practice MCAT questions and answers

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6/28/20 

THE CORRECT ANSWER IS C.

Dietary fats are stored as triglycerides, which have a glycerol backbone and three fatty acid chains which may or may not be the same (choice C is correct, and choice A is wrong). The inclusion of isoprene units is not relevant to dietary fats (choice B is wrong), and the inclusion of a phosphate group creates a phospholipid used in constructing membranes (choice D is wrong).

6/25/20 

THE CORRECT ANSWER IS B.

Vitamin D is a fat-soluble vitamin and is best absorbed along with some dietary fat; a lack of that consumption could explain this clinical result (choice B is correct). Consuming too little fiber would not have this impact on Vitamin D (choice A is incorrect), nor would taking oral contraceptives, which contain steroid hormones (choice C is incorrect). If the patient were spending more time outdoors, this would increase blood levels of Vitamin D rather than keeping them low (choice D is incorrect).

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6/21/20 

THE CORRECT ANSWER IS C.

Item I is true: total mechanical energy is conserved because the only force acting on the player is gravity, which is a conservative force (choice D can be eliminated). Item II is false: gravity is exerting impulse on the basketball player, causing the player's momentum to decrease over time on the way up (choice B can be eliminated). Item III is true: the displacement points upward and the force of gravity downward, making the work being done by gravity negative (choice A can be eliminated).

6/18/20 

THE CORRECT ANSWER IS C.

For this 2 x 2 type question, choices A and B may be eliminated, as heat is transferred from the ambient surroundings into the system. The final equilibrium will be 100% liquid water at room temperature. The liquid phase is higher in entropy (more random) than the solid phase, so melting the solid will increase the entropy of the system (eliminate choice D). In general, the addition of heat to a system increases molecular motion (rotational and vibrational motion, as well as translational motion), which results in an increase in randomness and higher entropy.

6/14/20 

THE CORRECT ANSWER IS A.

The medulla oblongata is the area of the brain that connects the spinal cord to the rest of the brain; it contains simple control centers for some of the most rudimentary functions necessary for life, including blood pressure, the vomit reflex, and the respiratory centers. The medulla is not involved with the experience of emotion, which is processed in higher brain centers (choice A is correct). In the brain, the limbic system is a collection of structures/areas that work together in processing emotional experiences. The main structure involved in emotion in the limbic system is the amygdala, which serves as the conductor of our emotional experiences (choice B is wrong). The amygdala communicates with the hypothalamus, which controls the physiological aspects of emotion, such as sweating and a racing heart (choice C is wrong), and it also communicates with the prefrontal cortex, located in the frontal lobe, which controls the conscious and behavioral aspects of emotion (choice D is wrong).

6/11/20 

THE CORRECT ANSWER IS A.

According to the James-Lange theory of emotion, our physiological reactions to stimuli precede and give rise to the emotional experience; in other words, first we have a physiological reaction, then we label the situation with an emotion; therefore, the James-Lange theory would suggest that first he experiences physiological arousal (heart races), and then he experiences the emotion (fear; choice A is correct). The Schachter-Singer theory of emotion suggests that cognitive assessment of the situation precedes the experience of emotion (choice B is wrong). The Cannon-Bard theory of emotion suggests that the physiological response and the emotion occur simultaneously (choice C is wrong). No theories of emotion suggest that the emotion is experienced before the physiological arousal (choice D is wrong).

6/7/20 

THE CORRECT ANSWER IS B.

According to Piaget’s theory of cognitive development, the acquisition of object permanence separates the first stage (the sensorimotor stage, which occurs from birth to roughly 1–2 years of age) and the second stage (the preoperational thought stage, which occurs from roughly 2–7 years of age); technically, object permanence marks the end of the sensorimotor stage (choice B is correct). Sensation (and motor movement) marks the sensorimotor stage (the first stage), but sensation is not the developmental milestone before the second stage (choice A is wrong). Concrete operations are a hallmark of the third stage, the concrete operational stage (choice C is wrong). Formal operations are a hallmark of the fourth and final stage, the formal operations stage (choice D is wrong).

6/4/20 

THE CORRECT ANSWER IS D.

