uworld missed questions

At which pH would oxalate adopt the greatest net dipole moment? A.1(13%) B.3(64%) C.5(8%) D.7(13%)

A dipole moment occurs when positive charge accumulates at one end of a molecule and negative charge accumulates at the other. The greater the difference in charge at each end of the molecule, the greater the dipole moment. A molecule may have multiple polar bonds, each with its own dipole moment. If the individual moments all point in the same direction, the overall moment is increased. If individual moments point in opposite directions, they cancel each other and the molecule as a whole has no dipole. For this reason, symmetrical molecules generally do not have net dipole moments and are considered nonpolar. As shown in Figure 2, oxalate can take on different forms depending on the pH to which it is exposed. When the pH < 1.25, the molecule is fully protonated and becomes oxalic acid. Resonance forms show that individual regions of this molecule have dipole moments. However, this form of the molecule is symmetrical so the dipoles cancel, giving no net dipole moment. Similarly, while the molecule is fully deprotonated at a pH > 4.14, it is still symmetrical and has no net dipole moment in this form either. When the pH is between 1.25 and 4.14, oxalate is half protonated and is no longer symmetrical. In this form, it has a dipole moment. (Choices A, C, and D) At a pH below 1.25 or above 4.14, oxalate becomes symmetrical and all dipoles cancel. Educational objective:Molecules have a net dipole moment (separation of charge) when the individual dipoles within it do not cancel each other. Symmetrical molecules typically do not have net dipole moments. Protonation and deprotonation can change whether a molecule is symmetrical and can induce or remove a dipole moment.

Suppose a chemist decides to conduct and monitor the reaction for 10 min at 298.15 K in the three environments described in the passage. Which of the three reactions is most likely to form the greatest amount of product? A.The reaction in a lipid environment(25%) B.The reaction in an aqueous environment(47%) C.The reaction in a gaseous environment(11%) D.Cannot be determined from the information given(15%)

A reaction can be under either kinetic or thermodynamic control. When the conditions are such that a reaction is irreversible (eg, low temperature), it is said to be under kinetic control, and the most favorable product is the one whose pathway has the lowest activation energy. Unless the reactions have had time to complete, the fastest reaction will yield the most product. When a reaction occurs under conditions such that it is reversible (eg, high temperatures), it is said to be under thermodynamic control. Under these conditions, all products form readily and the most stable product will be favored (ie, the most negative ΔG), as it is least likely to undergo the reverse reaction. According to the passage, the reactions are all irreversible at 298.15 K, and therefore are under kinetic control. As a result, the reaction in aqueous solution will likely produce the greatest amount of product over 10 min because it has the lowest activation energy and will proceed the fastest. (Choice A) Although the product is most stable for the reaction in a lipid environment, this attribute is irrelevant for reactions under kinetic control as the reverse reaction is unfeasible. Furthermore, this reaction has a higher activation energy than the same reaction in an aqueous environment. (Choice C) The reaction pathway in a gaseous environment has a very large activation energy and is less favorable under kinetic control. (Choice D) Because the passage states the reactions are under irreversible conditions, it can be assumed they are under kinetic control. Knowledge of the activation energies for the three reactions is sufficient to determine the most favorable product. Educational objective:Irreversible reactions tend to be under kinetic control, which favors products whose pathways have the lowest activation energy. Reversible reactions tend to be under thermodynamic control, which favors the most stable product.

In the alveoli, hypoventilation (decreased gas exchange) and hyperventilation (increased gas exchange) can lead to abnormalities in acid-base homeostasis. Which of the following is true of the immediate effects of abnormal ventilation? A.Hyperventilation decreases blood pH and decreases HCO3− levels.(10%) B.Hyperventilation increases blood pH and decreases HCO3− levels.(66%) C.Hypoventilation increases blood pH and increases HCO3− levels.(9%) D.Hypoventilation decreases blood pH and decreases HCO3− levels.(14%)

According to Le Châtelier principle, chemical reactions are in a state of dynamic equilibrium to maintain optimal ratios of reactants and products. At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction. If there are changes in conditions (eg, changes in concentrations or changes in temperature or pressure), the equilibrium will shift to counteract these changes. A decrease in the concentration of a chemical species shifts the equilibrium toward that species whereas an increase in concentration shifts the equilibrium away from that species. During ventilation, CO2 is expelled from the lungs. An increase in ventilation (hyperventilation) decreases levels of CO2 in the blood. Removal of CO2 then shifts the reaction to the left to maintain equilibrium. This shift results in a decrease in carbonic acid levels, which translates to a decrease in HCO3− and H+ (increase in pH) in pulmonary circulation. Clinically, this is referred to as respiratory alkalosis. (Choice A) Removal of CO2 decreases HCO3− and H+. A decreased H+ concentration corresponds to an increase in blood pH. (Choices C and D) Hypoventilation (decreased gas exchange) leads to an increase in CO2 levels in the blood. This shifts equilibrium to the right, resulting in increased levels of H2CO3, HCO3− and H+ (a decrease in pH). Clinically, this is referred to as respiratory acidosis. Educational objective:Chemical reactions are in a state of dynamic equilibrium to maintain equilibrium. Changes in conditions will shift the equilibrium to counteract the changes. If a reacting species is removed, the reaction shifts toward the removed species. If a species is added, the reaction shifts away from the added species.

The North American flying squirrel and the Draco lizard of Southeast Asia have both evolved a membrane between their limbs that allows them to glide between trees in their habitats. Given that the species are distantly related, which of the following patterns of evolution would explain the development of this anatomical structure in both organisms? Parallel evolution Divergent evolution Convergent evolution A.I only(25%) B.II only(13%) C.III only(44%) D.I and II only(17%)

According to the theory of natural selection, organisms possessing traits that are best suited to their environment are more likely to survive and reproduce (ie, pass on their genes) than those with less favorable traits. As a result, traits/phenotypes that increase chances of survival prevail in the population, causing the species to adapt to its environment over time (ie, evolve). However, the patterns of evolution across time often vary depending on the environmental pressures faced by different species. If two species inhabit similar environments, they often evolve analogous (comparable) characteristics in response to facing comparable environmental pressures (eg, habitat, food availability, predation). In contrast, if two species inhabit distinct environments with different environmental pressures, they are likely to evolve unique phenotypes that are best suited to their different environments. Accordingly, the flying squirrel and Draco lizard have a distant evolutionary relationship, yet both have evolved an anatomical structure for gliding between trees. Because they both live in tree-dense habitats, it is likely that both species independently acquired a membrane between their limbs to adapt to similar environmental pressures and improve their chances of survival. For example, enhanced mobility or "gliding" between trees may have simplified foraging for food or aided in predator avoidance. Because the evolution of this feature occurred independently in these two very distantly related species, this is an example of convergent evolution (Number III). (Number I) Parallel evolution occurs when two more closely related species (ie, descended from a more recent common ancestor) continue to evolve the same characteristics to adapt to similar environments. (Number II) Divergent evolution occurs when two species descended from a recent common ancestor inhabit contrasting environments and evolve distinct characteristics that allow them to better adapt to their differing environmental pressures. Educational objective:Convergent evolution leads to similar characteristics in distantly related species that are exposed to similar environmental pressures. Parallel evolution also leads to similar characteristics in species found in similar environments but occurs in species with a more recent common ancestor. Divergent evolution leads to unique characteristics in somewhat closely related species that face contrasting environmental pressures.

In an isolated population of 10,000 mice, 1,600 are homozygous for a Tlr4 defect. Assuming stable allele and genotype frequencies, how many mice are heterozygous for a Tlr4 defect? A.2,400(13%) B.3,600(13%) C.4,800(66%) D.5,200(7%)

Allele frequency describes the relative frequency of an allele or gene version within a given population, and genotype frequency reflects the relative frequency of a particular genotype. Usually, these frequencies are described as fractions or percentages. Hardy-Weinberg calculations can be used to relate allele and genotype frequencies in stable, nonevolving populations: p + q = 1: If two versions (alleles) exist for a given gene, respective allele frequencies are commonly denoted as p, which represents the major (most common) allele, and q, which represents the minor (less common) allele. Statistically, the sum of these frequencies must equal 1. p2 + 2pq + q2 = 1: Genotype frequency can be determined by the probability of inheriting a genotype and is therefore dependent on allele frequencies. The frequency of homozygotes is equal to p2 or q2 whereas the frequency of heterozygotes is equal to 2pq. In this example, p is the frequency of the normal-functioning Tlr4 allele and q is the frequency of the mutated Tlr4 allele. The frequency of mice homozygous for the mutated allele (q2) is 1,600/10,000, or 0.16. Therefore, q is the square root of 0.16, or 0.40, and this value can be used to calculate p: p = 1 − 0.40 = 0.60 The p and q allele frequencies can then be used to calculate the frequency of the heterozygous genotype and the total number of heterozygous mice in the population of 10,000: 2pq = 2(0.60)(0.40) = 0.48 (0.48)(10,000) = 4,800 mice (Choice A) 2,400 is one half of the number of heterozygous mice. Heterozygote frequency is equal to 2 times pq, which is the sum of probabilities of inheriting p from the father and q from the mother (1pq) or p from the mother and q from the father (1pq). (Choice B) 3,600 is equal to the number of mice homozygous for the normal functioning receptor: (10,000)(p2). (Choice D) 5,200 is equal to the number of mice containing at least one copy of the normal allele: (10,000)(p2 + 2pq) or (10,000)(1 - q2). Educational objective:Hardy-Weinberg equations can be used to relate allele frequencies and genotype frequencies. Genotype frequencies are equal to the probability of inheriting each genotype, with the frequency of homozygotes equal to p2 or q2 and the frequency of heterozygotes equal to 2pq.

Comparing the peak excitation wavelengths stated in the passage and the highest-intensity fluorescence peaks in Figure 2, which of the following is true about ZPP detection in blood samples? A.ZPP and PPIX have peak photon emissions that are equal in energy.(7%) B.ZPP requires less energy to excite its electrons from the ground state than does PPIX.(38%) C.The photons used to excite ZPP and PPIX were of equal energy, but the photons absorbed by each molecule were of different energy.(24%) D.The photons absorbed by ZPP and PPIX were of equal energy, but the resulting electronic transitions in the molecules were of different energy.(29%)

Because a photon's energy is inversely proportional to its wavelength, smaller wavelengths correspond to higher energies. Some molecules can absorb the energy of a photon in a process called excitation, causing an electron to move from the ground state to a higher energy (excited) state. The change in the electron's energy is equal to the energy of the absorbed photon. The electron can then relax back to the ground state when the molecule emits light, heat, or both. When some of the energy is lost as heat and the rest is lost as light, the emitted photon will have less energy than the absorbed photon, and therefore will have a longer wavelength. This process is known as fluorescence. As stated in the last sentence of the passage, ZPP has an excitation maximum of 425 nm and an emission maximum of 595 nm whereas PPIX is excited at 407 nm and emits a photon at 625 nm. Because ZPP can be excited by a longer wavelength than PPIX, ZPP requires less energy to excite its electrons from the ground state. (Choice A) The peaks of the emission spectra are at different wavelengths, so ZPP and PPIX do not have peak photon emissions of the same energy. (Choice C) Because ZPP and PPIX were excited using different wavelengths (425 nm and 407 nm), the photons exciting each molecule do not have equal energy. (Choice D) The energy of the absorbed photon is the same energy that excites electrons. Because ZPP and PPIX have different excitation wavelengths, they each absorb a different amount of energy, which indicates electronic transitions of different energy in each molecule. Educational objective:Electromagnetic radiation at a certain wavelength has photons of a particular energy. Energy is inversely proportional to wavelength.

Consider the trends in atomic radii on the periodic table. The bond in citrate that is the longest and weakest with the lowest bond dissociation energy is the: A.C-H bond.(30%) B.C=O bond.(2%) C.O-H bond.(24%) D.C-C bond.(42%)

Bond dissociation energy is the energy required to break a chemical bond; it is related to the bond length, or the distance between the nuclei of two bonded atoms. Shorter bonds are stronger and require more energy to break. Atoms with small atomic radii can form short, strong bonds whereas atoms with larger radii form longer, weaker bonds. Each subsequent row on the periodic table indicates an additional electron shell, and therefore a larger atomic radius, so atoms in the first row will have smaller atomic radii than atoms in the second row, and so on. Double bonds require more energy to break than single bonds. Citrate includes bonds between carbon and carbon, carbon and oxygen, carbon and hydrogen, and oxygen and hydrogen. Of the choices given, the C-C bond is the only single bond that does not involve a first row atom (hydrogen). Therefore, the C-C bond will be the longest and require the least energy to break. (Choices A and C) These options include hydrogen, which forms short, strong bonds. Note that although O-H bonds are commonly broken in acid-base reactions, these reactions also involve the formation of a new bond to hydrogen, which provides the high amount of energy necessary to break the old bond. (Choice B) C-O single bonds are of approximately the same strength as C-C single bonds. However, C=O double bonds are much shorter and stronger. Educational objective:The energy required to break a bond, known as the bond dissociation energy, is related to the bond length. Atoms with smaller radii (near the top of the periodic table) tend to form shorter, stronger bonds than atoms with larger radii.

