AAMC MCAT test 8 a

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1 With respect to bonding and electrical conductivity, respectively, sulfur hexafluoride, SF6(g), would be described as: A )covalent and a nonconductor The passage states that the vast majority of covalent compounds are comprised exclusively of nonmetallic elements, whereas binary ionic compounds are made up of a metal and a nonmetal Because neither sulfur nor fluorine is a metallic element, sulfur hexafluoride is a covalent compound The passage also states that aqueous solutions of covalent compounds not conduct electricity Sulfur hexafluoride is covalent and a nonconductor Thus, A is the best answer B )ionic and a nonconductor C )covalent and a conductor D )ionic and a conductor Where are nonmetals found in the periodic table? A) Right side The noble gases and halogens are found on the right side of the table These are nonmetals Thus, A is the best answer B ) Left side C ) Top half D ) Bottom half Which of the following pairs of compounds provides an example of ionic and covalent bonding, respectively? A ) HBr(g) and NaCl(s) B ) NaCl(s) and NaI(s) C ) NaI(s) and NaCl(s) D ) NaCl(s) and HBr(g) The passage states that the vast majority of covalent compounds are comprised exclusively of nonmetallic elements, whereas binary ionic compounds are made up of a metal and a nonmetal Sodium is a metal and chlorine is a nonmetal; consequently, NaCl is an ionic compound Hydrogen and bromine are both nonmetals, which means HBr is a covalent compound Thus, D is the best answer Which of the following compounds has the most ionic character? A ) KBr(s) B ) CsCl(s) The compound with the greatest difference in electronegativities between the metal and nonmetal has the most ionic character The data in Table show that electronegativities tend to decrease down a group of the periodic table Cs would have an electronegativity of approximately 0.8 or lower and Cl has an electronegativity of 3.0 The difference between the electronegativities of these two elements is the greatest of the compounds listed Thus, B is the best answer C ) NaI(s) D ) RbBr(s) Which of the following statements is consistent with the incorrect conclusion that HCl is an ionic compound? A ) It is a gas at room temperature B ) A M solution freezes below 0°C C ) A M solution conducts electricity The passage states that an aqueous solution of an ionic compound conducts electricity Thus, C is the best answer D ) It is composed of two nonmetals According to the passage, the magnitude of B3 at the position of a given hydrogen nucleus is determined by the: A ) chemical environment of the nucleus The passage states that B3 is the vector sum of the magnetic fields of the electrons and other nuclei near the H atom, so the chemical composition of the material around the H nucleus being examined will contribute to B3 Only Foil A relates to the material around the H nucleus Thus, A is the best answer B ) mass of the nucleus C ) radius of the nucleus D ) charge of the nucleus Consider an H nucleus with µ pointing in a direction 180° from a magnetic field When the nucleus relaxes, which of the following most likely will result? A ) The magnitude of µ will decrease to zero B ) The magnitude of the magnetic field will decrease to zero C ) The nucleus will emit a photon Based on the passage, µ is an intrinsic property of the atomic and subatomic particles, and the magnetic fields are either externally controlled (B1, B2) or intrinsic to the electrons and nuclei (B3) The passage also states that energy is emitted when an H nucleus relaxes, which is compatible only with emitting a photon Thus, C is the best answer D ) The nucleus will absorb a photon X-ray imaging sometimes requires the use of contrast dyes In MRI, dyes are: A ) less toxic B ) not needed The dyes used in X-ray imaging must consist of elements from the lower part of the periodic table to take advantage of attenuation’s being “roughly proportional to the atomic numbers of elements contained in the tissue.” In contrast, the passage states that “adjacent locations with different chemical compositions,” when imaged by MRI, already have “contrasts of several hundred percent.” This implies that a dye is not necessary Thus, B is the best answer C ) needed but not always used D ) always used Human proteins are composed mostly of the elements C, H, O, N, and S Without dyes, X-ray images of tissue containing different proteins NOT have high contrasts, most likely because: A dyes not bind well to proteins B protein bonds are broken by the radiation, resulting in the formation of free radicals C the differences in the atomic numbers of the elements are not large enough Because attenuation is “roughly proportional to the atomic numbers of elements contained in the tissue,” to see significant differences in the X-ray image one needs a sizable difference in atomic number Noting that bones, but not much else, easily appear in an X ray of undyed tissue, one can infer that Ca has an atomic number high enough to significantly attenuate X rays Of the elements C, H, O, N, and S, only sulfur has an atomic number approaching (but still less than) that of Ca Thus, C is the best answer D proteins are opaque to X rays 10 For a given magnitude of B1, the nucleus with the nonzero precession frequency will be which of the following? A4 He B1 O C1 F Because protons and neutrons have spin just as electrons do, to guarantee a nonzero net spin, an odd number of nucleons is needed Of the foils, the only element that has an odd number of nucleons is Thus, C is the best answer D 208 Pb 82 11 To adjust ωd of H nuclei, a diagnostician is most likely to vary which of the following? A ) B1 Based on the passage, the angular frequency ωd is One can see that B1 is the only externally controllable variable Thus, A is the best answer B ) B3 C) h D) µ 12 According to the passage, at resonance, B2 rotates an H nucleus through an angle of: A ) 45° B ) 90° C ) 180° The passage states that to precess µ at a frequency of ωd, µ must be parallel to B1 If the precesssing H atom becomes antiparallel, this means µ has turned by 180° Thus, C is the best answer D ) 270° 13 The effect of temperature on the rate of the reaction can best be determined by comparing Tube with which of the following tubes? A ) Tube B ) Tube C ) Tube To determine the effect of temperature on the rate of the reaction, Tube must be compared with another tube in which all conditions were the same, except the temperature Tube contained 20 mL each of solutions A and B and no water at 32ºC Tube contained 20 mL each of solutions A and B and no water at 12ºC Thus, C is the best answer D ) Tube 14 The results in Table would most likely NOT be affected if the students had added excess: A ) KI(aq) to Solution A B ) Na2S2O3(aq) to Solution A C ) (NH4)2S2O8(aq) to Solution B D ) starch to Solution B Starch is not a participant in any of the reactions, acting only as an