AAMC MCAT test 9 a

9R SOLUTIONS FROM AAMC Physical Sciences 1 A solution contains 0.1 M Mg2+(aq), 0.1 M Ca2+(aq), and 0.1 M Sr2+(aq) All three ions can be precipitated if which two reagents are added to the solution? A ) Reagents and B ) Reagents and Mg2+ can be precipitated from a solution of Reagent only Ca2+ can be precipitated from a solution of reagents or 4, and Sr2+ can be precipitated from a solution of reagents 2, 3, or All three ions can be precipitated from a solution containing Reagent and reagents or The ions will precipitate from a solution containing reagents and Thus, B is the best answer C D ) Reagents and ) Reagents and Solution Guess A test tube contains mL of 0.1 M Ca2+(aq) A precipitate will most likely form if which of the following reagents is added to the tube? A B ) 1.0 M HCl(aq) ) 1.0 M NaOH(aq) ) 1.0 M H2SO4(aq) ) 1.0 M Na2CO3(aq) C D Ca2+ forms a precipitate when either Reagent 3, a solution of (NH4)2C2O4, or Reagent 4, a solution of (NH4)2CO3, is added to the Ca(NO3)2 solution A precipitate would form when a solution of Na2CO3 is added Na2CO3, like (NH4)2CO3, is a source of CO32– and its addition would result in the formation of the insoluble CaCO3 Thus, D is the best answer Solution Guess The students added Reagent to a test tube containing 0.1 M Ca2+(aq) and 0.1 M Sr2+(aq) Which of the following procedures will best enable the students to recover a fairly pure sample of SrSO4(s) from this mixture? A ) the tube Allowing the water to evaporate and collecting the solid that remains in B ) Pouring the mixture through a filter, collecting the insoluble substance, and allowing the water to evaporate from the insoluble substance When Reagent is added to the Ca2+ solution, the resulting solution is clear When Reagent is added to the Sr2+ solution, a white precipitate is generated It follows that after the addition of Reagent to a solution containing Ca2+ and Sr2+, the Ca2+ would remain in the solution and the Sr2+ would precipitate out as SrSO4 Pure SrSO4 could be obtained by isolating the solid by filtration and allowing the water to evaporate from the solid Thus, B is the best answer C ) Pouring the mixture through a filter, collecting the filtrate containing the soluble substance, then allowing the water to evaporate from the filtrate D ) Adding Reagent 3, pouring the mixture through a filter, collecting the filtrate containing the soluble substance, and allowing the water to evaporate from the filtrate Solution Guess The information in Table suggests that which of the following substances has the smallest Ksp? A ) MgSO4 ) MgC2O4 ) CaSO4 ) CaC2O4 B C D The smaller the Ksp of a substance, the lower the solubility of the substance MgSO4, MgC2O4, and CaSO4 all remain dissolved, but CaC2O4 does not Therefore, CaC2O4 has the lowest solubility and the smallest Ksp Thus, D is the best answer Solution Guess A solution contains either Ca2+(aq) or Sr2+(aq) Which of the following actions will best enable the students to identify the ion in the solution? A ) Performing a flame test B ) Adding Reagent ) Adding Reagent C When Reagent is added to the Ca2+ solution, the resulting solution is clear When Reagent is added to the Sr2+ solution, a white precipitate forms The students will be able to determine which ion is present by adding Reagent Thus, C is the best answer D ) Adding Reagent Solution Guess Which of the following graphs best illustrates how charge accumulates on the plates of the capacitor after the switch is closed? A ) B ) As time increases, charging must increase as well Further, the charging of a capacitor is an exponentially decreasing process that must reach a constant value after a long time The graph in B most clearly shows this behavior Thus, B is the best answer C ) D ) Solution Guess If the speed of the charged particle described in the passage is increased by a factor of 2, the electrical force on the particle will: A B ) decrease by a factor of ) remain the same Electrical force depends on the particle’s charge and the strength of the electric field experienced by the particle, not on the particle’s speed Thus, B is the best answer C D ) increase by a factor of ) increase by a factor of Solution Guess Making which of the following changes to a circuit element will increase the capacitance of the capacitor described in the passage? A ) Replacing the 500-Ω resistor with a 250-Ω resistor ) Replacing the 10-V battery with a 20-V battery ) Increasing the separation of the capacitor plates ) Increasing the area of the capacitor plates B C D Capacitance C depends on