MCAT-Prep GS-1 Test - Questions I missed/to review

A renal stone is formed in the kidney and passed to the exterior of the body. Which of the following would be the normal route for the kidney stone? (A) renal pelvis → urethra → bladder → ureter. (B) bladder → urethra → ureter → renal pelvis. (C) urethra → renal pelvis → bladder → ureter. (D) renal pelvis → ureter → bladder → urethra.

(D) Of course, urine is produced in the kidneys (mostly by the filtration of blood) and is transported, with the help of peristaltic waves, down the tubular ureters to the muscular sack which can store urine, the bladder. Through the process of urination (= micturition), urine is expelled from the bladder to the outside via a tubular urethra. The renal pelvis (renal = kidney) is a part of the kidney that functions as a funnel for urine flowing to the ureter. Thus D is the correct answer.

Which of the following is MOST consistent with the process of inhalation? (A) The thoracic cage moves inward as the diaphragm moves downward. (B) The internal pressure is positive with respect to atmospheric pressure. (C) The phrenic nerve is stimulated. (D) The diaphragm relaxes.

Inhalation is active and requires the contraction of the diaphragm by the phrenic nerve. The diaphragm thus moves downward, while the thoracic cage is pushed outward, increasing the volume of the chest cavity. This causes a negative internal pressure, which allows air to enter the lungs. Hence, only answer choice C is correct. WIMI: When you breathe, your diaphragm moves downward and CONTRACTS, not relaxes. D is incorrect.

Dendrites

Parts of neurons, along with the nucleus and axons. Whereas axons send electric impulses from the nucleus of the nerve cell to other cells, dendrites receive electric impulses and conduct them toward the cell's nucleus. They are further responsible for capturing neurotransmitters (as axons release them)

Rods

Sensory visual photoreceptors that exist in the retina. They are responsible for low light intensity vision (night vision).

Temporal lobe

Thought to be mainly involved in primary auditory functions, such as the interpretation and production of speech, and memory processes (via the medial temporal lobe memory system).

A couple went to Africa, met a young boy, and decided to pay for his schooling. Helping the boy gave the couple a sense of meaning and purpose, made them feel happy, and decreased their inflammation levels. What type of happiness is being described? (A) Positive happiness (B) Agape happiness (C) Eudaimonic happiness (D) Hedonic happiness

(C) This is correct. Eudaimonic happiness is a type of happiness that derives from leading a good and virtuous life, doing worthy activities, and experiencing a sense of life purpose. Eudaimonic happiness has been found to be correlated positively to good physical and mental health. This was precisely what the couple experienced, as described in the question stem. WIMI: Did not know the definitions of the types of happiness. Hedonic happiness - achieved through experiences of pleasure and enjoyment Eudaimonic happiness - achieved through experiences of meaning and purpose Agape - one of the six emotions of love (unconditional love); not a type of happiness

Which of the following sensory receptors is involved in pain perception, and which lobe is thought to be responsible for processing that information (sensory receptor, lobe, respectively)? (A) Rods, temporal lobe (B) Dendrites, temporal lobe (C) Nociceptors, parietal lobe (D) Meissner corpuscles, parietal lobe

(C) This is correct. Nociceptors are cells that specialize in pain perception. They are one of the three types of free nerve endings that are spread throughout the skin, muscle, bone, connective tissue, joints, and viscera. The other types of free nerve endings, part of the same somatosensory system's modality, detect mechanical stimuli (touch, pressure, and stretch) and temperature (cold and heat). After tissue damage, pain peptides (e.g., histamine, globulin, and arachidonic acid) are released and captured by nociceptors. The information is sent to the parietal lobe. This lobe is thought to be mainly responsible for processing and integrating somatosensory and proprioceptive information (e.g., pain perception).

Polypeptides sloughed off in fingerprints react with ninhydrin (reacts with amino acids). Which of the following tetrapeptides would likely be most reactive with ninhydrin? (A) K-G-K-N (B) Y-V-V-T (C) H-D-E-E (D) C-C-G-C

(A) It is apparent from Figure 1 (note that in this case, X must represent OH; and R must be the side group) that it is the amine in the amino acid that is reacting with ninhydrin. So we should be looking for tetrapeptides with the maximum number of amine groups available for bonding (= answer choice A with 2 lysine groups, K). Certainly, the terminal amine of lysine residues in peptides are available to react with ninhydrin (recall: lysine has 2 amine groups). FYI: Answer choice A: K-G-K-N = lysine-glycine-lysine-asparagine Answer choice B: Y-V-V-T = tyrosine-valine-valine-threonine Answer choice C: H-D-E-E = histidine-aspartic acid-glutamic acid-glutamic acid Answer choice D: C-C-G-C = cysteine-cysteine-glycine-cysteine

ANLEQ is overexpressed in cell cultures as part of a short peptide sequence VSPGSANLEQ that is cleaved into two fragments and purified using ion exchange chromatography. Using a buffer of pH 7, the best purification strategy would be to use: (A) anion exchange chromatography. (B) cation exchange chromatography. (C) size exclusion chromatography. (D) gel filtration.

(A) Since ANLEQ is negatively charged in solution at pH 7, it would be best to use anion exchange chromatography, which preferentially binds anions. Size exclusion chromatography would be largely useless, as both fragments are relatively the same size. Background: Anion exchange chromatography uses an ion-exchange resin containing positively charged groups, such as diethyl-aminoethyl groups (DEAE). Thus anion exchange resins will bind to negatively charged molecules. This form of chromatography is commonly used to purify proteins, amino acids, sugars/carbohydrates and other acidic substances with a negative charge.

The Ksp for calcium oxalate is 2.7 x 10^-9. The typical concentration of calcium in urine is 1.5x the plasma concentration, which is 2.0 mmol/L. Determine the minimum oxalate ion concentration in urine that would be required to form kidney stones. (A) 9.0 x 10^-7 M. (B) 9.0 x 10^-4 M. (C) 6.0 x 10^-7 M. (D) 6.0 x 10^-4 M.

(A) The inference is that the precipitate (s = solid) calcium oxalate forms the stone, i.e., Ca(OOCCOO)(s). The Ksp for calcium oxalate is given in the passage, and its value can only refer to the reverse of the reaction (Ca++ + -OOCCOO-(aq) <-> Ca(OOCCOO)(s)), i.e., the product of the ion concentrations. The concentration of calcium ions in urine must be the concentration in blood multiplied by 1.5 (see Table 1) and then converted from mmol/L to mol/L. Ksp for calcium oxalate = [calcium ion][oxalate ion] 2.7 × 10^-9 = [2.0 mmol/L x 1.5 x (1 mol/1000 mmol)][oxalate ion] = [3.0 x 10^-3][oxalate ion] Thus, [oxalate ion] = (27 × 10^-10)/( 3.0 x 10^-3) = 9.0 x 10^-7 mol/L Going Deeper: Technically, precipitation occurs when the product of [calcium ion][oxalate ion] is above the Ksp by any amount, which may be a minuscule amount that is not obvious from the number of significant figures in the question. Given the large differences between the answer choices, the answer provided is by far the best option.