indicator of excess I2 Thus, D is the best answer 15 In Tube 6, what is the most likely function of CuSO4(aq)? A ) Reactant B ) Indicator C ) Inhibitor D ) Catalyst A comparison of the results for Tube and Tube 6, which are identical except for the addition of CuSO4 to Tube 6, shows that it takes longer for the combined solution in Tube to turn dark blue than it takes for the combined solution in Tube Thus, D is the best answer 16 The solution in Tube turned dark blue more rapidly than did the solution in Tube 4, because the: A ) rate of Reaction was slower in Tube than in Tube B ) average kinetic energies of I–(aq) and S2O8–(aq) were greater in Tube than in Tube The reaction conditions for tubes and are identical except Tube was run at 22ºC and Tube was run at 12ºC The higher the temperature, the greater the average kinetic energy of the components of the reaction Thus, B is the best answer C ) concentrations of I–(aq) and S2O8–(aq) were greater in Tube than in Tube D ) concentration of starch was greater in Tube than in Tube 17 Which of the following graphs best shows the number of moles of S4O62–(aq) in Tube as time passes? A) B) The data in Table show that the reaction is complete in 19 sec The amount of S4O62– would increase for 19 sec and then level off Thus, B is the best answer C ) D ) 18 According to the results of Galileo’s experiments described in the passage, the ratio of d to t2 attained its maximum value when: A ) the inclined plane was horizontal B ) the inclined plane was vertical Because the acceleration of gravity is in the vertical direction, the greatest acceleration of a sphere will occur when the plane is also vertical Thus, B is the best answer C ) natural motion began D ) violent motion ceased 19 As described in the passage, Aristotle’s theories of motion NOT deal with which of the following observations? A ) An object in a vacuum can move with constant velocity Of the foils, the only situation that does not occur naturally on Earth’s surface is that of an object in a vacuum Thus, A is the best answer B ) An object in free fall can reach a constant velocity C ) A mass on a spring undergoes violent motion D ) A heavy body falls with a greater velocity than a light one 20 When designing his experiment, Galileo could have allowed spheres to drop from a height of 10 m rather than using the 10m inclined plane described in the passage The main advantage to using the inclined plane is that on the inclined plane the: A ) final velocity of a sphere is smaller B ) final velocity of a sphere is larger C ) spheres take longer to reach the bottom Ignoring air resistance, rotation, and friction, the final velocity of a sphere that drops is the same as the final velocity of a sphere that moves down the inclined plane Meanwhile, the path is longer on the inclined plane than in free fall, leading to a longer time for a sphere to reach the bottom Thus, C is the best answer D ) spheres take less time to reach the bottom 21 Spheres A, B, C, and D have identical radii and masses of 10 g, 40 g, 20 g, and 30 g, respectively According to Aristotle’s theory, if the spheres are dropped to the ground from the same height, which object will have the highest terminal velocity? A ) Object A B ) Object B Aristotle’s theory states that an object’s time of fall t is inversely proportional to its weight W Symbolically, this is t ∝ 1/W The question asks one to determine the highest terminal velocity (when striking the ground) The highest terminal velocity should then be inversely proportional to t because spheres A–D all fall from the same height Because the largest mass in this group is Sphere B, its weight will also be the largest, so Aristotle’s theory predicts the shortest t for it Thus, B is the best answer C ) Object C D ) Object D 22 Object A has times the density and ½ the volume of Object B According to Aristotle’s theory, if A and B are dropped to Earth from the same height, which object will reach Earth first? (Note: Ignore the effects of friction.) A ) Object A, because it is denser than object B B ) Object A, because it is heavier than object B C ) Object B, because it is heavier than object A D ) The objects will reach Earth at the same time Object A is given as having twice the density of Object B (ρA = 2ρB) and having half of Object B’s volume (VA = VB/2) To find which object has the shorter time of fall under Aristotle’s theory (t ∝ 1/W), one must determine the weight of each object from its mass Because W = mg and m = ρV, WB = mBg = ρBVBg, and WA = mAg =ρAVAg = (2ρB)(VB/2)g = ρBVBg This means that WA = WB, and the time of fall for each object will be the same Thus, D is the best answer 23 A sparingly soluble metal hydroxide, M(OH)2 has a molar solubility of S mol/L at 25°C Its Ksp value is: A ) S2 B ) 2S2 C ) 2S3 D ) 4S3 The Ksp for a substance, AaBb, equals [A]a[B]b The Ksp for M(OH)2 = [M][OH–]2 If the solubility of M(OH)2 is S mol/L, then [M] = S mol/L and [OH–] = 2S mol/L The Ksp = S(2S)2 = S(4S2) = 4S3 Thus, D is the best answer 24 If the quantity of gas remains unchanged while its temperature increases, the volume of the gas will: A ) always increase, because volume is directly proportional to temperature B ) always decrease, because volume is inversely proportional to temperature C ) increase if pressure remains constant The ideal gas law shows that PV = nRT If n (the quantity of gas) is constant and T (temperature) increases, then PV (pressure × volume) will increase If the pressure remains constant, then the volume must increase Thus, C is the best answer D ) decrease if pressure remains constant 25 An astronaut on Earth notes that in her soft drink an ice cube floats with 9/10 of its volume submerged If she were instead in a lunar module parked on the Moon where the gravitation force is 1/6 that of Earth, the ice in the same soft drink would float: A ) with more than 9/10 submerged B ) with 9/10 submerged The floating ice cube implies that its weight is balanced by the buoyant force on it Wice = mg = ρfluidVsubmergedg Note that both the weight and the buoyant force are proportional to g, making the numerical value of g irrelevant to the volume of the ice cube that is submerged Thus, B is the best answer C ) with 6/10 submerged D ) totally submerged 26 A glass fiber carries a light digital signal long distances with a minimum loss of amplitude What optical property of glass allows this phenomenon? A ) Dispersion B ) Refraction C ) Reflection Light can be carried along a distance within a transparent material by means of total internal reflection Thus, C is the best answer D ) Diffraction 27 Reaction is an effective means of decreasing the hardness of an acidic water sample because it: A ) increases the pH and decreases the solubility of CaCO3 According to the passage, calcium ions in the water contribute to the hardness of the water and CaCO3 is soluble in acidic solutions Boiling the water causes Reaction to take place; the