MCAT MCAT Certifications MCAT-TEST Questions & Answers

• Question 41:

  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.

  If k = 40 000 N/m, then how much work does Substance Q42 do in compressing from its relaxed length to a length of 9 cm?

  A. 2 J

  B. 20 J

  C. 40 J

  D. 100 J

  Correct Answer: A

  Work = ?kx2 W = ?(40 000 N/m)(-0.01 m)2 = (20 000 N/m)(0.0001 m2) W = 2 Nm = 2 J

• Question 42:

  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.

  Substance Q42 is fully expanded and then contracts in response to a 5.0 amp current. Which of the following best represents the conversion of energies in the process described?

  A. Potential --> kinetic --> mechanical

  B. Potential --> mechanical --> kinetic

  C. Electrical --> mechanical --> potential

  D. Potential --> mechanical --> electrical

  Correct Answer: C

  According to the question and the passage, current is applied (Electrical Energy) to Substance Q42 causing it to contract (Mechanical Energy); and finally, in the contracted state, using the spring analogy, Substance Q42 has potential energy.

  Going deeper, if you chose an answer beginning with "Potential" energy then we should examine this closer. Certainly, if Q42 was a spring and it was "fully expanded" then it would have significant stored (potential) energy that would try to return the spring to its native state. This problem is different because the fully expanded state of Q42 is indeed the native state. The passage suggests that if you had Q42 fully expanded, it would do nothing unless a current is applied. In other words, expanding Q42 did not store energy in the sense of a spring. On the other hand, once contracted after the application of current, Q42 would expand spontaneously due to its stored potential energy.

• Question 43:

  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.

  If an artificial arm muscle must be capable of doing 8 J work in 0.5 seconds time in order to efficiently substitute for human tissue, what average power must the section of Substance Q42 be capable of?

  A. 16 Watts

  B. 22 Watts

  C. 32 Watts

  D. 36 Watts

  Correct Answer: A

  Average power is given by equation Pavg = W/T. Here, Pavg = 8J/0.5 sec = 8/(1/2) = 2(8)/1 = 16 J/s = 16 watts.

• Question 44:

  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. How much force does the section apply when it compresses from rest state to 9.5 cm in length? k = 40 000 N/m

  A. 100 N

  B. 200 N

  C. 500 N

  D. 1000 N

  Correct Answer: B

  Since extended is 10 cm and the passage has explained that this should be considered equivalent to the relaxed state of a spring, then we can look at what happens when it is compressed to 9.5 cm. Thus, the displacement x is 0.5 cm or

  0.005 m.

  Since Fs = -kx,

  Fs = (-40 000 N/m)(-0.005 m) = 200 N.

• Question 45:

  Arginine is one of the 20 most common natural amino acids. Most healthy people do not need to supplement with arginine because the body usually produces sufficient quantities. The pathway for arginine synthesis was studied using cells from a red bread mold. This natural form of arginine is illustrated below.

  

  The red bread mold Neurospora crassa grows well on a cultural plate with "minimal" medium which is a fluid containing only a few simple sugars, inorganic salts, and vitamin. Neurospora that grows normally in nature (wild type) has enzymes that convert these simple substances into the amino acids necessary for growth. Mutating any one of the genes that makes an enzyme can produce a Neurospora strain that cannot grow on minimal medium. The mutant would only grow if the enzyme product were to be added as a supplement. On the other hand, if a "complete" medium is provided, containing all required amino acids, then Neurospora would grow, with or without mutation.

  

  Figure 1 A synthesis pathway for the amino acid arginine. Each gene in italics in the diagram produces one enzyme necessary for the synthesis of this essential amino acid required for growth.

  

  Table 1 Growth response of mutant strains in "minimal" media with supplements (ornithine, citrulline, argininosuccinate, and arginine) as indicated. Strain growth is indicated by (+) and no strain growth is indicated by (-). Consider tetrapeptides containing 2 equivalents each of the natural forms of arginine and proline. How many different linear tetrapeptides can be synthesized?

  A. 2

  B. 3

  C. 6

  D. 8

  Correct Answer: C

  Keep in mind when considering linear polypeptides that there must be an amino end and a carboxyl end, thus RRPP is a different molecule than PPRR (Note the IUPAC official abbreviations. Arginine is abbreviated as arg or R, proline is

  abbreviated as pro or P). Thus, there are 6 possibilities: RRPP, RPPR, RPRP, PPRR, PRPR, PRRP.

