UWorld Wrong Answers

Assume a single-celled organism was discovered in water above 100°C. On closer inspection, it is determined that this organism is classified under the Archaea domain. Given this information, this organism most likely has: A.a peptidoglycan layer in its cell wall. B.a circular chromosome. C.telomeres. D.an endoplasmic reticulum.

B.a circular chromosome.

Before Sarah sought therapy, her cleaning rituals acted as: A.positive reinforcement. B.negative reinforcement. C.positive punishment. D.negative punishment.

B.negative reinforcement. Operant conditioning is a type of learning that occurs when the likelihood of an organism repeating a behavior is influenced by the outcome of that behavior (ie, reward or punishment). For example, when a rat receives a food pellet (ie, reward) after pushing a lever, the rat is more likely to push the lever again. Reinforcement increases (or maintains) behavior; negative reinforcement occurs when an undesirable stimulus is removed, which encourages a behavior to happen again. Sarah's cleaning rituals act as negative reinforcement because she experienced a reduction in anxiety (ie, removal of an undesirable stimulus) after performing cleaning rituals, leading her to perform the cleaning rituals more often (ie, behavior increases). (Choice A) Positive reinforcement occurs when a desirable stimulus is applied, which encourages a behavior to happen again. For Sarah, cleaning rituals remove an unpleasant stimulus (ie, reduce anxiety), an example of negative reinforcement, rather than apply a desirable stimulus. (Choices C and D) Punishment discourages a behavior from happening again. Positive punishment occurs when an undesirable stimulus is applied, and negative punishment occurs when a desirable stimulus is removed. For Sarah, the alleviation of anxiety (ie, removal of unpleasant stimulus) encourages her to perform the cleaning rituals again, which is an example of negative reinforcement, not punishment. Educational objective:In operant conditioning, reinforcement increases the likelihood a behavior will occur again. Positive reinforcement involves the application of a desirable stimulus, whereas negative reinforcement involves the withdrawal of an undesirable stimulus.

Standardized protocols, patient checklists, and clinical guidelines are meant to increase efficiency, calculability, predictability, and control in the clinical setting. However, critics of standardizing medicine suggest that these sorts of practices may lead to: A.a manifest function of medical care. B.the McDonaldization of health care. C.an increase in the cultural capital of doctors. D.a decrease in the ascribed status of patients.

B.the McDonaldization of health care. In sociology, bureaucracy is defined as the most efficient and rational way to organize human behavior. A critical perspective of bureaucracy, McDonaldization describes the process by which extreme efficiency and rationalization produce negative consequences. The term stems from the fast-food industry, in which processes to increase efficiency, calculability, predictability, and control ensure that all franchised restaurants produce a similar, standardized product and experience. McDonaldization describes when the following happens in society: Efficiency produces optimization at the cost of individuality. Calculability produces high quantities at the expense of quality. Predictability produces standardization at the expense of uniqueness. Control increases automation, reducing the need for a skilled workforce. Standardized protocols, patient checklists, and clinical guidelines may increase efficiency, calculability, predictability, and control at the expense of patient care. Therefore, critics would most likely argue that McDonaldization of health care has occurred.

If a frameshift mutation changes the number of amino acids in a protein from 591 to 626, the difference between molecular weights of the wild-type and mutant proteins would be closest to: A.1 kDa B.2 kDa C.4 kDa D.8 kDa

C.4 kDa Frameshift mutations can disrupt the location of stop codons and frequently result in elongated or truncated proteins. The question states that the frameshift mutation increased the length of the protein from 591 to 626 amino acids. The approximate molecular weight of a protein can be determined by multiplying the number of amino acids by the average weight of a single amino acid (110 Da), so a protein with 591 amino acids (wild type) would have a molecular weight of approximately 65,000 Da, or 65 kDa (110 Da/amino acid × 591 amino acids ≈ 65,000 Da). The molecular weight of the mutant protein is 110 Da/amino acid × 626 amino acids ≈ 69,000 Da, or 69 kDa. The difference in molecular weight between 69 kDa and 65 kDa is 4 kDa. Alternatively, the answer may be determined by the difference in the number of amino acids (626 − 591 = 35 amino acids) multiplied by 110 (35 amino acids × 110 Da/amino acid = 3850 Da ≈ 4 kDa). (Choices A, B, and D) Calculating the average molecular weight of amino acids incorrectly could yield these numbers. Educational objective:The average molecular weight of an amino acid is 110 Da. The molecular weight of a polypeptide can be estimated by multiplying the number of amino acids in the polypeptide by 110.

Which of the following best exemplifies instinctive drift? A.Children are born with a biological predisposition to prefer sweet foods and to dislike bitter foods, which are more likely to be toxic. B.In humans, it is easier to condition a fear response to innately dangerous stimuli, such as snakes, than to harmless stimuli, such as rabbits. C.Animals trained to perform a specific behavior will often lose that behavior in favor of innate behaviors, even when reinforcement is present. D.Animals who become ill after one exposure to a noxious stimulus will quickly learn to avoid that stimulus in the future.

C.Animals trained to perform a specific behavior will often lose that behavior in favor of innate behaviors, even when reinforcement is present. An instinct is an innate, fixed pattern of behavior that is more complex than a reflex, which is a simple response to a stimulus (eg, jerking hand away from hot stove). Instincts are not based on prior experience or learning. For example, newly hatched sea turtles instinctively know to move toward the ocean and swim. Instinctive (or instinctual) drift describes an animal's innate behaviors overshadowing a learned behavior. Animals can often be trained using operant conditioning, whereby a desired behavior is reinforced with a reward. However, even when reinforcement is provided, trained animals will often revert to innate behaviors. For example, researchers used food rewards to train pigs to pick up wooden coins and deposit them in a piggy bank. Over time, even though the pigs could be successfully trained to complete the behavior, the pigs began dropping the coins before reaching the piggy bank and pushing them along the ground with their snouts, a species-specific behavior known as rooting. (Choice A) Children are biologically predisposed to prefer sweet over bitter tastes, which is believed to confer an evolutionary advantage to babies who preferred more calorie-dense (sweet) foods and rejected foods more likely to be toxic (bitter). However, this describes an innate preference and is not an example of instinctive drift. (Choice B) Most animals have an innate fear of their predators. Although human behavior is more complex than animal behavior, studies suggest that it is easier to condition humans to fear certain stimuli, specifically snakes, spiders, and rats. However, this describes a fear instinct in humans, which is not an example of instinctive drift. (Choice D) Animals and humans will associate whatever they consumed (usually through sight or smell cues) with becoming ill and will avoid it in the future. This is known as a taste aversion, a powerful type of associative learning, and is not an example of instinctive drift.

An 84-mg sample of a compound is found to contain 36 mg of carbon, 3 mg of hydrogen, 21 mg of nitrogen, and 24 mg of oxygen. If the compound has a molecular weight of 112 g/mol, what is its molecular formula? A.C2H2NO B.C4H6N3O C.C5H6NO2 D.C4H4N2O2

D.C4H4N2O2 The composition of chemical compounds can be described in several ways, including the empirical, molecular, and structural formulae. The empirical formula describes only the ratios of each unique atom in a compound, whereas the molecular formula describes the actual number of each type of atom. The structural formula describes how the atoms are bonded to one another. An empirical formula may be calculated from the known mass of each type of atom in a compound sample by calculating the number of moles of each. Dividing each mass given in the question by the atomic mass of the atom yields the number of moles. For these calculations, grams and moles are scaled down to milligrams and millimoles: Carbon: 36 mg12 mg/mmol=3 mmol36 mg12 mg/mmol=3 mmol Hydrogen: 3 mg1 mg/mmol=3 mmol3 mg1 mg/mmol=3 mmol Nitrogen: 21 mg14 mg/mmol=1.5 mmol21 mg14 mg/mmol=1.5 mmol Oxygen: 24 mg16 mg/mmol=1.5 mmol24 mg16 mg/mmol=1.5 mmol Dividing each molar amount by the smallest molar amount (1.5 mmol) yields the relative ratios of each type of atom: C:H:N:O = 2:2:1:1. Therefore, the empirical formula of the compound is C2H2NO (Choice A). However, the question states that the compound has a molecular weight of 112 g/mol. A compound with a molecular formula of C2H2NO would only have a molecular weight of 56 g/mol, or half the observed molecular weight. Doubling the number of each atom (a two-fold multiple of the lowest whole-number ratio) yields the correct molecular formula C4H4N2O2, which is consistent with the compound composition. (Choices B and C) C4H6N3O and C5H6NO2 have the correct molecular weight but the wrong ratios of each type of atom. Educational objective:Compounds may be described by their empirical, molecular, and structural formulae. Empirical formulae describe only the relative ratios of each type of atom, molecular formulae describe the actual numbers of each type of atom, and structural formulae describe the spatial arrangement of the atoms.

Which of the following helps maintain the resting membrane potential of a neuron? Passive transport Active transport Membrane selective permeability

I, II, and III

A 100-g block of iron at 31°C is submerged in 50 g of water at 25°C in a thermally insulated container. If the temperature of the system reaches equilibrium at 26°C, what is the specific heat of iron? (Note: The specific heat of water is 4.2 J/(g⋅°C).)

0.42 J/(g⋅°C) The specific heat of a substance is an intrinsic property (does not depend on mass) and is the amount of heat required to increase a unit mass (1 g or 1 kg) by 1°C or 1 K. The total amount of heat gained or lost by an object is the product of its mass m, its specific heat c, and the change in temperature ΔT, as given by the calorimetry equation: q=mc∆Tq=mc∆T Because the block of iron is hotter than the water, heat flows from the iron to the water, and the temperature of the water increases from 25°C to 26°C (ΔT = 1°C). The heat gained by water is calculated using its given mass (50 g), specific heat (4.2Jg⋅°C)4.2Jg⋅°C , and ΔT: qwater=(50 g)(4.2Jg⋅°C)(1°C)=210 Jqwater=50 g4.2Jg⋅°C1°C=210 J Because the container is thermally insulated, the heat gained by the water is equal to the heat lost by the iron block, qiron = −210 J. According to the question, the 100-g iron block decreases in temperature from 31°C to 26°C (ΔT = −5°C). The specific heat of iron is calculated by rearranging the calorimetry equation and using these values: c=qm∆Tc=qm∆T ciron=−210 J(100 g)(−5°C)=210500Jg⋅°C=0.42Jg⋅°C

One horsepower (hp) is the amount of power required to lift a 75-kg mass a vertical distance of 1 m in 1 s. What is 2 hp equivalent to in watts (W)?

1,500 W Mechanical power P is the amount of work W done per unit time t: P=WtP=Wt From the work-energy theorem, the change in the potential energy (PE) of an object is equal to the amount of work done in the vertical direction. Gravitational potential energy is due to an object's position relative to Earth's gravitational field, and it is the product of mass m, gravitational acceleration g, and the height h. Therefore, the work done is equal to the change in PE, which depends on the change in height Δh: W=∆PE=mg∆hW=∆PE=mg∆h Substituting the above equation into the power equation, P=Wt=mg∆htP=Wt=mg∆ht The SI unit for power is the watt (W), and the value of g is 10 m/s2. One horsepower (hp) is calculated using the values provided in the question for m, Δh, and t: 1 hp=(75 kg)(10 m/s2)(1 m)1 s=750 W1 hp=75 kg10 m/s21 m1 s=750 W Because 1 hp is equal to 750 W, 2 hp is double this value, or 1,500 W.

A charged particle is accelerated in a uniform electric field. When its velocity is 2 m/s, its electric potential energy is 100 J and its kinetic energy is 10 J. What is the particle's potential energy when its velocity reaches 4 m/s?

70 J Electric charges generate electric fields, regions of space that exert an electrostatic force on charges. The electrostatic force is conservative and the total energy E of a charged particle in an electric field is conserved. In other words, the sum of the charge's electric potential energy (PE) and kinetic energy (KE) is constant: Einitial=EfinalEinitial=Efinal PEinitial+KEinitial=PEfinal+KEfinalPEinitial+KEinitial=PEfinal+KEfinal The initial E of the particle in the electric field is the sum of the given PE and KE: Einitial=PEinitial+KEinitialEinitial=PEinitial+KEinitial Einitial=100 J+10 J=110 JEinitial=100 J+10 J=110 J Furthermore, KE is proportional to mass m and the square of velocity v: KE=12mv2KE=12mv2 As the particle accelerates, its velocity increases by a factor of 2, from 2 to 4 m/s. Therefore, its final KE increases by a factor of 4: KEfinal=12m(2v)2=22(12mv2)=4(12mv2)KEfinal=12m2v2=2212mv2=412mv2 KEfinal=4(KEinitial)=4(10 J)=40 JKEfinal=4KEinitial=410 J=40 J The final PE of the particle at 4 m/s is the difference between the overall total energy and its final KE: PEfinal=Efinal−KEfinal=Einitial−KEfinalPEfinal=Efinal-KEfinal=Einitial-KEfinal PEfinal=110 J−40 J=70 J

Which range corresponds to the expected chemical shifts of the adamantane protons in the 1H NMR spectrum of Compound 4? A.1.0-2.0 ppm B.2.5-4.5 ppm C.4.5-6.5 ppm D.7.0-8.0 ppm

A.1.0-2.0 ppm In proton nuclear magnetic resonance spectroscopy (1H NMR), the chemical shift (ie, the location of the signals in the spectrum relative to a reference compound) is given in parts per million (ppm) with a typical range of 0-12 ppm. Tetramethylsilane (TMS) (ie, Si(CH3)4) is commonly used as a reference compound (ie, its peak is set to 0 ppm) in 1H NMR because its methyl groups are very shielded, resulting in a signal that is upfield (ie, has smaller chemical shift) relative to most NMR signals. The chemical shift of a proton depends on its electronic environment. An upfield signal arises when a proton is surrounded by an electron cloud, shielding it from the external magnetic field B0. A downfield signal (ie, a larger chemical shift) arises when an adjacent electronegative substituent withdraws electrons from a proton, deshielding it from B0. The passage and the structure of Compound 4 in Figure 1 indicate that the adamantane substituent is a hydrocarbon (ie, made of carbon and hydrogen atoms). Aliphatic protons are surrounded by an electron cloud and shielded from B0, resulting in an upfield chemical shift typically below 2 ppm. Therefore, the signals for the protons in the adamantane substituent in Compound 4 appear between 1.0 and 2.0 ppm. (Choice B) Protons adjacent to an electronegative substituent, such as a halogen or oxygen, are deshielded relative to aliphatic protons and generally appear between 2.5 and 4.5 ppm. (Choices C and D) Vinyl protons (ie, -C=C-H) and protons on an aromatic ring experience an anisotropic effect, causing the protons to be deshielded and have a downfield chemical shift. Vinyl protons do not experience as large of an effect and appear between 4.5 and 6.5 ppm whereas aromatic protons are more downfield between 7.0 and 8.0 ppm.

A radioactive atom decays by 5 alpha, 3 beta minus, and 2 gamma emissions to yield 211Po. What was the original nucleus? A.231Pa B.223At C.231U D.191Ir

A.231Pa Radioactive decay is the process by which an unstable nucleus becomes stable. There are three common modes of decay, which change the nucleus in different ways: Alpha emission is the release of a helium nucleus (two protons and two neutrons). Each alpha emission reduces the atomic mass and atomic number of the atom by 4 and 2, respectively. Beta minus emission is the release of an electron from the nucleus and turns a neutron into a proton; it increases the atomic number by 1. The mass of an electron is negligible compared to the nucleus, so beta emission does not alter the atomic mass. Gamma emission is the release of a high energy photon that occurs when the protons and neutrons in a nucleus change configuration. It does not alter the atomic mass or atomic number of an atom. The question states that 211Po was generated after 5 alpha, 3 beta minus, and 2 gamma emissions. The 5 alpha emissions reduced the atomic mass by a total of 20, so the initial atom had an atomic mass of 231. Also, the original nucleus lost 10 protons from alpha emissions but gained 3 back from beta minus emissions, so it had 7 more protons than polonium. The gamma emissions had no effect on atomic mass or number. The periodic table shows that polonium has 84 protons, so the original nucleus must have had 91 protons. Therefore, the original nucleus was 231Pa. (Choice B) 223At would be the original nucleus if the numbers of alpha and beta minus emissions were reversed. (Choice C) 231U would be the original nucleus if the numbers of beta minus and gamma emissions were reversed. (Choice D) 191Ir would be the product if 211Po underwent the described decay series.

