Your FREE Admission Test for Dental Hygiene (ATDH) Practice Test 2026 – 280+ Q&A

Read the passage, then answer the question. Cells rarely make more of a product than they need, and one of the fastest ways they avoid waste is feedback inhibition. In many biosynthetic pathways, the final product binds to the first enzyme of the pathway at a site separate from the active site. This binding changes the enzyme's shape and lowers its affinity for its substrate, so the whole pathway slows. When the product is used up, it leaves the enzyme and activity returns. A classic example comes from bacteria that make the amino acid isoleucine from threonine: isoleucine inhibits threonine deaminase, the first enzyme of that pathway. Regulating the first committed step, rather than a later one, matters because it keeps intermediate compounds from piling up. Unlike changes in gene expression, which can take minutes to hours, this form of control acts within seconds, because it alters the activity of enzyme molecules that already exist rather than the number of molecules the cell makes. Which statement best expresses the main idea of the passage?

• A.Acting on the first committed step keeps intermediate compounds of a pathway from piling up
• B.A pathway's end product can quickly slow its own synthesis by binding the first enzyme
• C.Isoleucine slows its own pathway by binding threonine deaminase away from its active site
• D.Cells mainly regulate metabolic pathways by changing how many enzyme molecules they make

Read the passage, then answer the question. When a pathogen enters the body for the first time, only a small number of lymphocytes carry receptors that happen to fit its antigens. Those few cells are selected: binding to the antigen, together with signals from helper T cells, triggers them to divide repeatedly, producing a clone of identical cells. Some members of the clone become effector cells, such as plasma cells that secrete antibodies, while others become long-lived memory cells. Because the starting population is so small, this primary response takes one to two weeks to reach its peak, and the person may become noticeably ill in the meantime. If the same antigen appears again, the memory cells, which far outnumber the original precursors, respond within days and produce more antibody, much of it binding the antigen more tightly. This secondary response is often fast enough that the infection is cleared before symptoms develop. Vaccines take advantage of this pattern by building the memory population without the risks of the disease itself. Which of the following best summarizes the passage?

• A.Lymphocytes that fit an antigen multiply into clones that speed up any later response
• B.Helper T cells kill infected cells directly, so antibodies matter only on second exposure
• C.Memory cells formed in a first infection give lifelong protection against any later illness
• D.Vaccines build a population of memory cells without exposing a person to the disease itself

Read the passage, then answer the question. Blood pH normally stays between 7.35 and 7.45. This stability depends less on the chemical strength of any single buffer than on the fact that the bicarbonate buffer system is linked to two organs. In the blood, carbonic acid and bicarbonate ions exist in equilibrium with dissolved carbon dioxide. When a strong acid enters the blood, bicarbonate accepts the extra hydrogen ions and forms carbonic acid, which breaks down into water and carbon dioxide. By itself, this reaction would soon use up the available bicarbonate. What makes the system effective is that both of its components can be adjusted: the lungs can exhale the added carbon dioxide within minutes, and the kidneys can, over hours to days, excrete hydrogen ions and generate new bicarbonate. Phosphate ions and proteins also bind hydrogen ions, and hemoglobin in particular buffers large amounts of acid inside red blood cells, but the body cannot replenish these buffers in the same way. Which detail from the passage most directly supports its central claim about what keeps blood pH stable?

• A.Hemoglobin buffers a large amount of acid inside the body's red blood cells
• B.Phosphate ions and proteins in the blood also bind some of the hydrogen ions
• C.Bicarbonate accepts the hydrogen ions from a strong acid and forms carbonic acid
• D.The lungs exhale carbon dioxide and the kidneys generate new bicarbonate ions

Read the passage, then answer the question. (1) Bone looks inert, but adult bone is constantly being rebuilt. In a process called remodeling, osteoclasts dissolve small pockets of old bone, and osteoblasts then fill each pocket with new matrix that later mineralizes. Roughly a tenth of the adult skeleton is replaced each year, which allows tiny fatigue cracks to be repaired before they spread. Remodeling also lets bone serve as a calcium reserve for the rest of the body. (2) The two cell types do not work independently. Cells of the osteoblast lineage produce a signaling protein called RANKL, which binds receptors on osteoclast precursors and drives them to mature into active osteoclasts. The same cells also release osteoprotegerin, a decoy receptor that binds RANKL and keeps it from acting. The balance between these two signals therefore sets how much bone is resorbed. Conditions that raise the ratio of RANKL to osteoprotegerin, such as the fall in estrogen after menopause, tip remodeling toward a net loss of bone. What is the main point of the second paragraph?

• A.Osteoclasts release a decoy protein that keeps osteoblasts from maturing
• B.Bone-forming cells set the amount of resorption through opposing signals
• C.Adult bone is continually broken down and rebuilt instead of staying inert
• D.Falling estrogen after menopause raises RANKL and leads to net bone loss

Read the passage, then answer the question. The concentration of calcium ions in blood plasma is held within a narrow range because nerves, muscles and blood clotting all depend on it. When calcium falls too low, nerves and muscles become overly excitable. When plasma calcium falls, cells of the parathyroid glands detect the change and release parathyroid hormone (PTH). PTH acts on two organs directly. In bone, it indirectly stimulates osteoclasts, which release calcium from the mineral matrix. In the kidneys, it increases the reabsorption of calcium from the filtrate, so less is lost in urine, and it stimulates the conversion of vitamin D to its active form, calcitriol. Calcitriol, in turn, increases the absorption of calcium from food in the small intestine. When plasma calcium rises, PTH secretion falls. The thyroid gland releases calcitonin when calcium is high, and calcitonin inhibits osteoclasts, but in adult humans, removing the thyroid does not noticeably disturb calcium balance, which suggests that calcitonin plays a minor role compared with PTH. Which statement is NOT supported by the passage?

• A.PTH raises blood calcium by acting directly on the intestine to absorb more
• B.PTH reduces the amount of calcium that the kidneys allow to be lost in urine
• C.PTH frees calcium from bone by way of its indirect effect on the osteoclasts
• D.Calcitonin seems to matter less than PTH for calcium balance in adult humans

Read the passage, then answer the question. The kidneys filter about 180 liters of plasma a day, and with it about 180 grams of glucose. In a healthy person, almost none of this glucose appears in the urine, because cells lining the proximal tubule reclaim it. On the side of these cells facing the tubule, a protein called SGLT2 moves glucose into the cell together with sodium ions. The sodium flows down a concentration gradient that is maintained by sodium-potassium pumps on the opposite side of the cell, and the glucose is carried along against its own gradient. Glucose then leaves the cell through a separate carrier and returns to the blood. SGLT2 accounts for about 90 percent of the glucose recovered; a related transporter farther along the tubule, SGLT1, recovers most of the rest. Because the number of transporters is limited, reabsorption has a maximum rate. When plasma glucose is so high that the filtered load exceeds this maximum, as in uncontrolled diabetes, the excess glucose stays in the filtrate and is excreted. Based on the passage, a drug that blocks SGLT2 in a person with normal plasma glucose would most likely have which effect?

• A.SGLT1 would reclaim the extra glucose, so the urine would stay nearly glucose-free
• B.Much more glucose would be excreted while blood levels remained in the usual range
• C.Glucose would reach the urine only after plasma glucose rose well above normal
• D.The sodium-potassium pumps would stop, so less glucose would leave the cells

Read the passage, then answer the question. Allergic diseases such as hay fever and asthma became markedly more common in wealthy countries during the second half of the twentieth century. In 1989, the epidemiologist David Strachan reported that children with several older siblings were less likely to develop hay fever, and he proposed that early infections, passed between siblings, might protect against allergy. This idea, later called the hygiene hypothesis, has been attractive because it offers a single explanation for a broad trend. The evidence, however, is mixed. Children raised on traditional farms do show lower rates of allergy, but many common childhood infections do not appear to protect, and some infections are linked to more asthma, not less. Many researchers now suspect that what matters is not infection itself but early contact with a diverse range of harmless microbes. Even this revised version rests largely on observational studies, in which families who differ in exposure may also differ in other ways. It would be premature to conclude that cleanliness causes allergy, though the pattern is too consistent to dismiss. The author's attitude toward the hygiene hypothesis is best described as

• A.firm skepticism, treating its pattern as a likely artifact of flawed studies
• B.qualified support, treating early infection as the most likely protective cause
• C.cautious interest, treating the trend as genuine but its explanation as open
• D.measured approval, treating microbial contact as a proven cause of less allergy

Read the passage, then answer the question. People with periodontitis, a chronic bacterial infection of the tissues that support the teeth, are more likely than people with healthy gums to develop cardiovascular disease. Several large observational studies have reported this association, and some investigators have proposed a causal explanation. Periodontitis produces persistent, low-grade inflammation, and bacteria from inflamed gums can enter the bloodstream during chewing or brushing. Because inflammation plays a central role in the formation of arterial plaques, these investigators argue that gum disease itself helps drive heart disease and that treating it might lower cardiovascular risk. Other researchers urge caution. Periodontitis and heart disease share several risk factors, including smoking, diabetes and older age, and people who neglect their gums may differ from others in diet, exercise and access to medical care. Separating these influences from any direct effect of the gum infection has proved difficult, and an association alone cannot show which factor, if any, is responsible. Which finding, if true, would most weaken the investigators' proposal that gum disease helps cause heart disease?

• A.Bacteria from the patients' inflamed gums were found inside arterial plaques
• B.The link vanished once the analysis adjusted for smoking and diabetes
• C.The link grew stronger as the severity of the patients' gum disease rose
• D.Gum treatment lowered the blood markers of inflammation in the patients

Cells lining the small intestine and the kidney's proximal tubules absorb glucose against its concentration gradient, often moving it from a region where it is scarce into a cell where it is already abundant. They manage this without spending ATP at the transporter itself. The protein responsible, a sodium-glucose cotransporter, binds a glucose molecule together with sodium ions and carries them inward at the same time. Because sodium is far more concentrated outside the cell than inside, sodium's movement down its gradient supplies the energy that drags glucose up its own gradient. The arrangement works only as long as the sodium gradient persists. That job falls to a separate protein on the opposite side of the cell, the sodium-potassium pump, which uses ATP to export three sodium ions for every two potassium ions it brings in. Glucose that accumulates inside the cell then leaves through a third protein, a carrier that lets it diffuse passively into the blood. Physiologists call the cotransporter's mechanism secondary active transport: active because it moves glucose uphill, secondary because the energy was spent earlier, by the pump. Based on the passage, if a drug completely blocked the sodium-potassium pump in these cells but left the cotransporter itself undamaged, which outcome would be expected?

• A.Glucose uptake would rise as sodium built up outside the cell
• B.Glucose uptake would dwindle as the gradient it relies on faded
• C.Glucose uptake would go on, but glucose could not exit to the blood
• D.Glucose uptake would go on, as the cotransporter uses no ATP itself

Bacteria acquire antibiotic resistance in two broad ways. A random mutation in the chromosome may alter the drug's target, and if the antibiotic is present, cells carrying that mutation survive and multiply while their neighbors die. Resistance can also arrive from outside. Many resistance genes sit on plasmids, small circles of DNA separate from the chromosome, which can be copied and passed from one cell to another through a bridge-like connection in a process called conjugation. Because plasmids can cross between different species, a gene that arose in a harmless soil bacterium may eventually turn up in a pathogen. A single plasmid often carries several resistance genes at once, so exposure to one antibiotic can select for resistance to drugs the cells have never encountered. Plasmids impose a cost, however: copying the extra DNA consumes resources, and in drug-free conditions plasmid-free cells sometimes outgrow their plasmid-carrying relatives. This observation has encouraged hopes that reducing antibiotic use will let resistance fade, although some plasmids acquire compensating mutations that lower their cost, allowing them to persist for many generations even when no drug is present. Which statement is NOT supported by the passage?

• A.A resistance gene found in a pathogen may have arisen in another species
• B.Chromosomal mutation is the more common source of resistance in bacteria
• C.Plasmid-bearing cells can be outgrown by plasmid-free cells without drugs
• D.Exposure to one antibiotic can select for resistance to another drug

Many flowering plants depend on animals to carry pollen between individuals, and biologists have long asked whether flower color alone can steer a pollinator's choices. In a meadow where a single wildflower species grows in both purple and white forms, a team of ecologists recorded bumblebee visits over two summers. Purple plants received nearly twice as many visits as white plants and, by the end of each season, had produced substantially more seed. The team concluded that bumblebees prefer purple flowers and that this preference gives purple plants a reproductive advantage. The conclusion fits a broader pattern: bumblebees see violet and blue wavelengths well, and in laboratory trials with artificial flowers, naive bees often approach blue-violet targets first. Yet a meadow is not a laboratory. Flowers differ in more than color, and the plants that bees visit most may also be the ones growing where conditions favor both nectar production and seed set. The team acknowledged this limitation and proposed a follow-up in which purple and white plants would be grown in pots and set out side by side at randomly chosen spots. Which finding, if true, would most seriously weaken the team's conclusion?

• A.At night, moths visited white plants more often than they visited purple plants
• B.In laboratory trials, naive bees approached white targets as often as blue ones
• C.Purple plants grew mostly in moist, sunny patches where white plants were rare
• D.In the potted follow-up, bees again visited purple plants about twice as often

Large population surveys consistently find that adults who report sleeping fewer than six hours a night are more likely to have high blood pressure than adults who sleep seven to eight hours. The association persists after researchers adjust for age, body weight, and smoking, which makes it harder to dismiss as a by-product of those factors. Several plausible pathways have been suggested. Short sleep is accompanied by heightened activity of the sympathetic nervous system, which constricts blood vessels and raises heart rate, and the normal nighttime dip in blood pressure is blunted when sleep is cut short. Even so, the direction of the relationship is not settled. Obstructive sleep apnea both fragments sleep and raises blood pressure, so some short sleepers may have an undiagnosed disorder driving both. Work stress, shift schedules, and depression can likewise shorten sleep while independently straining the cardiovascular system. Short-term laboratory experiments that restrict healthy volunteers' sleep for a few nights do produce small rises in blood pressure, but whether those changes persist over years, and whether lengthening sleep would lower pressure in people who already have hypertension, remains under study. Which statement is most strongly supported by the passage?

• A.Sleep apnea, not short sleep itself, explains the association the surveys found
• B.Lengthening sleep would lower blood pressure in adults who have hypertension
• C.Cutting sleep for a few nights can modestly raise pressure in healthy adults
• D.Short sleep raises blood pressure in adults regardless of their age or weight

For most of the twentieth century, physicians attributed peptic ulcers to excess stomach acid, often blamed on stress and spicy food. The stomach, with a pH that can fall below 2, was assumed to be too hostile for bacteria to colonize, and treatment centered on antacids and acid-suppressing drugs. Ulcers healed on these regimens but frequently returned once the drugs were stopped. Around 1980 the Australian pathologist Robin Warren observed curved bacteria in biopsies taken from inflamed stomach linings, and the physician Barry Marshall succeeded in growing the organism, later named Helicobacter pylori, in culture. Their claim that the bacterium caused gastritis and ulcers met resistance, and in 1984 Marshall drank a culture of it, developing gastritis within days. Later clinical trials showed that eradicating H. pylori with antibiotics sharply reduced ulcer recurrence. The bacterium survives in the stomach by burrowing into the mucus layer and producing urease, an enzyme that generates ammonia to neutralize the acid around it. Marshall and Warren received the Nobel Prize in Physiology or Medicine in 2005. Which choice best states the primary purpose of the passage?

