ACT Science — Practice Test 1

Passage 1 — Plant Growth vs Light Intensity

Use the passage to choose the best answer.

Passage 1 — Data Representation

A botanist grew identical seedlings of a tomato plant (Solanum lycopersicum) under controlled greenhouse conditions for 28 days. Each group of seedlings was exposed to a different light intensity, measured in micromoles of photons per square meter per second (µmol/m²/s). All other variables (temperature, water, soil, CO₂) were held constant. Table 1 shows the average stem height (cm) and average dry mass (g) of seedlings at the end of the trial. Figure 1 (described below) shows leaf-area data from the same trial.

Table 1. Stem height and dry mass after 28 days.
Light intensity (µmol/m²/s)	Avg. stem height (cm)	Avg. dry mass (g)
50	8.2	0.41
150	14.6	0.92
300	22.1	1.74
450	26.3	2.18
600	27.0	2.25
800	26.8	2.21

Figure 1. Average leaf area (cm²) per seedling vs. light intensity. The x-axis is light intensity (50 to 800 µmol/m²/s); the y-axis is leaf area (0 to 250 cm²). The curve rises steeply from (50, 35) to (300, 180), then climbs more slowly to a plateau near (600, 235) and (800, 232).

1. According to Table 1, the average stem height of seedlings grown at 300 µmol/m²/s was closest to:

2. Based on Figure 1, the average leaf area at 300 µmol/m²/s was closest to:

3. As light intensity increased from 50 to 600 µmol/m²/s, the average dry mass per seedling:

4. Based on BOTH Table 1 and Figure 1, which conclusion is BEST supported?

5. If the botanist grew an additional group of seedlings at 1,000 µmol/m²/s, the average dry mass would MOST LIKELY be closest to:

Passage 2 — Melting Points vs Molecular Weight

Use the passage to choose the best answer.

Passage 2 — Data Representation

A chemistry student measured the melting points (°C) of eight straight-chain alkanes (saturated hydrocarbons of the form C_nH_2n+2) at standard atmospheric pressure. The student also recorded the molecular weight (g/mol) of each compound. Table 1 lists the data. Figure 1 (described below) plots melting point vs. molecular weight for the same eight compounds.

Table 1. Alkane melting points.
Compound	Formula	Molecular weight (g/mol)	Melting point (°C)
Methane	CH₄	16	-182
Ethane	C₂H₆	30	-183
Propane	C₃H₈	44	-188
Pentane	C₅H₁₂	72	-130
Octane	C₈H₁₈	114	-57
Decane	C₁₀H₂₂	142	-30
Tetradecane	C₁₄H₃₀	198	6
Octadecane	C₁₈H₃₈	254	28

Figure 1. Melting point (°C) on the y-axis vs. molecular weight (g/mol) on the x-axis. The plotted points start near (16, -182), drop slightly to (44, -188), then rise steadily through (72, -130), (114, -57), (142, -30), (198, 6), and (254, 28). Above molecular weight ~70, the trend is a smooth, nearly linear increase.

6. According to Table 1, the melting point of octane (C₈H₁₈) is:

7. Which compound listed in Table 1 has a molecular weight of 142 g/mol?

8. For molecular weights above about 70 g/mol, as molecular weight increases, the melting point of these alkanes:

9. Based on the relationship in Figure 1, the melting point of an alkane with a molecular weight of about 170 g/mol would MOST LIKELY be closest to:

10. Which of the alkanes listed in Table 1 would be the ONLY one expected to be a SOLID at a room temperature of 22 °C?

Passage 3 — Enzyme Activity (pH and Temperature)

Use the passage to choose the best answer.

Passage 3 — Research Summaries

Researchers studied the activity of an enzyme called amylex-A, which breaks down starch into sugar. Activity was measured as the mass of sugar produced (mg) in 5 minutes when the enzyme was mixed with a fixed amount of starch in solution.

Experiment 1. The pH of the solution was varied from 4 to 10 (in steps of 1) while temperature was held at 37 °C. Substrate (starch) and enzyme amounts were identical in every trial.

Table 1. Sugar produced (mg) at varying pH, T = 37 °C.
pH	Sugar produced (mg)
4	12
5	38
6	72
7	95
8	61
9	25
10	8

Experiment 2. The pH was held at 7 while temperature was varied from 10 °C to 70 °C in 10-degree steps. Other conditions matched Experiment 1.

