Practice Test 9 - DAT Reading Comprehension

20 questions. Answer them in any order, then submit to see your score and every explanation.

It can be inferred from the passage that an inflammatory response is most likely triggered when...
As used in the passage, the word 'cascade' refers to a(n):
Based on the passage, a reader can conclude all of the following about the enteric nervous system (ENS) EXCEPT that it:
**Biological Mechanism: oxidative phosphorylation in mitochondria** Cells extract energy from nutrients by transferring electrons to carrier molecules and ultimately to oxygen. During glycolysis and the citric acid cycle, high-energy electrons are loaded onto NADH and FADH $_2$ , which deliver them to the electron transport chain (ETC) embedded in the inner mitochondrial membrane. The ETC comprises protein complexes that pass electrons through redox reactions, meaning electrons move from donors with lower reduction potential to acceptors with higher reduction potential. As electrons flow through complexes I, III, and IV, these complexes pump protons (H $^+$ ) from the mitochondrial matrix into the intermembrane space. This proton pumping creates an electrochemical gradient called the proton-motive force (PMF), consisting of a membrane potential (voltage) and a pH difference. The inner membrane is highly impermeable to protons, so the gradient stores free energy. ATP synthase is a rotary enzyme that allows protons to flow back into the matrix through a channel, coupling that flow to the phosphorylation of ADP to ATP. This coupling is chemiosmosis, the use of an ion gradient to drive chemical synthesis. The system depends on oxygen as the terminal electron acceptor at complex IV, where O $_2$ is reduced to water. If oxygen is limited, electron flow slows, NADH accumulates, and the citric acid cycle stalls because NAD $^+$ becomes scarce. Cells can partially compensate by fermentative pathways that regenerate NAD $^+$ , but these yield far less ATP than oxidative phosphorylation. Certain molecules, called uncouplers, dissipate the proton gradient by carrying protons across the membrane without ATP synthesis; this increases electron transport and oxygen consumption but reduces ATP output, often releasing energy as heat. In contrast, ETC inhibitors block electron transfer at specific complexes, preventing proton pumping and collapsing ATP production. For example, cyanide inhibits complex IV, halting oxygen reduction; as a result, electrons back up, NADH cannot be oxidized, and ATP synthesis stops rapidly. Mitochondrial dysfunction can therefore produce energy failure, particularly in tissues with high ATP demand such as brain and heart. What is the role of oxygen in the electron transport chain process described?
The passage most strongly suggests that one consequence of a disease that degrades the myelin sheath is...
As used in the passage, 'biocompatibility' most nearly means:
**Chemical Reaction: Haber–Bosch ammonia synthesis** Ammonia (NH $_3$ ) is industrially produced by the Haber–Bosch process, which combines nitrogen (N $_2$ ) and hydrogen (H $_2$ ) according to the reversible reaction: N $_2$ + 3H $_2$ ⇌ 2NH $_3$ . The N≡N triple bond is exceptionally strong, making N $_2$ kinetically inert under ambient conditions. A catalyst increases reaction rate by lowering activation energy without changing the equilibrium constant; in Haber–Bosch, iron-based catalysts with promoters (e.g., K $_2$ O, Al $_2$ O $_3$ ) provide active sites that weaken the N≡N bond through adsorption. Because the reaction is exothermic and reduces gas moles (4 moles reactants to 2 moles products), Le Châtelier's principle predicts that high pressure favors ammonia formation, while lower temperature favors products thermodynamically. However, low temperature slows kinetics; thus, industry uses a compromise temperature (typically 400–500°C) and high pressure (often 150–250 atm). Reactant gases are purified because catalyst poisons such as sulfur compounds bind irreversibly to active sites, decreasing activity. In a typical loop, N $_2$ and H $_2$ pass over the catalyst bed, and only a fraction converts per pass because equilibrium limits conversion at operating conditions. The mixture is cooled to condense NH $_3$ , separating it from unreacted gases, which are recycled to improve overall yield. This separation step effectively removes product, shifting equilibrium toward more NH $_3$ formation in subsequent passes. Energy integration is critical: heat released by synthesis can preheat incoming gases, improving efficiency. Ammonia is a precursor for fertilizers, enabling high crop yields but also contributing to environmental issues such as eutrophication and nitrous oxide emissions when mismanaged. Modern research explores alternative catalysts and electrochemical nitrogen reduction to reduce the process's carbon footprint, since H $_2$ is commonly produced from natural gas via steam methane reforming. What link does the passage establish between product condensation and increased overall ammonia yield?
The author of the passage would most likely agree with which of the following statements?
The passage explicitly states that the byproduct of fatty acid oxidation in peroxisomes is which specific molecule?
Based on the passage, the function of lactoferrin contributes to oral health by a mechanism that is most analogous to:
**Biological Mechanism: enzyme inhibition and pathway flux** Metabolic pathways are regulated to match cellular energy and biosynthetic needs. Enzymes catalyze individual steps, and the overall pathway flux (rate of product formation) is often controlled by one or a few rate-limiting enzymes. Competitive inhibition occurs when an inhibitor binds the active site, competing with substrate; it increases the apparent $K_m$ (substrate concentration needed for half-maximal velocity) without changing $V_{max}$ , because high substrate can outcompete inhibitor. Noncompetitive inhibition occurs when an inhibitor binds an allosteric site on the enzyme or enzyme–substrate complex, reducing catalytic capacity; it lowers $V_{max}$ without necessarily changing $K_m$ . Cells frequently use feedback inhibition, where the end product of a pathway inhibits an early enzyme, preventing overaccumulation. This is efficient because small changes at a key step can propagate through the pathway. In drug design, inhibitors can be tuned for selectivity by exploiting structural differences between isoenzymes. However, inhibiting a single enzyme may lead to metabolite buildup upstream and rerouting through alternative pathways, affecting efficacy and side effects. What is the relationship between competitive inhibition and overcoming inhibition by increasing substrate concentration described in the passage?
**Environmental Process: nitrogen transformations in soils** Nitrogen availability often limits plant growth, yet most atmospheric nitrogen exists as N $_2$ , which plants cannot directly use. In soils, reactive nitrogen cycles through microbial processes that change oxidation state and chemical form. Nitrogen fixation converts N $_2$ to ammonia (NH $_3$ ), usually by symbiotic bacteria using the enzyme nitrogenase, which is oxygen-sensitive and energy-intensive. Ammonia is protonated to ammonium (NH $_4^+$ ) in soil solution and can be taken up by plants or adsorbed onto clay minerals. Nitrification is an aerobic, two-step process in which specialized microbes oxidize NH $_4^+$ to nitrite (NO $_2^-$ ) and then to nitrate (NO $_3^-$ ). Nitrate is highly mobile and can leach into groundwater, especially when plant uptake is low. Under oxygen-poor conditions, denitrification reduces NO $_3^-$ through intermediates (NO $_2^-$ , NO, N $_2$ O) to N $_2$ , returning nitrogen to the atmosphere. Nitrous oxide (N $_2$ O) is a potent greenhouse gas, so incomplete denitrification can have climate implications. Agricultural fertilization increases NH $_4^+$ and NO $_3^-$ pools, often boosting yields but also increasing leaching and gaseous losses. Waterlogged soils promote denitrification because diffusion limits oxygen, while well-aerated soils favor nitrification. Management practices such as cover cropping and nitrification inhibitors aim to synchronize nitrogen availability with plant demand, reducing environmental losses. What link does the passage establish between soil oxygen levels and dominant nitrogen-loss pathways?
The passage indicates that the reversion of the pump to its original conformation is a direct effect of which preceding event?
According to the passage, the relationship between the final state of the cell membrane in apoptosis and in necrosis is best described as one of:
What is the main topic of the passage?
The passage identifies which of the following as necessary for the Fenton reaction to generate the hydroxyl radical?
The author's attitude toward the discovery of telomerase is best described as...
**Scientific Discovery: PCR and exponential amplification** The polymerase chain reaction (PCR) revolutionized molecular biology by enabling selective amplification of DNA segments from tiny starting amounts. PCR uses cycles of temperature changes to drive three steps. During denaturation (~95°C), double-stranded DNA separates into single strands. During annealing (~50–65°C), short DNA primers bind complementary sequences flanking the target region; primers define the boundaries of amplification. During extension (~72°C), a thermostable DNA polymerase (such as Taq polymerase) extends primers by adding dNTPs, synthesizing new strands. Each completed cycle ideally doubles the number of target DNA molecules, producing exponential growth ( $2^n$ ) after $n$ cycles. Thermostable polymerase was crucial because early polymerases denatured during high-temperature steps, requiring replenishment each cycle. Primer design determines specificity: mismatched primers reduce amplification efficiency, while primers binding multiple genomic sites can yield nonspecific products. Real-time quantitative PCR (qPCR) monitors amplification using fluorescent dyes or probes, enabling estimation of initial template quantity. PCR has applications in pathogen detection, genetic testing, forensics, and research cloning. However, contamination can produce false positives because even trace DNA can be amplified. Thus, workflow separation and negative controls are essential. How does primer binding lead to exponential target amplification according to the passage?
The author would most likely agree with which statement about the placebo effect?
**Chemical Reaction: electrochemical corrosion of iron** Corrosion is the degradation of metals through electrochemical reactions with the environment. Iron corrosion in aerated water involves coupled anodic and cathodic half-reactions occurring at different sites on the metal surface. At the anode, iron is oxidized: Fe → Fe $^{2+}$ + 2e $^-$ . Electrons travel through the metal to cathodic sites where dissolved oxygen is reduced, commonly: O $_2$ + 2H $_2$ O + 4e $^-$ → 4OH $^-$ . The Fe $^{2+}$ and OH $^-$ can form iron hydroxides that further oxidize into rust (hydrated iron oxides). Corrosion rate depends on factors that influence these half-reactions, including oxygen availability, electrolyte conductivity, and pH. Saltwater increases conductivity, facilitating ionic current and accelerating corrosion. Differential aeration can create localized cells: regions with lower oxygen become anodic relative to oxygen-rich regions, promoting pitting. Protection strategies include coatings that block water and oxygen, alloying to form passive oxide layers, and cathodic protection. In cathodic protection, the protected iron is forced to act as a cathode by attaching a more easily oxidized metal (a sacrificial anode) such as zinc. Zinc oxidizes preferentially, supplying electrons to the iron and suppressing iron oxidation. Alternatively, impressed current systems use an external power source to provide electrons. These methods exploit the relationship between electron flow and oxidation tendency. What is the role of a sacrificial anode in preventing iron oxidation in the corrosion process described?

Practice tests