geometric factors only, and in the case of parallel plates, C is proportional to the plate area and inversely proportional to the separation distance of the plates Thus, D is the best answer Solution Guess A charged particle with a mass of m and a charge of q is injected midway between the plates of a capacitor that has a uniform electric field of E What is the acceleration of this particle due to the electric field? A ) Eq/m The force on the charge is qE and force is also ma Setting qE = ma and solving for acceleration a yields Thus, A is the best answer B C ) Em/q ) mq/E ) Emq D Solution Guess 10 Another capacitor, identical to the original, is added in series to the circuit described in the passage Compared to the original circuit, the equivalent capacitance of the new circuit is: A ) 1/2 as great When in series, capacitors C1 and C2 add by the inverse rule Therefore, if C1 = C2 = C, then Thus, A is the best answer B ) the same ) times as great ) times as great C D Solution Guess 11 Which of the following best describes the motion of a negatively charged particle after it has been injected between the plates of a charged, parallel-plate capacitor? (Note: Assume that the area between the plates is a vacuum.) A ) It moves with constant speed toward the positive plate ) It moves with constant speed toward the negative plate ) It accelerates toward the positive plate B C Opposites attract, so the negatively charged particle will move toward the positive plate Because there is a constant force qE on the particle, it will accelerate toward the positive plate Thus, C is the best answer D ) It accelerates toward the negative plate Solution Guess 12 What type of intermolecular interaction can ETOH undergo with water that MTBE can NOT? A ) van der Waals ) Dipole–dipole ) Hydrogen bonding B C The –OH group in ETOH gives ETOH the capability of donating hydrogen bonds to water MTBE is incapable of donating hydrogen bonds to water Thus, C is the best answer D ) Covalent bonding Solution Guess 13 The formation of one mole of which oxygenate shown in Table releases the most energy? A B ) ETOH ) MTBE ) ETBE ) TAME C D The formation of mol of TAME gives off the most energy, 680 kJ Thus, D is the best answer Solution Guess 14 What are the coefficients for oxygen and carbon dioxide, respectively, if the equation shown below is balanced? 1CH3OCH3(ℓ ) + ? O2(g) ® H2O(g) + ? CO2(g) A B ) and ) and ) and ) and C D The six hydrogen atoms in CH3OCH3 on the left side of the equation must be balanced by giving H2O on the right side of the equation a coefficient of The two carbon atoms in CH3OCH3 on the left side of the equation must be balanced by giving CO2 on the right side of the equation a coefficient of Now, the seven oxygen atoms on the right side of the equation must be balanced by giving O2 on the left side of the equation a coefficient of Thus, D is the best answer Solution Guess 15 Which of the following nonoxygenated analogs of MTBE is most likely to mimic MTBE in its antiknock properties? A ) C4H9Si(CH3)3 ) C4H9N(CH3)2 ) C4H9SCH3 B C Because sulfur is in the same group as oxygen in the periodic table, these elements share many characteristics and it would be expected that replacing the O in MTBE with S would result in a compound that would most likely mimic the antiknock properties of MTBE Thus, C is the best answer D ) C4H9P(CH3)2 Solution Guess 16 The entropy change for the combustion reaction of gasoline is always greater than zero because the: A ) number of gaseous molecules in the products always exceeds the number of gaseous molecules in the reactants Entropy is a measure of disorder Gases have higher entropies than liquids, and liquids have higher entropies than solids The entropy of a reaction increases if the number of moles of gaseous products exceeds the number of moles of gaseous reactants Thus, A is the best answer B C ) enthalpy change is always positive ) temperature of the combustion is always more than 100°C ) free energy change is always positive D Solution Guess 17 Which compound shown in Table evaporates fastest at 30°C? A ) MTBE ) ETOH B The greater the vapor pressure, the greater the rate of evaporation ETOH has the highest vapor pressure at 25ºC Thus, B is the best answer C D ) ETBE ) TAME Solution Guess 18 If one mole of each additive shown in Table undergoes complete combustion, which compound requires the least amount of oxygen? A B ) MTBE ) ETOH The compound with the lowest carbon-to-oxygen ratio will require the least amount of oxygen for combustion ETOH has only two carbon atoms and