• A.To explain how a bacterium manages to survive the acid conditions of the stomach
• B.To compare how well antacid drugs and antibiotics prevent ulcers from returning
• C.To recount how new evidence overturned an accepted explanation for a disease
• D.To describe the method by which a stomach bacterium was first grown in culture

Penicillin and its relatives kill bacteria by sabotaging construction rather than attacking a finished structure. The bacterial cell wall is built from peptidoglycan, long sugar chains linked to one another by short peptide bridges, forming a mesh that resists the pressure of water pushing into the cell. As a bacterium grows and prepares to divide, it must continually loosen this mesh in places and insert new material. The final cross-linking step is carried out by enzymes called penicillin-binding proteins, and penicillin binds to them irreversibly. When cross-linking fails while the cell is still loosening its old wall, the mesh weakens, and the cell eventually bursts. Human cells have no peptidoglycan, which is why penicillin can be given in large doses with relatively little direct toxicity. Not all bacteria are equally vulnerable, though. In many Gram-negative species, an outer membrane surrounds the thin peptidoglycan layer and can slow the drug's entry, while some bacteria produce beta-lactamase enzymes that cut the penicillin molecule apart before it reaches its target. Which conclusion about penicillin can most reasonably be inferred from the passage?

• A.It would kill Gram-negative bacteria faster, since their wall layer is thinner
• B.It would have little effect on bacteria that have stopped growing and dividing
• C.It would work better when paired with drugs that halt the growth of bacteria
• D.It acts mainly by digesting peptidoglycan already present in a finished wall

Mitochondria, the organelles that carry out most of a eukaryotic cell's aerobic respiration, resemble bacteria living inside a larger cell. They are about the size of a typical bacterium, they are surrounded by two membranes, and they divide by splitting in two rather than being assembled by the cell from scratch. They also carry their own DNA, a small circular molecule resembling a bacterial chromosome, and their ribosomes are closer in size and structure to bacterial ribosomes than to those in the surrounding cytoplasm. These observations underlie the endosymbiotic theory, which holds that mitochondria descend from free-living bacteria that were engulfed by an ancestral cell and, rather than being digested, were retained as partners. Chloroplasts are thought to have arisen in a similar way from photosynthetic bacteria. Nevertheless, a mitochondrion today could not survive on its own. Over hundreds of millions of years, most of the genes its ancestor carried have been lost or transferred to the nucleus, so the great majority of mitochondrial proteins are now encoded by nuclear genes, made in the cytoplasm, and imported into the organelle. In the passage, the word "Nevertheless" primarily serves which purpose?

• A.To introduce a contrast between how chloroplasts and mitochondria arose
• B.To introduce a finding that casts doubt on the endosymbiotic theory itself
• C.To introduce more evidence that mitochondria descend from free-living bacteria
• D.To introduce a limit on how far the comparison with bacteria can be taken

The human immune system operates in two broad tiers. The innate immune system is present from birth and responds within minutes to hours of an infection. Its cells, such as neutrophils and macrophages, recognize molecular patterns shared by many kinds of microbes, for example components of bacterial cell walls, so a single receptor type can detect a wide range of invaders. Because these receptors are inherited and fixed, the innate response to a given microbe is essentially the same on the second encounter as on the first. The adaptive immune system works differently. Its lymphocytes, the B cells and T cells, each carry receptors generated by the random rearrangement of gene segments, so that collectively they can recognize an enormous variety of specific molecular shapes, or antigens. When a lymphocyte meets its matching antigen, it multiplies into a large population of identical cells, a process that takes several days during a first infection. Some of these cells persist as memory cells, so that a later exposure to the same antigen triggers a faster and stronger response. The two tiers are not independent, however: innate cells display fragments of microbes to T cells, helping to launch the adaptive response. According to the passage, the innate and adaptive immune systems differ in each of the following respects EXCEPT which one?

• A.Whether a second exposure brings a faster response than the first
• B.How quickly each responds at the start of a first infection
• C.Whether its receptors are inherited or built by gene rearrangement
• D.Whether it can respond to a microbe the body has not met before

Fish that live in fresh water and fish that live in the ocean face opposite water problems. A freshwater fish's body fluids are saltier than the water around it, so water constantly moves into its tissues by osmosis, especially across the thin membranes of the gills. To cope, the fish rarely drinks, and its kidneys produce large volumes of very dilute urine. Specialized cells in the gills also take up salt ions from the surrounding water, replacing what is lost in the urine. A marine bony fish, by contrast, has body fluids less salty than seawater. It therefore loses water to its surroundings and must drink seawater almost continuously. Its kidneys produce only small amounts of urine, and its gill cells pump excess salt out of the body. Sharks and rays, however, take a different route. They retain high concentrations of urea in their blood, which raises the concentration of their body fluids to roughly that of seawater. As a result, they gain little water and lose little by osmosis, and they need not drink nearly as much as bony marine fish do. In the passage, the word "however" in the sentence beginning "Sharks and rays" mainly serves to mark sharks and rays as

• A.an exception to the marine pattern described just before
• B.an exception to the rule that water moves by osmosis
• C.facing the opposite water problem from marine bony fish
• D.an exception to the freshwater pattern described at the start

Most plants, called C3 plants, fix carbon dioxide directly with the enzyme rubisco inside the mesophyll cells of the leaf. Rubisco has a costly flaw: it can bind oxygen instead of carbon dioxide, triggering a wasteful process called photorespiration that releases carbon the plant had already fixed. Photorespiration becomes more frequent on hot, dry days, when plants close their stomata to save water, so oxygen builds up inside the leaf while carbon dioxide runs low. Plants such as corn and sugarcane, called C4 plants, divide the work between two cell types. In the mesophyll, a different enzyme, PEP carboxylase, captures carbon dioxide; this enzyme does not react with oxygen. The captured carbon is passed as a four-carbon compound to tightly packed bundle-sheath cells deeper in the leaf, where it is released and concentrated around rubisco. Because rubisco there is surrounded by carbon dioxide, photorespiration is nearly eliminated. The arrangement is not free: shuttling carbon between the two cell types costs the plant extra ATP for each molecule of carbon dioxide fixed. In cool, moist climates, where photorespiration is modest, C3 plants often grow as well as or better than C4 plants. According to the passage, which statement correctly describes a difference between C4 plants and C3 plants?

• A.In C4 plants, rubisco works in bundle-sheath cells instead of mesophyll cells
• B.In C4 plants, PEP carboxylase takes over rubisco's job in the bundle sheath
• C.In C4 plants, each carbon dioxide fixed costs less ATP than it does in C3 plants
• D.In C4 plants, photorespiration is avoided by keeping stomata open on hot days

A skeletal muscle contracts only after a chain of events that begins in a motor neuron, although the chain is often easiest to describe from its end backward. The final step is mechanical: myosin heads bind to actin filaments and pull on them, shortening the muscle fiber. Myosin can reach actin only after calcium ions, released from a storage network inside the fiber called the sarcoplasmic reticulum, bind to regulatory proteins and shift them off actin's binding sites. That calcium release is triggered by an electrical signal, an action potential, that travels along the muscle fiber's membrane and dives into the fiber through small tunnels called T-tubules. The muscle's action potential, in turn, starts where the nerve meets the muscle. There, the neuron's own action potential opens channels that let calcium flow into the nerve ending, and this influx causes the nerve ending to release the neurotransmitter acetylcholine. Acetylcholine crosses a narrow gap and binds to receptors on the muscle membrane, opening channels that let sodium ions rush in. This depolarization is what launches the action potential in the muscle fiber. Based on the passage, which event occurs immediately before calcium is released from the sarcoplasmic reticulum?

• A.Regulatory proteins shift off the binding sites along actin
• B.Calcium ions flow into the nerve ending of the motor neuron
• C.An action potential spreads along the membrane and T-tubules
• D.Acetylcholine binds to receptors on the muscle fiber membrane

Plants cannot walk, yet their seeds routinely travel far from the parent. Ecologists sort these journeys by the agent that carries the seed. In anemochory, wind does the work: dandelion seeds ride on feathery parachutes, and maple fruits spin like propellers. In hydrochory, moving water is the carrier, as when a coconut floats for weeks before washing ashore. Zoochory, dispersal by animals, is split in two. In epizoochory, seeds travel on the outside of an animal, hooked into fur or stuck to feathers with sticky coatings. In endozoochory, an animal eats a fruit, and the seeds pass through its gut and are deposited, often with a ready supply of fertilizer, far from where they were swallowed. Researchers stress that the category follows the carrier, not the landscape the seed passes through or the shape of the seed itself. A seed that sticks to a duck's feet and crosses a lake is therefore classed with the hooked seeds in fur, not with the floating coconut. Many plants hedge their bets, and a single species may use more than one route; the classification then applies to each journey separately, not to the plant as a whole. Which journey would the passage's system classify as epizoochory?

• A.A sedge seed caught in the mud on a heron's legs as it flies to a pond
• B.A fig seed swallowed by a fish and released in its droppings downstream
• C.A mangrove seedling that drops into a creek and drifts to a new bank
• D.A hooked burr snapped off a dry stalk and rolled across a plain by wind

Over the past two decades, several large observational studies have tracked thousands of adults for many years, recording how much they slept and whether they later developed memory problems. Taken together, these studies suggest that people who regularly sleep fewer than six hours a night are more likely to experience cognitive decline in later life. Laboratory work offers a possible mechanism. In mice, sleep appears to speed the flow of fluid through the brain, which may help clear away proteins such as beta-amyloid that build up in Alzheimer's disease. Still, the human findings must be read with care. People in the early, undiagnosed stages of dementia often sleep poorly, so it is possible that the brain changes cause the short sleep rather than the reverse. Depression, chronic pain, and shift work can also disturb sleep and independently affect memory. Only randomized trials, in which some participants are helped to sleep longer and are then compared with those who are not, could show that improving sleep protects the brain, and such trials are difficult to run over the decades that dementia takes to develop. The author's choice of the word "suggest" in the second sentence indicates that the author views the observational studies as

• A.evidence of a cause that the mouse research has confirmed
• B.too small and too brief to show any real link between them
• C.evidence that short sleep causes the cognitive decline later
• D.evidence of a link whose direction of cause is unproven

Cytochrome c is a small protein that shuttles electrons between two large complexes in the inner membrane of the mitochondrion, a step essential to aerobic respiration. Because nearly every eukaryote depends on this step, biochemists have sequenced the protein from hundreds of species, from yeast to sunflowers to humans. The results are striking. Of the roughly 104 amino acids in the human version, a substantial share occupy the same positions in organisms whose last common ancestor lived more than a billion years ago. Researchers describe these positions as highly conserved. Their explanation is functional: residues that hold the heme group in place or form the docking surface for the partner complexes cannot change without crippling electron transport, so mutations at those sites are removed by natural selection almost as quickly as they arise. Positions on the protein's outer surface, by contrast, tolerate substitution, and they differ widely among species. This uneven pattern has made cytochrome c useful in two ways. The variable positions accumulate differences at a fairly steady pace, so counting them helps estimate how long ago two lineages diverged. The conserved positions, meanwhile, point experimenters toward the parts of the molecule that matter most for its job. A molecule only a hundred or so amino acids long can therefore preserve, in its sequence, a record stretching back to the earliest eukaryotes. As used in the passage, the word "conserved" most nearly means

• A.kept in reserve by the cell until a later demand arises
• B.kept shielded from damage by the protein's outer surface
• C.kept nearly unchanged across distantly related species
• D.kept at steady levels by the cell to sustain respiration

The marine bacterium Vibrio fischeri lives freely in seawater and also colonizes the light organ of the Hawaiian bobtail squid. A single free-living cell produces almost no light, yet the dense population packed inside the squid glows brightly. The switch depends on small diffusible molecules called autoinducers. Each cell releases autoinducers continuously at a low rate, and the molecules pass easily across cell membranes. In open water, they diffuse away almost as soon as they are made, so their concentration around any one cell stays negligible. In the confined light organ, where cell numbers reach very high densities, the molecules accumulate. Once their concentration crosses a threshold, they bind a receptor protein inside each cell, and the receptor-autoinducer complex switches on the lux genes, which encode the enzyme luciferase and the other proteins needed for light production. Because the response depends on how many neighbors are present, biologists call this kind of communication quorum sensing. The squid benefits too: the glow, matched to moonlight from above, hides the animal's shadow from predators below. Similar systems control toxin release and biofilm formation in many pathogens, which has prompted interest in drugs that block the signal rather than kill the bacteria. Based on the passage, autoinducers are best described as

• A.signal molecules whose local concentration rises with the density of the population
• B.receptor proteins that switch on the lux genes when enough neighboring cells are present
• C.enzymes encoded by the lux genes that produce light once a signal threshold is crossed
• D.signal molecules that cells begin releasing only after they colonize the squid's organ

Cells die in more than one way, and the manner of death matters to the tissue around them. Necrosis is typically the result of injury, such as a loss of blood supply, a toxin, or a burn. The damaged cell cannot keep water out, so it swells; its organelles break down, and eventually its outer membrane ruptures. The cell's contents spill into the surrounding tissue, where they attract immune cells and set off inflammation, which can injure neighboring cells that were otherwise healthy. Apoptosis, in contrast, is an orderly, energy-requiring program that the cell carries out on itself. Enzymes called caspases cut up proteins in a controlled sequence, the cell shrinks, its DNA is chopped into regular fragments, and the cell breaks into small membrane-wrapped packages. Because the membrane around each package stays intact, nothing leaks out; nearby phagocytes recognize signals on the packages' surfaces and engulf them quietly, without inflammation. Apoptosis is not only a response to damage. During embryonic development, it removes the webbing between the fingers, and throughout life it eliminates cells whose DNA is beyond repair. Which statement is NOT supported by the passage?

• A.A cell without working caspases would struggle to finish apoptosis
• B.A cell dying by necrosis shrinks before its membrane ruptures
• C.A cell unable to make ATP would be unlikely to die by apoptosis
• D.A cell can undergo apoptosis even when it has suffered no injury

Read the passage, then answer the question. For decades after community water fluoridation began, most dentists believed that fluoride worked mainly from the inside. Swallowed fluoride, the reasoning went, was carried by the blood to developing teeth and built into the enamel crystals as they formed, producing teeth that were permanently harder to dissolve. That view shaped advice for years, including the idea that fluoride mattered chiefly for young children whose teeth were still forming. Later laboratory and clinical work changed the picture. The amount of fluoride built into enamel during development turned out to be too small to explain the large drop in decay. What mattered far more was fluoride present in the mouth at low concentration, in saliva and in the film of plaque on the teeth. There it slows the dissolving of enamel when bacteria produce acid, and it speeds the rebuilding of mineral once the acid is cleared; the rebuilt mineral resists acid better than the original did. This shift explains why public health agencies now stress frequent exposure to small amounts of fluoride, from toothpaste and fluoridated water, throughout life rather than only in childhood. Adults, whose enamel formed long ago, still benefit. Which of the following best expresses the main idea of the passage?