Table 2. Sugar produced (mg) at varying T, pH = 7.
Temperature (°C)	Sugar produced (mg)
10	14
20	42
30	78
40	98
50	55
60	10
70	2

11. According to Table 1, the highest amount of sugar was produced at:

12. In Experiment 2, the INDEPENDENT variable that the researchers deliberately changed was:

13. Which conditions in Experiments 1 and 2 produced the GREATEST amount of sugar?

14. Based on Tables 1 and 2, both Experiments 1 and 2 BEST support which generalization about amylex-A?

15. If the researchers ran a new trial in Experiment 2 at 35 °C, the sugar produced would MOST LIKELY be closest to:

16. A student claims, "Amylex-A works best inside the human body." Which finding from these experiments BEST supports the claim?

Passage 4 — Erosion Rate vs Slope and Rainfall

Use the passage to choose the best answer.

Passage 4 — Research Summaries

A geology team built outdoor soil plots (each 2 m by 2 m) on identical loam-soil beds and exposed them to a simulated rainstorm using sprinkler nozzles. After each storm, they collected the runoff and measured the soil that had been carried off the plot, recorded as the erosion rate in grams of soil per square meter (g/m²).

Experiment 1. Plot slope was varied (5%, 10%, 20%, 30%) while rainfall intensity was held constant at 25 mm/hr for 60 minutes.

Table 1. Erosion rate vs. slope, rainfall = 25 mm/hr.
Slope (%)	Erosion rate (g/m²)
5	18
10	42
20	110
30	196

Experiment 2. Slope was held at 10% while rainfall intensity was varied (10, 25, 50, 75 mm/hr) for 60 minutes.

Table 2. Erosion rate vs. rainfall intensity, slope = 10%.
Rainfall (mm/hr)	Erosion rate (g/m²)
10	14
25	42
50	118
75	205

Experiment 3. A grass cover was added to the 10% slope plot, and Experiment 2 was repeated at the same four rainfall intensities. Erosion rates were 3, 9, 27, and 48 g/m², respectively.

17. According to Table 1, the erosion rate at a slope of 20% was:

18. In Experiment 1, the DEPENDENT variable was:

19. Comparing Experiments 2 and 3 at the same rainfall intensity, adding grass cover to the slope:

20. The result for slope = 10% in Experiment 1 (42 g/m²) and the result for rainfall = 25 mm/hr in Experiment 2 (42 g/m²) match because:

21. Based on Experiment 2, if rainfall intensity were 100 mm/hr on the bare 10% slope, the erosion rate would MOST LIKELY be:

22. A farmer hypothesizes that planting grass on a hillside will reduce soil loss during heavy rain. Which result BEST supports this hypothesis?

Passage 5 — Solubility of Salts vs Temperature

Use the passage to choose the best answer.

Passage 5 — Research Summaries

A chemistry team measured the solubility of three salts in 100 g of water at temperatures from 0 °C to 80 °C. Solubility is reported as the maximum mass of salt (g) that fully dissolves in 100 g of water at that temperature.

Experiment 1. Solubility of potassium nitrate (KNO₃) was measured at five temperatures.

Table 1. KNO₃ solubility (g per 100 g water).
Temperature (°C)	Solubility (g)
0	14
20	32
40	62
60	108
80	170

Experiment 2. The same procedure was repeated for sodium chloride (NaCl).

Table 2. NaCl solubility (g per 100 g water).
Temperature (°C)	Solubility (g)
0	35.7
20	36.0
40	36.6
60	37.3
80	38.1

Experiment 3. The same procedure was repeated for cerium sulfate (Ce₂(SO₄)₃), a salt that is known to behave unusually with temperature.

Table 3. Ce₂(SO₄)₃ solubility (g per 100 g water).
Temperature (°C)	Solubility (g)
0	21.0
20	10.1
40	5.6
60	3.9
80	2.6

23. According to Table 1, the solubility of KNO₃ at 60 °C is:

24. In each of Experiments 1, 2, and 3, the INDEPENDENT variable was:

25. Which salt's solubility CHANGED THE LEAST between 0 °C and 80 °C?

26. In comparing Experiments 1 and 3, the unusual behavior of Ce₂(SO₄)₃ is BEST described as:

27. Based on Table 1, the solubility of KNO₃ at 50 °C would MOST LIKELY be closest to:

28. A student hypothesizes, "For salts in water, solubility always increases with temperature." The data BEST support which conclusion about that hypothesis?

Passage 6 — Radioactive Isotope Decay Rates

Use the passage to choose the best answer.

