Medical Tests MCAT-TEST Online Practice Questions and Exam Preparation

Medical Tests MCAT-TEST Online Questions & Answers

• Question 441:

  ...Squeaking sand produces sounds with very high frequencies -- between 500 and 2,500 hertz, lasting less than a quarter of a second. The peals are musically pure, often containing four or five harmonic overtones. Booming sand makes louder, low-frequency sounds of 50 to 300 hertz, which may last as long as 15 minutes in larger dunes (although typically they last for seconds or less). In addition, they are rather noisy, containing a multitude of nearby frequencies. Booms have never been observed to contain more than one harmonic of the fundamental tone. These dramatic differences once led to a consensus that although both types of sand produce acoustic emissions, the ways in which they do so must be substantially different.... In the late 1970s, however, Peter K. Haff, then at the California Institute of Technology, produced squeaks in booming sand, suggesting a closer connection between the two. Both kinds of sand must be displaced to make sounds. Walking on some sand, for example, forces the sand underfoot to move down and out, producing squeaks. In the case of booming sand, displacement occurs during avalanches. It is within the avalanche that sound begins and where the answers must be hiding. Before an avalanche can occur, winds must build a dune up to a certain angle, usually about 35 degrees for dry desert sand. Once an angle is achieved, the sand on the leeward side of the dune begins to slump. Intact layers of sand slip over the layers below, like a sheared deck of cards. At the same time, the individual grains in the upper layers tumble over the grains underneath, momentarily falling into the spaces between them and bouncing out again to continue their downward journey. Their concerted up-and-down motion is believed to be the secret source of sound. Fully developed avalanches, in which sliding plates of sand remain intact for most of their motion, have the greatest acoustic output. In some places, where large amounts of sand are involved, booming can be heard up to 10 kilometers away. Because it is caused by large volumes of shearing sand, the roaring is also loud. In fact, sounds made by booming sand can be nearly deafening, and the vibrations causing them can be so intense that standing in their midst is nearly impossible. A good place to start in exploring the vibrational properties of sand is with the grains themselves. The mean diameter of most sand grains, whether acoustically active or not, is about 300 microns. Usually the grains in a booming dune are very similar in size, especially near the leeward crest, where the sound most often originates; such uniformity allows for more efficient shearing. Otherwise, the smaller grains impede the smooth motion of the larger ones. Similar sizes do not alone allow sand to boom. On the contrary, the booming sands of Korizo and Gelf Kebib, also in Libya, feature an uncharacteristically broad range of particle sizes. Moreover, silent dune sand often contains grains somewhat similar to nearby booming sand. Grains of booming sand also tend to have uncommonly smooth surfaces, with protrusions on the scale of mere microns. Booming dunes are often found at the downwind end of large sand sources; having bounced and rolled across the desert for long distances, the sand grains in these dunes are usually highly polished. Over time a grain can also be polished by repeated shifts within a moving dune. And squeaking sand as well tends to be exceptionally smooth.... ...Another important factor is humidity, because moisture can modify the friction between grains or cause sand to clump together, thus precluding shearing. Sounds occur in those parts of the dune that dry the fastest. Precipitation may be rare in the desert, but dunes retain water with remarkable efficiency. Sand near the surface dries quickly, however, and sand around a dune's crest tends to dry the fastest.

  Booming occurs mostly in big dunes deep in the desert. All of the following, if true, are factors that may plausibly account for this EXCEPT:

  A. The grains need to be carried over large distances by wind so they have a chance to be polished down.
  B. The sounds created by the booming dunes need a large distance to dissipate.
  C. A relatively large sand source is needed so dunes can build up to the requisite volume before an avalanche occurs.
  D. The dunes need to be far removed from any source of moisture.
  B. The sounds created by the booming dunes need a large distance to dissipate.