• A.Fluoride was added to water supplies long before scientists understood how it protected the teeth from acid
• B.Fluoride protects teeth chiefly through its presence in the mouth throughout life, not through forming enamel
• C.Fluoride rebuilds enamel after an acid attack, and the rebuilt mineral resists acid better than the original did
• D.Fluoride must be swallowed during childhood so that the blood can carry it into the enamel of forming teeth

Read the passage, then answer the question. (1) Saliva is the mouth's main defense against acid. After a person eats sugar, bacteria in dental plaque ferment it, and within minutes the pH at the tooth surface can fall below about 5.5, the level at which enamel begins to dissolve. Saliva reverses this drop. Its bicarbonate neutralizes acid, its calcium and phosphate ions allow lost mineral to be redeposited, and its flow washes sugar away. When saliva flow is stimulated, for example by chewing, its bicarbonate concentration rises and recovery is faster. (2) This protection has limits, however, and they depend on timing rather than on saliva itself. Recovery to a resting pH typically takes from twenty minutes to an hour after each sugar exposure. A person who sips a sweetened drink over an afternoon restarts the acid attack before saliva can finish its work, so the teeth spend much of the day below the critical level. The same amount of sugar taken at a single meal produces only one such period. For this reason, how often sugar is consumed can matter as much as how much is consumed. The main point of the second paragraph is that

• A.saliva neutralizes plaque acid faster when chewing increases the flow it delivers
• B.sweetened drinks harm enamel more than meals do because they contain more sugar
• C.saliva's defense can fail when acid attacks come too close together for it to recover
• D.the total amount of sugar consumed sets how long the enamel stays below its critical pH

Read the passage, then answer the question. For much of the twentieth century, tooth decay was explained by the specific plaque hypothesis. In this view, caries was an infection caused by a few particular species, above all Streptococcus mutans, and the logical goal was to suppress or eliminate those organisms, perhaps one day with a vaccine. The ecological plaque hypothesis, proposed in the 1990s by the microbiologist Philip Marsh, places the cause elsewhere. It holds that acid-producing and acid-tolerant bacteria, S. mutans among them, are normal minor members of a healthy plaque community. Disease follows when the environment changes, most often through frequent sugar intake, so that repeated drops in pH favor these species over their neighbors and shift the whole community toward one that makes and survives acid. The two views predict different things. The first predicts that people without S. mutans should be free of decay; in fact, caries occurs in some people in whom S. mutans is scarce or undetected, with other acid-tolerant species present instead. The second predicts that changing the conditions, by reducing how often sugar is eaten or by raising plaque pH, should restore a healthy balance without eradicating any single species. The primary purpose of the passage is to

• A.argue that a vaccine against a single species could one day prevent most cases of decay
• B.contrast two accounts of what causes tooth decay and the different outcomes each predicts
• C.explain how frequent sugar intake lowers plaque pH and lets acid-tolerant species take over
• D.recount how researchers identified the one species of bacteria responsible for tooth decay

Read the passage, then answer the question. When Frederick McKay opened a dental practice in Colorado Springs in 1901, he was puzzled to find that many local residents had brown stains on their teeth, a condition people there called Colorado brown stain. No dental textbook described it. McKay spent years documenting the mottling, at one point enlisting the noted dental researcher G. V. Black, and he observed two things: the stains appeared in people who had grown up in the area, and the stained teeth, though unsightly, seemed unusually resistant to decay. He came to suspect something in the water. The answer arrived in 1931, when chemical analysis of water from a town where the stain was common revealed unusually high levels of fluoride. Public health researchers then asked a new question: was there a level of fluoride low enough to avoid the staining while keeping the protection against decay? Surveys of many communities suggested that there was, and in the 1940s several cities began adding controlled amounts of fluoride to their water to test the idea. The passage is primarily concerned with

• A.showing that the stain found in one town was a cosmetic concern rather than a danger to health
• B.explaining how a mineral in water stains the enamel of children's teeth as the enamel is forming
• C.tracing how a puzzling stain led researchers to connect a water mineral with resistance to decay
• D.arguing that public water should hold the mineral levels once found in the water of Colorado towns

Read the passage, then answer the question. Diabetes has long been recognized as a risk factor for periodontitis: people whose blood glucose is poorly controlled develop more severe gum disease and lose supporting bone faster. A newer claim runs the other way, holding that periodontitis may worsen diabetes. The idea is biologically plausible. Infected gum tissue releases inflammatory signals such as tumor necrosis factor and interleukin-6 into the bloodstream, and these signals are known to interfere with the action of insulin. Clinical trials have tested the claim directly by treating periodontitis and then measuring HbA1c, a marker of average blood glucose over roughly the previous three months. A pooled analysis of these trials reports a drop of about 0.4 percentage points three to four months after treatment, an encouraging result for a treatment that targets the mouth rather than the pancreas or the liver. Still, many of the trials were small, several followed patients for only a few months, and it is not yet clear how long the benefit lasts. Periodontal care is worth offering to people with diabetes, but it cannot be regarded as a substitute for medical management of the disease. The author's attitude toward the claim that treating periodontitis improves blood glucose control is best described as

• A.measured optimism, treating the benefit as real but modest and of uncertain duration
• B.firm conviction, treating the benefit as proven large enough to replace some diabetes drugs
• C.deep doubt, treating the benefit as an artifact of trials too small and brief to be trusted
• D.even-handed neutrality, treating the benefit as equally likely to be genuine or illusory

Read the passage, then answer the question. Fever is often treated as a malfunction to be suppressed, but the body raises its temperature deliberately. When immune cells detect an infection, they release signaling molecules called pyrogens, which act on the hypothalamus and raise the temperature at which the body tries to hold itself. The person shivers and feels cold, not because the body is losing heat but because its normal temperature now falls below the new set point. Several lines of evidence suggest that this response is useful. Many bacteria and viruses multiply more slowly at temperatures a few degrees above normal, and some immune cells move and respond more effectively when warmed. Lizards, which cannot generate much body heat, seek out warm places when infected with bacteria, and in experiments those kept from doing so were more likely to die. Fever also has costs: each degree of increase raises the body's energy use, and very high fevers can damage tissue. Its benefit, then, is real but bounded, which is why physicians weigh comfort and risk rather than lowering every fever by reflex. Which of the following titles best fits the passage?

• A.Fever as a Reset of the Hypothalamic Set Point
• B.Fever as a Regulated Defense That Carries Costs
• C.Fever as a Defense Best Left Untreated by Doctors
• D.Fever as a Failure of Body Temperature Control

Read the passage, then answer the question. Nearly all infants produce lactase, the enzyme that splits milk sugar in the small intestine, but in most of the world's adults its production falls sharply after weaning. Adults who lack the enzyme can feel bloating and cramps after drinking milk, because undigested lactose passes to the colon, where bacteria ferment it. In some populations, however, most adults continue making lactase throughout life. This trait, called lactase persistence, is common in northern Europe and in some herding peoples of East Africa and the Middle East, and it is rare in East Asia. Genetic studies have shown that the trait is caused by different mutations in different regions, each lying in a stretch of DNA that controls the lactase gene rather than in the gene itself. That several separate mutations produce the same result, and that each became common only in populations with a long history of keeping animals for milk, points to strong natural selection: where fresh milk was a reliable food, adults who could digest it had an advantage. Which of the following best states the main idea of the passage?

• A.Lactase persistence arose more than once and spread where digesting milk gave adults an advantage
• B.The mutations behind lactase persistence alter DNA that controls the gene, not the gene's own code
• C.Lactase persistence arose in northern Europe and was later carried to herding peoples of East Africa
• D.Adults who lack lactase feel discomfort because bacteria in the colon ferment the undigested lactose

Read the passage, then answer the question. Many people feel a sharp, brief pain when cold air or a cold drink touches an exposed root surface. The most widely accepted explanation is the hydrodynamic theory. Dentin, the tissue beneath the enamel of the crown and the cementum of the root, is riddled with microscopic tubules that run from its outer surface toward the pulp, and each tubule is filled with fluid. Normally the tubule openings are covered by enamel or cementum. When the gums recede and the thin cementum wears away, the openings are exposed. A stimulus such as cold, a blast of air, or a sugary solution then makes the fluid inside the tubules move rapidly, and this movement deforms nerve endings near the pulp, which fire and produce pain. Treatments for sensitivity follow from this chain of events. Some toothpastes contain potassium salts that make the nerve less excitable, reducing its response to the fluid movement. Others deposit minerals or other particles that plug the tubule openings. Based on the passage, a treatment that completely plugged the exposed tubule openings would most likely reduce sensitivity by

• A.keeping the drop in temperature from reaching the nerve endings near the pulp
• B.stopping a cold stimulus from setting the fluid inside the tubules in motion
• C.lowering how excitable the nerve endings near the pulp become when fluid moves
• D.reducing the amount of fluid held inside each tubule between surface and pulp

Read the passage, then answer the question. Some bacteria living on the back of the tongue convert nitrate, a compound abundant in leafy vegetables and also secreted in saliva, into nitrite. Once swallowed, nitrite can be converted in the body to nitric oxide, a molecule that relaxes blood vessels and lowers blood pressure. Nitric oxide made by this route adds to the supply that the lining of the blood vessels produces on its own. In small short-term trials, volunteers who used a strong antiseptic mouthwash for a week had much less nitrite in their saliva and blood plasma and showed small rises in blood pressure. Building on this work, a research team followed about 1,000 adults for three years and found that those who used mouthwash at least twice a day were more likely to develop high blood pressure than those who used it less often or not at all. The team concluded that frequent mouthwash use raises the risk of high blood pressure by killing the bacteria that convert nitrate. Which of the following findings, if true, would most weaken the team's conclusion?

• A.The frequent rinsers had less nitrite in their saliva than the people who rinsed less often
• B.The trial volunteers' blood pressure fell back to normal within days of stopping the rinse
• C.The frequent rinsers more often smoked and drank heavily, habits that raise blood pressure
• D.The people who ate the most leafy vegetables had the lowest blood pressure in the cohort

Read the passage, then answer the question. Xylitol is a sugar alcohol used to sweeten chewing gum. Unlike sucrose, it cannot be fermented to acid by Streptococcus mutans and related bacteria, and some laboratory studies suggest it may reduce their numbers in plaque. A school district wanted to know whether xylitol gum could reduce tooth decay among its students. At one school, all 200 children in the third and fourth grades chewed xylitol gum three times a day for two years; no other school took part. At the start and end of the study, the school's own dental hygienist, who knew the purpose of the study, examined each child and recorded new cavities. Over the two years, new cavities per child fell by about a third compared with the two years before the study began. During the same two years, the town began adding fluoride to its water supply. The district reported that the gum had cut decay by a third. Which change to the study's design would best rule out the fluoridated water as an explanation for the drop in cavities?

• A.Doubling the number of children who chewed the xylitol gum during the two years
• B.Measuring the S. mutans counts in each child's plaque at the start and the end
• C.Having an examiner who was unaware of the study's purpose record the cavities
• D.Following a similar group in the same town who chewed gum made without xylitol

Read the passage, then answer the question. The thyroid gland makes its hormones through a chain of steps that the brain constantly monitors. The hypothalamus releases thyrotropin-releasing hormone (TRH), which prompts the pituitary to secrete thyroid-stimulating hormone (TSH). TSH acts on the thyroid in two ways: it speeds hormone production, and, over a period of weeks, it makes the gland's cells grow and multiply. Inside the gland, the enzyme thyroid peroxidase attaches iodine to a large protein called thyroglobulin, a step without which no thyroxine (T4) can be formed. Thyroxine and its more active relative, T3, then circulate to nearly every tissue, raising the rate at which cells use energy. The loop closes because both hormones act back on the hypothalamus and pituitary, suppressing the release of TRH and TSH. When thyroid hormone levels fall, that suppression weakens and TSH rises; when they climb, TSH falls. In a healthy person this arrangement holds hormone levels steady, but it also explains why the gland itself can change size when something interferes with the chain. Suppose a drug fully blocked thyroid peroxidase in a person whose thyroid was otherwise healthy. Based on the passage, which outcome would be expected after several weeks of treatment?

• A.A lower TSH level, caused by the fall in thyroxine
• B.A normal thyroxine level, restored by a rise in TSH
• C.A smaller gland, since it has less hormone to make
• D.A larger gland, driven by a sustained rise in TSH

Read the passage, then answer the question. Xylitol is a sugar alcohol used to sweeten chewing gum. Unlike table sugar, it cannot be fermented by Streptococcus mutans, the bacterium most closely tied to tooth decay, so it does not feed the acid production that dissolves enamel. Some laboratory studies also report that S. mutans grows more slowly when xylitol is present. Interest in the sweetener rose after a survey of 1,200 schoolchildren in one district found that those who said they chewed xylitol gum at least once a day developed about 30 percent fewer new cavities over two years than those who did not. A local health board has cited the survey as evidence that daily xylitol gum prevents decay and has proposed handing the gum out in schools. Critics note that no child was assigned to chew gum; the children, or their parents, made that choice themselves. Critics add that chewing any gum stimulates saliva, which rinses away food and neutralizes acid. Which finding, if true, would most weaken the health board's conclusion that the xylitol gum itself produced the lower rate of new cavities?

• A.Daily chewers had about as many cavities as nonchewers when the survey began
• B.Daily chewers also brushed with fluoride toothpaste more often than nonchewers
• C.Daily chewers had fewer S. mutans in their saliva than nonchewers had in theirs
• D.Twice-daily chewers had fewer new cavities than chewers who chewed once each day

Read the passage, then answer the question. Sickle-cell disease results when a person inherits two copies of a variant hemoglobin gene, one from each parent. The variant protein tends to clump when oxygen levels fall, bending red blood cells into rigid crescents that block small vessels and break apart early. Before modern treatment, most children with the disease died young, usually before they could have children of their own. People who inherit only one copy, a condition called sickle-cell trait, are generally healthy. In the mid-twentieth century, researchers in East Africa noticed that the variant was common in lowland areas where malaria was widespread and rare in highland areas where it was not. Later studies showed that children with sickle-cell trait who catch the malaria parasite are much less likely than other children to develop the severe, often fatal form of the illness. The protection is not complete; carriers can still be infected and can still fall ill. How the variant protects is still debated, though one proposal is that infected cells sickle and are removed by the spleen before the parasite can multiply. Which of the following conclusions is most strongly supported by the passage?