In accordance with Auguste Comte, what is the most important question to be asked in order to understand and interpret rites of passage? (A) How do rites of passage maintain stability in society? (B) How do rites of passage prompt and facilitate social inequalities within society? (C) How do rites of passage serve to oppress women in society? (D) How do rites of passage change in modern society?

(A) This is correct. Auguste Comte, together with Emile Durkheim and Herbert Spencer, was the founding father of structural-functionalism. Functionalism perceives society as an organic entity. Every element of society has to be understood with regard to the function it serves for the overall construction of society. Functionalism would ask how rites of passage contribute to the stable order of society. It is a macro-sociological approach. WIMI: (D) This is incorrect. Functionalism would assume that changes in rites of passage on a micro level would not really affect their function on a macro level. An example of a theory that would be concerned with changing rites of passage in modern society would be Ulrich Beck's risk society. His theory would observe how secularization and individualization processes affect rites of passage in modern society.

"Time heals all wounds." The pain of the extramarital affair fades over time because the harm done has faded in the victim's memory. The memory of this event is stored in the victim's: (A) episodic memory. (B) semantic memory. (C) multi-store memory. (D) procedural memory.

(A) This is correct. Episodic memory is a dimension of long-term memory. It is involved in storing information about individuals' experiences of events or incidents. The experience of the infidelity episode is stored in the victim's episodic memory. Distractors (B) This is incorrect. Semantic memory is the dimension of long-term memory where general facts of knowledge (ideas, concepts, words, meanings, etc.) are stored. (C) This is incorrect. There is no such thing as multi-store memory. Rather, there is a concept called the multi-store model, which argues that memory is composed of several "stores." Proposed by Richard Atkinson and Richard Shiffrin, this model resembles a flow chart in which information is processed through a linear system from sensory memory to short-term memory to long-term memory. (D) This is incorrect. Procedural memory is the dimension of long-term memory where information or knowledge about how to behaviorally perform tasks and make gestures that may not be easily expressed in words is stored. For example, knowledge about how to ride a bicycle.

Hemoglobin found in humans is composed of four chains that can each bind one oxygen molecule. Given a fully saturated hemoglobin molecule, the sigmoidal shape of the oxygen saturation curve in humans is an indication of which of the following? (A) The first oxygen molecule dissociates from the heme component, while the next three dissociate from the globin component. (B) It becomes easier to lose the second and third oxygen molecules. (C) It becomes more difficult to lose the second and third oxygen molecules. (D) The fourth oxygen molecule dissociates from the heme component, while the previous three dissociate from the globin component.

(B) All four oxygen molecules reversibly bind to iron associated with the heme component of hemoglobin (i.e., answer choices A and D are incorrect). Incidentally, it is the iron in hemoglobin that gives blood its red color. From left to right: cooperative binding means that each oxygen molecule makes the next one easier to bind (increasing the sharpness of the curve). And in reverse, the curve drops suddenly because losing oxygen makes it easier to lose (offload) oxygen. Thus, this process permits oxygen to be uploaded more easily in the lungs, where the partial pressure of oxygen is high, and offloaded more easily in body tissues, where the partial pressure of oxygen is low.

The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), specifies which symptoms help to diagnose people with "Schizophrenia Spectrum and Other Psychotic Disorders." Which of the following would be a negative symptom for this category? (A) Avolition (B) Hallucinations (C) Disorganized speech (D) Catatonic behavior

(A) This is correct. Positive symptoms amount to thoughts, behaviors, emotions, or sensory perceptions that are present in people with mental disorders but are not present in people in the general "normal" population. Negative symptoms are the opposite, in that these represent a loss or impairment of functions, thoughts, behaviors, emotions, or sensory perceptions that are present in people in the general "normal" population. Both negative and positive symptoms can be diagnostic criteria. They differ in that negative symptoms represent something that lacks in the mental disorder group, whereas positive symptoms represent something that is a surplus (additional biopsychosocial function). Avolition amounts to the overall lack of drive to perform activities and pursue objectives. For example, people with this symptom may not have the will to run errands or perform a task, even when those tasks will bring obvious advantages to their lives (e.g., cooking). It is thus a negative symptom, and the only negative symptom listed. WIMI: (D) This is incorrect. Catatonic behavior is a positive symptom. People diagnosed with schizophrenia often show changes in muscle tone or activity to the point of sometimes not moving at all (catatonic stupor) or being physically and excessively aggressive toward the self and others (catatonic excitement). This characteristic is not present in the general "normal" population.

Stigma is: (A) the social rejection of people who are thought to possess some negative attribute due to a held social group membership. (B) the belief that someone who belongs to some specific social group possesses an attribute or characteristic that is generally assigned to the whole group. (C) the process of labeling someone as a deviant "outsider" simply because they do not act like the dominant, more powerful group. (D) the strict set of moral and ethical norms about mandatory behaviors people should exhibit.

(A) This is correct. Stigma amounts to the assignment of one or more negative attributes to a person, simply due to that person's social group memberships, and consequent social exclusion or rejection. This process is thought to have been originally described by Erving Goffman in 1963, who defined stigma as "the situation of the individual who is disqualified from full social acceptance" for a deeply "discrediting attribute." The stigmatized person ends up internalizing his or her failure to conform to the social norm that others have identified as his/her shortcoming. WIMI: (B) This is incorrect. This amounts to the definition of a stereotype. Unlike stigma, stereotypes do not necessarily involve social rejection.

Individuals with damage to the anterior cingulate cortex tend to demonstrate: (A) impulsivity and unchecked aggression (B) inability to send messages to the adrenal gland to produce the hormone "fight or flight" (C) difficulty expressing their beliefs or thoughts verbally (D) challenges with vision and hearing

(A) This is correct. The anterior cingulate cortex is located behind the frontal lobe, is part of the limbic system, and is related to self-regulation, decision making, impulse control, and affect. Those who have damage to the anterior cingulate cortex are more impulsive and aggressive, as well as less able to direct attention to their behavior and regulate it. None of the other options describes functions that have been associated with this lobe.

Which of the following approaches to health is more commonly equated with traditional, unorthodox medicine? (A) Holistic approach (B) Treating diseases (C) Biopsychosocial approach (D) Boosting wellness

(A) This is correct. The term holistic is currently more commonly reserved to describe traditional, indigenous, complementary, alternative, or unorthodox medical approaches to health. This set includes every approach that differs from mainstream medicine, from Chinese medicine and acupuncture, to Shamanism, homeopathy, Shiatsu, art therapy, prayer, and etc. WIMI: (B) This is incorrect. Currently, modern, orthodox, scientific, or evidence-base medicine defines health as both the absence of disease and a state of well-being. Thus, it remains interested in the treatment of disease. It simply broadened its scope to embrace the maintenance and enhancement of population's well-being.