The availability heuristic is a tendency to make judgments based on how readily available information is in our memories. If information is readily available in our memory (like repeated reports of accidents on a specific highway), we may think something (like getting into an accident) is more common than it actually is. The man in question misinterprets the likelihood of being involved in an accident due to the availability of recent information (choice D is correct). Avoidance learning requires someone to first experience a negative outcome of a behavior in order to modify that behavior; since the question stem does not indicate that the man has had an accident on that highway in the past, avoidance learning does not explain his decision (choice A is wrong). Intuition involves understanding without conscious reasoning; since the question stem indicates that conscious thought was put into his decision, intuition is not a logical explanation (choice B is wrong). Functional fixedness is the tendency to perceive the functions of an object as fixed and unchanging, which makes it more difficult to think of different ways to use an object in solving a problem; functional fixedness does not explain the man's decision (choice C is wrong).

5/31/20 

THE CORRECT ANSWER IS B.

This is a 2 × 2 question. Organisms that thrive in extreme cold are called psychrophiles, whereas organisms that thrive in extreme heat are called thermophiles (choices A and C are wrong). Organisms that generate energy by oxidizing organic or inorganic compounds are chemotrophs, and if these organisms can produce their own carbon compounds, they are autotrophs (choice B is correct, and choice D is wrong). 

5/28/20 

THE CORRECT ANSWER IS A.

The fundamental attribution error is the error people make when they over-attribute a person’s behavior to internal factors (e.g., personality, etc.) while disregarding the impact of external factors, such as the impact of the stressful situation, on a person’s behavior. Giving a speech is a situation that typically elicits anxiety in people regardless of their disposition. Failure to acknowledge this reality when judging someone is an example of the fundamental attribution error (choice A is correct). Social facilitation occurs when individuals perform certain behaviors better in front of an audience; this does not apply to the situation described, as the classmate appears nervous, and there is no indication that his performance is improved (choice B is wrong). The actor/observer bias occurs when we attribute our own actions to situational constraints as opposed to dispositional ones; this does not apply to our conclusions about others (choice C is wrong). The optimism bias occurs when we believe bad things happen to others but not to us; there is no such thing as the pessimism bias (choice D is wrong). 

5/24/20 

THE CORRECT ANSWER IS C.

If the portion of the anterior pituitary that produces LH is destroyed, then LH levels will not surge during the menstrual cycle and ovulation would not occur (choice C is correct, and choices B and D are wrong). In the absence of ovulation, the corpus luteum would not develop either, although if FSH is unaffected, the follicle would most likely develop and release estrogen. Regardless, the menstrual cycle would be affected (choice A is wrong). 

5/21/20 

THE CORRECT ANSWER IS C.

The primary difference between prokaryotes and eukaryotes is that prokaryotes have no membrane-bound organelles, which means all cellular processes occur in the cytosol. Ribosomes are organelles, but they are not membrane-bound and are thus present in prokaryotes (choice C is correct). The nucleus, mitochondria, and Golgi apparatus are all membrane-bound organelles, which are only present in eukaryotes (choices A, B, and D are wrong).

5/17/20 

THE CORRECT ANSWER IS D.

People are social organisms, but this is not a tenet of reciprocal determinism (choice D is false and is the correct answer choice). On the other hand, reciprocal determinism does states that people choose their environments (choice A is true and can be eliminated); individual personality influences how people respond to their environments (choice B is true and can be eliminated); and individual personality influences how people respond to various situations (choice C is true and can be eliminated). 

5/14/20 

THE CORRECT ANSWER IS A.

Vapor pressure is dependent solely on the intermolecular forces a compound has and its temperature (choice A is correct). The amount of surface area has no impact (eliminate choices B and C), and while external pressure affects the boiling point, it does not affect the vapor pressure of a liquid (eliminate choice D).

5/10/20 

THE CORRECT ANSWER IS D.

Solid phases involve very limited mobility of molecules, and they are often very orderly arrangements of molecules into crystal lattices. When compared to the comparatively greater mobility available to molecules in the liquid and gas phases, the freezing and ordering of molecules results in low values of entropy. Choices A and B can be eliminated, as nonpolar molecules are capable of forming solid phases, as are non-ionic materials. Choice C can be eliminated with the knowledge that many solids sublimate directly to the gas phase with increasing temperatures, particularly at low pressures.

5/7/20 

THE CORRECT ANSWER IS A.