• A.The variant gene swaps a single amino acid in the beta chain of hemoglobin
• B.The spleen's removal of sickled cells is why variant carriers survive malaria
• C.Malaria likely sustains the variant though two copies were often fatal
• D.Variant carriers who catch malaria are likely to show no symptoms of it

Read the passage, then answer the question. When a blood vessel is cut, the body's response is often described by its most visible result, the clot, but the clot is a late arrival. Its framework is fibrin, a meshwork of protein threads that forms when the enzyme thrombin cuts a soluble plasma protein, fibrinogen, into sticky fragments that link together. Thrombin itself is the end product of a cascade of clotting factors, each activating the next, which is set off when blood meets tissue factor, a protein exposed by the injury. Well before any of this, within seconds of the cut, smooth muscle in the vessel wall contracts, narrowing the vessel and slowing the loss of blood. Platelets then stick to collagen fibers exposed in the damaged wall and release chemicals that draw in more platelets, forming a loose plug; the surfaces of these activated platelets also provide sites where the clotting factors assemble. Once fibrin has reinforced the plug, the platelets pull on the threads and the clot shrinks, drawing the wound's edges closer. Days later, as the vessel heals, an enzyme called plasmin dissolves the fibrin. According to the passage, which event occurs immediately before fibrinogen is cut into sticky fragments?

• A.Clotting factors activate one another until thrombin is made
• B.Platelets pull on the fibrin threads so that the clot then shrinks
• C.Smooth muscle in the vessel wall contracts to narrow the vessel
• D.Platelets gather into a loose plug where clotting factors assemble

Read the passage, then answer the question. The autonomic nervous system controls internal organs without conscious effort, and its two divisions usually pull in opposite directions. The sympathetic division prepares the body for exertion or emergency: it speeds the heart, widens the airways, and slows digestion. Its fibers leave the spinal cord in the chest and upper abdominal regions and almost at once enter chains of ganglia, clusters of nerve cell bodies lying just beside the spinal column, so the first neuron in each pathway is short and the second is long. The parasympathetic division favors rest and digestion, slowing the heart and stimulating the gut. Its fibers leave from the brainstem and from the lowest part of the spinal cord and travel nearly all the way to the target organ before reaching a ganglion, so its first neuron is long and its second is short. In both divisions, the first neuron releases acetylcholine onto the second. The divisions part ways again at the organ: most sympathetic second neurons release norepinephrine there, while parasympathetic second neurons release acetylcholine. Because many organs receive fibers from both divisions, their activity at any moment reflects the balance between the two. According to the passage, the sympathetic and parasympathetic divisions are alike in

• A.the part of the nervous system where the fibers of each pathway set out
• B.the place where the ganglia of each pathway sit relative to its organ
• C.the chemical that the first neuron of each pathway passes to the second
• D.the chemical that the second neuron of each pathway releases at its organ

Read the passage, then answer the question. Biochemists sort reversible enzyme inhibitors by how they change two measurements. Vmax is the fastest rate an enzyme can reach when substrate is plentiful. Km is the substrate concentration at which the rate is half of Vmax, so a higher Km means the enzyme needs more substrate to work at half its top speed. A competitive inhibitor resembles the substrate and occupies the active site; because enough substrate can crowd it out, it leaves Vmax unchanged but raises Km. A noncompetitive inhibitor binds elsewhere on the enzyme, whether or not substrate is present, and disables it. Extra substrate cannot rescue the disabled molecules, so Vmax falls, while Km stays the same because the enzymes still working bind substrate normally. An uncompetitive inhibitor binds only to an enzyme that already holds substrate, locking the pair together; this lowers Vmax and also lowers Km. Plotting reaction rate against substrate concentration, with and without the inhibitor, is usually enough to tell the three types apart. Without compound X, an enzyme's top rate is 80 units, and a rate of 40 units is reached at 5 mM substrate. With X added, the top rate is 40 units, and a rate of 20 units is reached at 5 mM. Under the passage's scheme, X is best classified as

• A.competitive, since more substrate is now needed for a rate of 40 units
• B.competitive, since it slowed the reaction even at only 5 mM substrate
• C.noncompetitive, since half its new top rate was still reached at 5 mM
• D.uncompetitive, since both its top rate and its Km went down

Read the passage, then answer the question. For more than a century the human appendix was held up as a textbook vestige, a shrunken remnant of a larger gut pouch that once helped our plant-eating ancestors digest tough leaves. Charles Darwin made this case, and the organ's habit of becoming inflamed, sometimes fatally, seemed to show that it served no purpose worth the risk. A growing number of researchers now argue that the appendix earns its keep. The organ is rich in lymphoid tissue, the kind that helps the immune system sample and respond to gut microbes. Its narrow, dead-end shape may let it shelter a film of helpful bacteria that can repopulate the large intestine after a bout of severe diarrhea flushes the gut. A comparison across mammal species found that an appendix has evolved independently many separate times and has rarely been lost once it appeared, a pattern hard to explain if the organ were useless. Removing the appendix remains a safe and common operation, and most people who have one show no obvious ill effects afterward, a point that defenders of the vestige view continue to raise. In the passage, the statement that most people show no obvious ill effects after the appendix is removed functions as

• A.a fact that critics of the author's view cite and the author admits
• B.a fact that shows the organ's risks outweigh the benefits it brings
• C.a fact that supports the author's view that the organ has a purpose
• D.a fact that explains why the organ was first considered a vestige

Read the passage, then answer the question. A fever is not simply the body overheating. The hypothalamus, a small region at the base of the brain, normally holds core temperature near 37 °C by comparing signals from temperature sensors with an internal reference value, much as a home thermostat compares room temperature with its setting. During an infection, immune cells release signaling molecules that cause the hypothalamus to produce prostaglandin E2, and this chemical, in effect, turns the dial up. The body now treats its normal temperature as too cold. Blood vessels in the skin narrow, the person feels chilled and may shiver, and heat is conserved until core temperature reaches the new reference value, perhaps 39 °C. When the infection subsides and prostaglandin levels drop, the dial returns to its usual position, and the same mechanisms run in reverse: skin vessels widen and the person sweats, shedding the excess heat. Drugs such as aspirin and ibuprofen reduce fever by blocking prostaglandin production. Heatstroke is different: there the reference value is unchanged, but heat gain overwhelms the body's ability to shed it. In the passage, the phrase "turns the dial up" refers to

• A.a rise in core body temperature produced by shivering muscles
• B.a rise in the body's output of prostaglandin E2 in the hypothalamus
• C.a rise in the setting that core temperature is held to
• D.a rise in heat gain that overwhelms the body's means of shedding it

Read the passage, then answer the question. Nearly every cell in the body keeps time with a molecular clock, but the cells take their cue from a master clock, a small cluster of neurons in the hypothalamus called the suprachiasmatic nucleus. Each morning, light reaching the eyes resets this master clock, and the daily reset keeps the body's roughly daily cycles of temperature, hormone release and sleepiness locked to the 24-hour day. Researchers have asked what happens when that reset is taken away. In studies in which volunteers lived for weeks in rooms with no windows, clocks or other time cues, the cycles did not fade. Free-running, they kept a steady rhythm, but one that no longer matched the day: in most people it averaged slightly longer than 24 hours, about 24.2 hours, so each day the volunteers woke a little later by the outside clock. Many totally blind people, whose eyes cannot pass light signals to the brain, experience the same drift in ordinary life, with spells of insomnia and daytime sleepiness whenever their internal cycle falls out of step with the world. As used in the passage, the term "free-running" describes a cycle that

• A.shifts at random so that no two days are the same length
• B.speeds up once the body is released from outside control
• C.follows whatever schedule of activity the person chooses
• D.keeps its own period because nothing resets it each day

Read the passage, then answer the question. Sore throats are among the most common reasons students visit a campus clinic, and in otherwise healthy young adults most are caused by viruses and fade within about a week. Researchers at one university health center wanted to know whether a lozenge containing zinc and honey shortens this illness. They enrolled 220 students who arrived within a day of their first symptoms, a group large enough, by the team's own calculation, to detect even a modest effect. Every student received the lozenges and was told to dissolve one every three hours while awake. Each morning, research nurses who had not been told the purpose of the study scored symptom severity on a standard ten-point scale, and students also reported how their throats felt. By the seventh day, 82 percent of the students said their throats felt normal, and the average nurse-rated score had fallen by more than two-thirds. The team concluded that the lozenge "substantially speeds recovery" and recommended it to the student body. Based on the passage, which weakness in the study most directly undermines the team's conclusion?

• A.The study gave all students the lozenge, so no untreated group was compared
• B.The study enrolled only healthy young adults, not older or sicker patients
• C.The study relied on students' own reports of whether their throats felt normal
• D.The study never checked that students took a lozenge every three hours awake

Read the passage, then answer the question. The light microscope opened up the cellular world, but it has a hard limit. Because light behaves as a wave, a lens cannot focus it to an infinitely small point; each point of an object is imaged as a tiny blurred disk. When two points lie closer together than about 200 nanometers, roughly half the wavelength of visible light, their disks overlap so much that they merge into one. No adjustment of the focus separates them, and a light microscope therefore cannot resolve structures closer than that, however much the image is magnified; enlarging it further only produces a bigger blur, which microscopists call empty magnification. This is why the ribosomes in a cell, each about 25 nanometers across, appear in a light microscope only as a faint graininess, if at all. Electron microscopes overcame the limit by using beams of electrons, whose wavelengths are thousands of times shorter than those of light. Since the 1990s, techniques known as super-resolution fluorescence microscopy have also found ways around it, by switching neighboring fluorescent molecules on at different moments so that each can be located on its own. As used in the passage, the word "resolve" most nearly means

• A.enlarge to a larger visible size
• B.detect as present in the sample
• C.bring into a sharp, clear focus
• D.show as distinct, separate items

Read the passage, then answer the question. In a small population, the frequency of an allele can change from one generation to the next purely by chance, a process called genetic drift. Imagine a population of ten wildflowers in which half the plants carry an allele for white petals. If, by luck, the white-flowered plants happen to leave more seeds one year, the allele becomes more common; if they leave fewer, it becomes rarer. Over many generations these random swings add up, and eventually one of two things happens: the allele disappears entirely, or it becomes fixed. Once an allele is fixed, drift can no longer alter its frequency, because there is no variation left for chance to act on; only a new mutation, or migrants carrying a different allele, could restore the alternative. Drift operates in large populations too, but far more slowly, because random gains and losses spread across many individuals tend to cancel out. For this reason, small isolated populations often lose genetic variation quickly, even when none of the alleles they lose is harmful. As used in the passage, the word "fixed" most nearly means

• A.favored by selection, so that it spreads faster than others
• B.carried by most plants, so that it is the common form
• C.carried by all plants, so that no alternative remains
• D.held steady at half the plants, neither rising nor falling

Read the passage, then answer the question. Most enzymes in the human body work best near 37 degrees Celsius, and heating them much above that temperature unfolds their chains and destroys their activity. Bacteria that live in hot springs are a striking exception. Thermus aquaticus, first isolated from a hot spring in Yellowstone National Park, grows at about 70 degrees Celsius, and its DNA polymerase, known as Taq, keeps working after repeated heating to about 95 degrees. That stability made Taq the enzyme of choice for the polymerase chain reaction, or PCR, a laboratory method that copies a stretch of DNA millions of times by cycling the reaction mixture between hot and cooler temperatures; an ordinary polymerase would be destroyed in the first hot step. Even so, Taq is not a perfect copier. It lacks the proofreading activity that allows many other polymerases to remove a wrongly paired nucleotide, so it introduces errors at a higher rate. Laboratories that need highly accurate copies therefore often use polymerases from other heat-loving microbes that do proofread. In the passage, the phrase "Even so" primarily serves to

• A.reverse the case for Taq as the enzyme of choice for PCR
• B.qualify the claim that Taq survives repeated heating to 95
• C.admit a weakness that remains despite the enzyme's merits
• D.mark an exception to the rule about heat and most enzymes

Identify the sentence that correctly uses subject-verb agreement in a complex context.

• A.The list of approved sealants were posted on the wall.
• B.Neither the dentists nor the aide have signed the log.
• C.A tray of sterile mirrors sits beside the second sink.
• D.Each of the four operatories need a new suction valve.

Choose the sentence that accurately uses a semicolon to connect closely related independent clauses.

• A.The office ordered new loupes; to replace the old, scratched eyepieces.
• B.The scaler tip buzzed loudly; therefore, the patient requested a break.
• C.The child sat quietly; while, the hygienist counted each primary tooth.
• D.The gums bled slightly; and, the concerned patient noted no discomfort.

Identify the sentence that demonstrates the correct use of commas in a list that includes conjunctions.

• A.Her setup tray holds mirrors, explorers, probes, and sharp scalers.
• B.The supply cabinet stores bandages, gloves, wax and, paper napkins.
• C.The team restocks, the gloves, masks, and disposable gowns nightly.
• D.Our patients brush, floss, and gargle, before each routine checkup.

Which sentence correctly uses a relative clause to provide additional information?

• A.The dentist, that trained abroad, now leads our weekly case reviews.
• B.This new mouthwash, which it reduces plaque, tastes much too bitter.
• C.The digital sensor, who broke last Friday, sits inside the cupboard.
• D.Our autoclave, which runs each night, holds two full cassette trays.

Select the sentence that correctly employs an appositive phrase to add detail.

• A.The senior hygienist, she trained in Boston, joins the clinic today.
• B.The lab technician, and a trained ceramist, will finish the veneers.
• C.The newest staff hire, a seasoned periodontist, starts in late June.
• D.The oral surgeon, who a retired paramedic, arrives here next Monday.

Identify the sentence that correctly uses the passive voice for emphasis.

• A.The sharp instruments was sorted by the new sterile tech.
• B.The recall reminder was mailed by our front office staff.
• C.The instrument trays got broke down by the weekend staff.
• D.The x-ray sensor been wiped by the assistant last Monday.

Choose the sentence that accurately uses conditional sentences to discuss hypothetical situations.

• A.If the sealant cracked, the tooth would need a restoration.
• B.If the patient flosses daily, the gums would have improved.
• C.If the curette had slipped, the tissue will have blistered.
• D.If she would have flossed, her teeth stayed much healthier.

Which sentence correctly uses the subjunctive mood to express a wish or hypothetical situation?

• A.She wishes she was born with much stronger tooth enamel.
• B.He wishes he studied harder before the state board exam.
• C.The dentist insists that she brushes twice each day now.
• D.I would reorder supplies if I were the senior hygienist.

Identify the sentence that correctly employs modifiers to clarify meaning.

• A.Rinsing the sink, the mouthwash spilled across the white floor.
• B.The dentist warned the patients after lunch to floss carefully.
• C.The assistant handed the mirror carefully to the nervous child.
• D.She almost polished each tooth within the lower right quadrant.

Select the sentence that demonstrates the correct use of an infinitive phrase.

• A.The purpose of this project is to reducing gum disease.
• B.The practice hopes to open a second office next spring.
• C.To find a good dentist, it requires plenty of patience.
• D.She looks forward to meet the new front office manager.

Which sentence accurately uses a dangling modifier and needs correction?

• A.Adjusting the operatory lights, the senior assistant discovered hidden calculus.
• B.Reviewing the recent radiographs, the approximal caries escaped early detection.
• C.Charting the pocket depths, the attentive hygienist recorded marginal recession.
• D.Polishing the mandibular crowns, the diligent student removed stubborn staining.

Choose the sentence that demonstrates incorrect use of a conjunction and needs correction.

• A.The assistant neither completed the wrapping nor sealed the sterile pouches.
• B.The student neither reviewed the charting nor measured the buccal recession.
• C.The clerk neither processed the billing nor scanned the insurance referrals.
• D.The hygienist neither polished the margins nor scaling the posterior molars.