Amino acids can be divided into the following four general categories based on their acid-base charge properties at intracellular pH (~6-7): Positively charged Negatively charged Hydrophobic Hydrophilic Consider the following amino acids. I.Phe II.Thr III.Lys IV.Asp Which of the following classification series best represents amino acids I, II, III, and IV, respectively? (A) Hydrophobic, hydrophilic, positively charged, negatively charged (B) Hydrophobic, positively charged, hydrophilic, negatively charged (C) Hydrophilic, negatively charged, hydrophobic, positively charged (D) Positively charged, negatively charged, hydrophilic, hydrophobic

(A) This question can be answered efficiently with some strategy and some basic info about amino acids, which is definitely presumed knowledge. Amino acid I. (phenylalanine = F) has the side group C6H5- which is the benzene ring which is neither ionic nor polar and is thus clearly hydrophobic. Amino acid II. (threonine = T) has the side group -OH which is certainly polar and thus hydrophilic. Therefore, without going any further, the answer must be A. For interest, we note that amino acid III. (lysine = K) has the amino side group which is protonated at neutral pH (= positively charged = 'basic' amino acid). Amino acid IV. (aspartic acid = D) has the carboxylic acid side group which loses a proton at neutral pH (= negatively charged = 'acid' amino acid).

A mutation in the gene that codes for acetylcholinesterase would likely inhibit all, but which of the following processes? (A) A hyperpolarization in the postsynaptic membrane (B) A depolarization in the postsynaptic membrane (C) The passage of a series of nerve impulses along the axon of the postsynaptic membrane (D) The development of an inhibitory postsynaptic potential

(B) Acetylcholine (ACh) can depolarize the postsynaptic membrane (P2). Acetylcholinesterase terminates the action of ACh. Thus, if acetylcholinesterase no longer had its normal activity (i.e., because of a mutation), then ACh could continue to depolarize the postsynaptic membrane uninhibited.

HPLC with a polar stationary phase and a nonpolar mobile phase was used to separate 4R and its metabolites. Based on the data in Figure 3 and Table 1 (showing that M10 has the longest retention time and M1 has the shortest retention time), which of the following statements describes the metabolites most accurately? (A) M1 is the most polar metabolite, and M10 is the least polar. (B) M10 is the most polar metabolite, and M1 is the least polar. (C) The dihydroxylated metabolites are more polar than the monohydroxylated metabolites. (D) There is no interconversion between di- and mono-hydroxylated metabolites.

(B) In normal-phase HPLC, which has a polar stationary phase and a nonpolar mobile phase, the least polar compounds elute first, whereas the most polar compounds elute last. Table 1 shows that metabolite M1 was eluted first and M10 was eluted last; therefore, M1 is the least polar and M10 is the most polar 4R metabolite. Similarly, the dihydroxylated metabolites were eluted before the monohydroxylated ones; therefore, they are less polar. For answer choice D, Figure 3 shows that the abundance of some of the monohydroxylated metabolites decreased over time, whereas the levels of some dihydroxylated metabolites increased over time. This suggests that they could be hydroxylated further into dihydroxylated forms, although the data do not provide direct evidence for this. Nevertheless, the data presented cannot confirm that there is no conversion, so answer choice D is incorrect.

Radio-labeled ligands represent a sensitive method for probing receptor binding. The interaction between norepinephrine and the adrenergic receptors is to be examined. Which of the following sites would be ideal for tritium (3H) labeling? (A) 2' -OH hydrogen on benzene ring (B) 3' hydrogen on benzene ring (C) Chiral carbon -OH hydrogen (D) Amino group hydrogen

(B) On the Surface: If you put the radiolabel 3H somewhere that can be exchanged (removed and replaced by normal hydrogen, H) then you won't be following the norepinephrine any more (instead you will be following the molecule that accepted the tritium). Of course, in biological systems, the solvent is water. Water can protonate and it can deprotonate. BUT, water cannot remove a proton from the very strong C-H bond. Thus answer choice B is correct. Going Deeper: The lone pair of electrons on N and O make it possible to accept a proton and once protonated, a proton can be released which means that if those atoms are tritiated, they may lose the radiolabel. Carbon has no lone pair and the C-H bond is very strong which makes labeling of the carbon a very reliable way to follow the activity of the ligand under examination.

The (anabolic) pathway in Figure 1 occurs spontaneously: (A) as written (B) only if coupled with a sufficiently exergonic reaction or series of reactions (C) only if coupled with a sufficiently endergonic reaction or series of reactions (D) in conditions that cannot be determined with the information provided

(B) The biosynthetic pathway is anabolic: subunits are used to build more complex molecules. Building requires energy and thus without energy cannot proceed. Figure 1 must be coupled with reactions that release sufficient energy to drive the synthesis of lanosterol. The release of free energy (Gibbs free energy) is signified by a negative change in Gibbs free energy, termed an exergonic reaction. Of course, an endergonic reaction requires free energy to occur (e.g., Figure 1) and has a positive Gibbs free energy. Adding the ∆G values of the endergonic and exergonic reactions must give a negative ∆G in order for the reaction to be spontaneous.

X-VUR has been shown to go through a multi-step activation cycle with multiple intermediate conformations. In one conformation, the glutamate in bound ANLEQ becomes protonated, even at physiological pH. What is a possible explanation for this occurrence? (A) The experiment is always conducted in a highly acidic buffer. (B) The microenvironment changes, such that the pKa of the glutamate side chain becomes significantly raised. (C) An adjacent residue forms a salt bridge with a glutamate side chain. (D) Conformation changes result in a highly hydrophilic environment.

(B) The microenvironment in which a peptide or residue exists inside a protein can be significantly different than in solution. In this case, changes to the microenvironment, such as increased hydrophobicity or a sudden proximity to another negatively-charged residue can cause an increase in pKa for the glutamate side chain. Thus it could be reasoned that a significant increase in pKa would allow the carboxyl to remain protonated, even at physiological pH. A is incorrect because the question already states that the protonation occurs at physiological pH. C and D are incorrect because such changes would actually decrease the pKa of the carboxyl side group.

At the neuromuscular junction, the receptors on the ACh-activated channels are likely located: (A) on the tubule of the T system. (B) in the sarcolemma. (C) on the muscle surface. (D) in the synaptic cleft.

(B) The synaptic terminal faces the muscle cell (= muscle fiber), and the acetylcholine released must reach receptors on the muscle cell (see paragraph 2 of the passage). These receptors should logically be located on the surface of the muscle cell (= plasma membrane = sarcolemma) with which the neurotransmitter will first come into contact (motor end plate). WIMI: Apparently, muscle surface and sarcolemma are NOT the same exact thing, as the explanation above implies. There are additional layers outside of the sarcolemma that characterize the muscle surface, and the receptors are not found in these outer layers, but in the sarcolemma (sarcolemma = plasma membrane of cell). Hence B is the better answer.

It is mentioned that "people with disabilities and mental illnesses tend to be defined socially in a way that overshadows all other aspects of their personality." This kind of ascription is called: (A) Sick status (B) Master status (C) Master role (D) Sick role

(B) This is correct. A master status is a form of social status that has the power to entirely define and shape a person's identity. This type of status can be negative or positive. Disability can work as a master status in a negative form. WIMI: (A) This is incorrect. Sick status does not exist as a psychological or sociological concept or construct. The difference between role and status is that status refers to a social position, while role means a social behavior. People hold a status but perform a role. Although people may perform the disability role in such way that it becomes ingrained in their personality, the passage referred to other people's views of disabled people; to the way people were "defined socially". Thus, the notion of master status is more appropriate.