one oxygen atom Thus, B is the best answer C D ) ETBE ) TAME Solution Guess 19 A collection of an unspecified number of neighboring gas columns, or pipes, can reasonably be used to represent the layer of a star in which pressure waves occur because the: A ) harmonic frequencies of a pipe are independent of its diameter The passage gives the relationship between frequency and pipe geometry and shows it being dependent on length only This makes A correct and B incorrect C is eliminated because the velocity is explicitly given as a function of gas density D is incorrect because gas density falls with height Thus, A is the best answer B ) harmonic frequencies of a pipe are independent of its length ) speed of sound in gas confined to a pipe is independent of gas density ) speed of sound propagating upward against gravity decreases with C D height Solution Guess 20 As an aid in identifying the various resonant pressure-wave frequencies in the Sun and stars, one can use the fact that: A ) the Doppler-shifted light is easily recognized, being polarized in a way that is characteristic of hydrogen B ) the Doppler-shifted light stands out, being steadier in intensity than the unshifted light emissions that accompany it C ) resonant frequencies are always separated by increments that are equal to a basic number multiplied by an integer Only C is given as a possibility in the passage, namely, the quantization of the resonant frequencies This is in fact the basis for the analogy to the pipe Thus, C is the best answer D ) resonant frequencies in hydrogen gas depend strongly on its degree of gas ionization, which, in turn, depends on temperature Solution Guess 21 In the newer observational technique discussed, one makes use of the fact that: A ) ionized the hydrogen gas in the observed stellar atmospheres is completely B ) stellar atmospheres are open to space, so that pressure and temperature are independent of volume C ) pressure waves in stars propagate upward very slowly, generally at about m/s D ) light is absorbed or emitted whenever electrons move from one energy level to another This item is fairly subtle in that only D is correct based on the passage The gas is in an excited state but not completely ionized, making A incorrect B is entirely incorrect, and C is true only for the gas velocity, not for the pressure wave velocity Thus, D is the best answer Solution Guess 22 The surface temperature of one of the observed stars is 6000 K The fraction of its surface hydrogen atoms having electrons in energy level then increases by how much for each K temperature rise? A ) (6001/5999)6 1.002, so parts in 1000 ) (6001/6000)6 1.001, so part in 1000 B The passage states that the population increases with T6 For an initial surface temperature of 6000 K, an increase in K must result in a population increase that is the ratio of the new temperature to the old temperature raised to the 6th power Thus, B is the best answer C ) (274/273)6 1.02, so parts in 100 ) (461/460) D Solution Guess 23 H2O is liquid at room temperature, whereas H2S, H2Se, and H2Te are all gases Which of the following best explains why H2O is liquid at room temperature? A ) Hydrogen bonds form between H2O molecules H2O is capable of forming intermolecular hydrogen bonds, but H2S, H2Se, and H2Te are not Thus, A is the best answer It is an isomer of ribose It is an isomer of xylose A B ) I only ) II only ) I and III only ) II and III only C D The figures in this item show that ribose, ribulose, and xylose are all isomers with the same molecular formula, but that deoxyribose has a different molecular formula It is reasonable therefore to conclude that xylulose would be an isomer of xylose and ribose Thus, D is the best answer Solution Guess 190 One characteristic common to arteries, veins, and capillaries is the: A ) presence of a layer of endothelial cells The question asks the examinee to identify one characteristic common to arteries, capillaries, and veins A is correct because all three types of vessels possess an inner layer of endothelial cells B is incorrect because only veins have valves C is incorrect because only certain types of arteries dilate or constrict to regulate blood flow D is incorrect because the exchange of nutrients with the surrounding tissues occurs only in capillaries Thus, A is the best answer B ) presence of numerous valves that prevent the backflow of blood ) ability to actively dilate or constrict in regulating blood flow C D ) diffusion ability to supply surrounding tissues with nutrients by filtration and Solution Guess 