Medical Tests MCAT-TEST Online Practice Questions and Exam Preparation

Medical Tests MCAT-TEST Online Questions & Answers

• Question 31:

  Down's cell is used for manufacturing sodium because:

  A. anode does not react with chlorine.
  B. sodium floats on the fused sodium chloride.
  C. graphite does not react with sodium.
  D. it is easy to fix graphite in circular form.
  B. sodium floats on the fused sodium chloride.

• Question 32:

  A spherical air bubble is rising in a test tube which is illuminated from one side by a flashlight. What happens to a ray of light incident on the air bubble at A?

  

  A. Reflection at both surfaces
  B. Reflection at A; no reflection at B
  C. Reflection at B; no reflection at A
  D. no reflection at either surface
  A. Reflection at both surfaces

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  Explanation/Reference:

  Reflection is the process by which light rays bounce back into a medium from a surface with another medium. Note that there are 2 surfaces, both A and B, which meet the criterion for reflection. Remember: just because some light reflects, does not mean that all of the light reflects. Specifically, some of the light will transmit completely through the bubble while some would have been reflected at A and some at B.

• Question 33:

  X-rays are produced by a device which beams electrons with an energy between 103 and 106 eV at a metal plate. The electrons interact with the metal plate and are stopped by it. Much of the energy of the incoming electrons is released in the form of X-rays, which are highenergy photons of electromagnetic radiation. An example of such a device is shown below. Electrons are accelerated from the cathode towards the anode by an electric field.

  

  There are two mechanisms by which the X-rays are produced within the metal. The first mechanism is called bremsstrahlung, which is German for "breaking radiation." X-rays are emitted by the electrons as they are brought to rest by

  interactions with the positive nuclei of the anode.

  The second mechanism occurs when an incoming electron knocks an inner electron out of one of the metal atoms of the anode. This electron is replaced by an electron from a higher energy level of the atom, and a photon making up the

  energy difference is emitted.

  X-rays are absorbed by a material when they pass through it. The amount of X-rays absorbed increases with the density of the material. In addition, lower energy X-rays are more likely to be absorbed than higher energy X-rays. (Note: 1 eV =

  1.6 x 1019J; Planck's constant h = 4.1 x 10–15 eV•s; speed of light c = 3 x 108 m/s.)

  Which of the following graphs best represents the relationship between the amount of X-rays absorbed per unit length of material and the energy of the X-rays, for lead, bone, and air?

  

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

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  Explanation/Reference:

  In this question we are asked to choose which of the four graphs best represents the absorption of X-rays versus the energy of X-rays for three materials with different densities. Now, we are told in the passage that lower energy X-rays are absorbed more readily than higher energy X-rays. Therefore, we are looking for a graph in which the absorption increases as the energy decreases, and this allows us to eliminate answer choices A and D, leaving us with choices B and C. We are also told in the passage that materials with high densities absorb X-rays more readily than materials with lower densities. Recall that lead has a higher density than air, and that bone is intermediate between the two. Therefore, we are looking for a graph that shows the materials in the following order for a particular energy; lead with highest absorption, then bone, then air. The only answer choice that fits this is B, and this is indeed the correct answer.

• Question 34:

  Band theory explains the conductivity of certain solids by stating that the atomic orbitals of the individual atoms in the solid merge to produce a series of atomic orbitals comprising the entire solid. The closely-spaced energy levels of the orbitals form bands. The band corresponding to the outermost occupied subshell of the original atoms is called the valence band. If partially full, as in metals, it serves as a conduction band through which electrons can move freely. If the valence band is full, then electrons must be raised to a higher band for conduction to occur. The greater the band gap between the separate valence and conduction bands, the poorer the material's conductivity. Figure 1 shows the valence and conduction bands of a semiconductor, which is intermediate in conductivity between conductors and insulators.

  

  Figure 1

  When silicon, a semiconductor with tetrahedral covalent bonds, is heated, a few electrons escape into the conduction band. Doping the silicon with a few phosphorus atoms provides unbonded electrons that escape more easily, increasing conductivity. Doping with boron produces holes in the bonding structure, which may be filled by movement of nearby electrons within the lattice. When a semiconductor in an electric circuit has excess electrons on one side and holes on the other, electron flow occurs more easily from the side with excess electrons to the side with holes than in the reverse direction.

