Medical Tests Medical Tests Certifications MCAT-TEST Questions & Answers

• Question 611:

  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.

  Correct Answer: C

  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 612:

  Hemoglobin (Hb) and myoglobin (Mb) are the O2-carrying proteins in vertebrates. Hb, which is contained within red blood cells, serves as the O2 carrier in blood and also plays a vital role in the transport of CO2 and H+. Vertebrate Hb consists of four polypeptides (subunits) each with a heme group. The four chains are held together by noncovalent attractions. The affinity of Hb for O2 varies between species and within species depending on such factors as blood pH, stage of development, and body size. For example, small mammals give up O2 more readily than large mammals because small mammals have a higher metabolic rate and require more O2 per gram of tissue.

  The binding of O2 to Hb is also dependent on the cooperativity of the Hb subunits. That is, binding at one heme facilitates the binding of O2 at the other hemes within the Hb molecule by altering the conformation of the entire molecule. This conformational change makes subsequent binding of O2 more energetically favorable. Conversely, the unloading of O2 at one heme facilitates the unloading of O2 at the others by a similar mechanism.

  Figure 1 depicts the O2-dissociation curves of Hb (Curves A, B, and C) and myoglobin (Curve D), where saturation, Y, is the fractional occupancy of the O2-binding sites. The fraction of O2 that is transferred from Hb as the blood passes through the tissue capillaries is called the utilization coefficient. A normal value is approximately 0.25.

  

  Figure 1

  Myoglobin facilitates transport in muscle and serves as a reserve store of O2. Mb is a single polypeptide chain containing a heme group, with a molecular weight of 18 kd. As can be seen in Figure 1, Mb (Curve D) has a greater affinity for

  than Hb.

  In sperm whales, the Mb content of muscle is about 0.004 moles/kg of muscle. If a sperm whale has 1000 kg of muscle, approximately how much O2 is bound to Mb, assuming that the Mb is saturated with O2?

  A. 4 moles

  B. 8 moles

  C. 12 moles

  D. 16 moles

  Correct Answer: A

  Basically what you need to do to solve this problem is figure out how much oxygen will be bound to myoglobin, if the myoglobin in this sperm whale is completely saturated with oxygen. If you look at the answer choices, all of the values are in moles. So to equate the number of moles of oxygen that will bind to myoglobin, you need to figure out how many moles of myoglobin are present in the sperm whale's muscles. From the question stem you know that there are 0.004 moles of myoglobin per kg of muscle and the whale has 1000 kg of muscle. Multiplying these two numbers together gives you 4 moles of myoglobin. This means that the whale has 4 moles of myoglobin in its muscles. So how many moles of oxygen will there be? You need to determine how many molecules of oxygen bind to a single molecule of myoglobin. The answer is one. Why? Because myoglobin consists of a single polypeptide chain, which contains a single heme group. Thus, myoglobin binds only one molecule of oxygen. If one molecule of oxygen binds to one molecule of myoglobin, then one MOLE of oxygen will bind to one MOLE of myoglobin. And since you know that the whale has 4 moles of myoglobin in its muscle, then 4 moles of oxygen will be bound to myoglobin, when myoglobin is completely saturated with oxygen. Therefore, choice A is correct.

• Question 613:

  Hemoglobin (Hb) and myoglobin (Mb) are the O2-carrying proteins in vertebrates. Hb, which is contained within red blood cells, serves as the O2 carrier in blood and also plays a vital role in the transport of CO2 and H+. Vertebrate Hb consists of four polypeptides (subunits) each with a heme group. The four chains are held together by noncovalent attractions. The affinity of Hb for O2 varies between species and within species depending on such factors as blood pH, stage of development, and body size. For example, small mammals give up O2 more readily than large mammals because small mammals have a higher metabolic rate and require more O2 per gram of tissue.

  The binding of O2 to Hb is also dependent on the cooperativity of the Hb subunits. That is, binding at one heme facilitates the binding of O2 at the other hemes within the Hb molecule by altering the conformation of the entire molecule. This conformational change makes subsequent binding of O2 more energetically favorable. Conversely, the unloading of O2 at one heme facilitates the unloading of O2 at the others by a similar mechanism.

  Figure 1 depicts the O2-dissociation curves of Hb (Curves A, B, and C) and myoglobin (Curve D), where saturation, Y, is the fractional occupancy of the O2-binding sites. The fraction of O2 that is transferred from Hb as the blood passes through the tissue capillaries is called the utilization coefficient. A normal value is approximately 0.25.

