MCAT-TEST MCAT Practice Questions

The bottleneck effect is a type of genetic drift that occurs when a population's size is drastically reduced by a random event, such as a natural disaster. The allele frequencies of the surviving population are determined by chance and may not be representative of the original population. The founder effect is similar but occurs when a small group breaks off to form a new population. Gene flow involves migration, and natural selection involves differential survival based on fitness, not a random event.

Monoamine oxidase (MAO) is an enzyme that breaks down monoamines, including neurotransmitters like norepinephrine, serotonin, and dopamine, as well as dietary amines like tyramine. When MAO is inhibited by an MAOI, ingested tyramine is not metabolized in the gut and liver. It enters the circulation and is taken up by sympathetic nerve terminals, where it displaces large amounts of stored norepinephrine from vesicles. This massive release of norepinephrine causes widespread vasoconstriction and cardiac stimulation, leading to a hypertensive crisis.

This is a key distinction. The somatic nervous system controls voluntary movements by innervating skeletal muscles. The autonomic nervous system regulates involuntary bodily functions by controlling smooth muscle (e.g., in blood vessels, gut), cardiac muscle, and glandular secretions.

Somatic motor neurons are exclusively cholinergic, releasing acetylcholine (ACh) to cause skeletal muscle contraction. In the autonomic system, all preganglionic neurons release ACh. Postganglionic parasympathetic neurons release ACh, while most postganglionic sympathetic neurons release norepinephrine.

At the half-equivalence point of a titration of a weak acid with a strong base, the concentration of the weak acid [HA] is equal to the concentration of its conjugate base [A-]. According to the Henderson-Hasselbalch equation, pH = pKa + log([A-]/[HA]). When [A-] = [HA], the ratio is 1, and log(1) = 0. Therefore, at the half-equivalence point, pH = pKa. So, the pKa of the acid is 4.76. To find the Ka, we use the relationship Ka = 10^-pKa. Ka = 10^-4.76. Since 10^-4.76 is between 10^-4 and 10^-5, and closer to 10^-5, we can estimate it as approximately 1.74 x 10^-5.

Social reproduction refers to the perpetuation of social inequalities, such as social class, across generations. The finding that children of physicians are more likely to become physicians demonstrates that the social standing and advantages of one generation are being passed down to the next, thus reproducing the existing social structure. This happens through the transmission of cultural capital (e.g., knowledge of the medical field) and social capital (e.g., networks).

The electron transport chain consists of four large protein complexes (Complex I, II, III, and IV) embedded in the inner mitochondrial membrane, along with two mobile electron carriers. One of these carriers is Cytochrome c (a small protein), and the other is Coenzyme Q (also called ubiquinone). Coenzyme Q is a small, lipid-soluble molecule, not a protein complex, that shuttles electrons from Complex I and Complex II to Complex III.

This statement is false. The Doppler effect, for both sound and light, is caused by the relative motion between the source and the observer. Light, as an electromagnetic wave, does not require a medium for propagation. Therefore, the motion of a medium is irrelevant to the Doppler effect for light. The shift in frequency (redshift or blueshift) depends only on the relative velocity of the source and observer.

Cooperative binding, characterized by a sigmoidal kinetic curve, is a hallmark of allosteric enzymes that are typically composed of multiple subunits (a multimeric structure). The binding of a substrate molecule to one active site induces a conformational change in the enzyme that is transmitted to the other subunits, altering their affinity for the substrate. This communication between subunits is the basis of cooperativity. A single active site cannot exhibit cooperativity. Non-competitive inhibitors affect Vmax but do not induce the characteristic sigmoidal curve of positive cooperativity. Covalent modification is a form of regulation but is not the direct structural cause of cooperativity itself.

This design directly manipulates the independent variable (stereotype threat activation) and measures its effect on the dependent variable (test performance) while using random assignment to control for confounding variables. This is a classic experimental design to test for stereotype threat.

This design tests stereotype threat by manipulating the context. Describing the test as 'diagnostic' is known to invoke stereotype threat for stereotyped groups, while framing it as a neutral 'problem-solving task' mitigates this threat. Comparing performance between these two randomly assigned groups effectively isolates the effect.

At pH 6.0, aspartic acid (pI=2.8) is well above its pI and will have a net negative charge. Valine (pI=6.0) will have a net charge of zero. Lysine (pI=9.7) is well below its pI and will have a net positive charge. A cation-exchange column contains a negatively charged stationary phase. Therefore, the negatively charged aspartic acid will be repelled and elute first. The neutral valine will have minimal interaction and elute next. The positively charged lysine will bind tightly to the column and elute last, likely requiring a change in buffer pH or salt concentration to be released.