A researcher replicates the study but continues to occasionally pair the 20-cm ring with an electric shock in phase 2. Which phenomenon is the researcher most likely trying to avoid? A.Extinction B.Acquisition C.Spontaneous recovery D.Stimulus discrimination

A.Extinction In classical conditioning, the strength of the conditioned response tends to follow a characteristic pattern over time: Acquisition refers to the learning that takes place as an association is formed between the unconditioned stimulus (eg, food) and the neutral stimulus (eg, bell). Extinction occurs when a conditioned response gradually stops occurring in the absence of the unconditioned stimulus. For example, a dog that has been conditioned to salivate in response to the sound of a bell will gradually stop salivating if the bell is repeatedly presented without food. Spontaneous recovery occurs when an extinct response reappears after a period of time (eg, a dog will salivate again upon hearing a bell a few days after extinction has occurred). If the 20-cm ring (conditioned stimulus) was repeatedly presented in the absence of the electric shock (unconditioned stimulus), this would eventually extinguish the startle (conditioned response). However, if an electric shock were occasionally paired with the 20-cm ring, this would maintain the conditioned fear response, thereby avoiding extinction. (Choice B) Phase 1 of the study, when the electric shock was repeatedly paired with the 20-cm ring, was the acquisition phase. Occasionally administering the electric shock with the 20-cm ring during phase 2 would not avoid acquisition, which has already occurred. (Choice C) Spontaneous recovery is the reappearance of the conditioned response after it has already been extinguished. Occasionally administering the electric shock during phase 2 would not avoid spontaneous recovery, which only occurs after a conditioned response has become extinct. (Choice D) Stimulus discrimination occurs when an organism distinguishes between two similar stimuli (eg, a dog that has been conditioned to salivate in response to a bell salivates only to the sound of that bell, not in response to other similar sounds). This concept does not apply to administering the electric shock during phase 2. Educational objective:In classical conditioning, extinction occurs when the conditioned stimulus alone no longer produces the conditioned response.

Which statement best describes the characteristics of hormones secreted from the pituitary gland? A.Hormones secreted from the posterior pituitary are synthesized in the hypothalamus. B.Hormones secreted from the posterior pituitary act on other endocrine glands. C.Hormones secreted from the anterior pituitary act directly only on nonendocrine tissues. D.Hormones secreted from the anterior pituitary are released by depolarization of the nerve terminals.

A.Hormones secreted from the posterior pituitary are synthesized in the hypothalamus. The pituitary gland is a small structure that sits inside a bony cavity below the hypothalamus at the base of the brain. It is attached to the hypothalamus via the pituitary stalk and can be divided into two separate lobes: The anterior lobe is made up of glandular tissue containing different cell types that synthesize and secrete follicle-stimulating hormone (FSH), luteinizing hormone (LH), adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), growth hormone (GH), β-endorphins, and prolactin. The synthesis and secretion of hormones from the anterior pituitary is controlled primarily by neurohormones released from hypothalamic neurons. These regulatory neurohormones are secreted into the hypophyseal portal system, a venous network of small blood vessels that enables small quantities of hormones secreted from the hypothalamus to directly reach the anterior pituitary without being diluted in the circulation. The posterior lobe, made up of axonal projections from the hypothalamus, stores and secretes the hormones oxytocin and vasopressin (also called antidiuretic hormone [ADH]). Posterior pituitary hormones are synthesized in hypothalamic neurons and then transported down the axon to the axon terminals in the posterior pituitary, where they are stored. The secretion of stored hormones from the posterior pituitary is mediated by action potentials that cause exocytosis of neurosecretory vesicles. (Choices B and C) Hormones can be classified by their modes of actions. Tropic hormones regulate the secretion of other hormones by acting on other endocrine glands. In contrast, direct or nontropic hormones act directly on nonendocrine tissues to cause physiological end points (eg, ADH-induced water reabsorption). The anterior pituitary releases both tropic (FSH, LH, ACTH, TSH, GH) and direct (GH, prolactin, endorphins) hormones, whereas the posterior pituitary releases only direct hormones (oxytocin, ADH). (Choice D) The secretion of hormones from the anterior pituitary is stimulated primarily by regulatory neurohormones released into the blood by hypothalamic neurons. In contrast, the secretion of stored hormones from the posterior pituitary is induced by depolarization of the nerve terminals. Educational objective:The synthesis and secretion of hormones from the anterior pituitary is regulated by the release of neurohormones into the blood from neurons located in the hypothalamus. In contrast, posterior pituitary hormones are synthesized in hypothalamic neurons and undergo anterograde axonal transport to the posterior pituitary. The secretion of stored posterior pituitary hormones from the axon terminals is mediated by depolarization of the nerve terminals.

Which of the following cell-cell junctions would help skin cells withstand mechanical stress by directly anchoring the intermediate filaments of adjacent cells? Desmosomes Gap junctions Tight junctions

A.I only Cell-cell junctions, such as desmosomes, gap junctions, and tight junctions, are structures that attach adjacent cells to one another. Cell junctions are prominent in epithelial tissue, which is composed of densely packed cells and very little extracellular matrix. Desmosomes provide tensile strength to epithelial cell sheets by anchoring the cytoskeletons, specifically the intermediate filaments, of two cells together. This creates a continuous cytoskeletal network that spans the entire epithelial sheet, one through which mechanical stress (eg, pulling, stretching, tension) can be distributed. Desmosomes are found predominantly in tissues that are subject to high levels of mechanical stress (eg, muscle tissue, epithelial layers of the skin) and prevent tissue tearing (Number I). (Number II) Gap junctions are cell-cell junctions that mediate communication between cells. Protein channels (connexons) in one cell align with complementary channels in another cell to form pores that facilitate the passive and bidirectional exchange of ions and small solutes. Gap junctions are found in cell populations that depend on coordinated activity, such as smooth muscle, cardiac muscle, or neural tissue. (Number III) Tight junctions are cell-cell junctions that prevent water and solutes from diffusing between cells and across the epithelial cell layer. These junctions form a watertight seal that fully encircles the apical end of every cell in the basal epithelial sheet. Tight junctions serve as a barrier and separate tissue space; they are found in a number of tissues, including skin, gastrointestinal tract, and testis.

conditioned fear response during phase 2 occurs as a result of which type of memory? A.Implicit memory B.Procedural memory C.Explicit memory D.Semantic memory

A.Implicit memory Research suggests that humans have two long-term memory systems, referred to as implicit and explicit. Implicit/nondeclarative memory is memory for things that cannot be consciously recalled, such as skills, tasks, emotions, and reflexes. Examples of implicit memory include: Procedural memory, which is memory for motor skills (eg, riding a bicycle) (Choice B). Emotional/reflexive memory, which is memory for associations between stimuli (eg, salty ocean air triggers pleasant emotions from childhood beach vacations). Classically conditioned fear responses are emotional, outside of conscious recall (ie, automatic/involuntary), and often elicit reflexive responses (eg, startle reflex). Therefore, the conditioned fear response during phase 2 occurs as a result of implicit memory. (Choices C and D) Explicit/declarative memory is memory for facts and events that can be consciously or intentionally recalled. Explicit memory consists of episodic memory, which is memory for personal experiences (eg, what you ate for dinner last night), and semantic memory, which includes knowledge about facts (eg, apples are a type of fruit). Educational objective:Implicit/nondeclarative memory is memory for things that cannot be consciously recalled, such as skills, tasks, emotions, and reflexes. Classically conditioned responses rely on implicit memory.

Which of the following does NOT describe why a nucleophile will react more quickly with acetic anhydride than with N,N-diisopropylisobutyramide? A.N,N-diisopropylisobutyramide has a greater inductive effect than acetic anhydride. B.Acetic anhydride is a stronger electrophile than N,N-diisopropylisobutyramide. C.Acetic anhydride is less sterically hindered than N,N-diisopropylisobutyramide. D.N,N-diisopropylisobutyramide has a less stable leaving group than acetic anhydride.

A.N,N-diisopropylisobutyramide has a greater inductive effect than acetic anhydride. Reactivity of carboxylic acid derivatives with a nucleophile depends on various factors, including inductive effects, steric effects, and leaving group stability. Induction is an electronic property in which electrons are donated through sigma bonds. Electronegative atoms or electron withdrawing substituents pull electrons away from an adjacent atom toward themselves, creating a dipole. The closer the electron withdrawing group to an atom, the greater the inductive effect that atom experiences. Acetic anhydride and N,N-diisopropylisobutyramide both have two electronegative atoms bonded to each carbonyl carbon. The anhydride carbonyl carbons are bound to two oxygen atoms whereas the amide carbonyl carbon is bound to an oxygen and a nitrogen. Because oxygen is more electronegative than nitrogen, it draws more electron density away from the carbonyl carbon than nitrogen does, creating a larger dipole on the anhydride than on the amide, as well as a more electrophilic carbonyl carbon on the anhydride (Choice B). Electron withdrawing groups also make good leaving groups. The leaving group of N,N-diisopropylisobutyramide is the amino group, and the leaving group of acetic anhydride is the carboxyl group. Amine groups are less stable leaving groups than carboxyl groups (Choice D) because carboxyl groups are stabilized by resonance delocalization of the negative charge obtained after being eliminated. Nucleophiles react more readily with less sterically hindered electrophiles. The methyl groups bonded to the carbonyls on acetic anhydride provide less steric hindrance than the bulky isopropyl groups on the nitrogen and adjacent to the carbonyl in N,N-diisopropylisobutyramide (Choice C), making it easier for a nucleophile to react with acetic anhydride. The question asks which statement does NOT describe why a nucleophile will react more quickly with acetic anhydride than with N,N-diisopropylisobutyramide. Because nucleophiles react more readily with stronger electrophiles and anhydrides contain stronger electron withdrawing groups than amides, anhydrides experience a greater inductive effect and react with a nucleophile more readily than amides. Therefore, N,N-diisopropylisobutyramide has a smaller rather than a greater inductive effect than acetic anhydride.

Based on Figure 1, which conclusion is most likely to be supported? A.Pretreatment expectation of nausea is correlated with AN at session #3. B.Pretreatment expectation of nausea is correlated with PN at session #1. C.Experiencing PN at session #1 is correlated with AN at session #3. D.Lack of PN at session #1 is correlated with AN at session #3.

A.Pretreatment expectation of nausea is correlated with AN at session #3. When random assignment to groups is not possible (or ethical) in research involving human subjects, researchers will often conduct a correlational research study. In these designs, predictor variables may be assessed for their association with outcome variables, although specific causal relationships cannot be determined. In Study 3, researchers investigated whether a pretreatment expectation of nausea or experience of PN from session #1 was a better predictor of AN at session #3. Because they could not randomly assign subjects to the condition of whether or not to expect nausea, this is a correlational study design. Stacked bar graphs are useful for depicting and comparing parts of a whole, with different colors representing different subgroups within a larger group. Figure 1 illustrates that the group with pretreatment expectations of nausea contained the highest percentage of those who went on to develop AN, which supports the role of cognitive processes (eg, expectations) in associative learning. (Choice B) Pretreatment expectation of nausea as a predictor of PN at session #1 is not shown in the graph. (Choices C and D) The percentage of patients who went on to develop AN at session #3 was similar to the percentage of patients who did and did not experience PN at session #1. Neither PN nor a lack of PN at session #1 was as strongly associated with AN at session #3 as pretreatment expectation of nausea. Educational objective:When random assignment to conditions is not possible, researchers may use a correlational study design in which predictor variables may be assessed for their association with outcome variables. Correlational designs do not allow for the determination of causal relationships. Stacked bar graphs depict data with subgroups that make up the whole.

In which of the following steps is 2-naphthoic acid separated from the mixture? A.Step 1 B.Step 3 C.Step 4 D.Step 5

A.Step 1 A mixture of organic molecules with acidic and basic functional groups can be separated by and acid-base extraction. The acid and base components in the mixture are initially in the organic layer but can enter the aqueous phase if converted to an ionic salt by deprotonation or protonation via extraction with an aqueous base or acid, respectively. Carboxylic acids can be deprotonated by strong and weak bases. Consequently, separating a mixture of a carboxylic acid and an organic base can be achieved by extraction with an aqueous base that can deprotonate the carboxylic acid and pull it into the aqueous layer. The organic base in the mixture is not reactive toward the aqueous base added for the extraction and remains in the organic layer. The passage states that in Step 1, the mixture of fluorene, 2-naphthoic acid, and diphenylamine is extracted with 1 M NaOH(aq). 2-naphthoic acid is a carboxylic acid and is deprotonated by NaOH(aq) during the extraction, forming a carboxylate salt that is pulled into the aqueous layer. Because fluorene is not sufficiently acidic (pKa = 22) and diphenylamine is a base, these molecules are not deprotonated by NaOH(aq) and remain in the organic layer. Therefore, Step 1 separates 2-naphthoic acid the mixture. (Choice B) Step 3 describes the separation of fluorene and diphenylamine by extraction with HCl(aq), which protonates diphenylamine to form an ammonium salt that goes into the aqueous layer. (Choice C) Step 4 describes the isolation of 2-naphthoic acid and diphenylamine (ie, the precipitates in Flask A and B, respectively) by vacuum filtration. (Choice D) Step 5 describes isolation of fluorene from the organic layer. Educational objective:A mixture of organic molecules with acidic or basic functional groups can be separated by an acid-base extraction. The acidic or basic molecule can enter the aqueous layer when extracted with a base or acid, respectively.

Which of the following is true, according to the Mead theory of identity development? A.The "me" is the aspect of self that is formed through interactions with others. B.The "I" is the aspect of self that is formed during the game stage. C.The "looking-glass self" results from an individual's cumulative lifetime of interactions with others. D.The "front-stage self" involves behaving in ways that align with social norms and expectations.

A.The "me" is the aspect of self that is formed through interactions with others. (53%) George Herbert Mead, who is most associated with the sociological theory of symbolic interactionism, argued that social (rather than biological) factors influence identity formation. Mead suggested that the experience of "self" emerges through social interaction with others who play important and formative roles in one's life (eg, family). The two aspects of the self are the "I" and "me," which develop in stages: Preparatory (or imitation): Babies/toddlers imitate others (eg, a parent's hand gesture) and begin using symbols and language (eg, repeating a phrase used by a parent) without meaning comprehension. At this stage, children have no sense of "self" as separate from the world around them. Play: Through play (eg, pretending to be a doctor), preschool-age children begin role-taking (ie, understanding the perspectives of others). When children understand themselves as individuals separate from others, the "I" component of the self has developed. Children then begin to imagine how others perceive them, which is the beginning of the development of the "me." Game: School-age children become aware of their position/role in relation to others. They begin to see themselves from the perspective of the more abstract generalized other, further developing the "me" to incorporate the values and rules of the society in which they live. (Choice B) According to the Mead theory, the "me," not the "I," is formed through interactions with others during the game stage. (Choice C) Charles Cooley (not Mead) proposed the concept of the looking-glass self, suggesting that beliefs about oneself are derived through social interactions with others throughout one's lifetime. The Mead theory differs from the Cooley theory by suggesting that interactions early in life result in one's conception of self or identity. (Choice D) The dramaturgical perspective of Erving Goffman (not Mead) explains social behavior using a theater metaphor; the front-stage self involves individuals behaving as "actors" in front of an "audience," whereas the back-stage self includes the behaviors in which an individual engages more privately.