solubility of CO2 decreases as the temperature increases Reaction decreases the hardness of an acidic water sample by removing CaCO3 from the sample and increasing the pH by reducing the amount of CO2 in the sample Thus, A is the best answer B ) decreases the pH and decreases the solubility of CaCO3 C ) increases the pH and converts HCO3– to water D ) decreases the pH and removes Ca2+ from solution 28 What is the effect of a high level of atmospheric CO2 on the hardness of water in limestone regions? A ) It would lower the pH and increase the solubility of CaCO3 High levels of CO2 in the atmosphere would result in CO2 dissolved in the water When CO2 dissolves in water it becomes carbonic acid, causing a decrease in the pH The passage states that CaCO3 is very soluble in acidic solutions The pH would be lowered and the solubility of CaCO3 would increase Thus, A is the best answer B ) It would raise the pH and increase the solubility of CaCO3 C ) It would lower the pH and decrease the solubility of CaCO3 D ) It would raise the pH and decrease the solubility of CaCO3 29 How many grams of CaCO3 would be formed in Reaction if the CO2 evolved occupies 11.2 L at STP? A ) 0.5 g B ) 11.2 g Solution Guess C ) 50 g At STP, mole of gas occupies 22.4 L; therefore, 0.5 mol CO2 was generated According to Reaction 1, mol CaCO3 forms for every mole of CO2 that forms There is 0.5 mol CaCO3, which has a formula weight of 100 g/mol The amount of CaCO3 formed is 50 g Thus, C is the best answer D ) 100 g 30 If the pH of the water sample were high such that all the carbonate is present as CO32–, what would be the concentration of Ca2+? (The Ksp of CaCO3 is 4.8 × 10–9.) A ) (4.8 × 10–9)2 M Solution Guess B ) (4.8 × 10–9)1/2 M The Ksp of CaCO3 = [Ca2+][CO32–] = 4.8 × 10–9 If all of the carbonate is in the form of CO32–, then [Ca2+] = [CO32–] = (4.8 × 10–9)1/2 M Thus, B is the best answer C ) 4.8 × 10–9 M D ) (4.8 × 10–9)1/3 M 31 The addition of excess Ca2+ to a solution containing Ca2+ and CO32– ions causes CaCO3 to precipitate because: A ) Ksp for CaCO3 would increase due to the increase in [Ca2+] B ) Ksp for CaCO3 would decrease due to the increase in [Ca2+] Solution C ) [CO32–] would increase to maintain Ksp D ) [CO32–] would decrease to maintain Ksp When CaCO3 is in solution, the following takes place: CaCO3(s) ↔ Ca2+(aq) + CO32–(aq) and Ksp = [Ca2+][CO32–] When excess Ca2+ is added, some CaCO3 precipitates in accordance with Le Châtelier’s principle [CO32–] therefore decreases and the Ksp is maintained Thus, D is the best answer Guess 32 What is the expression for the angular frequency ω of a pendulum? A ) 2πmg/L B ) (L/g)1/2 C ) 2π(g/L)1/2 D ) (g/L)1/2 Because the frequency f of a pendulum in Hz is the angular frequency ω (in rad/s) is Thus, D is the best answer 33 The equation for tension used in the passage requires θo to be units of radians How is an angle of 30° converted to radians? A ) θo = 30° × π Solution B ) θo = 30° × 2π C ) θo = 30° × π/180° Guess Because 2π rad = 360°, the appropriate conversion factor for degrees-to-radians is π rad/180° Thus, C is the best answer D ) θo = 30° × π/360° 34 If all the resistors in Figure are 200 Ω, what is the current from the battery when V0 = 12 V? A ) 30 mA Solution B ) 60 mA Guess There are two branches to this parallel circuit: one passes through R1 and R2 in series, and the other passes through R3 and RSG in series The total resistance of the parallel circuit is then Given that R1, R2, R3, and RSG are each 200 Ω, Rtotal is also 200 Ω, and the current Itotal = V/Rtotal is then 0.060 A Thus, B is the best answer C ) 120 mA D ) 240 mA 35 What is the magnitude of the restoring force on the pendulum bob at angle θ? A ) mg Solution Guess B ) mgsinθ The restoring force on a pendulum points along the tangent to the circular arc of its motion Figure shows the free-body diagram of the pendulum bob, and the only force acting along the direction of motion is mgsin θ Thus, B is the best answer C ) mgcosθ D ) mgtanθ 36 What mechanism supplies the tension in the string at the molecular level? A ) Magnetic forces Solution B ) Electron transfer C ) Gravitational forces Guess D ) Stretching bond lengths Intermolecular forces and the physical structure of the molecules determine the structure of the string at the molecular level Physically stretching the string affects the intermolecular forces (which are primarily electrostatic) and the bond lengths within the molecules Thus, D is the best answer 37 Each lead weight has a volume of × 10–6 m3 What buoyancy force does the water exert on a lead weight? A ) 4.0 × 10–2 N The buoyancy force FB is Thus, A is the best answer B ) 4.5 × 10–2 N C ) 4.1 × 10–1 N D ) 4.5 × 10–1 N 38 Which of the following items of information would NOT help in predicting the results shown in Figure 1? A ) The number of air molecules inside the balloon B ) The thermal conductivity of the rubber C ) The variation with depth in the speed of the balloon D ) The total mass of the water in the tank The mass of the water in the tank will not have an effect on the temperature of the air or the depth of the balloon Thus, D is the best answer 39 Which of the following statements best explains the temperature change shown in Figure 1? A ) The work done on the gas by the water pressure decreases its temperature B ) The work done by the gas in expanding decreases its internal energy Solution Guess The key to understanding the correct statement is to realize that in Figure 1, depth increases to the right This means that air temperature in a rising balloon will follow the plotted curve from right to left, and temperature falls as the balloon rises The true statement must reflect the decreasing temperature and pressure in the balloon as it rises Thus, B is the best answer C ) The balloon and water exchange heat, increasing the temperature of the gas D ) The compression of the gas decreases its temperature 40 Air-filled, thin-walled steel spheres were suggested for experiments in the tank instead of rubber balloons The most likely reason that this idea was rejected is that steel spheres would: A ) not be sufficiently flexible Solution Guess According to the passage, the tank is used to study the effects of pressure on gases If air-filled, thin-walled steel spheres were used, it would be difficult to vary the pressure on the gases Thus, A is the best answer B ) be too heavy C ) not be airtight D ) rust too quickly 41 What vertical forces are acting on a balloon as it ascends? A ) Weight only Solution B ) Buoyancy force only C ) Weight and buoyancy force only Guess The foils list only water pressure, buoyancy, and gravity as acting on a balloon Of these, gravity and buoyancy act in the vertical direction, while water pressure acts perpendicularly to all surfaces of the balloon Thus, C is the best answer D ) Water pressure and buoyancy force only 42 If the valve is opened to drain the tank, where is the speed of the flowing water