  Side Notes. If you have a statistics background, you can do "4 choose 2" = 4!/2!2! = (4)(3)(2)(1)/4 = 24/4 = 6.

  The ability to form multiple H-bonds make arginine ideal for binding negatively charged groups. For this reason, arginine prefers to be on the outside of proteins, where it can interact with the polar environment.

  A tetrapeptide is an oligopeptide since it only consists of four amino acids joined by peptide bonds. Tetrapeptides can be pharmacologically active including affinity to receptors involved in protein-protein signaling. Both linear and cyclic

  tetrapeptides can be found in nature.

• Question 46:

  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

  Correct Answer: A

  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 47:

  Arginine is one of the 20 most common natural amino acids. Most healthy people do not need to supplement with arginine because the body usually produces sufficient quantities. The pathway for arginine synthesis was studied using cells from a red bread mold. This natural form of arginine is illustrated below.

  

  The red bread mold Neurospora crassa grows well on a cultural plate with "minimal" medium which is a fluid containing only a few simple sugars, inorganic salts, and vitamin. Neurospora that grows normally in nature (wild type) has enzymes that convert these simple substances into the amino acids necessary for growth. Mutating any one of the genes that makes an enzyme can produce a Neurospora strain that cannot grow on minimal medium. The mutant would only grow if the enzyme product were to be added as a supplement. On the other hand, if a "complete" medium is provided, containing all required amino acids, then Neurospora would grow, with or without mutation.

  

  Figure 1 A synthesis pathway for the amino acid arginine. Each gene in italics in the diagram produces one enzyme necessary for the synthesis of this essential amino acid required for growth. Table 1 Growth response of mutant strains in "minimal" media with supplements (ornithine, citrulline, argininosuccinate, and arginine) as indicated. Strain growth is indicated by (+) and no strain growth is indicated by (-).

  

  Experiments using the two mutant strains P and Q, reveal that strain P accumulates citrulline, but strain Q does not. Which of the following statements is most consistent with the data provided?

  A. Strain Q has only one mutation.

  B. Strain P has a mutation in argF only.

  C. Strain P has mutations in argF, argG and argH.

  D. Strain P has a mutation in argG only.

  Correct Answer: D

  On the Surface. In the previous question, we established that the enzyme argininosuccinase must be functional for both strains and that means that argH is not defective (no mutation) for either P or Q. Thus, any answer choice suggesting an argH mutation is incorrect.

  Strain P accumulates citrulline. This means that the synthetic pathway was working up to citrulline but then was blocked from progressing. This means that the next step in the production line, the gene product from argG, is not functional (mutation). Thus, we have our answer.

  Going deeper, strain Q: no accumulation of citrulline means that there must be a blockage before that point, so given the information presented, argF must have a mutation meaning ornithine accumulates. Adding ornithine: no growth and it accumulates. Adding citrulline, no growth because there must ALSO be an argG mutation. This is consistent with adding something after the argG step/mutation, argininosuccinate, resulting in growth. Thus, strain Q must have 2 mutations in the synthesis pathway shown.

• Question 48:

  Arginine is one of the 20 most common natural amino acids. Most healthy people do not need to supplement with arginine because the body usually produces sufficient quantities. The pathway for arginine synthesis was studied using cells from a red bread mold. This natural form of arginine is illustrated below.

  

  The red bread mold Neurospora crassa grows well on a cultural plate with "minimal" medium which is a fluid containing only a few simple sugars, inorganic salts, and vitamin. Neurospora that grows normally in nature (wild type) has enzymes that convert these simple substances into the amino acids necessary for growth. Mutating any one of the genes that makes an enzyme can produce a Neurospora strain that cannot grow on minimal medium. The mutant would only grow if the enzyme product were to be added as a supplement. On the other hand, if a "complete" medium is provided, containing all required amino acids, then Neurospora would grow, with or without mutation.

  

  Figure 1 A synthesis pathway for the amino acid arginine. Each gene in italics in the diagram produces one enzyme necessary for the synthesis of this essential amino acid required for growth.

  

  Table 1 Growth response of mutant strains in "minimal" media with supplements (ornithine, citrulline, argininosuccinate, and arginine) as indicated. Strain growth is indicated by (+) and no strain growth is indicated by (-). Which of the following is most likely consistent with the overall synthetic pathway for arginine (accounting for coupled reactions)?

