MCAT-TEST Sample Questions & Answers

The continuity equation states that for an incompressible fluid, the product of the cross-sectional area (A) and velocity (v) is constant. As the artery constricts, A decreases, so the velocity (v) must increase. Bernoulli's principle states that for a horizontal pipe, an increase in fluid speed is associated with a decrease in pressure. Therefore, as the blood velocity increases through the stenosis, the lateral pressure it exerts on the artery walls decreases.

Aldosterone's primary functions in the distal convoluted tubule and collecting duct are to increase the reabsorption of sodium (Na+) and water, and to increase the secretion of potassium (K+) and hydrogen ions (H+). Excessive aldosterone would lead to increased Na+ reabsorption (hypernatremia), increased K+ secretion (hypokalemia), and increased H+ secretion (metabolic alkalosis).

Social exclusion refers to the process by which individuals or groups are pushed to the fringe of society and prevented from participating fully due to factors like poverty, lack of skills, or discrimination. In this context of gentrification, the original residents are being socially and culturally excluded from their own changing neighborhood, even if they haven't been physically displaced yet. Anomie is normlessness, cultural lag is the gap between material and non-material culture, and residential segregation is the physical separation of groups, which is related but less specific than the feeling of exclusion described.

2,3-BPG is a negative allosteric regulator of hemoglobin. It binds preferentially to the deoxygenated (T-state) form of hemoglobin, stabilizing this low-affinity conformation. By stabilizing the T-state, it makes it more difficult for oxygen to bind, thereby decreasing hemoglobin's overall affinity for oxygen. This results in a rightward shift of the oxygen-hemoglobin dissociation curve, which facilitates oxygen release to the tissues.

Cyanogen bromide (CNBr) specifically cleaves the peptide bond on the carboxyl (C-terminal) side of methionine (Met) residues. In the sequence Ala-Gly-Cys-Met-Lys, the cleavage will occur after the Met residue. This will break the bond between Met and Lys, resulting in two fragments: the tetrapeptide Ala-Gly-Cys-Met and the single amino acid Lys.

The formal operational stage, which typically begins around age 12, is characterized by the development of abstract reasoning. Individuals in this stage can think about hypothetical scenarios, deduce consequences (hypothetical-deductive reasoning), and understand abstract principles like justice and algebra. The concrete operational stage is limited to logical thought about concrete events, while the earlier stages are pre-logical.

The operator is the binding site for the repressor protein. Normally, the repressor binds to the operator in the absence of lactose, blocking transcription. If a mutation prevents the repressor from binding, this negative control is lost. In the absence of glucose, cAMP levels are high, and CAP is active, promoting transcription. Since the repressor cannot bind to the mutated operator, RNA polymerase will be free to transcribe the genes regardless of whether lactose is present or not. This results in constitutive (continuous) expression.

The repolarization phase of the action potential follows depolarization. It is caused by the closing of voltage-gated sodium (Na+) channels and the opening of voltage-gated potassium (K+) channels. The opening of K+ channels allows potassium ions to flow out of the cell (efflux), down their electrochemical gradient. This outward movement of positive charge makes the membrane potential more negative, returning it toward the resting potential.

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.