the greatest? A ) At the top of the tank B ) At the bottom of the tank Solution C ) At the wide end of the pipe D ) At the narrow end of the pipe Guess For a given volume flow rate, the speed of fluid flow is inversely proportional to the cross-sectional area through which the fluid flows Thus, D is the best answer B ) An excess of glucagon C ) A shortage of thyroxine D ) A shortage of insulin 159 What mechanism probably would be responsible for the increased urine output induced by hypertension according to Hypothesis B? A ) Increased blood flow to the bladder Solution B ) Increased renal tubular reabsorption of solutes and water C ) Increased collecting duct permeability to water Guess D ) Increased glomerular filtration rate The glomerular filtration rate is proportional to the glomerular capillary blood pressure minus the sum of the plasma osmotic pressure and the Bowman’s capsule hydrostatic pressure An increase to the systemic blood pressure would initially increase the glomerular capillary blood pressure, which would increase the glomerular filtration rate Without a corresponding increase in the rate of tubular reabsorption of water, this would lead to an increase in urine output Thus, D is the best answer Solution 160 If restriction of blood flow to the kidneys (by placing clamps on the renal arteries) resulted in an immediate but small increase in blood pressure, followed by the gradual development of severe hypertension, which hypothesis would these results best support? A ) Hypothesis A, because the clamps increased the vascular resistance to blood flow B ) Hypothesis A, because the clamps caused the kidneys to receive less blood Guess C ) Hypothesis B, because the kidneys were responding to decreased glomerular blood pressure The reduced flow of blood through the renal arteries due to the clamps would cause a decrease in glomerular blood pressure The kidneys respond to this drop in pressure by activating the renin–angiotensin system of hormones This increases the amount of sodium and water that is reabsorbed by the kidneys, therefore increasing blood volume and pressure Thus, C is the best answer D ) Hypothesis B, because the volume of body fluids was probably decreasing 161 If blood pressure doubled and the resistance to blood flow increased by 50%, the amount of blood pumped by the heart would have: A ) increased by 1/3 Solution Guess The passage states that P = CO × VR Solving the equation for cardiac output (CO) and letting the original CO equal , the new CO would then equal the old CO, or an increase of is B ) increased by 1/2 Reducing this equation shows that the new CO Thus, A is the best answer C ) decreased by 1/3 D ) decreased by 1/2 162 According to Hypothesis A, enhanced activity of which of the following basic muscle types would be most likely to cause hypertension? A ) Striated Solution B ) Smooth C ) Cardiac Guess C ) Cardiac D ) Multinucleate 163 Synthesis of antibody proteins in eukaryotic cells is associated with what organelle? A ) Nucleus B ) Mitochondrion C ) Endoplasmic reticulum As secreted proteins, antibodies are translated by ribosomes attached to the rough endoplasmic reticulum Thus, C is the best answer D ) Golgi apparatus 164 In the human "knee-jerk" reflex, the knee is struck and the lower leg jerks forward Which of the following represents the complete pathway that the nerve impulse travels in effecting this response? A ) Sensory neuron, motor neuron Solution The knee-jerk reflex is a simple monosynaptic stretch reflex A tap to the tendon that connects the quadriceps to the patella activates a sensory neuron that directly synapses with a motor neuron in the spinal cord, causing the quadriceps to contract Thus, A is the best answer B ) Sensory neuron, brain, motor neuron Guess C ) Sensory neuron, associative neuron, brain, associative neuron, motor neuron D ) Sensory neuron, associative neuron, motor neuron, associative neuron, motor neuron 165 The most effective way to remove triethylamine during the workup of an organic reaction would be to extract the reaction mixture with aqueous: A ) sodium bicarbonate Solution B ) sodium bisulfite C ) sodium sulfate D ) hydrochloric acid Guess Triethylamine would most likely be soluble in an organic solvent Washing with aqueous hydrochloric acid will result in the formation of triethylamine hydrochloride This salt is water-soluble and will be removed with the water wash Thus, D is the best answer 166 Solution Guess What is the orientation of the tert-butyl and chloro substituents, respectively, in the predominant conformation of Compound 1? A ) Axial, axial B ) Axial, equatorial C ) Equatorial, axial Compound is cis-1-tert-butyl-4-chlorocyclohexane The predominant conformation of this compound is also the most stable one and has the cyclohexane ring in the chair conformation with the larger tert-butyl substituent in the equatorial orientation and the smaller chloro substituent in the axial orientation Thus, C is the best answer D ) Equatorial, equatorial 167 Uric acid enters the urine both through filtration and secretion in the kidney The process of filtration of uric acid in the kidney takes place in the: A ) glomerulus Filtrate is formed as fluid passes from the glomerular capillaries through the glomerular membrane into the Bowman’s capsule This region of the nephron is known as the glomerulus Thus, A is the best answer B ) loop of Henle C ) distal convoluted tubule D ) proximal convoluted tubule 168 Colchicine most likely relieves gout symptoms through what mechanism? A ) Prevention of uric acid diffusion through cell membranes B ) Inhibition of leukocyte phagocytosis of uric acid crystals Solution Guess Phagocytosis requires that the cell change shape dramatically as it surrounds and engulfs large extracellular particles Microtubules are one of the cytoskeletal elements that help determine cell shape This function relies on the ability of the microtubules to disassemble and reorganize The drug colchicine inhibits microtubule reorganization and would therefore inhibit phagocytosis of uric acid crystals by leukocytes Thus, B is the best answer C ) Inhibition of uric acid crystal formation D ) Maintenance of the pH optimum for PRPP synthetase 169 What nitrogenous base would promote the formation of uric acid crystals in gout? A ) Cytosine B ) Uracil Solution Guess C ) Guanine The passage states that uric acid is formed by the breakdown of purines to xanthine, a uric acid precursor Guanine is one type of purine that is found in cells Thus, C is the best answer D ) Thymine 170 In the patient described in the passage, the likely genetic basis of the increased levels of uric acid is a mutation: Solution A ) affecting an allosteric site of PRPP synthetase The passage indicates that the patient produces the normal amount of PRPP synthetase but its activity in Guess allosteric site on the enzyme has been affected The mutant PRPP can most likely bind an intracellular