Experimental results suggest that the mutated Tlr4 allele exhibits which quality? A.Codominance(33%) B.Recessivity(20%) C.Reduced penetrance(16%) D.Variable expressivity(29%)

Codominance describes the co-expression of alleles as observed in the phenotype of heterozygous individuals. In the case of codominant traits, neither allele is fully dominant or fully recessive. Common examples of codominance include the co-expression of both red (R) and white (W) alleles in a speckled offspring (RW). In the passage, in vitro studies of F1 spleen cells suggest that both wild-type and mutant TLRs are observable by protein electrophoresis. This co-expression of the normally functioning receptor and the mutated receptor can be attributed to the codominance of tlr4(+) and tlr4(d) alleles. F1 cells [tlr4(+)/tlr4(d)] display intermediate production of anti-SRC antibodies and interferon because half of their TLR receptors are functional while the other half are mutant. As a result, the quantitative data for their immune response were lower than He-N mice [tlr4(+)/tlr4(+)] mice but higher than He-J mice [tlr4(d)/tlr4(d)]. (Choice B) If the mutant allele were recessive, F1 mice would exhibit a full response to LPS, and measurements observed in the F1 generation would be indistinguishable from measurements observed in the He-N mice [tlr4(+)/ tlr4(+)]. (Choice C) Penetrance refers to the portion of offspring that express a genetic trait. If the tlr4(d) mutation had reduced penetrance, only a fraction of the F1 offspring would show decreased response to LPS compared to He-N mice. As seen in Table 1, immune response was relatively uniformly decreased among F1 mice. (Choice D) Expressivity refers to the range of symptoms observed in individuals with a given genetic condition. If the tlr4(d) allele had variable expressivity, the mutation would result in a range of different phenotype characteristics. Educational objective:Codominance refers to the co-expression of two alleles at the same locus, where both allelic products are observable in the phenotype of heterozygous individuals.

Which of the following does NOT describe the coordinate covalent bonds formed between Fe2+ and the four nitrogen ligands in Figure 1? A.Each nitrogen atom provides both bonding electrons.(16%) B.The net charge of heme is zero.(54%) C.Nitrogen's electrons interact with iron's d orbitals.(10%) D.Iron's electron configuration determines bond strength.(18%)

Coordinate covalent bonds are a special type of bond between a central atom, such as a metal, and a ligand. Both electrons in the bond come from the ligand. Although classified as covalent bonds, coordination bonds do share some of the characteristics of ionic bonds. For example, the metal ion maintains its oxidation state, as in the case of an ionic bond, but the ligands are not charged and are usually electronegative, as in covalent bonds. The metal and its ligands together form a complex, and the number of coordinate bonds to the metal is known as the coordination number. The metal ion Fe2+ is positively charged whereas the donor atoms (nitrogen) are neutral, resulting in a net charge of +2 for the complex. Unlike ionic bonds, the donor atoms do not give electrons to the positively charged metal. Instead counterions often surround the complex in solution to balance the metal's positive charge. (Choice A) The nitrogen ligands each have a lone pair of electrons that provide the bonding electrons in the coordinate covalent bond. (Choice C) The lone pairs of nitrogen's electrons interact with iron's d orbitals to form the coordinate bond. In a coordination bond, the d orbitals are no longer degenerate and have distinct shapes, some of which point directly at the negatively charged ligands. (Choice D) The strength of the coordination bond depends on which d orbitals have electrons in them. Educational objective:Coordinate covalent bonds are a special bond between a central atom and its ligands. The number of coordinate bonds indicates the coordination number and the ligands provide bonding electrons, which interact with the metal's d orbitals to form the coordinate covalent bond.

What conclusion can be drawn from the results shown in Figure 1? A.The samples were analyzed under denaturing conditions.(21%) B.The samples were analyzed under reducing conditions.(26%) C.The samples were analyzed using a native gel.(39%) D.The samples were analyzed using a stable pH gradient.(11%)

DNA molecules can be separated by size via gel electrophoresis using a polyacrylamide gel (PAGE) or an agarose gel. The polyacrylamide gel is generally used to analyze proteins or shorter fragments of DNA because it has smaller pores through which the molecules can traverse without falling through. Based on the passage, the blood samples were taken from family members and the mtDNA segment containing the 3243 region was extracted and amplified via PCR. The PCR products were then treated with the restriction enzyme ApaI and visualized using PAGE. Based on the procedure, it can be concluded that this experiment was performed using a native gel. The native gel contains no denaturants or reducing agents and allows DNA molecules to maintain their double-helical structure and traverse the gel in their native (unaltered) state. Individuals with the mtDNA mutation would be expected to show the characteristic features of heteroplasmy: one 161-bp band, representing the undigested PCR mtDNA product lacking the A3243G mutation, and two bands, representing ApaI-digested fragments of mtDNA containing the A3243G mutation. Samples without the mutation would show only the undigested 161-bp band, as shown in lanes 3-5. (Choice A) A denaturing substance is added to separate double-stranded DNA into single strands by breaking hydrogen bonds between the two DNA strands. However, only double-stranded mtDNA is amplified via PCR and was used in this experiment; no denaturing substance was added. Denaturants are also often used to separate proteins in PAGE gels. (Choice B) These samples were analyzed in nonreducing conditions as DNA has no disulfide bonds. Reducing substances are used to break disulfide bonds in protein, not DNA, PAGE. (Choice D) DNA molecules are separated in PAGE using an electric field, not a pH gradient. However, isoelectric focusing does use a stable pH gradient to separate proteins based on their isoelectric point. Educational objective:Polyacrylamide gel electrophoresis (PAGE) can be used to separate DNA molecules by size. A native PAGE gel contains no denaturants or reducing agents, and allows double-stranded DNA molecules to traverse the gel in their native (unaltered) state.

Self-administration of nicotine in animal models is most likely suppressed by means of: A.blocking dopaminergic pathways.(65%) B.blocking adrenergic pathways.(15%) C.enhancing dopaminergic pathways.(14%) D.enhancing adrenergic pathways.(3%)

Dopamine is a neurotransmitter released during pleasurable or rewarding experiences, making it a key player in the brain's reward pathway. The reward pathway includes a region of dopaminergic cell bodies located in the midbrain called the ventral tegmental area (VTA). The VTA sends projections to the prefrontal cortex, nucleus accumbens, amygdala, hippocampus, and other areas. These areas are responsible for perceiving and remembering the pleasurable or rewarding experience. Rewarding stimuli (including commonly abused drugs) increase dopaminergic activity in the brain by increasing the production of dopamine, interfering with its clearance from receptors, or directly stimulating dopamine receptors in the brain. In turn, the reward system is activated and the brain learns to associate the drug with reward. Self-administration in animal models is used as a measure of how addictive a substance is. The more addictive the drug, the more an animal will engage in self-administering behavior. Antagonists can be used to bind to receptors and block the activity of specific neurotransmitters. Studies show that blocking the activity of dopamine can disrupt the reward pathway and decrease addictive behavior. (Choices B and D) Adrenergic receptors are found throughout the body and are involved with the regulation of a variety of functions such as heart rate, bronchodilation, vasodilation, and gastrointestinal tone. Adrenergic receptors respond to epinephrine and norepinephrine, and are involved in autonomic nervous system responses. Blocking or enhancing adrenergic pathways should not impact the reward system in the brain. (Choice C) Enhancing dopaminergic pathways would not suppress self-administration of nicotine in animal models but would likely reinforce the behavior. Educational objective:Dopamine is a neurotransmitter associated with the experience of pleasure. Dopaminergic activity in the reward pathway contributes to the development and maintenance of addictive behaviors. Blocking the action of dopamine in the reward pathway is expected to decrease addictive behavior.

preferentially fire in response to a bar of light that is oriented at a specific angle, and that different neurons similarly respond to bars of light oriented at different angles. This finding provides the strongest evidence for: A.feature detection.(63%) B.parallel processing.(15%) C.spreading activation.(11%) D.sensory adaptation.(8%)

Feature detection involves the perceptual discrimination of specific aspects of a given stimulus via feature detectors. Feature detectors are specific neurons that preferentially fire in response to very specific stimuli. Feature detection occurs for all the senses but is most often described regarding vision. Feature detectors in the visual system respond to aspects of the visual stimulus, such as horizontal lines or right angles (among others). The visual system is organized such that feature detectors synapse on neurons that respond to more complex stimuli (eg, faces) localized in certain areas of the brain (eg, fusiform face area). An experiment in which researchers find that certain neurons in the visual cortex preferentially fire in response to specific stimuli (eg, a bar of light oriented at a specific angle) provides the strongest evidence for feature detection. (Choice B) Parallel processing describes the brain's ability to simultaneously process various components (eg, color, motion) of a visual stimulus. This experiment did not demonstrate the simultaneous firing of different neurons detecting different components of a stimulus, so it does not provide strong evidence for parallel processing. (Choice C) Spreading activation occurs when a node (ie, concept) within an individual's semantic network (a uniquely organized cognitive web of information) triggers the activation of other, related nodes, a process known as priming. Because the experiment did not test priming, its findings do not provide evidence for spreading activation. (Choice D) Sensory adaptation is a diminished nervous system response over time to stimuli that remain constant, resulting in diminished stimulus perception (eg, a constant odor becomes less noticeable over time). This experiment did not present stimuli until the response diminished, so its findings do not provide evidence for sensory adaptation. Educational objective:Feature detection involves feature detector neurons that preferentially fire in response to specific stimuli (eg, a right angle causes feature detectors in the visual system to respond).

What is the correct systematic name for the compound shown below? A.(2R, 3S, 5S)-2-amino-5-hydroxy-3-methyl-4-oxohexanal(50%) B.(2S, 4S, 5R)-5-amino-2-hydroxy-4-methyl-6-oxohexan-3-one(9%) C.(1S, 3S, 4R)-4-amino-1,3-dimethyl-2,5-dioxopentan-1-ol(20%) D.(2R, 3S, 5S)-5-hydroxy-3,5-dimethyl-1,4-dioxopentan-2-amine(18%)

For compounds with multiple functional groups, the highest-priority functional group should be used as the basis for assigning a compound name. This group determines the compound name ending(suffix), and all lower-priority functional groups are named as substituent branches using unique prefixes associated with each. Carbon atoms of the longest continuous carbon chain within the structure should be numbered to specify the location of the substituents. The selected carbon chain must incorporate the highest-priority functional group and must be numbered in the direction that assigns it the lowest possible number. Stereocenter configurations are also specified in parentheses using the same numbers at the beginning of the compound name. In Compound 1, four functional groups are present, with an aldehyde group as the highest-priority group. Therefore, the compound is named as an aldehyde using the -al suffix. The longest continuous carbon chain containing the aldehyde is six carbon atoms long, and the chain is numbered to give the lowest position to the aldehyde carbon. The amine, ketone, and alcohol groups are subsequently located along the position reference numbers and are named as substituents using their respective prefixes. The configurations of the three stereogenic carbon atoms are then specified by position number at the beginning of the name to give (2R, 3S, 5S)-2-amino-5-hydroxy-3-methyl-4-oxohexanal. (Choice B) The suffix and numbering for (2S, 4S, 5R)-5-amino-2-hydroxy-4-methyl-6-oxohexan-3-one incorrectly treat the ketone as the highest-priority group. Also, if an aldehyde substituent were present, the correct prefix should be formyl, not oxo. (Choice C) The suffix and numbering for (1S, 3S, 4R)-4-amino-1,3-dimethyl-2,5-dioxopentan-1-ol incorrectly treat the alcohol as the highest-priority group, and five carbon atoms is not the longest chain containing the highest ranked group. (Choice D) The suffix and numbering for (2R, 3S, 5S)-5-hydroxy-3,5-dimethyl-1,4-dioxopentan-2-amine incorrectly treat the amine as the highest-priority group, and five carbon atoms is not the longest chain containing the highest ranked group. Educational objective:Organic compounds with multiple functional groups are named using the highest-priority functional group to determine the suffix. All other functional groups are named as substituents using prefixes. Numbering of the longest carbon chain provides location references for substituents and stereocenter configurations and must assign the lowest possible number to the highest-priority group.

In Reaction 1, what hybridization state changes do the methylated carbon atom in the ringed structure of vitamin K hydroquinone and the oxygen atom involved in epoxide formation undergo? A.sp2 to sp3 for the methylated carbon and sp2 to sp3 for the oxygen atom(64%) B.sp2 to sp3 for the methylated carbon and sp to sp2 for the oxygen atom(16%) C.sp2 to sp3 for the methylated carbon and sp2 to sp2 for the oxygen atom(17%) D.sp to sp2 for the methylated carbon and sp2 to sp3 for the oxygen atom(1%)

Hybrid orbital theory is used to explain molecular geometry and the bonding of atomic orbitals into molecular orbitals. It states that the electrons not involved in pi bonds (p orbitals) are fused into mixed hybrid orbitals, or electron domains. Hybrid orbitals average the characteristics of s and p orbitals, and lead to orbitals with equivalent energy and shape. To determine atom hybridization, count the number of electron domains by adding up the number of lone electron pairs and sigma bonds involving the atom of interest. (Recall that double and triple bonds both include one sigma bond.) The resulting number corresponds to the number of hybrid orbitals. The sum of s and p superscripts on the hybrid name should match this number: sp3-, sp2-, and sp-hybridized atoms have four, three, and two electron domains, respectively. The superscript of 1 is implied when there is none present. The methylated carbon atom on vitamin K hydroquinone has three sigma bonds (sp2) and becomes sp3 with four sigma bonds when the epoxide is formed. The oxygen atom (from O2) has one sigma bond and two lone pairs of electrons (sp2). The epoxide oxygen atom on vitamin K 2,3-epoxide has two sigma bonds and two lone pairs of electrons (sp3). (Choice B) The oxygen atom (O2) is sp2 hybridized rather than sp because it has one sigma bond and two lone pairs. (Choice C) The oxygen atom changes hybridization states, going from sp2 to sp3. (Choice D) The methylated carbon atom in vitamin K hydroquinone is sp2 hybridized because it has three sigma bonds rather than two sigma bonds (sp). This carbon atom becomes sp3 when the epoxide forms because it now has four sigma bonds. Educational objective:Hybrid orbital theory combines bound atomic orbitals into mixed hybrid orbitals of equivalent energy and shape. To determine an atom's hybridization, count the number of lone electron pairs and sigma bonds. The resulting number corresponds with the number of hybrid orbitals or electron domains

Compared with the study described in the second paragraph, the proposed follow-up study should demonstrate: A.less internal and external validity.(0%) B.less internal validity but greater external validity.(8%) C.greater internal validity but less external validity.(47%) D.greater internal and external validity.(42%)

In general, as a study becomes more tightly controlled and confounding variables are limited, internal validity tends to increase but external validity tends to decrease. Internal validity is mostly concerned with causality, or the extent to which changes in the dependent variable can be attributed to changes in the independent variable. The presence of confounding variables, which are additional variables that might influence results or outcomes, decreases internal validity by introducing the possibility that results are attributable to a confounding variable and not to the independent variable of interest. External validity is mostly concerned with generalizability, or the extent to which results can be applied to other situations (eg, outside the laboratory) or beyond the sample to the larger population. Allowing participants a single night's sleep at home introduces many variables not controlled by the study, such as time of sleep onset, quality of sleep, and duration of sleep. Standardizing the timing and duration of sleep by having participants sleep in a sleep lab creates an unnatural sleeping environment for the subjects. Therefore, the proposed follow-up study should demonstrate greater internal validity, because there should be fewer confounding variables, but less external validity, because the findings will be less applicable to a population with a more natural sleep experience. (Choices A and B) If the researchers repeat the study and better control for sleep onset and duration, this will result in greater (not less) internal validity. (Choice D) Limiting confounding variables occurring in real life decreases the external validity of a study. Educational objective:Internal validity measures the extent to which a causal relationship can be concluded from the study, and external validity measures the extent to which the study results can be generalized beyond the study. Typically, increases in internal validity result in decreases in external validity, and vice versa.

