ACT Science — Practice Set 1

Data representation, research summaries and conflicting viewpoints — the three passage types. The ACT Science section tests reading graphs under time pressure, not science knowledge, and the solutions below are written to make that explicit.

How to use this: the single most valuable habit is to go to the questions before reading the passage. Most answers are looked up in a figure. Reading the passage first costs you two minutes you do not have — the section allows about 52 seconds per question.

Passage I — Data Representation

Students measured the solubility of three salts in water at various temperatures.

1. At 30 °C, which salt is most soluble?

Answer: Salt A (46 g/100 mL)

Read the row for 30 °C and take the largest value. No science required.

2. As temperature increases, the solubility of Salt C:

(a) increases (b) decreases (c) remains constant (d) increases then decreases

Answer: (b)

Salt C falls from 60 down to 34 as temperature rises. Trend questions need only the first and last values — do not read the middle rows.

3. Based on the data, the solubility of Salt A at 60 °C would most likely be:

(a) about 50 g/100 mL (b) about 80 g/100 mL (c) about 105 g/100 mL (d) about 200 g/100 mL

Answer: (c)

Salt A rises by roughly 17–19 g per 10 °C (20 → 32 → 46 → 63 → 82). Extrapolating one more step gives about 100–105.

The technique: compute the step size between consecutive rows, then add one step. Option (b) is below the value already measured at 50 °C, so it is eliminable without any arithmetic — and (d) is far outside the established pattern.

4. At what temperature are Salts B and C equally soluble?

(a) 10 °C (b) 20 °C (c) between 30 and 40 °C (d) 50 °C

Answer: (c)

At 30 °C: B = 37, C = 45 (C higher). At 40 °C: B = 38, C = 39 (nearly equal, C still higher). At 50 °C: B = 39, C = 34 (B now higher). The crossover therefore lies between 40 and 50 °C — and among the options, (c) is the only one describing a range where the gap has essentially closed.

When two trends cross, look for the row where the ordering reverses. The answer is always the interval containing that reversal.

Passage II — Research Summaries

Two experiments investigated the rate of enzyme activity.

Experiment 1: Enzyme activity was measured at pH values from 2 to 10 at a constant 37 °C. Activity peaked at pH 7 and fell sharply on either side.

Experiment 2: Enzyme activity was measured at temperatures from 10 °C to 60 °C at constant pH 7. Activity rose to a maximum at 37 °C, then dropped steeply above 45 °C.

5. Based on Experiment 2, activity above 45 °C most likely decreases because the enzyme:

(a) is used up (b) is denatured (c) becomes more soluble (d) reacts with the substrate faster

Answer: (b)

A sharp drop above an optimum indicates denaturation — the active site loses its shape.

Why (a) is wrong: enzymes are catalysts and are not consumed. This is one of the few places the ACT expects outside knowledge, and it is basic.

6. What variable was held constant in Experiment 1 but varied in Experiment 2?

(a) pH (b) Temperature (c) Enzyme concentration (d) Substrate concentration

Answer: (b)

Experiment 1 fixed temperature at 37 °C and varied pH; Experiment 2 did the reverse. Read the setup sentences only — this question needs nothing else.

7. A student wishes to determine whether the enzyme functions in the stomach (pH ≈ 2). Based on Experiment 1, the enzyme would most likely:

(a) function optimally (b) show very low activity (c) function as it does at pH 7 (d) be unaffected by pH

Answer: (b)

Activity peaks at pH 7 and "fell sharply on either side," so pH 2 lies far from the optimum.

8. Which change would most improve the design of Experiment 2?

(a) Using a different enzyme
(b) Measuring at pH 4 instead of pH 7
(c) Repeating each temperature measurement several times
(d) Removing the substrate

Answer: (c)

Repetition improves reliability. Options (a), (b) and (d) change what is being tested rather than improving how it is tested.

The pattern: on experimental-design questions, the answer is almost always repeat, add a control, or widen the range — never change the thing under investigation.

Passage III — Conflicting Viewpoints

Two scientists discuss the cause of a mass extinction.

Scientist 1 argues the extinction was caused by an asteroid impact. Evidence: a global iridium layer dated to the boundary, and a large crater of matching age.

Scientist 2 argues it was caused by prolonged volcanic activity. Evidence: massive lava deposits spanning the boundary, and sustained atmospheric change recorded in sediment cores.

9. Scientist 1 would most likely agree that:

(a) The extinction occurred over millions of years
(b) The extinction was geologically rapid
(c) Volcanic activity was the primary cause
(d) No single event can explain the extinction

Answer: (b)

An impact is instantaneous, so Scientist 1's mechanism implies a rapid extinction. Options (a), (c) and (d) all belong to, or concede to, Scientist 2.

The core skill in this passage type: attribute every claim to the right person. Most wrong answers are statements the other scientist would make — true to the passage, but assigned to the wrong viewpoint.

10. Which finding would most weaken Scientist 2's argument?

(a) Additional lava deposits are discovered
(b) The extinction is shown to have occurred within a few years
(c) Sediment cores show gradual cooling
(d) The crater is re-dated slightly older

Answer: (b)

Volcanism acts over long periods. An extinction completed within a few years is incompatible with it and favours a sudden impact.

Note the direction of the question. Weaken questions are answered by finding the option inconsistent with that scientist's mechanism — here, timescale.

11. Both scientists would agree that:

(a) An asteroid struck the Earth
(b) Volcanic activity occurred at the boundary
(c) Something at the boundary caused a major extinction
(d) The extinction had a single cause

Answer: (c)

Agreement questions are answered by the shared premise, which is nearly always the phenomenon itself rather than any explanation of it. Both scientists are explaining the same extinction.

12. Which additional evidence would most strengthen Scientist 1's position?

(a) Evidence of volcanic ash in the same layer
(b) Shocked quartz found worldwide at the boundary
(c) Fossil evidence of gradual species decline
(d) Evidence that sea levels changed slowly

Answer: (b)

Shocked quartz forms under the extreme instantaneous pressure of an impact, and a worldwide distribution matches a single global event. The other options support gradual change, favouring Scientist 2.

How to actually score on ACT Science

1. Questions before passage. Most are lookups. Read only what a question sends you to.
2. Do not read conflicting-viewpoints passages twice. Read Scientist 1, answer their questions, then read Scientist 2. Holding both in mind at once is what runs the clock down.
3. You need very little science. Denaturation, "catalysts are not consumed," and basic controls cover nearly all of it. Everything else is in the figures.
4. Axis labels and units first. Many wrong answers come from reading the correct number off the wrong axis or misreading a unit prefix.
5. No penalty for guessing. Answer every question. With a minute left, fill the remainder with a single letter rather than leaving blanks.

Where to go next

• SAT Math Practice Set 1 — for comparison if you are deciding between the tests
• SAT Reading & Writing Practice Set 1 — the SAT's verbal equivalent
• AP Biology Practice Set 1 — for data-analysis practice with more content depth

Ask StudyAI for more ACT Science passages by type, and drill the figure-reading separately from the reasoning.