Practice Test 8 - ACT Science

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

Consider the plant in Chamber 3 and the plant in Chamber 7. Which of the following statements about these two plants is most accurate?
Which measurement shows the greatest precision?
A public health team studies why a new respiratory virus spreads rapidly in some indoor workplaces but not others. Three scientists propose explanations. Scientist 1: Scientist 1 argues that ventilation rate is the main driver. Higher air exchange dilutes airborne virus particles, lowering infection probability. Scientist 1 predicts that increasing ventilation (or adding HEPA filtration) will reduce transmission even if employees continue meeting in person. Scientist 2: Scientist 2 argues that close-contact networks drive spread. Transmission occurs mainly through repeated close interactions among the same people, so workplace layout and social grouping matter most. Scientist 2 predicts that reorganizing teams to reduce repeated close contacts will reduce spread even without improving ventilation. Scientist 3: Scientist 3 argues that surface contamination is the key route. People touch shared objects and then touch their faces. Scientist 3 predicts that frequent disinfection and reduced sharing of tools will lower infections even if ventilation and contact patterns remain unchanged. Which statement is consistent with Scientist 1's viewpoint but not Scientist 2's?
Student X claims that deforestation primarily affects carbon dioxide levels, while Student Y argues it impacts biodiversity more significantly. On which point would Student X and Student Y most likely disagree?
A psychology lab finds that students who sleep after studying often remember more. Researchers debate why sleep helps memory. Scientist 1: Scientist 1 proposes sleep improves memory by reducing interference. While asleep, students are not exposed to new information that could overwrite or confuse recently learned material. Scientist 1 predicts that any quiet period with minimal new input (even awake rest) should improve recall similarly to sleep. Scientist 2: Scientist 2 argues sleep actively consolidates memories through neural replay. During certain sleep stages, the brain reactivates patterns from learning, strengthening connections. Scientist 2 predicts that disrupting specific sleep stages will reduce the benefit, even if total time without new information is the same. Scientist 3: Scientist 3 claims the main factor is improved attention at test time. Sleep reduces fatigue, so students perform better on recall tests, even if the memory trace is unchanged. Scientist 3 predicts sleep will help most on tasks requiring sustained attention and less on simple recognition. Which statement is consistent with Scientist 1's viewpoint but not Scientist 2's?
Based on Table 1, what was the force required to pull the block when the angle of the incline was 40°?
A materials lab finds that a metal wire becomes more brittle after being repeatedly bent. Scientists debate the cause of the embrittlement. Scientist 1: Scientist 1 attributes brittleness to work hardening. Repeated deformation increases dislocation density, making further deformation difficult and leading to cracking. Scientist 1 predicts the wire's hardness will increase with bending cycles and that annealing (heating) should restore ductility. Scientist 2: Scientist 2 argues oxidation and corrosion at microcracks are the main cause. Tiny cracks form, oxygen and moisture enter, and corrosion weakens the metal, promoting fracture. Scientist 2 predicts embrittlement will be much less in an inert atmosphere and that surface analysis will detect oxide buildup near crack tips. Scientist 3: Scientist 3 proposes the main cause is fatigue crack growth due to cyclic stress, independent of hardness changes. Scientist 3 predicts cracks will grow with each cycle and that failure depends strongly on stress amplitude. Which statement is consistent with Scientist 1's viewpoint but not Scientist 2's?
According to Scientist 2, the high levels of iridium found in the K-Pg boundary layer originated from:
According to Figure 1, which labeled arrow represents the normal force on the block?
A student tests the hypothesis that caffeine increases heart rate. The experiment measures heart rate before and after consuming a caffeinated drink. Which factor introduces a confounding variable?
A new study finds that some bacteria survive antibiotic treatment without having genetic resistance. Scientists propose explanations for these "persister" cells. Scientist 1: Scientist 1 hypothesizes that persisters arise because a small fraction of cells enter a dormant, low-metabolism state before exposure. Many antibiotics target active processes (cell wall synthesis, DNA replication), so dormant cells are less affected. Scientist 1 predicts that conditions that slow growth (low nutrients, low temperature) will increase the fraction of persisters, and that persisters will resume normal growth after the antibiotic is removed. Scientist 2: Scientist 2 hypothesizes that persisters are created by stress responses triggered during antibiotic exposure. According to Scientist 2, the drug induces toxin–antitoxin systems and protective pathways that temporarily shut down key cellular targets. Scientist 2 predicts that persister formation will increase with higher antibiotic concentration (up to a point) and that blocking stress-response signaling will reduce persisters even in rich media. Scientist 3: Scientist 3 hypothesizes that persisters mainly result from physical shielding in biofilms. In this view, the extracellular matrix slows antibiotic penetration, creating microenvironments with low drug concentration. Scientist 3 predicts that persisters will be far more common in biofilm-grown cultures than in free-floating cultures, and that disrupting the biofilm matrix will reduce survival. How do the hypotheses of Scientist 1 and Scientist 2 differ?
A weather balloon is launched from sea level and ascends to an altitude of 25 km. Based on the provided data, during the balloon's flight, the atmospheric pressure it experiences will most likely:
A city reports that summer nights are getting warmer, with higher minimum temperatures than decades ago. Researchers debate why. Scientist 1: Scientist 1 attributes warmer nights mainly to the urban heat island effect. Dark surfaces (asphalt, roofs) absorb sunlight during the day and release heat slowly at night, reducing cooling. Scientist 1 predicts the warming will be strongest in densely built neighborhoods with low tree cover, even if regional greenhouse gas levels were constant. Increasing albedo (lighter roofs) and adding trees should lower nighttime temperatures locally. Scientist 2: Scientist 2 argues the trend is mainly due to global greenhouse gas increases. In this view, extra greenhouse gases reduce Earth's ability to radiate heat to space, raising nighttime temperatures across both cities and nearby rural areas. Scientist 2 predicts similar warming trends in rural stations near the city. Local interventions like cool roofs may slightly help but will not eliminate the long-term trend. Scientist 3: Scientist 3 proposes that changes in cloud cover and humidity are the key. More humid air and more frequent nighttime clouds trap heat and reduce radiative cooling, raising minimum temperatures. Scientist 3 predicts the warming will correlate most strongly with increases in nighttime humidity and cloud frequency, regardless of land cover. Which statement is consistent with Scientist 2's viewpoint but not Scientist 1's?
According to the results of Study 1, as the angle of the incline increases, the force required to pull the block:
Which of the following statements best describes how Scientist 3's hypothesis relates to the hypotheses of Scientists 1 and 2?
A student records temperature using the glass thermometer shown. The smallest marked division is 1 $^{\circ}$ C, and the liquid column ends slightly above 22 $^{\circ}$ C, about 0.3 of the way to 23 $^{\circ}$ C. Based on the measuring instrument shown, the temperature should be recorded as:
A study investigates the effect of light intensity on the rate of photosynthesis in aquatic plants. The independent variable is light intensity. The dependent variable is oxygen production. Which change would make the experiment more reliable?
Based on Figure 1, which rifle is precise but not accurate?
An experiment was set up to test the effect of varying concentrations of salt water on seed germination. The concentration of salt was changed, and the number of seeds that germinated was recorded. Light and temperature were kept constant. Which factor is the dependent variable?
Based on the results of both experiments, which of the following best describes the mathematical relationships between voltage, resistance, and current?

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