MCAT Quiz Answers & Explanations

Question #1

Chemical and Physical Foundations of Biological Systems

An object is projected from the ground at an angle of 30^o above the horizontal and returns to the ground 8 seconds later. What is the object’s maximum height?

1. 40 m
2. 80 m
3. 160 m
4. There is not enough information to solve.

The correct answer is B. The time of the entire flight was given, but since we are looking for the maximum height (that is, the y-displacement traveled during each half of the flight), it is useful to remember the fact that, in the absence of air resistance, time up equals time down. This allows us to focus on either the first half of the trip (the way up) or the second half (the way down). Since we are not given the initial launch velocity, it is easier to look at the second half of the journey, where the initial vertical velocity is zero. Calling the positive y-direction downward, we have a_y = g and t = 4 s. We want y and we’re missing v_y, so we use Big 5 #3: y = v_0yt + (1/2)a_yt², we have y = 0 + (1/2)(10 m/s²)(4 s)² = 80 m, or choice B. Alternatively, we would get the same answer by focusing on the way up and using y = v_yt – (1/2)a_yt². Note that the angle does not factor into the answer.

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Question #2

Biological and Biochemical Foundations of Living Systems

All of the following types of bonds are involved in synthesizing double-stranded DNA EXCEPT:

1. β-N-glycosidic linkages.
2. disulfide bridges.
3. phosphodiester bonds.
4. hydrogen bonds.

The correct answer is B. Disulfide bridges are formed as part of post-translational protein modification and are not one of the bonds involved in double-stranded DNA (choice B is wrong and therefore the correct answer). β-N-glycosidic linkages connect the ribose in a nucleotide (or nucleoside) to its aromatic base (choice A is correct and can be eliminated), phosphodiester bonds connect nucleotides (choice C is correct and can be eliminated), and hydrogen bonds connect the aromatic bases to create the double-stranded property of the DNA molecule (choice D is correct and can be eliminated).

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Question #3

Psychological, Social, and Biological Foundations of Behavior

According to the elaboration likelihood model, which of the following does NOT predict whether a message will be persuasive?

1. The length of the message
2. The attractiveness of the person delivering the message
3. The truthfulness of the message
4. The trustworthiness of the person delivering the message

The correct answer is C. According to the elaboration likelihood model, the truthfulness of the message itself is not actually a characteristic used to determine whether a message will be persuasive (choice C is correct). The message characteristics (including length) do predict persuasiveness (choice A is wrong), as do the source characteristics (including the attractiveness and the trustworthiness of the person delivering the message; choices B and D are wrong).

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Question #4

Chemical and Physical Foundations of Biological Systems

Which of the following best characterizes the differences between fatty acids and phospholipids?

1. Fatty acids have two tails and form micelles; phospholipids have one tail and form membranes.
2. Fatty acids have two tails and form membranes; phospholipids have two tails and form micelles.
3. Fatty acids have one tail and form micelles; phospholipids have two tails and form membranes.
4. Fatty acids have one tail and form membranes; phospholipids have two tails and form micelles.

The correct answer is C. This is a 2 x 2 question, which can be attacked based on the number of tails and by 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).

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Question #5

Psychological, Social, and Biological Foundations of Behavior

Cooley’s looking-glass self states that a person’s sense of self is the result of the perception of others. The sociological theory that best captures this idea is:

1. conflict theory.
2. labeling theory.
3. symbolic interaction theory.
4. functionalist theory.

The correct answer is C. Symbolic interactionism argues that meaning is a social product derived from interaction. The foundation of this theory rests in the work of George Herbert Mead. Mead’s belief was that people’s selves are derived, in part, from social interaction. The symbolic interaction theory serves as a framework for the looking-glass self (choice C is correct). The remaining fundamental sociological theories, conflict theory and structural functionalism, are concerned with power and social stability, respectively, which are not concepts related to Cooley’s looking-glass self (choices A and D are wrong). Labeling theory is concerned with the influence of terms attributed to individuals. This theory is closely related to symbolical interactionism; however, its primary use is in relation to deviance (choice B is wrong).

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Question #6

Biological and Biochemical Foundations of Living Systems

Which of the following organisms would be forced to undergo fermentation in the presence of a toxin that blocks oxidative phosphorylation in mitochondria?

