Medical Tests MCAT-TEST Online Practice Questions and Exam Preparation

Medical Tests MCAT-TEST Online Questions & Answers

• Question 21:

  The equation for Ampere law is:

  A. µoI = Br
  B. µoI = Br2
  C. µoI = B2r
  D. µoI = B2r2
  C. µoI = B2r

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  Explanation/Reference:

• Question 22:

  An object at rest with the shape of an equilateral triangle is subject to three external forces as shown in the diagram. If the object does not exhibit translational motion, what must F and be, respectively?

  

  A. 20 N, 120°
  B. 20 N, 165°
  C. 10 N, 120°
  D. 10 N, 165°
  B. 20 N, 165°

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  Explanation/Reference:

  This problem can be solved by examining the angles and noting that the two given forces are antiparallel. First, each of the angles in an equilateral triangle is 60°, adding up to the 180° characteristic of all triangles. We know that the forces are antiparallel because they make the same angle, 75°, with a line that intersects both of them. That line is the left edge of the equilateral triangle.

  

  Once we determine that the two given forces are antiparallel, we know that the third force must be applied along the same angle (in order to cancel out with the other two.) Summing the two given forces, we get a net force of 20N to the upper left.

  

  So we know that the answer must be 20N towards the bottom right. This narrows the choices to A and B. Now we must determine the angle. The supplementary angle is 120? as shown below. Knowing that the two forces are parallel, we can calculate the 45? as shown below. This allows us to calculate .

  

• Question 23:

  Electromagnetic radiation from space constantly bombards the earth. Most wavelengths are absorbed by the atmosphere; however, there are two "windows" of nonabsorption through which significant amounts of radiation reach the ground. The first transmits ultraviolet and visible light, as well as infrared light or heat; the second transmits radio waves. As a result, terrestrial organisms have evolved a number of pigments that interact with light in various ways: some capture light energy, some provide protection from light- induced damage, and some serve camouflage or signaling purposes.

  Among these compounds are many conjugated polyenes, which play important roles as photoreceptors. For every chemical compound, there are certain wavelengths of light whose quanta possess exactly the correct amount of energy to raise electrons from their ground state to higher-energy orbitals. For most organic compounds, these wavelengths are in the UV range. However, conjugated double bond systems stabilize the electrons, so that they can be excited by lower-frequency photons with wavelengths in the visible spectrum. Such a pigment, known as a chromophore, will then transmit the "subtraction color," a color complementary to the one absorbed. For instance, carotene, a hydrocarbon compound with eleven conjugated double bonds, absorbs blue light and transmits orange. The wavelength that is absorbed generally increases with the number of conjugated bonds; rings and side-chains also affect wavelength.

  Wavelength Color Subtraction Color 480 nm blue orange 580 nm yellow violet 680 nm red green

  Among the many biological molecules that are affected by light is DNA, the genetic material of living organisms. DNA absorbs ultraviolet light, and may be damaged by UVC (< 280 nm) and UVB (280-315 nm). UVA (315-400 nm) and visible light can actually repair light-induced damage to DNA by a process called photorepair. For this reason, UVA, which also stimulates tanning, was once considered beneficial. However, there is now increasing evidence that UVA can damage skin.

  The color-producing quality of conjugated polyenes is attributable to:

  A. antibonding orbitals.
  B. resonance.
  C. polarity.
  D. optical activity.
  B. resonance.

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  Explanation/Reference:

  As we mentioned earlier, resonance is responsible for reducing the frequency of light needed to excite an electron -- that is, raise it to a higher-energy, antibonding orbital. Choice A is wrong because almost any molecule can absorb light and have an electron raised to an antibonding orbital. This process does not normally produce color because the frequency of light involved is usually outside the visible range. Resonance reduces the amount of energy needed, bringing the frequency into the visible spectrum. Optical activity, choice D, is the property of being able to rotate plane-polarized light; this doesn't have anything to do with color. Polarity, choice C, also has nothing to do with color. Therefore, both of these are wrong. The correct answer is B.

• Question 24:

  If a person having Rh-negative blood is given Rh-positive blood by mistake, it will stimulate formation of:

  A. Rh-antigens.
  B. blood clots.
  C. Rh-antibodies.
  D. None of them.
  C. Rh-antibodies.

• Question 25:

  Our sense of smell is arguably the most powerful of our five senses, but it also the most elusive. It plays a vital yet mysterious role in our lives. Olfaction is rooted in the same part of the brain that regulates such essential functions as body metabolism, reaction to stress, and appetite. But smell relates to more than physiological function: its sensations are intimately tied to memory, emotion, and sexual desire. Smell seems to lie somewhere beyond the realm of conscious thought, where, intertwined with emotion and experience, it shapes both our conscious and unconscious lives.