The graph below shows the firing rate of preganglionic neurons within the rat gustatory-salivary reflex arc when the lateral hypothalamic area (LHA) is electrically stimulated at various time intervals before the tongue is stimulated. The results are compared to the preganglionic firing rate following tongue-only stimulation, which was used as a baseline that represented 100% activity. The results of this experiment indicate that at shorter time intervals: A.LHA signaling has no effect on the magnitude of salivation of the reflex.(3%) B.LHA signaling increases the magnitude of salivation of the reflex.(74%) C.LHA signaling decreases the magnitude of salivation of the reflex.(12%) D.There is not enough data to determine the effect of LHA signaling on the reflex.(10%)

In this scenario, researchers are trying to determine whether the lateral hypothalamic area (LHA) of the brain modulates the gustatory-salivary reflex response and, if it does, whether that modulation results in a diminished or enhanced reflex. First, the researchers measured baseline activity in the preganglionic fiber of the gustatory-salivary parasympathetic reflex pathway, which was represented by the firing rate of the preganglionic fiber in response to tongue stimulation alone. The researchers then measured the activity of the fiber in response to sequential stimulation of the LHA and the tongue such that the LHA was stimulated at various time intervals before the tongue. According to the data, the preganglionic fiber responded to this sequential stimulation by exhibiting greater activity at shorter time intervals. This effect was most pronounced when the LHA was stimulated shortly prior to the tongue (<100 msec). The effect weakened as more time elapsed between LHA stimulation and tongue stimulation, and the firing rate of the fiber returned to baseline at a time difference of approximately 200 msec. Therefore, properly timed LHA signaling, which increases the activity of the preganglionic fiber of the gustatory-salivary pathway, would be expected to increase the quantity of salivation due to this reflex pathway. (Choice A) The graph demonstrates a clear relationship between sequential LHA-tongue stimulation and the amount of activity within preganglionic fibers. (Choice C) According to the passage, activation of the gustatory-salivary reflex arc (including the preganglionic fibers that are part of this pathway) results in salivation. Therefore, enhanced activity along this pathway would be expected to increase, not decrease, the magnitude of salivation. (Choice D) The graph indicates that signaling from the LHA affects the gustatory-salivary reflex, which is known to influence the amount of salivation. This suggests that salivation is likely responsive to stimulation of the LHA. Educational objective:Input from higher areas in the central nervous system can modulate the activity of reflexes by either strengthening or weakening the magnitude of the response.

Based on the reaction in the passage, what are the charges of the oxalate and citrate ions, respectively? A.−1, −3(6%) B.−2, −2(8%) C.−2, −3(74%) D.−3, −2(11%)

Ionic bonds form between positively charged and negatively charged ions such that both positive and negative charges are neutralized. If the charges of the cations are known, the charges of the anions can be determined by balancing the charges. The arrangement of the periodic table indicates charges that atoms are likely to adopt. Metals in the first column of the periodic table, including potassium, ionize by losing one electron; potassium has a charge of +1. Metals in the second column, such as calcium, lose two electrons and have a +2 charge. The reaction in the passage shows that one calcium ion is neutralized by one oxalate ion, and three potassium ions are neutralized by one citrate ion. Therefore, oxalate must have a charge of −2 and citrate a charge of −3 to neutralize their respective cations. (Choice A) As a second column element, calcium acquires a +2 charge. Therefore, a single calcium cation can be neutralized by a single anion such as oxalate only if that anion has a charge of −2. (Choice B) Citrate is neutralized by three potassium ions, each of which has a +1 charge. Therefore, citrate must have a charge of −3. (Choice D) This option reverses the charges of oxalate and citrate. Educational objective:Ionic bonds form when positive charges neutralize negative charges. One ion may carry multiple charges, and must be neutralized by the same number of opposite charges.

Which of the following sequences accurately describes the pathway of communication between neurons? A.Axon, soma, dendrite, synapse(10%) B.Axon, synapse, dendrite, soma(57%) C.Dendrite, axon, soma, synapse(15%) D.Synapse, soma, axon, dendrite(16%)

Neurons are cells that receive, integrate, and transmit information in the nervous system. Communication between neurons involves an electrochemical process in which electric signals are converted to chemical signals, and vice versa, as they travel from the pre-synaptic to post-synaptic neuron. An electric signal in the pre-synaptic neuron travels down a thin nerve fiber called an axon which conducts the signal to the axon terminals. From there, chemical messengers called neurotransmitters are released into the synaptic cleft (synapse), the region between the axon terminals and the dendrites of the next neuron. Neurotransmitters bind to receptors on the dendrites of the post-synaptic neuron, altering the electric potential of the cell. Lastly, the change in electric potential spreads to the cell body (soma). The information transmitted from the pre-synaptic to post-synaptic neuron can have either an excitatory or inhibitory effect, increasing or decreasing the likelihood of the signal being transmitted, respectively. If the summed excitatory and inhibitory signals exceed a certain threshold in the post-synaptic neuron, the electric signal is transmitted down the axon and the cycle continues as this neuron communicates with the next neuron. Educational objective:The electric signal from the axon of the pre-synaptic neuron is converted to the release of neurotransmitters into the synaptic cleft between neurons. Neurotransmitters then bind to receptors on post-synaptic dendrites, changing the electric potential of the cell.

The assertion made in the first paragraph of the passage would be best supported by a study demonstrating that: A.positive impression management strategies implemented by physicians correspond to increased patient trust.(39%) B.front- and backstage behaviors of hospital patients do not correlate with length of hospital stay.(2%) C.nonverbal communication between patient and physician is a better predictor of patient outcomes than verbal communication.(43%) D.patients are more likely to make assumptions about their physicians based on salient social roles than on attire.(15%)

Nonverbal communication involves all of the wordless cues that convey meaning when exchanged between individuals. Some examples of nonverbal communication cues include distance between speakers, body language and other physical movements, facial expressions, and vocal modifications (tone, volume, emphasis, inflection). Research suggests that social interaction is largely influenced by nonverbal communication. The first paragraph asserts that physicians make assumptions about their patients, which impacts patient care and outcomes. A study showing that nonverbal communication between patient and physician is a better predictor of patient outcomes than verbal communication (the actual words spoken) would best support this assertion because the interpretation of nonverbal cues involves making assumptions. (Choice A) Impression management involves all of the conscious and unconscious ways that individuals try to present themselves to others including appearance, speech, and behavior. Impression management strategies implemented by physicians relate to the passage study, not to the assertion made in the first paragraph. (Choice B) Stemming from symbolic interactionism, dramaturgy is a social theory proposing that individuals behave as actors: front-stage behaviors occur in front of others and align with social norms whereas backstage behaviors occur when an individual is alone and can relax and be him- or herself. According to the assertion made in the first paragraph, front-stage behaviors should correlate with length of hospital stay. (Choice D) The assumptions made by patients about their doctors based on social roles (eg, race, gender) rather than attire directly support the study, not the assertion made in the first paragraph. Educational objective:Nonverbal communication includes all of the wordless cues meant to convey meaning, such as vocal inflections, volume, body language, and facial expressions.

During Task 1, the researcher found that subjects' response time was slower and color identification accuracy was worse during the natural condition. Which of the following best accounts for this finding? A.Color and motion are processed simultaneously.(43%) B.Color information is processed slower than motion.(30%) C.Motion is processed in the retina whereas color is processed in the occipital lobe.(6%) D.Color and motion information are transmitted to the brain via the same pathway.(18%)

Parallel processing describes the brain's ability to simultaneously process the various components of visual stimuli. Information from the retina is transmitted to the primary visual cortex (V1) of the occipital lobe via two separate pathways, which are named according to where they project in the lateral geniculate nucleus (LGN), the region of the thalamus that receives visual input. The parvo pathway travels from the retina to the ventral (lower) layers of the LGN, then to the V1, and eventually to the ventral brain regions. This pathway, known as the "what" pathway, is responsible for the perception of finer detail, such as form and color. The magno pathway travels from the retina to the dorsal (upper) layers of the LGN, then to the V1, and eventually to the dorsal brain regions. This pathway, known as the "where" pathway, is responsible for the perception of coarser detail, such as depth and motion. Color and motion are processed simultaneously via two different pathways. The artificial condition involved identifying the color of a fixed, nonmoving object, which required processing of only one component (color), whereas the natural condition required the simultaneous processing of two components, motion and color. Therefore, subjects' response time and accuracy should be worse during the natural condition. (Choice B) Information about color (parvo pathway) and motion (magno pathway) is processed simultaneously via two different pathways. One is not processed faster than the other. (Choice C) Detection refers to the recognition of the stimulus (eg, light wavelengths); processing involves making sense of the information. Both color and motion are detected by cells in the retina and processed by the occipital lobe. Cones detect information about color whereas specialized cells in the retina (eg, amacrine cells) detect information about motion and transfer that information to the occipital lobe for processing. (Choice D) Color and motion information are both transmitted to the brain via different pathways. Color is transmitted via the parvo pathway and motion is transmitted via the magno pathway. Educational objective:Parallel processing is the cognitive ability to process color, form, motion, and depth simultaneously. Color and form are processed by the parvo pathway; motion and depth are processed by the magno pathway.

Two separate reactions are conducted in which a compound containing a ketone, an ester, and a carboxylic acid is reacted with borane (BH3) in THF in one reaction and with NaBH4 in methanol in the other. Which of the following explains why different products are observed? A.BH3 will selectively reduce ketones, and NaBH4 will only reduce carboxylic acids.(24%) B.BH3 does not reduce ketones, and NaBH4 will selectively reduce esters.(13%) C.BH3 reduces carboxylic acids and esters, and NaBH4 will only reduce esters.(13%) D.BH3 will selectively reduce carboxylic acids, and NaBH4 will selectively reduce ketones.(48%)

Reduction of a functional group results in a gain of electrons from the transfer of a hydride, a decreased oxidation state of carbon, and a decreased number of C-O bonds. Several reagents can be used to reduce a functional group, including borane (BH3) and NaBH4. These reducing agents transfer one or more hydrides to the carbon atom being reduced. BH3 reacts most readily with carboxylic acid carbonyl groups and therefore will selectively reduce carboxylic acids. As a result, the intermediate aldehyde will be further reduced to a primary alcohol. NaBH4 reduces the reactive carbonyls—ketones and aldehydes—and will not reduce the less reactive esters and carboxylic acids. If a compound that contains a ketone, an ester, and a carboxylic acid is reacted with BH3, the carboxylic acid will be selectively reduced to a primary alcohol, leaving the ketone and ester intact. When the same compound is reacted with NaBH4, only the ketone will be reduced, generating a secondary alcohol. Therefore, the products of the two reactions will be different. (Choice A) BH3 and NaBH4 are both reducing agents, but BH3 selectively reduces carboxylic acids rather than ketones, and NaBH4 is not strong enough to reduce carboxylic acids. NaBH4 selectively reduces ketones and aldehydes. (Choice B) Although it is true that BH3 does not reduce ketones, NaBH4 does not reduce esters. (Choice C) Esters cannot be reduced by BH3 or NaBH4; this functional group can only be reduced to a primary alcohol by LiAlH4. Educational objective:Carboxylic acids can be selectively reduced to primary alcohols by the reducing agent BH3. They cannot be reduced by NaBH4, which is selective for the reactive carbonyls ketones and aldehydes.

