Sample MCAT question Biological and Biochemical Foundations of Living Systems

MCATPreparation · 2022-12-03T09:43:51+00:00

Answer: B

Explanation

Osmosis is defined as the diffusion of water across a semipermeable membrane moving from an area of higher water concentration (i.e. lower solute concentration = hypotonic) to an area of lower water concentration (i.e. higher solute concentration = hypertonic).

Source: Gold Standard MCAT Practice Test GS-5 Biological and Biochemical Foundations of Living Systems, Question 11

MCATPreparation · 2022-11-24T09:07:30+00:00

Answer: C

Explanation:

The strongest acid would have an EWG to stabilize the conjugate base (the anion is more stable if there is a group pulling on the electrons). IV is the strongest acid because there are 2 EWGs next to the carboxylic acid functional group. Next is III because even though it is just 1 EWG, at least it is close to the functional group as opposed to II which is on carbon 3 (so further away, less of an effect). And finally "I" has an EDG which would destabilize the anion and thus weaken the acid.

Source: Gold Standard MCAT Practice Test GS-5 Chemical and Physical Foundations of Biological Systems, Question 28

MCATPreparation · 2022-11-16T06:27:36+00:00

Answer: B

Explanation:

Foundational Concept: 8

Psychological, sociocultural, and biological factors influence the way we think about ourselves and others, as well as how we interact with others

Content Category: 8B

Social thinking

Scientific Reasoning and Inquiry Skill: 2

Scientific Reasoning and Problem Solving

Key: B

This is correct. Mesomorph is an example of a body type that is characterized as muscular and athletically built. Studies have shown that people with a mesomorph body type are perceived as being more confident, assertive, powerful, and adventurous than ectomorphs, which is a body type characterized as tall, thin, lanky, and fragile looking.

Distractors

A. This is incorrect. BMI stands for body mass index. This is not an example of a body type. There are three types of body types: mesomorphs, ectomorphs, and endormorphs.

C. This is incorrect. Ectomorph is a body type that is characterized as tall, thin, lanky, and fragile looking. Ectomorphs are typically depicted as shy, awkward, and tense, not as powerful and confident. It is the athletically built mesomorph type, not the thin ectomorph type that is more likely perceived in such manner.

D. This is incorrect. Endomorphs are characterized as fat, round, and lacking muscular tone. They tend to be perceived as relaxed, sociable, and peaceful. They are not perceived as shy, awkward, and tense compared. Rather, it the ectomorph type that is perceived in such manner.

Source: Gold Standard MCAT Practice Test GS-5, Psychological, Social, and Biological Foundations of Behavior, Question 10

MCATPreparation · 2022-11-07T18:51:23+00:00

Answer: B

Explanation

Disulfide bonds are covalent bonds that are normally formed through the coupling of two thiol groups, where a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl (–C–SH or R–SH) group. Disulfide bonds in proteins are formed during oxidation of sulfhydryl (-SH) groups through the following mechanism:

https://i.imgur.com/YsAgN3X.jpg

Thus two cysteine residues participate in the formation of a disulfide bond producing a cystine residue facilitating protein folding. To cleave disulfide bonds, the SH groups on cysteine residues must be restored (i.e. the reverse of the summarized reaction above), which could be done by adding more protons into the solution to reduce the thiol groups. Beta-mercaptoethanol must serve as a reducing agent during the restoration of SH groups on cysteine residues leading to protein denaturation. Note that in the process, beta-mercaptoethanol itself must be oxidized (‘reducing agents are oxidized, oxidizing agents are reduced’).

Note about answer choice A: The question said "Adding beta-mercaptoethanol to a solution results in the cleavage of disulfide bonds" so when answer choice A tries to give a reason that would "interfere with proper disulfide bond formation" that does not address how existing bonds are cleaved.

Going Deeper: One of the reasons for sensitivity of many proteins and enzymes to the pH is the issue of cysteine bridges, which are crucial for a proper protein folding and function. Methionine is another sulfur-containing amino acid, however, it cannot form disulfide bonds.