191 Tissue that is very active metabolically, such as skeletal muscle, contains large numbers of: A B ) nuclei ) fat deposits ) blood capillaries C The question asks the examinee to identify the feature that is abundant in metabolically active tissue Metabolically active tissue requires a large supply of oxygen and produces many waste products Such tissue needs ample capillary blood flow to provide oxygen and to remove waste products As a result, the best answer is C A (nuclei) is incorrect because although mature skeletal muscle cells have multiple nuclei, these nuclei result from the fusion of individual muscle cells during muscle development, each of which contributes one nucleus Thus, the total number of nuclei in the muscle itself is no greater than if a muscle were composed of individual cells B is incorrect because even though fat deposits are useful for long-term energy storage, metabolically active skeletal muscle relies primarily on glycogen stores that provide energy in a more easily utilized form Answer D is incorrect because lymphatic vessels not deliver materials needed for metabolism Thus, C is the best answer D ) lymphatic vessels Solution Guess 192 The finches observed by Darwin on the Galapagos Islands are an example of adaptive radiation In order to set up conditions that would produce adaptive radiation, it would be necessary to place members of: A ) one species in one rapidly changing environment ) one species in several different environments B The question refers to the finches of the Galapagos Islands as an example of adaptive radiation and asks the examinee to identify the conditions required for adaptive radiation Adaptive radiation involves the divergence of one species into multiple species over time, which can occur when subgroups of the original species are separated or isolated in different environments so that these subgroups evolve independently of one another B is correct because it describes this situation A is not the best answer because a single rapidly changing environment does not encourage adaptive radiation Rather, as the environment changes, the species would be more likely to collectively evolve into a single new species adapted to the new environment C and D are incorrect because adaptive radiation begins with one species, not several, regardless of whether the species are similar (C) or unrelated (D) Thus, B is the best answer C ) several very similar species in the same environment D ) resources several unlike species in one environment to compete for the same Solution Guess 193 Which of the compounds shown below can form hydrogen bonds with water? CH3–CH2–CH3 Compound CH3–CH2–NH2 Compound A B ) Compound only ) Compound only In Compound 2, which is an amine, two hydrogen atoms are covalently bonded to the nitrogen atom, and nitrogen is an electronegative element Compound 1, an alkane, does not contain any hydrogen atoms covalently bonded to an atom of an electronegative element Thus, B is the best answer C ) Both compounds ) Neither compound D Solution Guess 194 The term α-helix refers to what kind of protein structure? A ) Primary ) Secondary B The term α-helix describes a helical conformation of a protein chain that is created by hydrogen bonding between groups on the protein backbone This is an example of the secondary structure of a protein Thus, B is the best answer C ) D ) Solution Tertiary Quaternary Guess 195 Which conclusion about Peptide A receptor binding can be reached from Figure 1? A ) osteoblatin Peptide A requires 100% receptor binding to produce the most B ) Peptide A produces the most osteoblatin possible at less than 100% receptor binding The question asks the examinee to identify the conclusion that can be drawn about Peptide A receptor binding based on the results presented in Figure Figure shows the percentage of Peptide A binding to receptors (solid line) and the concentration of osteoblatin produced (dashed line) as a function of Peptide A concentration As the concentration of Peptide A increases, so does the percentage of Peptide A binding and the concentration of osteoblatin However, the curve for osteoblatin concentration levels off at a Peptide A concentration of about 25 ng/mL, while the curve for the percentage of Peptide A receptor binding slows and begins to level off at approximately twice this concentration When Peptide A concentration is 25 ng/mL, about 50% of Peptide A has bound to receptors Because the maximal production of osteoblatin occurs when only 50% of the Peptide A receptors are occupied, B is the best answer