Identify the sentence that correctly employs the use of an Oxford comma for clarity in a series.

• A.The hygienist debrided the quadrant, recorded the bleeding, and polished the amalgams.
• B.The assistant wiped the counters, restocked the bibs, and sterilizing the instruments.
• C.The dentist checked the crowns, reviewed the films, and bitewing interpretation notes.
• D.The student documented the crowding, described the attachment, and the chart remained.

Which sentence demonstrates the correct use of a colon to introduce a list?

• A.The new morning huddle briefly reviews: scheduling, conflicts, referrals, and emergencies.
• B.The afternoon sterilization cycle finishes with: washing, drying, wrapping, and packaging.
• C.The recall appointment covers several tasks: scaling, polishing, charting, and varnishing.
• D.The surgical cassette waiting for extractions: forceps, elevators, hemostats, and sutures.

Select the sentence that accurately uses a nonrestrictive clause to add information.

• A.The oral rinse that contains chlorhexidine carries a printed prescription label.
• B.The adhesive which bonds to etched enamel requires continual moisture isolation.
• C.The instrument, that reaches deep pockets, belongs inside the sterile cassettes.
• D.The sterilizer, which cycles unattended overnight, needs a validated spore test.

Identify the sentence that correctly uses a hyphen in a compound adjective.

• A.The practice hired a well-trained hygienist before the evening recall sessions.
• B.The trainee opened a newly-sterilized cassette before the second morning visit.
• C.The dentist ordered a highly-polished handpiece from the local dental supplier.
• D.The student filed a poorly-scanned radiograph inside the wrong patient folders.

Choose the sentence that correctly avoids a split infinitive.

• A.The clinician hopes to quickly finish after the bridge preparation begins.
• B.The office plans to gradually reopen after the operatory repairs conclude.
• C.The patient attempts to rinse thoroughly after the fluoride varnish dries.
• D.The student wants to correctly respond after the clinical instructor asks.

Identify the sentence that correctly uses a possessive pronoun.

• A.The owner decided its unfair after the insurance company refused coverage.
• B.The practice revised its handbook after the annual state inspection ended.
• C.The hygienist realized its unusual after the second sealant cracked early.
• D.The assistant reported its overdue after the compressor alarm rang loudly.

Select the sentence that accurately employs ellipsis to indicate an omission.

• A.The frightened child whispered, "The scaler...feels strange against my teeth."
• B.The elderly patient complained, "The drilling...bothers me during each visit."
• C.The dental assistant hesitated, "The sensor...shifted while the child turned."
• D.The printed manual states, "The sealant...shields molars against early decay."

Identify the sentence that correctly uses quotation marks for titles of short works.

• A.She quoted the article "Pediatric Fluoride Varnish Application Guidelines" during her lecture.
• B.She praised the textbook "Clinical Periodontology Treatment Planning Manual" during her class.
• C.She consulted the journal "Modern Dental Materials Quarterly Reviews" during her presentation.
• D.She screened the documentary "Silent Epidemic Threatening Young Children" during her training.

Choose the sentence that correctly uses a comma to set off a tag question.

• A.The autoclave, finished its cycle before the morning huddle didn't it?
• B.The clear sealant hardening quickly under the bright light, didn't it?
• C.The flowable bonding resin cured under the operatory light, didn't it?
• D.The patient rinsed, before the student applied the varnish didn't she?

Identify the sentence that correctly uses "who" or "whom" in a question.

• A.Whom did the assistant assume scheduled the emergency extraction visits?
• B.Whom did the committee appoint despite the repeated calendar objections?
• C.Whom did the instructors believe misplaced the sterilization logs today?
• D.Whom did the coordinator think submitted the duplicate insurance claims?

Which sentence correctly uses a complex sentence to describe a condition and its outcome?

• A.If the patient flosses regularly, a reduced index appears before the recall.
• B.If the sealant cracks early, a lengthy repair appointment before the recall.
• C.If the varnish dries slowly, a thick patchy coating across the restorations.
• D.If the scaler vibrates loudly, a possible bearing fracture inside the motor.

Identify the sentence that correctly demonstrates the use of a predicate adjective.

• A.The unusually swollen tissue was clearly bleeding after the probing appointment.
• B.The freshly polished enamel was sharply reflecting the operatory overhead light.
• C.The carefully charted pocket depths were slowly exceeding the acceptable ranges.
• D.The inflamed periodontal tissue was noticeably firmer after the initial scaling.

Choose the sentence that accurately uses a restrictive clause to define a specific element.

• A.The dental floss, which glides between contacts, arrives in waxed varieties.
• B.The prophy paste that contains fine pumice removes extrinsic surface stains.
• C.The topical ointment, that numbs soft tissues, works within several minutes.
• D.The scaler insert which reaches deep calculus needs gentle sterile cleaning.

Identify the sentence that correctly uses an absolute phrase.

• A.Her stomach growled loudly, the assistant scurried through the instrument trays.
• B.Her pager vibrated loudly, the receptionist moved toward the sterilization area.
• C.Her gloves securely fastened, the hygienist reclined the padded operatory chair.
• D.Her shoulders ached badly, the student repositioned the rolling operatory stool.

Which sentence correctly uses a gerund phrase as the subject?

• A.Bleeding gums signal inflammation from the reddened marginal papillae.
• B.Erupting molars displace premolars during the mixed primary dentition.
• C.Aching incisors indicate lesions beneath the existing amalgam margins.
• D.Polishing restorations removes stain from the visible enamel surfaces.

Select the sentence that correctly uses an infinitive phrase to express purpose.

• A.The assistant returned early to restock the sterilization supply cabinets.
• B.The receptionist decided quickly to reschedule the busy afternoon columns.
• C.The technician forgot completely to calibrate the panoramic imaging units.
• D.The student refused firmly to duplicate the blurred radiographic exposure.

Identify the sentence that demonstrates the correct use of a participle phrase for description.

• A.Sharpening the curette carefully, the cassette stored the instruments.
• B.Explaining the procedure gently, the hygienist reassured the children.
• C.Sterilizing the handpiece quickly, the cabinet remained totally empty.
• D.Charting the attachment quickly, the probes scratched the restoration.

Choose the sentence that employs a correlative conjunction correctly.

• A.Fluoride not only strengthens enamel but also improved acid defense.
• B.Scaling not only removes calculus but also smoother dental surfaces.
• C.Sealants not only protect fissures but also reduce replacement cost.
• D.Varnish not only covers dentin but also reduced sensitivity reports.

Which sentence correctly uses a modal auxiliary to express necessity?

• A.The sharps must be discarded inside locking containers, since regulations demand logs.
• B.The autoclave must be running unusually short cycles, since indicators changed colors.
• C.The patient must be skipping frequent flossing sessions, since heavier plaque appears.
• D.The compressor must be leaking beneath heavy cabinets, since pressure drops overnight.

Identify the sentence that accurately uses a prepositional phrase to indicate location.

• A.The insurance statements circulate in the seventh week of the semester.
• B.The treatment discussion proceeds in the opening minutes of the visits.
• C.The bonding technique improves in the closing months of the internship.
• D.The replacement handpieces rest in the second drawer of the sterilizer.

Select the sentence that correctly uses a determiner in a specific context.

• A.The receptionist scheduled an one-hour recall for the anxious young child.
• B.The hygienists selected a interdental brush for the wide molar embrasures.
• C.The dentists ordered an ultrasonic scaler for the busy surgical operatory.
• D.The assistant opened a instrument cassette for the busy afternoon clinics.

Which sentence correctly uses a quantifier with countable nouns?

• A.Much hygienists complete fluoride training before the summer break begins.
• B.Many hygienists renew clinical licenses before the annual state deadlines.
• C.Many equipment requires annual repair before the yearly safety inspection.
• D.Much sealants safeguard the occlusal fissures from early carious cavities.

Identify the sentence that correctly uses a conjunction to connect an independent and a dependent clause.

• A.Although the patient brushes nightly, a visible film persists across the arches.
• B.Although the sealant hardened quickly, a faint yellow coating across the enamel.
• C.Although the appointment ran late, a lengthy unusual delay inside the reception.
• D.Although the scaler vibrated loudly, a steady coolant stream inside the turbine.

Identify the sentence that accurately uses complex prepositions to indicate time relationships.

• A.Before the appointment ended, he noted the bleeding in his chart.
• B.In spite of the delay, she polished the largest quadrant quickly.
• C.In advance of the surgery, she reviewed his full medical history.
• D.By means of the mirror, she inspected behind both lower incisors.

Choose the sentence that correctly employs subjunctive mood to express a hypothetical situation or wish.

• A.If the hygienist was on call, he would take the impression now.
• B.She wishes she was a little better at flossing after each meal.
• C.If the clinic opens at seven, the office can see more patients.
• D.If he were a dentist, he would recommend a checkup each spring.

Identify the sentence that demonstrates the correct use of inverted syntax for emphasis.

• A.Rarely do patients replace a toothbrush before the bristles fray.
• B.Often patients delay their checkup until the gums start bleeding.
• C.Quickly the plaque returns between the crowded lower front teeth.
• D.Yesterday the dentist photographed a hairline crack in her molar.

Which sentence correctly uses an adverbial clause to indicate cause?

• A.When the visit finally ended, she booked a second cleaning today.
• B.Because she flossed each night, her gums healed within six weeks.
• C.Although the swelling worsened, he refused to try a milder rinse.
• D.If the sealant chips again, the practice will replace it quickly.

Select the sentence that accurately employs ellipsis for dramatic effect.

• A.The clinic opens at eight... and closes at five each afternoon.
• B.The consent form... the signature of a parent and today's date.
• C.The dentist read the report twice... then set it quietly aside.
• D.The label says to rinse for thirty seconds... twice each night.

Which sentence contains a nonstandard expression that should be replaced in formal academic writing?

• A.The solvent, being highly inflammable, was stored well away from the burner.
• B.The samples, irregardless of storage temperature, degraded within one week.
• C.The results, inasmuch as the sample was small, should be read with caution.
• D.The cultures, notwithstanding the brief power outage, grew at the usual rate.

A researcher uses a solution with a 15\% concentration of a certain substance. If she needs 2 liters of a 45\% concentration, how much of the 15\% solution should she use if she plans to evaporate the water to increase the concentration to the desired level?

• A.6 liters
• B.3 liters
• C.4 liters
• D.5 liters

In a sequence, the nth term is given by the formula $3n^2 - 2n + 1$. What is the 5th term?

• A.76
• B.66
• C.86
• D.96

If the odds against an event are 5 to 3, what is the probability that the event will occur?

• A.$\frac{3}{8}$
• B.$\frac{5}{8}$
• C.$\frac{3}{5}$
• D.$\frac{5}{3}$

A set of data has a mean of 50 and a standard deviation of 5. If all values in the set are increased by 10, what will be the new mean and standard deviation?

• A.Mean: 60, standard deviation: 15
• B.Mean: 60, standard deviation: 5
• C.Mean: 50, standard deviation: 15
• D.Mean: 50, standard deviation: 5

A rectangle's length is three times its width. If the perimeter is 64 cm, what are the rectangle's dimensions?

• A.Length: 24 cm, Width: 8 cm
• B.Length: 15 cm, Width: 5 cm
• C.Length: 18 cm, Width: 6 cm
• D.Length: 21 cm, Width: 7 cm

A car travels 150 miles in 2.5 hours. What is its average speed in miles per hour?

• A.70 mph
• B.60 mph
• C.80 mph
• D.90 mph

A sequence is defined as $a_n = 3^n + 2^n$. What is $a_4$?

• A.73
• B.97
• C.81
• D.89

If $3x - 7 < 2(x + 4)$, what is the range of possible values for $x$?

• A.$x > 15$
• B.$x > 11$
• C.$x < 15$
• D.$x < 11$

What is the coefficient of $x^3$ in the expansion of $(2x - 1)^4$?

• A.$-32$
• B.$-64$
• C.$-48$
• D.$-16$

A rectangle's length is twice its width, and its area is $128$ square cm. What is the perimeter of the rectangle?

• A.32 cm
• B.40 cm
• C.48 cm
• D.56 cm

In how many ways can 5 books be arranged on a shelf if two of the books must stay together?

• A.24
• B.72
• C.96
• D.48

A tank is filled by Pipe A in 3 hours and by Pipe B in 6 hours. When both pipes are opened together, how long will it take to fill the tank?

• A.2.0 hours
• B.2.5 hours
• C.3.0 hours
• D.3.5 hours

If $5^x = 125$ and $5^y = 1/25$, what is the value of $x + y$?

• A.0
• B.1
• C.2
• D.3

What is the smallest positive integer value of $n$ for which $2^n > 1,000$?

• A.9
• B.11
• C.10
• D.12

If $x^3 - 6x^2 + 11x - 6 = 0$, what are the sum and product of its roots?

• A.Sum = +6, Product = +6
• B.Sum = +6, Product = -6
• C.Sum = -6, Product = +6
• D.Sum = -6, Product = -6

A set contains all integers $x$ such that $2 < x^2 < 50$. How many elements are in the set?

• A.10
• B.11
• C.12
• D.13

If the interquartile range of a data set is 15 and the range is 30, what is the minimum possible number of elements in the set?

• A.4
• B.5
• C.6
• D.7

A survey conducted on a sample of 1000 people found that 60\% prefer tea over coffee. If the margin of error is 4\%, what is the confidence interval for the population proportion who prefer tea?

• A.58\% to 62\%
• B.56\% to 64\%
• C.60\% to 64\%
• D.56\% to 60\%

If a fair die is rolled twice, what is the probability that the sum of the two rolls is 9?

• A.$\frac{2}{36}$
• B.$\frac{3}{36}$
• C.$\frac{4}{36}$
• D.$\frac{5}{36}$

A line intersects the $x$-axis at $(4,0)$ and the $y$-axis at $(0,2)$. What is the area of the triangle formed by the line and the coordinate axes?

• A.2
• B.4
• C.6
• D.8

When interpreting a complex chart that tracks the progression of gum disease in patients over time, which of the following abilities is MOST important for understanding the chart's data?

• A.Converting the plotted units to a different scale
• B.Grouping the patients by the practice they attend
• C.Relating each plotted value to the earlier points
• D.Deciding what other chart would display the trend

When interpreting a complex chart detailing the pH levels in the mouth after consuming various foods, which skill is MOST essential?

• A.Recalling each food's acid level without the chart
• B.Ranking the sampled foods by their calorie content
• C.Reading the values straight off each plotted curve
• D.Naming the acids released inside each sampled food

When interpreting a chart that compares the fluoride release rate of different dental materials, which aspect is MOST crucial for understanding the long-term efficacy of the materials?

• A.The units the chart uses to report the released fluoride
• B.The count of materials the chart lists within its legend
• C.The medium the samples rest inside for the fluoride test
• D.The number of days the chart displays along the baseline

A dental hygiene clinic has 250 milliliters of a 4 percent antiseptic solution. To prepare a 1 percent rinse, water is added without changing the amount of antiseptic. How many milliliters of water must be added?