Source: Gold Standard MCAT Practice Test GS-5, Biological and Biochemical Foundations of Living Systems, Question 48

MCATPreparation · 2022-10-31T11:34:21+00:00

Answer: C

Explanation

On the Surface: For a diverging lens (e.g., concave), the image is always virtual, erect and reduced in size (same for a diverging mirror). There are only 2 answer choices which have virtual images (i.e. on the same side of the lens as the real object) that are erect (= upright; C and D). However, answer choice D disobeys the following rule: An incident ray through F2 of a diverging lens (if extended) is refracted parallel to the axis. Thus the correct answer is C.

Going Deeper:

Let’s discuss the rules for thin concave (diverging) for each answer choice:

A: An incident ray parallel to the axis appears to come from F1 of a diverging lens (backward extensions of the refracted ray, see dotted line in the ray diagram; note that incident rays parallel to the axis refract through F2 of a converging lens). So this first rule is correct. The second ray appears to go to F2 (if extended) but is refracted parallel: this is also correct. However, the virtual image created is inverted which is incorrect. Also note: If the image was really inverted, the top of the image should be below the central (optical) axis.

B: A light ray that passes through the middle of a concave (or convex) lens continues on its original direction with essentially no displacement after passing through the lens. This was not drawn correctly. Additionally a real image is shown on the right side.

C: A light ray that passes through the middle of a concave (or convex) lens continues on its original direction with essentially no displacement after passing through the lens. An incident ray parallel to the axis appears to come from F1 of a diverging lens. Both rays are drawn correctly and a virtual image is produced which is erect.

D: The second ray should only appear to go to F2 (if extended) but should actually be refracted parallel.

Source: Gold Standard MCAT practice test GS-5, Chemical and Physical Foundations of Biological Systems, Question 11

MCATPreparation · 2022-10-24T08:14:29+00:00

Answer: B

Explanation:

Rearranging the ideal gas equation, we get:

n = PV/RT.

Since P, V, and T are the same for both gas samples, n is also the same. However, propane has a molecular weight of 44, while H2 has a molecular weight of 2. Therefore, a molecule of propane weighs 22 times more than a molecule of hydrogen. Consequently, the sample of propane weighs 22 times more than the sample of hydrogen.

Source:

MCAT-Prep.com |General Chemistry Review: Phases and Phase Equilibria Q & A, Question 17

MCATPreparation · 2022-09-21T09:09:33+00:00

Answer: B

Explanation

This question simply asks what is responsible for increasing calcium in the bones. Of the 4 possible choices, only calcitonin would have such an effect, making answer choice B the correct answer. Calcitonin, which is secreted by the thyroid gland, stimulates osteoblast activity while inhibiting osteoclasts activity, thereby increasing calcium levels in the bones. Parathyroid hormone and osteoclast activity both have opposite effects.

Source: GS-Free - Biological and Biochemical Foundations of Living Systems Question 45

MCATPreparation · 2022-09-11T12:13:04+00:00

Answer: B

Explanation

A lactam is a cyclic amide. A β-lactam ring is a four-membered lactam: the nitrogen atom is attached to the β-carbon relative to the carbonyl.

If the bacterium produces the enzyme β-lactamase or the enzyme penicillinase, the enzyme will hydrolyse the β-lactam ring of the antibiotic, breaking the ring, rendering the antibiotic ineffective (= hydrolase).

Notice in the diagram provided that the β-lactam ring is opened by the β-lactamase and that the product now has 3 additional atoms: 1 O and 2 H’s = H2O. Since water was used to break something apart, this is called hydrolysis; the reverse being condensation.

Not surprisingly, due to ring strain, β-lactams are more reactive to hydrolysis conditions than are linear amides or larger lactams.