A is incorrect because maximal osteoblatin production occurs at 50% receptor binding; 100% receptor binding is not required C is incorrect because 50% binding of Peptide A results in maximal osteoblatin production, not 50% production D is incorrect because there is no increased synthesis of osteoblatin at over 50% receptor binding Thus, B is the best answer C ) At 50% binding to its receptors, Peptide A produces 50% of the maximal amount of osteoblatin D ) Peptide A continues to stimulate increasing levels of osteoblatin production at over 50% receptor binding Solution Guess 196 When OB is incubated with a constant concentration of Peptide A (25 ng/mL) and increasing concentrations of Peptide B, osteoblatin concentration: A B ) increases exponentially ) increases linearly ) remains constant ) decreases C D The question asks the examinee to identify the relationship between osteoblatin concentration and increasing concentrations of Peptide B when osteoblasts are incubated with a constant concentration of Peptide A Peptide A stimulates the production of osteoblatin, but Peptide B does not Furthermore, Peptide B competitively inhibits Peptide A by binding to the same receptor sites on the cell membranes As the concentration of Peptide B increases, more and more receptor sites are occupied by Peptide B rather than by Peptide A This prevents Peptide A from being able to activate expression of osteoblatin, therefore decreasing the osteoblatin concentration (D) A, B, and C are incorrect because the osteoblatin concentration does not increase exponentially (A), increase linearly (B), or remain constant (C) Thus, D is the best answer Solution Guess 197 What can be concluded about Peptide A from Experiment 2? A ) It is ineffective in stimulating osteoclastic activity ) It acts directly on OC to increase bone resorption ) It acts indirectly through OB to increase bone resorption B C The question asks the examinee to identify the conclusion that can be drawn about Peptide A based on the results of Experiment The first key observation from the experiment is that Peptide A stimulates the synthesis of osteoblatin, but only when OB are present The second key observation is that OC activity cannot be stimulated by the presence of either Peptide A or OB alone; only when both Peptide A and OB are present is OC activity stimulated This implies that Peptide A functions indirectly to increase bone resorption by stimulating OB to produce osteoblatin, which in turn stimulates OC activity (C) A is incorrect because Peptide A does stimulate OC activity through its interaction with OB B is incorrect because Peptide A must interact with OB in order to increase OC activity D is incorrect because although Peptide A acts directly on OB, it stimulates the production of osteoblatin, not bone formation (Table 1, Group 2) Thus, C is the best answer D ) It acts directly on OB to increase bone formation Solution Guess 198 In Experiment 2, which three groups demonstrated cell line viability and allowed the determination of basal cellular activities? A ) Groups 1, 2, and ) Groups 1, 3, and B The question asks the examinee to identify which three groups in Experiment demonstrated cell line viability and allowed the determination of basal cellular activities Essentially, this question is asking the examinee to identify the three control groups—the groups that provide the basis for comparison to see the effects of Peptide A The correct answer is B because the control groups include all groups in which Peptide A was omitted This includes groups 1, 3, and A, C, and D are incorrect because each contains at least one experimental group that includes Peptide A Thus, B is the best answer C D ) Groups 2, 4, and ) Groups 4, 5, and Solution Guess 199 To most effectively study the effect of Peptide A on transcription of the osteoblatin gene, a scientist should determine the: A B ) sequence of the osteoblatin gene ) amount of osteoblatin mRNA in the cell The question asks the examinee to identify the most effective method that could be used to study the effect of Peptide A on transcription of the osteoblatin gene RNA is the direct product of transcription; therefore, the amount of osteoblatin mRNA in a cell would be a direct measure of transcription of the osteoblatin gene (B) A is incorrect because regulatory sequences within the DNA only indirectly indicate the amount of mRNA the cell will produce C is not the best answer because the amount of osteoblatin peptide in the cell would be a direct indicator of translation but only an indirect indicator