  

  Figure 1

  Myoglobin facilitates transport in muscle and serves as a reserve store of O2. Mb is a single polypeptide chain containing a heme group, with a molecular weight of 18 kd. As can be seen in Figure 1, Mb (Curve D) has a greater affinity for than Hb.

  The utilization coefficient is continually being adjusted in response to physiological changes. Which of the following values most likely represents the utilization coefficient for human adult Hb during strenuous exercise?

  A. 0.0

  B. 0.125

  C. 0.25

  D. 0.75

  Correct Answer: D

  You're told that the utilization coefficient is the fraction of the blood that releases its oxygen to tissues under normal conditions, and that under these conditions, the value of the coefficient is approximately 0.25. During strenuous exercise, there is a greater demand for oxygen, especially in skeletal muscle, where oxygen supplies are rapidly depleted during cellular respiration. Under such conditions, one would expect that a greater fraction of the blood would give up its oxygen, and that the utilization coefficient would therefore be some value greater than 0.25. Since choice D is the only value greater than 0.25, choice D is the right answer, and choices A, B, and C are wrong. During strenuous exercise, the utilization coefficient has been recorded at values ranging between 0.75 and 0.85 meaning that 75?5% of the blood gives up its oxygen in tissue capillaries.

• Question 614:

  Hemoglobin (Hb) and myoglobin (Mb) are the O2-carrying proteins in vertebrates. Hb, which is contained within red blood cells, serves as the O2 carrier in blood and also plays a vital role in the transport of CO2 and H+. Vertebrate Hb consists of four polypeptides (subunits) each with a heme group. The four chains are held together by noncovalent attractions. The affinity of Hb for O2 varies between species and within species depending on such factors as blood pH, stage of development, and body size. For example, small mammals give up O2 more readily than large mammals because small mammals have a higher metabolic rate and require more O2 per gram of tissue.

  The binding of O2 to Hb is also dependent on the cooperativity of the Hb subunits. That is, binding at one heme facilitates the binding of O2 at the other hemes within the Hb molecule by altering the conformation of the entire molecule. This conformational change makes subsequent binding of O2 more energetically favorable. Conversely, the unloading of O2 at one heme facilitates the unloading of O2 at the others by a similar mechanism.

  Figure 1 depicts the O2-dissociation curves of Hb (Curves A, B, and C) and myoglobin (Curve D), where saturation, Y, is the fractional occupancy of the O2-binding sites. The fraction of O2 that is transferred from Hb as the blood passes through the tissue capillaries is called the utilization coefficient. A normal value is approximately 0.25.

  

  Figure 1 Myoglobin facilitates transport in muscle and serves as a reserve store of O2. Mb is a single polypeptide chain containing a heme group, with a molecular weight of 18 kd. As can be seen in Figure 1, Mb (Curve D) has a greater affinity for than Hb.

  A sample of human adult Hb is placed in an 8 M urea solution, resulting in the disruption of noncovalent interactions. After this procedure, the chains of Hb are isolated. Which of the four curves most closely resembles the O2-dissociation curve for the isolated chains? [Note: Assume that Curve B represents the O2-dissociation curve for human adult Hb in vivo.]

  A. Curve A

  B. Curve B

  C. Curve C

  D. Curve D

  Correct Answer: D

  From the passage you know that the four subunits in Hb are held together by noncovalent interactions. So placing a sample of human adult hemoglobin in an 8 M urea solution, which you're told disrupts noncovalent interactions, will cause the subunits to break apart. You're also told in the question stem that the alpha chains of this sample of hemoglobin were isolated. So you need to figure out what the oxygen dissociation curve of a single peptide chain would look like. From the passage you also know that myoglobin consists of a single polypeptide chain. Therefore, the oxygen-dissociation curve for one polypeptide chain of Hb would be expected to look similar to the curve for myoglobin. In fact, both the individual alpha chains and the beta chains of hemoglobin resemble the tertiary structure of myoglobin. Thus, the curve for the alpha chain will look like Curve D and so, choice D is correct. The single chain of Hb will NOT look like Curves A, B or C because these curves have a unique shape due to the cooperativity of the four hemoglobin subunits. And since you're now dealing with a single chain, because of that treatment with an 8 M urea solution, no cooperativity is possible.

