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Practice Test 6 - ACT Science

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

  1. A geoscience team studies why a river's water becomes unusually cloudy (high turbidity) after some storms but not others. Three scientists propose explanations. Scientist 1: Scientist 1 proposes that turbidity spikes are driven mainly by rainfall intensity. Short, intense storms generate strong runoff that erodes soil and carries sediment into the river. Scientist 1 predicts that storms with higher peak rainfall rates will produce larger turbidity spikes even if total rainfall is moderate. Scientist 2: Scientist 2 proposes that turbidity spikes are driven mainly by antecedent soil moisture. If soils are already saturated, even moderate rain produces more surface runoff and sediment transport. Scientist 2 predicts that turbidity will be high after storms following wet weeks, even when rainfall intensity is not extreme. Scientist 3: Scientist 3 proposes that turbidity spikes are driven mainly by land use in the watershed. Construction sites and bare agricultural fields supply loose sediment. Scientist 3 predicts that two storms with similar rain patterns will produce different turbidity depending on how much exposed soil exists upstream. Which statement best describes how Scientist 1 and Scientist 2 differ?​​
  2. Which procedural change would most effectively reduce measurement error in an experiment measuring reaction time using a stopwatch?
  3. In a chromatography experiment, if the paper is not level, the results would most likely show:
  4. A chemist wants to find out if temperature affects the rate of a reaction. In a series of experiments, the chemist conducted reactions at 20°C, 30°C, and 40°C and recorded the time taken for each reaction to complete. What is the dependent variable in this experiment?
  5. In a study measuring the refractive index of a liquid, if the light source intensity fluctuates, the measured index would most likely:
  6. Based on Figure 1, Strain A has its highest relative enzyme activity at a temperature closest to:
  7. A physics student tested whether ramp angle affects the distance a toy car travels after leaving the ramp. The independent variable was ramp angle: 15°, 30°, or 45°. The dependent variable was horizontal distance traveled on the floor after leaving the ramp. The student used the same ramp and car, releasing the car from the top each time. However, the floor surface changed: 15° trials were on carpet, 30° on tile, and 45° on wood, because of space constraints. The student concluded steeper ramps increase distance. Which of the following is the best criticism of this experiment?
  8. Based on Figure 1, as the environmental temperature increases from 5°C to 25°C, the metabolic rate of the Mouse:
  9. A student wants to launch the ball a horizontal distance of exactly 17.3 meters. Based on the data in both studies, which of the following combinations of launch angle (θ) and spring compression distance (x) will achieve this?
  10. Which of the following variables was kept constant in Study 3?
  11. A student tested how the temperature of water affects the time it takes a tablet to dissolve. She placed one identical effervescent tablet into 200 mL of water at each of four temperatures: 10°C, 20°C, 30°C, and 40°C. She used the same beaker type, did not stir the water in any trial, and used the same brand of tablets. She started a timer when the tablet touched the water and stopped the timer when bubbling ceased and no solid remained. Which of the following is the independent variable?
  12. A researcher tested whether adding fertilizer increases the growth rate of duckweed (Lemna). Hypothesis: higher fertilizer concentration increases duckweed growth. Procedure: (1) Place 10 duckweed fronds into each of 12 identical cups containing 100 mL pond water. (2) Add fertilizer to reach concentrations of 0, 1, 2, or 4 g/L (3 cups per concentration). (3) Place all cups on the same windowsill for 7 days. (4) Count fronds in each cup on day 0 and day 7; compute growth as fronds gained. (5) Compare mean growth among fertilizer concentrations. A flaw in the experimental design is that:
  13. An environmental lab measured nitrate concentration in river water at different distances downstream from a wastewater outlet. Samples were collected the same day and analyzed with the same instrument. Table 1 reports the results. At a distance of 5.0 km downstream, the nitrate concentration was:
  14. An experiment was conducted to test the effect of diet on cholesterol levels by assigning participants different diets and measuring their cholesterol after 4 weeks. Which factor introduces a confounding variable?
  15. What do the measurements in Table 1 establish about the two models?
  16. Based on the information provided, all three scientists would likely agree with which of the following statements?
  17. Which of the following variables was the independent (manipulated) variable in Study 2?
  18. An experiment tests the effect of humidity on mold growth. The independent variable is humidity level, and the dependent variable is mold coverage area. Which of the following is the best criticism of this experiment?
  19. In an experiment measuring how soil pH affects plant leaf color, the pH of the soil was altered while light exposure and water availability were kept constant. The color intensity of the leaves was measured. Which variable was held constant?
  20. A student measured the concentration of carbon dioxide (CO2_2) in a classroom over a class period. Figure 1 shows CO2_2 concentration versus time. According to Figure 1, the CO2_2 concentration at 40 minutes is closest to:

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