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Practice Test 9 - ACT Science

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

  1. Researchers examine the impact of different diets on mice weight gain. The independent variable is diet type, and the dependent variable is weight gain. To better test the hypothesis, the researchers should:
  2. Based on Table 1, as the distance of the light source from the plant increases, the rate of photosynthesis:
  3. A researcher examined whether listening to music improves memory recall. Participants studied a list of 30 words for 2 minutes, then recalled as many as possible. The independent variable was audio condition during studying: silence or instrumental music at 60 dB. The dependent variable was number of words recalled. The researcher tested 8 participants in silence in the morning and 8 participants with music in the afternoon. The same room and word list were used. Results: silence mean 18 words; music mean 22 words. The researcher concluded music improves recall. Which of the following is the best criticism of this experiment?
  4. Two geologists are debating the causes of earthquakes. Geologist A believes tectonic plate movement is the main cause. Geologist B suggests human activities, like mining, significantly contribute. How do the hypotheses differ?
  5. A chemistry student tested whether activated charcoal removes dye from water. Materials: 6 flasks, 100 mL blue dye solution (same initial absorbance), activated charcoal, filter paper, spectrophotometer. Procedure: (1) Add 0 g, 0.5 g, or 1.0 g charcoal to flasks (2 flasks per amount). (2) Swirl for 60 s and let sit for 5 min. (3) Filter each mixture to remove charcoal particles. (4) Measure absorbance of the filtrate at the dye's peak wavelength. Expected outcome: higher charcoal mass yields lower absorbance. Step 3 was included in order to:
  6. A student tested whether washing hands with soap reduces bacterial growth compared with rinsing with water. Hypothesis: soap washing reduces bacterial colonies on skin more than water rinsing. Procedure: (1) Before washing, press the fingertips of the right hand onto a sterile agar plate for 5 s (Pre plate). (2) Wash hands for 20 s using either liquid soap and water (Soap group) or water only (Water group). (3) After washing, press the same fingertips onto a second agar plate for 5 s (Post plate). (4) Incubate plates at 37°C for 24 hours. (5) Count the number of visible colonies on each plate. (6) Use 12 volunteers, randomly assigned to Soap or Water groups. Step 1 was included in order to:
  7. Which difference between the measurements and the model does Figure 1 show?
  8. According to the results of Study 1, as the mass of the falling object increases, the terminal velocity:
  9. A teacher tested whether rinsing rice reduces starch in the cooking water. Materials: 6 identical pots, 300 g uncooked white rice per pot, water, sieve, timer, colorimeter, iodine solution. Procedure: (1) For 3 pots, rinse rice under running water for 60 s, then drain. For 3 pots, do not rinse. (2) Add 600 mL water to each pot and boil for 12 min with lids on. (3) Collect 10 mL cooking water from each pot and add 2 mL iodine solution. (4) Measure absorbance at 620 nm; higher absorbance indicates more starch. Results: rinsed mean absorbance = 0.35; not rinsed = 0.62. The primary purpose of Step 3 was to:
  10. Which of the following is the strongest reason the model cannot be correct for five layers?
  11. Astronomers observe that a star's brightness dips by 1% every 10 days for about 3 hours. They debate what causes the periodic dimming. Scientist 1: Scientist 1 proposes a planet transits the star, blocking a small fraction of light. A planet would produce dips of consistent depth and duration, with a very regular period. Scientist 1 predicts the star's spectrum will show a small, periodic Doppler shift (radial velocity wobble) matching the 10-day period. Scientist 2: Scientist 2 suggests starspots rotating in and out of view. Large cooler spots can reduce brightness, and rotation can be periodic. Scientist 2 predicts the dip depth will vary as spots change size, and the star's spectrum will show activity indicators (like emission in certain lines) correlated with dimming, not necessarily a consistent radial velocity signal. Scientist 3: Scientist 3 argues the dips are caused by a cloud of dust orbiting the star. Dust could cause wavelength-dependent dimming (more dimming at shorter wavelengths). Scientist 3 predicts the dip depth will be larger in blue light than in red light. Both Scientist 1 and Scientist 3 would agree that:
  12. A chemistry class observes that iron objects rust faster near the ocean than inland. Three students propose explanations. Student A: Student A claims that salt in sea spray dissolves in water on the metal surface and increases the water's electrical conductivity. This speeds electrochemical reactions involved in rusting. Student A predicts that adding salt to water on iron will increase rust rate even if oxygen concentration stays the same. Student B: Student B claims that higher humidity near the ocean keeps the metal surface wet for longer periods, allowing rusting to proceed. Student B predicts that if inland iron is kept constantly wet (same wetness duration as coastal iron), rust rates will become similar even without added salt. Student C: Student C claims that coastal air contains more oxygen, which directly increases oxidation rate. Student C predicts that increasing oxygen concentration around iron will increase rust rate even in dry conditions. On which point would Student A and Student B most likely disagree?​​
  13. Researchers conducted an experiment to see how water salinity affects seed germination rate. Salinity levels were varied while keeping light exposure and temperature constant. The number of seeds germinated was counted. Which of the following is the independent variable?
  14. An environmental science student tested whether the amount of activated carbon changes how well it removes dye from water. She poured 100 mL of a blue dye solution into each of four identical jars. She added activated carbon in amounts of 0 g, 0.5 g, 1.0 g, and 2.0 g, then sealed and shook each jar for exactly 60 s. After letting the carbon settle for 5 minutes, she measured the solution's color intensity using the same colorimeter (reported in absorbance units). The dye concentration, solution volume, shaking time, settling time, jar type, and instrument were kept constant. In this experiment, the dependent variable is:
  15. Which finding, if true, would most weaken Glaciologist 2's hypothesis?
  16. Using reaction-rate data from 20-60°C, a student predicts the rate at 100°C. The main risk is:
  17. Two scientists are discussing the causes of bee population decline. Scientist 1 believes that chemical pesticides are primarily responsible, citing studies showing pesticide residues in bees. Scientist 2 argues that habitat loss is the primary cause, noting the correlation between urbanization and bee decline. On which point would Scientist 1 and Scientist 2 most likely disagree?
  18. At which temperatures does the model predict more dissolved gas than was measured?
  19. A student tested whether the number of paper clips affects how far a rubber band launches a small paper ball. The same rubber band was stretched to the same length each time using a marked ruler line. The student attached 0, 2, 4, or 6 paper clips to the paper ball before launching it from the same height. The distance traveled along the floor was measured in centimeters with a tape measure. The room floor type and launch angle were kept the same. In this experiment, the dependent variable is:
  20. Which of the following best explains the relationship between the two records in Figure 1?

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