of control Werblin had over NBC, with Kintner as its representative. Choice A is irrelevant to the question. Choice B can perhaps be inferred from the relationship between MCA and NBC, but the weakness of NBC's leadership is not a point that the author is making specifically. Choice D is incorrect because it does not contradict the implication that Kintner was unduly influenced by Werblin.

• Question 228:

  When a radio station is broadcasting a musical program, the antenna of its transmitter:

  A. radiates AF electromagnetic waves.
  B. radiates longitudinal waves.
  C. radiates RF electromagnetic waves.
  D. radiates AF longitudinal waves.
  C. radiates RF electromagnetic waves.

• Question 229:

  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

  

  Which of the following shows the correct Lewis structure of carbon monoxide?

  

  A. Option A
  B. Option B
  C. Option C
  D. Option D
  C. Option C

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  Explanation/Reference:

  The first thing that should be done is to determine which choices have the proper number of valence electrons. Carbon monoxide must have a total of 10 electrons: six from the oxygen and four from the carbon. Choice B and choice D can be

  eliminated because they both have 12 electrons.

  In choice A, the carbon has one pair of unbonded electrons, plus four more electrons in the double bond. This gives the carbon a total of only six electrons in its valence shell, so the carbon doesn't have a complete octet, and choice A must

  be wrong. Choice C shows the correct Lewis structure for carbon monoxide: each atom has a complete octet, and there is a total of ten electrons.

• Question 230:

  Synthetic dyes constitute a commercially significant area of organic chemistry. The color producing properties of these compounds are the result of highly delocalized electron systems giving rise to electronic transitions whose absorptions occur in the visible region. Most commercially useful dyes can be classified as one of three types -- anthraquinones, azo dyes, or triarylmethyl salts. Examples of each type are illustrated in Figure 1.

  

  Figure 1

  In order for a dye to be useful in the fabric industry, it must have sufficient affinity for the polymeric fibers of which the material is composed; the dye must not only impart a color to the fabric, but must also do so in a relatively permanent manner (color fastness). Proper design of synthetic polymers requires the placement of acidic or basic side chains along the polymer backbone such that binding sites are available for dying. Similarly, dyes must be produced not only with the appropriate color-producing structure, but also with an affinity for the fabric in question. The structural units of several common synthetic fibers are shown in Figure 2.

  

  Figure 2

  Nylon, Dacron, and many other synthetic fibers are produced via condensation reactions. Which of the following would be the best starting materials for the production of nylon 66?

  A. cis-2-butenoic acid and 1,6-hexanediamine
  B. butanedioic acid and 1,6-hexanediamine
  C. n-hexanoic acid and 2,5-hexanediamine
  D. hexanedioic acid and 1,6-hexanediamine
  D. hexanedioic acid and 1,6-hexanediamine

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  Explanation/Reference:

  Amides are produced by the condensation of amines with carboxylic acids:

  

  To produce a repeating chain, or polyamide, one would need to condense a diamine with a dicarboxylic acid. As indicated in figure 2, nylon 66 has a straight chain of six carbons between the two nitrogen atoms and six more carbon atoms, also unbranched, in the dicarbonyl portion of the monomer. As such, the amine starting material must therefore be 1,6-hexanediamine, while the carboxylate reactant is hexanedioic acid:

  Choice A is incorrect because cis-2-butenoic acid has only one carboxylate functionality and therefore would not condense on both ends, and it would produce a condensation product in which the butane double bond is still present. It also contains only four carbon atoms, rather than the required six. Choice B is incorrect since, while butanedioic acid can polymerize with the diamine, it would produce a polymer with only two methylene groups between the carbonyl carbons in each monomer. (This product would be called nylon 64.) Choice C is wrong on two counts: first, the hexanoic acid is a monocarboxylic acid, and thus will not combine with two amine molecules; second, any polyamide formed via condensation of an appropriate diacid and the suggested amine, 2,5- hexanediamine, would have two methyl group side chains.