The HP group peer mentor would have been most likely to have participants focus on: A.accepting the circumstances of their child's condition and pursuing personal growth. B.replacing negative, maladaptive thoughts with positive, adaptive thoughts. C.uncovering unconscious conflicts and feelings about their child's condition. D.treating underlying physiological causes of their depression before engaging in therapy.

A.accepting the circumstances of their child's condition and pursuing personal growth. Humanistic psychology emphasizes the higher aspects of human nature, including the drive toward self-actualization (ie, achieving one's full potential) and personal growth. Humanistic psychologists take an optimistic view of human nature, believing that people have an innate drive toward self-improvement. Humanistic psychotherapy utilizes a person- or client-centered approach (the word "patient" is not used), so the intervention is unique to the individual. Therefore, participants in the HP group, guided by humanistic psychology interventions from their peer mentor, would have most likely focused on accepting the circumstances of their child's condition and pursuing personal growth. (Choice B) Cognitive-behavioral therapy attempts to replace negative thoughts and behaviors with healthier thoughts and behaviors. The HP group participants would not have focused on replacing maladaptive thoughts with adaptive ones (a cognitive-behavioral approach). (Choice C) The psychodynamic approach focuses on revealing the unconscious and on understanding how previous conflict influences the present. The HP group participants would not have focused on uncovering unconscious conflicts and feelings about their child's condition (a psychodynamic approach). (Choice D) The biomedical approach views physiological causes (eg, abnormal brain chemistry) as the basis for psychological symptoms, emphasizing treatment with medical interventions (eg, medication). The HP group participants would not have focused on treating underlying physiological causes (a biomedical approach). Educational objective:Humanistic psychology takes an optimistic approach, emphasizing the positive and creative aspects of human nature. It asserts that individuals strive toward self-actualization (fullest potential) and personal growth.

To investigate attributions related to exercise, an experimenter interviewed primary care physicians (PCPs) about their own exercise habits and their patients' reported exercise habits. The experimenter found that PCPs were more likely to attribute their own lack of exercise to factors such as being too busy, but were more likely to attribute their patients' lack of exercise to factors such as laziness. These results best illustrate the: A.actor-observer bias. B.experimenter bias. C.fundamental attribution error. D.self-serving bias.

A.actor-observer bias. Attributional biases are cognitive biases (common errors in thinking) that occur when people attempt to explain their own behavior or the behavior of someone else. Attributions can be dispositional, based on internal characteristics (eg, personality), or situational, based on external factors (eg, environment). The actor-observer bias is an attributional bias that describes the tendency to attribute one's own actions to external factors but the actions of others to internal factors. The physicians' tendency to make external attributions for their own lack of exercise (eg, "I'm too busy") while attributing their patients' lack of exercise to internal factors (eg, "they are lazy") best supports the actor-observer bias. (Choice B) Experimenter bias occurs when researchers deliberately or inadvertently influence their study, often leading to results that confirm what the researcher was expecting. Experimenter bias is not a type of attributional bias, and it is not illustrated by the results. (Choice C) The fundamental attribution error, an attributional bias, is the tendency to blame others' behavior on internal (eg, "they are lazy") instead of external factors. The fundamental attribution error fails to account for the finding regarding physicians' attributions for their own behaviors. (Choice D) Self-serving bias is an attributional bias that occurs when individuals credit their successes to internal factors but blame their failures on external factors. The results do not provide information about attributions related to success. Educational objective:Attributional biases are common errors in thinking that occur when people attempt to explain behavior (their own or someone else's). The actor-observer bias occurs when individuals attribute their own behavior to external factors but attribute the behavior of others to internal factors.

A drug that blocks the release of adrenocorticotropic hormone from the anterior pituitary would most likely: A.decrease secretion of cortisol from the adrenal cortex. B.decrease secretion of thyroid-stimulating hormone from the anterior pituitary. C.increase secretion of oxytocin from the posterior pituitary. D.increase secretion of calcitonin from the thyroid.

A.decrease secretion of cortisol from the adrenal cortex. The adrenal glands are located atop each kidney. Each adrenal gland can be subdivided into two portions: a central inner portion called the adrenal medulla, and an outer portion called the adrenal cortex, which is responsible for secreting corticosteroids (eg, cortisol, aldosterone). The hypothalamic-pituitary-adrenal pathway (HPA axis) controls the secretion of glucocorticoids from the adrenal cortex as follows: The hypothalamus secretes corticotropin-releasing hormone (CRH) in response to low glucocorticoid levels and increased stress. CRH acts on the anterior pituitary, which causes the release of adrenocorticotropic hormone (ACTH). ACTH stimulates the adrenal cortex to synthesize and release cortisol. Cortisol targets tissues (eg, muscle and liver) to increase the ability to cope with stressors. In addition, cortisol functions as a negative feedback signal by inhibiting the secretion of CRH and ACTH. A drug that blocks the release of ACTH would also block the stimulatory effect of ACTH on the adrenal cortex, thereby decreasing the secretion of cortisol. (Choice B) The secretion of thyroid-stimulating hormone (TSH) from the anterior pituitary is mediated by the HPA axis. In this pathway, secretion of TSH is controlled by the release of thyrotropin-releasing hormone (TRH) from the hypothalamus, not ACTH. (Choice C) The release of oxytocin from the posterior pituitary is stimulated by pressure against the cervix during childbirth. In response to oxytocin, uterine contractions increase, which further stimulate the release of oxytocin until the baby has been delivered. Oxytocin also targets breast tissue to stimulate milk ejection. (Choice D) In response to an increase in blood calcium levels, the parafollicular cells of the thyroid secrete calcitonin. The primary purpose of calcitonin is to reduce calcium levels; however, the impact on plasma calcium concentrations has been found to be insignificant. Educational objective:Corticosteroids (glucocorticoids and mineralocorticoids) are steroid hormones released by the adrenal cortex. The release of cortisol from the adrenal cortex is mediated by the secretion of adrenocorticotropic hormone from the anterior pituitary.

Which prediction is compatible with the sociologists' assertion in the fourth paragraph? The increase of medicalization in society will result in medical professionals having: A.greater power and authority. B.reduced power and authority. C.greater authority, but with no effect on their power. D.greater power, but with no effect on their authority.

A.greater power and authority. In sociology, power refers to the ability to control and influence others. Authority refers to whether others believe that the power is legitimate. There are three types of authority: Traditional authority comes from longstanding patterns in society (eg, a queen is seen as having legitimate power in a monarchy). Charismatic authority stems from the personal appeal and/or extraordinary claims of an individual (eg, Gandhi was seen as having legitimate power due to his ability to inspire people). Rational-legal authority arises from the professional position a person holds (eg, a physician is seen as having legitimate power due to extensive training). Medicalization, the process of defining human behaviors or characteristics as medical conditions, often results from shifting attitudes, new scientific evidence, or new treatments. For example, menopause, a natural condition, is now viewed by some as a deficiency in hormones that can be treated with pharmaceuticals. Medicalization leads individuals to look to medical professionals as the experts in diagnosing, preventing, or treating such conditions. As medicalization increases in a society, individuals will increasingly rely on medical professionals, rather than clergy, as legitimate sources of guidance on lifestyle behaviors. Therefore, medical professionals will have more power (ie, influence on people) and authority, as that power will be seen as legitimate. (Choice B) Increasing medicalization will increase, not reduce, the power and authority of medical professionals. (Choices C and D) As medicalization increases, both the power (the ability to influence people) and authority (power being perceived as legitimate) of medical professionals will increase. Educational objective:In sociology, power refers to the ability to influence and control others. Authority refers to whether others perceive that power as legitimate.

The IR spectrum of the organic layer is obtained before and after extraction with HCl(aq), and the disappearance of an N-H stretch is observed. Compared to the IR spectrum before the extraction, the IR spectrum after the extraction is expected to be missing a peak at which wavenumber as a result of the lost N-H stretch? A.1480 cm−1 B.1710 cm−1 C.3050 cm−1 D.3434 cm−1

B.1710 cm−1 In infrared (IR) spectroscopy, the functional groups in a molecule absorb IR radiation at different frequencies and different intensities depending on the types of atoms and bonds present. Therefore, the signal for each functional group appears in a particular region of the IR spectrum (ie, a plot of transmittance vs. wavenumber). IR spectroscopy can be used to detect the structural changes in a molecule during a chemical reaction or changes in a mixture before and after separation of some mixture components by observing the appearance or disappearance of peaks that are unique to a given molecule. Step 3 of the passage describes an extraction with HCl(aq), in which diphenylamine is protonated, forming a water-soluble ammonium salt. Because the ammonium salt of diphenylamine goes into the aqueous layer during the extraction, stretches unique to diphenylamine, such as an N-H stretch, will be absent in the IR spectrum of the organic layer after the extraction. N-H stretches absorb infrared light between 3600 - 3200 cm−1. Therefore, the disappearance of a peak at 3434 cm−1 corresponds to an N-H stretch. (Choices A and C) Peaks at 1480 cm−1 and 3050 cm−1 correspond to a C=C stretch and an sp2 C-H stretch, respectively. These peaks are present in the IR spectra before and after the extraction because both fluorene and diphenylamine contain C=C and sp2 C-H bonds. (Choice B) A peak at 1710 cm−1 corresponds to a C=O stretch. A peak at this frequency should not be observed in either IR spectrum because neither diphenylamine nor fluorene contain a C=O bond. Educational objective:Functional groups in a molecule absorb at different frequencies and intensities in an infrared (IR) spectrum. N-H stretches have a characteristic absorption between 3600 - 3200 cm−1. IR spectroscopy can be used to detect structural changes to a molecule during a chemical reaction or changes in a mixture due to separation of the mixture components by observing the appearance or disappearance of peaks that are unique to a given molecule.

Formic acid (HCOOH), the simplest carboxylic acid, occurs naturally in a variety of sources including the venom of bee and ant stings. Due to its commercial availability, HCOOH is commonly used as a preservative and antibacterial agent in the food and pharmaceutical industries. Various industrial methods for synthesizing HCOOH have emerged in response to an increased demand. For example, one synthetic route produces HCOOH through the spontaneous reaction between gaseous CO and NH3 in the presence of an acidified aqueous medium. CO(g) + NH3(g) + H3O+(aq) ⇄ HCOOH(aq) + NH4+(aq) Reaction 1 Formation of HCOOH through Reaction 1 occurs via a three-step reaction mechanism. The first step proceeds according to Reaction 2 and is catalyzed by sodium methoxide. CH3OH(l) + CO(g) ⇄ HCO2CH3(l) Reaction 2 (slow step) The second and third steps of the mechanism proceed according to Reactions 3 and 4, respectively. HCO2CH3(l) + NH3(g) ⇄ HCONH2(l) + CH3OH(l) Reaction 3 (fast step) HCONH2(l) + H3O+(aq) ⇄ HCOOH(aq) + NH4+(aq) Reaction 4 (fast step) The role of sodium methoxide in Reaction 2 is to: A.increase the amount of CH3OH(l) and CO(g) consumed per unit of time. B.increase the total amount of HCO2CH3(l) produced. C.decrease the number of productive collisions between CH3OH(l) and CO(g). D.decrease the rate of the reverse reaction.

A.increase the amount of CH3OH(l) and CO(g) consumed per unit of time. The rate of a reaction indicates how quickly the reactant molecules are consumed and the product molecules produced (ie, the change in the species concentrations per unit time). A catalyst is a substance that increases the reaction rate but is not consumed in the overall reaction. Catalysts work by providing an alternative reaction mechanism that forms a more stable (ie, less energetic) transition state, and thereby lowers the activation energy Ea of the rate-determining step (ie, less energy is required to initiate the reaction). The passage states that Reaction 2 is catalyzed by sodium methoxide. Therefore, sodium methoxide lowers the Ea of the reaction, which increases the amount of CH3OH(I) and CO(g) consumed per unit of time (ie, the rate of reactant consumption increases). (Choice B) The sodium methoxide catalyst increases the amount of HCO2CH3(l) produced per unit time (ie, how fast the product forms), not the total amount of HCO2CH3(l) produced. (Choice C) A catalyst increases the number of productive collisions between reactant molecules that result in a reaction. (Choice D) The rates of both the forward and reverse reactions increase in the presence of the sodium methoxide catalyst. Educational objective:Catalysts decrease the activation energy of the rate-determining step of a reaction, thereby increasing the reaction rate (ie, the change in species concentration per unit of time).

In the 1H NMR spectrum of Compound 4, the protons bonded to the carbon atom marked with an asterisk appear as a:

A.singlet.

Which statement most accurately applies the general adaptation syndrome to the stress associated with parenting children with disabilities (first paragraph)? A.The stress resulting from the prejudice of others would not impact physiological processes because it is a social stressor. B.At the first onset of a child's symptoms, parents experience increased resistance to stress. C.The psychological impact of parenting a child with a serious disability will be similar for all parents. D.As a child's medical condition continues over a prolonged period, parents experience decreased resistance to stress.

As a child's medical condition continues over a prolonged period, parents experience decreased resistance to stress. The general adaptation syndrome (GAS), proposed by Hans Selye, is a model describing how the body reacts to stress. According to this model, there are three stages of the stress response: The alarm stage occurs during the first few minutes of the stress response, in which the sympathetic nervous system prepares the body to act (ie, fight-or-flight response). The resistance stage can last for hours (eg, exercise), days (eg, final exams), or months (eg, preparing for the MCAT). During this stage, the body attempts to resist the stressor and establish a new equilibrium. The exhaustion stage occurs when prolonged stress produces arousal with depleted energy, making the body more vulnerable to negative health effects (eg, depression, hypertension). As a child's medical condition continues over a prolonged period, parents typically move into the exhaustion stage, according to the general adaptation syndrome, where they will experience decreased resistance to stress. (Choice A) According to the GAS, the stress response follows a similar pattern over time, regardless of the type of stressor. Therefore, the stress resulting from the prejudice of others would impact physiological processes as the type of stressor (ie, social) is irrelevant. (Choice B) In the alarm stage, the first onset of a child's symptoms, parents should experience decreased (not increased) resistance to stress. (Choice C) The passage states that some parents eventually experience positive psychological outcomes while others experience negative mental health outcomes (eg, depression, anxiety). Therefore, the psychological impact of parenting a child with a serious disability will vary among individuals and is not necessarily similar for all parents. Educational objective:According to the general adaptation syndrome, the body's response to stress involves an alarm stage (initial fight-or-flight response), resistance stage (increased resistance to stress), and exhaustion stage (eventual decreased resistance to stress) that may lead to the development of mental and physical health issues. Although most stressors elicit similar physiologic stress response course over time, not all individuals experience negative mental outcomes.

