Answer Explanations to the Previously Released 2021-22 ACT Science Test

Below are answer explanations to the full-length Science test of the previously released ACT from the 2021-2022 “Preparing for the ACT Test” (form 2176CPRE) free study guide available here for free PDF download.

The ACT Science test explained below begins on page 38 of the guide (40 of the PDF). Other answer explanations in this series of articles:

When you’re finished reviewing this official practice ACT test, start practicing with our own 10 full-length practice ACT tests.

Answer Explanations to the 2021-2022 ACT Practice Science Test

Passage I “In a particular playa…”

Question 1, “According to Scientist 2, friction between the rocks…”. The correct answer is “Mud and algae only”.

    1. This question tests your ability to read the passage carefully.
    2. In the paragraph describing the explanation provided by scientist 2 we see that Scientist 2 states that the “presence of mud and algae” reduces friction between the rock and the clay.
    3. Hence the correct answer is D “mud and algae only

    Question 2, “Suppose a researcher observed that wind speeds greater than 80 miles per hour are needed…”. The correct answer is “Scientist 2 and 3 only”.

    1. This question tests your ability to compare and contrast the explanations provided by the three different scientists.
    2. The first scientist says that “even light winds can push the rocks”.
    3. The second scientist states that “relatively strong winds are required to push the rocks”
    4. The third scientist states that the rocks move only a few meters due to a combination of tectonic plates and “strong winds”
    5. Of these three scientists, both scientists 2 and 3 suggest that strong winds (greater than 80 miles per hour) are needed to move the rocks.
    6. Hence, the correct answer is H “scientist 2 and 3 only”

    Question 3, “Suppose that no seismic activity was recorded in the playa…”. The correct answer is “Scientist 3 only”.

    1. This question tests your ability to identify the features of each of the scientist’s explanations.
    2. Of all three scientists, only scientist 3 suggests that the movement of the rocks is due to tectonic plate movement.
    3. Hence, evidence that showed no seismic activity would negate the idea of the role of the tectonic plate thereby weakening the explanation provided by Scientist 3 only (answer B).

    Question 4, “Suppose it were discovered that a particular rock formed a 200 m long trail…”. The correct answer is “Yes; Scientist 1 indicated the rocks can move several hundred meters in a few days”.

    1. This question tests your ability to understand and apply the explanation provided by scientist 1.
    2. Specifically, scientist 1 states that because of a combination of “ice, mud and light winds” rocks move “several hundred meters” in a few days.
    3. Evidence that shows that a rock moved 200 meters in 72 hours (3 days) would be in line with the explanation provided by scientist 3.
    4. Hence, the correct answer is G “Yes; Scientist 1 indicates the rocks can move several hundred meters in a few days”.

    Question 5, “Suppose that during one year there was no measurable movement…”. The correct answer is “Snowmelt”.

    1. This question tests your ability to find what is similar between the explanations provided by scientist 1 and scientist 2.
    2. Scientist 1 states that snowmelt from the mountains runs downhill and collects in the playa. This is said to be the starting point for the movement of the rocks.
    3. Scientist 2 states that snowmelt from the mountains collects in the playa during the spring. This is said to cause the playa’s surface to get wet.
    4. Both of these explanations rely on the snowmelt. If there was no measurable movement of the rocks, both scientists would suggest that the snowmelt was absent.

    Question 6, “Suppose that air temperature in the playa varies between 4℃ and 47℃…”. The correct answer is “Yes, because ice cannot form in the temperature range”.

    1. This question tests your understanding of the freezing point of water.
    2. If the air temperature of the playa ranges from 4℃ to 47℃, then, it can be assumed that water would remain in its liquid state and not freeze since the freezing point of water is 0℃.
    3. Scientist 2 states that the “temperature in the playa does not get cold enough for ice to form”. This would support this statement by scientist 2.

    Question 7, “Based on Scientist 1’s explanation, a rock trail that is 33 cm wide…”. The correct answer is “50 cm”.

    1. This question tests your ability to apply a mathematical relation provided in the text.
    2. Specifically, scientist 1 states that the trail left by the rocks is only 2/3 as wide as the rocks themselves.
    3. This would indicate that if the rock trail was 33 cm wide, the width of the rock itself would be 3/2 * 33 cm = 49.5 cm ~ 50cm.

    Passage II

    Question 8, “If another trial had been performed in Experiment 2 and 450 mL of liquid…”. The correct answer is “greater than 60℃”.