Gases behave most ideally at high T and low P (eliminate choices B and D). Ideal gases do not experience forces of attraction between molecules; thus gases with weaker intermolecular forces are more ideal. CO2 is nonpolar, while H2S is polar and experiences dipole-dipole interactions. Thus, CO2 behaves more ideally (eliminate choice C; choice A is correct).

5/3/20 

THE CORRECT ANSWER IS D.

Negative punishment occurs when something desirable (recess) is “removed" (in this case, this child loses the desirable privilege for the day) in order to reduce a behavior (choice D is correct). Positive reinforcement is the addition or application of something desirable in order to increase a behavior; for example, if students who behaved well in class all received 20 extra minutes of recess time, this would be an example of positive reinforcement (choice A is wrong). Negative reinforcement is the removal of something undesirable to increase behavior; for example, if students who behaved well in class did not have to take the test at the end of the day, this might be an example of negative reinforcement (assuming that the test was undesirable; choice B is wrong). Positive punishment occurs when something undesirable is applied to decrease behavior; for example, if the students who behaved poorly were spanked, this would be an example of positive punishment (choice C is wrong).

4/30/20 

THE CORRECT ANSWER IS B.

The stock is speculative and can rise or fall at any time. Consequently, the buyer is not able to determine when his purchasing actions will be reinforced; therefore, the interval of reinforcement is variable (choices C and D can be eliminated). The buyer also cannot predict how much the stock will rise (or fall). This makes the ratio of reinforcement also variable (choice A can be eliminated). Thus, the correct answer is a variable-interval, variable-ratio schedule of reinforcement (choice B is correct).

4/26/20 

THE CORRECT ANSWER IS D.

Multiple personalities are characteristic of dissociative identity disorder, not schizophrenia (choice D is correct). Schizophrenia does affect approximately 1% of the population in the world (choice A is wrong), and it is characterized by both positive and negative symptoms (choices B and C are wrong).

4/23/20 

THE CORRECT ANSWER IS C.

Token economies involve the use of secondary reinforcers, which are non-intrinsic motivators that can be exchanged for other pleasurable activities or rewards. A primary reinforcer (food, water, sex, etc.) is not considered part of a token economy system (choice C is correct). Each of the other choices describes a secondary reinforcer that is given in exchange for completing a task: coins, stars, and stickers (choices A, B, and D are wrong). 

4/19/20 

THE CORRECT ANSWER IS D.

Parkinson’s disease is associated with a loss of dopaminergic cells in the substantia nigra of the basal ganglia (choice D is correct). While schizophrenia is also associated with the dopaminergic system, the problem is an excess of dopamine production rather than a decrease (choice A is wrong). Alzheimer’s disease is most strongly associated with neurofibrillary tangles and plagues in the brain, not the systematic loss of dopaminergic neurons (choice B is wrong). Depression is most associated with serotonin, not dopamine (choice C is wrong). 

4/16/20 

THE CORRECT ANSWER IS A.

A negative incentive is an external stimulus that helps discourage certain behaviors (choice A involves a stimulus that leads to avoidance and is therefore correct). Drive reduction theory concerns basic physiological needs, such as hunger, thirst, sex, and sleep, all of which motivate the organism to seek something, rather than avoid something, to reduce the imbalance (choice B is wrong). The need for belonging derives from Maslow's hierarchy of needs, which is irrelevant to the question scenario (choice C is wrong). The optimal level of arousal is when one's performance is at its peak, which does not seem relevant to the question scenario (choice D is wrong).

4/12/20 

THE CORRECT ANSWER IS D.

Borderline personality disorder is characterized by profound instability in identity and self-image, often resulting in labile behavior that fluctuates between extremes (choice D is correct). While histrionic personality disorder involves excessive emotionality and attention-seeking, which may resemble the individual's behavior, that pattern is typically stable and consistent, unlike that exhibited in this case (choice A is wrong). Individuals with antisocial personality disorder display a pervasive pattern of callous disregard for the rights and feelings of others and for societal rules. While such individuals are often abusive, their behavior is not characterized by instability, mood swings, or prominent changes in personality (choice B is wrong). People with paranoid personality disorder may be abusive, as they experience intense anger and unjustified feelings of persecution. However, as with the other personality disorders mentioned, their sense of identity and self-image (however inaccurate) is much more stable than would be the case with a borderline personality (choice C is wrong).