• Question 615:

  Hemoglobin (Hb) and myoglobin (Mb) are the O2-carrying proteins in vertebrates. Hb, which is contained within red blood cells, serves as the O2 carrier in blood and also plays a vital role in the transport of CO2 and H+. Vertebrate Hb consists of four polypeptides (subunits) each with a heme group. The four chains are held together by noncovalent attractions. The affinity of Hb for O2 varies between species and within species depending on such factors as blood pH, stage of development, and body size. For example, small mammals give up O2 more readily than large mammals because small mammals have a higher metabolic rate and require more O2 per gram of tissue.

  The binding of O2 to Hb is also dependent on the cooperativity of the Hb subunits. That is, binding at one heme facilitates the binding of O2 at the other hemes within the Hb molecule by altering the conformation of the entire molecule. This conformational change makes subsequent binding of O2 more energetically favorable. Conversely, the unloading of O2 at one heme facilitates the unloading of O2 at the others by a similar mechanism.

  Figure 1 depicts the O2-dissociation curves of Hb (Curves A, B, and C) and myoglobin (Curve D), where saturation, Y, is the fractional occupancy of the O2-binding sites. The fraction of O2 that is transferred from Hb as the blood passes through the tissue capillaries is called the utilization coefficient. A normal value is approximately 0.25.

  

  Figure 1

  Myoglobin facilitates transport in muscle and serves as a reserve store of O2. Mb is a single polypeptide chain containing a heme group, with a molecular weight of 18 kd. As can be seen in Figure 1, Mb (Curve D) has a greater affinity for than Hb.

  The sigmoidal shape of the O2-dissociation curve of Hb is due to:

  A. the effects of oxidation and reduction on the heme groups within the Hb molecule.

  B. the concentration of carbon dioxide in the blood.

  C. the fact that Hb has a lower affinity for than Mb.

  D. the cooperativity in binding among the subunits of the Hb molecule.

  Correct Answer: D

  The sigmoidal shape of the oxygen-dissociation curve for hemoglobin can be explained by the cooperativity among the subunits of the hemoglobin molecule. According to the passage, hemoglobin is composed of four subunits, each with its own heme group. Each heme unit is capable of binding to one molecule of oxygen, and so the entire molecule is capable of binding four molecules of oxygen. The binding of oxygen at the first heme group induces a conformational change in the hemoglobin molecule such that the second heme group's affinity for oxygen increases. Likewise, the binding of oxygen at the second heme group increases the third heme's affinity for oxygen; and the binding of oxygen at the third heme groups increases the fourth's affinity for oxygen. Therefore, the partial pressure of oxygen and the % oxygen-saturation of hemoglobin are NOT linearly proportional. As a consequence of these shifts in oxygen affinity with each binding, the line representing the oxygen-dissociation curve for hemoglobin is not straight, but rather a sigmoidal, or S-shaped, curve. Thus, choice D is the right answer. Let's take a look at the wrong answers for a minute. When the iron molecule of the heme group binds to oxygen, it is reduced; when the iron releases the oxygen, it is oxidized. However, this neither results in the sigmoidal shape of the curve, nor does it affect it. So, choice A is wrong. The concentration of carbon dioxide in the blood, choice B, is a factor that does affect hemoglobin's affinity for oxygen, and therefore affects the positioning of the curve, but it is NOT RESPONSIBLE for the sigmoidal shape. A high concentration of carbon dioxide in the blood will decrease hemoglobin's affinity for oxygen, and will therefore shift the curve to the right. So, choice B is also wrong. Choice C is also a true statement -- myoglobin does have a higher affinity for oxygen than does hemoglobin, as shown in Figure 1. However, this does not affect the shape of the sigmoidal curve. Therefore, choice C is also wrong.

• Question 616:

  Hemoglobin (Hb) and myoglobin (Mb) are the O2-carrying proteins in vertebrates. Hb, which is contained within red blood cells, serves as the O2 carrier in blood and also plays a vital role in the transport of CO2 and H+. Vertebrate Hb consists of four polypeptides (subunits) each with a heme group. The four chains are held together by noncovalent attractions. The affinity of Hb for O2 varies between species and within species depending on such factors as blood pH, stage of development, and body size. For example, small mammals give up O2 more readily than large mammals because small mammals have a higher metabolic rate and require more O2 per gram of tissue.