The gustatory-salivary reflex can be modulated (dampened or enhanced) by input from higher centers in the central nervous system. To modulate the salivary response, descending pathways from the brain would most likely synapse onto which part of the reflex arc? A.The taste receptor(5%) B.The salivary gland(17%) C.The preganglionic neuron(38%) D.The postganglionic neuron(38%)

Reflexes are involuntary responses to stimuli that do not require input from the brain. A reflex arc is the specific neuronal pathway that facilitates the direct muscular or glandular effect associated with a particular reflex. Reflex arcs begin with the stimulation of a sensory neuron, which leads to an electrical impulse that travels toward the spine along a sensory nerve. This impulse enters the spine via the dorsal root ganglia and can be transmitted in one of two ways: Directly to the effector neuron (ie, a monosynaptic reflex arc), or Indirectly through an interneuron that interfaces with the effector neuron (ie, a polysynaptic reflex arc) Subsequently, electrical impulses initiated in the effector neuron leave the spinal cord through the ventral root and travel along the effector neuron's axon to synapse with and stimulate a muscle fiber, gland, or ganglionic neuron. When the effector neuron synapses with a muscle fiber, it is referred to as a motor neuron. Reflexes can be modulated (dampened or enhanced) by input from the brain. Descending signals from higher areas in the central nervous system (CNS) travel along spinal tracts to act on neurons in the reflex arc whose cell bodies lie within the spine. Based on the gustatory-salivary reflex arc depicted in Figure 1, the cell bodies of both the interneuron and the preganglionic neuron lie within the spine. Therefore, descending input could act on either of these two neurons to alter the gustatory-salivary reflex. (Choices A and B) The taste receptor and salivary glands lie outside the spine (the tongue and oral cavity, respectively) and would not receive direct input from higher CNS areas. (Choice D) By definition, a ganglion is a collection of neuron cell bodies outside the CNS. The cell body of the postganglionic neuron lies within this ganglion, not the spine. A nucleus is a collection of neuron cell bodies inside the CNS. Educational objective:A reflex is an involuntary response to a stimulus that does not require input from the brain. Reflexes are mediated by reflex arcs, neuronal pathways that include a sensory neuron, an effector neuron, and possibly an interneuron.

Which of the following are true concerning the overall reaction in an aqueous environment? The rate constant increases exponentially with increasing temperature. The rate constant increases exponentially with decreasing activation energy. The reaction rate decreases exponentially with increasing activation energy. The rate constant of the catalyzed reaction will be smaller than the rate constant of the uncatalyzed reaction. A.I and II only(18%) B.I, II, and III only(58%) C.II and IV only(11%) D.I, III, and IV only(12%)

The Arrhenius equationk=Ae-EaRTk=Ae-EaRT relates the rate constant k of a reaction with its activation energy and temperature. The negative exponent in the equation can be rewritten with the exponential term eEaRTeEaRT in the denominator as k=AeEaRTk=AeEaRT . Increasing the temperature of a reaction gives a smaller value of the exponential term. Because it is in the denominator, a smaller exponential term gives an increased value for k (Number I). Decreasing the activation energy Ea also gives a smaller exponential term, and therefore k increases exponentially with decreasing Ea (Number II). Conversely, k decreases exponentially with increasing Ea. According to the rate law equation, the rate of a given reaction is directly proportional to the rate constant. Therefore, the reaction rate also decreases exponentially with increasing Ea (Number III). (Number IV) Catalysts lower the value of Ea of reactions, and therefore an uncatalyzed reaction has a higher Ea than the catalyzed reaction. Because uncatalyzed reactions have a higher Ea, the reaction has a decreased rate constant with respect to the rate constant of the catalyzed reaction. Educational objective:The Arrhenius equation describes the relationship between the rate constant and the temperature and activation energy of a reaction. Both the rate constant and the rate of reaction decay exponentially with increasing activation energy and increase exponentially with increasing temperature. Because catalysts lower the activation energy of a reaction, the rate constant is greater for a catalyzed reaction than for an uncatalyzed reaction.

The innovative strategies employed by PD villagers and bright spotters suggest an ability to overcome all of the following, EXCEPT: A.mental set.(2%) B.confirmation bias.(14%) C.functional fixedness.(4%) D.the Hawthorne effect.(78%)

The Hawthorne effect, which describes when research subjects behave differently as a result of knowing that they are being observed, does not describe an obstacle that PD villagers and bright spotters overcome when developing their innovative problem-solving strategies. Problem solving describes the mental processes involved in trying to accomplish a goal that has an unknown solution. Common barriers to effective problem solving include mental set, confirmation bias, and functional fixedness. (Choice A) Mental set describes when a problem solver gets stuck on a method that worked in the past but is not right for the current problem. Most villagers were feeding their children as they had always done (eg, certain foods, twice a day), even though this method resulted in malnutrition. Innovative PD strategies involve new methods (eg, feeding children more often), which overcomes a mental set. (Choice B) Confirmation bias occurs when a problem solver selectively prefers information that confirms an already held belief or ignores evidence refuting the belief. The more entrenched the belief, the more susceptible it is to confirmation bias. Although most patients tend to ignore information about alternatives for controlling their illness (confirmation bias), bright spotters overcome confirmation bias by implementing innovative tactics. (Choice C) Functional fixedness prevents a problem solver from conceiving different uses or functions for an object. Using the edge of a coin to tighten a screw is an example of overcoming functional fixedness to solve a problem. Similarly, eating sweet potato plant leaves, not considered "food" by the rest of the villagers, suggests an ability to overcome functional fixedness. Educational objective:The mental processes required to accomplish a goal with an unknown solution are known as problem solving. Common barriers to problem solving include applying an old technique to a new problem (mental set), a focus only on information that supports a prior belief (confirmation bias), and an inability to see innovative uses for an object (functional fixedness).

The image below shows a population of unicellular organisms. In each organism, the shaded mitochondria express a deleterious mutant allele of a mitochondrial gene, and the nonshaded mitochondria express the wild-type allele of that same gene. Which of the following events most likely occurred between Generation 1 and Generation 2? A.Meiosis(9%) B.Population bottleneck(58%) C.Natural selection(24%) D.New mutation(6%)

The bottleneck effect is the drastic reduction in population size that occurs in response to some sudden and uncontrollable disaster (eg, flood, famine, human-induced catastrophe). In a bottleneck event, no genotype or phenotype is protective, and members of the population are eliminated randomly. This substantially alters the genetic diversity and allele frequencies of the population in a way that doesn't necessarily follow the principles of natural selection (where organisms with beneficial alleles are more likely to survive). For example, an allele can be eliminated completely from the gene pool if no members carrying that allele survive. Likewise, rare mutant alleles can become more prevalent than wild-type alleles if most members carrying the mutant allele survive and most carrying the wild-type allele do not. In this way, a bottleneck event may allow a deleterious mutant allele (such as that found in the shaded mitochondria) to become more prevalent in the population than the wild-type allele (such as that found in the nonshaded mitochondria) (Choice B). (Choice A) Meiosis is a specialized type of cell division that reduces the chromosome number of diploid parent cells by half to generate four genetically distinct haploid gamete cells. If meiosis had occurred in this scenario, Generation 1 would have generated 16 haploid cells in Generation 2. (Choice C) In natural selection, alleles that produce environmentally beneficial phenotypes are more likely to be selected for and passed on to the next generation than alleles that are harmful. In this scenario, only organisms that primarily express the deleterious mutant mtDNA survived and reproduced, a result opposite of what would be expected had natural selection occurred. (Choice D) A mutation is described as a permanent, heritable change in the gene sequence. Generation 2 contains the same mitochondrial alleles as Generation 1 (shaded and nonshaded), meaning no new mutation was generated. Educational objective:Natural selection is the tendency for alleles that make an organism better suited for survival and reproduction to be passed along to the next generation. Bottleneck events reduce genetic diversity and change the allele frequencies of a population in a random way.

Given that entropy is negative (disorder decreases) in the reaction, which of the following statements is true regarding the formation of aqueous nitrotyrosine? A.The formation of nitrotyrosine is less thermodynamically favorable than the formation of ROI at 298.15 K. (14%) B.The overall reaction becomes more thermodynamically favorable at higher temperatures.(21%) C.Neither the formation of ROI nor nitrotyrosine is thermodynamically favorable at 298.15 K.(5%) D.The overall reaction becomes less thermodynamically favorable at higher temperatures.(57%)

The change in Gibbs free energy ΔG of a process occurring at constant temperature and pressure is calculated from two state functions: the changes in enthalpy ΔH and entropy ΔS of a system. Gibbs free energy determines the process's spontaneity. A spontaneous process has a negative value for ΔG and is said to be thermodynamically favorable; a nonspontaneous process is the opposite. According to the equation ΔG = ΔH − TΔS the sign of the change in ΔS for a process determines whether the process becomes more or less thermodynamically favorable as the temperature increases. A negative ΔS causes ΔG to increase with temperature, whereas a positive ΔS causes ΔG to decrease with temperature. Table 1 shows that the changes in enthalpy and entropy for the reaction are both negative. Therefore, increasing the temperature leads to an increasingly greater (more positive) ΔG as shown by the above equation, making it less thermodynamically favorable at higher temperatures. (Choice A) The formation of nitrotyrosine is more thermodynamically favorable than the formation of ROI at 298.15 K because the ΔG = −85.9 kJ/mol for the formation of ROI (step 1), but ΔG = −85.9 + (−13.1) = −99.0 kJ/mol for the formation of nitrotyrosine (step 1 + step 2). (Choice B) The reaction becomes less thermodynamically favorable at higher temperatures because ΔS is negative for this reaction, causing an increase in ΔG as the temperature rises. High ΔG values correspond to thermodynamically unfavorable processes. (Choice C) The production of both ROI and nitrotyrosine are thermodynamically favorable at 298.15 K because they both have negative ΔG terms. Educational objective:The Gibbs free energy ΔG equation is used to determine the spontaneity of a system, where negative ΔG is spontaneous and positive ΔG is nonspontaneous. The sign of the change in entropy ΔS for a process determines whether it becomes more or less thermodynamically favorable (ie, spontaneous) as the temperature changes.

According to the elaboration likelihood model, which of the following should generate the most concern about the risks of contracting hepatitis C in the two-uncommon-behaviors group from Study 2? A television commercial showing: A.text detailing the scientific facts about contracting hepatitis C.(5%) B.actual drug addicts sharing needles.(16%) C.an attractive celebrity using a catchy phrase to summarize the main hepatitis C risk factors.(45%) D.a medical expert from a prestigious university summarizing the main hepatitis C risk factors.(32%)

The elaboration likelihood model of persuasion describes two routes by which a message can cause attitude change in the receiver (the person for whom the message was intended). Either route can result in persuasion, but the central route is more effective when people are willing and able to pay attention to the facts, whereas the peripheral route is more effective when people are not paying close attention to the content of the message. The central route of processing occurs when the message characteristics engage the receiver in a deep, meaningful way, often through the use of a well-reasoned argument emphasizing the logical content of the message. The peripheral route of processing occurs when the message characteristics engage the receiver in a more superficial way, often through methods that do not require a great deal of thought. According to the elaboration likelihood model, the most persuasive strategy for people who have low motivation and/or ability to process the message (such as the uncommon behaviors groups in Study 2) is to use the peripheral route of processing. Therefore, a television commercial with an attractive celebrity using a catchy phrase to summarize the main hepatitis C risk factors would be the best way to structure a persuasive health message about hepatitis C to this group. (Choices A and D) Detailed scientific facts and information presented by experts rely on the central route of processing, which is most effective for receivers who are highly motivated by the message. The results of Study 2 suggest that the uncommon behaviors groups are not highly concerned about contracting hepatitis C. (Choice B) Needle sharing is an uncommon behavior; therefore, it does not appear to increase the concern for contracting hepatitis C as much as information regarding how common behaviors can spread the disease. Educational objective:The elaboration likelihood model defines two routes of persuasion: The central route (focusing on the logical content of the message) is most effective when the audience is motivated by the message, whereas the peripheral route (focusing on superficial characteristics of the message) is more effective when people are not motivated by the message.

If researchers repeated the analyses using F2 generation mice, spleen cell cultures exposed to SRC plus 1.0 μg Ph-LPS would be expected to have anti-SRC titers of: 1600 1200 800 A.II only(15%) B.I and II only(15%) C.I and III only(10%) D.I, II, and III(58%)

The experiment describes a monohybrid cross, or a mating between individuals with different alleles at one genetic locus. The first cross is performed between homozygous He-N [tlr4(+)/tlr4(+)] and He-J mice [tlr4(d)/tlr4(d)], members of the parental or P generation, and produces a heterozygous F1 generation [tlr4(+)/tlr4(d)]. The second cross would be performed between members of the F1 generation and would produce an F2 generation with a mix of genotypes. Depending on the genotype, some F2 offspring would be phenotypically similar to members of the P generation whereas some F2 offspring would resemble members of the F1 generation. For instance, expected F2 genotypes can be used to deduce anti-SRC titers when spleen cell cultures are exposed to SRC plus 1.0 μg Ph-LPS: tlr4(+)/tlr4(+): An estimated 25% of F2 mice would be homozygous for the normal functioning Tlr4 allele. These mice would have an immune response similar to that seen in He-N mice. According to Table 1, this corresponds to an antibody titer of 1605 ± 55 (Number I). tlr4(+)/tlr4(d): An estimated 50% of mice would be heterozygous for the Tlr4 gene mutation. These mice would have an immune response similar to F1 generation mice, or an antibody titer of 1240 ± 58 (Number II). tlr4(d)/tlr4(d): An estimated 25% of mice would be homozygous for the Tlr4 gene mutation. These mice would have an immune response similar to He-J mice, or an antibody titer of 810 ± 17 (Number III). Educational objective:In a monohybrid cross, members of the P generation are homozygous for different alleles at one locus. The first cross produces heterozygous offspring in the F1 generation. The second cross produces a mix of genotypes and phenotypes observed in members of the F2 generation.