    1. This question tests your ability to project from the data provided.
    2. In experiment 2, we see that as the volume of liquid in the cylinder decreases from 598 mL to 476 mL, the associated temperature increases from 10℃ to 60℃.
    3. Since, the additional trial has 450 mL which is lower than that of Trial 8, we can assume that the temperature would be greater than that of Trial 8.
    4. Hence, the correct answer is J (greater than 60℃).

    Question 9, “Suppose Trial 6 had been repeated, but the bottle of diet cola…”. The correct answer is “Less, because over the 12 hours, the concentration of Co2 in the diet cola would have decreased”.

    1. This question tests your ability to evaluate a hypothetical situation.
    2. If the diet cola had been opened and left undisturbed without being attached to the apparatus, we would expect some CO2 to escape.
    3. This would mean that the mass of CO2 measured would be lower.
    4. Hence, the correct answer is C (Less, because over the 12 hours, the concentration of CO2 in the diet cola would have decreased).

    Question 10, “One millimole (mmol) of CO2 has a mass of 0.044 g. How many trials…”. The correct answer is “8”.

    1. This question tests your ability to calculate the number of moles of carbon dioxide.
    2. We know that 1 mmol of CO2 has a mass of 0.044 grams.
    3. Hence, any trial that produced at least 0.044 grams of CO2 produced 1 mmol of CO2.
    4. All 8 of the trials produced over 0.044 grams of CO2 hence, the correct answer is J (8).

    Question 11, “According to Figure 1, which of Tube A and Tube B…”. The correct answer is “Tube B only”.

    1. This question tests your ability to interpret a figure.
    2. In the figure, Tube A is not submerged in either the liquid in the bottle nor is it submerged in the liquid in the jar.
    3. In the figure, Tube B is submerged in the liquid in the jar.
    4. Hence, the correct answer is B (tube B only).

    Question 12, “Is the relationship between the volume of liquid in the cylinder at the end of the experiment…”. The correct answer is “Direct; as the volume of liquid that was measured in the cylinder increased, the mass of CO2 produced increased”.

    1. This question tests your ability to interpret the information provided in tables.
    2. In Experiment 1, we see that as the volume of liquid in the cylinder increases from 525 mL to to 699 mL, the mass of CO2 produced in grams also increases from 1.02 to 1.36 grams.
    3. In Experiment 2, we see that as the volume of liquid in the cylinder increases from 476 mL to 598 mL the mass of Co2 produced in grams also increases from 0.766 to 1.13 grams.
    4. Hence, we can conclude that the relationship between the volume of liquid and the mass of CO2 produced is a direct relationship.
    5. The correct answer is F (Direct; as the volume of liquid that was measured in the cylinder increased, the mass of Co2 produced increased).

    Question 13, “Consider these steps that were performed in each trial…”. The correct answer is “3, 4, 1, 2”.

    1. This question tests your ability to understand the procedure of an experiment.
    2. In the passage, we see that first, a solid substance is inserted into Tube A.
    3. Second, Tube A is attached to a bottle of diet cola.
    4. Third, the clamp is removed.
    5. Finally, the liquid in the cylinder is measured.
    6. Based on this series of steps, we can conclude that the correct answer is B (3, 4, 1, 2).

    Question 14, “Assume that room temperature is 25℃. In how many trials…”. The correct answer is “5”.

    1. This question tests your ability to collect data from tables.
    2. In experiment 1, all 4 trials were carried out with a bottle of diet cola at 3℃ which is less than 25℃.
    3. In Experiment 2, only trial 5 has a temperature that is lower than 25℃.
    4. Hence, there are 4 trials in experiment 1 and 1 trial in experiment 2 that had a diet cola tested at a temperature lower than room temperature (25℃).
    5. Based on this, the correct answer is H (5).

    Passage III

    Question 15, “According to Figure 1, as the nickel concentration in the nutrient…”. The correct answer is “decreased only”.

    1. This question tests your ability to interpret a figure.
    2. This question asks you to look at the average iron content of Species M plants as the nickel concentration increases.
    3. This means that we are being tested on the trend of the shaded-square line.
    4. We see that average iron content decreases from 400μg/g to 50μg/g as the nickel concentration increases from 0μM to 15μM.
    5. Hence the correct answer is B (decreased only).

    Question 16, “According to Table 1, the Species U plants that were fed the solution…”. The correct answer is “8.1 g”.

    1. This question tests your ability to interpret a table.
    2. Solutions 5, 6, 7, 8 had a pH of 6.
    3. Solution 7, has a nickel concentration of 10 μM.
    4. For the plants of Species U, solution 7 had an average dry mass (g) of 8.1 grams.
    5. Hence the correct answer is G (8.1 g).