• A.250 milliliters
• B.500 milliliters
• C.1,000 milliliters
• D.750 milliliters

Instruments in a sterilization tray are sorted into scalers and probes in a ratio of 3 to 5. If the tray holds 64 instruments total, how many are probes?

• A.24
• B.32
• C.40
• D.48

A student's first five quiz scores have a mean of 82. After a sixth quiz, the mean of all six scores drops to 80. What score did the student earn on the sixth quiz?

• A.64
• B.70
• C.76
• D.82

The numbers of patients seen by a hygienist over seven days were 12, 7, 9, 15, 7, 20, and 11. What is the median number of patients seen per day?

• A.11
• B.9
• C.13
• D.15

A jar contains 4 blue and 6 red toothbrushes. If two toothbrushes are drawn at random without replacement, what is the probability that both are blue?

• A.3 over 25
• B.4 over 25
• C.1 over 15
• D.2 over 15

For which values of x is the inequality 5 minus 2x greater than or equal to 11 true?

• A.x is no less than negative 8
• B.x is no more than negative 3
• C.x is no less than negative 3
• D.x is no more than negative 8

What is the sum of all solutions to the equation absolute value of (2x minus 5) equals 9?

• A.9
• B.5
• C.2
• D.7

Simplify the expression (2 to the 3rd power times 2 to the 5th power) divided by 2 squared. What is the result?

• A.2 to the 8th power
• B.2 to the 3rd power
• C.2 to the 6th power
• D.2 to the 4th power

A dental supply item priced at $200 is first marked up by 20 percent, then the new price is discounted by 15 percent. What is the final price?

• A.$240
• B.$170
• C.$276
• D.$204

A clinic's appointment log shows that 3 cleanings together took 75 minutes, and each cleaning takes the same amount of time. Based on this rate, how long should 8 cleanings take?

• A.200 minutes
• B.120 minutes
• C.240 minutes
• D.160 minutes

Evaluate (3.2 × 10^-4)(5 × 10^6) ÷ (8 × 10^-3) and express the result in scientific notation.

• A.2 × 10^4
• B.2 × 10^7
• C.2 × 10^-1
• D.2 × 10^5

In a large dental group, the ratio of hygienists to assistants is 3 to 4, and the ratio of assistants to front-desk staff is 6 to 5. If the group employs 90 hygienists, how many front-desk staff does it employ?

• A.150
• B.100
• C.81
• D.144

Each of the following quadratic equations has two distinct real solutions EXCEPT:

• A.3x^2 + 7x + 4 = 0
• B.5x^2 + 9x + 4 = 0
• C.4x^2 - 9x + 5 = 0
• D.2x^2 - 5x + 4 = 0

Young's rule estimates a child's dose C from the adult dose A and the child's age a in years: C = A × a / (a + 12). Solved for the age a, which expression is correct?

• A.12C / (C - A)
• B.12A / (C - A)
• C.12A / (A + C)
• D.12C / (A - C)

A clinic recorded 200 patients. Of the 60 smokers, 36 had gingivitis; of the 140 nonsmokers, 42 had gingivitis. If a patient with gingivitis is chosen at random, what is the probability, to the nearest whole percent, that the patient is a smoker?

• A.46 percent
• B.30 percent
• C.18 percent
• D.60 percent

A table shows the percent of a clinic's child patients with untreated caries: 48 percent in 2023, 40 percent in 2024, and 36 percent in 2025. By what percent did this rate decrease from 2023 to 2025?

• A.25 percent
• B.about 27 percent
• C.12 percent
• D.about 33 percent

A supply table lists four chlorhexidine rinse bottles: 240 mL for $4.20, 473 mL for $9.46, 1,000 mL for $18.50, and 1.89 L for $36.00. Which bottle has the lowest cost per milliliter?

• A.The 473 mL bottle at $9.46
• B.The 1,000 mL bottle at $18.50
• C.The 240 mL bottle at $4.20
• D.The 1.89 L bottle at $36.00

A clinic's yearly patient survey reports the share of patients who say they floss daily: 2023, 16 percent; 2024, 20 percent; 2025, 24 percent. By what percent did the share of daily flossers increase from 2023 to 2025?

• A.33 percent
• B.25 percent
• C.50 percent
• D.8 percent

A hygienist needs 200 mL of a 15 percent solution but has only a 10 percent solution and a 30 percent solution on hand. To the nearest mL, how many mL of the 30 percent solution should be used in the mixture?

• A.67 mL
• B.100 mL
• C.150 mL
• D.50 mL

Restocking a clinic's supply room takes Assistant A 6 hours working alone, Assistant B 12 hours alone, and Assistant C 4 hours alone. A and B start together at 9:00 AM, and C joins them at 10:00 AM. Working at these steady rates, at what time do they finish?

• A.12:00 PM
• B.1:00 PM
• C.11:30 AM
• D.11:00 AM

The price of a case of nitrile gloves rises 25 percent in March and then another 20 percent in June. In September, the clinic negotiates a 30 percent discount off the June price. Compared with the price before March, the September price is how much higher?

• A.20 percent higher
• B.15 percent higher
• C.5 percent higher
• D.1.5 percent higher

A clinic's continuing-education budget was cut by 20 percent one year and then increased by 20 percent the next year. The budget is now $5,760. What was the budget before the cut?

• A.$5,990.40
• B.$6,000.00
• C.$5,760.00
• D.$5,529.60

A medication order calls for 1.5 mg per kilogram of body weight. The drug is supplied as 25 mg per mL, and the patient weighs 110 pounds. Using 1 kg = 2.2 lb, how many mL should be drawn up?

• A.14.5 mL
• B.3.0 mL
• C.6.6 mL
• D.0.3 mL

A rectangular instrument tray measures 10 inches by 6 inches. Using 1 inch = 2.54 centimeters, what is the tray's area in square centimeters, to the nearest whole number?

• A.387 square centimeters
• B.152 square centimeters
• C.305 square centimeters
• D.24 square centimeters

Three sections took the same dental terminology quiz. Section 1 had 18 students with a mean of 84, Section 2 had 12 students with a mean of 74, and Section 3 had 10 students. The mean for all 40 students was 79. What was the mean score of Section 3?

• A.78
• B.82
• C.79
• D.76

A hygienist deposits $4,000 in an account that pays 5 percent annual interest, compounded semiannually. No other deposits or withdrawals are made. How much interest has the account earned after 3 years, to the nearest cent?

• A.$638.77
• B.$600.00
• C.$307.56
• D.$630.50

A line graph shows the cell count of a yeast culture, in thousands of cells per milliliter, measured every 2 hours: 200 at hour 0, 480 at hour 2, 1,100 at hour 4, 1,750 at hour 6, and 2,000 at hour 8. Between which two consecutive readings was the percent increase in the cell count greatest?

• A.From hour 4 to hour 6
• B.From hour 2 to hour 4
• C.From hour 0 to hour 2
• D.From hour 6 to hour 8

A table lists applicants and admissions for three dental hygiene programs: Program A, 80 applicants and 36 admitted; Program B, 150 applicants and 60 admitted; Program C, 50 applicants and 24 admitted. Which statement is NOT supported by the table?

• A.Program A admitted a larger share of its applicants than Program C did.
• B.Program B rejected more applicants than Programs A and C did combined.
• C.Program B admitted a smaller share of its applicants than Program A did.
• D.Program C rejected fewer of its own applicants than Program A did.

A lab table shows two shifts last month: the day shift processed 240 samples with a mean processing time of 18 minutes, and the night shift processed 160 samples with a mean of 23 minutes. Next month the night shift is expected to process 260 samples while the day shift stays at 240, and both shifts keep the same means. What is the projected mean processing time for all samples next month?

• A.20.6 minutes
• B.20.0 minutes
• C.20.4 minutes
• D.20.5 minutes

A science museum sold 420 tickets in one day and collected $3,960. Adult tickets cost $12.00 and student tickets cost $7.50. How many student tickets were sold?

• A.108
• B.240
• C.180
• D.210

In a perceptual ability test, which of the following skills is MOST important when determining the relationship between two-dimensional patterns that can be folded into three-dimensional objects?

• A.Folding a flat pattern into a solid object mentally
• B.Recalling a flat pattern printed in an earlier item
• C.Judging a solid shape's mass from its faint outline
• D.Matching a flat pattern to a printed template sheet

A solid cube measuring 3 units on each edge is built from 27 small unit cubes. The entire outer surface of the large cube is painted, and then it is taken apart into the 27 unit cubes. How many of the small cubes have paint on exactly two of their faces?

• A.24
• B.12
• C.26
• D.18

A square sheet of paper is folded exactly in half from left to right, and then the resulting rectangle is folded exactly in half from top to bottom, producing a small square that is one quarter of the original area. A single hole is punched through all the layers near the center of this small folded square. When the paper is completely unfolded back to the original square, how many holes appear?

• A.2
• B.8
• C.4
• D.1

Four angles must be ranked from smallest to largest. Angle W is described as a sharp, narrow wedge only slightly open. Angle X is a right angle. Angle Y is obtuse, opening just past a right angle. Angle Z is nearly a straight line, almost fully opened. Which ordering lists the angles from smallest opening to largest opening?

• A.W, Y, X, Z
• B.Z, Y, X, W
• C.W, X, Y, Z
• D.X, W, Y, Z

A solid object is a cylinder with a hemispherical dome on its top, like a capsule that is flat on the bottom. An aperture must exactly match a true outline of this object as seen from one direction so the object can pass through. Which opening exactly matches one of this object's true silhouettes?

• A.a rectangle with a notched top edge
• B.a rectangle with a slanted top edge
• C.a rectangle with a pointed top edge
• D.a rectangle with a rounded top edge

A view-recognition task gives the top view and the front view of a solid and asks what the object is. The top view is a solid circle, and the front view is a solid square (taller than it is wide is not specified; it is a true square). Which single solid object is consistent with both of these views?

• A.a cylinder standing on a flat base
• B.a cone rising from a circular base
• C.a sphere resting on a smooth table
• D.a cube standing flat on its bottom

A view-recognition task provides three orthographic views of an object: the front view is a square, the top view is a square, and the right-side view is also a square, with no internal lines or notches shown in any view. What single solid is represented?

• A.a cylinder with a curved side wall
• B.a pyramid with a broad square base
• C.a block with two long narrow sides
• D.a cube with six equal square faces

A staircase shape is built from unit cubes in three rows. The bottom row has 4 cubes in a line, the second row has 3 cubes stacked directly on the leftmost 3 bottom cubes, and the top row has 2 cubes stacked directly on the leftmost 2 of the second row. How many unit cubes were used to build this stepped structure?

• A.6
• B.9
• C.8
• D.7

In a cube-counting figure, unit cubes are stacked and then the whole assembly is painted on every exposed surface, including any faces facing down toward the table, except where cubes touch each other. A single unit cube is fully surrounded on all six faces by other cubes in the stack. How many of its faces are painted?

• A.2
• B.6
• C.0
• D.4

A square sheet is folded in half along its vertical centerline, then the doubled sheet is folded in half again along its vertical centerline, giving a tall narrow rectangle of four layers. A hole is punched once through all four layers. After the paper is fully unfolded, how are the holes arranged across the original square?

• A.four holes lying in one straight row
• B.four holes forming a big square grid
• C.two holes sitting one over the other
• D.one hole showing at the sheet center

A 3D form-development task describes a flat pattern (net) that, when folded, should form a closed cube. The net consists of six squares: a vertical column of four squares, with one extra square attached to the right side of the second square from the top and another extra square attached to the left side of that same second square. When this net is folded, does it form a complete cube, and why?

• A.Yes, but a single square face stays clear
• B.No, two of the squares would overlap once
• C.No, the column of four cannot bend around
• D.Yes, the six squares cover each face once

Under the aperture rules the object may be turned any way before it starts, then must pass straight through without twisting, and the opening is the exact outside outline of the object seen from one direction. A solid rectangular block is 8 cm long, 4 cm wide and 2 cm tall. A groove 2 cm wide and 1 cm deep is cut across its top face at the middle of its length, running the full 4 cm width. Which opening can the block pass through?

• A.An 8 by 2 cm outline with a 4 by 1 cm notch at the middle of a long side
• B.An 8 by 2 cm outline with a 2 by 1 cm notch at the middle of a long side
• C.A 4 by 2 cm outline with a 1 by 1 cm notch at the middle of a long side
• D.A 4 by 2 cm outline with a 2 by 1 cm notch at the middle of a long side

Under the aperture rules the object may be turned any way before it starts, then must pass straight through without twisting, and the opening is the exact outside outline of the object seen from one direction. Two solid square bars, each 2 cm by 2 cm in cross section, are joined at a right angle to form an L lying flat. Measured to the outer corner, one leg is 6 cm long and the other is 4 cm long. Which opening can the L pass through?

• A.A rectangle 3 cm long and 2 cm wide
• B.A rectangle 4 cm long and 2 cm wide
• C.A rectangle 2 cm long and 2 cm wide
• D.An L with 6 and 4 cm legs, 1 cm wide

A rectangular block is 6 units wide, 3 units tall, and 3 units deep. A round hole 1 unit across is drilled into the center of its left face and runs 2 units into the block, stopping well short of the right face. In the standard top, front, and end views, how does this hole appear in the end view?

• A.As a dashed circle drawn at the center of the view
• B.As two dashed lines that run across the whole view
• C.As a solid circle drawn at the center of the view
• D.As no lines, because the hole ends inside the block

An object is made of three rectangular blocks set side by side from left to right, each running the full 2-unit depth. In the front view the left block is 1 unit tall, the middle block 3 units tall, and the right block 2 units tall. The top view is a rectangle divided by two solid vertical lines at the block boundaries. Which describes the end view?

• A.A rectangle with a solid line at height 1 and a solid line at height 2
• B.A rectangle with a solid line at height 2 and a dashed line at height 1
• C.A rectangle with a solid line at height 1 and a dashed line at height 2
• D.A rectangle with a dashed line at height 1 and a dashed line at height 2

A block is 4 units wide, 4 units tall, and 6 units deep. The front view shows a solid circle 2 units across at the center of the front face. The top view shows two dashed lines that run from the front edge 3 units toward the back, joined by a short dashed line across their ends. Which describes the two long lines the hole produces in the end view?

• A.Two dashed lines that start at the right edge and stop halfway across
• B.Two dashed lines that start at the left edge and stop halfway across
• C.Two dashed lines that run the full distance from one edge to the other
• D.Two solid lines that start at the right edge and stop halfway across

An object is 4 units wide and 3 units deep. Its front view is a four-sided outline whose left side is 4 units tall, whose right side is 2 units tall, and whose top is one straight slanted line joining them. Its top view is a plain rectangle with no lines inside. Which describes the end view?

• A.A rectangle with a dashed horizontal line 2 units above its base
• B.A rectangle with a solid horizontal line 2 units above its base
• C.A rectangle with a solid diagonal line running corner to corner
• D.A rectangle with a dashed diagonal line running corner to corner

A block is 6 units wide, 4 units tall, and 3 units deep. A channel 2 units wide and 1 unit deep is cut into the center of the top face and runs from the front face to the back face. The front view shows this channel as a notch in the top edge, and the top view shows two solid vertical lines 2 units apart. Which describes the end view?