molecule at an allosteric site, which changes the shape of the enzyme, enhancing its activity This activityenhancing molecule most likely is not present in the in vitro reaction mix Thus, A is the best answer B ) affecting the active site of PRPP synthetase C ) in a promotor gene regulating the rate of transcription of the PRPP synthetase gene D ) in a gene coding for a transcription factor for the PRPP synthetase gene Solution 171 Some animals have developed the ability to excrete nitrogenous waste largely in the form of uric acid, which is nontoxic and does not require large amounts of water for its excretion Considering its lifestyle, what animal would excrete nitrogen primarily in the form of uric acid? A ) Wild pig B ) Flying bird Guess Species of flying birds have evolved many characteristics that reduce their overall body mass, including the ability to excrete nitrogenous waste in the form of uric acid Because the excretion of uric acid does not require large amounts of water, the amount of water that birds must ingest is decreased, making the birds lighter Thus, B is the best answer C ) Carnivorous shark D ) Herbivorous bony fish 172 The first step of the Hofmann rearrangement involves the abstraction of one of the protons on the nitrogen The amide N– H proton is slightly acidic because the: A ) resulting anion is resonance-stabilized The removal of the amide proton results in the formation of an anion with the negative charge on the nitrogen The adjacent carbonyl group stabilizes the anion through resonance A resonance structure of the anion can be drawn in which the negative charge resides on the oxygen Thus, A is the best answer B ) N–H bond is polar C ) aromatic ring is electron-donating D ) amide is not basic 173 What is the major product when 2-phenylacetamide, below, is treated with bromine and aqueous base under the conditions in the passage? Solution A) Guess B) C) D) According to the passage a Hoffman rearrangement of a primary amide results in the loss of the carbonyl D) 174 It has been reported that under some conditions hydrolysis of the amide can compete with the Hofmann rearrangement What product would be expected if this side reaction were important for Compound 1? A ) Benzamide B ) 3-Nitroaniline Solution C ) 3-Nitrobenzamide D ) 3-Nitrobenzoic acid Guess Hydrolysis of Compound would result in the formation of the corresponding carboxylic acid, 3nitrobenzoic acid Thus, D is the best answer 175 The students monitored the conversion of Compound to m-nitroaniline by infrared spectroscopy The disappearance of which band would indicate that the starting material had been consumed? A ) 1550 cm–1 B ) 1650 cm–1 Solution As Compound is consumed, the IR spectrum will show the loss of absorptions attributed to the carbonyl group The C=O stretch of an amide appears at approximately 1650 cm–1 Thus, B is the best answer C ) 2200 cm–1 Guess D ) 3300 cm–1 176 The conversion of Compound to m-nitroaniline can also be monitored by 13C NMR spectroscopy The disappearance of the signal at which frequency accompanies the consumption of the starting material? A ) 65 ppm Solution B ) 107 ppm C ) 120 ppm D ) 165 ppm Guess As Compound is consumed, the 13C NMR spectrum will show the loss of the signal attributed to the carbonyl group The carbon of the carbonyl group appears at approximately 160–170 ppm Thus, D is the best answer 177 When glycerol reacts with three different fatty acids, how many stereogenic centers does the product triacylglycerol contain? A) B) When glycerol reacts with three different fatty acids, only carbon in the resulting triacylglycerol is attached to four different groups Thus, B is the best answer C) D) 178 Which of the following formulas represents a general structure of a fatty acid salt produced in Reaction 1? (Note: Rn = R1 R2 or R3 ) A ) Rn—CH2– Na+ B ) Rn—CH2O– Na+ Solution B ) Rn—CH2O– Na+ C ) Rn—C(O)– Na+ Guess D ) Rn—CO2– Na+ A fatty acid would have the general formula Rn–CO2H The corresponding fatty acid salt would have the general formula Rn–CO2–Na+ Thus, D is the best answer 179 Which of the following is the most plausible explanation for the fact that the saponification of the triacylglycerol in the passage resulted in four different fatty acid salts? A ) The triacylglycerol molecule consisted of four different fatty acid units Solution B ) Glycerol was transformed into a fatty acid salt under the reaction conditions C ) One of the fatty acid salts was unsaturated, and it completely isomerized under the reaction conditions Guess D ) One of the fatty acid salts was unsaturated, and a small percentage isomerized under the reaction conditions If one of the R groups in the triacylglycerol contained a carbon–carbon double bond and if isomerization of the double bond occurred during the saponification reaction, four fatty acids would be obtained instead of three Thus, D is the best answer 180 A triacylglycerol can also be accurately described as a: A ) triacid of glycerol Solution B ) triether of glycerol C ) triester of glycerol Guess The three acyl groups are joined to the glycerol backbone through ester linkages Thus, C is the best answer D ) trihydroxy glycerol 181 How much sodium hydroxide is needed to completely saponify a triacylglycerol? A ) A catalytic amount, because OH– is continuously being regenerated during saponification B ) One-third of an equivalent, because each OH– ion reacts to form three fatty acid salts Solution C ) One equivalent, because each OH– ion reacts to produce one molecule of glycerol D ) Three equivalents, because one OH– ion is required to saponify each of the three fatty acid groups Guess One hydroxide ion is required to hydrolyze one ester linkage of a triacylglycerol molecule Because there are three ester linkages in a triacylglycerol, three equivalents of sodium hydroxide will be needed to completely saponify the triacylglycerol Thus, D is the best answer 182 Which of the following statements most accurately describes the solubility properties of fatty acid salts? A ) They are soluble in polar media only B ) They are soluble in nonpolar media only Solution Guess C ) They can partially dissolve in both polar and nonpolar media A fatty acid salt contains a long hydrocarbon chain, which is soluble in nonpolar solvents The salt also contains the charged group –CO2–Na+, which is soluble in polar solvents Thus, C is the best answer D ) They are completely insoluble in both polar and nonpolar media 183 A male taking excess testosterone may become infertile because of reduced spermatogenesis According to Figure 2, this could result directly from: A ) an increase in inhibin concentration B ) a reduction in inhibin concentration B ) a reduction in inhibin concentration C ) a reduction in FSH concentration Figure indicates that testosterone is part of a negative feedback loop that acts on the hypothalamus to prevent the release of GnRF In the presence of testosterone, less GnRF would