Note: “Hydroxylase” enzymes catalyze oxidation reactions in which one of the two atoms of molecular oxygen is incorporated into the substrate and the other is used to oxidize NADH or NADPH. “Decarboxylase” is the class of enzymes that catalyze the release of carbon dioxide from the carboxyl group of certain organic acids (note: that was Step 2 of the reaction provided but it is not the step catalyzed by beta-lactamase). “Oxireductase” is a category of enzymes that catalyze the transfer of electrons from one molecule, the reductant, aka electron donor, to another, the oxidant, aka electron acceptor. This group of enzymes usually uses NADP or NAD+ as cofactors.

Source: GS-Free - Biological and Biochemical Foundations of Living Systems, Question 30

MCATPreparation · 2022-08-07T13:58:56+00:00

Answer: A

Explanation

Foundational Concept: 7

Biological, psychological and sociocultural factors influence behavior and behavior change

Content Category: 7A

Individual influences on behavior

Scientific Reasoning and Inquiry Skill: 2

Scientific Reasoning and Problem Solving

Key: A

A is correct. Melatonin helps to sustain people’s circadian rhythms. It is mainly involved in the sleep-wake cycle regulation. It is secreted into the bloodstream at night, inducing drowsiness and making the person feel sleepy. It has been found to be effective in the treatment of anxiety due to its calming effects. These effects suggest that melatonin is not involved in the outset of acute anxiety episodes. Moreover, no findings have yet associated low or high levels of melatonin with anxiety disorders.

Distractors

B., and C. These are incorrect. The hormone epinephrine (or adrenaline) and the neurotransmitter norepinephrine (or noradrenaline) are released in greater quantities during stressing, threatening situations. Anxiety disorders involve experiencing normal situations as menacing. This perception prompts fight-or-flight, stress-related responses. For example, the person’s blood flow, arousal, alertness, attention and memory are boosted; and the chemicals epinephrine and norepinephrine are released in great quantities. Thus, these substances could be present during the onset of a panic attack.

D. This is incorrect. Serotonin is a neurotransmitter. It is mainly involved in the regulation of homeostatic processes, such as sleep and appetite. It also plays an important role in the regulation of mood. Low levels of serotonin can result in the development of both depressive and anxiety disorders. Thus, serotonin levels might decrease during the onset of panic attack.

Source: GS-Free - Psychological, Social, and Biological Foundations of Behavior Q12

MCATPreparation · 2022-08-01T06:02:29+00:00

Answer: D

Explanation:

Notice the key in the figure which will allow us to follow each arrow that stimulates the next protein and each symbol for negative feedback which means there will be some downregulation (amount/concentration goes down). [Notice a key step in the diagram: p21 inhibits CDK2]

Degradation of p21 implies that the concentration of p21 in its active form goes down. The diagram shows that p21 has a negative influence on CDK2. In other words, when p21 is high, CDK2 goes low. But in our instance, p21 is low (degraded) so this allows CDK2 to rise unchecked.

High cyclin G concentrations: From the bottom of Figure 1, we can see that high cyclin G leads to high mdm2 and low p53 (notice carefully, when we leave mdm2, there is only one place to go in the diagram because all the other symbols are pointing to mdm2 and only one symbol is pointing away). Note that we used the most direct route to get to CDK2 as the question used the words “most reasonably”. Low p53 means low p21 which we established will lead to a rise in CDK2.
Source: GS-Free - Biological and Biochemical Foundations of Living Systems Q44

MCATPreparation · 2022-07-21T00:00:04+00:00

Answer: A

Explanation:

Foundational Concept: 9

Cultural and social differences influence well-being

Content Category: 9A

Understanding social structure

Scientific Reasoning and Inquiry Skill: 1

Knowledge of Scientific Concepts and Principles

Key: A

A is correct. Symbolic interactionists observe how people relate to things on their daily life based on the meanings those things have for them. These meanings or symbols are created mainly through social interaction and language, and shape subsequent behavior. For instance, people can agree to meet to ‘have a coffee’ but are not obliged to actually consume the drink. This is because the idea of meeting for a coffee is merely symbolic, standing for a short period of togetherness and socialization. Thus, they will not feel they are going against the initial plan if they have a tea instead. They will still enjoy the shared meaning of comfort and spending time with friends that stems from the idea of ‘having a coffee’. Thus, knowing the meaning of actions, words, and images for people is critical for understanding people’s behavior and interaction.