Studies on the catalytic activity of hexokinase provided the following data: ExperimentUrea(M)Reaction rate(µmol∙min−1∙mg-1)Temperature(°C)I3.40.2730II1.50.6842III2.90.1471IV1.00.4253 Which experiment would contain the greatest percentage of folded protein? A.Experiment I B.Experiment II C.Experiment III D.Experiment IV

B.Experiment II Proteins have evolved to function within a narrow range of cellular conditions. In particular, enzymes can remain functional only when their three-dimensional shape, or tertiary structure, is maintained. Noncovalent interactions, such as hydrogen bonds, ionic bonding, and hydrophobic effects, allow proteins to fold into secondary structures (eg, α-helices, β-sheets) that combine to form tertiary structures. The disruption of noncovalent bonds that causes proteins to unfold and lose their function is referred to as denaturation. Proteins unfold rapidly at conditions outside their optimal range because denaturation is a cooperative process. Although heat energy increases the rate of an enzymatic reaction, high temperatures can also cause denaturation of the enzymes. The excess kinetic energy provided by increasing temperatures generates vibrations that disrupt hydrogen bonding between polar atoms and hydrophobic interactions in nonpolar regions. Denaturation also occurs in the presence of urea, which is a polar amide produced by protein metabolism and excreted by the body. Urea induces the unfolding and denaturation of proteins by exposing hydrophobic groups and interfering with hydrogen bonding in the amino acid backbone. Proteins exposed to high temperatures or to high concentrations of urea unfold easily and lose their function. Therefore, high temperatures or high urea concentrations decrease the enzymatic reaction rate, indicating a smaller percentage of folded protein. Of the choices listed, Experiment II provides the best conditions for enzymatic function because the temperature and urea concentration used allow for the highest enzymatic reaction rate. Consequently, Experiment II must contain the highest percentage of folded, functional protein. (Choices A, C, and D) These experiments all show lower enzymatic activity than Experiment II, indicating that a higher percentage of enzymes were no longer folded nor functional in these experiments. The enzymes in Experiments III and IV were likely denatured by high temperatures whereas the enzyme in Experiment I was likely denatured by the high urea concentration.

Based on the passage, the control subjects in Study 2 could also develop which additional conditioned response? A.Hair loss from the chemotherapy medication B.Fatigue when entering the chemotherapy room C.Difficulty concentrating when drinking novel-flavored beverages D.Nausea and/or vomiting while riding a rotating ride at an amusement park

B.Fatigue when entering the chemotherapy room n classical conditioning, a previously neutral stimulus causes an organism to react in a manner similar to the reaction to a natural or unconditioned stimulus after the two stimuli have been paired. Unconditioned stimuli (eg, meat) are biologically arousing, causing an innate (untrained) reaction called an unconditioned response (eg, salivation). Neutral stimuli (eg, bell) do not produce a meaningful response. After being paired with the unconditioned stimulus, the previously neutral stimulus, now termed the conditioned stimulus, causes the organism to react with a learned, or conditioned response (eg, salivation in response to a bell). The conditioned response is typically similar to the unconditioned response. For patients receiving chemotherapy, the room, apparatus, smells, and other characteristics of the context (neutral stimuli) could become associated with the experience of nausea because it is in this environment that the cytotoxic medication (unconditioned stimulus) caused the nausea (unconditioned response). After learning, those contextual characteristics of the room (conditioned stimulus) will provoke AN (conditioned response) before the cytotoxic medication is administered. Similarly, a patient could develop the additional conditioned response of feeling fatigue when entering the chemotherapy room. (Choices A and D) Unconditioned responses occur naturally (or biologically) as a result of unconditioned stimuli; they are not learned. Hair loss follows chemotherapy medication because it destroys the hair follicle cells, and nausea naturally results from motion sickness. (Choice C) Control subjects in Study 2 received only water, so they would not develop a conditioned response (ie, difficulty concentrating) in association with novel-flavored beverages. Educational objective:Unconditioned responses occur naturally, without learning (eg, nausea in response to cytotoxic medication). Conditioned responses occur when a neutral stimulus (eg, chemotherapy equipment) is paired with an unconditioned stimulus (eg, cytotoxic medication).

Activity assays were performed to determine the best purification method for a crude, cell-free extract of Protein X. The crude extract was separated into three samples of 800 mg each, and each sample was purified by a different technique. The results are shown in the table below. Sample Specific Activity(u/mg protein) Total Protein Mass(mg) Crude extract 500 800 Ammonium sulfate precipitation 750 500 Column chromatography 2,000 150 Native PAGE 2,500 5 Based on the data, which of the following is (are) true? Ammonium sulfate precipitation provided the highest total yield of Protein X of the purification techniques. Column chromatography provided the highest percent yield of Protein X relative to crude extract. Native PAGE resulted in the highest purity of Protein X. A.III only B.I and III only C.II and III only D.I, II, and III

B.I and III only Extracts from cells are complex mixtures that contain many different proteins, lipids, and carbohydrate molecules. To isolate a specific enzyme, purification methods such as native gel electrophoresis, precipitation, and column chromatography are needed. The effectiveness of each purification method or step is confirmed by performing activity assays that measure the rate of the reaction catalyzed by the enzyme of interest. In any purification step, some of the desired protein is lost. The total yield achieved by a purification step represents how much desired protein (in this case, protein X) is recovered. Yield can be determined by calculating the total activity of the purified protein. The activity values in an assay have arbitrary units (u) that represent some functional activity of the protein (eg, the catalytic reaction rate for enzymes): Total activity(TA)=total protein(mg)×specific activity(umg)Total activityTA=total proteinmg×specific activityumg Based on the given table, the TA of each purification technique can be calculated as: TA of ammonium sulfate precipitation=500 mg×750umg=375,000 uTA of ammonium sulfate precipitation=500 mg×750umg=375,000 uTA of column chromatography=150 mg×2000umg=300,000 uTA of column chromatography=150 mg×2000umg=300,000 uTA of native PAGE=5 mg×2500umg=12,500 uTA of native PAGE=5 mg×2500umg=12,500 u Therefore, the ammonium sulfate technique provides the highest total yield of the three methods used (Number I). However, a high yield of the desired protein does not mean the protein is pure (ie, that undesired proteins were removed). Protein purity is represented as specific activity (u/mg), which is a ratio of the activity of the desired protein to the total mass of protein obtained in a purification step. Consequently, specific activity increases during purification as unwanted protein is removed. Based on the table, native PAGE gives the highest specific activity (2,500 u/mg); thus, native PAGE produced the highest purity of Protein X (Number III). (Number II) To determine the efficiency of a purification technique, the percent yield can be calculated as the ratio of purified protein activity to unpurified protein activity. Because all three purification techniques started with the same amount of crude extract, the technique with the highest total yield (ammonium sulfate precipitation, not column chromatography) will also have the highest percent yield.

Researchers wished to mimic the conditions of the medial Golgi (pH ≈ 6.3). Which of the buffers shown in Table 1 would be best suited for this experiment? Table 1 Acid Dissociation Constants for Several Buffers BufferKaAcetic acid1.7 x 10-5MES7.1 x 10-7HEPES2.8 x 10-8Tris6.3 x 10-9 A.Acetic acid B.MES C.HEPES D.Tris

B.MES A buffer is a mixture of a weak acid or base and its corresponding conjugate salt, resulting in a system that contains both acidic and basic species that can be protonated or deprotonated over a specific pH range. Within this range, known as the buffering range, the buffer can neutralize added hydronium or hydroxide ions and therefore resist changes in pH. The buffering range is generally 1 pH unit away from the buffer's pKa (the pH at which the species in the buffer are half protonated and half deprotonated) moving in either direction along the pH scale. Outside this range, the constituent buffer species are either fully protonated or deprotonated and the buffer loses the ability to resist pH changes. The pKa of a buffer is related to its acid dissociation constant Ka by: pKa = −log(Ka) or Ka = 10−pKa The question states that the medial Golgi maintains a pH of approximately 6.3. To stably maintain this pH during an experiment, researchers must use a buffer with a pKa within 1 pH unit of 6.3 in either direction (pH 5.3-7.3). A buffer with a pKa of 6 has a Ka of 10-6, and a buffer with a pKa of 7 has a Ka of 10-7, so a buffer with a Ka value between 10-6 and 10-7 would have a pKa near 6.3. MES meets this requirement with a Ka of 7.1 x 10-7 and would therefore be the best of the available buffers for mimicking the pH of the medial Golgi. (Choices A, C, and D) These options have Ka values that correspond to pKas outside the range of 5.3-7.3. They would not be good buffers at a pH of 6.3. Educational objective:Buffers are mixtures of a weak acid or base and its corresponding conjugate salt that can resist changes in pH by neutralizing added hydronium or hydroxide ions. They are effective within 1 pH unit of their pKa. The pKa of a buffer is related to its acid dissociation constant Ka by the equation pKa = −log(Ka).

A feminist theorist would be most interested in which of the following? A.Equalizing pay between females in pink-collar and blue-collar occupations B.Removing barriers to entry in all occupations for females C.Creating more access for males in pink-collar occupations D.Balancing the percentage of females and males within each occupation

B.Removing barriers to entry in all occupations for females In sociology, feminist theory explains differences in power between males/masculinity and females/femininity in society, known as gender inequality. Feminist theory includes both macro- and micro-level approaches. At the macro-level, feminist theory considers how social structures maintain gender inequality. For example, workplace practices that discriminate against women (eg, less pay, fewer promotions) result in the underrepresentation of women in certain fields (eg, surgery). At the micro-level, feminist theory considers how one-on-one interactions also maintain gender inequality by objectifying or devaluing females/femininity. For example, patients often assume a female surgeon is a nurse. Removing barriers to female entry into a variety of occupations is consistent with a macro-level feminist theory concern as it addresses structural factors that contribute to gender inequality. (Choice A) Feminist theory would not suggest that females in different occupational fields, which require different skill sets and qualifications, should be paid at the same rate. Instead, feminist theory would focus on how men and women within the same occupational field should be compensated equivalently. (Choice C) In a patriarchal society, males possess most of the power and prestige; therefore, focusing on increasing access for males is less likely to be the goal of feminist theorists than is providing access to power and prestige to females who have less of it. (Choice D) Balancing the number of males and females in a given occupation would seem to remove career choice, which is not a feminist goal. Removing the barriers to access so that all occupations become legitimate options for females would be the feminist focus. Educational objective:Feminist theory explains differences in power between males/masculinity and females/femininity (gender inequality). Feminist theory examines both macro-level impacts of social structures as well as micro-level factors such as individual prejudice and discrimination.

Which of the following cellular processes would most likely lead to increased genetic variation in a population of organisms? A.DNA replication during S phase of the cell cycle B.Synapsis involving two homologous chromosomes C.Alternative splicing of gene transcripts D.Cell division via mitosis

B.Synapsis involving two homologous chromosomes In eukaryotes, reproductive cells (gametes) are produced via meiosis, during which a diploid (2n) parent cell divides to produce four genetically distinct haploid (n) daughter cells. Meiosis has four phases (like mitosis) but these phases occur in two successive cell division stages (meiosis I and II). In prophase I of meiosis, homologous chromosomes line up side-by-side during synapsis. Because each homologous chromosome consists of two identical (sister) chromatids, this adjacent chromosomal alignment forms a tetrad (ie, four chromatids total). Tetrads arise when a synaptonemal complex (protein structure) forms between homologous chromosomes and holds them together tightly. The tetrad structure allows physical contact between the paternal and maternal chromosomes at the chiasma, a point where a chromosome segment can break off and rejoin with the opposite homologous chromosome. This exchange of DNA is the hallmark feature of the process called crossing over. Crossover events result in daughter cells with chromosomes containing combinations of alleles that differ from those in the parent cell, leading to eukaryotic genetic recombination and increased genetic variation. Because crossover events produce genetically unique gametes, the offspring that develops after fertilization is genetically different from either parent, leading to increased genetic variation.

What are the conditioned and unconditioned stimuli in the study, respectively? A.The 1-cm ring and the electric shock B.The 20-cm ring and the electric shock C.The electric shock and the 20-cm ring D.The 20-cm ring and the 1-cm ring

B.The 20-cm ring and the electric shock Classical conditioning occurs when a stimulus that did not previously elicit a meaningful response takes on the properties of a biologically arousing stimulus. For example, when a dog hears the sound of a bell every time it receives food, the sound of the bell alone will eventually produce salivation (eg, a meaningful response). Unconditioned (ie, biologically arousing) stimuli cause unconditioned responses (ie, innate reactions). Neutral stimuli do not produce meaningful responses. After being paired with an unconditioned stimulus, the previously neutral stimulus becomes a conditioned stimulus when it causes the organism to react with a learned (ie, conditioned) response, which is typically similar to the unconditioned response. In this study, the 20-cm ring (neutral stimulus) was paired with an electric shock (unconditioned stimulus), which elicited a startle (unconditioned response). After repeated pairings, the 20-cm ring (originally the neutral stimulus) became the conditioned stimulus because it was associated with the electric shock. After learning has taken place, the 20-cm ring (conditioned stimulus) will provoke a startle (conditioned response). Therefore, in this study the 20-cm ring was the conditioned stimulus, and the electric shock was the unconditioned stimulus, not vice versa (Choice C). (Choices A and D) The 1-cm ring, which was not paired with the electric shock, remained a neutral stimulus in this study. Educational objective:Unconditioned stimuli (eg, food) are biologically arousing, causing an innate (untrained) reaction called an unconditioned response (eg, salivation). Neutral stimuli (eg, bell) do not produce a meaningful response. After being paired with the unconditioned stimulus, the previously neutral stimulus, now termed the conditioned stimulus, causes the organism to react with a learned, or conditioned, response (eg, salivation in response to a bell).

Which statement is best supported by Figure 1? A.Depressive symptoms in the M group continued to decline after the discontinuation of therapy. B.While in therapy, the M group experienced fewer depressive symptoms compared to the HP group. C.Both M and HP therapies resulted in similar levels of depressive symptoms at post-test 2. D.At baseline, the HP group had higher levels of depressive symptoms compared to the M group.

B.While in therapy, the M group experienced fewer depressive symptoms compared to the HP group. Relaxation is a physiological state of reduced arousal and sympathetic activity. Research indicates that relaxation, which can be achieved through many different techniques (eg, massage, meditation), is effective for reducing stress. Meditation is a practice whereby individuals regulate their awareness and attention with the goal of achieving mental clarity and emotional calmness. Although meditation techniques vary, they can include focusing on one's own breathing or other present-moment stimuli (eg, the sound of rain), or mentally repeating a mantra (short saying or thought). Neuroimaging studies have shown that meditation not only results in relaxation, but also produces an altered state of consciousness, demonstrated by an increase in alpha brain waves. Regular meditation provides benefits outside of the meditative state, such as improved attention and emotional self-regulation. Depressive symptoms were measured only once during the therapeutic intervention, at the midpoint (ie, halfway through). Figure 1, which shows that the M group had significantly fewer depressive symptoms than the HP group (as indicated by the asterisks) at the midpoint, supports the statement that while in therapy, the M group experienced fewer depressive symptoms compared to the HP group. (Choice A) The M group had approximately similar (not reduced) levels of depressive symptoms from post-test 1 to post-test 2. (Choice C) Although the M and HP therapies resulted in similar levels of depressive symptoms at post-test 1, the HP group showed significantly fewer depressive symptoms than the M group at post-test 2 (as indicated by the asterisks between post-test 2 scores in Figure 1). (Choice D) There was no significant difference in the level of depressive symptoms at baseline between the two groups (no asterisks between pre-test scores in Figure 1), so the statement that the HP group had higher levels of depressive symptoms at baseline as compared to the M group is not supported. Educational objective:Meditation is a relaxation technique whereby individuals regulate their awareness and attention. Meditation may improve mental clarity and emotional calmness. Regular meditation provides benefits outside of the meditative state, such as improved attention and emotional self-regulation.

Based on the passage and the principles of taste aversion, which strategy should physicians suggest to their patients undergoing chemotherapy? On the day of chemotherapy, patients should: A.pair their favorite foods with a novel beverage. B.eat favorite foods several hours before chemotherapy treatment. C.only consume favorite beverages, not water. D.avoid eating their favorite foods entirely.