be present to stimulate the release of FSH from the pituitary gland, causing a decrease in FSH available to act on the Sertoli cells Therefore, FSH is less able to promote and maintain spermatogenesis Thus, C is the best answer D ) a reduction in LH concentration 184 The cell type in the male reproductive system that is most analogous to the female ovum is the: A ) spermatogonium Solution B ) primary spermatocyte C ) spermatid Guess D ) spermatozoon The mature ovum is the female gamete that has completed meiosis and contains the haploid number of maternally derived chromosomes This makes it most analogous to spermatozoa, the mature male gametes that contain the haploid number of paternally derived chromosomes Thus, D is the best answer Solution 185 Some drugs used in cancer chemotherapy kill proliferating cancer cells by selectively inhibiting various stages of the life cycle Which of the following normal reproductive processes is likely to be most affected by the use of chemotherapy? A ) Sertoli cell function B ) Testosterone production Guess C ) Spermatogenesis Spermatogenesis is the production of spermatozoa by the meiotic division of spermatocytes Therefore, it would be the most affected by the use of chemotherapy Thus, C is the best answer D ) Inhibin production 186 Which of the following hormones is(are) directly required for spermatogenesis? Solution Guess I II III IV Luteinizing hormone (LH) Follicle-stimulating hormone (FSH) Inhibin Testosterone A ) IV only B ) I and IV only C ) II and IV only Sertoli cells support and nourish the spermatocytes and promote the process of spermatogenesis Spermatogenesis would not occur without Sertoli cells The two hormones that directly stimulate Sertoli cells are FSH and testosterone Thus, C is the best answer D ) I, II, and III only 187 On the basis of their function as “nurse” cells, which of the following organelles are most likely to be prominent in Sertoli cells? A ) Golgi apparatus Solution B ) Lysosomes B ) Lysosomes Guess C ) Mitochondria D ) Cilia 188 Which of the following statements correctly describes the distinction between the exocrine and endocrine portions of the testis? A ) The exocrine portion secretes only peptides; the endocrine portion secretes only steroids Solution Guess B ) The exocrine portion releases its products into ducts; the endocrine portion releases its products into the blood Exocrine glands secrete their products through ducts; endocrine glands release their products into the bloodstream Thus, B is the best answer C ) The exocrine portion secretes only cellular elements; the endocrine portion secretes only chemical substances D ) The exocrine portion is the target tissue for the products of the endocrine portion 189 The pancreas produces which of the following substances for the digestive system? A ) Bile salts B ) Emulsifier C ) Gastric juices D ) Proteolytic enzymes The pancreas produces several proteolytic enzymes, which are released into the small intestine where they are converted to their active forms of trypsin, chymotrypsin, and carboxypeptidase Thus, D is the best answer 190 Which of the following characteristics clearly marks fungi as eukaryotes? A ) They have cell walls B ) They contain ribosomes Solution Guess C ) They contain mitochondria One characteristic that distinguishes eukaryotic cells from prokaryotic cells is that eukaryotic cells contain membrane-bound organelles such as mitochondria Thus, C is the best answer D ) They exhibit sexual reproduction 191 If the ester shown below were hydrolyzed in acidic H218O, which product would be expected to contain 18O? Solution A ) CH3CO2H Guess The first step of the hydrolysis would be the protonation of the carbonyl oxygen The H218O would then act as a nucleophile, attacking the protonated carbonyl carbon Cyclopentanol is the leaving group The products are cyclopentanol and 18O-labeled acetic acid Thus, A is the best answer B ) CH3OH C) D) 192 From which germ layer(s) the tissues of the heart and blood vessels differentiate? Solution I II III Ectoderm Mesoderm Endoderm A ) II only Guess The heart and blood vessels both differentiate from the mesoderm Thus, A is the best answer B ) III only C ) I and II only D ) I and III only 193 The most effective method for producing an increase in the total amount of water lost through the skin during a certain period would be: A ) inhibiting kidney function Solution B ) decreasing salt consumption C ) increasing water consumption Guess D ) raising the environmental temperature Water is lost through the skin primarily as a means to keep the body at normal temperatures Therefore, raising the environmental temperature would cause a person to perspire, releasing water to the environment where it can evaporate and cool down the body Thus, D is the best answer 194 To determine the significance of UV reflectance by the dewlap, it would be most useful to compare the behavior of: A ) sighted and sightless lizards, in response to flashing of the dewlap B ) lizards responding to flashing of normal dewlaps versus treated dewlaps that absorb UV To determine the significance of UV reflectance by the dewlap, it would be most useful to compare the response of lizards to dewlaps that reflect UV light to the response of lizards to dewlaps that not reflect UV light If the reflectivity of the dewlap is kept as the only variable, it can be determined whether a correlation exists between the lizards’ behavior and the reflectivity of the dewlap with which the lizards were flashed Thus, B is the best answer C ) the five lizard species, when they are placed together in the same habitat D ) the five lizard species under illumination by red light only 195 If these lizards use UV light in communication, a mutation that eliminated UV photoreceptors would probably cause the LEAST disadvantage to: A ) species A Solution B ) species B C ) species D Guess D ) species E Assuming that the lizards use the UV-reflectivity of the dewlap primarily as a means of intraspecies communication, species E would most likely be least affected by a mutation that eliminated UV photoreceptors Its dewlaps are the least UV-reflective of the five lizard species, which indicates that species E is least likely to rely heavily upon this form of communication in the first place Thus, D is the best answer 196 If Anolis lizards have X-Y chromosomal sex determination, the locus of a gene for the UV reflectance pigment: A ) must be on the X chromosome Solution B ) must be on the Y chromosome C ) must be on an autosome Guess D ) could be on a sex chromosome or on an autosome Based on the information presented, the gene encoding UV-reflectance pigment could be on a sex chromosome or an autosome The fact that the pigment is expressed in the dewlap, a structure found only in males, is not sufficient to eliminate any chromosome as the location of this gene Thus, D is the best answer 197 Two neighboring lizard populations would be