1. Escherichia coli, a facultative anaerobic bacterium
2. Saccharomyces cerevisiae, a facultative anaerobic yeast
3. Propionibacterium acnes, an obligate anaerobic bacterium
4. Mycobacterium tuberculosis, an obligate aerobic bacterium

The correct answer is B. Facultative anaerobes are capable of both aerobic and anaerobic respiration. However, only eukaryotic cells have mitochondria, so a toxin that targets mitochondria should have no effect on prokaryotes (choices A, C, and D are). Yeast are eukaryotic, and would be sensitive to a mitochondrial toxin (choice B is correct).

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Question #7

Psychological, Social, and Biological Foundations of Behavior

Researchers want to explore the experience of subjects as they engage in the Stroop task, a task in selective attention that measures the ability to distinguish between discordant stimuli. The researchers are not merely interested in response time but want to know qualitative details about the subjects’ internal experiences. Which of the following methodologies should the researchers implement?

1. Correlational method
2. Observational method
3. Survey method
4. Phenomenological method

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).

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Question #8

Chemical and Physical Foundations of Biological Systems

Compound J reacts with Compound K at 20^oC to form a mixture of two products, L (20%) and M (80%). When the reaction is performed at 60^oC, Compounds L and M are formed in 80% and 20% yields, respectively. When the reaction mixture obtained at 20^oC is heated to 60^oC and allowed to stand overnight, the composition of the mixture slowly changes to 80% L/20% M and remains invariant at longer reaction times. Which of the following statements is most consistent with the information given above?

1. An equilibrium mixture of L and M is obtained at 60^oC.
2. The activation energy for formation of L is lower than that for M.
3. M is more stable than L.
4. L is formed faster than M.

The correct answer is A. The observation that the composition of the reaction mixture remains constant at 80% L/20% M when the reaction mixture is maintained at 60^oC over a long period of time indicates that this product ratio represents the equilibrium product composition at that temperature (choice A is correct), thereby demonstrating that L is more stable than M (choice C is wrong). The fact that M is the major product when the reaction of K with L is performed at 20^oC suggests that the activation energy for formation of M is lower than that for L, thus M is formed faster than L (choices B and D are wrong).

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Question #9

Biological and Biochemical Foundations of Living Systems

Which of the following would best describe a scenario involving directional selection?

1. Turtles living on an island become physically separated into two groups when a tropical storm divides the habitat and eventually they are no longer able to mate.
2. Breeding creates dogs that produce little to no dander and thus are hypoallergenic for pet owners with allergies.
3. The ability to collect a wide variety of food is valued by a certain type of monkey, and females who exhibit this skill are able to attract more sexual partners.
4. Field mice that are able to escape into small spaces are less likely to be consumed by predators and thus larger mice are selected against over time.

The correct answer is D. When natural selection removes those exhibiting the extremes of a trait, then the average of that trait will shift over time, creating directional selection. Choice D describes just such a situation and is the correct answer. Choice A describes the force of allopatric isolation as a trigger for speciation and can be eliminated. Choice B describes artificial selection, and choice C describes sexual selection; thus both can be eliminated.

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Question #10

Biological and Biochemical Foundations of Living Systems

Bisphosphonates are a class of medications that function to inhibit bone resorption. They are frequently used by physicians to prevent or reduce the bone loss that occurs during osteoporosis. Which of the following is a potential mechanism of action for bisphosphonates?

1. Increase calcium absorption in the small intestine
2. Trigger apoptosis, or programmed cell death, in osteoclasts
3. Stimulate osteoblasts
4. Prevent renal losses of calcium into the urine

The correct answer is B. The question stem states that bisphosphonates function to “inhibit bone resorption.” By directly targeting the osteoclasts (the predominant cell type involved in bone resorption) for apoptosis, bone loss should be reduced (choice B is correct). Increasing calcium absorption from the intestines and preventing its loss in the urine would increase serum calcium concentrations and potentially improve bone formation. However, promoting bone formation is not equivalent to preventing bone loss, and the question text specifies that bisphosphonates act to inhibit bone resorption (choices A and D are wrong). Similarly, stimulating osteoblasts would target bone formation, not resorption (choice C is wrong).

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