  The peculiar intimacy of this sense may be related to certain anatomical features. Smell reaches the brain more directly than do sensations of touch, sight, or sound. When we inhale a particular odor, air containing volatile odiferous molecules is warmed and humidified as it flows over specialized bones in the nose called turbinates. As odor molecules land on the olfactory nerves, these nerves fire a message to the brain. Thus olfactory neurons render a direct path between the stimulus provided by the outside environment and the brain, allowing us to rapidly perceive odors ranging from alluring fragrances to noisome fumes.

  Certain scents, such as jasmine, are almost universally appealing, while others, like hydrogen sulfide (which emits a stench reminiscent of rotten eggs), are usually considered repellent, but most odors evoke different reactions from person to person, sometimes triggering strong emotional states or resurrecting seemingly forgotten memories. Scientists surmise that the reason why we have highly personal associations with smells is related to the proximity of the olfactory and emotional centers of our brain. Although the precise connection between emotion and olfaction remains a mystery, it is clear that emotion, memory, and smell are all rooted in a part of the brain called the limbic lobe.

  Even though we are not always conscious of the presence of odors, and are often unable to either articulate or remember their unique characteristics, our brains always register their existence. In fact, such a large amount of human brain tissue is devoted to smell that scientists surmise the role of this sense must be profound. Moreover, neurobiological research suggests that smell must have an important function because olfactory neurons can regenerate themselves, unlike most other nerve cells. The importance of this sense is further supported by the fact that animals experimentally denied the olfactory sense do not develop full and normal brain function.

  The significance of olfaction is much clearer in animals than in human beings. Animal behavior is strongly influenced by pheromones, which are odors that induce psychological or behavioral changes and often provide a means of communicating within a species. These chemical messages, often a complex blend of compounds, are of vital importance to the insect world. Honeybees, for example, organize their societies through odor: the queen bee exudes an odor that both inhibits worker bees from laying eggs and draws drones to her when she is ready to mate. Mammals are also guided by their sense of smell. Through odors emitted by urine and scent glands, many animals maintain their territories, identify one another, signal alarm, and attract mates.

  Although our olfactory acuity can't rival that of other animal species, human beings are also guided by smell. Before the advent of sophisticated laboratory techniques, physicians depended on their noses to help diagnose illness. A century ago, it was common medical knowledge that certain bacterial infections carry the musty odor of wine, that typhoid smells like baking bread, and that yellow fever smells like meat. While medical science has moved away from such subjective diagnostic methods, in everyday life we continue to rely on our sense of small, knowingly or not, to guide us.

  Which of the following evidence does NOT support the author's statement that smell has an important physiological function?

  A. Olfaction and metabolic function are located in the same area of the brain.
  B. Animals with impaired olfaction frequently exhibit abnormal brain function.
  C. A considerable amount of human brain tissue is devoted to olfaction.
  D. Human beings with impaired olfaction are usually able to behave and function normally
  D. Human beings with impaired olfaction are usually able to behave and function normally

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  Explanation/Reference:

  This requires one to select the one statement that does not support the author's statement that smell has an important physiological function. The best approach to this type of question is to consider the answer choices in order. Choice (A) suggests that evidence that olfaction and metabolic function are located in the same area of the brain would support the author's contention that smell has an important physiological function. The proximity of olfactory and metabolic centers in the brain is mentioned in the third sentence of the first paragraph -- a fact that does indeed support the author's claim to the important physiological function of smell. So (A) is incorrect. Choice (B) presents the hypothesis that animals with impaired olfaction often exhibit abnormal brain function. The last sentence of the fourth paragraph gives this fact as evidence of the importance of smell, so it's certainly reasonable to apply this to the author's belief that smell plays an important physiological role. Choice (C) says that a considerable amount of human brain tissue is devoted to olfaction. This is true and is mentioned in the second sentence of the fourth paragraph as evidence that the role of smell must be profound. Choice (D) gives the evidence that human beings with impaired olfaction are usually able to behave and function normally. This completely contradicts the author's belief that smell has an important physiological function. If someone with an impaired sense of smell can function perfectly well, that is evidence against the author's theory of the importance of smell. Therefore, choice (D) does not support the author's statement.

