Practice Test 7 - ACT Science

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

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1. A student uses a calorimeter to measure heat released by dissolving a salt in water. Figure 1 shows the calorimeter cup, lid, thermometer, and stirrer, including which parts contact the solution. According to Figure 1, which component is inserted through the lid and extends into the solution to measure temperature?
2. In Study 3, the students used the same mass (0.5 g) of Magnesium in both trials. This was necessary to ensure that:
3. A chemist tested whether the concentration of hydrochloric acid (HCl) affects the reaction rate with magnesium ribbon. She prepared 4 beakers containing 50.0 mL of HCl at 0.5 M, 1.0 M, 1.5 M, or 2.0 M. In each trial, she added a 2.0 cm strip of magnesium ribbon (same thickness and mass) and recorded the time (seconds) until bubbling stopped. The same beaker size, solution volume, and room temperature were used for all trials. In this experiment, the dependent variable is:
4. In a chemistry lab, a student measures the concentration of a solution but uses impure solvents. The concentration results would most likely:
5. A study investigates the effect of humidity on paper's tensile strength by varying humidity levels. Step 2 involves acclimating paper samples to each humidity level. This step was included to:
6. A forest ecologist studies why a certain wildflower blooms earlier in spring over the last 20 years. Scientist 1: Scientist 1 claims earlier blooming is driven mainly by warmer spring temperatures. They reason that many plants use accumulated heat (growing degree days) to trigger flowering. Scientist 1 predicts that in years with warmer March–April temperatures, flowering will occur earlier, even if winter conditions are similar. Scientist 2: Scientist 2 claims earlier blooming is driven mainly by reduced snowpack. They argue that snow insulates soil and delays exposure to light and air; less snow leads to earlier soil warming and earlier emergence. Scientist 2 predicts that flowering date will correlate more strongly with date of snowmelt than with average air temperature. Scientist 3: Scientist 3 claims earlier blooming reflects evolutionary change in the population. They argue that plants that bloom earlier may have produced more seeds under recent conditions, shifting genetic traits. Scientist 3 predicts that seeds collected from modern populations will bloom earlier than seeds from historical populations when grown together under identical conditions. On which point would Scientist 1 and Scientist 3 most likely disagree?
7. In a study, Scientist 1 argues that exercise reduces stress by releasing endorphins. Scientist 2 suggests it's due to social interactions during exercise. Both scientists would agree that:
8. In an experiment measuring the electric resistance of a wire, which factor would most likely introduce random error?
9. Based on Figure 1, in how many of the five years did both glaciers lose mass?
10. A student tested how the amount of soap affects the size of bubbles produced. She mixed soap solutions by adding 0 mL, 5 mL, 10 mL, or 15 mL of liquid soap to water to make a total volume of 100 mL each time. Using the same bubble wand and the same blowing time, she produced one bubble per trial and measured bubble diameter (cm) with a ruler held behind the bubble. The room airflow was minimized by closing windows. Which factor was controlled in this experiment?
11. A chemist examined how temperature affects the rate of an effervescent tablet reaction. She placed one 2.0 g tablet into 200 mL of water in the same 400 mL beaker at four water temperatures: $10^\circ\text{C}$, $20^\circ\text{C}$, $30^\circ\text{C}$, and $40^\circ\text{C}$. She used the same brand of tablet, the same water volume, and stirred at the same speed with a magnetic stirrer. She measured reaction rate as the time (in seconds) until bubbling stopped. Which of the following is the independent variable?
12. Two researchers are studying plant growth. Researcher A claims that sunlight is the most critical factor, as it drives photosynthesis. Researcher B argues that soil nutrients are more important, stating that plants in nutrient-rich soil grow faster even with less light. How do the hypotheses differ?
13. Consider the solubility trend of Oxygen gas shown in Figure 2. If the temperature of a lake increases from 20°C to 40°C due to thermal pollution, the amount of dissolved oxygen available to fish would likely:
14. Scientists conducted an experiment to evaluate the impact of water hardness on soap effectiveness. The hardness of the water was varied, and the amount of lather produced was measured. The type of soap and temperature of water were controlled. Which of the following is the manipulated variable?
15. A student measures the mass of a sample using a balance that is sensitive to air currents. Which procedural error would have the greatest effect on the results?
16. A student tested whether colored light affects plant growth. Identical seedlings were placed under red, blue, or white LED lamps for 14 days. The independent variable was light color. The dependent variable was final plant mass. The student set all lamps to the same electrical power (10 W) and placed plants the same distance from each lamp. Results: red 3.1 g, blue 2.4 g, white 2.9 g. The student concluded red light produces the most growth. A teacher noted that equal electrical power does not guarantee equal light intensity (photon flux) across colors. Which of the following is the best criticism of this experiment?
17. Students test why an enzyme's reaction rate decreases at very high substrate concentrations. Two models are proposed. Model 1 (Saturation Only): Rate approaches a maximum as substrate increases, then stays near that maximum. Prediction: At very high substrate, rate should plateau, not decrease. Model 2 (Substrate Inhibition): Excess substrate binds to an inhibitory site, reducing activity. Prediction: Rate should increase at first, then decrease at very high substrate. Figure 1 shows reaction rate versus substrate concentration. Which model is best supported by the results in Figure 1?
18. Star X is a Main Sequence star that is exactly twice as hot at its surface as Star D. Based on the mathematical trend shown on the H-R diagram, the luminosity of Star X is approximately:
19. Based on Figure 1, if a new layer were discovered at a depth of 1,000 km where the material was liquid magma, the S-wave velocity curve at that depth would likely:
20. In an experiment to test the effect of sugar concentration on yeast fermentation, different sugar concentrations were used while the type of yeast and temperature were kept constant. The amount of carbon dioxide produced was measured. What was the independent variable?

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