  

  Figure 2

  If the semiconductor orientation in Figure 2 were reversed so that the boron-doped silicon was on the left and the phosphorus-doped silicon on the right, what could be said about the electron flow of the new setup?

  A. The electron flow is easier in the new direction than in that of Figure 2.
  B. The electron flow is the same in either direction.
  C. The electron flow is more difficult in the new direction than in that of Figure 2.
  D. The electrons cannot flow in the new setup.
  C. The electron flow is more difficult in the new direction than in that of Figure 2.

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  Explanation/Reference:

  The passage provides almost all the necessary information to answer this question. The only piece of background information needed is that electrons flow from the negative terminal to the positive terminal. The passage states that phosphorus-doped silicon has more electrons than pure silicon and that boron-doped silicon has fewer electrons than pure silicon. In addition, it is stated that electrons flow more easily from a side with excess electrons -- the phosphorus-doped silicon -- to a side with fewer electrons -- the boron-doped silicon. So, if the semiconductor orientation were switched, electron flow would not be as easy as the original configuration. Choice C is therefore the correct response.

• Question 35:

  The process of depolarization triggers the cardiac cycle. The electronics of the cycle can be monitored by an electrocardiogram (EKG). The cycle is divided into two major phases, both named for events in the ventricle: the period of ventricular contraction and blood ejection, systole, followed by the period of ventricular relaxation and blood filling, diastole.

  During the very first part of systole, the ventricles are contracting but all valves in the heart are closed thus no blood can be ejected. Once the rising pressure in the ventricles becomes great enough to open the aortic and pulmonary valves, the ventricular ejection or systole occurs. Blood is forced into the aorta and pulmonary trunk as the contracting ventricular muscle fibers shorten. The volume of blood ejected from a ventricle during systole is termed stroke volume.

  During the very first part of diastole, the ventricles begin to relax, and the aortic and pulmonary valves close. No blood is entering or leaving the ventricles since once again all the valves are closed. Once ventricular pressure falls below atrial pressure, the atrioventricular (AV) valves open. Atrial contraction occurs towards the end of diastole, after most of the ventricular filling has taken place. The ventricle receives blood throughout most of diastole, not just when the atrium contracts.

  Figure 1: Electronic and pressure changes in the heart and aorta during the cardiac cycle.

  

  The first heart sound represented in Fig. 1 is probably made when:

  A. During ventricular systole, blood in the ventricle is forced against the closed atrioventricular valve.
  B. During ventricular diastole, blood in the ventricles is forced through the aortic and pulmonary artery valves.
  C. During ventricular diastole, blood in the ventricle is forced against the closed atrioventricular valve.
  D. During ventricular systole, blood in the arteries is forced through the aortic and pulmonary artery valves.
  A. During ventricular systole, blood in the ventricle is forced against the closed atrioventricular valve.

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  Explanation/Reference:

  This entire passage relies little on your previous knowledge or understanding of cardiovascular physiology; rather, emphasis is on your ability to read a graph and, at times, correlate the information with the passage. This question indicates that we should be looking at the graph representing "Heart sounds" in Figure 1. The graph for heart sounds can be described thus: a horizontal line is followed by a narrow burst of spikes or activity; prior to the spikes is the label "1st" implying that the spikes represent the 1st heart sound. The first heart sound begins immediately after the first long vertical line. By following this vertical line downwards, we can note any other events which may initiate or occur at the time as the first heart sound: beginning near the bottom of Figure 1, note that the first heart sound occurs (i) in phase 2 of the cardiac cycle; (ii) at the beginning of ventricular SYSTOLE; (iii) during a period that the aortic and pulmonary valves are not opened

  (i.e. closed); and (iv) the first heart sound begins exactly when the position of the AV valves just become closed. Therefore, strictly according to the figure, during ventricular systole the AV valves suddenly close just as the first heart sound is created. Thus, answer choice A is the only plausible answer.