The foot-in-the-door phenomenon predicts that: A.individuals who have just taken a hepatitis C blood test would be the most likely to agree to participate in Study 2.(7%) B.if the Study 2 researchers first ask individuals to take a hepatitis C blood test, those who decline will be more likely to participate in the research study.(2%) C.more participants in Study 2 would be willing to take a hepatitis C blood test than participants in Study 1.(4%) D.after agreeing to participate in Study 2, individuals would be more likely to agree to a request to take a hepatitis C blood test.(86%)

The foot-in-the-door strategy is a compliance technique (meant to persuade someone to act) that involves first asking a small favor of someone, something that is easy to do and requires little effort or expense (eg, participation in a research study). Once the small favor is granted, a much larger favor (eg, taking a hepatitis C blood test) is requested. The foot-in-the-door phenomenon can be explained by the fact that behavior influences attitude: granting a small favor causes the individual to have a more positive attitude toward the person just helped, increasing the likelihood that the individual will agree to the larger favor. (Choice A) Agreeing to a big favor first and then a smaller favor is the opposite of the foot-in-the-door phenomenon. (Choice B) The door-in-the-face phenomenon predicts that an individual declining a big request (taking a hepatitis C blood test) will be more likely to comply with a subsequent request that is much smaller (participating in the research study). (Choice C) There is nothing about the foot-in-the-door phenomenon to suggest that the participants in Study 2 would be more agreeable to taking a hepatitis C test than those in Study 1 as the relative difficulties of the tasks in both studies were approximately the same. Educational objective:The foot-in-the-door phenomenon predicts that people are more likely to comply with a big request after they have already complied with a small request. This can be explained by a change in attitude: people tend to have more favorable attitudes toward those they have just helped, increasing the likelihood they will agree to the larger request.

The experiments allowed researchers to determine the effect of genotype variation on all of the following EXCEPT: A.in vitro versus in vivo studies.(12%) B.innate versus adaptive immune responses.(38%) C.responses modulated by LPS exposure.(2%) D.qualitative and quantitative phenotypic traits.(46%)

The innate and adaptive immune systems are two subdivisions of immune defense: The innate immune system consists of cells poised to attack antigens in a nonspecific manner. These cells include macrophages, dendritic cells, natural killer cells, and granulocytes. This system responds to foreign antigens within minutes to hours and can recognize unique and common motifs present on pathogens. The adaptive immune system contributes specialized or acquired immunity based on learned recognition of specific antigens. Responses of adaptive immune system can be further subdivided into cell-mediated and humoral immunity:In cell-mediated immunity, mainly driven by T cells, receptors on immune cells recognize and bind directly to receptors on target cells.In humoral immunity, B cells produce antibodies specific to a new antigen (primary immune response). These antibodies enable the immune system to respond more quickly if the antigen is encountered later (secondary immune response). In these experiments, antibody and interferon levels were used as markers of immune response. Although antibody production is specific to the adaptive immune response, interferons represent a large class of signaling molecules that act in both the innate and adaptive immune systems. Because none of the experiments are specific to innate immunity, researchers would not be able to differentiate the influence of genotype on innate versus adaptive immune response. (Choice A) Experiment 1 represents an in vitro study, as spleen cells were exposed to LPS and antigen after removal from mice. In contrast, Experiments 2 and 3 were in vivo studies performed on live mice. (Choice C) Experiment 1 allowed researchers to examine the effect of LPS exposure on antibody responses to foreign antigens and to compare these effects among mice with different genotypes. (Choice D) Researchers examined both quantitative phenotypic effects (antibody and interferon levels) and qualitative phenotypic effects (protein expression observed by protein electrophoresis). Educational objective:The innate immune system is a nonspecific system that responds within minutes to hours to foreign antigens. The adaptive immune system is based on learned recognition of specific antigens and can be subdivided into cell-mediated (T cells) and humoral (B cells) immunity. Antibodies are specific to humoral immunity whereas interferons play roles in both innate and adaptive immunity.

Ozone (O3) in the atmosphere protects against harmful UV radiation. The overall reaction for ozone formation is 3O2 → 2O3 and proceeds in two steps. Step 1 is initiated when molecular oxygen (O2) absorbs UV light and splits into two oxygen atoms: O2→ 2O Which of the following second steps would yield the net reaction for ozone formation? A.O + O2 → O3(11%) B.2O + 2O2 → 2O3(71%) C.O2 + 2O → 2O3(13%) D.O + 2O2 → O3(3%)

The law of conservation of mass says that in a chemical reaction, atoms are neither created nor destroyed: they can only be rearranged. Therefore, in any chemical reaction the same number of each type of atom must be present on the left and right sides of the reaction arrow. Reactions may proceed in multiple steps, producing intermediates along the way. If the reaction goes to completion (the maximum possible amount of product is formed), all intermediate species must be consumed in subsequent steps to form the final products. In the formation of ozone (O3), first, one molecule of oxygen (O2) is split into two oxygen atoms as intermediates (O2 → 2O). The oxygen atoms are then consumed as each reacts with an oxygen molecule to form ozone. For the reaction to go to completion, the two oxygen atoms must combine with two O2 molecules to form two ozone molecules (2O + 2O2→ 2O3) in the second step. This yields the net reaction 3O2 → 2O3. (Choice A) O + O2 → O3 correctly shows the reaction of one oxygen atom with one O2 molecule to form one ozone molecule. However, if this were the second step it would not yield the correct net reaction. Instead, the resulting net reaction would be 2O2 → O3 + O. (Choice C) O2 + 2O → 2O3 has four oxygen atoms on the left and 6 oxygen atoms on the right, so it is unbalanced. If it were the second step, the resulting net reaction would be 2O2 → 2O3, which is also unbalanced. (Choice D) O + 2O2 → O3 has five oxygen atoms on the left side and only three on the right, leaving two oxygen atoms unaccounted for. If it were the second step, the resulting net reaction would be 3O2 → O3, which is unbalanced. Educational objective: According to the law of conservation of mass, atoms are neither created nor destroyed in a chemical reaction. The same number of each type of atom must be present on both the left and right sides of a reaction arrow. Multistep reactions that go to completion must consume all intermediates produced before or during the final step.

Researchers have identified a set of factors associated with an increased risk of developing chronic obstructive pulmonary disease, including low birth weight, respiratory infections before age 2, low socioeconomic status in childhood, adolescent smoking, and occupational exposure to airborne irritants as an adult. This finding best reflects: A.the sick role theory approach.(1%) B.the illness experience perspective.(4%) C.the social construction of chronic disease.(27%) D.the life course approach to illness.(65%)

The life course approach is a holistic, multidisciplinary framework for understanding how psychological, biological, and sociocultural factors across a lifetime have a cumulative effect on health outcomes. This perspective considers how personal life events (eg, illness in infancy), individual choices/behaviors (eg, having unprotected sex), and sociocultural and historical context (eg, being born during wartime) impact health and illness. Research suggesting that lifetime exposure to biological (eg, respiratory infections), sociocultural (eg, low socioeconomic status), and behavioral (eg, smoking) risk factors increases the likelihood of developing chronic obstructive pulmonary disease (COPD) is most reflective of the life course approach to illness. (Choice A) Sick role theory is a functionalist approach describing how disruption to typical social activity (eg, work) caused by illness is minimized through the sick role, which legitimizes illness as socially acceptable deviance. Biological and sociocultural factors impacting health/illness across a lifetime are not relevant to sick role theory. (Choice B) The illness experience is a symbolic interactionist approach to understanding how people incorporate and make sense of illness as part of their self-identity and daily routines. The illness experience is not best reflected by evidence that biological and sociocultural factors impact health/illness across a lifetime. (Choice C) Social constructionism suggests that social reality is created through interpersonal interactions, which result in shared meanings and expected roles/behaviors. The social construction of chronic illness would not be concerned with the cumulative impact of factors across a lifetime contributing to risk of chronic illness. Educational objective:The life course approach to illness is holistic and multidisciplinary, examining the cumulative effect of psychological, biological, and sociocultural factors across a lifetime on health outcomes.

Which of the following conclusions is supported by these data reflecting the relationship between cigarette craving and smoking behavior before and after MT intervention? A.Before beginning MT intervention, high levels of craving caused an increase in smoking behavior.(20%) B.A significant difference in smoking behavior was observed before and after MT intervention.(6%) C.A significant difference in cigarette craving was observed before and after MT intervention.(6%) D.The relationship between craving and smoking was weaker after the MT intervention.(66%)

The linear relationship between two variables can be described by calculating the Pearson correlation coefficient r. The value of r ranges from −1 to 1 and indicates the strength of the linear relationship between two variables. A negative correlation (r < 0) means as one variable increases, the other decreases. A positive correlation (r > 0) means both variables increase or decrease together. At baseline, a strong positive correlation exists between craving and smoking (r = 0.72), and the relationship is statistically significant (p = 0.0013). After the MT intervention, the correlation is very weak (r = 0.13) and not statistically significant (p = 0.4611). Therefore, there is a weaker relationship between craving and smoking at the end of treatment. Correlation does not imply causation. A large r-value does not indicate whether the increase or decrease in one variable causes the increase or decrease in the second variable. Changes in either variable may be caused by other factors. Therefore, it is not possible to conclude that craving caused increased smoking (Choice A). (Choices B and C) In the data shown, no direct comparison of smoking behavior or cigarette smoking is found at baseline versus the end of treatment. In fact, no p-value directly compares these groups by any measure; therefore, no statistically significant relationship can be stated. Educational objective:The correlation coefficient r measures the strength of a linear relationship between two variables. Correlations can be positive or negative, and the strength of a correlation increases as the absolute value of r approaches 1. Correlation does not imply causation.

The gustatory-salivary reflex pathway is part of which of the following branches of the nervous system? Peripheral Somatic Autonomic A.I and II only(4%) B.I and III only(67%) C.III only(20%) D.I, II, and III(8%)

The nervous system is responsible for the control and integration of all body systems by receiving and processing information from the external environment and coordinating purposeful reactions to that incoming information. The nervous system can be broadly divided into two major components, the central and peripheral nervous systems. The central nervous system (CNS) is responsible for the integration of information and includes nuclei (bundles of cell bodies) and tracts (bundles of axons) within the brain and spinal cord. In contrast, the peripheral nervous system (PNS) is composed of a sensory division and a motor division. The sensory (afferent) division functions to carry sensory impulses toward the CNS whereas the motor (efferent) division carries motor impulses away from the CNS. The PNS includes ganglia (bundles of cell bodies) and nerves (bundles of axons) that lie outside the CNS. The motor division of the PNS can be further divided into the somatic and autonomic nervous systems. The somatic nervous system (SNS) activates voluntary skeletal muscle responses, and the autonomic nervous system (ANS) activates involuntary smooth muscle, cardiac muscle, and glandular responses. Finally, the ANS is composed of the sympathetic and parasympathetic divisions. These two systems are considered antagonistic because they promote opposing effects. The passage states that the gustatory-salivary reflex is part of the parasympathetic division of the nervous system. Therefore, the gustatory-salivary reflex is also part of the peripheral and autonomic branches of the nervous system (Numbers I and III). (Number II) The SNS mediates skeletal muscle movement. The gustatory-salivary reflex pathway does not modulate target tissue activity through skeletal muscle. Educational objective:The nervous system can be divided into two major branches, the central and peripheral nervous systems. The peripheral nervous system can be further divided into the sensory (afferent) and motor (efferent) divisions, with the motor division being composed of the somatic and autonomic nervous systems. Furthermore, the autonomic nervous system is divided into the parasympathetic and sympathetic branches.

Based on the information given in Table 1, the results of this examination may be explained by all of the following EXCEPT: A.moderate hearing loss is influenced by autosomal recessivity at the 3243 locus.(39%) B.severe hearing loss is influenced by a single nucleotide mutation.(19%) C.the mutant tRNAleu gene causes variable expressivity of the phenotype.(27%) D.the mutant tRNAleu gene exhibits incomplete penetrance.(14%)

The passage states that family members tested in this study carry no other genetic mutations known to affect hearing loss. Therefore, in these subjects, only the A→G single nucleotide mutation in the 3243 tRNAleu gene locus of mtDNA influences hearing loss, which ranges from mild to severe (Choice B). The results of the audiometry examination, as shown in Table 1, support that this A→G mutation leads to variable expressivity and incomplete penetrance of the hearing phenotype: Variable expressivity refers to the ability of a single genotype to give rise to multiple phenotypes. In the context of disease, two patients with the same mutated allele may exhibit markedly different clinical symptoms. The A3243G mutation is a prime example of variable expressivity because as described in the passage, individuals with the mutation exhibit variable phenotypes such as mild to severe degrees of hearing loss (Choice C), diabetes mellitus, lactic acidosis, and strokelike episodes. Penetrance is defined as the proportion of individuals with a genotype who express the corresponding phenotype. When every individual with a specific genotype displays the associated phenotype, the allele is said to show complete penetrance. When all individuals have the same genotype but only some express the corresponding phenotype, the disease is said to show incomplete penetrance (eg, not all patients with the A3243G mtDNA mutation exhibit hearing loss, as shown in Table 1) (Choice D). (Choice A) In both male and female offspring, mitochondrial DNA (and any associated mitochondrial disease) is inherited only from the mother, meaning mitochondrial genes do not follow Mendelian inheritance patterns, which occur when organisms inherit two copies of each gene, one from the father and one from the mother. Due to heteroplasmy, the phenotype of a given tissue, organ, or whole organism, is influenced by the relative amounts of wild-type and mutant mtDNA, not by Mendelian patterns of dominance or recessivity. Educational objective:Variable expressivity and incomplete penetrance are common features of mitochondrial diseases. Penetrance is defined as the proportion of individuals with a specific genotype who express the corresponding phenotype. Variable expressivity refers to the range of phenotypic outcomes shown by individuals who carry the same genotype.