• A.A rectangle crossed by two dashed vertical lines spaced 2 units apart
• B.A rectangle crossed by a solid horizontal line 1 unit below its top
• C.A rectangle crossed by a dashed horizontal line 1 unit below its top
• D.A rectangle crossed by two solid vertical lines spaced 2 units apart

An object is 4 units wide, 4 units tall, and 3 units deep. Its front view is an outline made of a 1-unit-wide post on the left, rising the full 4 units, topped by a 1-unit-thick shelf spanning the full width, with open space under the shelf to the right of the post. Its end view is a rectangle with a solid horizontal line 1 unit below its top. Which describes the top view?

• A.A rectangle with a solid vertical line 1 unit from its right edge
• B.A rectangle with a solid vertical line 1 unit from its left edge
• C.A rectangle with a dashed vertical line 1 unit from its left edge
• D.A rectangle with a solid horizontal line 1 unit from its bottom edge

Three blocks sit side by side from left to right. The left block is 2 units tall and the full 2-unit depth, the middle block is 4 units tall and the full depth, and the right block is 2 units tall but only fills the front half of the depth. Ignoring the outline and the short vertical edge of the right block, how is the horizontal line at a height of 2 units drawn in the end view?

• A.Dashed along the left half and solid along the right half
• B.Solid along the left half and solid along the right half
• C.Solid along the left half and dashed along the right half
• D.Solid along the left half and absent from the right half

A block is 6 units wide, 3 units tall, and 5 units deep. A groove 1 unit square in cross-section is cut into the bottom face and runs left to right across the full width, starting 1 unit behind the front face. The front view shows a dashed horizontal line 1 unit above the base, and the top view shows two dashed horizontal lines. Which describes the end view?

• A.An outline with a 1-unit notch in its base starting 1 unit from its left end
• B.A full rectangle with a dashed 1-unit square on its base 1 unit from its right end
• C.An outline with a 1-unit notch in its base starting 1 unit from its right end
• D.A full rectangle with a dashed 1-unit square on its base 1 unit from its left end

A block is 6 units wide, 4 units tall, and 5 units deep, with a round hole 1 unit across drilled straight down through it. In the top view the hole is a solid circle whose edges lie 1 unit and 2 units below the top edge of the view, and the front view shows two dashed vertical lines running the full height. Which describes the end view?

• A.Two dashed vertical lines, 3 and 4 units from the left edge
• B.Two dashed vertical lines, 1 and 2 units from the left edge
• C.Two solid vertical lines, 1 and 2 units from the left edge
• D.Two solid vertical lines, 3 and 4 units from the left edge

Each of four angles is defined by the compass bearings of its two arms, measured clockwise from north, and each angle is the smaller opening between its arms. Angle 1 has arms at 15° and 98°, each 2 cm long. Angle 2 has arms at 341° and 66°, each 6 cm long. Angle 3 has arms at 200° and 284°, each 3 cm long. Angle 4 has arms at 110° and 196°, each 1 cm long. Which ordering ranks the angles from smallest to largest?

• A.1, 4, 3, 2
• B.1, 3, 2, 4
• C.4, 1, 3, 2
• D.1, 3, 4, 2

Four angles are each drawn against a horizontal or vertical arm. For P, one arm points right along the horizontal and the other is tilted 1° from vertical toward that arm. For Q, one arm points right along the horizontal and the other is tilted 2° from vertical away from that arm; Q's arms are drawn three times as long as the rest. For R, one arm points straight up and the other points right, tilted 2° above horizontal. For S, one arm points straight up and the other points right, tilted 1° below horizontal. Which ordering ranks the angles from smallest to largest?

• A.R, S, P, Q
• B.Q, P, S, R
• C.R, P, S, Q
• D.Q, S, P, R

An accurate analog clock is read at four times: 12:16, 4:38, 6:16 and 9:32. At each time, the angle is the smaller opening between the hour hand and the minute hand, and the hour hand is drawn much shorter than the minute hand. Which ordering ranks these four angles from smallest to largest?

• A.4:38, 12:16, 6:16, 9:32
• B.4:38, 6:16, 12:16, 9:32
• C.12:16, 4:38, 6:16, 9:32
• D.9:32, 6:16, 12:16, 4:38

A square sheet 8 inches on a side is folded by bringing its right edge over to the left so that the crease runs top to bottom 5 inches from the left edge, which lays a 3-inch-wide flap on top. The sheet is then folded in half by bringing its top edge down onto its bottom edge. One hole is punched 1 inch from the left edge and a second 3.5 inches from the left edge, each through every layer at that spot. How many holes are in the sheet once it is fully unfolded?

• A.8
• B.5
• C.6
• D.4

A square sheet is folded along the diagonal from its top-left corner to its bottom-right corner by lifting the bottom-left corner onto the top-right corner. The triangle that results is folded in half by bringing its top-left corner onto its bottom-right corner. One hole is punched through all layers close to the folded triangle's sharp corner that sits at the sheet's original top-right corner. Where are the holes once the sheet is fully unfolded?

• A.One hole near each of the four corners of the unfolded square sheet
• B.Two holes near the top-left corner and two near the bottom-right corner
• C.One hole near the midpoint of each of the four edges of the sheet
• D.Two holes by the top-right corner and two by the bottom-left corner

A square sheet is ruled into a 4-by-4 grid of cells, with rows 1 to 4 running top to bottom and columns 1 to 4 left to right. It is folded by laying the right half over the left half, then by laying the top half down over the bottom half, so the folded square covers rows 3 and 4 of columns 1 and 2. That small square is then folded along its diagonal by lifting its bottom-left corner onto its top-right corner. One hole is punched through every layer in the cell at row 3, column 2. Which cells hold holes once the sheet is fully unfolded?

• A.Every cell in the two middle columns of the grid
• B.Every cell in the two middle rows of the grid
• C.The four cells forming the central block of the grid
• D.Every cell on the two diagonals of the grid

A figure of 12 identical cubes is cemented together on a table. Seen from directly above, it covers a 3-by-3 square of positions, and the number of cubes stacked at each position is: back row, left to right, 3, 2, 1; middle row 2, 1, 1; front row 1, 1, 0, so the front-right position is empty. Every cube rests on the table or on another cube. The figure is painted on all exposed faces except the bottom faces resting on the table. How many cubes have exactly three painted faces?

• A.5
• B.4
• C.3
• D.1

A flat pattern of six squares is drawn on a grid. The top row has squares A and B side by side, with A on the left. The second row has square C directly below B and square D to the right of C. The third row has square E directly below D and square F to the right of E. The pattern is folded along every shared edge to form a cube. Which square ends up on the face opposite square A?

• A.Square D
• B.Square F
• C.Square E
• D.Square C

A flat pattern of six equal squares folds into a cube. The top row has two squares, labeled 1 and 2 from left to right. A middle row of three squares, labeled 3, 4, and 5 from left to right, sits below it so that square 3 is directly under square 2. Square 6 is directly under square 5. When the pattern is folded into a cube, which square ends up opposite square 1?

• A.Square 6
• B.Square 4
• C.Square 5
• D.Square 3

A cube pattern is a vertical column of four squares, labeled 1 to 4 from top to bottom. Square 5 is attached to the left edge of square 2, and square 6 is attached to the right edge of square 2. The cube is folded with square 2 as the front face. On square 4 an arrow points straight down the page, toward the edge of square 4 that touches no other square. After folding, which face does the arrow point toward?

• A.The top face, square 1
• B.The bottom face, square 3
• C.The right face, square 6
• D.The left face, square 5

Each pattern below is made of six equal squares in two horizontal rows. The leftmost square of the lower row sits directly beneath the named square of the upper row, counting from the left. Which pattern folds into a closed cube?

• A.Upper row of 3, lower row of 3, under the upper row's 3rd square
• B.Upper row of 2, lower row of 4, under the upper row's 1st square
• C.Upper row of 3, lower row of 3, under the upper row's 2nd square
• D.Upper row of 2, lower row of 4, under the upper row's 2nd square

A flat pattern has five identical rectangles joined side by side in a row. A regular pentagon is attached to the top edge of the second rectangle, and another regular pentagon is attached to the bottom edge of the fourth rectangle. When the pattern is folded into a closed solid, how many edges and vertices does the solid have?

• A.14 edges and 9 vertices
• B.15 edges and 10 vertices
• C.10 edges and 10 vertices
• D.10 edges and 6 vertices

A flat pattern has a small square in the center. Four identical isosceles trapezoids are attached to it, each by its shorter parallel side, one on each side of the square. A larger square is attached to the longer parallel side of one trapezoid. When the pattern is folded closed, which solid does it form?

• A.A pyramid on a square base
• B.A box with two square ends
• C.A prism with trapezoid ends
• D.A truncated square pyramid

A cube pattern is a vertical column of four squares, labeled 1 to 4 from top to bottom. Square 5 is attached to the left edge of square 1, and square 6 is attached to the right edge of square 4. After the pattern is folded into a cube, which three squares meet at a single corner?

• A.Squares 1, 3, and 5
• B.Squares 3, 5, and 6
• C.Squares 1, 4, and 5
• D.Squares 1, 3, and 6

A pattern for a closed triangular prism has three identical rectangles joined side by side along their long edges. An equilateral triangle is attached to the top of the left rectangle, and another is attached to the bottom of the right rectangle. After folding, how are the left and right rectangles related?

• A.They share an edge and meet at a 60-degree angle
• B.They share an edge and meet at a 120-degree angle
• C.They lie parallel on opposite sides of the solid
• D.They share an edge and meet at a 90-degree angle

Aperture rules: the object may be turned any way before it enters, must then pass straight through without twisting, and the opening must exactly match its outside outline seen straight on from the top, front or end (or from the opposite side). A solid cube 4 cm on each edge has a solid cylinder 2 cm across and 3 cm long fixed to the center of one face, sticking straight out from it. Which opening can the object pass through?

• A.A 4 cm square with a round-ended tab 3 cm wide and 2 cm long centered on one side
• B.A 4 cm square with a round-ended tab 2 cm wide and 3 cm long centered on one side
• C.A 4 cm square with a flat-ended tab 2 cm wide and 3 cm long centered on one side
• D.A 4 cm square with a flat-ended tab 3 cm wide and 2 cm long centered on one side

Third-angle layout: the top view sits above the front view, so the bottom edge of the top view is the object's front; the end view sits to the right of the front view, so its left edge is the object's front. A block is 6 units wide, 5 units deep and 4 units tall. Its top view is a 6 by 5 rectangle containing a solid 2 by 2 square whose sides are 2 and 4 units from the left edge and whose bottom side is 1 unit above the bottom edge. Its front view is a 6 by 4 rectangle with dashed vertical lines 2 and 4 units from the left, running from the top down to 1 unit above the base and joined there by a dashed line. Inside its plain 5 by 4 outline, which describes the end view?

• A.Dashed lines 2 and 4 units from the left edge, from the top to 1 unit above the base, joined there
• B.Dashed lines 1 and 3 units from the left edge, from the top to 1 unit above the base, joined there
• C.Dashed lines 1 and 3 units from the left edge, running the full height, with nothing joining them
• D.Dashed lines 2 and 4 units from the left edge, running the full height, with nothing joining them

Views follow the standard layout: the top view sits above the front view, and the end view sits to the right of the front view and shows the object as seen from the right. Solid lines are visible edges and dashed lines are hidden edges. A block is 4 units wide, 3 units tall and 4 units deep. Its front view is a 4-by-3 rectangle with a solid horizontal line 1 unit above its base. Its top view is a 4-by-4 square with a solid horizontal line halfway between its top and bottom edges. Which describes the end view?

• A.An L-shaped outline, 3 units tall on its left half and 1 unit tall on its right half
• B.An L-shaped outline, 1 unit tall on its left half and 3 units tall on its right half
• C.A 4-by-3 rectangle with a solid vertical line drawn halfway across the width of the view
• D.A 4-by-3 rectangle with a solid horizontal line drawn 1 unit above the base of the view

Views follow the standard layout: the top view sits above the front view, and the end view sits to the right of the front view and shows the object as seen from the right. Solid lines are visible edges and dashed lines are hidden edges. A flat slab is 4 units wide, 4 units deep and 1 unit tall. A 1-unit cube sits on top of the slab at its back-right corner. In the top view and in the end view, where does the small cube appear?

• A.Top view: the bottom-right corner; end view: a raised bump at the left end
• B.Top view: the bottom-right corner; end view: a raised bump at the right end
• C.Top view: the top-right corner; end view: a raised bump at the right end
• D.Top view: the top-right corner; end view: a raised bump at the left end

Each angle is formed by two arms whose directions are given as quadrant bearings (N 12° E means 12° east of due north), and each angle is the smaller opening between its arms. Angle P: arms at N 12° E and S 33° E, each 1 cm long. Angle Q: arms at N 47° W and N 86° E, each 4 cm long. Angle R: arms at S 10° W and N 34° W, each 2 cm long. Angle S: arms at N 4° W and S 42° W, each 3 cm long. Which ordering ranks the angles from smallest to largest?

• A.R, P, S, Q
• B.Q, S, R, P
• C.Q, S, P, R
• D.P, R, S, Q

Four angles are described by how they relate to other angles. Angle A: the reflex angle on its outside measures 316°. Angle B: placed beside a 134° angle, it completes a straight line. Angle C: placed beside a 47° angle, it completes a right angle. Angle D: it is the smaller of the angles formed where two straight lines cross, and the larger one there is 135°. Which ordering ranks the angles from smallest to largest?

• A.D, B, C, A
• B.C, D, B, A
• C.A, D, B, C
• D.C, A, D, B

Each angle is formed by two arms from one vertex, and each arm is described by its tilt from the horizontal. Angle W: one arm points right, tilted 20° up, and the other points left, tilted 25° up. Angle X: both arms point right, one tilted 41° down and the other 5° up. Angle Y: both arms point left, one tilted 31° up and the other 76° up. Angle Z: one arm points left, tilted 48° down, and the other points right, tilted 4° up. Which ordering ranks the angles from smallest to largest?

• A.X, Y, Z, W
• B.Y, X, Z, W
• C.Y, X, W, Z
• D.X, Y, W, Z

A protractor has two scales. The outer scale reads 0 at the right and increases counterclockwise to 180, and at any mark the inner scale reads 180 minus the outer value. For each angle, the vertex is at the protractor's center, one arm crosses the outer scale at the value given and the other arm crosses the inner scale at the value given. A: outer 20, inner 115. B: outer 30, inner 104. C: outer 100, inner 36. D: outer 12, inner 121. Which ordering ranks the angles from smallest to largest?

• A.D, B, A, C
• B.C, B, A, D
• C.C, A, B, D
• D.A, C, B, D

Each angle starts with both arms pointing due east. One arm is then turned counterclockwise by the amount given, and the angle is the smaller opening between the two arms. A: turned 224°, arms 5 cm long. B: turned 135°, arms 2 cm long. C: turned 227°, arms 4 cm long. D: turned 134°, arms 1 cm long. Which ordering ranks the angles from smallest to largest?