    Question 17, “According to Table 1, Species M plants taht were fed a nutrient solution with which…”. The correct answer is “pH = 6, and Nickel concentration = 0 μM”.

    1. This question tests your ability to interpret a table.
    2. If we look at the average dry mass of plants of Species M, we can figure out which had the greatest dry mass.
    3. Of all the solutions, solutions 1 and 5 had the greatest average dry mass.
    4. Solution 1 has a pH of 7, hence that is not relevant to the answers presented.
    5. Solution 5 has a pH of 6, and a nickel concentration of 0 μM.
    6. Hence the correct answer is A (pH of 6 and nickel concentration of 0 μM).

    Question 18, “According to Table 1 and Figure 1, the Species M plants…”. The correct answer is 200 μg/g.

    1. This question tests your ability to combine the information in the table and the figure.
    2. Based on Table 1, the species M plants that were fed Solution 3 had a Nickel concentration (μM) of 10μM.
    3. Based on Figure 1, the species M plant that measures the average zinc content has empty squares.
    4. Hence, we would see the average zinc content at a nickel concentration of 10 μM.
    5. The average zinc content was 200 μg/g. Hence, the correct answer is H (200 μg/g).

    Question 19, “According to Table 1 and Figure 1, for the Species M plants that were fed Solutions 1-4…”. The correct answer is “4, 3, 2, 1”.

    1. This question tests your ability to combine the information present in the table and the figure
    2. Since the question asks us to order the solutions from lowest iron content to highest iron content, we know that the last number has the highest average iron content.
    3. Among the answer choices, we see that the last number is different between all 4 choices, so if we find the solution with the highest iron content we would find our answer.
    4. We begin by looking at Figure 1 for species M relating nickel concentration to iron content. This is represented by the shaded squares.
    5. The highest average iron content of 400 μg/g occurs with a nickel concentration of 0μM.
    6. Looking to table 1, we see that the solution with a nickel concentration of 0μM is solution 1.
    7. Hence, the correct answer has the final number as 1. This is answer choice D (4, 3, 2, 1).

    Question 20, “According to Table 1, compared to the average dry mass of Species U plants, that were fed solution 3…”. The correct answer is “3 times as great”.

    1. This question tests your ability to compare different values in the Table.
    2. The average mass of Species U plants that were fed Solution 3 was 9.6 grams.
    3. The average mass of Species M plants that were fed Solution 6 was 28.8 grams.
    4. We know that 9.6 is approximately 10, and that 28.8 is approximately 30. Hence, we can say the ratio is 3.
    5. The correct answer is therefore J (3 times as great).

    Passage IV

    Question 21, “According to the results of Experiment 1…”. The correct answer is “increased only”.

    1. This question tests your ability to interpret a graph.
    2. For Experiment 1, figure 1 shows the change in the number of cycles as the temperature (℃) increases.
    3. For all 4 catalysts, as the temperature increased from 300℃ to 500℃, the number of cycles increased.
    4. Hence the correct answer is A, (increased only).

    Question 22, “In Experiment 1, 26 cycles were needed…”. The correct answer is “Catalyst X”.

    1. This question tests your ability to interpret a graph.
    2. For experiment 1, we see that the curve with the triangles has 26 cycles at a temperature of 450℃.
    3. The curve with the triangles is Catalyst X. Hence the correct answer is G (Catalyst X).

    Question 23, “The movement of H2 and N2 through the apparatus…”. The correct answer is “Reactor –> Pipe A –> condenser –> Pipe B”.

    1. This question tests your ability to summarize the methods of an experiment.
    2. Step 1 tells us that H2 and N2 are placed in the reactor.
    3. Step 3 tells us that NH3, and any unreacted H2 and N2 flow through Pipe A and then to the condenser.
    4. Step 4 tells us that unreacted H2 and N2 flow into Pipe B.
    5. Hence the correct order is the answer choice C (Reactor –> Pipe A –> condenser –> Pipe B).

    Question 24, “Consider the results of Experiment 1…”. The correct answer is “Catalysts X, Y, and Z only”.

    1. This question tests your ability to interpret a graph.
    2. At 375℃, Catalyst W required 22 cycles while Catalysts X, Y, and Z all required less than 15 cycles.
    3. Hence the correct answer is J (Catalysts X, Y and Z only).

    Question 25, “If a trial had been performed in Experiment 2…”. The correct answer is “between 230 kg and 320 kg”.

