practice MCAT questions and answers

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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).

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