Which one of the following is NOT a factor that modernization theory would point to in order to explain poverty and inequalities? (A) Population growth (B) Global power relationships (C) Technology (D) Cultural patterns

(B) This is correct. Global power relationships would not be the main focus of modernization theories. These are more focused on investigating the process of social evolution and the development of societies. Dependency theory, for example, would explain poverty as a result of unequal distribution of power around the world. This theory would look at colonialism and neo-colonialism as a cause of global social inequalities.

Some cultural groups are matrifocal, which means that: (A) a woman can have multiple husbands. (B) a married pregnant mother will move into her mother's home. (C) the authority and power structure are run by women. (D) women are forbidden to marry partners who do not belong to their clan.

(B) This is correct. In matrifocal societies, women hold a pre-eminent place in kinship structures. This can involve having households with people from different generations that are linked by blood to the mother and passing on family's propriety to the women in the family. Matrifocality does not imply that the decision-making and the power is held by women. It simply regulates where and who should cohabit and how the family structure should be organized, being the anchor point a woman. Distractors (A) This is incorrect. This option describes polyandry, which is the practice of one woman having more than one husband. (C) This is incorrect. This option describes matriarchal societies, which refers to societies where the power and authority run in the female line. (D) This is incorrect. This option describes endogamy, which refers to social norms that dictate that in-group members are the only viable marriage partners. However, endogamic societies usually do not apply this norm exclusively to women.

The passage described how religion was sometimes regarded as a taboo. Which of the following is NOT the aim or purpose of a social taboo? (A) To prevent the sacred from being defiled (B) To increase self-awareness and social facilitation (C) To enact systems of social control (D) To prevent ordinary people from performing dangerous actions

(B) This is correct. Taboos are norms about actions that cannot be performed by ordinary people, being either too sacred or too dangerous. Taboos exist in every culture in different forms, acting as (usually ancestral) culturally transmitted social control systems. People are often unaware of the taboo they are abiding by, yet they feel compelled as a social group to avoid acting in certain ways or discussing certain topics. Sigmund Freud explored taboos extensively, principally incest. Both more primitive and more civilized societies avoid incestuous sexual relations. The mere thought of incest normally provokes immediate feelings of revulsion and anger. The violation of this prohibition is commonly censured and severely punished by the whole society. This exemplifies how taboos work socially. WIMI: (A), (C), and (D). These are incorrect. The main aims of taboos are to enact some sort of social control that culminates in individuals' avoidance of dangerous actions and in their respect for sacred values.

Diisopropylfluorophosphate (DFP) acts as an irreversible inhibitor at the active site of acetylcholinesterase. This enzyme deactivates the chemical transmitter, acetylcholine. The main effect of DFP would be to: (A) prevent the passage of nerve impulses along the postsynaptic neuron. (B) prevent the entry of Ca^2+ into the synaptic knob. (C) initiate muscular tetany. (D) generate a very large action potential.

(C) At the neuromuscular junction, a depolarization of the cell due to an action potential causes the opening of Ca2+ channels in the presynaptic terminal. An increase in intracellular calcium leads to the fusion of acetylcholine-filled vesicles to the membrane. Acetylcholine (ACh) diffuses into the synapse, where it binds to receptors on the postsynaptic membrane, leading to the activation of muscle fibers. The enzyme acetylcholinesterase, also present in the junction, terminates the signal by deactivating ACh. The deactivation of the enzyme by DFP will lead to a relative increase in ACh in the synapse, and consequently the ACh signal will be amplified, leading to muscle tetany (= successive activation of a muscle fiber over a short period of time such that the muscle does not have time to recover from an action potential and is in a constant state of activation). Note that an action potential is referred to as an "all-or-none" phenomenon; once the minimal threshold has been reached for a particular cell, the action potential has a characteristic magnitude and duration, which cannot be altered by an increase in stimulus. Therefore, an increase in ACh binding as a result of DFP deactivation will lead to an increase in frequency of activation of the action potential in the postsynaptic membrane, as opposed to an increase in the magnitude of the action potential (as stated by answer choice D).

Doppler ultrasound is a noninvasive test that can be used to estimate blood flow through vessels by bouncing high-frequency sound waves (ultrasound) off circulating red blood cells (RBCs). A probe can be positioned such that blood in a vessel under investigation may appear to be moving toward or away from the probe. Consider a sound wave emanating from a stationary Doppler ultrasound probe that bounces off RBCs in blood approaching the probe with velocity, v. Assuming the Doppler ultrasound waves are only transmitted through fluid, the original wave relative to the reflected wave has: (A) a higher wavelength but a lower velocity. (B) a lower wavelength and the same velocity. (C) a higher wavelength and the same velocity. (D) a lower wavelength but a higher velocity.

(C) From the equation for the frequency of the sound observed (o) from the frequency of the sound from the source (s = frequency emitted) using the velocity of the sound in that medium, V:fo = fs(V +/- vo)/(V +/- vs) Since the distance between object and observer is decreasing, use vo (velocity of observer) and -vs (velocity of source), and given vo = 0, we get fo = fs(V)/(V - vs) > fs, thus fo > fs (The preceding is true because the term (V)/(V - vs) is necessarily greater than 1 (plug in any real, which means positive, imaginary values), thus fo must be greater than fs.) Therefore, the observed frequency is greater, which means the wavelength is lower from the observer's point of view (from velocity = frequency x wavelength). Thus, the wavelength from the source (= the original wavelength) is higher. As long as the environment (e.g., temperature, fluid) is relatively constant, the velocity of sound wave is constant.

Assuming that two equivalents of the electrophile, X, react with catechol (benzene-1,2-diol), how many tetrasubstituted isomers of catechol [C6H2(OH)2X2]—as compared with trisubstituted isomers of catechol—are possible? (A) Fewer. (B) Same. (C) Twice as many. (D) More than twice as many.

(C) Here are the four tetrasubstituted isomers: 3,4-dihalobenzene-1,2-diol 3,5-dihalobenzene-1,2-diol 3,6-dihalobenzene-1,2-diol 4,5-dihalobenzene-1,2-diol

A longitudinal study followed the workers of a plant until it closed. The study began as soon as the news of the impending closure was announced and finished one year after the closure. Which of the following would affect the least the validity and reliability of the study? (A) Generalizability (B) Selection bias (C) Endowment effect (D) Attrition bias

(C) This is correct. Endowment effect does not amount to a methodological limitation. Instead, it amounts to the hypothesis that people ascribe more value to the things they own than to the things they do not possess. Therefore they would tend to demand more money or assets to sell or give up their possessions than they would be willing to pay to acquire them.