4/9/20 

THE CORRECT ANSWER IS C.

This is a 2 × 2 question, which can be attacked based on the number of tails and the type of structure formed by the different lipids. Fatty acids have a single hydrocarbon tail, whereas phospholipids have two hydrocarbon tails (eliminate choices A and B). Because of the structural arrangement of these hydrophobic tails, fatty acids spontaneously form spherical micelles, whereas phospholipids organize into membranes (choice D is wrong; choice C is correct). 

4/5/20 

THE CORRECT ANSWER IS B.

The switch in both directions and permeability that occurs between the descending and ascending limbs of the loop of Henle enhance the ability of the kidney to generate powerful concentration gradients within the medulla. This leads to greater fluid movement out of the collecting duct, and thus urine with an osmolarity that can exceed that of the blood (choice B is correct). The loss of Na+ to the filtrate and the movement of K+ into the blood is determined by aldosterone at the DCT, not the loop of Henle (choice A is wrong). Renin is not produced by the liver (choice C is wrong), and the descending limb is always permeable to water (choice D is wrong). 

4/2/20 

THE CORRECT ANSWER IS D.

In the Milgram experiments, all of the subjects were asked to draw lots (along with a confederate pretending to be a naive subject) in order to determine who would be assigned to the teacher and learner roles. Accordingly, the experiment was designed so that the subjects would believe that they could have just as easily been receiving the shocks as administering them to the “learner” (a confederate). Regardless, the majority of subjects demonstrated a high level of obedience in administering the purported shocks to the “learner” (choice D was not associated with a decrease in obedience and is the correct choice). When the “learner” was moved closer to the “teacher” in the experiment, the “teacher” was less likely to administer the shocks (choice A was associated with a decrease in obedience and can be eliminated). When the experimenter left the room and thus was no longer physically present, the “teacher” was also less likely to administer the shocks (choice B was associated with a decrease in obedience and can be eliminated). When confederates (whom the subjects believed were naive subjects like themselves also acting in the “teacher” role) refused to comply with the experimenter’s instructions to shock the learner, the “teachers” were less likely to do so as well (choice C was associated with a decrease in obedience and can be eliminated). 

3/29/20 

THE CORRECT ANSWER IS B.

According to the self-fulfilling prophecy, a person’s belief(s) about other people or groups will cause the person to behave in a manner that leads to an outcome consistent with his/her beliefs. Therefore, if the teacher believes that some of his students are gifted and some are normal, the self-fulfilling prophecy predicts that he will treat his students in a manner that leads to the “gifted” students performing better in the class, thereby confirming his initial belief (choice B is correct). If the non-gifted students earn higher grades, this is an outcome that serves as the polar opposite to the outcome predicted by the self-fulfilling prophecy (choice A is wrong). If students earn similar grades regardless of status, this outcome is also at odds with the self-fulfilling prophecy (choice C is wrong). Since the teacher has a pre-existing belief and an opportunity to apply it to the targets of his belief, the self-fulfilling prophecy does apply (choice D is wrong).

3/26/20 

THE CORRECT ANSWER IS C.

The pentose phosphate pathway (PPP) produces NADPH, which is used to neutralize the ROS (reactive oxygen species) to which a cell is constantly exposed as part of engaging in ATP production through cellular respiration (choice C is correct). While PPP does produce ribose-5-phosphate for use in nucleotide synthesis, mismatch repair occurs during replication and is not as consistent a need as the need to neutralize ROS (choice A is incorrect). Other pathways besides PPP are the primary producers of glycolytic intermediates (choice B is incorrect). NADPH is used to synthesize fatty acids, not to break them down (choice D is incorrect).

3/22/20 

THE CORRECT ANSWER IS C.

Functionalism postulates that inequality is beneficial to society (choice C is correct). Conflict theory views inequality as detrimental to society (choice A is wrong). Symbolic interactionism takes a more specific approach by viewing individual social interactions as indicative of larger trends (choice B is wrong). Social constructionism examines ways in which social realities are created by groups and individuals, typically on a much smaller scale than functionalism or conflict theory (choice D is wrong).