If a neuroimaging study compared normal dreaming with lucid dreaming, in what brain region would more activity be expected during lucid dreaming? A.Cerebellum(5%) B.Prefrontal cortex(84%) C.Amygdala(2%) D.Primary visual cortex(7%)

The prefrontal cortex is associated with executive functions, such as critical thinking, problem solving, planning, impulse control, and executive decision-making. Because lucid dreaming involves critical analysis and executive decision making, a neuroimaging study would be expected to demonstrate greater activation of the prefrontal cortex during lucid dreaming as compared with normal dreaming. The prefrontal cortex is the anterior portion of the frontal lobe, which also contains the primary motor cortex (responsible for the initiation of voluntary movement) and Broca area (involved in speech production). (Choice A) The cerebellum is positioned underneath the occipital lobe at the back of the skull and is associated with motor coordination and motor learning. This region would not necessarily be more active during lucid dreaming compared with normal dreaming. (Choice C) The amygdala is part of the limbic system located on either side of the thalamus deep in the cortex; it is associated with processing emotion, particularly fear and anger. Although this region may be active during lucid dreaming, it is probably no more active than during normal dreaming. (Choice D) Located in the occipital lobe, the primary visual cortex is associated with processing visual input from the retinas and is not expected to be as active during dreaming, when there is no external visual input. However, secondary visual areas of the brain have been associated with the visual imagery that occurs during dreaming. Educational objective:The prefrontal cortex is involved in executive decision making and critical analysis. It is located in the frontal lobe, which also contains the primary motor cortex.

If the first step of the nitration of tyrosine in a lipid environment is slower than the second step, what is the rate law for the overall reaction? A.Rate = k1[tyrosine][O3](82%) B.Rate = k1[tyrosine][O3][NO2](9%) C.Rate = k2[ROI][NO2](5%) D.Rate = k2[tyrosine][O3](2%)

The rate law is an equation that quantitatively describes the relationship between the reaction rate and reactant concentrations. For elementary reactions (ie, one-step reactions, individual steps of a multistep reaction), the rate law is written as the product of the rate constant k and the concentration of the reactants, in which the stoichiometric coefficient of each reactant is its exponent. If the reaction is not elementary (ie, requiring more than one step), the slowest elementary step (or rate-determining step) determines the rate law for the entire reaction. This step can only be determined experimentally. If the initial step is the slowest, the rate law is determined simply from that step using the coefficients of each reactant as exponents in the rate law. However, if the slowest step is the second step, reaction intermediates play a role in the rate law. The nitration of tyrosine is a multistep reaction in which the first step is the rate-determining step. Therefore, the rate law can be written using the reactants of step 1: Rate = k1[tyrosine][O3] (Choice B) This expression was written using reactants of the overall reaction instead of those of the rate-determining (slow) step. (Choice C) The fast step of the reaction was used as the rate-determining step for this expression when the slow step should have been used. (Choice D) The incorrect rate constant k2 is used for this expression instead of the rate constant k1 from the rate-determining step. Educational objective:Rate laws for molecular reactions relate the rate of reaction to the concentrations of reactants. For a multistep reaction, the rate law must be determined experimentally by determining the rate-limiting step. Multistep reactions are determined according to the slowest or rate-determining step.

Which of the following conclusions is most supported by Figure 1? A.An individual from the "lucid practice" group demonstrated the lowest improvement of all members.(1%) B.The difference in task improvement between the "lucid practice" group and the "no practice" group was statistically significant.(44%) C.The "lucid practice" group's lowest quartile improved more on the task than the "no practice" group's highest quartile.(26%) D.The mean score for the "waking practice" group was higher than the mode scores for the other two groups.(26%)

The results of the lucid dreaming study described in the passage are illustrated with a box-and-whisker plot, which is used to visually represent the median and the distribution of the data into quartile ranges: The upper quartile (Q3; 75% of the data lies below this value), shown as the top edge of the box. The median (50% of the data lies below this value), which is the line inside the box. The lower quartile (Q1; 25% of the data lies below this value), shown as the bottom edge of the box. The maximum and minimum data points, shown as whiskers, are data values no more than 1.5 times the interquartile range (IQR) from the edge of the box. The IQR is equal to the difference between the upper and lower quartiles. Outliers, shown as data points outside the maximum and minimum data points. Confidence intervals (CIs) represent a measure of uncertainty in a reported value by indicating how far the value reported might be from the true value (eg, true median). Theoretically, a 95% CI indicates that if the same population were sampled countless times and CIs were calculated each time, the resulting intervals would contain the true population value in approximately 95% of the cases. A notch that represents the 95% CI of the median is used on the box-and-whisker plot to estimate visually whether the medians of two groups are significantly different. If the notches across two groups do not overlap, the medians of the two groups are probably significantly different. In Figure 1, the notches of both the "waking practice" and "lucid practice" groups are higher than and do not overlap with the notch of the "no practice" group, so the two practice groups are assumed to have improved significantly more on the task than the "no practice" group. However, one cannot conclude from the figure that a significant difference exists between groups when notches do overlap. (Choice A) An individual from the "waking practice" group (not the "lucid practice" group) demonstrated the lowest improvement of all members. (Choice C) The "lucid practice" group's lowest quartile was completely below the "no practice" group's highest quartile, indicating less improvement for the "lucid practice" group's lowest quartile. (Choice D) Box-and-whisker plots provide information about the median, not the mean or the mode. Educational objective:Box-and-whisker plots visually represent the median value and interquartile range. Notched box plots show the 95% confidence interval around the median. If notches do not overlap, medians can generally be inferred to be statistically significantly different.

A pharmaceutical company is testing how much sugar should be added to a pediatric oral liquid suspension to make the medication more palatable. Researchers determine that adding 0.2 g of sugar to 20 mL of oral suspension Z results in children detecting a just noticeable difference in taste. Based on Weber's law, should the addition of 0.2 g of sugar to 50 mL of oral suspension Z be detectable 50% of the time? A.Yes, because 0.2 g sugar is the just noticeable difference(9%) B.Yes, because Weber's law is based on a constant value(3%) C.No, because 0.2 g is below the absolute threshold(20%) D.No, because Weber's law is based on a ratio(66%)

The smallest difference between two stimuli a person can detect 50% of the time is called the just noticeable difference (JND), or difference threshold. As the intensity of the original stimulus increases, the difference threshold also increases. For example, although the difference between weights of 100 and 102 g may be detectable, the difference between weights of 500 and 502 g is not, even though the difference is also 2 g. This relationship is quantified by Weber's law, which states that the ratio of the size of the JND to the original stimulus intensity remains constant. In other words, the change in a stimulus needed to detect a difference is a constant proportion (ie, if one can just detect a difference between weights of 100 and 102 g, the difference between weights of 500 and 510 g would also be just detectable). If the addition of 0.2 g of sugar to 20 mL of suspension Z is just noticeable 50% of the time, then for a volume that is 2.5 times bigger (20 mL × 2.5 = 50 mL), 0.5 g of sugar (0.2 g × 2.5 = 0.5 g) would be the JND. Therefore, the addition of 0.2 g of sugar to 50 mL of oral suspension Z would not be detectable because Weber's law is based on a ratio. (Choice A) The addition of 0.2 g of sugar is the JND for 20 mL of suspension; for 50 mL of suspension the JND is 2.5 times greater, or 0.5 g. Therefore, anything less than 0.5 g should not be detectable 50% of the time. (Choice B) Weber's law is based on a constant proportion, not a constant value, so the addition of 0.2 g of sugar to 50 mL of oral suspension Z should not be detectable 50% of the time. (Choice C) The absolute threshold is the intensity value at which an individual can detect a stimulus 50% of the time; 0.2 g represents the difference threshold, or the smallest difference between two stimuli that can be detected 50% of the time, not the absolute threshold. Educational objective:Weber's law states that the proportion of the just noticeable difference (the smallest difference between two stimuli a person can detect 50% of the time) to the original stimulus intensity is a constant.

Which hypothetical result from a study on tetrachromatic monozygotic (MZ) twins separated at birth and raised by different parents would provide the strongest evidence contradicting the conclusion in the final paragraph of the passage? Tetrachromatic MZ twins' color discrimination abilities are more similar to each other than to: A.the general population.(5%) B.their biological siblings.(9%) C.their biological parents.(13%) D.their adoptive siblings.(71%)

Twin studies and adoption studies are used to estimate the importance of genetic and environmental factors on complex human traits, such as color perception. Although they are rare, twin adoption studies can help clarify the role of genes versus the environment for specific traits. MZ twins raised together share the same genes and an extremely similar environment (eg, same household, same schools, similar experiences), so it is not possible to determine if similar traits are the result of genes, environment, or a combination of the two. However, if MZ twins are each adopted and raised apart, traits that they share are most likely determined by genes whereas traits that are more similar to those of their adoptive families are most likely determined by environmental influences. If tetrachromatic MZ twins (same genes) are raised apart (different environment) and perceive color more similarly to each other than to their adoptive siblings, this would suggest that genes play a major role in color perception, which would strongly contradict the researcher's conclusion that language (an environmental factor) influences this trait. (Choices A, B, and C) Adopted twins do not share a home environment with their biological parents, biological siblings, or the general population. Therefore, the hypothetical finding that includes a comparison to adoptive siblings (with whom they have a shared environment) provides the strongest evidence against the passage's conclusion that language (an environmental factor) influences color perception abilities. Educational objective:For human traits, particularly complex ones, twin studies and adoption studies can help explain the extent to which genes and/or the environment play a role in that trait. Twin adoption studies are a rare but powerful tool for elucidating the role of genes versus the environment for specific traits.

The study described in the passage would best be categorized as which of the following? A.Longitudinal study(1%) B.Case study(39%) C.Cross-sectional study(40%) D.Randomized controlled trial(18%)

Types of studies in the health sciences Experimental Randomized controlled trial Random allocation into treatment & placebo groups Can determine efficacy of the intervention Nonrandomized design Nonrandom allocation into treatment & placebo groups Can determine efficacy of the intervention Observational Longitudinal Data gathered at multiple time points Can assess risk factors or outcomes Cross-sectional Data gathered at one point in time Can determine prevalence of an outcome in a population Case-control Data gathered from individuals with the condition of interest (cases) & compared to individuals without the condition (controls) Case Detailed information gathered about one individual (or a small group of individuals) Review Meta-analysis Data from multiple studies are statistically combined & analyzed It is often impossible to study a rare condition or illness in large numbers of people. In such instances, case studies are used to study one or a few individuals who possess a trait or condition of interest, such as a genetic mutation causing four distinct cone types. Case studies also allow for a more thorough, in-depth analysis of the trait or condition of interest. Because of the relatively small sample size of this study and the multifaceted nature of the research approach, this study would best be considered a case study of three women who possess a trait of interest (four retinal cone classes). (Choice A) In a longitudinal study, variables are repeatedly measured over time, which can reveal how or if these variables change over time (eg, if color perception changes as we age). This study did not collect data over time, so it would not be considered a longitudinal study. (Choice C) A cross-sectional study is a type of observational study that measures an outcome or variable of interest (generally, a disease or trait) in a population or subpopulation at one point in time. Cross-sectional studies measure prevalence, the percentage of people with a disease or trait at a given point. This study did not attempt to quantify the prevalence of four distinct cone types in the population, so it is not a cross-sectional study. (Choice D) A randomized controlled trial is an experimental study in which participants are randomly allocated to two or more experimental groups that receive different treatments or exposures. For example, if each group receives a different treatment, the incidence (rate of new disease cases) per group can be compared. This study did not allocate subjects into groups receiving different treatments, so it was not a randomized controlled trial. Educational objective:Case studies are used to study one or a few individuals who possess a trait or condition of interest. Case studies allow for a more thorough, in-depth analysis.

Some models of rechargeable hearing aids use lithium-ion batteries composed of a carbon (graphite) anode and a cobalt oxide-based cathode. Reaction 1 shows the half-reaction that occurs at the anode during battery discharge, and Reaction 2 shows the balanced net reaction. LiC6 → Li+ + e− + C6 Reaction 1 LiC6 + CoO2 → LiCoO2 + C6 Reaction 2 When the hearing aid is operating, what half-reaction occurs at the cathode? A.CoO2 + Li+ + e− → LiCoO2(73%) B.LiCoO2 → CoO2 + Li+ + e−(7%) C.CoO2 + Li+ → LiCoO2 + e−(7%) D.LiCoO2 + e− → CoO2 + Li+(11%)

When a battery discharges, the half-reaction at the anode gives up electrons (oxidation), which are transferred to the cathode (reduction) to complete the other half-reaction. An electron balance must be present between the half-reactions to achieve the balanced net reaction from the sum of the two half-reactions: Electrons present as reactants in one half-reaction should appear as products in the other half-reaction. This may require multiplication of one or both half-reactions by a constant to ensure that all electrons cancel. Identical species appearing as reactants in one half-reaction and as products in the other cancel and are not part of the net reaction expression. Based on these principles, an unknown half-reaction can be found by adding the balanced net reaction to the inverse of the known half-reaction. Species in the inverse known half-reaction that do not participate in the discharge (LiC6 and C6) will cancel with the balanced net reaction, leaving only those species present in the other half-reaction occurring during discharge: CoO2 + Li+ + e− → LiCoO2 (Choice B) This half-reaction is the reverse of the half-reaction that occurs at the cathode during discharge. It occurs only when the battery is being charged. (Choice C) This half-reaction has the correct chemical species as products and reactants; however, reduction occurs at the cathode. The electron should be included with the reactants. (Choice D) Although this half-reaction correctly shows an electron on the reactant side (reduction), Li+ should also be on the reactants side of the half-reaction because it receives the electron. Educational objective:The balanced net reaction for an electrochemical cell may be found by taking the sum of the half-reactions, written to be consistent with the direction of electron flow within the cell. Half-reactions may be scaled stoichiometrically to achieve an electron balance. Species matching in type and number on both sides of the summation are not included in the net reaction.