• Question 36:

  Agonistic behavior, or aggression, is exhibited by most of the more than three million species of animals on this planet. Animal behaviorists still disagree on a comprehensive definition of the term, but aggressive behavior can be loosely described as any action that harms an adversary or compels it to retreat. Aggression may serve many purposes, such as food gathering, establishing territory, and enforcing social hierarchy. In a general Darwinian sense, however, the purpose of aggressive behavior is to increase the individual animal's -- and thus, the species' -- chance of survival. Aggressive behavior may be directed at animals of other species, or it may be conspecific -- that is, directed at members of an animal's own species. One of the most common examples of conspecific aggression occurs in the establishment and maintenance of social hierarchies. In a hierarchy, social dominance is usually established according to physical superiority; the classic example is that of a pecking order among domestic fowl. The dominance hierarchy may be viewed as a means of social control that reduces the incidence of attack within a group. Once established, the hierarchy is rarely threatened by disputes because the inferior animal immediately submits when confronted by a superior. Two basic types of aggressive behavior are common to most species: attack and defensive threat. Each type involves a particular pattern of physiological and behavioral responses, which tends not to vary regardless of the stimulus that provokes it. For example, the pattern of attack behavior in cats involves a series of movements, such as stalking, biting, seizing with the forepaws and scratching with the hind legs, that changes very little regardless of the stimulus -- that is, regardless of who or what the cat is attacking. The cat's defensive threat response offers another set of closely linked physiological and behavioral patterns. The cardiovascular system begins to pump blood at a faster rate, in preparation for sudden physical activity. The eyes narrow and the ears flatten against the side of the cat's head for protection, and other vulnerable areas of the body such as the stomach and throat are similarly contracted. Growling or hissing noises and erect fur also signal defensive threat. As with the attack response, this pattern of responses is generated with little variation regardless of the nature of the stimulus. Are these aggressive patterns of attack and defensive threat innate, genetically programmed, or are they learned? The answer seems to be a combination of both. A mouse is helpless at birth, but by its 12th day of life can assume a defensive threat position by backing up on its hind legs. By the time it is one month old, the mouse begins to exhibit the attack response. Nonetheless, copious evidence suggests that animals learn and practice aggressive behavior; one need look no further than the sight of a kitten playing with a ball of string. All the elements of attack -- stalking, pouncing, biting and shaking -- are part of the game which prepares the kitten for more serious situations later in life.

  The author suggests that the question of whether agonistic behavior is genetically programmed or learned:

  A. still generates considerable controversy among animal behaviorists.
  B. was first investigated through experiments on mice.
  C. is outdated since most scientists now believe the genetic element to be most important.
  D. has been the subject of extensive clinical study.
  D. has been the subject of extensive clinical study.

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  Explanation/Reference:

  Question 12, an inference question, centers on the nature-versus-nurture argument discussed in the final paragraph. Keep the author's conclusion — that aggressive patterns are both innate and learned — in mind when you’re looking for the

  right choice. It allows you to rule out Choice C immediately, since it is clear that scientists have not resolved the question in favor of genetics.

  The only thing the passage says is controversial is the definition of aggression, so Choice A is wrong.

  Choice B is out because the author never says that the experiments on mice were the first investigations done to answer the nature-nurture question. This leaves Choice D as the only possible correct answer, and it seems reasonable to infer

  from the author's remark, “copious evidence suggests that animals learn and practice aggressive behavior,” that there has been a lot of study devoted to this subject.

• Question 37:

  Hypoxia refers to a physiological condition in which the body lacks sufficient oxygen for normal cellular functioning. Prolonged hypoxia generally leads to an inhibition of mental capacity and a reduction in the work capacity of muscle. Severe

  cases of hypoxia can lead to coma or even death. Depending on the cause, hypoxia can be classified into four general types:

  Hypoxic hypoxia is a type of hypoxia that occurs when the partial pressure of oxygen in the blood is too low. For example, climbers at high altitude, where the air contains less oxygen, might experience hypoxic hypoxia because the partial pressure of oxygen in the air inhaled is very low, leading to insufficient partial pressure of oxygen in the blood.