D.avoid eating their favorite foods entirely. A conditioned taste aversion is a specific and powerful type of classical conditioning that occurs when an organism becomes ill after consuming something (eg, food, alcohol). Whatever was consumed prior to the N/V can become associated with the illness (even if it did not cause the illness) and is avoided afterward, long term. Taste aversions almost always link illness with foods (or smells), which is thought to be an evolutionary adaptation. Of the given choices, a physician should suggest that patients avoid eating their favorite foods on the day of chemotherapy. This strategy will prevent patients from developing a taste aversion to these foods. If a favored food is consumed prior to the experience of nausea (resulting from chemotherapy), it is possible that the food will be permanently associated with the nausea. (Choice A) Although there is a chance that a salient, novel-flavored beverage could overshadow the favorite food and become linked to the nausea, there is nothing in the passage that suggests it would prevent a taste aversion if paired with a favorite food. (Choice B) Taste aversions can develop even with hours passing between food consumption and becoming ill. Consuming a favorite food hours before chemotherapy would not prevent the development of a taste aversion. (Choice C) Patients could develop a taste aversion to their favorite beverages if consumed prior to becoming ill. Educational objective:Taste aversion is a specific and powerful type of classical conditioning that occurs after just one instance of becoming ill following food/beverage consumption. Taste aversions are long lasting and can develop despite many hours passing between consumption and illness.

Researchers asked 100 Americans to describe their recollections of the September 11, 2001, terrorist attacks at two time points: 2 days and 10 years after the attacks. Comparing the descriptions for each individual, researchers are LEAST likely to find that: A.individuals are extremely confident in their memories, even 10 years after the attacks. B.individuals' recollections are extremely accurate 10 years after the attacks. C.individuals vividly recall seemingly insignificant details from the day of the attacks. D.individuals vividly recall their emotional reactions to the events of that day.

B.individuals' recollections are extremely accurate 10 years after the attacks. A flashbulb memory is a vivid, detailed type of autobiographical explicit memory for an event that was extremely emotional, distinct, or significant to the individual. Flashbulb memories occur not only for negative events (eg, 9/11), but also for positive events (eg, the birth of a child). It is easier to use national events, such as the 9/11 terrorist attacks, to study flashbulb memory. Once thought to be extremely accurate snapshots (hence the term "flashbulb") of emotionally arousing events, studies suggest that flashbulb memories may be less accurate/consistent than individuals believe. People tend to be extremely confident of their recollections, even though their flashbulb memories are not 100% accurate or consistent over time. Flashbulb memories are defined by the following characteristics: Individuals feel extremely confident about the memory, even after a long time has elapsed (Choice A). Individuals are able to vividly recall specific details surrounding the event, including ones of seeming insignificance, such as what one was wearing or doing at the time of the event (Choice C). Individuals are able to vividly recall their emotional state at the time of the event (Choice D).

Compared to women's social networks, men's social networks tend to be larger, have more weak ties, and provide more information about work-related topics; therefore, men's social networks most likely confer: A.less social capital and less social mobility. B.more social capital and more social mobility. C.less social capital but more social mobility. D.more social capital but less social mobility.

B.more social capital and more social mobility. Social networks are informal and nonhierarchical webs of interaction between nodes, which are linked by ties. Nodes can either be individuals or organizations. Ties describe the connections between the nodes and are defined as strong or weak. Weak ties are loose/flimsy connections, such as those between acquaintances, whereas strong ties are more solid connections, such as those between family and close friends. Social capital refers to a person's networks of people that can be converted into economic gain. Men's networks are larger and provide information about work-related topics, such as where there are job openings or promotion possibilities. Therefore, men's network connections confer more social capital because these connections can be more easily converted into economic gain. Social mobility refers to the movement of individuals, groups, or families between or within status categories in society (eg, from middle class to upper class). Social mobility can be horizontal or vertical and is related to a multitude of other factors, such as education, job loss, marriage, and institutionalized discrimination. By providing more social capital (potential economic gain), men's networks also provide more social mobility. (Choices A, C, and D) Compared to women's networks, men's social networks provide more (not less) social capital and more (not less) social mobility. Educational objective:Social networks are informal, nonhierarchical webs of nodes (eg, individuals) connected by ties, which can be weak (eg, acquaintances) or strong (eg, family). Social networks confer social capital through connections that can be converted into economic gain (eg, new job), which can improve one's social status, resulting in social mobility.

A researcher wants to train a mouse to run on an exercise wheel. The LEAST effective way to train this new behavior would involve: A.rewarding the mouse at first for touching the wheel, then for climbing on it, then for running on it. B.providing reinforcement every 5 minutes, as long as the mouse runs on the wheel at some point during that time. C.first depriving the mouse of food for 24 hours, then using food pellets as a reward. D.providing positive reinforcement each time the mouse runs on the exercise wheel.

B.providing reinforcement every 5 minutes, as long as the mouse runs on the wheel at some point during that time. In operant conditioning, reinforcement is used to encourage certain behaviors, and punishment is used to discourage unwanted behaviors. Reinforcement (eg, rewarding desirable behavior with food) tends to be more effective than punishment. Furthermore, providing a reward after every single desired behavior, known as continuous reinforcement, is the best way to train animals to perform a new behavior. In operant conditioning, partial reinforcement schedules provide reinforcement after a certain number of behaviors (ratio) or amount of time (interval). The schedules are either fixed (consistent) or variable (inconsistent). Partial reinforcement schedules are best used to maintain behaviors that have already been learned through continuous reinforcement. Rewarding the mouse after some amount of time has passed is a fixed (ie, consistent) interval (ie, time-based) reinforcement schedule. A fixed interval reinforcement schedule is not an optimal way to train an animal to perform a new behavior because it is more difficult for the animal to associate the desired behavior with the reward. (Choice A) When first training an animal to perform a new behavior, it is often necessary to reward successive approximations of the desired behavior, known as shaping. Rewarding the mouse for behaviors that increasingly resemble the desired response (eg, touching the wheel, climbing on it, running on it) would be an appropriate strategy during training. (Choice C) During the training phase, the best way to increase the desirability of the food reward is to deprive the mouse of food for a certain period before training. This greatly increases the motivational state of the animal, making it more likely to respond to a food reward during training. (Choice D) Continuous reinforcement (eg, rewarding the mouse each time it runs on the exercise wheel) is the best way to condition new behavior.

Consider the dimerization of nitrogen dioxide at room temperature: 2 NO2(g) ⇄ N2O4(g)Kp = 8 atm−1 If the equilibrium partial pressure of nitrogen dioxide in a container is 0.5 atm, what is the partial pressure of dinitrogen tetroxide? A.0.03 atm B.0.5 atm C.2 atm D.4 atm

C.2 atm The equilibrium constant for any chemical reaction is the molar ratio of products to reactants when the system is equilibrium. The partial pressure of a gas is directly proportional to the number of moles of that gas according to the ideal gas law; therefore, partial pressure can be substituted for molar concentration. If more than one of a given molecule is involved in a reaction, each molecule involved is counted separately. Therefore, each product or reactant must be raised to the power of its stoichiometric coefficient to account for all molecules involved in the reaction. Nitrogen dioxide (NO2) can combine with itself to form dinitrogen tetroxide (N2O4). The equilibrium constant for this reaction (Kp = 8 atm−1) is the ratio of the partial pressure of N2O4 to that of NO2 when equilibrium is achieved. However, because two NO2 molecules are required for each reaction, the NO2 partial pressure ( PNO2PNO2= 0.5 atm) must be squared. Therefore, the equilibrium partial pressures of NO2 and N2O4 in the described scenario are related by the equation: Kp=PN2O4(PNO2)2Kp=PN2O4PNO22 Substituting the values into the equation yields: 8 atm−1=PN2O4(0.5 atm)2=PN2O40.25 atm28 atm-1=PN2O40.5 atm2=PN2O40.25 atm2 This equation can be rearranged and solved as follows: PN2O4=0.25 atm2×8 atm−1=2 atmPN2O4=0.25 atm2×8 atm-1=2 atm (Choice A) 0.03 atm would be correct if N2O4 were the reactant and NO2 were the product, in which case N2O4 would be in the denominator of the equilibrium expression. (Choice B) 0.5 atm would be correct if "equilibrium" meant that all components are at equal concentration. Instead, equilibrium is the state in which the forward and reverse reactions occur at equal rates and no net change is observed. More stable compounds dominate at equilibrium. (Choice D) 4 atm would be correct if only one molecule of NO2 were involved in the reaction and its partial pressure were not squared in the equilibrium expression.

Laser Doppler vibrometers detect the Doppler shift of a laser beam reflected off an individual's chest to measure respiratory rate. The calculated displacement of the chest during a breath using a 500-nm laser is shown below. If the laser source is stationary, at which point(s) would the observed frequency of the reflected laser be 6 × 1014 Hz?

I and III only

A student adds 5 bacterial cells to a test tube containing fresh medium and incubates it for 3 hours at 37°C. The bacterial population shows an initial lag phase of 20 minutes followed thereafter by a growth phase with a doubling time of 40 minutes. Given this, what is the approximate number of bacterial cells present at the end of the incubation period? (Note: Assume unrestricted growth during incubation.) A.20 cells B.40 cells C.80 cells D.160 cells

C.80 cells Binary fission is the process by which unicellular organisms such as bacteria reproduce asexually. During this process, the parental bacterial cell doubles in size and then divides into two identical daughter cells. Subsequently, each daughter cell also divides into two, yielding four cells that then continue to divide in a similar manner. This type of growth is called exponential (ie, growth in which the rate of reproduction increases over time). The generation time (doubling time) is the time needed for a bacterial population to double, or the time needed for a single bacterium to divide into two. When a single cell divides by binary fission, the number of cells that result after a specified time is calculated by multiplying the original number of bacterial cells by 2n, where n equals the number of generations. The rate at which a bacterial population grows can be demonstrated by plotting a typical growth curve, which has a lag, log, stationary, and death phase. Before they begin dividing, transplanted bacteria often exhibit an initial lag phase as they become accustomed to the local conditions and synthesize the components (eg, enzymes, RNA) required for metabolism. In the subsequent log phase, the bacterial population grows exponentially as bacteria are able to effectively metabolize nutrients. According to the question, 5 bacterial cells were incubated for 3 hours (180 minutes); these exhibited a 20-minute lag phase and a 40-minute generation time. Assuming unrestricted growth during incubation, the bacterium could only have had a log phase and a lag phase. Therefore, the number of cells that result after incubation can be calculated as follows: Calculate the amount of time in which the bacterial population was in log phase:180 min incubation time − 20 min lag phase = 160 min log phase Find the number of generations in the log phase period:160 min log phase / 40 min generation time = 4 generations Multiply the original number of bacterial cells by 2n to get the final population size:5 bacterial cells × 24 = 80 cells Educational objective:Binary fission is the process by which a unicellular organism (eg, bacterium) divides into two identical daughter cells. The generation time refers to the time in which a bacterial population doubles. When a single cell divides by binary fission, the number of cells that result is calculated by multiplying the original number of bacterial cells by 2n, where n equals the number of generations.

Which hypothetical result would provide support for the researcher's hypothesis? A.Compared to participants with OCD, controls show a greater startle response to the 1-cm ring. B.Controls and participants with OCD do not differ in startle response to any of the rings. C.Compared to controls, participants with OCD show a greater startle response to the 15-cm ring. D.Controls and participants with OCD show the greatest startle response to the 20-cm ring.

C.Compared to controls, participants with OCD show a greater startle response to the 15-cm ring. Stimulus generalization occurs when the conditioned response is elicited by stimuli similar to the original conditioned stimulus. For example, an infant who has been conditioned to fear a white rat may also display fear in response to other stimuli, such as a white rabbit or white ball of yarn. In this study, all participants were conditioned to associate the 20-cm ring with an electric shock. After conditioning, the presentation of the 20-cm ring (conditioned stimulus) would elicit a startle (conditioned response). The researcher hypothesized that compared to controls, participants with OCD would show a more generalized fear response to safe stimuli. Therefore, a finding that participants with OCD showed a greater startle response to the 15-cm ring (ie, a safe stimulus that resembles the conditioned stimulus) than controls supports the hypothesis. (Choice A) The finding that controls startle more to a safe stimulus (ie, 1-cm ring) than the participants with OCD does not support the researcher's hypothesis (ie, it is the opposite finding). (Choice B) Finding no difference between the groups does not support the researcher's hypothesis that the participants with OCD would show a more generalized fear response to safe stimuli. (Choice D) Both groups would be expected to show the greatest startle response to the 20-cm ring; however, the researcher's hypothesis did not address the intensity of startle response to the 20-cm ring relative to the other rings. Therefore, both groups showing the greatest startle response to the 20-cm ring would not support the hypothesis. Educational objective:Stimulus generalization occurs when stimuli (eg, white rabbit) similar to the original conditioned stimulus (eg, white rat) elicits the conditioned response (eg, fear).

Compared with blood in the pulmonary veins, blood in the pulmonary arteries has higher concentrations of: O2 H+ CO2 A.I and II only B.I and III only C.II and III only D.I, II, and III

C.II and III only Blood is circulated throughout the body by the repetitive contraction of the heart, which enables continuous delivery of oxygen and nutrients to the body's tissues, as well as removal of CO2 (the major metabolic by-product of cellular respiration) and other waste products. The blood vessels involved in circulation can be divided into two circuits: The systemic circuit distributes oxygenated blood (high O2, low CO2, low H+) containing nutrients to all body tissues via arteries, which carry blood away from the heart. When oxygenated blood reaches the capillaries within the systemic tissues, it delivers O2 (becomes deoxygenated) and nutrients to the tissues and picks up CO2. Veins then return the deoxygenated blood (low O2, high CO2, high H+) back to the heart so that it can enter the pulmonary circuit. The pulmonary circuit pumps deoxygenated blood through the pulmonary arteries to capillaries in the lungs to facilitate gas exchange. The capillaries are in close contact with lung alveoli (air sacs), and at this site, the blood becomes reoxygenated (O2 is transferred from alveolar air to the blood, and CO2 is transferred from the blood to the alveolar air). The pulmonary veins then return the oxygenated blood to the heart so that it can be pumped through the systemic circuit (Number I). Compared with oxygenated blood in the pulmonary veins, deoxygenated blood in the pulmonary arteries has higher concentrations of CO2 (Number III). Blood that is richer in CO2 is also generally richer in H+ ions due to the following reaction that takes place in red blood cells: CO2(g)+H2O(l)↔H2CO3(aq)↔HCO3−(aq)+H+(aq)CO2g+H2Ol↔H2CO3aq↔HCO3-aq+H+aq The higher the CO2 concentration, the more the forward reaction is favored. Therefore, the CO2-rich blood in the pulmonary arteries also contains more H+ ions (has a slightly lower pH) than the CO2-poor blood of the pulmonary veins (Number II). Educational objective:Within the pulmonary circuit, the pulmonary arteries carry CO2-rich, O2-poor blood from the heart to the lungs, where CO2 is exchanged for O2. The pulmonary veins then carry CO2-poor, O2-rich blood from the lungs to the heart, which then pumps the oxygenated blood to all body tissues.

Based on the passage, which statement is most consistent with a symbolic interactionist perspective? A.The definition for what is sacred may differ depending on the religion. B.Dynamic equilibrium is maintained when social control gradually shifts from religion to medicine. C.Individuals create meaning through serving others in faith-based mission work. D.Some religious groups attempt to reduce health care disparities that stem from class inequalities.