  The binding of O2 to Hb is also dependent on the cooperativity of the Hb subunits. That is, binding at one heme facilitates the binding of O2 at the other hemes within the Hb molecule by altering the conformation of the entire molecule. This conformational change makes subsequent binding of O2 more energetically favorable. Conversely, the unloading of O2 at one heme facilitates the unloading of O2 at the others by a similar mechanism.

  Figure 1 depicts the O2-dissociation curves of Hb (Curves A, B, and C) and myoglobin (Curve D), where saturation, Y, is the fractional occupancy of the O2-binding sites. The fraction of O2 that is transferred from Hb as the blood passes through the tissue capillaries is called the utilization coefficient. A normal value is approximately 0.25.

  

  Figure 1

  Myoglobin facilitates transport in muscle and serves as a reserve store of O2. Mb is a single polypeptide chain containing a heme group, with a molecular weight of 18 kd. As can be seen in Figure 1, Mb (Curve D) has a greater affinity for than Hb.

  If Curve B represents the O2-dissociation curve for human adult Hb, which of the following best explains why Curve A most closely resembles the curve for fetal Hb?

  A. Fetal tissue has a higher metabolic rate than adult tissue.

  B. Fetal tissue has a lower metabolic rate than adult tissue.

  C. Fetal Hb has a higher affinity for than adult Hb.

  D. Fetal Hb has a lower affinity for than adult Hb.

  Correct Answer: C

  Fetuses are 100% dependent on their mothers for all of their nutritional needs, oxygen being one of them. Oxygen is delivered to the fetus by way of diffusion across the placenta. According to the question stem, Curve A most closely resembles the oxygen-dissociation curve for fetal hemoglobin assuming that Curve B is the curve for adult hemoglobin. This means that a given oxygen pressure, fetal hemoglobin is more saturated with oxygen than adult hemoglobin is. This implies that fetal hemoglobin has a greater affinity for oxygen than adult hemoglobin. In fact, at low partial pressures of oxygen, fetal hemoglobin has a 20-30% greater affinity for oxygen than adult hemoglobin. That is why oxygen binds preferentially to fetal hemoglobin in the capillaries of the placenta. Thus, choice C is correct and choices A, B, and D are wrong. In addition, fetal blood has a 50% higher concentration of hemoglobin than maternal blood, which increases the amount of oxygen that enters fetal circulation.

• Question 617:

  Hemoglobin (Hb) and myoglobin (Mb) are the O2-carrying proteins in vertebrates. Hb, which is contained within red blood cells, serves as the O2 carrier in blood and also plays a vital role in the transport of CO2 and H+. Vertebrate Hb consists of four polypeptides (subunits) each with a heme group. The four chains are held together by noncovalent attractions. The affinity of Hb for O2 varies between species and within species depending on such factors as blood pH, stage of development, and body size. For example, small mammals give up O2 more readily than large mammals because small mammals have a higher metabolic rate and require more O2 per gram of tissue.

  The binding of O2 to Hb is also dependent on the cooperativity of the Hb subunits. That is, binding at one heme facilitates the binding of O2 at the other hemes within the Hb molecule by altering the conformation of the entire molecule. This conformational change makes subsequent binding of O2 more energetically favorable. Conversely, the unloading of O2 at one heme facilitates the unloading of O2 at the others by a similar mechanism.

  Figure 1 depicts the O2-dissociation curves of Hb (Curves A, B, and C) and myoglobin (Curve D), where saturation, Y, is the fractional occupancy of the O2-binding sites. The fraction of O2 that is transferred from Hb as the blood passes through the tissue capillaries is called the utilization coefficient. A normal value is approximately 0.25.

  

  Figure 1

  Myoglobin facilitates transport in muscle and serves as a reserve store of O2. Mb is a single polypeptide chain containing a heme group, with a molecular weight of 18 kd. As can be seen in Figure 1, Mb (Curve D) has a greater affinity for than Hb.

  If Curve B represents the O2-dissociation curve for elephant Hb, which curve most closely resembles the curve for mouse Hb?