  Anemic hypoxia describes a diminished ability of the blood to transport oxygen. Several factors can influence the oxygen-carrying capacity of the blood. Primary causes of anemic hypoxia include a lower than normal number of functional erythrocytes or an insufficient quantity of hemoglobin, the oxygen- carrying molecules of the blood. Abnormal hemoglobin can also decrease the blood's capacity to carry oxygen and lead to anemic hypoxia.

  Ischemic hypoxia is caused by a decreased delivery of blood to the tissues. Localized circulatory deficiencies, such as blood clots, and global circulatory deficiencies, such as heart failure, decrease the delivery of blood to the tissues, and can therefore cause ischemic hypoxia.

  Histotoxic hypoxia results from the inability of cells to utilize the oxygen available in the blood. Causes of histotoxic hypoxia include the poisoning of cellular enzymes involved in aerobic respiration, as well as the decreased metabolic capacity of the oxidative enzymes due to vitamin deficiency. Cyanide poisoning causes histotoxic hypoxia by blocking the action of cytochrome oxidase in the electron transport chain so that tissues cannot use oxygen even though it is available.

  Hypoxia can often be treated by ventilation with pure oxygen. The increased PO2 in the alveoli will lead to an increased PO2 in the blood. Treatment with pure oxygen is LEAST effective in treating which of the following types of hypoxia?

  A. Hypoxic hypoxia caused by hypoventilation
  B. Anemic hypoxia caused by sickle cell anemia
  C. Ischemic hypoxia caused by poor circulation
  D. Histotoxic hypoxia caused by the disease beri beri
  D. Histotoxic hypoxia caused by the disease beri beri

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  Explanation/Reference:

  Oxygen therapy will help any condition which would be alleviated by an increase in the p of oxygen in the blood. The question stem states that beri beri leads to histotoxic hypoxia. The passage tells us that histoxic hypoxia occurs when the tissues cannot utilize oxygen. So, increasing the amount of oxygen transported in the blood through ventilation with pure oxygen will not serve any purpose. Choice A is incorrect because breathing pure oxygen will greatly help an individual suffering from hypoventilation. If pure oxygen is inhaled, much more oxygen will diffuse into the blood and be carried to the tissues. Choice B is incorrect because, although sickle cell anemia reduces the oxygen carrying capacity of the blood (anemic hypoxia), inhaling pure oxygen will allow more oxygen to dissolve in the plasma, somewhat increasing delivery of oxygen to the tissues. Choice C is incorrect because increasing the concentration of oxygen in the blood will increase delivery of oxygen to the tissues and take full advantage of the carrying capacity of the poor circulation.

• Question 38:

  ...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.

  Which of the following discoveries would give the most support to the hypothesis that squeaking sand and booming sand differ only in the mechanism by which the sounds are produced?

  A. Avalanches can be induced in squeaking sand.
  B. Squeaking sand can be made to generate booming sounds.
  C. Booming sounds made by dunes can be generated by mechanisms other than avalanches.
  D. Smooth grains are not a requirement for booming sand.
  B. Squeaking sand can be made to generate booming sounds.

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  Explanation/Reference:

  Paragraph two of the passage contains a rather tantalizing piece of information about the two kinds of sand: squeaking sounds can be produced by sand that normally "booms." This is however not developed in the rest of the passage. In this

  question we are asked to consider what may be a rather radical hypothesis: that there is nothing unique about either squeaking or booming sand in terms of intrinsic physical or chemical properties; the same sand can be either kind,

  depending simply upon how the sound is created. We already know that booming sand can generate squeaking sounds; if, conversely, sand that is traditionally characterized as squeaking can actually produce booming, then this would

  strongly suggest that the hypothesis may be correct.