If a 0.2-mL blood sample with a PaCO2 of 40 mm Hg diffuses across a membrane into the E2 electrode containing 0.3 mL of solution, the final PaCO2 in the blood sample will be: A.exactly 0 mm Hg.(4%) B.less than 16 mm Hg.(45%) C.exactly 16 mm Hg.(14%) D.greater than 16 mm Hg.(35%)

When a membrane permeable to an uncharged species is used to separate two solutions, the species diffuses down its concentration gradient until its concentration is equal on both sides. For instance, if 0.2 mL of solution with a PaCO2 of 40 mm Hg diffuses into 0.3 mL of solution, diffusion continues until the CO2 is dissolved at the same concentration in both volumes on each side of the electrode membrane. Essentially, this diffusion scenario can be viewed as a dilution of the CO2. Initially, all of the CO2 is confined to the 0.2 mL volume of the blood sample. After diffusion, the CO2 is distributed within a total volume of 0.5 mL (0.2 mL sample + 0.3 mL electrode solution). As such, the final concentration after diffusion can be calculated as follows: PaCO2(initial)×Vinitial=PaCO2(final)×VfinalPaCO2initial×Vinitial=PaCO2final×Vfinal (40 mm Hg)(0.2 mL)=PaCO2(final)×(0.5 mL)40 mm Hg0.2 mL=PaCO2final×0.5 mL PaCO2(final)=16 mm HgPaCO2final=16 mm Hg In this example, CO2 diffuses from blood into a reaction solution, where some of the CO2 is removed as it is converted to HCO3−. As CO2 is removed from the reaction solution, it will continue to diffuse from the blood into the reaction solution. Therefore, the final CO2 in the blood sample will be less than 16 mm Hg. (Choice A) The CO2 in the blood will equilibrate with the HCO3− solution. It is not completely consumed, so its concentration will not reach zero. (Choices C and D) If CO2 did not react with the second solution, its equilibrium concentration would be exactly 16 mm Hg. Because CO2 is removed during the reaction, the final concentration will be less than 16 mm Hg. Educational objective:An uncharged species will diffuse across a semipermeable membrane until its concentration is equal on both sides. If the species is removed from one side of the membrane, diffusion will continue in that direction until equilibrium is regained.

The reference electrode for E2 should be maintained at a known, stable concentration of: A.H+(aq).(43%) B.HCO3−(aq).(20%) C.dissolved CO2.(28%) D.dissolved O2.(7%)

A reference electrode is an electrode that has a known electric potential and standard concentration of reacting species. The passage states that the mechanism used at E2 to measure CO2 is a modification of the mechanism used at E1 to measure pH: E1 is a concentration cell, meaning both electrodes contain the same chemical species. In this case the species is H+, which diffuses from the blood sample into E1. The pH is calculated from the voltage difference between E1 and its reference electrode, which is maintained at a standard pH. pH is directly related to the concentration of H+ by the equation pH = −log[H+]. CO2 diffuses from the blood sample into a reaction solution at E2. The reaction produces H+, and the change in pH is determined by the voltage difference between E2 and its reference electrode. Therefore, the reference electrode for E2 should also be maintained at a standard concentration of H+. (Choices B and C) As stated in the passage, CO2 reacts to produce H+, and it is this change, not the change in CO2 or HCO3−, that is measured. Therefore, the reference electrode should be maintained at a standard concentration of H+. (Choice D) O2 gas is not involved in the mechanism used at E2. Educational objective:A reference electrode contains a known electric potential and concentration of ions. When both electrodes in a cell contain the same chemical species (a concentration cell), the electric potential difference (voltage) between the electrodes depends only on the relative concentrations of these species.

Blood gas analysis results are listed below. From the data, determine the HCO3− concentration in the blood sample resulting from the decomposition of carbonic acid. pH 7.35 PaCO2 40 mm Hg PaO2 90 mm Hg A.0.12 mEq/L(12%) B.1.2 mEq/L(43%) C.2.4 mEq/L(11%) D.12.0 mEq/L(32%)

Buffers consist of a weak acid and its conjugate base. They help maintain H+ concentration when the pH of a solution is within the "buffering region," or within 1 pH unit of the buffer's pKa (the pH at which half of the buffer molecules are protonated and half are deprotonated). The Henderson-Hasselbalch equation relates the pH of the buffered solution to pKa of the buffer and the ratio of the conjugate base to the acid. For the HCO3− buffer system that functions at physiologic pH, the acid is carbonic acid (H2CO3) and its conjugate base is HCO3−. According to the passage, the pKa is 6.35. pH=6.35+log[HCO−3][H2CO3]pH=6.35+logHCO3-H2CO3 The question asks for the concentration of HCO3− given a pH of 7.35 and a PaCO2 of 40 mm Hg. As described in the passage, the H2CO3 concentration in mEq/L can also be calculated from PaCO2 in mm Hg. [H2CO3]=0.03×PaCO2=0.03×40=1.2 mEq/LH2CO3=0.03×PaCO2=0.03×40=1.2 mEq/L The HCO3− concentration can then be calculated by incorporating the pH and the H2CO3 concentration into the Henderson-Hasselbalch equation: 7.35=6.35+log[HCO3−]1.27.35=6.35+logHCO3-1.2 log[HCO3−]1.2=1logHCO3-1.2=1 Removal of the logarithm (base 10) is achieved by taking the inverse logarithm of both sides of the equation (ie raising 10 to the power of each side): 10(log[HCO3−]1.2)=10110logHCO3-1.2=101 [HCO3−]1.2=10HCO3-1.2=10 Solving for [HCO3−] yields: [HCO3−]=12.0 mEq/LHCO3-=12.0 mEq/L (Choice A) This value is the result of using the Henderson-Hasselbalch equation with the positions of H2CO3 and HCO3− inverted. The appropriate ratio is the conjugate base divided by the conjugate acid. (Choice B) This value is the H2CO3 concentration. The Henderson-Hasselbalch equation shows that there is ten times as much HCO3− as H2CO3. (Choice C) This value corresponds to a ratio of 2:1 for the concentrations of HCO3− to H2CO3. Because the log of [HCO3−]/[H2CO3] is equal to 1, the quotient of [HCO3−]/[H2CO3] is equal to 101, which corresponds to an HCO3−concentration of 12.0 meq/L. Educational objective:Consisting of a weak acid and its conjugate base, buffers help maintain the pH of a solution near the pKa. The Henderson-Hasselbalch equation is used to relate pH, pKa, and the concentration ratio of the acid and conjugate base.

When oxalate anions, C2O42−, are added to a solution of [Fe(H2O)6]3+, the formation of [Fe(C2O4)3]3− occurs in a series of steps that together result in the following overall reaction: [Fe(H2O)6]3+(aq) + 3 C2O42−(aq) → [Fe(C2O4)3]3−(aq) + 6 H2O(l) During the first step of the reaction, two new coordinate bonds are formed to produce an intermediate ion of: A.[Fe(H2O)4(C2O4)]+(aq).(42%) B.[Fe(H2O)2(C2O4)2]−(aq).(39%) C.[Fe(C2O4)3]3−(aq).(6%) D.[Fe(H2O)5(C2O4)]2−(aq).(11%)

Complex ions (coordination complexes) consist of a central metal ion surrounded by one or more ions or molecules called ligands that are bound to the metal center by coordinate bonds. The coordinate bonds form because the ligands surrounding the metal center act as Lewis bases and donate a lone pair of electrons to the metal center, which acts as a Lewis acid. These Lewis acid-base coordinations hold the complex together, but stronger Lewis bases can displace weaker Lewis bases as ligands within the complex. In the [Fe(H2O)6]3+ complex ion, an uncharged water molecule serving as a ligand is a weak Lewis base and can be displaced by the oxalate (C2O42−) anion, a stronger Lewis base. Each C2O42− anion displaces two water molecules and decreases the overall charge of the resulting complex ion by −2. Displacement of water within the complex occurs in a stepwise sequence. In the first step, two water molecules are displaced from [Fe(H2O)6]3+ by a single C2O42− anion to form an intermediate complex ion: [Fe(H2O)6]3+(aq) + C2O42−(aq) → [Fe(H2O)4(C2O4)]+(aq) + 2 H2O(l) In the second and third steps, additional C2O42− anions displace the remaining water ligands to form the final product. (Choice B) This is the intermediate ion formed during the second step of the reaction, not the first step. (Choice C) This is not an intermediate ion; it is the end product formed during the final third step of the overall net reaction. (Choice D) Both the ion charge and this formula are incorrect. The first step adds one C2O42− ion to the complex, but each oxalate ion displaces two water molecules and decreases the overall charge of the complex by −2.

Would (R,R)- and (S,S)-labetalol be expected to rotate plane-polarized light in the same direction? A.Yes, because they are diastereomers.(3%) B.Yes, because the rotations would have the same magnitude.(2%) C.No, because they are enantiomers.(73%) D.No, because the rotations would cancel out each other.(20%)

Normal light is made up of waves that vibrate in all planes perpendicular to the direction of travel. When the light meets a polarizer, only waves that are aligned with the polarizer can pass through, so all of the light that passes through vibrates in one direction. This resulting light is known as plane-polarized (linear) light. When chiral molecules interact with polarized light, the interactions cause the angle of oscillation to rotate. An R or S configuration is not predictive of the direction of rotation. Every molecule is different, and the concentration and length of the path through which the light travels affect the angle. The direction and magnitude of rotation can only be determined experimentally. Taking into account experimental parameters such as concentration and path length, the observed rotation can be standardized with the calculation of specific rotation. Enantiomers always have specific rotations of equal magnitude but opposite directions. (R,R)-labetalol and (S,S)-labetalol are enantiomers, and therefore would rotate plane-polarized light by the same amount but not in the same direction. (Choice A) (R,R)- and (S,S)-labetalol are enantiomers, not diastereomers. No correlation exists between diastereomers and the magnitude or direction of plane-polarized light rotation. (Choice B) If two samples rotated plane-polarized light by the same magnitude and direction, they would likely be the same compound. Although (R,R)- and (S,S)-labetalol, which are enantiomers, do rotate plane-polarized light by the same magnitude, they cause the light to rotate in opposite directions. (Choice D) If a sample were to have a rotation of zero, it would mean that the rotations have canceled one another out. This occurs when the sample is a 50:50 mixture of enantiomers (ie, 50% R and 50% S) known as a racemic mixture. Educational objective:Enantiomers rotate plane-polarized light by the same magnitude in opposite directions. No correlation exists between diastereomers and the magnitude or direction of rotation. Racemic mixtures have a rotation of zero because they consist of equal amounts of each enantiomer.

For the electron configuration of iron, Fe(0), do electrons fill the 4s orbitals before the 3d orbitals are filled? A.Yes, because electrons fill the s and p orbitals before they fill the d orbitals, even if they are in different energy levels.(13%) B.No, because 3d orbitals are lower in energy than 4s orbitals.(15%) C.Yes, because according to the Aufbau principle, electrons fill lower energy levels first.(66%) D.No, because orbitals are filled based on the order of the principal quantum number, and 3d comes before 4s.(5%)

Electron orbitals are defined by a set of quantum numbers. The principal quantum number n represents the distance of an orbital shell from the nucleus. Each orbital shell can be divided into subshells, defined by the angular quantum number l and the magnetic quantum number m. The angular quantum number represents the shape of a subshell, the most common being s, p, d, and f. The magnetic number describes the orientation of a given subshell in which s orbitals can exist in one orientation, p orbitals can exist in three orientations, d orbitals can exist in five orientations, and f orbitals can exist in seven orientations. Each subshell can hold 2 electrons, so s, p, d, and f orbitals can hold 2, 6, 10, and 14 electrons, respectively. Each orbital is associated with a different energy level, and the Aufbau principle states that electrons will fill the lowest energy levels first. The periodic table is arranged to reflect the relative energies of each orbital type and, therefore, the order of electron orbital filling. The orbitals are arranged into different blocks on the periodic table: s orbitals are in the first two columns (except helium), the p orbitals are on the right, the d orbitals are in the middle, and the f orbitals are at the bottom. Therefore, the order of orbital filling can be determined simply by finding an atom's position on the table. Iron is within the 3d orbital section, which comes after the 4s section, so 4s is filled first. (Choice A) The order of orbital filling is determined by energy level, which is reflected in the periodic table. (Choice B) Although the 4s and 4p orbitals have a higher principal quantum number n, indicating they are further away from the nucleus than 3d, the periodic table shows that 4s is slightly lower in energy and will be filled first. (Choice D) An atom's position on the periodic table, not its principal quantum number, determines how its orbitals are filled. Educational objective:The Aufbau principle states that low energy orbitals are filled first. The periodic table can be used as a guide to orbital filling. Each block on the table represents different orbital types, with s orbitals in the two left columns, p orbitals in the six right columns, and d orbitals in the middle, and f orbitals at the bottom.