  A. Curve A

  B. Curve B

  C. Curve C

  D. Curve D

  Correct Answer: C

  According to the passage, small mammals have higher metabolic rates and require a greater amount of oxygen per gram of tissue than larger mammals, and as a result, have hemoglobin that dissociates oxygen more readily than the hemoglobin of large mammals. A high metabolic rate implies that there's a whole lot of aerobic respiration going on. Metabolically active tissue needs lots of oxygen. The benefit of having Hb that easily dissociates oxygen is that when hemoglobin delivers oxygen to metabolically active tissue, it will readily give up its oxygen to the tissue. This means that for a given value of oxygen pressure, mouse hemoglobin will be less saturated with oxygen than elephant hemoglobin, since an elephant is much larger than a mouse and therefore has a much lower metabolic rate. In terms of Figure 1, the mouse Hb curve will be to the right of the elephant Hb curve. So if Curve B represents oxygen dissociation for elephant hemoglobin, then Curve C most closely resembles the curve for mouse Hb. Therefore, choices A and B are wrong and choice C is correct. As for choice D, we're twice told in the passage that Curve D represents oxygen dissociation for myoglobin. So Curve D isn't even an option since we're dealing with hemoglobin in this question.

• Question 618:

  Hemoglobin (Hb) and myoglobin (Mb) are the O2-carrying proteins in vertebrates. Hb, which is contained within red blood cells, serves as the O2 carrier in blood and also plays a vital role in the transport of CO2 and H+. Vertebrate Hb consists of four polypeptides (subunits) each with a heme group. The four chains are held together by noncovalent attractions. The affinity of Hb for O2 varies between species and within species depending on such factors as blood pH, stage of development, and body size. For example, small mammals give up O2 more readily than large mammals because small mammals have a higher metabolic rate and require more O2 per gram of tissue.

  The binding of O2 to Hb is also dependent on the cooperativity of the Hb subunits. That is, binding at one heme facilitates the binding of O2 at the other hemes within the Hb molecule by altering the conformation of the entire molecule. This conformational change makes subsequent binding of O2 more energetically favorable. Conversely, the unloading of O2 at one heme facilitates the unloading of O2 at the others by a similar mechanism.

  Figure 1 depicts the O2-dissociation curves of Hb (Curves A, B, and C) and myoglobin (Curve D), where saturation, Y, is the fractional occupancy of the O2-binding sites. The fraction of O2 that is transferred from Hb as the blood passes through the tissue capillaries is called the utilization coefficient. A normal value is approximately 0.25.

  

  Figure 1

  Myoglobin facilitates transport in muscle and serves as a reserve store of O2. Mb is a single polypeptide chain containing a heme group, with a molecular weight of 18 kd. As can be seen in Figure 1, Mb (Curve D) has a greater affinity for than Hb.

  The llama is a warm-blooded mammal that lives in regions of unusually high altitudes, and has evolved a type of Hb that adapts it to such an existence. If Curve B represents the O2-dissociation curve for horse Hb, which curve would most closely resemble the curve for llama Hb?

  A. Curve A

  B. Curve B

  C. Curve C

  D. Curve D

  Correct Answer: A

  The key to answering this question lies in knowing that at high altitudes, atmospheric pressure is low, meaning that there is less oxygen in the air than at sea level. We're told that the llama has adapted to life at high altitudes by evolving a different type of hemoglobin. Since the partial pressure of oxygen is lower up in the mountains, llama hemoglobin must be able to bind oxygen MORE readily at low partial pressures of oxygen. And this means that for a given value of oxygen pressure on the X-axis of Figure 1, the llama's hemoglobin will be more saturated with oxygen than the horse's hemoglobin, since horses don't typically live in regions of unusually high altitude. In terms of Figure 1, this means that the llama oxygen- dissociation curve will be to the left of the horse's. So if Curve B is the horse curve, then the llama curve most closely resembles Curve A. Thus, choices B and C are wrong. As for Curve D; remember, we're told in the passage that Curves A, B, and C are hemoglobin curves, while Curve D is the myoglobin curve. So, choice D is wrong.

• Question 619:

  Saul Hoffman's scientific journal paper published in 2015 in Societies explores the relationship between two topics that at the surface are very distant from each other. As he goes on to state, "It is relatively easy, at least for an economist, to see why economists would be attracted to issues like teen pregnancy and teen childbearing, despite their apparent distance from the core topics of economics. First, economics ?especially microeconomics ?is fundamentally the study of choices that individuals make, traditionally and most often in formal markets with monetary prices, but now more and more frequently outside that sphere. Viewed from that perspective, choices involving sexual and fertility behavior among teens are an incredibly challenging, but inviting, target. Is it possible to identify the role of economic incentives, including government policy, on these behaviors? Is it sensible to apply traditional models of rational choice decision-making to teens?