• A.D, B, C, A
• B.A, C, D, B
• C.D, B, A, C
• D.C, D, B, A

Four angles must be ranked from smallest to largest, where each angle is the smaller opening between its two arms. Angle P has arms pointing along compass bearings 352° and 38°, and each arm is 6 cm long. Angle Q is formed by the hour hand and the minute hand of an accurate clock at 4:30, and each arm is 1 cm long. Angle R is an angle whose larger, reflex opening measures 316°, and each arm is 4 cm long. Angle S forms a straight line together with an adjacent 133° angle, and each arm is 2 cm long. Which ordering ranks the angles from smallest to largest?

• A.P, R, Q, S
• B.R, Q, P, S
• C.R, P, S, Q
• D.Q, S, R, P

A square sheet is ruled into a 4-by-4 grid of cells, with rows 1 to 4 running top to bottom and columns 1 to 4 left to right. Column 1 is folded over onto column 2 along the line between them, and then row 4 is folded up onto row 3 along the line between them. Holes are punched through every layer at three cells of the folded sheet: row 3 column 2, row 2 column 2, and row 1 column 4. How many holes are in the sheet once it is fully unfolded?

• A.5
• B.6
• C.4
• D.7

A square sheet is folded in half by laying its right half over its left half, then folded in half again by laying its top half down over its bottom half, leaving a small square in the sheet's original bottom-left quarter. A round punch is centered exactly on the small square's top-right corner, the one point where both folded edges meet, and it cuts through every layer. What does the sheet show once it is fully unfolded?

• A.One round hole at the center of the sheet
• B.A quarter-round notch cut from every corner
• C.Four round holes set evenly around the center
• D.Two round holes on the vertical center line

Seventeen identical cubes are cemented together on a table. The footprint has a back, a middle and a front row, each with four positions numbered 1 to 4 from left to right. Layer 1, resting on the table, fills every position except back position 4. Layer 2 holds five cubes in a plus shape, on back 2, middle 1, middle 2, middle 3 and front 2. Layer 3 is a single cube on middle 2. Every exposed face of the figure is painted, including the back and the sides, except the bottom faces resting on the table. How many cubes have exactly four painted faces?

• A.Five
• B.Nine
• C.Three
• D.Four

A flat pattern of six equal squares folds into a cube. The top row holds squares 1, 2 and 3 from left to right. The bottom row holds squares 4, 5 and 6 from left to right, placed so that square 4 sits directly below square 3. After folding, which list gives all three pairs of opposite faces?

• A.1 and 5, 2 and 4, 3 and 6
• B.1 and 6, 2 and 4, 3 and 5
• C.1 and 4, 2 and 6, 3 and 5
• D.1 and 3, 2 and 5, 4 and 6

A flat pattern for a cube has a horizontal row of four squares, labeled A, B, C and D from left to right. Square E is attached to the top edge of square B, and square F is attached to the bottom edge of square D. When the pattern is folded into a cube, which edge does the top edge of square D meet?

• A.The bottom edge of square F
• B.The top edge of square E
• C.The right edge of square E
• D.The left edge of square E

A cube pattern has a top row of three squares, labeled 1, 2 and 3 from left to right. A column of three squares hangs from the bottom edge of square 2, labeled 4, 5 and 6 from top to bottom. The lower-left corner of square 6 is shaded. After folding, the shaded corner is shared by square 6 and which two other squares?

• A.Squares 1 and 2
• B.Squares 1 and 5
• C.Squares 3 and 5
• D.Squares 2 and 3

A pattern for a square pyramid starts with square base PQRS, whose corners are labeled in order around the square. Identical isosceles triangles are attached by their bases to sides PQ, QR and RS. A fourth identical triangle is then attached along the edge named, by its base if on the square and by a slanted edge if on a triangle. Which attachment does NOT let the pattern fold into a closed square pyramid?

• A.Along the slanted edge of the PQ triangle that runs from corner P
• B.Along the slanted edge of the QR triangle that runs from corner R
• C.Along the open side SP of the square, the edge that runs to corner P
• D.Along the slanted edge of the RS triangle that runs from corner S

A pattern for a hexagonal prism has six identical rectangles joined side by side in a row, labeled A to F from left to right. A regular hexagon is attached to the top edge of rectangle A, and a second regular hexagon is attached to the bottom edge of rectangle D. After folding, the edge of the top hexagon that is parallel to its attached edge meets the top edge of which rectangle?

• A.Rectangle F
• B.Rectangle C
• C.Rectangle D
• D.Rectangle E

Four identical equilateral triangles are joined edge to edge in a straight strip, labeled 1 to 4 from left to right. Triangles 1 and 3 point up with a horizontal bottom edge, and triangles 2 and 4 point down with a horizontal top edge. The strip folds into a regular tetrahedron. Which edge does the horizontal edge of triangle 1 meet?

• A.The horizontal edge of triangle 2
• B.The horizontal edge of triangle 3
• C.The horizontal edge of triangle 4
• D.The free slanted edge of triangle 4

A flat pattern has seven pieces: three squares, three pentagons that are squares with one corner clipped off, and one small equilateral triangle whose sides match the clipped edges. It folds into a cube with one corner sliced off. How many edges and vertices does the folded solid have?

• A.15 edges and 11 vertices
• B.15 edges and 10 vertices
• C.12 edges and 7 vertices
• D.12 edges and 11 vertices

In mammalian cells, which component is primarily responsible for the detoxification of drugs and poisons?

• A.Golgi apparatus compartments
• B.Mitochondrial inner membrane
• C.Lysosomal digestive vesicles
• D.Smooth endoplasmic reticulum

During which phase of the cell cycle does DNA replication occur?

• A.The S phase of each cycle
• B.The M phase of this cycle
• C.The G1 phase of the cycle
• D.The G2 phase of one cycle

Which of the following enzymes is responsible for unwinding the DNA double helix during replication?

• A.Double-stranded DNA ligase
• B.Bidirectional DNA helicase
• C.Replicative DNA polymerase
• D.Circular DNA topoisomerase

What role do microtubules play during mitosis?

• A.Contractile ring constriction with myosin
• B.Chromatin condensation into compact coils
• C.Nuclear envelope reformation at telophase
• D.Chromosome movement toward opposite poles

Which of the following processes is an example of a catabolic reaction?

• A.Glycolysis inside the cytoplasm
• B.Gluconeogenesis within the cell
• C.Glycogenesis across the myocyte
• D.Lipogenesis inside fatty tissue

In the context of membrane transport, what is the primary function of a uniporter?

• A.Pulls two solutes along matched routes
• B.Transfers one solute down its gradient
• C.Drives one solute against its gradient
• D.Swaps two solutes along reverse routes

Which of the following molecules acts as a second messenger in signal transduction pathways?

• A.Serine-specific protein kinase
• B.Transmembrane adenylyl cyclase
• C.Cyclic adenosine monophosphate
• D.Bloodborne epinephrine hormone

In the lac operon model of gene regulation in E. coli, what triggers the expression of lactose-metabolizing enzymes?

• A.Lactose removes the repressor from the operator
• B.Tryptophan activates the promoter of the operon
• C.The repressor protein fastens onto the promoter
• D.Glucose raises the repressor count inside cells

Which of the following best describes the role of antioxidants in cellular processes?

• A.Peptide synthesis inside the ribosomes
• B.Electron donation to unstable radicals
• C.Oxygen transport across cell membranes
• D.Phosphate transfer to adenosine groups

In the human body, which type of cell is primarily involved in the process of antibody production?

• A.T lymphocytes of each cortical lobule
• B.Natural killer cells of the periphery
• C.B lymphocytes of each germinal center
• D.Dendritic cells of each cortical zone

Which cellular structure is primarily responsible for the synthesis of proteins destined for secretion?

• A.Golgi apparatus cis-face compartment
• B.Nucleolar fibrillar center component
• C.Smooth endoplasmic reticulum network
• D.Rough endoplasmic reticulum cisterna

In the context of gene expression, what is the role of a promoter?

• A.Binding platform for RNA polymerase
• B.Starting signal for DNA replication
• C.Release trigger for RNA transcripts
• D.Attachment signal for poly(A) tails

What is the main function of the enzyme telomerase?

• A.Seals the small breaks between fragments
• B.Adds repeated units onto chromosome ends
• C.Splits the paired strands before copying
• D.Trims the introns from young transcripts

Which of the following best describes the function of microRNAs (miRNAs) in gene regulation?

• A.Transfers amino acids toward working ribosomes
• B.Assembles catalytic cores inside new ribosomes
• C.Sends matching messages toward rapid breakdown
• D.Governs intron removal inside the spliceosomes

During which process do sister chromatids separate to opposite poles of the cell?

• A.Prophase
• B.Metaphase
• C.Telophase
• D.Anaphase

What is the primary role of the sodium-potassium pump in neuronal cells?

• A.Keeps the resting membrane potential steady
• B.Springs open quickly during neural impulses
• C.Breaks apart transmitter inside the synapse
• D.Discharges vesicles into the synaptic cleft

Which of the following is a characteristic feature of apoptosis?

• A.The cell swells before its membrane ruptures
• B.The cell shrinks and its chromatin condenses
• C.The cell spills enzymes and inflames tissues
• D.The chromosome's DNA breaks at random points

In the Calvin cycle of photosynthesis, what molecule acts as the initial carbon acceptor?

• A.Fructose bisphosphate
• B.Sedoheptulose bisphosphate
• C.Ribulose bisphosphate
• D.Erythrose phosphate

What is the primary function of chaperone proteins in the cell?

• A.Nucleotide excision
• B.Vesicle trafficking
• C.Lysosomal digestion
• D.Polypeptide folding

In eukaryotic cells, where does the Krebs cycle (Citric Acid Cycle) occur?

• A.Mitochondrial matrix
• B.Cytoplasmic interior
• C.Chloroplast envelope
• D.Peroxisomal interior

Which type of bond is primarily responsible for the secondary structure of proteins?

• A.Covalent bonds
• B.Hydrogen bonds
• C.Cysteine links
• D.Ionic contacts

In genetics, what is the significance of Mendel's law of independent assortment?

• A.Paired alleles part as the gametes are formed
• B.Linked genes on one chromosome travel in step
• C.Genes for two traits are passed on separately
• D.One allele hides the effect of another allele

Which enzyme is responsible for relieving the supercoiling tension in DNA ahead of the replication fork?

• A.Endonuclease
• B.Recombinase
• C.Telomerase
• D.Topoisomerase

In a eukaryotic cell, which organelle is primarily involved in the synthesis and processing of lipids and steroids?

• A.Smooth endoplasmic reticulum
• B.Lysosomal hydrolase vesicles
• C.Peroxisomal oxidase granules
• D.Vacuolar storage compartment

What is the primary outcome of meiosis I in germ cells?

• A.Four haploid cells with single chromatids
• B.Two haploid cells with doubled chromatids
• C.Two diploid cells with paired chromosomes
• D.Four diploid cells with copied chromatids

Which molecule serves as the final electron acceptor in the electron transport chain of aerobic respiration?

• A.Elemental sulfur
• B.Carbonate anions
• C.Molecular oxygen
• D.Gaseous nitrogen

In the Hardy-Weinberg principle, which condition is NOT required for a population to be in genetic equilibrium?

• A.Random pairing within the overall population
• B.Complete absence of migration between groups
• C.Sufficiently large numbers of breeding pairs
• D.Unequal survival among the various genotypes

What type of cell signaling involves a cell targeting itself with signal molecules?

• A.Autocrine stimulation
• B.Endocrine circulation
• C.Paracrine propagation
• D.Juxtacrine attachment

A biochemistry student measures the rate of an enzyme-catalyzed reaction at increasing substrate concentrations, both with and without a small molecule that binds reversibly to the enzyme's active site. In the presence of this molecule, the apparent Km increases but the Vmax is unchanged. What type of inhibition is occurring?

• A.Classical competitive inhibition
• B.Simple noncompetitive inhibition
• C.Partial uncompetitive inhibition
• D.Covalent irreversible inhibition

Carl Woese's three-domain system reorganized the classification of cellular life based largely on small-subunit ribosomal RNA sequence comparisons. According to this system, which two domains share a more recent common ancestor with each other than either does with the third?

• A.Bacteria and Archaea
• B.Archaea and Eukarya
• C.Monera and Protista
• D.Bacteria and Eukarya

After a person eats a carbohydrate-rich meal, blood glucose rises sharply. Which pancreatic hormone is secreted in response, and what is its primary effect on target tissues?

• A.Glucagon, freeing stored sugar from the liver
• B.Epinephrine, releasing sugar out of the liver
• C.Insulin, driving blood glucose into the cells
• D.Cortisol, pushing the tissues to burn glucose

Which of the following is NOT a characteristic of organisms in kingdom Fungi?

• A.Nuclei bounded by a nuclear membrane
• B.Cell walls made largely of cellulose
• C.Glycogen stored as the reserve sugar
• D.Digestion that starts outside a cell

A recessive disorder affects 1 in every 2,500 newborns in a population assumed to be in Hardy-Weinberg equilibrium. About what percentage of the population are unaffected carriers?

• A.3.92%
• B.0.08%
• C.0.04%
• D.2.00%

An isolated population of 40,000 people is in Hardy-Weinberg equilibrium for an autosomal recessive condition, and 16 people have the condition. About how many people in the population are heterozygous carriers?

• A.1,584 carriers
• B.1,568 carriers
• C.800 carriers
• D.1,600 carriers

During a hard sprint, the working leg muscles produce more CO2, more H+, and more heat. Compared with blood in resting muscle, how does the oxyhemoglobin dissociation curve of blood in these muscle capillaries change?

• A.It shifts left with a raised P50, so more O2 unloads at a given PO2
• B.It shifts right with a raised P50, so more O2 unloads at a given PO2
• C.It shifts left with a reduced P50, so more O2 unloads at a given PO2
• D.It shifts right with a reduced P50, so more O2 unloads at a given PO2

In a bird population, the share of individuals in three beak-size classes was tracked for ten generations after a change in the seeds available. Small beaks went from 20% to 33%, medium beaks from 60% to 34%, and large beaks from 20% to 33%. The average beak size stayed about the same. Which type of natural selection does this pattern show?

• A.Directional selection, since the seed change shifted which beak sizes were favored
• B.Disruptive selection, since both extreme classes gained as the middle class shrank
• C.Stabilizing selection, since the average beak size held at about the same value
• D.Stabilizing selection, since the medium class is still the most common class

In the context of chemical equilibrium, which statement accurately describes the effect of increasing the temperature on an exothermic reaction at equilibrium?

• A.Applied heat drives the system ahead toward products
• B.Applied heat pushes the system back toward reactants
• C.The equilibrium constant grows larger as heat enters
• D.The equilibrium constant holds steady as heat enters

What is the hybridization of the carbon atoms in ethylene ($\ce{C2H4}$)?

• A.$sp$
• B.$sp^3$
• C.$sp^2$
• D.$sp^3d$

What is the pH of a 0.01 M HCl solution?

• A.1
• B.3
• C.4
• D.2

Which of the following elements has the highest electronegativity?

• A.Fluorine
• B.Chlorine
• C.Nitrogen
• D.Hydrogen