of transcription D is incorrect because the total amount of RNA in the cell would depend on the transcription of many genes, not just the gene that codes for osteoblatin Thus, B is the best answer C D ) amount of osteoblatin peptide in the cell ) total RNA in the cell Solution Guess 200 The overall effect of Peptide A on bone is to: A ) increase bone mass ) decrease bone mass B The question asks the examinee to identify the effect of Peptide A on bone The passage states that Peptide A binds to specific sites on the plasma membrane of osteoblasts (OB), the bone-forming cells Experiment results show that the effect of Peptide A on OB was to increase secretion of osteoblatin, which markedly stimulates bone resorption This indicates that the overall effect of Peptide A on bone is to decrease bone mass (B) A is incorrect because bone mass decreases rather than increases C is incorrect because there is no evidence to support the idea that haversian canals undergo change D is incorrect because bone mass decreases rather than stays the same Thus, B is the best answer C ) narrow haversian canals D ) Solution maintain constant bone mass Guess 201 According to the passage, which of the following compounds can serve as an antioxidant? A ) B ) Based on the passage, to serve as an antioxidant, the compound must have a hydrogen atom that can be removed to form a radical and an aromatic ring that will permit subsequent coupling with a peroxy radical A hydrogen atom attached to the nitrogen in the compound in B can be removed, and the resulting radical would be able to couple with the peroxy radical at position Thus, B is the best answer C ) D ) Solution Guess 202 Compared to the activation energy for the hydrogen-atom abstraction from BHT, the activation energy for the reaction between a BHT radical and peroxy radical is: A ) less The passage states that the rate-controlling step in the antioxidation process is the formation of the BHT radical, indicating that the reaction of the BHT radical with the peroxy radical occurs more quickly Thus, A is the best answer B ) equal ) greater ) impossible to determine from the data given C D Solution Guess 203 Which of the following phenols can undergo intra- molecular hydrogen bonding? A ) B ) C ) D ) The compound in D can form intramolecular hydrogen bonds between the adjacent – OH and –CO2H groups Thus, D is the best answer Solution Guess 204 A 1H NMR spectrum of BHT contains how many unique (nonequivalent) proton signals? A ) In BHT, the 18 protons in the tert-butyl groups at positions and are equivalent, giving rise to one signal The protons in the methyl group at position give rise to a second signal The ring protons at positions and are equivalent, resulting in a third signal, and the –OH proton gives rise to a fourth signal A 1H NMR spectrum of BHT will contain unique signals Thus, A is the best answer B ) ) 12 ) Solution 24 C D Guess 205 When used as described in the passage, antisense drugs prevent: A B ) DNA replication ) RNA transcription C ) RNA translation The question asks the examinee to identify the effect of an antisense drug When antisense mRNA molecules are used as described in the passage, the antisense molecules bind specifically to the sense mRNA, preventing the process of translation As a result, C is the best answer A, B, and D are not the best answers because the passage describes the effect of antisense RNA binding to mRNA, and mRNA is directly involved in translation However, because RNA can hybridize with either RNA or DNA, a role for antisense RNA in the regulation of DNA replication, transcription, and even cell replication may be possible, but these processes are not the focus of the passage Thus, C is the best answer D ) cell replication Solution Guess 206 To be an effective therapy, an antisense gene that is incorporated into a genome that contains the target gene must be: A ) on the same chromosome as the target gene but not necessarily be physically adjacent B ) adjacent C ) on the same chromosome as the target gene and must be physically regulated in a similar manner as the target gene The question focuses on antisense genes that are incorporated into the genome of their target gene and asks the examinee to identify which antisense gene characteristic would be required for the gene to be therapeutically effective To provide effective therapy, this antisense gene would need to be regulated in a manner similar to the manner in which the target gene is regulated so that the antisense RNA is produced at the same time that the sense mRNA is