  Second, the traditional concern about teen fertility was predicated on the notion that it was an economically catastrophic act. In a famous and oft-quoted 1968 article, Arthur Campbell wrote that 'The girl who has an illegitimate child at the age of 16 suddenly has 90 percent of her life's script written for her,' including reduced opportunities for schooling, the labor market, and marriage. But it doesn't take too much reflection to appreciate that more may be going on in leading to these poor outcomes than just a teen birth. Disentangling the causal effect of teen childbearing on subsequent socio-economic outcomes from its correlational effect is another deliciously inviting and challenging target, this time well-suited for the applied economist or econometrician.

  Just to make all this yet more inviting, the two research strands are closely related. Suppose it could be demonstrated that for some teens the socio-economic impact of a teen birth was negligible. For example, maybe future prospects for some teens were equally poor with or without a birth or perhaps government programs provided substantial benefits, so that the net impact on socio-economic well-being was consequently small or even positive. Then, it might well be 'rational' in an economic sense to have a teen birth in the first place, thereby linking the research on the causal impact of a teen birth with the research on the choice determinants of a teen birth. So what came to be known as the teen birth `causes' literature and the teen birth `consequences' literature were clearly interrelated.

  And then, to add yet another layer of challenge, the teen fertility rate in the U.S. has fallen at a rate that is totally unprecedented. Teen fertility was once widespread, with most of it occurring within early and sometimes not entirely voluntary marriage. In 1960, the teen fertility rate was approximately 90 births per 1000, which implied that more than 40% of women ever had a teen birth. When I published my first article on teen births 25 years ago, the teen fertility rate was 60 births per 1000, down one-third from 1960, but it had increased six years in a row in what turned out to be a deviation from the downward trend. Since then the rate has declined every single year, except for a short but puzzling uptick between 2005 and 2007. In 2014, the teen fertility rate was 24.2 births per 1000, the lowest teen fertility rate ever recorded in the U.S., though still shockingly high by European standards. Thus, the rate fell by more than 50% during my professional association with the topic and by 70% since 1960. Of course, at the same time teen marital births largely disappeared, falling from 85% of teen births to 12%.

  This adds yet another focus for economic research. Why did the rate fall? Did it have anything to do with changes in the costs of teen childbearing or changes in policy? Is it a good thing or not?

  In this article I try to make sense out of these various research strands by providing a personal narrative through the economics literature on teen childbearing, with a special emphasis on the three issues discussed above. My goal is to make the literature, including some reasonably technical content, accessible and valuable to a non-economist."

  Hoffman, S. (2015). Teen Childbearing and Economics: A Short History of a 25-Year Research Love Affair. Societies, 5(3), 646-663. doi:10.3390/soc5030646

  What is the most likely reason for the author's use of quotation marks around "rational" in paragraph 3?

  A. The author disagrees with the idea that teen birth is rational and wishes to distance himself from it.

  B. The author disagrees with the way the term "rational" is used to indicate that economists might perceive teen birth as financially beneficial.

  C. The possible benefits of a teen birth are so small that it is not necessarily meaningful to describe them as "rational."

  D. The choice of having a teen birth might not have been thought out methodically, but makes sense according to a monetary cost/benefit analysis.

  Correct Answer: D

  This Reasoning-Within-the-Text question asks you to make sense of a stylistic choice in the passage. The author writes that "maybe future prospects for some teens were equally poor with or without a birth or perhaps government programs provided substantial benefits, so that the net impact on socio-economic well-being was consequently small or even positive. Then, it might well be 'rational' in an economic sense to have a teen birth in the first place..." The author thus clarifies that he is using "rational" in a specialized sense. He is trying to express that having a child could be financially advantageous, while distancing this sense of "rationality" from a more commonsensical one. A ?incorrect. The author does not express a strong personal opinion on the matter as opposed to what this answer choice suggests. Rather, the author seems to agree that it is meaningful to analyze behavior in terms of how it affects financial prospects. In saying that the author wishes to distance himself from it, it implies more of a moral than an economic approach. B ?incorrect. The author actually agrees with the use of the term";rationa"; within the context of teen birth. C 璱ncorrect. The author does suggest the hypothetical benefits of a teen birth may be small, but the focus of his argument is on why giving birth may not be financially catastrophic ?not that the benefits are rational.