Organic chelating agents have been used to bind calcium ions thereby dissolving calcium oxalate kidney stones. What can be inferred regarding the interaction between the chelating agent and the the calcium ions? (A) The calcium ions bond ionically to the chelating agent. (B) The coordination of calcium ions is the carbon and hydrogen. (C) The binding is via coordinate covalent bonds. (D) The chelating agent must be a strong conjugate acid.

(C) On the Surface: Chelation is the bonding of ions and molecules (= the ligand) to metal ions. Chelation involves two or more separate coordinate covalent bonds between a polydentate (poly = multiple bonded; dent = teeth) ligand and a single central atom (in our case, calcium cations; the ligand bites the metal!). Usually these ligands are organic compounds, and are called chelators (AKA: chelating agents, sequestering agents). Note that the bonds are covalent, not ionic (answer choice A). Since calcium is positively charged (cation), the attraction must be to a negative charge (either a formal negative or partial negative charge as one typically sees for oxygen or nitrogen in organic compounds; thus answer choice B is dubious). And since the charge should be negative, a conjugate base (e.g. Cl-) would be more likely than a strong conjugate acid (e.g. HCl; answer choice D is upside down).

Based on the results of both experiments, four regions of XBR were selected for mutagenesis studies. The goal was to eradicate the relationship between XBR and pyx by creating mutation(s) such that the XBR mutant would no longer be able to regulate pyx expression. Which of the following XBR amino acid sequences, if altered by mutation, presents the most promise for such a study? (A) Ala-Val-Phe-Leu-Ala-Val-Ile (B) Ala-Val-Asn-Leu-Gln-Val-Leu (C) Ala-Ile-Arg-Gly-Lys-Leu-Pro (D) Ala-Asp-Asn-Leu-Pro-Gly-Glu

(C) The answer to this question is based on common electrostatics: opposites attract, like charges repel. This basic idea will come in handy for several questions on the real MCAT, including biochemistry and organic chemistry. Because DNA is negatively charged (due to its phosphate backbone), many of the DNA-binding grooves in proteins tend to be positively charged at physiological pH. Thus residues like arginine, lysine, and histidine are good targets for mutagenesis, as they are more likely to be critical for DNA binding. It should be mentioned that charge is not the only thing that determines the specificity of DNA binding (the shape of the pocket and the overall conformation of the protein are important as well for a variety of reasons, including access), but the presence of positively charged amino acids is common for most DNA-binding pockets. "Essentially, the question is asking which of the 4 sequences presented have the potential to disrupt binding once mutated. In another word, these are sequences of PRE-mutation peptides, and one of these 4 sequences should be able to bind to pyr gene by having positively charged amino acid. When you consider answer choices A, B, and D, none of these contain positively charged amino acids. This is also another clue showing that 3 of the choices are not like the remainder one (which turns out to be the correct choice). Arg and Lys amino acids are positively charged, and when mutated, can potentially disrupt binding to negatively-charged DNA."

It was argued that social media networks have a curating function in creating narrative identities. Posts such as pictures reinforce memories about a particular situation. Memories that are not captured in a timeline tend to fade away more quickly. What is the most likely explanation for these observations? (A) The retrieval of information is highly dependent on the person's psychological of physical state. When there is a mismatch between the emotional or physical states at the moments of memorization and retrieval, recall might fail. (B) The brain can only store a limited amount of information. The memory that has been stored the longest is displaced by new memories when the storage is full. Social media timelines provide the possibility of restoring the event as a fresh memory at the beginning of the chain. (C) Recall is highly dependent on the availability of contextual cues. Social media works as a contextual cue, and as such enhances recall. (D) When the brain is recording information, neurons form patterns of excitatory stimulation and inhibition. Social media posts available in the timeline lead to the formation of inhibition patterns.

(C) This is correct. Context cues are external cues and their availability was found to enhance recall. Being presented with an image of a past event in social media can work as a context cue, and thus facilitate recall. Distractors: (A) This is incorrect. The recall of information can be facilitated or hindered by the matching of a person's psychological or physical state at the moments of encoding and retrieval. Those state-dependent cues can help to recall memories. However, these mechanisms do not explain why it is easier to recall memories that were posted on a social media network. (B) This is incorrect. The displacement theory of memory that was described in the answer has been applied to short-term memory rather than the episodic long-term memory involved in storing social media posts. This theory was popular during the 1930s, 1940s, and 1950s but has now been widely criticized due to lack of empirical evidence. (D) This is incorrect. Neurological consolidation processes can make memories stronger or weaker by creating excitatory stimulation or inhibition patterns, respectively. As such, memories become easier or harder to recall. Social media posts would likely increase the strength of a pattern, i.e., increase its excitatory stimulation pattern, and thereby facilitating recall. They would unlikely create inhibition patterns.

Timothy Leary coined the term "reality tunnel." It describes how every individual's perception of the world is filtered through his or her own experiences and beliefs. Which psychological concept or theory is most closely related to this idea? (A) Talcott Parson's gloss (B) Benjamin Bloom's taxonomy (C) Donald Broadbent's attention model (D) Metacognition

(C) This is correct. Donald Broadbent's outdated attention filter theory is a model in which attention is regarded as a sustained focus of cognitive resources on a task that filters off extraneous stimuli. Only the information that is filtered in or targeted would be further processed, interpreted, recognized, and stored in memory. The remainder would be discarded. This is similar to what is described in the question stem, in that everything that lies outside one's experience is not perceived or registered. WIMI: (A) Gloss is a sociological, rather than a psychological construct. It was used by Talcott Parsons to describe the mind constructs reality, "filtering" information unconsciously due to cultural pressures like language, personal experience, and beliefs. (B) Bloom's taxonomy is a concept named after the American educational psychologist Benjamin Samuel Bloom. It is used to assess whether educational objectives fit into the categories of cognitive, affective, or psychomotor. (D) Metacognition describes how humans are able to observe their own minds at work. Metacognition helps us understand learning processes and evaluate the extent to which a new concept is successfully comprehended and stored.

What is ego depletion theory? (A) tendency to divert one's attention from information that challenges one's beliefs or attitudes (B) internal state of tension or conflict that arises when one's attitude and behavior are not consistent (C) capacity to self-regulate or control oneself when prior energies and resources have been reduced (D) heightened consciousness.

(C) This is correct. Ego depletion refers to the capacity to self-regulate or control oneself when prior energies and resources have been reduced. For example, a study assumed that subjects who could not eat the chocolate had to spend energy refraining from doing so, and those who failed to follow such instruction demonstrated ego depletion. They explained the "infidelity" result by stating that the energy depletion experienced in the experimental condition led to lack of restraint to resist other temptations, such as agreeing to a coffee date or giving out their phone number. WIMI: (A) This is selective attention, not ego depletion. (B) This is cognitive dissonance, not ego depletion. (D) Heightened consciousness does not pertain to ego depletion theory.

Which prior procedures below would best test the facial feedback hypothesis for the emotions of guilt and grief? (A) Subjects are randomly assigned to a control condition, where nothing happens, or to an experimental condition, where they are exposed to videos of diseased people. (B) During pre-screening, research participants are photographed both smiling and frowning. They are then randomized to the condition described in the question stem or to the control condition of describing the room they are in. (C) Research subjects are randomized to a condition in which they are injected with a drug that temporarily paralyzes the muscles involved in facial expressions, and a condition in which they are injected with a placebo drug that does not paralyze any facial expressions. (D) Research subjects are randomized to a condition in which they smell shirts worn by ovulating women, and a condition in which they smell freshly laundered shirts.