Passage 6 — Research Summaries

A physics lab placed three pure samples of radioactive isotopes — Isotope X, Isotope Y, and Isotope Z — into a shielded counter and measured the percentage of original atoms remaining after each whole hour for 8 hours. Each sample started with 100% of its original atoms.

Experiment 1. Sample masses were equal at 1.00 g.

Table 1. % of original atoms remaining (1.00 g samples).
Time (hr)	Isotope X	Isotope Y	Isotope Z
0	100	100	100
1	50	71	87
2	25	50	76
4	6.3	25	57
6	1.6	12.5	43
8	0.4	6.3	33

Experiment 2. The procedure was repeated using 2.00 g samples of each isotope. The percentage of original atoms remaining at every time point was the same as in Experiment 1, within measurement error. (For example, at t = 2 hr the values were Isotope X = 25%, Isotope Y = 50%, Isotope Z = 76%.)

29. According to Table 1, after 2 hours the percentage of Isotope Y remaining is:

30. The HALF-LIFE of an isotope is the time required for half of the original atoms to decay. Based on Table 1, the half-life of Isotope X is approximately:

31. Based on Table 1, which ranking BEST orders the isotopes from FASTEST to SLOWEST decay?

32. What is the BEST conclusion to draw from comparing Experiment 1 and Experiment 2?

33. If the trial were extended to t = 10 hr, the percentage of Isotope Z remaining would MOST LIKELY be closest to:

Passage 7 — Conflicting Viewpoints: The Argosian Mass Extinction

Use the two viewpoints to choose the best answer.

Passage 7 — Conflicting Viewpoints

About 215 million years ago, near the end of the (fictional) Argosian Period, more than 60% of marine species and many land species disappeared from the fossil record over a relatively short geologic interval. Two scientists offer competing explanations for this Argosian Extinction Event.

Scientist 1 — Asteroid Impact Hypothesis

Scientist 1 argues that a single large asteroid struck Earth and caused the Argosian Extinction. Evidence cited: a 180-km-wide buried crater dated to 215 million years ago has been found in modern-day southern Africa. A thin global layer of clay at the same depth contains unusually high levels of iridium, an element rare in Earth's crust but common in asteroids. The fossils of Argosian marine plankton drop sharply right at this clay layer, with no recovery for several hundred thousand years. Scientist 1 contends that the impact threw enough dust into the atmosphere to block sunlight, halt photosynthesis, and collapse the food chain in months.

Scientist 2 — Volcanism Hypothesis

Scientist 2 argues that the Argosian Extinction was caused by a long episode of massive volcanic eruptions. Evidence cited: thick basalt flows from the Siberian Argosian Traps date to between 217 and 213 million years ago — straddling the extinction. Carbon-isotope shifts in marine fossils show repeated, gradual disruptions to ocean chemistry over more than two million years, not a single sudden event. Many fossil groups (especially shallow-water reef builders) decline progressively across multiple sediment layers, not in a single layer. Scientist 2 contends that volcanic CO₂ warmed the climate, acidified the oceans, and deoxygenated the seafloor over a long interval, gradually wiping out species.

34. According to Scientist 1, the MAIN cause of the Argosian Extinction was:

35. Which finding is presented as evidence by Scientist 1 BUT NOT by Scientist 2?

36. Scientist 2 BEST disagrees with Scientist 1 about which feature of the extinction?

37. A new core sample shows that ocean acidity rose slowly and steadily for about 1.8 million years across the extinction interval. This finding would be MOST consistent with:

38. Suppose researchers find that 90% of Argosian species disappear within a single thin sediment layer corresponding to less than 10,000 years. This new finding would BEST:

39. How would Scientist 1 MOST LIKELY respond to Scientist 2's claim that the Siberian Argosian Traps caused the extinction?

40. Both scientists would AGREE with which of the following statements?

Passage 1 — Plant Growth vs Light Intensity

Passage 1 — Data Representation

Passage 2 — Melting Points vs Molecular Weight

Passage 2 — Data Representation

Passage 3 — Enzyme Activity (pH and Temperature)

Passage 3 — Research Summaries

Passage 4 — Erosion Rate vs Slope and Rainfall

Passage 4 — Research Summaries

Passage 5 — Solubility of Salts vs Temperature

Passage 5 — Research Summaries

Passage 6 — Radioactive Isotope Decay Rates

Passage 6 — Research Summaries

Passage 7 — Conflicting Viewpoints: The Argosian Mass Extinction

Passage 7 — Conflicting Viewpoints

Scientist 1 — Asteroid Impact Hypothesis

Scientist 2 — Volcanism Hypothesis

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