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  Explanation/Reference:

  We are given an observation and are asked to determine what could provide an explanation for it. Note that we are not asked to evaluate the truthfulness of the statements in the choices: we are told to assume that they are true. Nor are we asked to decide if each is indeed the correct explanation necessarily; we only need to decide if they could conceivably play a role. Choice B is the correct answer because whether the sounds created are dissipated or not cannot be a factor in where the dunes are located: dunes do not form in anticipation of what happens to the acoustic emissions they send out. All the other choices provide at least a partial rationalization of the location of booming sand dunes. Choice A states that sand grains that have traveled large distances can be smoothened in the process. We know that smooth grains are generally a requisite for booming (as well as squeaking) sand. Grains that have traveled large distances therefore have a higher probability of forming booming (as opposed to silent) sand dunes. A large distance also suggests that the desert needs to be large enough to provide the distance that needs to be covered. One can therefore see how choice A could play a role in leading to the preferential formation of booming dunes deep in large deserts. Choice C also accounts for at least part of the observation. Booming is produced by the avalanching of dunes, which need to build up before shearing can occur to generate acoustic emissions. If it is indeed the case that a large sand source is needed to achieve a requisite volume (and we have been told in the question stem to assume the statement to be true), this will definitely translate to a preference for booming dunes to form in large deserts, where the probability of having dunes meeting the conditions would be higher. Choice D is also a perfectly reasonable explanation as to why booming dunes form where they do: the need for the absence of moisture (which can impede avalanching) would mean that booming dunes need to be in an environment where water is scarce and far removed. Deep in large deserts would be an appropriate location.

• Question 442:

  Which blood vessel carries absorbed food material from intestine to the liver?

  A. Vena cava
  B. Hepatic artery
  C. Hepatic vein
  D. Hepatic portal vein
  D. Hepatic portal vein

• Question 443:

  A researcher in a molecular biology lab planned to carry out an extraction procedure known as an alkaline plasmid prep, which is designed to purify plasmids, small pieces of the hereditary material DNA, from bacterial cells. The bacteria are first placed into a test tube containing liquid nutrient medium and allowed to grow until they reach a high population density. The culture, which consists of solid cells suspended in the medium, is then centrifuged; a solid pellet is formed. The supernatant is poured out, leaving the pellet behind, and the cells are resuspended in a mL of lysis buffer solution (50 mM glucose, 25 mM Tris buffer and 10 mM ethylenediaminetetraacetic acid (EDTA), with 5 mg of the enzyme lysozyme added). They are then incubated for 30 minutes at 0°C, during which time the bacterial cell walls break down and the cell contents are released into the solution. After incubation, 1 mL of 0.4 N sodium hydroxide and 1 mL of 2% sodium dodecyl sulfate (SDS) are added, and the solution is again incubated on ice for 10 minutes. 2 mL of 3 M sodium acetate are added and the mixture is incubated for 30 minutes at 0°C. The test tube is centrifuged once more and the supernatant is decanted into a clean tube, leaving behind the protein and most other cell components in the pellet. Finally, 10 mL of pure ethanol are added to the supernatant from the previous step to precipitate out the DNA, and the test tube is incubated at ?0°C for 60 minutes, during which the mixture remains liquid. The mixture is centrifuged a final time and the supernatant removed. The translucent precipitate that results is washed with 70% ethanol (70% ethanol and 30% water by volume), allowed to dry, and resuspended in 1 mL of TE buffer (10 mM Tris, 1 mM EDTA). In preparation for this experiment, the researcher prepared stock solutions of the various chemicals that she will need in the experiment. Stock solutions are highly concentrated solutions of commonly used chemicals in water from which dilute solutions are prepared for daily use. Table 1 shows the chemicals, their molecular formulas and weights, and the composition of commonly used stock solutions.

  

  Tris (Tris(hydroxymethyl)aminomethane) is generally used as a buffer. If pH 8.0 is a good buffering region for Tris, then:

  I) the pKa of Tris must be near pH 8.0

  II) if Tris is titrated with acid, the titration curve will possess a steep region near pH 8.0.

  III) a great deal of NaOH would have to be added to pH 8.0 Tris in order to significantly affect the pH.

  A. I only
  B. III only
  C. I and II only
  D. I and III only
  D. I and III only

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  Explanation/Reference:

  A buffer is a mixture of either a weak base and its conjugate acid, or a weak acid and its conjugate base. Tris, as it happens, is a base. Buffer solutions resist changes in pH when acid or base is added. If pH 8 is a good buffering region for Tris, the ratio of base (Tris) to its conjugate acid (protonated Tris) will be near to 1. The pH of this solution is equal to the pKa + log [base]/[conjugate acid]. Therefore, if the ratio of base to its conjugate acid is near to 1, the pKa must be near to the pH. Thus Roman numeral I is a true statement. To evaluate Roman numeral II, we have to recall what a titration curve looks like. Titration is a procedure used for determining the normality of an acid or base. The procedure consists of adding an acid to a base, or a base to an acid, until the pH of the mixture reaches 7. The titration curve is a plot showing the pH of the solution as a function of the amount of acid or base added. Since the pH, as the dependent variable, is plotted on the y axis, a steep part of a titration curve represents a rapid change in pH. But we just said that a buffer solution in its effective pH range, such as a pH 8 Tris solution, resets pH change, so the titration curve for Tris will actually be quite flat near pH 8, and so Roman numeral II is false. Adding sodium hydroxide, which is a base, to a pH 8.0 Tris solution also wouldn't change the pH easily, so a large amount of the base would have to be added to affect the pH very much, and Roman numeral III is true. Since I and III are true, the correct answer choice is D.

• Question 444:

  As Alice Echols went on to claim, "Nothing seems to conjure up the 1970s quite so effectively as disco. Even at the time, critics remarked upon disco's neat encapsulation of that decade's zeitgeist. `It must be clear by now to everyone with an ear or an eye that this era,' wrote journalist Andrew Kopkind in 1979, `is already the Disco Years, whether it will be called by that name or not.' A former sixties radical, Kopkind was by turns fascinated, bemused, and appalled by the disco epoch, and he likely imagined that in years to come fellow cultural critics would share his interest. But the seventies have not loomed large in our national imagination, except perhaps as comic relief. For many Americans, these were the forgettable years.

  That forgettability owes a lot to the 1960s, the outsized decade that dwarfs all others in recent memory. The sixties will always be remembered for their audacity, whether found in the courage of civil rights protesters who put their bodies on the line or in those doomed but beautiful rock stars who tried breaking through to the other side. By contrast, the seventies seem the decade when nothing, or nothing good, happened ?an era memorable for the country's hapless presidents, declining prestige, bad fashions, ludicrous music, and such over-the-top narcissism that Tom Wolfe dubbed it the `Me Decade.' Before the decade was out, this narrative of decline had become routine. `After the poetry of the Beatles comes the monotonous bass-pedal bombardment of Donna Summer,' huffed one New York Times writer in 1979. It is a measure of the era's persistent bad press that a recent book challenging this view carries the pleading title Something Happened.

  As for the sixties, it doesn't matter how much silliness went down, we still invest those times with seismic significance. Take Joe Cocker's performance at Woodstock. His spasmodic thrashing about and his vocals, slurred to the point of incomprehensibility, are something of a joke today. Cringe-inducing though it may be, however, Cocker's performance is never made to stand in for the whole of the sixties. The sixties remain enveloped in the gauzy sentimentalism of what might have been. Yet the iconic image of John Travolta as dance-floor king Tony Manero in white polyester suit, arm thrust to the disco heavens, has come to symbolize the narcissistic imbecility and inconsequentiality of the disco years.

  Were it not for the Rubaiyat, I, too, might well regard the seventies as a lamentable and regrettable period in American history. The Rubaiyat was, yes, a disco. It was located in the heart of sixtiesland: Ann Arbor, Michigan, the home of the University of Michigan and legendary incubator of radical activism. At the height of the seventies, the town's annual Hash Bash ?a smoke-in to reform marijuana laws ?was still going strong and so were its two food co-ops-one reform, the other orthodox when it came to selling white foods (that is, rice, sugar, and flour of the white variety). Ann Arbor also had bookstores galore, including the original, wonderful Borders Bookstore, and any number of hippie-ish restaurants and bars such as the Fleetwood Diner, the Del Rio, and the Blind Pig. Musically, it prided itself on its vintage music (it hosted one of the earliest blues festivals), but at heart it was a rock town besotted with Iggy Pop and the Stooges and Sonic's Rendezvous, a band fronted by Patti Smith's future husband, Fred Smith. Its leading music store, Schoolkids' Records, stocked disco, but never played it. All of this is to say that disco-averse Ann Arbor came close to providing something of a safe haven from glitterball culture.

  The Rubaiyat was no red-velvet-rope disco where fashionista doormen determined who was sufficiently fabulous to gain entry. This would never have worked in a town where down jackets and army surplus were hardly an unusual sight. The club did have some pretensions to classiness, but the mismatched, sagging booths and bordello red defeated occasional efforts at upmarket sophistication. What the Rubaiyat did have were better-than-average speakers, a heterogeneous cliente, and a weekend cover of three dollars."