C.Individuals create meaning through serving others in faith-based mission work. Symbolic interactionism is a micro-sociological perspective concerned with the interpersonal interactions through which the subjective meanings that shape social reality are developed. Subjective meanings differ by context and culture (eg, avoiding eye contact is a sign of respect in Japan but is considered rude in the US) and can change over time. The statement that individuals create meaning through serving (ie, interacting with) others in faith-based mission work is most consistent with symbolic interactionism. Under the symbolic interactionist perspective, mission work may become a meaningful expression and symbol of a believer's faith. (Choice A) Social constructionism suggests that reality is created through shared meanings and definitions arising from social interactions. A definition for what is sacred that depends on the religion reflects a perspective that is most consistent with social constructionism (not symbolic interactionism). (Choice B) Structural functionalism emphasizes how social structures maintain dynamic equilibrium (ie, homeostasis) in society. The maintenance of dynamic equilibrium through the gradual shifting of social control from religion to medicine reflects a functionalist (not symbolic interactionist) perspective. (Choice D) Conflict theory focuses on how inequalities between social classes cause conflict. A situation in which religious groups attempt to reduce health care disparities that stem from class inequalities aligns with a conflict (not symbolic interactionist) perspective. Educational objective:Symbolic interactionism is a micro-sociological perspective that suggests that people develop subjective meanings for things (eg, objects, behaviors) through social interaction.

Results from a survey of believers indicated a positive correlation between the incorporation of religion into an individual's life and participation in FBLDs. This illustrates what type of study, and what concept was being assessed? A.Observational, religious affiliation B.Experimental, religious affiliation C.Observational, religiosity D.Experimental, religiosity

C.Observational, religiosity In sociology, there is a distinction between religiosity and religious affiliation. Religiosity refers to the extent to which a religious doctrine is internalized and incorporated into an individual's life (eg, behaviors, beliefs). For example, Jewish individuals with a high degree of religiosity demonstrate many beliefs and behaviors that align with Judaism, and "being Jewish" is an important part of how they define themselves. Observational studies are conducted when it is unethical or unfeasible to manipulate a variable of interest. For example, it would not be feasible (or ethical) to manipulate the degree to which religion is internalized. Therefore, the survey findings presented are from an observational study (ie, no manipulation of variables) that assessed religiosity, the incorporation of religion into an individual's life. (Choices A and B) Religious affiliation describes the specific religious group to which an individual identifies, which is not synonymous with living one's life according to the principles, behaviors, or customs of that religion. For example, one may consider oneself to be Catholic but not attend church. A study in which believers are surveyed about the incorporation of religion into their lives is assessing religiosity, not religious affiliation. (Choices B and D) In an experimental design, the researcher manipulates independent variables to measure their effect on dependent variables. In this study, no variables were manipulated, making it an observational, not experimental, design. Educational objective:Religious affiliation describes an individual identifying with a specific religious group, whereas religiosity (or religiousness) is the degree to which an individual internalizes and incorporates that religion into their lives, as demonstrated by the individual's behaviors and beliefs.

Does the gender pay gap depicted in Figure 1 illustrate intersectionality? A.No; race and class are not represented in Figure 1. B.No; males are also negatively affected by the gender pay gap when they approach retirement age. C.Yes; the gender pay gap reflects income inequalities as a result of multiple social identities. D.Yes; the gender pay gap is negatively correlated with age.

C.Yes; the gender pay gap reflects income inequalities as a result of multiple social identities. Intersectionality describes the multiple, interconnected social identities (eg, gender, age, race, class) that intersect to impact individuals' lives, perspectives, and treatment in society. The gender pay gap (or gender wage gap) depicted in Figure 1 illustrates how the inequality in pay between female and male workers is related to both gender and age, which is an example of intersectionality. (Choice A) Despite the fact that race and class are not depicted, Figure 1 does display how two social identities (ie, gender and age) intersect to impact wages, which is an example of intersectionality. (Choice B) Males, who consistently earn more money than females across their lifetime according to Figure 1, are not directly negatively affected by the gender pay gap. (Choice D) According to Figure 1, the gender pay gap appears to be positively (not negatively) correlated with age: For most of the adult lifespan, as age increases, the gap in pay between males and females also increases. The gender pay gap only shows a slight decrease for age 65+. Educational objective:Intersectionality suggests that for each individual, multiple social identities (eg, gender, age, race, class) intersect to impact one's life, perspective, and treatment by others in society.

A woman who wants a baby but is opposed to using medical intervention to become pregnant is informed by her doctor that she will never conceive without medical intervention. Cognitive dissonance theory predicts that this woman is most likely to do all of the following, EXCEPT: A.seek a second opinion from another doctor. B.change her attitude about using medical intervention to become pregnant. C.accept her doctor's diagnosis while maintaining her own opposition to medical intervention. D.decide that she does not want to have a baby.

C.accept her doctor's diagnosis while maintaining her own opposition to medical intervention. (39%) According to cognitive dissonance theory, cognitive dissonance (mental conflict) results from beliefs, attitudes, or behaviors that are contradictory or incompatible. Cognitive dissonance causes a state of discomfort that results in motivation to reduce the conflict by aligning thoughts and/or behaviors. A woman who wants a baby but does not believe in medical intervention to conceive should experience cognitive dissonance if her doctor says she cannot become pregnant without such intervention, because the new information directly contradicts her belief. Therefore, cognitive dissonance theory predicts that she will alter her attitudes, beliefs, or behaviors to reduce the resulting discomfort. The only course of action that will not reduce the discomfort would be accepting her doctor's diagnosis and maintaining her stance against medical intervention. This course of action would maintain the dissonance, which is not consistent with the central tenet of cognitive dissonance theory. (Choice A) A second opinion that undermines the first diagnosis would reduce cognitive dissonance, so seeking a second opinion from another doctor is something the woman is likely to do. (Choice B) If the woman changes her attitude about using medical intervention to become pregnant, she would align her beliefs with her doctor's diagnosis, thereby reducing cognitive dissonance. (Choice D) If the woman does not want to alter her belief about using medical intervention to become pregnant, she could instead alter her attitude about wanting a baby. Deciding that she does not want a baby would also reduce cognitive dissonance.

A group of five health care professionals is presented with a complex system-based problem in a large hospital and asked to generate multiple possible solutions. Research on group processes suggests that: A.if group members get along, more options will be discussed and considered. B.the group is more likely to come up with an effective solution if there is a strong group leader. C.if group members start with similar opinions, they will support an option that is more extreme. D.on average, individuals working alone will produce fewer options than when working in a group.

C.if group members start with similar opinions, they will support an option that is more extreme. Group polarization occurs when group members adopt a more extreme attitude or course of action after group discussion. Group polarization is more likely to occur if group members have similar opinions before group discussion. Group discussion strengthens and reconfirms individuals' opinions, resulting in an average viewpoint that is more extreme. Group polarization can occur in either direction (ie, extremely positive or extremely negative). (Choice A) Groupthink occurs when a group arrives at an incorrect or irrational decision because group members value getting along and reaching a consensus more than they value critical evaluation of alternatives. Therefore, if group members get along, fewer (not more) options will be discussed and considered. (Choice B) Groupthink is more likely to occur in groups that have strong, well-liked leaders. Groupthink results in irrational decision making because group members do not want to cause discord or thwart progress, so they do not speak up. Groupthink is more likely to produce inaccurate or ineffective (not effective) group decisions. (Choice D) Social loafing occurs when an individual exerts less effort as a member of a group than when alone. Individuals working alone tend to come up with more (not fewer) options than when working in a group, on average. Educational objective:Group polarization occurs when the views of individuals within a group become more extreme after discussion with like-minded members. Opinions can be polarized in either direction (extremely positive or extremely negative).

The sects and churches with FBLDs described in the passage are most likely to be categorized as: A.countercultures, because members' values and norms oppose those of mainstream society. B.utilitarian organizations, because membership is voluntary and based on shared values. C.subcultures, because members' values and norms are distinct from mainstream society. D.aggregates, because membership is based on a sense of unity and identification with the group.

C.subcultures, because members' values and norms are distinct from mainstream society. Religious organizations can be categorized as churches, sects, and cults. Churches are established formal organizations that tend to be well integrated into society. Sects are formed after believers split from an established church, often in pursuit of a more pure or traditional form of faith. Cults are radical groups of believers organized around a charismatic leader. The dominant culture includes the established set of norms, values, and beliefs that define a society. A subculture is a group of individuals who are characteristically distinct from the dominant culture, but whose values and norms still generally align with the dominant culture. The sects and churches described in the passage have values and norms (eg, FBLDs) that differ somewhat (ie, are distinctive) from mainstream society, but that are not opposed to it; therefore, they would best be categorized as subcultures. (Choice A) A counterculture opposes and rejects the norms/values of the dominant culture (eg, much of the antiwar movement of the 1960s). The sects and churches described in the passage are distinct from mainstream culture, but there is no indication that they are opposed to it, making them subcultures, not countercultures. (Choice B) Utilitarian organizations compensate members for their involvement (eg, money, certification/diploma). The sects and churches described in the passage could be considered normative organizations (ie, membership based on shared values), not utilitarian organizations. (Choice D) An aggregate is a collection of individuals who share a common location but do not identify as a group (eg, all the people at a given store at 11:00 AM). The sects and churches described in the passage could be considered in-groups (ie, groups to which members identify and belong), not aggregates. Educational objective:A subculture is distinct from the dominant culture but is still aligned with the general norms and values of the dominant culture.

Acetylation of lysine residues in histones increases gene expression because: A.DNA is tightly bound to negatively charged amino acids on histones. B.the carboxyl oxygen atoms in acetyl groups form hydrogen bonds with nitrogenous bases. C.the salt bridges between charged amino acids and phosphate groups are disrupted. D.lysine residues in histones associate with positively charged phosphate groups in DNA.

C.the salt bridges between charged amino acids and phosphate groups are disrupted. DNA winds tightly around proteins referred to as histones to form structural units known as nucleosomes. Gene expression depends partially on the association of histones with DNA. Genes that are actively transcribed are found on unwound stretches of chromatin called euchromatin, which transcription machinery can easily access. Inactive genes are usually in highly condensed DNA known as heterochromatin, which is much less accessible. Covalent post-translational modifications such as methylation, acetylation, and phosphorylation alter the association of histones with DNA. DNA is predominantly negatively charged due to the phosphate groups on the backbone. Histones associate with DNA by forming salt bridges between positively charged amino acid residues and negatively charged phosphate groups. These ionic interactions allow histones to bind tightly to DNA and prevent genes from being transcribed. Acetylation of histones involves the transfer of acetyl groups from acetyl coenzyme A to positively charged amino groups on lysine or arginine residues. This modification disrupts salt bridges by reducing the positive charge on histones, which allows DNA to unwind and become more accessible to transcription machinery. As a result, the acetylation of histones causes nucleosomes to relax and increases gene expression. (Choice A) Negatively charged amino acids (aspartate and glutamate) would be repelled by the negatively charged phosphate groups on DNA. (Choice B) The carboxyl oxygen atoms in the acetyl groups form hydrogen bonds with water rather than the nitrogenous bases on DNA. Acetylation neutralizes the positive charge on histones and decreases their interaction with DNA. (Choice D) Lysine residues are positively charged, and associate with negatively charged phosphate groups in DNA. If phosphate groups were positively charged, they would repel lysine. Educational objective:Histones associate with DNA by forming salt bridges between their positively charged residues and negatively charged phosphate groups on DNA. Acetylation of histones involves the transfer of an acetyl group to positively charged amino groups on lysine or arginine residues, increasing gene expression by disrupting salt bridges between histones and DNA.

Based on Figure 2, the most accurate conclusion is that: A.parents of children with disabilities reported less distress overall when they viewed the future expectancy appraisal of an event as "changeable." B.for either type of future expectancy appraisal, problem-focused coping resulted in lower levels of distress than emotion-focused coping. C.whether one coping strategy resulted in lower distress than the other depended on the future expectancy appraisal of the event. D.using a problem-focused coping strategy for an "unchangeable" future expectancy appraisal resulted in increased levels of distress compared to baseline.

C.whether one coping strategy resulted in lower distress than the other depended on the future expectancy appraisal of the event. Appraisal theory states that one's appraisal (evaluation) of a stimulus determines one's emotional response. In a primary appraisal, an individual classifies a stimulus as threatening, positive, or irrelevant. For stimuli deemed threatening, a secondary appraisal takes place in which the individual evaluates whether their resources/abilities are sufficient to cope with the stressor. Study 2 investigated the level of distress resulting from different coping strategies, depending on whether participants viewed a threatening event (ie, primary appraisal) as "changeable" or "unchangeable" in the future (ie, an aspect of secondary appraisal). Results (Figure 2) showed that for "unchangeable" events, average levels of distress were not significantly different between participants who used either emotion-focused or problem-focused coping. For "changeable" events, participants who used problem-focused coping experienced significantly less distress than those who used emotion-focused coping. Therefore, the most accurate conclusion is that whether one coping strategy results in lower distress than the other depends on the future expectancy appraisal of the event. (Choice A) Figure 2 does not combine emotion-focused and problem-focused coping for either type of appraisal (ie, changeable or unchangeable) and compare the overall distress levels. (Choice B) For events viewed as "unchangeable," there was no significant difference in the level of distress resulting from emotion-focused and problem-focused coping. (Choice D) Study 2 did not assess baseline levels of distress, so it is not possible to determine how distress changed compared to baseline. Educational objective:Appraisal theory states that one's evaluation of a stimulus determines one's emotional response. In a primary appraisal, an individual determines whether a stimulus is a threat, positive, or irrelevant. If it is deemed a threat, the individual evaluates whether their resources are sufficient to cope with the stressor in the secondary appraisal.

A researcher is testing a patient's neurological function. When a word is flashed briefly in the patient's right visual field, he can correctly vocalize what he saw. When a word is flashed briefly in the patient's left visual field, he is unable to say what he saw but can correctly draw it. Which of the following is most likely damaged in this patient? A.Left retina B.Wernicke area C.Right occipital cortex D.Corpus callosum

Corpus callosum The corpus callosum is a bundle of myelinated axonal projections connecting the right and left hemispheres of the brain, allowing the two hemispheres to communicate. The right and left hemispheres are specialized for certain processes, known as cortical lateralization. Each hemisphere is responsible for contralateral control of the body: The left hemisphere controls touch and movement on the right side of the body, and vice versa. Each hemisphere is also specialized for certain cognitive processes. The left hemisphere is specialized for language functions, including speech production (Broca area) and language comprehension (Wernicke area). Severing the corpus callosum is most frequently used to treat severe epileptic seizures. Individuals with a severed corpus callosum ("split-brain") experience a disconnection between information processed on the right and left sides of the brain. Information presented in a patient's left visual field is processed in the right hemisphere; without interhemispheric communication, the patient is unable to express what is seen using language but would be able to draw it. (Choice A) If the patient's left retina were damaged, he would be unable to receive and transmit information presented to the left visual field. Therefore, he would not be able to process the word or correctly draw it. (Choice B) The patient is correctly able to vocalize what is seen when it is flashed briefly in the right visual field, suggesting that both language centers in the left hemisphere (speech production in Broca area and language comprehension in Wernicke area) are intact. (Choice C) Damage to the right occipital cortex would result in an inability to process visual information presented in the left visual field. This patient is still able to draw the image represented by the word even though he cannot speak it, suggesting that the occipital lobe is intact.

A sample of water vapor undergoes deposition and then melting. What happens to its entropy after each phase change? A.Increased both times. B.Decreased both times. C.Increased with deposition, decreased with melting D.Decreased with deposition, increased with melting

D.Decreased with deposition, increased with melting Matter can exist in three different states (or phases): solid, liquid, and gas. These phases describe the uniform physical state of a substance's molecules: Molecules in a solid are tightly packed in an ordered structure and retain a fixed shape. Molecules in a liquid move past each other but stay close together. A liquid retains a fixed volume but assumes the shape of its container. Molecules in a gas move past each other and are well separated. A gas assumes the shape and volume of its container. Entropy is the thermodynamic quantity that measures the disorder of a substance (or system). Solids have relatively low entropy because the structure of the molecules is ordered and their motion is more constrained. Conversely, gases have relatively high entropy because the molecules are disordered and their motion is less constrained. Therefore, entropy changes as matter transitions from one phase to another. The sample of water vapor first undergoes deposition and then melting. Deposition is the phase transition from gas to solid, and solids have lower entropy than gases; therefore, entropy decreases (Choices A and C). Melting is the phase transition from solid to liquid, and liquids have higher entropy than solids; therefore, entropy increases (Choice B).