3/19/20 

THE CORRECT ANSWER IS A.

This question can be resolved more quickly by noticing that the first part of the answer choices is divided in half. The first step is to determine whether personality type or symbolic interpretation is the independent variable. The study described is designed to measure how personality affects symbolic interpretation. Therefore, the independent variable—the variable manipulated by the researcher—is personality type (choices C and D are wrong). The five factor model is a common measure of personality (choice A is correct). Sympathetic arousal and amygdala activation do not define personality type (choice B is wrong). 

3/15/20 

THE CORRECT ANSWER IS C.

The results described in the question are curvilinear in nature. They do not represent a linear relationship and would show up as a bell on a graph. Correlational research does not pick up nonlinear trends (choice C is correct; choices A, B, and D are wrong).

3/12/20 

THE CORRECT ANSWER IS D.

The phenomenological method is a technique used to evaluate the experience of some phenomenon and often obtain more introspective details about an event than is possible with other methods. This method is also usually qualitative, or descriptive, as the question stem suggests (choice D is correct). The correlational method is a quantitative measure of the relationship between two variables (choice A is wrong). The observational method involves observation and minimal interference by the researcher. It would be very difficult to know about subjects’ internal experiences by simply observing them (choice B is wrong). The survey method tends to give general characteristics of an event or experience, since it contains general questions that are tested on numerous individuals. This characteristic would make it difficult to know about subjects’ unique internal experiences. The survey method is also quantitative in most cases, since subjects often provide a numerical assessment of their self-reported beliefs or feelings (choice C is wrong). 

3/8/20 

THE CORRECT ANSWER IS B.

Longitudinal studies are best for exploring how variables develop over time. They involve conducting periodic measurements of the same individuals over many years to see how certain variables change. This is the ideal methodology for exploring the question presented in the stem (choice B is correct). Case studies are best for understanding individuals in a comprehensive way. This would be an ideal methodology for understanding one person’s memory development, but would not allow for generalization to human memory (choice A is wrong). An observational study could meet the criteria, but observational studies do not specifically deal with the development of variables over a long period of time. This study methodology usually involves observing events in a naturalistic setting, and although this could be done over time intervals, this is not usually a feature of observational research (choice C is wrong). Archival studies would be best for exploring how a phenomenon was different many years ago, to use as a comparison with other epochs. However, archival research would not be ideal for understanding how age evolved for groups of individuals, since it is impossible to control for variables with data taken many years ago, and there are often gaps in the data available (choice D is wrong).

3/5/20 

THE CORRECT ANSWER IS A.

Attrition is primarily a threat to internal validity, because there may be some non-trivial reason that subjects are dropping out. This would present a confounding variable, because if the reason for attrition were related to the hypothesis, it could provide an alternative explanation for the results (choice A is correct). Non-representative samples are a threat to external, not internal validity (choice B is wrong). Confounding variables are a threat to internal, not external validity (choice C is wrong). It is less likely that enough subjects drop out to threaten the external validity of the study. Also, if participants began to drop out, internal validity would be threatened first, such that it would be difficult to draw a conclusion that would then be applied to the external population (choice D is wrong). 

3/1/20 

THE CORRECT ANSWER IS C.

External validity is an issue in ethnographic studies, mainly because the methodology involves deep exploration of a single culture or subculture, so it provides limited information on how the results might apply to other cultures (choice C is correct). Cultural validity is not a type of validity checked for by researchers (choice A is wrong). Experimental conditions in ethnographic research are usually very close to the real world, since the researcher makes every attempt to not disrupt the environment. The goal of ethnographic research is to observe the culture in a naturalistic setting (choice B is wrong). Ethnographic researchers do not usually use surveys, but deep analysis, in their evaluations of the cultures they study, so construct validity is very unlikely to be a consideration. Construct validity most usually applies to psychometric instruments such as surveys (choice D is wrong). 

2/27/20 

THE CORRECT ANSWER IS A.

This question can be completed more quickly with the observation that the first part of the answer choices divides the set of choices in half. The first step is to determine if the situation described in the question stem is a threat to internal or external validity. The recruitment method is problematic because the experiment will not sample individuals who have different schedules and are not available at that time. A sample that is not representative of the population is a threat to external validity, not internal validity (choices B and D are wrong). Selection criteria are the processes used to select participants for an experiment. This describes the scheduling issue presented in the question stem (choice A is correct). A lack of control group is a threat to internal validity, since this attribute is related to how well-designed the study is and to what extent researchers can draw conclusions based on findings (choice C is wrong). 