  Echols, A. (2011). Hot stuff: Disco and the Remaking of American Culture. New York: W. W. Norton.

  The author most closely means which of the following in paragraph 2 by "narrative of decline"?

  A. A work of history that focuses on a period when culture was becoming more stagnant, such as the 60s- 70s.
  B. A version of 20th century history in which 60s idealism, peace and progress gave way to 70s crime, violence and racism.
  C. A version of history in which an author fits the facts into an overarching schema in which things were becoming dramatically worse.
  D. A version of 20th century history that claims the 60s was a failure because its ambitions were not fulfilled.
  C. A version of history in which an author fits the facts into an overarching schema in which things were becoming dramatically worse.

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  Explanation/Reference:

  This Reasoning Within the Text question is asking you to make sense of a phrase the author does not fully explain. In the surrounding text, the author writes that "The sixties will always be remembered for their audacity... By contrast, the seventies seem the decade when nothing, or nothing good, happened--an era memorable for the country's hapless presidents, declining prestige, bad fashions, ludicrous music." She then quotes a critic unfavorably comparing the Beatles to Donna Summer. Thus, the author is saying that when authors compare the 60s and 70s, they choose details that make the latter decade seem much worse, fitting this 10-year time period into a story in which culture is stagnant ?and even in decline, at some points in the narrative. A ?incorrect. The author does not argue that culture was actually becoming stagnant in the 60s-70s, but that only the 70s was portrayed and remembered with negative overtones. B ?incorrect. The passage does not argue that the 70s was portrayed as a violent or turbulent time, but as a time of stagnation when "nothing happened," and "decline" was occurring. D ?incorrect. The author argues elsewhere that commentators see the 60s in an idealized way based on "what might have been," not that they were a failure altogether.

• Question 445:

  A mountain climber living at sea level ascends to a very high altitude during the course of a day long climb. By the end of the day, all of the following acclimatizations will occur EXCEPT:

  A. increased tidal volume.
  B. increased respiration rate.
  C. right shift of the hemoglobin dissociation curve.
  D. increased concentration of erythropoietin in the blood.
  C. right shift of the hemoglobin dissociation curve.

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  Explanation/Reference:

  The affinity of hemoglobin for oxygen will not decrease. The adaptation of hemoglobin's affinity for oxygen would take longer than one day. Besides, even if given time to adjust, in order to maintain delivery of oxygen to tissues at high altitudes (low pO2), the affinity of hemoglobin for oxygen would increase so as to maximize the amount of oxygen transported by the hemoglobin in the blood. Choices A, B, and D are incorrect because these are all acclimatizations that occur immediately. The body will make rapid adjustments to the low pO2 of high altitude in order to maintain delivery of oxygen to the tissues. Tidal volume and respiration rate will increase, in order to increase the minute volume (amount of air inhaled and exhaled in a minute). Inhaling more air than normal will compensate for the fact that the inhaled air has less oxygen than normal. In addition, the body will secrete erythropoietin to increase the number of erythrocytes in the blood and thus increase the oxygen carrying capacity of the blood.

• Question 446:

  Gauguin's attitude toward art marked a break from the past and a beginning to modern art. Like all Post- Impressionist artists, he passed through an Impressionist phase but became quickly dissatisfied with the limitations of the style, and went on to discover a new style that had the directness and universality of a symbol and that concentrated on impressions, ideas and experiences. The beginning of his modern tradition lay in his rejection of Impressionism. He considered naturalism an error to be avoided. He was preoccupied with suggestion rather than description, seeking to portray not the exterior, but the essence of things in their purest, simplest, and most primitive form, which could only be achieved through simplification of the form. He firmly believed throughout his life that "art is an abstraction" and that "this abstraction [must be derived] from nature while dreaming before it." One must think of the creation that will result rather than the model, and not try to render the model exactly as one sees it. This was the birth of "Synthetism" or rather Synthetist-Symbolic, as Gauguin referred to it, using the term "symbolic" to indicate that the forms and patterns in his pictures were meant to suggest mental images or ideas and not simply to record visual experience.