considered separate species if: A ) one population inhabited the forest and the other lived in a field B ) one population had a UV-reflective dewlap and the other did not Solution C ) they did not communicate with each other D ) they did not interbreed and produce fertile offspring Guess One of the key factors that determines a species is the ability to successfully breed and produce fertile offspring Two organisms that not meet this criteria are considered separate species Thus, D is the best answer 198 Which of the following conclusions about dewlap reflectance is supported by information in the passage? A ) Lizard habitat is determined by dewlap reflectance for each species B ) High dewlap reflectance is most important in brightly lit habitats Solution Guess Figure shows that the three species of lizards that live in unshaded fields possess dewlaps that are significantly more capable of reflecting UV light than the two species of lizards that live in the shaded understory This supports the conclusion that high dewlap reflectance is most important in brightly lit habitats Thus, B is the best answer C ) High dewlap reflectance is most important in dimly lit habitats D ) Dewlap reflectance is highest at the blue end of the visible spectrum 199 Dewlaps that reflect UV light would evolve by natural selection only if: A ) individuals with UV-reflective dewlaps produced more offspring than did individuals without them Solution Guess Although many different types of adaptations may help an individual organism survive, they will not be passed on to the next generation unless the organism produces offspring, passing on the genes that cause the advantageous phenotype To evolve by natural selection and become a general characteristic of the species, the genes that cause dewlaps to reflect UV light must become a significant portion of the gene pool, which will most likely occur if individuals with UV-reflective dewlaps produce more offspring than individuals without them Thus, A is the best answer B ) individuals with UV-reflective dewlaps were better able to communicate than individuals without them C ) individuals with UV-reflective dewlaps were less subject to predation than individuals without them D ) individuals with UV-reflective dewlaps mated more frequently than did individuals without them 200 At what concentration of free actin will the + end of the microfilament grow faster than the – end? C ) At any concentration greater than µM Figure shows that at free actin concentrations greater than 1µM, actin is added to the + end of a microfilament At concentrations lower than 1µM, the + end loses actin subunits The – end of the microfilament does not begin to add actin until the free actin concentration is greater than 5.5µM The rate at which actin is added to the + end is greater than the rate it is added to the – end, implying that at any concentration greater than 1µM, the + end of the microfilament grows faster than the – end Thus, C is the best answer D ) At any concentration 201 Below is a diagram of a muscle sarcomere Based on the passage, which statement best explains why the microfilament lengths NOT change when the sarcomere shortens in a muscle contraction? Solution Guess A ) The – ends of the microfilaments are capped by Z lines, and the actin subunit concentration is kept above µM in muscle cells B ) The – ends of the microfilaments are capped by Z lines, and the + ends are capped by another protein Within a sarcomere, the microfilament length remains stable Because one end of the microfilament is anchored in the Z line, actin monomers are prevented from being added to or subtracted from that end This rules out the possibility of treadmilling Therefore, to retain a stable length, both ends of the microfilament must be capped Thus, B is the best answer C ) The actin subunit concentration is kept above µM in muscle cells D ) The – ends polymerize and the + ends depolymerize at the same rate 202 The theory of force generation proposed in the passage is best supported by which of the following observations about Amoeba locomotion? A ) Amoeboid movement stops upon exposure to cytochalasins Solution Guess The passage proposes that force is generated as a microfilament elongates and pushes against a structure such as the plasma membrane This is representative of how an amoeba moves Cytochalasins are drugs that inhibit the growth of microfilaments Therefore, if amoeboid movement stops upon exposure to cytochalasins, microfilaments and their ability to elongate are both implicated as being necessary to generate the force for movement in an amoeba Thus, A is the best answer B ) Amoeboid movement cannot occur if mitosis is blocked C ) Moving Amoeba cells produce more troponin than stationary ones D ) The rate of movement is inversely proportional to the viscosity of the medium in which the Amoeba moves 203 Based on Figure 1, at what free actin subunit concentration (or range of concentrations) will the microfilament treadmill? Solution A ) 0.25 µM B ) 1.0 µM Guess Figure shows that at a free actin concentration of 1.5µM, the rate at which actin subunits are added to the + end of the microfilament is equal to the rate at which actin filaments are removed from the – end This fits the definition of treadmilling Thus, C is the best answer D ) Any concentration between 1.0 µM and 4.0 µM 204 Based on Figure 1, at what free actin subunit concentration (or range of concentrations) will both the + and – ends of the microfilament experience a net loss of subunits? A ) At any concentration below µM Solution Guess Figure shows that at free actin concentrations less than 1µM, both the + and the – ends of the microfilament experience a net loss of actin subunits Thus, A is the best answer B ) Exactly at µM C ) At any concentration above µM D ) Only between µM and µM 205 Which of the following observations supports the hypothesis that microfilaments are involved in the release of viral particles? A ) Exocytosis of viral particles from an infected cell is proportional to the rate of microfilament polymerization Solution Guess During exocytosis of viral particles the plasma membrane goes through many distortions of its shape This requires polymerization of microfilaments, making it likely that the rate at which the viral particles can be expelled from the cell is dependent upon the rate of microtubule polymerization Thus, A is the best answer B ) Treatment with phalloidin does not prevent the exocytosis of virus particles from the infected cell C ) No known virus carries genes coding for actin subunits D ) Some viruses have capsules composed of myosin 206 Assuming that Amoeba uses microfilament-generated forces for locomotion, which of the Amoebas pictured below will move from left to right? Solution Guess A) B) D) Diagram D shows a cell with a free actin concentration of 2µM with the + end of the microfilament oriented toward the right side of the cell At this