A patient who has been diagnosed with schizophrenia is prescribed a neuroleptic medication. Which of the following symptoms, if present, is this medication most likely to improve? A.Apathy B.Inability to experience pleasure C.Emotional flattening D.Disorganized speech

D.Disorganized speech Psychotic disorders are severe psychological disorders characterized by a loss of contact with reality. Schizophrenia is the most common psychotic disorder, with a prevalence of about 1% in the United States. Schizophrenia typically involves both positive symptoms, which are "pathological excesses" (eg, hallucinations, delusions, disorganized speech), and negative symptoms, which are "pathological deficits" (eg, apathy, inability to experience pleasure). Many people with schizophrenia also experience psychomotor symptoms (ie, changes in muscle tone or activity), which can occur either as a symptom of schizophrenia or as a side effect of medication. Schizophrenia is often treated with neuroleptic (conventional, typical, or first-generation) or atypical (second-generation) antipsychotic medication; both are generally effective in reducing positive symptoms. However, neuroleptics may exacerbate (worsen) negative symptoms through sedation or cognitive dulling, and they carry the risk of movement (eg, tremors) and other side effects. Atypical antipsychotics pose less risk of many of these side effects and in some cases may improve negative symptoms. A neuroleptic medication would be most likely to effectively treat (improve) disorganized speech, which is a positive symptom of schizophrenia. (Choices A, B, and C) Apathy, inability to experience pleasure, and emotional flattening are all negative symptoms of schizophrenia. Neuroleptic medications are generally not effective in treating negative symptoms, and the side effects may even exacerbate them. Educational objective:Schizophrenia is a psychotic disorder characterized by positive symptoms (ie, hallucinations, delusions, disorganized speech) and negative symptoms (eg, apathy, emotional flattening). Schizophrenia is often treated with either neuroleptic or atypical antipsychotics; both are generally effective in reducing positive symptoms, but neuroleptics have a greater risk of side effects (eg, sedation, psychomotor disturbances).

Based on information in the passage, which of the following best represents a latent function of FBLDs? A.Believers incorporating FBLDs as an expression of their faith B.Reduction of health disparities in the community C.Believers founding hospitals and clinics D.Lower rates of chronic illnesses in believers who follow FBLDs

D.Lower rates of chronic illnesses in believers who follow FBLDs Structural functionalism is a macro-sociological perspective that compares modern society to a biological organism. This theory proposes that, just as the various organ systems cooperate to maintain an organism's homeostasis, social institutions work together in the interest of societal balance, known as dynamic equilibrium. From the structural functionalist perspective, social institutions have manifest functions, which are expected, and latent functions, which are unintended. For example, social media allows people to keep in touch with friends and family (ie, manifest function), but police departments have used suspect's social media profiles to gather information (ie, latent function). The passage does not state that religions advocate FBLDs to reduce the incidence of chronic illness. Therefore, lower rates of chronic illnesses in believers are unintended, latent functions of FBLDs from the functionalism perspective. (Choices A, B, and C) As described in the passage, the incorporation of FBLDs as an expression of believers' faith, the founding of hospitals and clinics, and the reduction of health disparities in the community are all manifest (ie, expected) directives and consequences of religions with FBLDs and health-related values. Educational objective:Structural functionalism is a macro-level sociological perspective proposing that social institutions work together to maintain societal balance (dynamic equilibrium). Social institutions have manifest (intended) functions and latent (unintended) functions.

A researcher hypothesizes that there is a positive correlation between symptom severity of post-traumatic stress disorder (PTSD) and external locus of control. Which hypothetical finding would support this hypothesis? A.A more distorted and unstable self-image is associated with a stronger belief that the outcomes of events are controlled by one's own actions. B.A more distorted and unstable self-image is associated with a stronger belief that the outcomes of events are due to luck, fate, or powerful others. C.More severe hyperarousal is associated with a stronger belief that the outcomes of events are controlled by one's own actions. D.More severe hyperarousal is associated with a stronger belief that the outcomes of events are due to luck, fate, or powerful others.

D.More severe hyperarousal is associated with a stronger belief that the outcomes of events are due to luck, fate, or powerful others. Locus of control (LOC) refers to an individual's beliefs about who or what controls the outcome of an event or situation. Individuals with an external LOC feel that outcomes are due to factors beyond their control, such as luck, fate, or powerful others. Individuals with an internal LOC feel that outcomes are due to factors within their control, such as their own behaviors. Post-traumatic stress disorder (PTSD) is a trauma- and stressor-related disorder that can arise after exposure to trauma, an event that resulted or almost resulted in death or serious injury (eg, assault). A PTSD diagnosis requires evidence of several types of symptoms, including hyperarousal (eg, exaggerated startle response, insomnia); intrusive symptoms (eg, nightmares, flashbacks); avoiding reminders of the trauma; and negative thoughts and moods. The researcher's hypothesis would be supported by the finding that more severe hyperarousal (a symptom of PTSD) is associated with a stronger belief that the outcomes of events are due to luck, fate, or powerful others (external LOC).

f the survey from Study 3 that assessed the patients' level of AN was determined to be reliable, which of the following statements is true? A.Researchers can confidently extrapolate from Study 3 to all patients with cancer. B.Survey administration is consistent across medical settings. C.The survey is an accurate measure of nausea symptoms. D.Nausea scores on the survey will be similar from one survey administration to the next.

D.Nausea scores on the survey will be similar from one survey administration to the next. A variety of criteria are used to judge the extent to which scientific findings are credible (ie, can be trusted or believed). Both the overall study design and particular measures used must be examined for reliability and validity. Reliability refers to the consistency of an experiment or measure. Reliable measures produce similar results every time. For example, two MCAT examinations taken at the same time by the same person on two consecutive days should produce comparable scores. Similarly, if a study is well designed, it should produce similar results when repeated with new subjects. This is an indication that an experimental design is highly reliable, also referred to as replicability or reproducibility. Validity refers to the accuracy of a study or measure (Choice C). Reliability is typically a necessary, but not sufficient, condition for validity; simply producing the same results does not mean your results reflect reality. For example, a broken digital thermometer might consistently read 2 degrees above the actual temperature (ie, it is reliable but not valid). (Choice A) External validity, also known as generalizability, is the extent to which study results can be applied outside the laboratory to real-life situations. Experiments in which all variables are tightly controlled may have a high degree of reliability and internal validity but not be very generalizable to the real world. (Choice B) Standardization refers to test administration and/or scoring being done in a uniform manner. Consistency of test administration and scoring allows researchers to better compare one subject or group to the next. Educational objective:Reliability describes the degree to which a measure or experiment is consistent (eg, a test produces a similar score for one person who takes it twice). Validity refers to the accuracy of a measure or experiment (eg, a test accurately assesses what it was designed to measure).

Which of the following is the LEAST concerned with the role of nonverbal communication in influencing the social behavior of individuals? A.Elaboration likelihood model B.Dramaturgical perspective C.Symbolic interactionism D.Structural functionalism

D.Structural functionalism Nonverbal communication involves all the wordless cues that convey meaning when exchanged between individuals. Cues include physical distance between face-to-face speakers, body language and other physical movements, facial expressions, and vocal modifications (eg, tone, volume, emphasis, inflection). Research suggests that social interaction is largely influenced by nonverbal communication. Structural functionalism is a macro-level (large-scale) sociological perspective suggesting that all aspects of society work together to maintain dynamic equilibrium (societal balance). Structural functionalism is not concerned with micro-level (small-scale) interactions between individuals, so this theory would be the least concerned with how nonverbal communication influences the social behavior of individuals. The elaboration likelihood model, dramaturgical perspective, and symbolic interactionism each deal with how individuals interact with and attempt to influence each other, partly through the use of nonverbal cues. (Choice A) The elaboration likelihood model of persuasion proposes that when an individual is uninterested in a message, superficial factors (eg, an attractive celebrity spokesperson) might be most persuasive. Therefore, the elaboration likelihood model is concerned with how nonverbal cues can influence the behavior of individuals. (Choices B and C) Symbolic interactionism is a micro-level sociological theory that suggests that people communicate using symbols (eg, hand gestures). Stemming from symbolic interactionism, the dramaturgical perspective proposes that individuals behave as actors, behaving in front of others in ways that align with social norms. Both approaches are concerned with how nonverbal cues influence the behavior of others. Educational objective:Nonverbal communication includes all the wordless cues meant to convey meaning to another individual, such as body language, hand gestures, facial expressions, and vocal inflections. Research suggests that nonverbal communication has an important impact on social interactions.

In a surgical residency program that does not allow maternity leave, a female resident becomes pregnant and takes three weeks off to have her baby. A male resident misses a similar amount of time due to an accident. Later, only the female resident is required to make up the time missed. Is this an example of institutional discrimination? A.No, because maternity leave policies can apply only to females, not males. B.No, because the policy would treat all females seeking maternity leave the same. C.Yes, because the policy reflects the medicalization of female health concerns like pregnancy. D.Yes, because the policy disadvantages females but does not apply to males in similar situations.

D.Yes, because the policy disadvantages females but does not apply to males in similar situations. Unlike prejudice (negative or positive ideas/beliefs about a specific group), discrimination involves actions that negatively impact specific groups. Individual discrimination occurs at the person-to-person level (eg, a male manager refusing to hire females). Institutional discrimination occurs when social institutions have systematic policies and procedures that result in unfair treatment of individuals based on their group membership. This scenario is an example of institutional discrimination because the policy disadvantages females but not males; therefore, it demonstrates unfair treatment of female surgical residents at the institutional level. These types of policies often have long-term consequences, such as fewer women choosing to pursue surgery or completing surgical residencies, resulting in far fewer female surgeons than male surgeons. (Choices A and B) Any systematic policy that negatively impacts only one social group is discriminatory. The policy in this example, which requires females to make up time for maternity leave but does not require males to make up time for rehabilitation following an accident, is an example of institutional discrimination. (Choice C) Medicalization is the process of defining and characterizing a given condition or behavior as a medical illness, which can have both positive (eg, funding for research) and negative (eg, stigmatization) consequences. The medicalization of pregnancy does not explain why this policy demonstrates institutional discrimination. Educational objective:Discrimination involves actions that negatively affect certain social groups (eg, a certain race or gender). Individual discrimination involves person-to-person interactions that involve unfair treatment (eg, male manager refusing to hire females). Institutional discrimination involves policies at the organizational, rather than individual, level that result in the unfair treatment of certain people based on group membership.

One function of endothelial cells is to: A.contract to increase blood pressure. B.line the inside of the gastrointestinal tract. C.bind sites of vascular damage to form clots. D.line the inside of blood vessels.

D.line the inside of blood vessels. The endothelium is the one-cell-thick layer of specialized epithelial cells (ie, endothelial cells) that line the interior of the cardiovascular system, which includes the heart, arteries, capillaries, and veins. This layer of cells is in direct contact with the blood in the lumen (inner cavity) and provides a relatively smooth, friction-reducing surface that enables the efficient movement of blood through the vasculature. The endothelium also acts as a barrier that regulates the exchange of substances between the blood and nearby tissues. For example, in response to inflammatory chemicals released during an infection, endothelial cells facilitate the movement of white blood cells out of the bloodstream to the affected tissue. (Choice A) In arteries and veins, the interior layer of endothelial cells is surrounded by a layer of smooth muscle. Contraction of the smooth muscle layer results in vasoconstriction, thereby promoting increased blood pressure, whereas relaxation of the smooth muscle layer results in vasodilation and promotes decreased blood pressure. This smooth muscle contraction is regulated by several factors, including the autonomic nervous system, certain hormones (eg, renin and angiotensin), and factors derived from the endothelium; however, the endothelium itself does not contract. (Choice B) Epithelial cells are packed together tightly into sheets that make up the outer layer of the skin (the epidermis), the secretory components of glands, and the lining of the inner cavities of the body (eg, the lumen of hollow organs such as the gastrointestinal tract). Endothelial cells are a specialized type of epithelial cell that line the inside of the heart, blood vessels, and lymph vessels specifically. However, endothelial cells do not line the lumen of the gastrointestinal tract. (Choice C) When the blood vessel wall is damaged, platelets (non-nucleated cellular fragments generated from large bone marrow cells called megakaryocytes) adhere to the exposed connective tissue and form a plug at the site of injury. This plug is later stabilized as a clot by fibrin, an insoluble protein that polymerizes into long fibers that cross-link like a net over the damaged area. Platelets and fibrin, not endothelial cells, bind sites of vascular damage to form clots. Educational objective:The endothelium is a single-cell layer that makes up the innermost surface of the cardiovascular system (heart and blood vessels). The endothelium promotes blood fluidity and functions as a selective barrier between the blood and surrounding tissues.

Cirrhosis of the liver is characterized by hepatic cell death, tissue scarring, and altered liver function. All of the following would be disrupted by cirrhosis of the liver EXCEPT: A.the production of ketone bodies. B.the metabolism of most drugs. C.the oncotic pressure within capillaries. D.the secretion of digestive proteolytic enzymes.

D.the secretion of digestive proteolytic enzymes. The liver is located in the upper right side of the abdominal cavity, just below the diaphragm, and performs various functions within the body. According to the question, cirrhosis causes hepatic cell death and scarring. As a result, the following normal functions of the liver are severely impacted: Ketogenesis: Ketogenesis (synthesis of ketone bodies) occurs mainly in the liver and plays a critical role in energy metabolism when glycogen stores are depleted and blood glucose levels become low. During times of fasting, mitochondria within liver cells convert acetyl coenzyme A into ketone bodies, which are then used by the brain to make ATP (Choice A). Detoxification of drugs: Drugs are often exogenous compounds that may have toxic effects if allowed to accumulate in the body. The liver is a critical organ for the breakdown and detoxification of many drugs (Choice B). Synthesis of plasma proteins: Osmotic pressure within capillaries is due to the presence of plasma proteins that cannot easily cross the capillary membrane. Oncotic pressure causes a "pulling force" inside capillaries, which balances the pushing force of hydrostatic pressure, helping keep fluid in the vasculature. The majority of plasma proteins such as albumin are synthesized in the liver. Therefore, cirrhosis is expected to impact the production of plasma proteins, which in turn would affect oncotic pressure in the capillaries (Choice C). (Choice D) Digestive proteolytic enzymes, which hydrolyze polypeptides, are synthesized and secreted from the pancreas, stomach, and small intestine. Cirrhosis of the liver is not expected to affect the secretion of digestive proteolytic enzymes because they are secreted by other tissues.

Which of the following correctly describes the total change in Gibbs free energy and the change in entropy, respectively, during Reaction 1? A.ΔG > 0, ΔS < 0 B.ΔG < 0, ΔS > 0 C.ΔG > 0, ΔS > 0 D.ΔG < 0, ΔS < 0

D.ΔG < 0, ΔS < 0 The change in Gibbs free energy ΔG of a chemical reaction indicates the spontaneity (ie, thermodynamic favorability) of the process. A value of ΔG < 0 (ie, a negative value) indicates that the reaction is spontaneous (ie, favorable), and a value of ΔG > 0 (ie, a positive value) indicates that the reaction is nonspontaneous (ie, unfavorable). In the passage, the industrial synthesis of formic acid is stated as being a spontaneous reaction. Consequently, ΔG < 0 for the overall reaction. Entropy S is a measure of the molecular disorder of a system. Solids contain atoms in a fixed arrangement with little room to move, resulting in relatively low entropy. Conversely, gases have relatively high entropy because they are free to move and reconfigure into many different arrangements. The entropy of liquids is between that of solids and gases (Ssolid < Sliquid < Sgas ). During a reaction, the entropy of a system changes and the change in entropy is calculated as ΔS = Sfinal − Sinitial. The process of converting a gas to a liquid or a solid generally involves a decrease in ΔS. According to Reaction 1, the 2 moles of gas and 1 mole of aqueous species react to form 2 moles of an aqueous species. Because the initial state of the system is more disordered (ie, 2 moles of gas) than the final state (ie, only aqueous species and 0 moles of gas), ΔS < 0 for the reaction (ie, entropy decreases, and ΔS is negative). (Choices A, B, and C) Reaction 1 occurs spontaneously (ie, ΔG < 0) and produces a more ordered final state (ie, ΔS < 0). Educational objective:The change in Gibbs free energy ΔG indicates whether a reaction is spontaneous (ΔG < 0) or nonspontaneous (ΔG > 0). Entropy describes the disorder of a molecular system. Gases are disordered (ie, high entropy) and solids are highly ordered (ie, low entropy). The entropy of liquids is between that of solids and gases.