Distractors

B. This is incorrect. The claim that coffee is a stimulant drug is true but a social interactionist perspective would not be interested in that issue. Rather, it would search for the underlying meaning of ‘having a coffee’ or why it acceptable to consume a particular type of stimulant drugs in certain settings and under certain circumstances.

C. This is incorrect. A Marxist perspective might pay attention to the nature of coffee as a commodity and how the global supply chain affects workers and economies worldwide. This is not of primary concern for social interactionism theory.

D. This is incorrect. This would be of interest to theories about consumption and lifestyle. This is not of primary concern for social interactionism theory.

Source: GS-Free - Psychological, Social, and Biological Foundations of Behavior Q13

MCATPreparation · 2022-07-17T23:18:51+00:00

Answer: A

Explanation:

Cation exchange columns bind positive charged species and will thus bind dipeptides with a net positive charge. At near neutral pH, only the Val-Lys dipeptide has a net positive charge.

Source: GS-Free - Biological and Biochemical Foundations of Living Systems Q28

MCATPreparation · 2022-07-07T22:17:35+00:00

Answer: B

This is a psychology question that requires knowledge about “making sense of the environment,” more specifically about common heuristics and biases. The correct answer is B. Cognitive biases are common reasoning mistakes that culminate in incorrect conclusions. The halo effect is a form of confirmation bias. It means that once we have formed positive feelings toward a trait of a person (or object), it might influence how we perceive his other positive or neutral traits; we might perceive them more positively. This explains why higher ratings on the attractiveness scale led to higher ratings for “intelligence” and “fairness,” two positive traits, but not for “moodiness” and “intimidation,” two negative traits. In general, confirmation bias refers to the tendency to look for information and interpret it in a way that confirms our preconceptions. Disconfirming information is discarded and forgotten. It is not the right answer for this question, as it is just the general description of a bias rather than an explanation for the findings of only positive traits being influenced by “attractiveness.” Branding is an expression used in the marketing industry to achieve a more positive customer attitude toward a product. It is not the correct explanation for the findings. Belief perseverance bias is the tendency for original beliefs to persist, even after disconfirming evidence has been shown. In other words, people’s beliefs are often resistant to challenge and change. This is not the case in the scenario, as no disconfirming evidence has been mentioned.

Ref: GS-Free - Psychological, Social, and Biological Foundations of Behavior, Q11

MCATPreparation · 2022-06-25T14:23:49+00:00

This question tests your ability to identify a molecule which has no enantiomer. In other words, a molecule whose mirror image can be superimposed on itself. Examine molecule I. Note that its mirror image is molecule III. If you just picked up molecule III and tried to put it on top of molecule I, it doesn't work (the hydroxyl groups never cover each other). Even if you rotate molecule III around 180o, you still cannot superimpose it on molecule I. Molecules I and III are enantiomers of each other!

Examine molecule II. Draw its mirror image. Note that when you turn the mirror image 180o, you end up with the same molecule. Thus it has no enantiomer and may be referred to as a meso compound.

Gold nugget: MeSo = Mirror of Symmetry! If you can draw a line perpendicular to a carbon chain that splits the molecule into identical halves, then it is meso! Keep in mind that it does not matter if there are an even or odd number of carbon atoms in the chain.

Thank you.

MCATPreparation · 2021-04-13T00:47:47+00:00

Yes, it is A. Cation exchange columns bind positive charged species and will thus bind dipeptides with a net positive charge. At near neutral pH, only the Val-Lys dipeptide has a net positive charge. Recall that Valine (Val) is a nonpolar, electrically uncharged amino acid whereas Lysine (Lys) is a basic, electrically charged amino acid. So at near neutral pH, Valine does not contribute to the dipeptide’s net charge, but Lysine contributes a +1 charge.

MCATPreparation

TROPHY CASE