(C) This is correct. The facial feedback hypothesis maintains that there is a bidirectional relationship between individuals' emotions and their facial expressions. In other words, people's facial expressions reflect their internal emotional states. However, facial expressions can also trigger emotional states. This bidirectional process is thought to occur simultaneously, in a biofeedback manner, where facial expressions of emotions intensify the subjective experience of emotions, which in turn increase the tendency to facially express it, and so forth, in a continuous loop. In a study wherein an injection that temporarily paralyzed the facial expressions of subjects, the subjects cannot facially express their feelings, and the loop is halter. In an empirical study utilizing this procedure, experimental subjects actually reported less negative states than their counterparts in the control group.

Which of the following is an example of indirect cultural diffusion? (A) A 3-year-old child who attends church for the first time and learns the appropriate behavior in religious places through a mixture of advice from her parents and her own observations of the churchgoers (B) A mother telling her daughter about the rituals that were performed on her wedding day and the daughter deciding to set up her own wedding rituals in a similar way (C) The traditionally Western ritual of the bride and groom exchanging wedding rings becoming more and more popular as a part of Chinese wedding ceremonies (D) The popularity of playing both hockey and baseball in the border region between Canada and the United States

(C) This is correct. The traditionally Western ritual of exchanging wedding rings becoming more and more popular as a part of Chinese wedding ceremonies is an example of indirect cultural diffusion. Cultural diffusion describes how elements from one culture such as practices or objects spread among individuals from a single culture or from different cultures. Direct cultural diffusion usually happens between neighboring countries when there is a lot of contact between the citizens. Indirect diffusion describes the spread of cultural items even if there is no strong personal contact between members of the different cultures. Indirect cultural diffusion is very common and is aided through mass media and Internet use.

In a study that used a voxel-based morphometry of 160 adults, all of whom had no history of psychiatric illnesses, half of them did have a history of childhood maltreatment. What were the findings that were most probably uncovered? (A) There is a correlation between childhood maltreatment and sleep disorders. (B) There is a statistically significant correlation between propriocepters' sensitivity and childhood maltreatment. (C) There is a relationship between childhood maltreatment and reduced hippocampal volumes. (D) There is a relationship between childhood maltreatment and medulla oblongata decay.

(C) This is correct. Voxel-based morphometry is a neuroimaging method for looking at brain anatomy. Therefore a study using this technique would involve the study of the brain. In addition, studies have indicated that early life stress is correlated with reduced hippocampal gray-matter volumes. WIMI: (A) This is incorrect. Although there is a correlation between childhood maltreatment and sleep disorders, voxel-based morphometry is a technique for looking at brain anatomy.

Extracts of the intestinal parasite Ascaris were found to contain irreversible noncompetitive inhibitors of human enzymes. The enzymes were likely: (A) HMG Coa synthetase and lyase. (B) NADH dehydrogenase and carboxypeptisomerase. (C) trypsin and pepsin. (D) hexokinase and vitamin D.

(C) This question is asking "Which of the following enzymes are present in the gastrointestinal tract?" Among the answer choices, carboxypeptidase, trypsin, and pepsin are correct. (Note: In order for a parasite to have gained access to the intestines, it must have passed through the stomach.) WIMI: Thought that trypsin and pepsin would not be found in the intestine and ruled them out. Makes sense that they are tho because parasite would have had to pass through stomach. It also contains irreversible noncompetitive inhibitors for those enzymes, suggesting that it is not affected by them.

Prostaglandins are complex lipid molecules, some of which mediate the sensation of pain. Aspirin, a common pain reliever, likely works by:​ (A) acting like a noncompetitive reversible inhibitor and binding to the active site on the prostaglandin molecule. (B) acting like a competitive inhibitor and binding to a site other than the active site on the prostaglandin molecule. (C) acting like an allosteric inhibitor of the prostaglandin molecule. (D) inhibiting the synthesis of the prostaglandin molecule.

(D) Aspirin is a reversible inhibitor (think about it: your pain will come back after a certain time) that inhibits the synthesis of prostaglandins. This answer is best reached through elimination. Answer choices A, B, and C can be discounted because they describe various types of inhibition of the prostaglandin molecule by aspirin; however, prostaglandins are not enzymes and consequently are unaffected by inhibitors (note the question states that prostaglandins are lipids, but enzymes are proteins).

"Cimetidine (Tagamet) was among the first of the rational drug-design structures, and the process BEGAN BY ASSESSING THE STRUCTURE OF HISTAMINE. Cimetidine is now a popular inexpensive antacid that can reduce the incidence of gastritis, reflux, and peptic ulcer disease." Cimetidine likely functions by: (A) not binding to the histamine receptor and acting as an agonist. (B) not binding to the histamine receptor and acting as an antagonist. (C) binding to the histamine receptor and acting as an agonist. (D) binding to the histamine receptor and acting as an antagonist.

(D) By binding to the histamine receptor, cimetidine prevents histamine from binding, and therefore there is less acid produced by the parietal cells. If cimetidine was an agonist, it would bind to the receptor AND stimulate the production of acid (not good for an antacid medication)! Thus, it is the first designed histamine receptor (H2) antagonist, and hence it inhibits stomach acid production.

Vomiting normally results in the expulsion of gastric contents, but prolonged vomiting may also include the expulsion of contents from the upper small intestine. Consider a person who begins vomiting and then the process becomes prolonged. Prior to the onset of compensatory mechanisms, that person would be expected to have experienced all of the following EXCEPT one. Which one is the EXCEPTION? (A) Metabolic alkalosis (B) Dehydration (C) Metabolic acidosis (D) Respiratory alkalosis

(D) On the Surface: "Respiratory" means that the origin of the problem is the lungs (hyperventilation vs. hypoventilation), which is not consistent with the act of vomiting; thus, D must be the exception. Going Deeper: Vomiting results in a loss of fluids (dehydration, B) and the loss of gastric acid, leaving the body relatively basic (metabolic alkalosis, A). However, prolonged vomiting may lead to the vomiting of intestinal contents including bile and pancreatic juice (which is high in bicarbonate to neutralize acid from the stomach, thus the body loses base). This could lead to metabolic acidosis (C).

A collection of nerve cell bodies in the central nervous system is generally referred to as: (A) nerve. (B) Schwann node. (C) ganglion. (D) nucleus

(D) Only two of the answer choices should seem possible: the ganglion and the nucleus. A ganglion is a cluster of nerve cell bodies in the peripheral nervous system, while a nucleus is a cluster of nerve cell bodies in the central nervous system. Side note: There is no such thing as a 'Schwann node'. Schwann cells are glial cells of the peripheral nervous system which can sometimes wrap around axons of motor and sensory neurons to form the myelin sheath. The gaps between adjacent Schwann cells are called nodes of Ranvier.