2/23/20 

THE CORRECT ANSWER IS B.

In the scenario, the representative asks for a large amount of money first (with the expectation of being turned down, or having a proverbial door slammed in his face), followed by a smaller request, that is more likely to be accepted because it seems so much less ridiculous than the large request. The door-in-the-face technique begins with a large request that is likely to be turned down, followed by a smaller request that is likely to be accepted (choice B is correct). The foot-in-the-door technique involves making a small request first, followed by a more substantial request (choice A is wrong). Justification of effort occurs when people modify their attitude to match the amount of behavior they are putting forth (choice C is wrong). Role-playing occurs when people are asked to behave in a certain way, and that role begins to influence their attitudes (choice D is wrong). 

2/20/20 

THE CORRECT ANSWER IS B.

According to Piaget’s theory of cognitive development, the acquisition of object permanence separates the first stage (the sensorimotor stage, which occurs from birth to roughly 1–2 years of age) and the second stage (the preoperational thought stage, which occurs from roughly 2–7 years of age); technically, object permanence marks the end of the sensorimotor stage (choice B is correct). Sensation (and motor movement) marks the sensorimotor stage (the first stage), but sensation is not the developmental milestone before the second stage (choice A is wrong). Concrete operations are a hallmark of the third stage, the concrete operational stage (choice C is wrong). Formal operations are a hallmark of the fourth and final stage, the formal operations stage (choice D is wrong). 

2/15/20 

THE CORRECT ANSWER IS B.

Alternative splicing is the process by which different exons are included in or excluded from the final mRNA (choice A directly leads to unique mRNAs and variable proteins and can be eliminated). Exon shuffling connects exons from different genes and occurs via recombination or transposons (choice C can lead to variable mRNAs and proteins and can be eliminated). Nesting of genes occurs when the exons of one gene lie entirely within an intron of a separate gene. The spliced out intron has the proper start and stop signal for translation, but of course translates a different protein (choice D can lead to variable mRNAs and proteins and can be eliminated). However, interruption is the phenomenon by which introns separate exons on the mRNA strand; this is the typical situation, and it is not implicated directly in the generation of variable protein products (choice B is not a variability process and is the correct answer choice). 

2/13/20 

THE CORRECT ANSWER IS D.

Since Item III appears in exactly two of the answer choices, start by analyzing it. Regardless of whether it is true or false, you’ll be able to eliminate half the answer choices. Item III is true: bile is derived by the liver from cholesterol (choices A and B can be eliminated). Since both remaining answer choices include Item II, it must be true and you can focus on Item I. Item I is true: vitamin D is produced in the skin photochemically from cholesterol, then activated by the liver and kidney (choice C can be eliminated, and choice D is correct). Note that Item II is in fact true: all steroid hormones are derived from cholesterol. 

2/9/20 

THE CORRECT ANSWER IS D.

Rigor mortis is caused by the muscles remaining in a partially contracted state, due to the lack of ATP. During sliding filament contraction, the presence of ATP is required for the myosin head groups to release actin (choice D is correct). Although ATP is necessary for the process of muscle contraction, its presence does not directly drive the power stroke (choice C is wrong). Decomposition would result in the softening of muscle tissue as it begins to break down (choice B is wrong). Although the body does become cold in the absence of thermoregulation, temperature is not the primary factor determining mobility of the tissues (choice A is wrong), with the exception of complete freezing.

2/6/20 

THE CORRECT ANSWER IS D.

This is a 2 × 2 question since you first need to decide if testosterone levels will increase or decrease. When an anabolic androgenic steroid (AAS) mimics testosterone, the naturally produced testosterone level decreases (choices A and B are wrong). This is due to negative feedback; the presence of the AAS causes the hypothalamus to release less gonadotropin releasing hormone (GnRH), which in turn causes the anterior pituitary to release less luteinizing hormone (LH) and follicle stimulating hormone (FSH). Since LH typically stimulates testosterone production, the reduced levels of LH lead to a decreased production of testosterone (choice D is correct, and choice C is wrong).