    1. This question tests your ability to project the information provided in a graph.
    2. We are asked to evaluate the amount of NH3 produced at 425℃ and 225 atm.
    3. To evaluate the amount of NH3 produced at 425℃, we would find the difference between the star curve and the shaded-square curve.
    4. At 225 atm, the amount of NH3 produced at 450℃ is around 230 kgs and the amount of NH3 produced at 400℃ is around 320 kgs.
    5. Hence the correct answer is B (between 230 kg and 320 kg).

    Question 26, “At 1 atm of pressure, the melting point of NH3 is…”. The correct answer is “Liquid, because the temperature of the condenser was between the melting point of NH3 and the boiling point of NH3”.

    1. This question tests your ability to understand the methods of an experiment.
    2. Step 3 tells us that the Mixture of NH3 and unreacted H2 and N2 flowed into a -50℃ condenser at 1 atm.
    3. This temperature is warmer than the melting point of NH3 (-77℃) but less than the boiling point of NH3 (-33℃). NH3 would likely be a liquid.
    4. Hence, the correct answer is J (Liquid, because the temperature of the condenser was between the melting point of NH3 and the boiling point of NH3).

    Question 27, “Consider the trial in Experiment 2 that produced…”. The correct answer is “less than 5”.

    1. This question tests your ability to integrate information provided in two graphs.
    2. Based on Figure 2, the trial that produced 550 kg of NH3 was the 300℃ trial performed at 150 atm.
    3. Based on Figure 1, the number of cycles that Trial Z required at 300℃ was less than 5.
    4. Hence, the correct answer is A (less than 5).

    Passage V

    Question 28, “What is the approximate maximum α shown in Figure 1…”. The correct answer is “α = 3.0; Temperature = -5℃”.

    1. This question tests your ability to interpret a figure.
    2. The question asks you to calculate the α shown in figure 1 for a 200 Hz sound with 10% relative humidity. Looking at the legend we can see that the bottom curve is the one representing 200 Hz.
    3. The peak of this curve has an α of 3 dB/km. The temperature at which this happens is -5℃.
    4. Hence the correct answer is F (α = 3.0; Temperature = -5℃).

    Question 29, “Based on Figure 2, the attenuation coefficient for a 1,000 Hz sound wave…”. The correct answer is “45%”.

    1. The question tests your ability to interpret a figure.
    2. The question asks you to find the relative humidity of the 1,000 Hz curve when the α reaches a minimum. Looking at the legend we can see that the solid line is the 1,000 Hz curve.
    3. The minimum of this curve is just below 5 dB/km and this occurs at a relative humidity of 45%.
    4. Hence the correct answer is B (45%).

    Question 30, “For the range of temperatures and the range of relative humidities shown in Figures 1 and 2…”. The correct answer is “Temperature, because the maximum variation in α is about 2.5 dB/km in Figure 1 but about 0.5 dB/km in figure 2.”

    1. This question tests your ability to combine the information present in two figures.
    2. In Figure 1, we see that the maximum variation of α for the 200 Hz sound wave is about 2.5 dB/km.
    3. In Figure 2, we see that the maximum variation of α for the 200 Hz sound wave is about 0.5 dB/km.
    4. The 200 Hz sound wave is more affected by temperature.
    5. Hence, the correct answer is G (Temperature, because the maximum variation in α is about 2.5 dB/km in Figure 1 but about 0.5 dB/km in figure 2)

    Question 31, “Consider a 1,000 Hz sound wave in air at 10% relative humidity…”. The correct answer is “4”.

    1. The question tests your ability to analyze the information present in Figure 1.
    2. For the 1,000 Hz curve, we begin by drawing a horizontal line at α = 18 dB/km.
    3. Doing this, we see that this line intersects the 1,000 Hz curve 4 times.
    4. Hence the correct answer is C (4).

    Question 32, “Suppose that 2 sound waves -a 150 Hz wave and a 1,100 Hz wave…”. The correct answer is “The 1,100 Hz wave, because the value of α is greater for the 1,100 Hz wave than for the 150 Hz wave”.

    1. This question tests your ability to project information presented in Figure 2.
    2. The 150 Hz wave has a frequency that is slightly smaller than the 200 Hz wave and the 1,100 Hz has a frequency that is slightly larger than the 1,000 Hz wave.
    3. At 20℃ and 45% humidity, the 200 Hz wave has an α of 1 dB/km. At the same conditions, the 1000 Hz wave has an α of 5 dB/km.
    4. Since the α for the 1000 Hz wave is larger, we can assume that the α for the 1,100 Hz wave will also be larger than that of the 150 Hz wave.
    5. Hence the correct answer is J (The 1,100 Hz wave, because the value of α is greater for the 1,100 Hz wave than for the 150 Hz wave).