  Symbolism flourished around the period of 1885 to 1910 and can be defined as the rejection of direct, literal representation in favor of evocation and suggestion. Painters tried to give a visual expression to emotional experiences, and therefore the movement was a reaction against the naturalistic aims of Impressionism. Satisfying the need for a more spiritual or emotional approach in art, Symbolism is characterized by the desire to seek refuge in a dreamworld of beauty and the belief that color and line in themselves could express ideas. Stylistically, the tendency was towards flattened forms and broad areas of color, and features of the movement were an intense religious feeling and an interest in subjects of death, disease, and sin.

  Similarly, "Synthetism" involved the simplification of forms into large-scale patterns and the expressive purification of colors. Form and color had to be simplified for the sake of expression. This style reacted against the "formlessness" of Impressionism and favored painting subjectively and expressing one's ideas rather than relying on external objects as subject matters. It was characterized by areas of pure colors, very defined contours, an emphasis on pattern and decorative qualities, and a relative absence of shadows.

  Gauguin's new art form merged these two movements and succeeded in freeing color, form, and line, bringing it to express the artists' emotions, sensibilities, and personal experiences of the world around them. His style created a break with the old tradition of descriptive naturalism and favored the synthesis of observation and imagination. Gauguin sustained that forms are not discovered in nature but in one's wild imagination, and it was in himself that he searched rather than in his surroundings. For this reason, he scorned the Impressionists for their lack of imagination and their mere scientific reasoning. Furthermore, Gauguin used color unnaturalistically for its decorative or emotional effect and reintroduced emphatic outlines. "Synthetism" signified for him that the forms of his pictures were constructed from symbolic patterns of color and linear rhythms and were not mere scientific reproductions of what is seen by the eye.

  Dempsey, A., and Dempsey, A. (2010). Styles, Schools and Movements: The Essential Encyclopaedic Guide to Modern Art. London: Thames and Hudson.

  Given the passage's discussion of Synthetist-Symbolism, and some undiscussed remarks about how Japanese art influenced Gauguin's work, which of these features of Japanese painting can be reasonably assumed to characterize Gauguin's art form?

  A. Use of strong colors and compositional freedom
  B. Use of fluid curved lines
  C. Use of animals and landscapes as subjects
  D. Use of narrative elements to express ideas
  A. Use of strong colors and compositional freedom

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  Explanation/Reference:

  This Reasoning-Beyond-the-Text question asks you to infer connections between Japanese painting and Gauguin's Synthetist-Symbolist art. Even without prior knowledge of Japanese art nor any discussions of it in the passage, the question itself implies that a reasonable assumption can be made using the descriptions provided in the passage. Since Synthetist-Symbolism was described as "characterized by the desire to seek refuge in a dreamworld of beauty and the belief that color and line in themselves could express ideas," it could be inferred that the use of strong colors and compositional freedom might characterize both types of art.

  Most of these descriptions are found in paragraph 4, particularly about how Gauguin used colors freely and "unnaturalistically for its decorative or emotional effect. . . the forms of his pictures were constructed from symbolic patterns of color and linear rhythms." B ?incorrect. The passage does state that Gauguin used outlines but does not suggest the importance of fluidity or of curved vs. straight lines. Hence, there were no indications that this option might be correct. C ?incorrect. Paragraph 2 states that Symbolism, one of the two movements from which Gauguin formed his "new" art, has death, disease, and sin as its typical subjects. No reference is made to animals and landscapes as motives. In paragraph 4 it is stated that "it was in himself that he searched rather than in his surroundings." Hence, it could be inferred that this option was likely incorrect. D ?incorrect. Gauguin was particularly interested in suggesting mental images and ideas in an art work as opposed to merely representing visual reality. Nothing in the passage mentions narrative as a factor in his artistic process or form. Hence, there were no indications that this option might be correct.

• Question 447:

  Researchers are currently trying to develop materials which could be used to replace damaged or destroyed human muscle tissue. One of the more promising avenues of research involves the use of substances that contract with the application of a small electric current.

  Two physicists published an article relating to their work with Substance Q42, a material which contracts with the application of very small electric currents.

  The atomic structure of the substance, they report, is designed so that the magnetic fields from each atom maintain a certain distance between adjacent atoms. With the application of an electrical current, the atoms' magnetic fields are

  dampened slightly, causing them to draw closer together. The extent to which it contracts is dependent upon the strength of the current passing through it, but will at any rate never exceed a 20% reduction in length.