2/2/20 

THE CORRECT ANSWER IS A.

Since all of the items appear exactly twice in the answer choices, it doesn’t matter which one you start with. Item I is true: without aldosterone, much of the necessary Na+ reabsorption from the distal convoluted tubule will not take place, and it would be difficult to maintain a systemic rise in blood pressure; ADH will not be subsequently triggered. Thus, these patients do suffer from hypotension (choices B and D can be eliminated). Since Item II is not in either of the remaining answer choices, it must be false, and you can focus on Item III. Item III is false: hematocrit is the percentage of whole blood made up of red blood cells. Aldosterone has no effect on red blood cell production (choice C can be eliminated, and choice A is correct). Note that Item II is in fact false: if Na+ is not being reabsorbed, urine osmolarity would be higher, not lower.

1/30/20 

THE CORRECT ANSWER IS D.

A decrease in serum potassium concentration would increase the potassium gradient, causing more potassium to leave neurons. This would result in their hyperpolarization and inhibition, along with a general reduction of all neurally-mediated reflexes and functions in the body, including bowel activity; the decrease in bowel activity would lead to constipation (choice D is correct). However, this is not immediately obvious, and the best way to tackle this question is to use POE. The absolute refractory period is a product of the inactivation of the voltage-gated sodium channels and the repolarization of the cell; if anything, due to the increased potassium efflux, the cell would repolarize faster and the absolute refractory period would be shorter (choice A can be eliminated). The threshold potential is a function of the voltage-gated channels and does not depend on ion concentration (choice B can be eliminated). Hyperreflexia would be expected with neuron depolarization or a decrease in threshold potential (choice C can be eliminated). Patients with hypokalemia generally experience hyporeflexia.

1/26/20 

THE CORRECT ANSWER IS C.

Actions potentials with rapid depolarization are found in the atrial and ventricular myocardial cells (choices A and B are wrong). Slow action potentials (slow depolarization, slow repolarization, no plateau phase) are found in the autorhythmic cells of the SA and AV nodes only (choice D is wrong, and choice C is correct).

1/24/20 

THE CORRECT ANSWER IS C.

Histones are the proteins around which DNA is wrapped (choice C is correct). Nucleosomes are formed when multiple DNA-wrapped histones are bundled together (choice A is wrong). The endosome is a membrane-bound compartment of the eukaryotic cell responsible for transport of materials from the plasma membrane to the lysosome (choice B is wrong). The centrosome is an organelle that is responsible for organizing microtubules during cell divi- sion (choice D is wrong).

1/16/20 

THE CORRECT ANSWER IS B.

Genetic drift is the idea that over time, some alleles become more frequent than others due to random events (choice B is correct). Natural selection is a similar idea, but the alleles do not randomly become more or less frequent. Their frequency is determined by the phenotypic advantage or disadvantage displayed in the individual organism (choice C is wrong). The founder effect describes the idea that if a small population of a species becomes isolated from the rest of the species, their allelic frequency will predominate in future generations (choice A is wrong). Adaptations are structures or behaviors that enhance a specific function, causing organisms to become better at surviving and reproducing. They are produced by a combination of the continuous production of small, random changes in traits, followed by natural selection of the variants best-suited for their environment (choice D is wrong).

1/12/20 

THE CORRECT ANSWER IS C.

In the lysogenic cycle of bacteriophages, the genomic DNA of one bacterium can be transferred to another bacterium through a viral vector in a process called transduction (choice C is correct). Conjugation is the transfer of genomic material between bacteria via a physical bridge (choice A is wrong). Transfection and transformation are the process of incorporating DNA from the external environment in eukaryotes and prokaryotes, respectively (choices B and D are wrong).

1/9/20 

THE CORRECT ANSWER IS A.

The endosymbiotic theory describes a potential unicellular origin for both mitochondria and nuclei. If a researcher found that the inner lipid bilayer present in the nucleus possessed a fatty acid profile more similar to bacteria, it would lend support to the theory, as the unicellular organism (which likely possesses similarities to modern prokaryotes) might have been phagocytosed and incorporated into the cell in an earlier organism (choice B is wrong, and choice A is correct). The nuclear envelope contains two lipid bilayers, and given cholesterol is found in nearly all eukaryotic membranes, it would not support the theory proposed here (choices C and D are wrong).