Which of the following nucleic acid complexes would undergo correction by the DNA mismatch repair system?

During DNA replication, DNA polymerase may mistakenly incorporate an incorrect nucleotide into the newly synthesized strand, creating a base pair mismatch between the daughter and the parent strands (ie, G-T and A-C mispairing instead of the proper G-C and A-T pairing). The presence of the mismatched base activates the DNA mismatch repair (MMR) machinery, in which a nuclease enzyme excises the erroneous nucleotide, as well as several nucleotides flanking either side of the incorrectly matched base, from the daughter strand. DNA polymerase then incorporates the appropriate nucleotides, and DNA ligase catalyzes the formation of new phosphodiester bonds to seal the gap between the strands. In this scenario, the MMR machinery would operate on the DNA sequence with a pair of mismatched bases. The DNA complex in Choice C has a mismatch at the twelfth base pair that, once corrected, would produce an accurate complementary DNA strand.

Which step(s) of the viral life cycle would most likely occur in lytic phages? Injection of viral genetic material into the bacterial host Integration of viral DNA into the bacterial genome Degradation of the host genome

I and III only All viruses are obligate intracellular parasites because they cannot replicate independently outside of a host cell. Bacteriophages (sometimes shortened to phages) are viruses that exclusively infect bacteria. The life cycle of a particular bacteriophage can be lytic or lysogenic, which determines the method by which the phage uses the host's cellular machinery to create new progeny. The general steps involved during the lytic life cycle are described as follows: Attachment: The bacteriophage contacts the bacterial cell wall and attaches to the host bacterium using its tail fibers. Viral genome entry: The phage uses its tail sheath to inject its genome into the cytoplasm of the bacterial host (Number I). Host genome degradation: Viral enzymes degrade the host genome into its nucleotide components to provide the building blocks for replication of the viral genome (Number III). Synthesis: Loss of the bacterial (ie, host) chromosome ends the synthesis of host molecules, now under the control of the viral genome. As a result, the host machinery (eg, ribosomes) begins to synthesize the components needed for new viral progeny, which then assemble inside the host cell. Release: Many newly assembled viral progeny (virions) are released as the bacterium disintegrates (lysis) due to the action of lysozymes on the host cell wall. Therefore, the steps of a viral life cycle that would most likely occur in lytic phages are injection of viral genetic material into the bacterial host and degradation of the host genome.

Which of the following structures represents the Fischer projection of a β-d-glucose unit found in cellulose?

b Fischer projections are two-dimensional representations of molecules that are often used to distinguish among carbohydrate anomers, epimers, and enantiomers. Carbohydrate enantiomers (l- and d-conformations) are nonsuperimposable mirror images of each other. They have the same chemical formula but with every stereocenter reversed. In a Fischer projection, d-sugars always show the second-to-last carbon (carbon 5 in glucose) as having its oxygen atom to the right. Naturally occurring sugars generally adopt the d-conformation. Epimers are carbohydrates that differ at only one stereocenter. Fischer projections of d-glucose always show one hydroxyl group to the right of carbon 2, one to the left of carbon 3, and one to the right of carbon 4. Carbohydrates that differ at exactly one of these positions are epimers of d-glucose. Anomers are a special case of epimers that differ from each other at the anomeric carbon. They can exist only in cyclized sugars (furanose or pyranose) because in the linear form, the anomeric carbon is a carbonyl and cannot be a stereocenter. In Fischer projections, cyclic d-sugars with a hydroxyl group to the right of the anomeric carbon are in the α-conformation, whereas those with the hydroxyl group on the left are in the β-conformation. The opposite is true for l-sugars. Cellulose is composed of multiple β-d-glucose units in the pyranose form. Therefore, a Fischer projection of β-d-glucose must display a six-member ring with a hydroxyl group to the right of carbon 5 (d-sugar) and one to the left of the anomeric carbon (β-conformation). Of the choices available, only the Fischer projection in Choice B has the correct stereochemistry. (Choice A) This structure is α-d-mannose, a glucose epimer that differs at carbon 2. (Choice C) This structure is β-d-fructose. (Choice D) This is β-l-glucose, the enantiomer of β-d-glucose. Because this is an l-sugar, the β anomer positions the anomeric hydroxyl on the right. Educational objective:Fischer projections help distinguish anomers, epimers, and enantiomers. Enantiomers are compounds with the same chemical formula but differ at every stereocenter, whereas epimers and anomers differ at only one stereocenter. Anomers exist only in cyclized sugars and differ at the anomeric carbon.

n a neuron, mitochondrial biogenesis is believed to occur primarily in the cell body, but mitochondria are often positioned at the presynaptic terminal, a distal site with high metabolic demand. Given this information, which molecular mechanism is most likely responsible for mitochondrial transport from the cell body to the presynaptic terminal?

Kinesin motors transport mitochondria along microtubules A eukaryotic cell's cytoskeleton is an intracellular scaffolding (network) of fibers interspersed throughout the cytoplasm. The cytoskeleton is composed of three types of fibers: Microfilaments, intermediate filaments, and microtubules. Together, these fibers function to organize cellular components, support cellular motility (eg, cell movement, intracellular transport), and give the cell its shape. Microtubules are structural cytoplasmic filaments composed of tubulin subunits. These filaments have a number of critical functions, including serving as tracks for intracellular transport of organelles and vesicles. The movement of intracellular cargo along microtubules is mediated by two motor proteins: Kinesin: Moves intracellular cargo along microtubules in anterograde axonal transport (ie, away from the nucleus and toward distal sites). Dynein: Participates in retrograde axonal transport of intracellular cargo (ie, from distal sites toward the nucleus) (Choice D).

Interleukin-1β is a cytokine that upregulates the synthesis of PGE1, the final enzyme in the arachidonic acid pathway that generates prostaglandin E. Which of the following plots most likely represents the change in the kinetics of prostaglandin E production from cellular lysates obtained from cells incubated with (dashed line) and without (solid line) interleukin-1β?

Lineweaver-Burk plots are used to determine Michaelis-Menten kinetic parameters. These linear plots relate the inverse of reaction velocity (1/V) on the y-axis to the inverse of substrate concentration (1/[S]) on the x-axis. This linear relationship is based on rearrangements of the Michaelis-Menten equation. On a Lineweaver-Burk plot, the x-intercept corresponds to the negative inverse of the Michaelis constant (x-intercept = −1/Km) and the y-intercept corresponds to the inverse of the maximum velocity (y-intercept = 1/Vmax). Because the y-intercept in a Lineweaver-Burk plot is 1/Vmax, an increase in Vmax would correspond to a lower y-intercept value. The enzyme affinity for substrate (Km) is independent of enzyme concentration, so the x-intercept (−1/Km) would remain unchanged with varying enzyme concentration. In this example, interleukin-1β upregulates the synthesis of the enzyme PGE1, which results in increased enzyme concentration. The maximum velocity Vmax of the enzyme-catalyzed reaction, which occurs when the enzyme is saturated with substrate, is equal to the product of the catalytic rate constant kcat and the concentration of enzyme in solution: Vmax=kcat[Etot]Vmax=kcat[Etot] Therefore, increasing the enzyme concentration would result in an increase in the maximum velocity of the reaction and a decrease in the y-intercept value.

Which structure is the product of the reaction of 4-tert-butyl-2-octanone and NaCN under acidic conditions?

Molecular structure determines how a reaction will proceed. The following steps describe how to determine the structure of an organic molecule from its name: Determine the number of carbon atoms in the parent chain, which is the longest chain containing the highest priority functional group. The prefix of the parent alkane determines the number of carbons, and the suffix describes the high priority functional group. The number prior to the chain name describes the carbon to which the main functional group is attached. Determine the position and identity of each substituent, if any. All substituent names are placed at the beginning of the compound name, together with the number of the carbon to which the substituent is attached. The reactant 4-tert-butyl-2-octanone has an eight-carbon parent chain denoted by the prefix oct-, and the suffix -one indicates the compound is a ketone with the carbonyl at carbon 2. The substituent is a tert-butyl on carbon 4. The reaction of a ketone or an aldehyde with a cyanide ion (from NaCN) acting as a nucleophile and attacking the electrophilic carbonyl (C=O) carbon produces a cyanohydrin. The cyanohydrin functional group contains a hydroxyl group (-OH) and a cyano group (C≡N) attached to the same carbon.

Which of the following is NOT accurate regarding antiemetic medications, which are administered to patients undergoing chemotherapy to treat or prevent N/V? A.An antiemetic that prevents a recurrence of N/V acts as positive reinforcement. B.An antiemetic that treats current PN acts as negative reinforcement. C.An antiemetic that treats current PN may produce escape learning. D.An antiemetic that prevents a recurrence of N/V may produce avoidance learning.

N/V is an aversive stimulus. Antiemetic medications can be administered while patients are experiencing N/V to treat their N/V, or before chemotherapy to prevent N/V entirely. Either scenario may result in operant conditioning, in which the likelihood of an individual repeating a behavior is influenced by the outcome of that behavior (ie, by reward or punishment). Behavior is increased or maintained by reinforcement; positive reinforcement occurs when a desirable stimulus is applied, encouraging a behavior to happen again. For example, a young child receives a lollipop (desirable stimulus) for good behavior during a medical appointment, which increases the likelihood of future good behavior. In terms of the answer choice that is not accurate regarding antiemetic medications, an antiemetic that prevents a recurrence of N/V is inhibiting an undesirable stimulus, not adding a desirable stimulus; therefore, it is not an example of positive reinforcement. (Choice B) Negative reinforcement occurs when an undesirable stimulus is withdrawn, which encourages a behavior to happen again. For example, taking an antiemetic to treat (remove) current PN (unpleasant stimulus) increases the likelihood of the individual taking the medication in the future, which is negative reinforcement. (Choice C) Escape learning occurs when an individual learns how to terminate a current unpleasant stimulus. For example, an antiemetic that treats current PN may produce escape learning, as the individual learns that taking the medication stops N/V (unpleasant stimulus). (Choice D) Avoidance learning occurs when an individual figures out how to prevent experiencing the unpleasant stimulus in the future. For example, taking an antiemetic before chemotherapy, thereby preventing a recurrence of N/V (unpleasant stimulus), is an example of avoidance learning. Educational objective:In operant conditioning, the outcome of a behavior impacts the likelihood that the behavior will be repeated; behavior increases due to reinforcement, and it decreases due to punishment. Positive reinforcement refers to a desirable stimulus being applied, whereas negative reinforcement is an undesirable stimulus being withdrawn.

The genetic code is said to be degenerate because there are 64 different codons, but translation produces only 20 unique amino acids. The degeneracy of the genetic code is due to which mechanism?

Nontraditional base pairing of the anticodon with the third base of the codon

Formic acid (HCOOH), the simplest carboxylic acid, occurs naturally in a variety of sources including the venom of bee and ant stings. Due to its commercial availability, HCOOH is commonly used as a preservative and antibacterial agent in the food and pharmaceutical industries. Various industrial methods for synthesizing HCOOH have emerged in response to an increased demand. For example, one synthetic route produces HCOOH through the spontaneous reaction between gaseous CO and NH3 in the presence of an acidified aqueous medium. CO(g) + NH3(g) + H3O+(aq) ⇄ HCOOH(aq) + NH4+(aq) Reaction 1 Formation of HCOOH through Reaction 1 occurs via a three-step reaction mechanism. The first step proceeds according to Reaction 2 and is catalyzed by sodium methoxide. CH3OH(l) + CO(g) ⇄ HCO2CH3(l) Reaction 2 (slow step) The second and third steps of the mechanism proceed according to Reactions 3 and 4, respectively. HCO2CH3(l) + NH3(g) ⇄ HCONH2(l) + CH3OH(l) Reaction 3 (fast step) HCONH2(l) + H3O+(aq) ⇄ HCOOH(aq) + NH4+(aq) Reaction 4 (fast step) Which of the following diagrams best illustrates the energy profile for Reaction 1? A. B. C. D.

The energy change that occurs over the duration of a reaction is depicted by a reaction energy diagram, which is a plot of energy (y-axis) versus reaction progress as represented by the reaction coordinate (x-axis). The reaction coordinate reflects the change in molecular geometry of the system, starting with the reactants and ending with the products. During an elementary reaction, existing bonds are broken and new bonds are formed, resulting in a momentary transition state located at an energy maximum (ie, a peak on the energy diagram). As such, multistep reactions have a corresponding transition state for each step (ie, one peak per step), and the intermediates formed during the multistep process appear as "valleys" between the peaks. The energy difference between the reactants (or intermediates) and the transition state (ie, the activation energy Ea) affects the reaction rate. An elementary reaction with a large Ea will have a small rate constant (ie, a "slow" step) because more energy is required to initiate the reaction. Conversely, an elementary reaction with a small Ea will have a large rate constant (ie, a "fast" step) because less energy is required to initiate the reaction. According to the passage, the formation of formic acid occurs in three steps, and step 1 has a slower rate than steps 2 and 3 (fast steps). This indicates that the reaction energy diagram should have three peaks, and the Ea peak for step 1 should be larger than the Ea peaks for steps 2 and 3. Therefore, the energy diagram shown in Choice B best matches the three-step reaction mechanism. (Choice A) This energy diagram corresponds to a one-step reaction mechanism (ie, one peak). (Choice C) Because step 1 is slow in the three-step mechanism, the Ea for step 1 is greater than the Ea for step 2 and step 3. (Choice D) An energy diagram with two peaks corresponds to a two-step reaction mechanism, but the passage states that Reaction 1 follows a three-step reaction mechanism. Educational objective:In a reaction energy diagram, one transition state peak is seen for each elementary step in the reaction mechanism. The greater the difference in energy between the reactants and the transition state, the slower the reaction rate and vice versa.

Human sperm and oocytes are substantially different in all of the following aspects EXCEPT:

the number of nuclear chromosomes contributed to a zygote. Ploidy is defined as the number of homologous chromosome sets in the nucleus of a cell. In the human body, with the exception of sperm and egg cells (reproductive cells), nucleated cells are diploid and known as somatic cells. Somatic cells have 46 individual chromosomes that appear as 23 pairs. Each somatic cell has two sets/copies (2n) of each chromosome. These include 22 pairs of homologous chromosomes (autosomes) and 1 pair of sex chromosomes. In contrast, a mature egg and sperm are both haploid (1n), meaning that each contains 22 (unpaired) autosomes and 1 sex chromosome, resulting in 23 chromosomes. During fertilization, the egg and sperm form a zygote with a nucleus containing the full complement of 46 chromosomes. These 46 chromosomes are found in pairs, and in each pair one chromosome comes from the mother and one comes from the father. Accordingly, egg and sperm cells are similar in ploidy because they both are haploid cells and contribute the same number of nuclear chromosomes to a zygote.