concentration, the microfilament should show a net increase in length toward the right When it reaches the plasma membrane it should continue to lengthen and generate a force that pushes the membrane outward, causing the cell to move in a left-to-right direction Thus, D is the best answer 207 In which of the experiments is a rearrangement of the carbon skeleton observed? A ) only In Equation 1, one of the methyl groups moves to the adjacent carbon This rearrangement is not seen in equations and Thus, A is the best answer B ) only C ) only D ) and only 208 Which set of reagents or condition could be used to prepare the alcohol in the following reaction? Solution Guess A ) H2SO4/H2O B ) Hg(OAc)2/THF-H2O; NaBH4/OH– C ) THF:BH3; H2O2/OH– Among the methods represented by the three equations in the passage, the one represented by Equation is the only method of alcohol formation that results in the hydroxyl group adding to the less substituted carbon Thus, C is the best answer D ) Heat 209 Alcohols have higher boiling points than hydrocarbons of comparable molecular weight This is a result of: A ) hydrogen bonding Solution Guess Alcohols contain hydroxyl groups, which enable them to undergo hydrogen bonding Alcohols have higher boiling points because hydrogen bonds are strong intermolecular forces and more energy is needed to overcome them Thus, A is the best answer B ) van der Waals forces C ) covalent bonding D ) resonance 210 Another way to prepare an alcohol is via a Grignard synthesis Which of the following reactants can be used in a Grignard reaction to produce the same alcohol that was produced in Experiment 1? A) Solution Guess 2,3-Dimethyl-2-butanol was prepared in Experiment As shown in answer choice A, the reaction of isopropylmagnesium bromide (a Grignard reagent) with acetone will result in the addition of the isopropyl group to the carbonyl carbon and the formation of 2,3-dimethyl-2-butanol Thus, A is the best answer B) C) D) 211 The discovery that the amount of thymine equals that of adenine and the amount of guanine equals that of cytosine in a given cell provides supporting evidence that: A ) the Watson and Crick model of DNA is correct In the Watson and Crick model of DNA structure, the nitrogenous bases form hydrogen bonds with each other in a 1:1 ratio: guanine pairs with cytosine, and adenine pairs with thymine This implies that the amount of guanine and cytosine would be the same, and the amount of adenine and thymine would be the same Thus, A is the best answer B ) DNA is the genetic material C ) the genetic code is universal D ) the code for one amino acid must be a triplet of bases 212 Consider an organism that has three pairs of chromosomes, AaBbCc, in its diploid cells How many genotypically different kinds of haploid cells can it produce? A) Solution Guess B) The number of different possible gametes that can be formed by diploid organisms as a result of independent assortment of chromosomes during meiosis can be calculated using the formula 2n where n is the haploid number of chromosomes In this case, the haploid number is 3, making the number of different haploid cells 23, or Thus, B is the best answer C ) 16 D ) 32 Solution 213 What is the net volume of fresh air that enters the alveoli each minute, assuming that the breathing rate is 10 breaths/min, the tidal volume is 800 mL/breath, and the nonalveolar respiratory system volume (dead space) is 150 mL? A ) 65 mL B ) 95 mL C ) 6500 mL Guess The amount of air entering the lungs in a single breath, or tidal volume, is given as 800 mL/breath Of that 800 mL only 650 mL reaches the alveoli per breath (800 mL of air inhaled minus 150 mL of nonalveolar respiratory volume) Therefore the net volume of air that reaches the alveoli each minute is equal to 650 mL/breath multiplied by 10 breaths/min, or 6500 mL Thus, C is the best answer D ) 7850 mL 214 In mammals, which of the following events occurs during mitosis but does NOT occur during meiosis I? A ) Synapsis B ) The splitting of centromeres Solution Guess One of the key differences between mitosis and meiosis occurs during their respective anaphases During anaphase of mitosis, sister chromatids are pulled apart at the centromeres, each becoming an independent chromosome in the two diploid daughter cells During anaphase I of meiosis I, homologous pairs of chromosomes are separated into the two daughter cells However, each chromosome still consists of two sister chromatids joined to each other at the centromere It is not until anaphase II of meiosis II that the centromere is split and the sister chromatids separate Thus, B is the best answer C ) The pairing of homologous chromosomes D ) The breaking down of the nuclear membrane Solution 215 In a particular species of plant, tall vine depends on a dominant gene (T), and a pink flower is the result of the heterozygous condition of the genes for red and white flowers (Rr) What fraction of the offspring from the cross of a tall, pink plant (heterozygous for height) with a short, pink plant would be expected to be pink AND tall? A ) 3/4 B ) 1/2 C ) 3/8 Guess D ) 1/4 Based on the given information, the tall pink plant would have the genotype TtRr and could form the following gametes: TR, Tr, tR, and tr The short pink plant would have the genotype ttRr and could form the following gametes: tR and tr The possible genotypes of the offspring are displayed in the following Punnett square TR tR tr TtRR TrRr Tr TtRr Ttrr tR ttRR ttRr tr ttRr ttrr Of these, 1/4 would be both pink (Rr) and tall (TT or Tt) Thus, D is the best answer 216 During prokaryotic protein synthesis, translation begins as soon as the newly synthesized mRNA strand begins to extend from the DNA strand This situation differs from that in eukaryotes, because eukaryotes: A ) carry out translation without using ribosomes Solution B ) transcribe mRNA molecules without using DNA C ) destroy most mRNA as soon as it is synthesized Guess D ) localize the processes of transcription and translation in the nucleus and cytoplasm, respectively Eukaryotes have membrane-bound organelles including the nucleus, which contains the DNA Transcription of DNA into RNA occurs in the nucleus The RNA is then transported to the cytoplasm where ribosomes translate it into proteins Thus, D is the best answer ... location of algae-free area could be determined, passage information indicates that could change, especially since algae can increase rapidly and algal cells are widespread—“In some cases a milliliter... rationale D D ) compare a literary analysis and a scientific analysis of a literary work This approach would be most effective, because the author maintains that literary scholarship shares methods... by a gain of electrons According to the passage, H2(g) was produced at the cathode The reaction taking place at the cathode was 2H+(aq) + 2e– → H2(g), which means the H+ was gaining electrons and
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