What condition of the cladding will ensure that light signals are confined in the core? (A) The cladding must be conducting. (B) The dielectric nature of the cladding. (C) The cladding must have a higher index of refraction than the core. (D) The cladding must have a lower index of refraction than the core.

(D) The answer was always going to be between answer choices C and D for this question - not just because they are saying exactly the opposite statements (which is always a reason for suspicion on the real exam!) - but also because answer choices A and B are not strong options. A dielectric is a medium or substance that transmits electric force without conduction and thus a dielectric is an insulator (even if you were not sure, silica is a form of glass which is an insulator). Paragraph 1 establishes 2 points: 1) we are dealing with dielectric materials and 2) light is confined to the core because of the difference in index of refraction between the 2 layers of silica. On the Surface: By definition, total internal reflection can occur on the condition that 0 < n2 < n1. The external medium with refraction index n2 being the cladding, and the incident medium with refraction index n1 being the core, the result follows. Easy to remember: Light can be retained (e.g. total internal reflection) in the medium with the higher index of refraction (= higher optical density). "I found it easier to think of it in terms of Snell's Law. n1sin(theta1)=n2sin(theta2). At the critical angle, theta2=90, so sin(theta2)=1 and n1sin(theta1)=n2. sin(theta1) is going to be some number between 0 and 1, so n1(number between 0 and 1)=n2, so n1>n2"

An important function of the pentose phosphate pathway is the generation of: (A) NAD+, which is used for glycolysis. (B) NADH for the production of ATP via the electron transport chain. (C) NADP, which is a substrate in amino acid metabolism. (D) NADPH for fatty acid synthesis.

(D) The pentose phosphate pathway (PPP) generates NADPH, which is used for reductive biosynthesis reactions within cells (i.e., fatty acid synthesis and the synthesis of other compounds such as cholesterol and other steroids). PPP is responsible for almost two-thirds of cellular NADPH. PPP does not produce NAD, NADP, or NADH. Going Deeper: You should have a clear "big picture" for each of the biochemistry pathways that are on the AAMC syllabus. Here is the big picture for the pentose phosphate pathway: PPP (aka the phosphogluconate pathway; aka the hexose monophosphate shunt) functions in parallel with glycolysis and generates NADPH and pentoses (= 5-carbon sugars, which include ribose-5-phosphate required for the synthesis of RNA and DNA). There are two distinct phases: 1) the oxidative phase, in which NADPH is generated; and 2) the non-oxidative synthesis of 5-carbon sugars. For most organisms, the pentose phosphate pathway takes place in the cytosol. Note: Although PPP does begin with the oxidation of glucose-6-phosphate, PPP's primary role is anabolic rather than catabolic.

What would be the primary proposal put forth by conflict theory to reduce the social gradient in health? (A) Give more power to the patients (B) Redefine malnutrition in order to fight obesity (C) Give health providers more freedom to adjust to the needs of patients (D) Put hospitals under state control rather than market control

(D) This is correct. Conflict theory is based on the Marxist tradition. It argues that market control of the health system in a country translates into the regulation of the access to healthcare by income and wealth status factors. Conflict theory would advocate for a medical system that provides free access to all citizens. Furthermore, conflict theory argues that institutions (e.g., the health organizations) should be regulated by the state in order to ensure the provision of good service.

As discussed in the passage, many disability studies perceive the disabled body as a cultural construct. This means that those studies believe that: (A) disability is something that bodies display. (B) society and culture can be major facilitators or barriers for people affected by disabilities. (C) even someone with a severe disability could cope better if the culture was adjusted to their needs. (D) disability is not an inevitable result of biology but highly contingent on social and historical processes.

(D) This is correct. Disability studies that perceive the disabled body as a cultural construct usually follow the tradition of social constructionism. This theory of knowledge critically examines people's subjective and shared understandings of the world. It further proposes that these understandings shape that which is known about the world, and the way people relate to it. Hence, without denying the importance of the physical, medical side of disability, these studies would likely suggest that the shared normative assumptions about the "able body" and the "disabled body" would shape the impact of disability on people's daily, worldly life. WIMI: (B) This is incorrect. Disability studies do investigate how society and culture can be major facilitators or barriers for people affected by disabilities. Yet, this is not the most accurate interpretation of the statement provided.

In a study in which 81.9% were female, which of the conclusions below about validity is most important? (A) The study lacks internal validity. (B) The study is highly likely to be subjected to confounding bias. (C) The study is highly likely to be subjected to social desirability bias. (D) The study lacks external validity.

(D) This is correct. External validity is the generalizability of a study. A study has external validity when the findings can be applied to a setting that is different from the one that was originally tested. One criterion for external validity is that the sociodemographic variables of the sample should match the sociodemographic distribution of the general population as closely as possible. In this study the participants were mainly female (81.9%). This sociodemographic distribution of gender does not match the gender distribution of the general population and therefore reduces the generalizability (external validity) of the findings. WIMI: (C) This is incorrect. Social desirability bias describes the phenomenon in which participants answer questions in a way that will be viewed positively by others. Social desirability bias leads to underreporting of "bad" attitudes. Although social desirability bias might have played a role in this study as it was measuring self-reported attitudes, no conclusions can be drawn about the occurrence or strength of this bias from the table.

Ants are eusocial animals that form superorganisms; they live in groups, do not survive when alone over extended periods of time, show division of labor, and have highly specialized skills. How did the sociologist Herbert Spencer understand superorganisms like the ants within human society? (A) He explained that superorganisms, because of their division of labor, would form an evolutionary disadvantage for human societies. (B) He criticized the concept of superorganisms, as it does not apply to the extremely individualistic human society. (C)He used the term to explain how nature influences social structures. (D) He used it to explain how human societies form structures that are not organic but social.

(D) This is correct. Herbert Spencer used the term superorganism to explain how societies evolved in a way that was not similar to an organism. He understood the interaction between humans as essential to forming structures that have their own organizational forms, and which can adapt to changing circumstances. This, for Herbert Spencer, was a way to better understand the division between nature and culture.

Longitudinal data on baby name choices has shown that names that are popular with higher-class parents are subsequently chosen by lower-class parents for their children. Usually when this happens the name goes out of fashion for parents from higher classes. Georg Simmel observed a similar tendency in the fashion industry and described this phenomenon as: (A) social transmission (B) proletarian drift (C) false consciousness (D) trickle-down effect

(D) This is correct. Simmel understood the fashion consumption of lower-class people as an attempt at upward social mobility. Lower-class people adopt the tastes of higher-class people, which in return renders certain products undesirable for the upper classes. This effect is named the trickle-down effect, referring to Thorstein Veblen's theory about markets. He claimed that markets operate by making consumer goods available at a price point that initially only people from higher classes can afford. Lower classes begin to purchase those products when they are produced in larger quantities and are therefore more affordable. WIMI: (B) This is incorrect. Although proletarian drift describes the same process, this term was not used by Simmel to describe what was happening in the fashion industry, namely, the tendency of upscale products to become popular with the lower classes.