    Question 33, “The graph below shows, for sound waves of 3 different frequencies…”. The correct answer is “0℃”.

    1. The question tests your ability to apply the information from one figure to analyze a second figure.
    2. We know that Figure 1 shows data that was collected at 10% relative humidity.
    3. In the new figure, the α for 1,000 Hz is 14 dB/km, the α for 500 Hz is 9 dB/km and the α for 200 Hz is 3 dB/km.
    4. In Figure 1, we then see that these three values of α for the respectives curves happens at a temperature of 0℃.
    5. The correct answer is B (0℃).

    Passage VI

    Question 34, “In Study 1, as the ratio of fructose to glucose…”. The correct answer is “decreased only”.

    1. The question tests your ability to interpret Table 1 and Table 2.
    2. Based on Table 1 we see that the ratio of fructose to glucose increases as the Sweetener changes from Q to U.
    3. Based on Table 2 we see that the amount of sweetener solution consumed per rat per day decreased from Q to U.
    4. Hence, as the ratio of fructose to glucose increases the amount of sweetener solution consumed per rat per day decreased only.
    5. The correct answer is G (decreased only).

    Question 35, “In study 1, the amount of sweetener solution consumed daily by each rat…”. The correct answer is “The rats had been placed in separate cages”.

    1. The question tests your ability to understand the methods of an experiment.
    2. We are told in the description of Study 1 that each rat was placed in a separate cage.
    3. This allows the researchers to measure the amount of sweetener solution consumed daily by each rat.
    4. The correct answer is D “The rats had been placed in separate cages”.

    Question 36, “Suppose that a sweetener composed of 46% fructose and 54% glucose by mass…”. The correct answer is “between 1,125 pM and 1,279 pM”.

    1. The question tests your ability to interpret information present in two Tables.
    2. A sweetener composed of 46% fructose and 54% glucose would be between sweetener R and sweetener S.
    3. Based on Table 4, we see that the Ghrelin concentration for Sweetener R is 1,125 pM and the ghrelin concentration for Sweetener S is 1,279 pM.
    4. Hence the correct answer is H (between 1,125 pM and 1,279 pM).

    Question 37, “Consider the claim “the group of rats that consumed the lowest amount of solid food…”. The correct answer is “No; the rats in Group 1 consumed the lowest amount of solid food per rat per day, but the rats in Group 5 had the lowest concentration of leptin per sample”.

    1. The question tests your ability to combine the information present in two tables.
    2. In Table 2, the lowest amount of solid food is 9 grams which is found in Group 1.
    3. In Table 3, we see that the Leptin concentration for Group 1 is 804 pM while that of Group 5 is 251 pM.
    4. Hence, the correct answer is C (No; the rats in Group 1 consumed the lowest amount of solid food per rat per day, but the rats in Group 5 had the lowest concentration of leptin per sample).

    Question 38, “Which of the following groups of rats should have been included in Study 1…”. The correct answer is “only to water and solid food”.

    1. This question tests your ability to understand the purpose of a control for an experiment.
    2. A control is used to serve as a baseline to understand what the effect of the independent variable has on the dependent variable.
    3. In Study 1, we see that the independent variable is the sweetener solution that was given to each rat.
    4. Hence, to understand the effect of only the sweetener solution, we would want the control to have rats that had access to water and solid food.
    5. The correct answer is H (only to water and solid food).

    Question 39, “Consider the sweetener that resulted in a solid food consumption of…”. The correct answer is “100 g”.

    1. This question tests your ability to apply percentages and interpret tables.
    2. In Study 1, the sweetener that resulted in a solid food consumption of 16 g per rat per day was Sweetener S.
    3. Based on Table 1, we see that the percentage by mass of fructose and glucose was 50% each.
    4. Since the sweetener was 50% by mass fructose, we can say that 50% of 200 g of this sweetener would be fructose.
    5. Hence, the number of grams of fructose would be 100 g (answer choice B).

    Question 40, “The experimental designs of Studies 2 and 3 were identical with respect…”. The correct answer is “Neither I nor II”.

    1. The question tests your ability to compare the designs of two different studies.
    2. In Study 2, the chemical indicator that was used was Indicator N. In Study 3, the chemical indicator that was used was Indicator P.
    3. In Study 2, the relevant hormone was Leptin. In Study 3, the relevant hormone was ghrelin.
    4. Hence, neither the indicator nor the hormone is identical between Studies 2 and 3.
    5. The correct answer is J (Neither I nor II).