Because step 2 of the reaction in aqueous phase is rate-limiting, the formation of ROI from tyrosine and ozone in step 1 can be assumed to reach a state of equilibrium. Tyrosine(aq)+ O3(aq)⇌ ROI(aq) + HO3(aq)Tyrosine(aq)+ O3(aq)⇌ ROI(aq) + HO3(aq) Which of the following will occur if the temperature of this system is raised from 298.15 K to 350 K? A.Keq will increase.(15%) B.The reaction will be driven toward the reactants.(46%) C.The reaction will be driven toward the products.(22%) D.Keq will remain the same.(15%)

Equilibrium is reached in a reaction when the rate at which products are formed is equal to the rate at which reactants are formed. Per Le Châtelier principle, if a system in equilibrium is disturbed by a change in temperature, pressure, or a component's concentration, the system will counteract the disturbance by driving the reaction in a given direction such that equilibrium is restored. Changes in pressure and concentration achieve this without altering the equilibrium constant Keq, whereas a change in temperature leads to a change in Keq. The effect of temperature on an equilibrium reaction can be illustrated by treating heat as a chemical reagent and applying Le Châtelier principle. Step 1 of the nitration of tyrosine in an aqueous environment is an exothermic reaction, and heat can be viewed as a product of the reaction. Raising the temperature causes a shift toward the reactants as heat is consumed to rebalance the equilibrium reaction. The shift toward reactants leads to an increase in reactant concentration, and therefore a decrease in Keq. (Choices A, C and D) Because the reaction is exothermic, raising the temperature causes the reaction to be driven toward the reactants, increasing their concentration and causing a decrease in Keq rather than an increase or remaining the same. Educational objective:Equilibrium is reached in a reaction when the rate at which products are formed is equal to the rate at which reactants are formed. The equilibrium constant Keq is defined as the ratio of the reactants and products when a reaction is in equilibrium, and only changes in temperature can alter Keq. Le Châtelier principle states that a system responds to disturbances in equilibrium by shifting the reaction to counter the effect of the disturbance.

Which of the following would be true regarding the inheritance of the A3243G mutation? (Note: Assume affected individuals inherited the mutation.) A.All daughters of an affected father are affected.(6%) B.Only offspring of affected mothers are affected.(71%) C.All affected males have asymptomatic carrier mothers.(9%) D.Affected offspring must have two copies of the defective gene.(12%)

Mitochondria are cellular organelles that have their own genome; their main functions include ATP generation, heat production, and beta-oxidation of fatty acids. Mitochondrial genes are extranuclear and inherited in a distinctly different manner than nuclear genes (autosomal and sex-linked). During fertilization, mitochondria within sperm do not pass into the ovum; therefore, only maternal mitochondria are transmitted to the fetus. Only affected females transmit abnormal mitochondria to offspring; transmission never occurs through males, even if they are affected. As a result, only affected mothers with the mtDNA A3243G mutation can pass it on to their offspring. (Choice A) Only one copy of the dominant allele of the gene is necessary to inherit an X-linked dominant condition. These diseases are characterized by a lack of father-son transmission, but all daughters of an affected father are affected. Affected mothers have a 50% probability of having an affected child. (Choice C) Affected males have asymptomatic carrier mothers in X-linked recessive conditions, which are inherited via the X chromosome. Two mutant alleles must be inherited to cause disease in females (XX), but only one mutant allele is required to cause the disease in males (XY). (Choice D) Autosomal recessive conditions require the presence of two copies of the defective gene for disease manifestation and show no predilection for males or females. About 25% of children are affected if both parents carry one copy of the defective gene (most common scenario). Educational objective:Mitochondria have their own genome, known as mitochondrial DNA, which is inherited in a maternal fashion (ie, no paternal contribution). Mitochondria within sperm are not transferred into the ovum during fertilization; therefore, males never pass on their mitochondria.

Based on the passage, which of the following reagents was most likely used during PCR? A.Free ribonucleoside triphosphates(11%) B.RNA polymerase(21%) C.A template sequence containing deoxyribonucleotides(52%) D.Primer pairs with minimal GC content(14%)

Polymerase chain reaction (PCR) uses thermal cycling to amplify small DNA fragments, which can then be screened for mutations or used in further genomic analysis. PCR reagents include the following: A source DNA template (containing deoxyribonucleotides) that includes the target region to be amplified and its adjacent flanking sequences (Choice C) Primer pairs designed from the oligonucleotide sequence of the regions flanking the target sequence A thermostable DNA polymerase (ie, not denatured at high temperatures) to replicate the DNA template using a pool of supplied deoxyribonucleotide triphosphates (dNTPs) A buffer solution with positively charged ions (cations) to provide an optimal environment for DNA polymerase to function (ie, cations bind the negatively charged phosphates on the DNA backbone and those on dNTPs, neutralizing the negative charge of DNA and stabilizing primer-template binding) In PCR, thermal separation (denaturation) of the DNA template is accomplished by exposing the sample to high temperatures. Subsequent cooling allows primers to anneal to the single-stranded flanking ends of the target region. DNA polymerase uses the primers to elongate the new daughter strands in the 5′ to 3′ direction. These steps are repeated to obtain millions of copies of the target DNA segment in a short time. (Choice A) Deoxyribonucleotide triphosphates, not ribonucleoside triphosphates, are used during PCR to synthesize new DNA strands. dNTPs are free nucleic acids that contain deoxyribose (sugar) whereas ribonucleoside triphosphates are used during the transcription of RNA as they contain ribose (sugar). (Choice B) RNA polymerase is not used during PCR as this enzyme synthesizes new RNA molecules from DNA during transcription (ie, does not participate in DNA replication). (Choice D) GC-rich DNA fragments tend to be more stable at high temperatures; therefore, primers must have a substantial amount of GC content (40%-60%) to avoid premature denaturation during PCR. Educational objective:Polymerase chain reaction (PCR) is a thermal cycling technique used to amplify DNA fragments. PCR reagents include a source DNA template, GC-rich primer pairs, a thermostable DNA polymerase, and a buffer solution with positively charged ions.

A proponent of social cognitive theory would suggest that the self-positivity bias is unlikely to influence an individual: A.with hepatitis A.(14%) B.studying hepatitis C in a liver cell line.(5%) C.with several friends who have hepatitis C.(51%) D.who has never heard of hepatitis C.(28%)

Social cognitive theory suggests that people learn through observing others. Watching a model (someone else, often a friend or family member) engaging in a behavior and the consequences associated with that behavior is a powerful method of learning called vicarious learning. Depending on the outcome for the model, the observer may replicate or avoid that behavior. According to social cognitive theory, people would be least susceptible to the self-positivity bias (the belief that they are immune to negative outcomes such as contracting hepatitis C) if they had friends with the disease. People tend to share similar characteristics with and behave in ways similar to those of their friends. Therefore, individuals who have friends with hepatitis C would have already observed the behaviors associated with contracting it and so would be less inclined to assume they are immune to the disease. (Choices A, B, and D) Social cognitive theory is most concerned with how individuals learn through observing the behaviors of others. Therefore, a proponent of this theory would be concerned with how an individual's behavior and attitudes are shaped by interacting with others, rather than through personal experience with a similar disease, professional experience with the disease, or lack of knowledge about the disease. Educational objective:Social cognitive theory posits that people learn by observing others. Vicarious learning takes place through watching other people behave in a certain way and then get rewarded or punished for it. Depending on the outcome, the observer may or may not choose to behave in the same way as the model.

Which term can be used to classify the relationship between two isomers that have the same connectivity but specific rotations of +40° and −25°, respectively? A.Enantiomers(19%) B.Racemic mixture(9%) C.Diastereomers(48%) D.Conformational isomers(22%)

Specific rotation, the degree to which chiral molecules rotate plane-polarized light, is unique to each chiral molecule. The value of specific rotation consists of direction (+ or −) and magnitude (number of degrees). Clockwise rotations are designated as (+), whereas counterclockwise rotations are (−). Isomers are molecules with the same molecular formula but have either different connectivity (constitutional isomers) or spatial orientation (stereoisomers). Diastereomers differ at one or more stereocenters but have the orientation of at least one stereocenter in common. The specific rotations of diastereomers differ in magnitude and may differ in direction. The same is true for constitutional isomers. Because the question states that the two molecules have the same connectivity, they cannot be constitutional isomers. Because they have different specific rotations (direction and magnitude), it can be concluded that the two molecules are diastereomers. (Choice A) Enantiomers have specific rotations of equal magnitude but opposite directions. If the molecules were enantiomers, they would either have specific rotations of +40° and −40° or +25° and −25°. (Choice B) A racemic mixture is composed of 50% of one enantiomer and 50% of the other. Racemic mixtures have a specific rotation of 0° because the specific rotations of the two isomers cancel each other. Each isomer in the question has a nonzero specific rotation and therefore cannot be racemic. (Choice D) Conformational isomers are versions of the same molecule that form when an atom rotates about its bond. Because these isomers are the same compound, they cannot have different specific rotations. Educational objective:Specific rotation is the degree to which a chiral molecule rotates plane-polarized light. The value of specific rotation contains direction (+ is clockwise, − is counterclockwise) and magnitude. Diastereomers differ in the magnitude of their specific rotations (and may differ in direction), whereas enantiomers have specific rotations of the same magnitude but opposite direction.

S,R)- and (R,R)-labetalol, the active forms of the drug, can be described as which of the following? Diastereomers Enantiomers Conformational isomers A.I only(81%) B.I and II only(5%) C.II and III only(9%) D.I, II, and III(3%)

Stereoisomers are molecules that contain the same atom connectivity but differ in the spatial arrangements of the atoms. Diastereomers are stereoisomers that are not mirror images. These molecules contain at least two stereocenters in which one or more, but not all, of the corresponding stereocenters are in opposite configurations. (S,R)- and (R,R)-labetalol are stereoisomers that are not mirror images, and each compound contains two stereocenters. The two compounds have different configurations at the stereocenter in position 1 (one S and one R) and have the same configuration at the stereocenter in position 2 (both R). Therefore, (S,R)- and (R,R)-labetalol are diastereomers (Number I). (Number II) Enantiomers are stereoisomers that are nonsuperimposable mirror images. These molecules contain one or more stereocenters, and each stereocenter is the opposite configuration from the corresponding stereocenter in the other molecule. For example, the enantiomer of (S,R)-labetalol is (R,S)-labetalol. (Number III) Conformational isomers are different forms of the same molecule that are generated as atoms rotate about their bonds. Unlike other stereoisomers, conformational isomers can rapidly interconvert by rotation without the need to break any bonds. Educational objective:Diastereomers are stereoisomers that are not mirror images. They contain at least two stereocenters in which one or more, but not all, are in opposite configurations.

How would a proponent of Malthusian theory most likely interpret the data in Figure 1? A.Increased suicide rates provide evidence for a Malthusian catastrophe.(14%) B.The decline in suicide rates during World War II supports Malthusian theory.(13%) C.The Great Depression would be considered a positive check.(40%) D.Increased suicide rates during recessions are negative checks.(30%)

The Malthusian theory of population growth suggests that the human population increases exponentially while resources increase at a slower rate. According to this theory, the population growth rate can be slowed by preventative checks and positive checks. Preventative checks are those that decrease the birth rate (and are typically voluntary, such as waiting to marry and having fewer children). Positive checks increase the death rate, slowing population growth by shortening the average life span. Positive checks can be small-scale (eg, increased death rate due to a flu virus) or large-scale (eg, an epidemic that wipes out half the population). Large-scale positive checks, called Malthusian catastrophes (eg, widespread famine, disease epidemics, large-scale wars), dramatically reduce the population to a level that the available resources can easily sustain, by slowing or stopping population growth entirely. (Choice A) Increases in suicide rates, even up to the highest rates in Figure 1 (15-20 suicides per 100,000 people), will not have a large enough impact on the population to be considered a Malthusian catastrophe. (Choice B) According to Malthusian theory, the increased death rate (not the decreased suicide rate) during World War II would be considered a positive check, supporting the theory. (Choice D) A negative check does not exist in Malthusian theory, only positive checks and preventative checks. Educational objective:The Malthusian theory of population growth asserts that when the population grows faster than the resources necessary to sustain that population, preventative checks (reducing the birthrate) or positive checks (increasing the death rate) can slow down growth. A Malthusian catastrophe is a large-scale positive check that slows or stops population growth.

The researcher's conclusion is best aligned with the: A.nativist hypothesis.(16%) B.opponent-process theory.(6%) C.Sapir-Whorf hypothesis.(68%) D.Young-Helmholtz theory.(8%)

The Sapir-Whorf hypothesis, also known as linguistic relativity, posits that language influences our perception and cognition. For example, if a person's native language does not have separate names for the colors blue and indigo (instead referring to both as "blue"), that person may have difficulty discriminating blue from indigo in isolation but could learn to differentiate them with practice. Linguistic determinism, a stronger version of this hypothesis, states that language controls perception and cognition. For example, if a person's native language does not have separate names for blue and indigo, linguistic determinism predicts that this person would not be able to perceive these two colors as distinct. The researcher's conclusion that color perception may be limited by vocabulary and language is best aligned with the Sapir-Whorf hypothesis. (Choice A) The nativist hypothesis states that language is not learned the way other skills/behaviors are learned but is rather an innate process hardwired in the brain. As long as humans are exposed to language during a critical (time-sensitive) period in early life, language development is biologically predetermined. (Choice B) The opponent-process theory states that color information from cones is combined in such a way that we perceive three opposing pairs of colors: black/white, blue/yellow, and red/green. No two members of a pair are seen simultaneously, which is why we do not see colors such as "reddish green" or "bluish yellow." (Choice D) The Young-Helmholtz theory, also known as the trichromatic theory, states that all the colors we see are the result of the combined activity of three types of photoreceptors: Those that respond to short (blue), medium (green), and long (red) wavelengths of light. Educational objective: The Sapir-Whorf hypothesis (linguistic relativity) states that language influences/shapes cognition and perception. A stronger version of the hypothesis (linguistic determinism) states that language controls/limits cognition and perception.