1/5/20 

THE CORRECT ANSWER IS D.

The expression of genes is influenced by how the DNA is packaged in chromosomes and base modifications, such as methylation, can be involved in packaging. Regions that have low or no gene expression usually contain high levels of methylated cytosine bases; for example, cytosine methylation is important in X chromosome inactivation (choice A is true and can be eliminated). Bacteria methylate their genomes at the sequences recognized by restriction enzymes. This prevents binding of the bacterial genome to the active site of the enzyme, preventing digestion (choice B is also true). Methylation can lead to domination, leaving behind a thymine base where there used to be a cytosine; methylated cytosines are therefore particularly prone to mutations (choice C is true, as well). However, methylation of bases interferes with the ability of the DNA to interact with transcription factors; this decreases the rate of transcription in methylated regions (choice D is false and is the correct answer).

1/2/20 

THE CORRECT ANSWER IS D.

Euchromatin represents the least tightly packed sequence of DNA and thus the sequence that is most likely to be transcribed to produce needed cellular products. Given their state of "information readiness," they are least likely to contain confounding or unstable repetitious elements (choice D is correct).

12/22/19 

THE CORRECT ANSWER IS B.

In order to compute the voltage for the overall reaction, the two constitutive half reactions must be summed. The reactions in choices C and D result in negative cell potentials, and can therefore be eliminated. The overall size of the potential for the reaction Pb4+ → Pb2+ is much larger than any of the other reduction potentials. This points to the fact that the best overall equation is going to include this half-reaction in the forward (reducing) direction. Choice B includes the reduction of Pb4+, and in conjunction with the oxidation of Pb(s), has an overall cell potential of +1.82 V. This is far larger than possible for the Sn reaction in choice A.

12/19/19 

THE CORRECT ANSWER IS A.

The inability to encode new memories is called anterograde amnesia (choice A is correct). The inability to recall memories from the past is called retrograde amnesia (choice B is wrong). Proactive interference occurs when previously learned information interferes with the ability to recall information learned later; it does not prevent the encoding of memories but rather refers to the inability to recall them (choice C is wrong). Retroactive interference occurs when newly learned information interferes with the ability to recall previously learned information; it does not prevent the encoding of memories but rather prevents the ability to recall them (choice D is wrong).

12/14/19 

THE CORRECT ANSWER IS C.

A conditioned stimulus is a stimulus that produces a response following learning (choice C is correct). Continuous reinforcement is when a certain behavior is reinforced every time it occurs. Partial reinforcement is when a certain behavior is reinforced at certain times. For instance, there may be a reward attached to the behavior. Continuous and partial reinforcement are based on schedules in operant conditioning, not the stimuli themselves (choices B and D are wrong). A conditioned response is a response that has been learned: in this case, the greeting (choice A is wrong).

12/9/19 

THE CORRECT ANSWER IS B.

Longitudinal studies are best for exploring how variables develop over time. They involve conducting periodic measurements of the same individuals over many years to see how certain variables change. This is the ideal methodology for exploring the question presented in the stem.

12/4/19 

THE CORRECT ANSWER IS D.

Neutralization of a weak acid with a strong base will result in a basic solution, and our indicator should therefore change color at a pH greater than 7. Note that without the specific concentration of acetic acid and the base we begin with, it is not possible to determine the precise final pH upon complete neutralization (adding an equal molar quantity of strong base to the acetic acid).

11/30/19 

THE CORRECT ANSWER IS B.

While calcium does enter the cytoplasm of cardiac muscle cells from both the extracellular space and sarcoplasmic reticulum (SR), the predominate source is the SR (choices A and C can be eliminated). Note that all cardiac muscle cells must function the same way (choice D is wrong).

11/20/19

The correct answer is B.


Item I is true: the lymphatic system is responsible for returning water, dissolved solutes, and protein from the periphery to the blood (choice C can be eliminated). Item II is true: the lymphatic system also carries dietary fat, in the form of chylomicrons, including fat-soluble vitamins (choice A can be eliminated). Item III is false: under normal circumstances, red blood cells cannot exit the circulatory system and would therefore not be transported back to the blood via the lymphatic system (choice D can be eliminated, and choice B is correct).