  Moreover, the physicists report, Substance Q42 essentially operated like a spring, but one which can compress itself. The force generated by a spring, Fs, is given by the following equation:

  Fs = -kx,

  where k is the spring of constant in N/m, and x is the distance of compression (or expansion, but that is irrelevant for this example, since Substance Q42 only compresses).

  With this in mind, it is possible to calculate the feasibility of using Substance Q42 as a replacement for human muscle tissue. Assume a section of test Substance Q42 is hooked to a scalable electrical source. The section is 10 cm long at its

  fully extended state, and 8 cm long when fully compressed due to an electrical current.

  A force-meter is attached to one end of a section of Substance Q42; the other end of the section is secured to a non-moving surface. When fully compressed, the force-meter registers a force exerted by the section of 250 N. What is the

  spring constant?

  A. 12 500 N/m
  B. 12 800 N/m
  C. 16 700 N/m
  D. 20 500 N/m
  A. 12 500 N/m

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  Explanation/Reference:

  Since Fs = -kx, 250 N = -k(-0.02 m).

  k = 250 N/0.02 m = 250/(2/100) N/m = 250 * 50 N/m = 12 500 N/m.

  Note. Had this been a traditional spring with a fully extended point of 10 cm and full compressed at 8 cm, then the equilibrium point would be considered at 9 cm. However, the passage (P4) describes a key difference in this case for the application of Hooke's law: the distance from 10 cm to 8 cm occurs due to contraction, the relaxed state is at 10 cm, and there is no extension from the relaxed state to some point greater than 10 cm. The elastic property of a spring returning to its equilibrium point is not the same as Q42 requiring stimulation to contract in order to go from 10 cm to 9 cm, etc. Thus, from P4 in the passage, "x is the distance of compression ... since Substance Q42 only compresses".

• Question 448:

  In 1965, Boris Deryagin reported the discovery of an unusual substance formed during the condensation of water vapor in quartz capillaries. The material, called poly-water, appeared to be a polymer of water monomers and differed from normal water in a number of ways. It had a freezing point of ?0?C and solidified into a glass-like solid with substantially less volumetric expansion than that of ordinary water upon freezing. It had a density 40% greater than water and a refractive index of 1.48.

  An intricate apparatus was used to produce the poly-water. Ordinary distilled water was placed in a chamber held at 160?C with pressure below atmospheric pressure. This chamber was connected to a second chamber by a tube held at 500?C in order to prevent the passage of liquid water. The second chamber was held at 0?C and contained a drawn quartz capillary in which the water vapor condensed, forming poly-water.

  

  Hypothesis 1

  Deryagin proposed that polywater was a polymer of water monomers arranged in a network of hexagonal units. The polymerization was catalyzed by the silicate surface of the quartz capillary.

  

  Proposed Structure of Polywater Hypothesis 2

  

  Another researcher was skeptical. Analysis indicated that polywater was merely a solution of water and dissolved particles including silicon, carbon dioxide, and substantial concentrations of ions These contaminants dissolved from the quartz capillary and from materials used in the apparatus.

  

  (constants for normal water : density = 1 g/c , index of refraction = 1.33 , freezing point depression constant = 1.86°C ) According to the passage, polywater has all of the following properties EXCEPT:

  A. light entering polywater from air will bend more towards the normal than light entering normal water.
  B. polywater can be produced in a variety of conditions.
  C. 1 g of water has a larger volume than 1 g of polywater, at room temperature.
  D. polywater exists in the liquid state at 0?C.
  B. polywater can be produced in a variety of conditions.

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  Explanation/Reference:

  The passage describes a very intricate mechanism for producing polywater and does not support the fact that polywater can be produced in a variety of conditions. Choice A is incorrect because polywater has a higher index of refraction than normal water and so would bend light more towards thenormal (smaller angle).

  

  Choice C is incorrect because polywater is 40% more dense than water. So, an equal mass of polywater will have a smaller volume.Choice D is incorrect because the passage states that polywater has a freezing-point of ?0?C.

• Question 449:

  Just as the ingestion of nutrients is mandatory for human life, so is the excretion of metabolic waste products. One of these nutrients, protein, is used for building muscle, nucleic acids, and countless compounds integral to homeostasis.