A research methodology for analyzing sleep duration and CHD involves listing a set of studies, and summarizing and comparing their results. What is the research methodology that was used? (A) Solomon four-group design (B) Longitudinal cohort design (C) Ethnography (D) Meta-analysis

(D) This is correct. This is correct. Meta-analysis is a quantitative method that employs statistical techniques to synthetize, or summarize the empirical results of multiple independent studies. It involves collecting a set of independent studies that defined similarly and studied the same set of targeted variables. Then, the findings of the multiple studies are compared to one another via some chosen technique (e.g., relative risk, means, and differences). Finally, it may provide a summary result of the strength of the association between the targeted variables. WIMI: (A) Solomon four-group design is an experimental design. It includes two experimental and two control groups. Each of the groups is exposed to different components of the intervention. (B) Longitudinal cohort design involves selecting a group that shares a similar characteristic (e.g., age), and following that group over a period of time to monitor the effect of time on a set of dependent variable(s). (C) Ethnography is a qualitative method often used in anthropology to study a cultural group and its norms, values, and cultural practices by observing the way they live from within, as a participant observer.

Consider the following sequence of reactions: 1) HOOCCOOH <-> HOOCCOO- + H+ 2) HOOCCOO- <-> -OOCCOO- + H+ 3) Ca++ + -OOCCOO-(aq) <-> Ca(OOCCOO)(s) When the body's intake of calcium is low, in order to maintain homeostasis, there is an increased renal absorption of calcium. Based on the information provided, which of the following changes in urine is most consistent with a decrease in calcium intake in a person with kidney stones? (A) Decreased oxalate ions (B) Increased solubility product (C) Decreased pH (D) Increased pH

(D) We learn from the question stem that a decrease in calcium intake is associated with increased renal absorption of calcium, which means there will be less calcium in the urine. Now we just apply Le Chatelier's principle: Beginning with reaction (3), if calcium is low (i.e., being removed), the reaction shifts to the left, producing more oxalate ions; reaction (2) shifts to the left; and then reaction (1) shifts to the left. The net result of the latter two reactions is the net removal of hydrogen ions, which means that the pH increases.

The reaction P + 3Q → R was studied and the data in Table 1 collected. TABLE 1 Exp. [P] in M [Q] in M Initial rate of reaction A 0.30 0.90 5.0 x 10-6 B 0.30 1.80 1.0 x 10-5 C 0.90 0.90 4.5 x 10-5 The rate-determining step in this reaction probably involves: (A) two molecules of P and two molecules of Q. (B) three molecules of P and one molecule of Q. (C) one molecule of P and three molecules of Q. (D) two molecules of P and one molecule of Q.

(D) When [P] is increased by a factor of 3 (Exp A and C, [Q] is constant), the initial rate of reaction is increased by a factor of 9 (= 3^2). Thus, the order of reaction with respect to P is 2. When [Q] is increased by a factor of 2 (Exp A and B, [P] is constant), the initial rate of reaction is also increased by a factor of 2 (= 2^1). Therefore, the order of reaction with respect to Q is 1. The order of reaction with respect to a certain component tells you how many molecules of that component are involved in the rate-determining step of the reaction, which may not be equivalent to the stoichiometric coefficients.

The developing fetus has a blood vessel, 'the ductus arteriosus', which connects the pulmonary artery to the aorta. When a baby is born, the ductus arteriosus closes permanently. Which of the following is the dominant feature found in a newborn whose ductus arteriosus failed to obliterate? (A) Increased O2 partial pressure in systemic arteries (B) Decreased CO2 partial pressure in pulmonary arteries (C) Increased O2 partial pressure in pulmonary arteries (D) Decreased O2 partial pressure in systemic arteries

(D) You can only understand fetal circulation if you understand normal adult circulation. The ductus arteriosus connects the pulmonary artery to the aorta. If the ductus arteriosus remains open, or patent, after birth, some of the deoxygenated blood from the pulmonary artery will flow through the ductus into the aorta, which contains fresh oxygenated blood from the newborn's lungs. Thus, the mixing causes a decrease in oxygen and an increase in carbon dioxide partial pressures in the aorta. The aorta leads the blood into systemic arteries and circulation.

At a given temperature, T in Kelvin, the relationship between the three thermodynamic quantities including the change in Gibbs free energy (ΔG), the change in enthalpy (ΔH), and the change in entropy (ΔS) can be expressed as follows: ΔG = ΔH - TΔS The sublimation of carbon dioxide occurs quickly at room temperature. What might be predicted for the three thermodynamic quantities for the reverse reaction? (A) Only ΔS would be positive. (B) Only ΔS would be negative. (C) Only ΔH would be negative. (D) Only ΔG would be positive.

(D) ΔG = ΔH - TΔS "The sublimation of carbon dioxide occurs quickly at room temperature" hopefully reminds you that solid carbon dioxide ("dry ice") spontaneously (ΔG must be negative by definition) converts to the gaseous state (fog machines in nightclubs, theaters, etc.) because carbon dioxide cannot exist in liquid form at room temperature (reason: no H-bonds, nonpolar molecule, only held together by very weak van der Waals forces).Sublimation means: Solid CO2 + heat -> vapor Entropy (randomness) is clearly increasing (thus, positive ΔS) because we are moving from a structured, ordered solid to randomly moving gas particles. Heat is required, so it is endothermic, meaning ΔH is positive. The question is asking about the reverse reaction, so all three signs are reversed: ΔG is now positive; ΔH is now negative; ΔS is now negative. Going Deeper: Notice that a negative ΔS multiplied by a -T (see the Gibbs free energy equation) creates a positive term that overshadows the effect of the negative ΔH, and thus, ΔG is still positive. Also, please keep in mind that sometimes the MCAT will provide the Gibbs free energy equation, but sometimes it will not.

When glucose monomers are joined together by glycosidic linkages to form a glycogen polymer, the changes in free energy, total energy, and entropy would be consistent with which of the following? (A) +ΔG, -ΔH, -ΔS (B) -ΔG, +ΔH, +ΔS (C) +ΔG, +ΔH, -ΔS (D) +ΔG, +ΔH, +ΔS

At a given temperature, T in kelvin, the relationship between the three thermodynamic quantities, including the change in Gibbs free energy (ΔG), the change in enthalpy (ΔH), and the change in entropy (ΔS) can be expressed as follows: ΔG = ΔH - TΔS Building a molecule (anabolic) requires energy, thus +∆H. Going from more than one molecule (dimer or polymer) to just one molecule (monomer) is more ordered, less entropy, thus -∆S. Keeping in mind that the temperature, T in kelvin is always positive, we get ΔG = ΔH - TΔS = (+) - (+)(-) = (+) + (+) = (+) We cannot be surprised that Gibbs free energy is positive, which suggests that building complex molecules is not a spontaneous reaction. Of course we know these reactions can occur as long as they are coupled with a favorable reaction that gives off even more energy (i.e., the hydrolysis of ATP).

Meissner corpuscles

Cells that belong to the modality of the somatosensory system that processes pressure, vibration, and texture. These cells are NOT responsible for pain perception.