  All the other answer choices fail to address the hypothesis. Choice A is very close to the correct choice:

  we know that avalanches are what create booming in booming sand. If squeaking sand can be induced to undergo avalanches, this might lead us to think that squeaking sand is similar to booming sand. However, we are not told in choice A

  that these avalanches produce the booming sound that essentially defines booming sand: it may be that the avalanches in squeaking sand are silent, and thus there may be something about booming sand that produces noise when

  undergoing an avalanche. Choice C is incorrect because even if we discover that there are alternate ways to generate "booming," there is no reason to believe that squeaking sand will boom via these mechanisms. It is possible that only sand

  with certain characteristics will boom through these processes, but that squeaking sand just does not possess these characteristics.

  Choice D is also incorrect since even if rough sand grains can boom, there may be other requirements for the sand that squeaking sand does not satisfy.

• Question 39:

  Which observation is consistent with the Doppler effect?

  A. An ambulance siren sounds high pitched as the ambulance moves away from you.
  B. The absorption spectrum of light emitted from a star moving away from Earth appears to be blue.
  C. The absorption spectrum of light emitted from a star moving towards Earth appears to be red.
  D. An ambulance siren sounds high pitched as the ambulance moves towards you.
  D. An ambulance siren sounds high pitched as the ambulance moves towards you.

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  Explanation/Reference:

  According to the Doppler effect, as a source moves towards an observer, the wavelength decreases and the frequency increases. When a source moves away from an observer, the wavelength increases and the frequency decreases.

• Question 40:

  The process by which individuals decide and choose to seek assistance for health or mental health problems is called help-seeking. Table 1 displays the percentage of American Indian/Alaska Native and non-Hispanic White adults who received mental health or counseling treatment in 2008

  Help-seeking is a complex process and individuals will choose to obtain treatment for a variety of reasons. One of the strongest individual-related help-seeking predictors amounts to perceiving the need to do so. Other individual-related factors are the educational and the socioeconomic status. There may also be systematic factors that prevent people from doing so, such as general mistrust of health, mental health, and social service institutions, particularly among racial and ethnic minorities. It has been speculated that some of the mistrust stems from research studies, sponsored by medical establishments, where racial and ethnic minorities express concerns of being recruited for the purpose of serving as guinea pigs. Focus groups with African Americans and Chinese immigrants confirmed this anxiety and fear.

  Thus, cultural factors also play a role in the help-seeking process. Western cultural norms about medicine are premised on norms of individualism. However, individuals from other cultures and racial and ethnic minority groups tend to be both more collectivistic and fatalist. Disease, both medical and mental, is believed to occur because of fate. It is not something where one should spend much time and effort fighting; the needs of the family and even of the extended family are to come first.

  Table 1 Access to health care: Percentage of adults who received mental health treatment or counseling in the past year, 2008

  

  Source: Adapted from U.S. Department of Health and Human Services,"Mental Health and American Indians/ Alaska Natives" Research makes a strong case that racial minorities' mistrust in the healthcare system stems from historical incidents, including:

  A. Shays' Rebellion.
  B. the Tuskegee Syphilis Study.
  C. the publication of the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5).
  D. the glass ceiling effect.
  B. the Tuskegee Syphilis Study.

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  Explanation/Reference:

  B is the correct answer. Starting in 1932, the Public Health Service conducted a study on syphilis with African American men in Tuskegee, Alabama. This study is now known as the Tuskegee Study. The objective of the research was to observe how the disease progressed over time among African American men. However, none of research subjects was informed they had syphilis. Over the course of the study, penicillin became the accepted course of treatment in 1945, but researchers also did not inform the research subjects of the available treatment. Thus, the ethical principles that presently regulate research, and include the requirement of gathering informed consent, or allow for non-disclosure of intents in very specific circumstances, censor the procedures adopted at the time. This study, along with alike now deemed unethical studies, are argued to have generated mistrust in the system among minorities. A. This is incorrect. Shays' Rebellion related to general economic and civil rights. It was not a rebellion against racial disparities in the healthcare system. C. This is incorrect. The Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) was never subjected to race-related criticism or mentioned as a cause of racial minorities' mistrust in healthcare system. D. This is incorrect. The glass ceiling effect is a term used to describe the barriers women encounter in their careers that impede them from attaining higher positions. It is not concerned with racial minorities and their distrust in health systems.