produced This would ensure that the antisense RNA is available to bind with the sense mRNA, thereby preventing its subsequent translation As a result, C is correct A, B, and D are incorrect because the key feature determining whether an antisense drug will work is the timing of the expression of the antisense gene This is controlled by specific regulatory elements, not necessarily the location of the antisense gene relative to the target gene Thus, C is the best answer D ) coded on the same strand of DNA as the target gene Solution Guess 207 Phenylketonuria is a genetic disorder caused by a mutation in the gene for the enzyme phenylalanine hydroxylase, which eliminates its enzymatic activity Could an antisense drug help individuals with this disorder? A ) Yes, if it binds to the mRNA of the phenylalanine hydroxylase gene and prevents its translation B ) Yes, if it is incorporated into the chromosome and prevents the expression of the phenylalanine hydroxylase gene C ) No, because mRNA does not persist in the cytoplasm of the cell D ) No, because blockage of phenylalanine hydroxylase gene expression will not remedy the original disorder The question indicates that phenylketonuria (PKU) is a genetic disorder caused by a mutation in the gene for an enzyme, which results in the elimination of enzymatic activity The question asks the examinee to consider whether an antisense drug could help individuals who have PKU An antisense drug works to prevent the expression of undesirable genes but does nothing to remedy the problem of a gene that produces an ineffective product The only way to cure PKU would be to add a gene or gene product that could lead to the production of effective enzymes to replace the ones that not function correctly D is the best answer because a blockage of gene expression would only prevent the production of defective enzymes but would not remedy the problem caused by the absence of effective enzymes A and B are incorrect because preventing expression of an inactive protein is not a cure C is incorrect because the stability of the mRNA is irrelevant to the situation Thus, D is the best answer Solution Guess 209 An effective and efficient method for the delivery of an antisense gene could be: A ) orally as an emulsified product ) microinjection into individual body cells B C D ) intravenously as a nonantigenic, blood-stable product ) infection of an embryo by a virus modified to carry the gene The question asks the examinee to identify an effective and efficient method for the delivery of an antisense gene For an antisense gene to work, it must be incorporated into the cell in which it will perform its job so that its product is available to hybridize with the sense mRNA that needs to be blocked Of the options listed, the best way to deliver the antisense gene into all the cells of the individual would be to infect an embryo with a virus that carries the antisense gene The appropriate virus could become incorporated into the genome of the embryonic cells, thus causing all cells derived from these embryonic cells to contain the antisense gene Therefore, D is the best answer A is incorrect because the gene would most likely be destroyed in the acidic environment of the stomach B is not the best option because microinjection of a gene into all cells would be extremely impractical C is incorrect because even though the gene could be injected as a blood-stable product, it is not likely that the drug would enter its intended target cells Thus, D is the best answer Solution Guess 211 Which of the following describes a primary function of the myelin sheath? A B ) It provides nutrients to motor neurons ) It regulates synaptic vesicle discharge ) It guides dendrite growth and branching ) It increases the rate of conduction of action potentials C D The question asks the examinee to identify a primary function of the myelin sheath The myelin sheath is a fatty layer surrounding the long axons of neurons in vertebrates A primary function of this layer is to enable nerve impulses (action potentials) to travel more quickly by jumping from node to node rather than traveling continuously along the entire length of the neuron This supports D, which states that the myelin sheath increases the rate of conduction of action potentials A, B, and C are incorrect because they describe roles that the myelin sheath does not provide Thus, D is the best answer Solution Guess 212 When muscles in the skin contract and cause the hair of an animal to “stand on end,” the skin could be functioning as a regulator of: A B ) pH ) salt excretion ) body temperature C The question asks the examinee to identify a likely regulatory function of an animal’s skin when its muscles contract, causing the animal’s hair to stand on end A major function of hair is to help mammals regulate body temperature by reducing the amount of heat lost to the environment Hair provides insulation When the hair stands on end, trapping air within the layer of hair, then its insulating effect becomes even more effective Thus, as C indicates, a primary function of this action is to help regulate body temperature The contraction of skin muscles that causes the hair to stand on end would have little effect on skin pH (A), salt excretion (B), or skeletal muscle tone (D) Thus, C is the best answer D ) skeletal muscle tone Solution Guess 213 Of the isomeric alcohols (compounds 1–4), which is most reactive in an SN1 reaction with HBr? A ) Compound ) Compound ) Compound ) Compound B C D The most reactive alcohol in an SN1 reaction is the one that will generate the most stable intermediate carbocation The 3º carbocation generated by Compound is the most stable, and therefore Compound will be the most reactive Thus, D is the best answer Solution Guess 214 If chromosomal duplication before tetrad forma-tion occurred twice during spermatogenesis, while the other steps of meiosis proceeded normally, which of the following would result from a single spermatocyte? A B ) One tetraploid sperm ) Four diploid sperm The question asks the examinee to predict the result if chromosomal duplication occurred twice before tetrad formation, but if all other steps in spermatogenesis occurred normally If all other steps occur normally, then four sperm would be produced Because replication occurred twice instead of once prior to tetrad formation, each sperm would have twice the normal amount of DNA As a result, four diploid sperm would be produced instead of four haploid sperm Therefore, B is the best answer A, C, and D are incorrect because they describe results that contain an incorrect number of sperm or ploidy number for the sperm produced Thus, B is the best answer C D ) Four haploid sperm ) Eight haploid sperm Solution Guess 215 All of the following occur during normal inspiration of air in mammals EXCEPT: A ) elevation of the rib cage ) relaxation of the diaphragm B The question asks the examinee to identify which one of four actions is not associated with normal inspiration in mammals B is the best answer because the diaphragm does not relax during inspiration The diaphragm contracts and pulls downward, causing air to enter the lungs A, C, and D all describe actions that occur during inspiration Elevation of the rib cage increases the volume inside the chest cavity (A), reduction of pressure inside the pleural cavity causes air to move into the lungs (C), and contraction of the external intercostal rib muscles helps the chest expand (D) Thus, B is the best answer C ) reduction of pressure in the pleural cavity ) contraction of the external intercostal rib muscles D Solution Guess 216 Radioactively labeled uracil is added to a culture of actively dividing mammalian cells In which of the following cell structures will the uracil be incorporated? A B ) Chromosomes ) Ribosomes The question asks the examinee to predict the cell structure in which radioactively labeled uracil will become incorporated if added to a culture of actively dividing mammalian cells Uracil is a component of RNA Therefore, one would expect to find the radioactively labeled uracil in cell structures that contain RNA B is the best answer because ribosomes contain rRNA and proteins A is incorrect because chromosomes, by definition, consist primarily of proteins and DNA Although DNA is composed of nucleic acids, DNA contains thymine instead of uracil C and D are incorrect because RNA is not an integral component of either lysosomes (C) or the nuclear membrane (D) Thus, B is the best answer C D ) Lysosomes ) Nuclear membrane ... motion of a negatively charged particle after it has been injected between the plates of a charged, parallel-plate capacitor? (Note: Assume that the area between the plates is a vacuum.) A ) It... hexafluoroaluminate ion (AlF63–)? A ) Octahedral An ion consisting of a central metal ion and six ligands is expected to have an octahedral geometry Thus, A is the best answer B C ) Tetrahedral... with each component present at a concentration of 0.1 M, has a pH closest to 7? A ) HClO(aq) and NaClO(aq) When the acid and conjugate base concentrations are equal, the pH of a buffer equals the