  A. H < 0

  B. G = 0

  C. net ATP production

  D. G > 0

  Correct Answer: D

  Synthesis or building a molecule (anabolic) requires energy (endothermic; BCM 2.3) thus +H. We cannot be surprised that Gibbs free energy is positive which suggests that building complex molecules is not a spontaneous reaction. Of course, we know these reactions can occur as long as they are coupled with a favorable reaction (i.e. the hydrolysis of ATP).

• Question 49:

  Arginine is one of the 20 most common natural amino acids. Most healthy people do not need to supplement with arginine because the body usually produces sufficient quantities. The pathway for arginine synthesis was studied using cells from a red bread mold. This natural form of arginine is illustrated below.

  

  The red bread mold Neurospora crassa grows well on a cultural plate with "minimal" medium which is a fluid containing only a few simple sugars, inorganic salts, and vitamin. Neurospora that grows normally in nature (wild type) has enzymes that convert these simple substances into the amino acids necessary for growth. Mutating any one of the genes that makes an enzyme can produce a Neurospora strain that cannot grow on minimal medium. The mutant would only grow if the enzyme product were to be added as a supplement. On the other hand, if a "complete" medium is provided, containing all required amino acids, then Neurospora would grow, with or without mutation.

  

  Figure 1 A synthesis pathway for the amino acid arginine. Each gene in italics in the diagram produces one enzyme necessary for the synthesis of this essential amino acid required for growth.

  

  Table 1 Growth response of mutant strains in "minimal" media with supplements (ornithine, citrulline, argininosuccinate, and arginine) as indicated. Strain growth is indicated by (+) and no strain growth is indicated by (-).

  According to the information provided, a conclusion that can be made with certainty is that neither mutant strain P nor Q have the defective enzyme:

  A. carbamoyltransferase.

  B. argininosuccinate synthase.

  C. argininosuccinase.

  D. None of the above enzymes are defective in either mutant strain P nor Q.

  Correct Answer: C

  You should recognize that enzymes typically end with 璦se and so you can see that the figure provided indicates the 3 enzymes that are catalysts for the three reactions as shown. Now let's reinterpret the question: if neither P nor Q have a defective enzyme X, then both P and Q must have a functioning enzyme X (the other interpretation is that they have no enzyme but that is not consistent with the data in the table provided). In other words, "Which of the answer choices corresponds to an enzyme that is fully functional in strains P and Q?"

  The information in the table shows a (+) symbol in the last two columns indicating that both P and Q are able to convert argininosuccinate to arginine (see Table 1). This necessarily means that both P and Q have a functioning enzyme argininosuccinase (see Figure 1).

  Going deeper, more about the 1 gene, 1 enzyme hypothesis and the importance within a metabolic pathway. Let's consider some hypothetic examples using Figure 1 but no longer considering Table 1 so we can explore other possibilities and their consequences.

  For example, let's say that Mutant #1 couldn't make ornithine. So, the gene that makes the enzyme for ornithine synthesis must have been mutated. If ornithine is added to the media, citrulline and then arginine would be made and Mutant #1 could grow.

  Similarly, consider a genetic mutation in Mutant #2 affecting the enzyme that makes the arginine precursor citrulline. Adding citrulline as a supplement complements the mutation and drives arginine synthesis to completion. And consider a genetic mutation #3 affecting the final step of arginine synthesis -- the conversion of citrulline to arginine. By adding arginine as a supplement, the mutation is complemented (like a `work around') and Mutant #3 could grow. With each mutated gene, only one step of the metabolic pathway is affected. Therefore, one gene is responsible for one enzyme or protein (of course, it's a little more complicated because some genes are responsible for polypeptides which combine with other polypeptides to form a functioning protein).

• Question 50:

  In order to determine the Doppler shift in perceived sound frequency, the following variables must be known:

  speed of sound in medium time of interaction between sound source and detector distance between source and detector frequency of emitted sound

  A. I only

  B. I and III

  C. II and IV

  D. I an IV

  Correct Answer: D

  The equation for calculating the Doppler effect on perceived frequency relies on the actual frequency of emitted sound, speed of sound in the transmitting medium, and the relative velocities of the source and detector.

  A ?incorrect. Choice IV is also required.

  B ?incorrect. Distance is not a variable in the Doppler equation.

  C ?incorrect. Time of interaction is not a variable in the Doppler equation.

  D ?correct. Furthermore, the relative velocities of the detector and source are required.