• Question 620:

  Saul Hoffman's scientific journal paper published in 2015 in Societies explores the relationship between two topics that at the surface are very distant from each other. As he goes on to state, "It is relatively easy, at least for an economist, to see why economists would be attracted to issues like teen pregnancy and teen childbearing, despite their apparent distance from the core topics of economics. First, economics ?especially microeconomics ?is fundamentally the study of choices that individuals make, traditionally and most often in formal markets with monetary prices, but now more and more frequently outside that sphere. Viewed from that perspective, choices involving sexual and fertility behavior among teens are an incredibly challenging, but inviting, target. Is it possible to identify the role of economic incentives, including government policy, on these behaviors? Is it sensible to apply traditional models of rational choice decision-making to teens?

  Second, the traditional concern about teen fertility was predicated on the notion that it was an economically catastrophic act. In a famous and oft-quoted 1968 article, Arthur Campbell wrote that 'The girl who has an illegitimate child at the age of 16 suddenly has 90 percent of her life's script written for her,' including reduced opportunities for schooling, the labor market, and marriage. But it doesn't take too much reflection to appreciate that more may be going on in leading to these poor outcomes than just a teen birth. Disentangling the causal effect of teen childbearing on subsequent socio-economic outcomes from its correlational effect is another deliciously inviting and challenging target, this time well-suited for the applied economist or econometrician.

  Just to make all this yet more inviting, the two research strands are closely related. Suppose it could be demonstrated that for some teens the socio-economic impact of a teen birth was negligible. For example, maybe future prospects for some teens were equally poor with or without a birth or perhaps government programs provided substantial benefits, so that the net impact on socio-economic well-being was consequently small or even positive. Then, it might well be 'rational' in an economic sense to have a teen birth in the first place, thereby linking the research on the causal impact of a teen birth with the research on the choice determinants of a teen birth. So what came to be known as the teen birth `causes' literature and the teen birth `consequences' literature were clearly interrelated.

  And then, to add yet another layer of challenge, the teen fertility rate in the U.S. has fallen at a rate that is totally unprecedented. Teen fertility was once widespread, with most of it occurring within early and sometimes not entirely voluntary marriage. In 1960, the teen fertility rate was approximately 90 births per 1000, which implied that more than 40% of women ever had a teen birth. When I published my first article on teen births 25 years ago, the teen fertility rate was 60 births per 1000, down one-third from 1960, but it had increased six years in a row in what turned out to be a deviation from the downward trend. Since then the rate has declined every single year, except for a short but puzzling uptick between 2005 and 2007. In 2014, the teen fertility rate was 24.2 births per 1000, the lowest teen fertility rate ever recorded in the U.S., though still shockingly high by European standards. Thus, the rate fell by more than 50% during my professional association with the topic and by 70% since 1960. Of course, at the same time teen marital births largely disappeared, falling from 85% of teen births to 12%.

  This adds yet another focus for economic research. Why did the rate fall? Did it have anything to do with changes in the costs of teen childbearing or changes in policy? Is it a good thing or not?

  In this article I try to make sense out of these various research strands by providing a personal narrative through the economics literature on teen childbearing, with a special emphasis on the three issues discussed above. My goal is to make the literature, including some reasonably technical content, accessible and valuable to a non-economist."

  Hoffman, S. (2015). Teen Childbearing and Economics: A Short History of a 25-Year Research Love Affair. Societies, 5(3), 646-663. doi:10.3390/soc5030646

  The author would likely view the choice of whether to use birth control as:

  A. a personal choice that should be governed by one's beliefs about the morality of using it.

  B. a decision governed by cost-benefit analyses including factors such as cost of the birth control.

  C. a sign of innate intelligence.

  D. an ethical choice involving having children only when one can provide them with a good life.

  Correct Answer: B

  This Reasoning-Beyond-the-Text question asks you to make inferences about the author's overall style of thought and how it might apply to a new topic. He describes economics as "fundamentally the study of choices that individuals make," with a focus on incentives, especially financial ones. A focus on incentives that prompt the choice to use birth control, and the factors that prevent them, could interest an economist. A ?incorrect. The author never describes behavior as moral or immoral, suggesting this is irrelevant to his explanatory framework in the passage. C ?incorrect. The passage does not discuss innate qualities of a person, but focuses on the outward forces that shape their choices. D ?incorrect. As with A, this choice focuses on ethics, while the passage discusses choices in an amoral way, as based on incentives.