  However, the catabolism of the amino acids generated from protein digestion produces ammonia, which, if not further degraded, can become toxic. Similarly, if the same salts that provide energy and chemical balance to cells are in excess,

  fluid retention will occur, damaging the circulatory, cardiac, and pulmonary systems.

  One of the most important homeostatic organs is the kidney, which closely regulates the excretion and reabsorption of many essential ions and molecules. One mechanism of renal function involves the secretion of antidiuretic hormone

  (ADH).

  Diabetes insipidus (DI), is the condition that occurs when ADH is ineffective. As a result, the kidneys are unable to concentrate urine, leading to excessive water loss. There are two types of DI -- central and nephrogenic. Central DI occurs when there is a deficiency in the quantity or quality of ADH produced. Nephrogenic DI occurs when the kidney tubules are unresponsive to ADH. To differentiate between these two conditions, a patient's urine osmolarity is measured both prior to therapy and after a 24-hour restriction on fluid intake. Exogenous ADH is then administered and urine osmolarity is measured again. The table below gives the results of testing on four patients. Assume that a urine osmolarity of 285 mOsm/L of H2O is normal.

  

  An elevated and potentially toxic level of ammonia in the blood (hyperammonemia) would most likely result from a defect in an enzyme involved in:

  A. glycolysis.
  B. fatty acid catabolism.
  C. the urea cycle.
  D. nucleic acid degradation.
  C. the urea cycle.

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  Explanation/Reference:

  According to the passage, the catabolism of amino acids, which are the molecules that make up proteins, produces ammonia. First of all, what does catabolism mean? You know that metabolism can be divided into catabolism and anabolism. Catabolism refers to pathways in which larger molecules are broken down into smaller parts. If you have trouble remembering the difference between catabolism and anabolism, just associate anabolism with anabolic steroids. And anabolic steroids are used by weight lifters to BUILD muscle, therefore anabolism must refer to the pathways in which smaller molecules are BUILT into larger molecules. And once you've committed that to memory, you'll always remember that catabolism must be the opposite. We know from the passage that if the ammonia that is produced as a by-product of amino acid breakdown is not further degraded, it can become toxic, depending on its concentration in the blood. To answer the question, you need to recall that the end product of amino acid degradation is urea, which means that ammonia must feed into the urea cycle. The concentration of ammonia in the blood would become elevated and potentially toxic if one of the enzymes involved in the urea cycle was defective. Thus choice C is the correct answer. Choice A, glycolysis, refers to the catabolism of glucose into pyruvate. Choice B, fatty acid catabolism, refers to the breakdown of fatty acids into acetyl CoA. Choice D, nucleic acid degradation, refers to the breakdown of DNA and RNA into nucleotides. Therefore choices A, B, and D are not involved in protein or ammino acid catabolism, and so they are all incorrect.

• Question 450:

  A local politician starts a task force to reduce prejudice and hate crimes, and the task force provides recommendations for increased access to education, paid community improvement projects open to people from different, possibly conflicted, groups, and stricter anti-hate ordinances to be passed at the local level. These recommendations are based on:

  I. Self-esteem hypothesis

  II. Contact hypothesis

  III. Hypothesis

  IV.

  Legal hypothesis

  A. I, II, and III
  B. II, III, and IV
  C. I, III, and IV
  D. I, II, and IV
  I. Self-esteem hypothesis II. Contact hypothesis III. Hypothesis IV. Legal hypothesis
  D. I, II, and IV

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  Explanation/Reference:

  Four main hypotheses are speculated to reduce prejudice. The self-esteem hypothesis states that when people have access to education and greater self-esteem, prejudices will go away. The contact hypothesis states that when members of different groups are brought together in order to appreciate their common experiences, prejudices will go away. Similarly, the cooperation hypothesis (not an answer choice) suggests that when conflicting groups work together towards shared goals, prejudices will go away. Finally, the legal hypothesis suggests that when laws are enforced against discriminatory behavior, prejudices will go away. There is no assimilation hypothesis, assimilation refers to blending of minority groups into the dominant society. In this question, the task-force has recommended increased access to education (I. Self-esteem hypothesis), paid community improvement projects open to people from varied backgrounds (II. Contact hypothesis, and would include Cooperation hypothesis if this were a choice), and stricter anti-hate ordinances (IV. Legal hypothesis). All choices are correct except for III.