• Question 26:

  Silicon, a common element, is found in rocks. Which of the following is mostly combined with the silicon?

  A. Chorine
  B. Oxygen
  C. Carbon
  D. Sulfur
  B. Oxygen

• Question 27:

  Alleles are created when a single gene undergoes several distinct mutations. These alleles may have different dominance relationships with one another; for example, there are three alleles coding for the human blood groups, the IA, IB, and i alleles. Both the IA and IB alleles are dominant to the i allele, but IA and IB are codominant to each other.

  A multiple-allele system has recently been discovered in the determination of hair coloring in a species of wild rat. The rats are found to have one of three colors: brown, red, or white. Let B = the gene for brown hair; b = the gene for red hair; and w = the gene for white hair. The results from nine experimental crosses are shown below. The males and females in Crosses 1, 2, and 3 are all homozygous for hair color.

  

  If it were discovered that the alleles for red and white hair were actually incompletely dominant and produced a pink hair color in rats with one copy of each allele, what would be the expected phenotypic ratio in a cross between a Bb male and a pink female?

  A. 2 brown : 1 red : 1 white
  B. 2 brown : 1 red : 1 pink
  C. 1 brown : 2 white : 1 pink
  D. 1 brown : 1 white
  B. 2 brown : 1 red : 1 pink

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  Explanation/Reference:

  What we need to do is figure out the genotype of the pink female. That's not so hard, since the question stem tells us that rats with pink hair have one copy of the red allele -- little b, and one copy of the white allele -- w. So, the genotype of the pink female would be little b, w. So if this pink female is crossed with a brown male, the cross is big B, little b ?little b, w. If we work out the Punnett square, 25% of the progeny would be big B, little b, which is phenotypically brown; 25% would be big B, w, which is also brown; 25% would be little b, little b, which is red; and finally 25% would be little b, w, which is pink if these two alleles are incompletely dominant. Thus, the phenotypic ratio of the offspring is 2 Brown: 1 Red : 1 Pink, which is choice B.

• Question 28:

  Which of the following reactants should be used to form the product shown below?

  

  A. Sodium ethanoate
  B. 1-propanol
  C. Ammonia and ethane
  D. Dimethyl ether
  B. 1-propanol

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  Explanation/Reference:

  This question is primarily testing your knowledge of nomenclature. Reacting an alkanoyl halide with an alcohol will lead to formation of an ester, as shown. Note that we have added 3 carbons to our molecule, and so the unknown reactant must have three carbons. Propanol is the only three carbon choice, and the only alcohol.

• Question 29:

  If a spring is 64 cm long when it is unstretched and is 8% longer when a 0.5-kg mass hangs from it, how long will it be with a 0.4-kg mass suspended from it?

  A. 66 cm
  B. 68 cm
  C. 70 cm
  D. 74 cm
  B. 68 cm

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  Explanation/Reference:

  To solve this problem, apply Hooke's law F = kx, where F is the force applied to the spring, x is the distance the spring stretches, and k is the spring constant. The forces applied in this case are weights. Since weight is proportional to mass, the distance the spring stretches is also proportional to the mass of the object attached to the spring.

  The spring starts out with a length of 64 cm. When the 0.5 kg mass is attached, it stretches 8% longer, or 64(0.08) = 5.12 cm. Since the distance stretched and the mass attached are proportional, the ratio of the distance stretched to the mass attached is (5.12 cm)/(0.5 kg) 5/(0.5) = 10 cm/kg. In other words, each kilogram attached to the spring stretches it 10 cm. Thus, when the 0.4 kg mass is attached, the spring is stretched a distance (0.4 kg)(10 cm/kg) = 4 cm. Therefore, the total length of the spring is its original length plus the distance it stretches, or 64 + 4 = 68 cm. This is choice B.

• Question 30:

  You are standing next to a river which is 10 m wide and you may assume that the profile of the river bed is a semicircle. What other piece of information do you need to estimate the volume of water that will flow past a 1-meter stretch of the river within 24 hours?

  A. the density of the water
  B. the speed of the water
  C. more than one piece of additional information is required
  D. the total length of the river
  B. the speed of the water

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  Explanation/Reference:

  You can estimate the volume of water in the 1-meter cross section by calculating the area of the semicircular river bed and multiplying by the length of the stretch of river. If you know the speed of water flow, you can determine how many seconds it will take for this volume of water to travel across the 1-meter stretch. Divide 24 hours by this time and multiply the result by the cross-sectional volume to get the total volume in 24 hours.