ACT Science Practice Test: Practice Test 10

A student investigated how the number of paper towel layers affects water absorption. She cut paper towels into identical $10\text{ cm} \times 10\text{ cm}$ squares and stacked them to make pads with 1, 2, 3, or 4 layers. She poured exactly 50 mL of water onto each pad placed in the same type of tray. After 60 seconds, she measured how much water remained in the tray (in mL) and calculated water absorbed by the pad. All trials used the same brand of paper towel and were performed at room temperature. Which of the following is the independent variable?

A student examined whether fertilizer amount changes the number of flowers produced by marigold plants. She grew identical seedlings in 12 identical pots with the same soil type. Pots were assigned to receive 0 g, 5 g, 10 g, or 15 g of fertilizer per week (3 pots per group). All plants received the same volume of water each day, were kept in the same greenhouse with the same light schedule, and were grown for 6 weeks. At the end, she counted the number of flowers on each plant.

Which factor was controlled in this experiment?

A botanist studied the effect of water frequency on plant health. Plants were watered daily, weekly, or not at all, and health was assessed. The primary purpose of this experiment was to:

The consistency of results in a viscosity measurement experiment would most likely be affected by:

PASSAGE V

BIOLOGY: This passage is adapted from a study on the metabolic rates of vertebrates. Introduction

Metabolism is the set of chemical reactions that occur in living organisms to maintain life. The metabolic rate is often measured by the amount of oxygen ($O_2$) consumed per gram of body mass per hour.

Animals can be classified based on how they regulate body temperature:

•Endotherms (e.g., mammals, birds) generate their own body heat to maintain a constant internal temperature.

•Ectotherms (e.g., reptiles, amphibians) rely on external heat sources to regulate their body temperature.

Students conducted two studies to compare the metabolic rates of a Mouse (Endotherm) and a Lizard (Ectotherm) of similar body mass.

Study 1

The students placed the mouse and the lizard in separate metabolic chambers. They varied the environmental temperature from 5°C to 35°C in 10°C increments. The animals were kept at rest. The rate of oxygen consumption ($mL \ O_2 / g \cdot hr$) was measured after the animals had acclimated to each temperature for 30 minutes. Findings were reported in Figure 1.

Study 2

The students investigated the effect of activity level on metabolic rate. They maintained the environmental temperature at 25°C for both animals. They measured the oxygen consumption while the animals were at rest and while they were running on a treadmill at 1.0 km/hr. Findings were reported in Table 1.

Study 3

To determine if body mass affects metabolic rate within the same group, students measured the resting metabolic rate of three different lizards at 25°C. Findings were reported in Table 2.

Based on Table 2, what is the relationship between body mass and metabolic rate per gram for lizards?

A lab tested whether a disinfectant (Solution D) reduces bacterial growth on countertops. Identical countertop squares were inoculated with bacteria and then treated with either Solution D or water (Control). After 4 hours, technicians counted colony-forming units (CFU). The experiment was repeated at two room humidities.

Based on the data, which conclusion is most strongly supported?

A chemist investigated how temperature affects the rate of a reaction that produces gas. The same concentrations of reactants were used each time. The chemist measured the time required to produce 50 mL of gas at three temperatures.

Based on the data, which conclusion is most strongly supported?

A study aimed to find the effect of exercise duration on weight loss. Participants engaged in different lengths of exercise routines while their diet and sleep were kept constant. The change in weight was recorded. Which is the dependent variable?

An experiment is conducted to test the effect of air pressure on sound speed. The independent variable is air pressure, and the dependent variable is the speed of sound. Which change would make the experiment more reliable?

A student tested the hypothesis that increasing salt concentration lowers the freezing point of water. She prepared 4 beakers, each with 100 mL of distilled water, and added NaCl to reach concentrations of 0%, 2%, 4%, or 6% (mass/volume). Each beaker was placed in the same freezer set to $-10^\circ\text{C}$ for 45 minutes. The student stirred each beaker for 10 seconds every 5 minutes using the same stirring rod and then recorded the temperature at which the first ice crystals appeared (freezing point). All beakers were identical and started at $20^\circ\text{C}$. Which of the following is the independent variable?

Two hypotheses explain the increase in jellyfish populations. Hypothesis 1 states warmer ocean temperatures increase jellyfish numbers. Hypothesis 2 suggests overfishing of predators is the cause. Data correlates higher jellyfish numbers with warmer temperatures. Which hypothesis is more supported?

PASSAGE II

BIOLOGY: This passage is adapted from a study on the factors affecting the rate of photosynthesis in aquatic plants.

Introduction

Photosynthesis is the process by which green plants use sunlight to synthesize nutrients from carbon dioxide ($CO_2$) and water ($H_2O$). The process releases oxygen ($O_2$) as a byproduct according to the following chemical equation: $6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$ Students conducted three studies to investigate how different environmental factors affect the rate of photosynthesis in Elodea, an aquatic plant. The rate was measured by counting the number of oxygen bubbles produced by a cut stem of Elodea submerged in water over a 5-minute period.

Study 1

To test the effect of light intensity, students placed a 10 cm sprig of Elodea into a test tube filled with a 0.5% sodium bicarbonate ($NaHCO_3$) solution (a source of $CO_2$). A light source was placed at various distances from the test tube. The temperature was maintained at 25°C. The number of bubbles produced in 5 minutes was recorded.

Study 2

To test the effect of light color (wavelength), students used the same setup as in Study 1. The light source was kept at a constant distance of 10 cm. Colored filters were placed between the light and the plant to isolate specific wavelengths. Clear cellophane was used as a control.

Study 3

To test the effect of $CO_2$ availability, students prepared five test tubes with different concentrations of sodium bicarbonate ($NaHCO_3$). A 10 cm sprig of Elodea was placed in each. The light source was kept constant at 10 cm (white light).

Based on the chemical equation provided in the Introduction, the bubbles counted in these experiments consisted primarily of:

PASSAGE IV

PHYSICS: Research Summary

Introduction

A group of physics students investigated the motion of a projectile. They used a toy cannon that utilizes a compressed steel spring to launch a 50-gram (g) plastic ball. The students investigated how the horizontal distance traveled by the ball ($D$) was affected by two variables:

1. The launch angle ($\theta$), measured in degrees from the horizontal.

2. The spring compression distance ($x$), which is the distance the spring is pushed inward before being released.

Study 1

The students set up the cannon on a flat, level field. They kept the spring compression distance ($x$) constant at $4.0\text{ cm}$ for all trials. They launched the ball at five different angles ($\theta$) and measured the horizontal distance ($D$) the ball traveled before hitting the ground. The results are shown in Table 1.

Study 2

Next, the students kept the launch angle ($\theta$) constant at $45^\circ$ (the angle that yielded the greatest distance in Study 1). They varied the spring compression distance ($x$) and measured the resulting horizontal distance ($D$). The results are shown in Table 2.

Based on the trend in Table 1, if the students had launched the ball at an angle of 90° (straight up), the horizontal distance traveled by the ball would most likely be:

Which statement about measurement precision is supported by the data?

A meteorology club recorded wind speed and air pressure during five afternoon observations. Use Table 1 to answer the question.

Which observation had the highest air pressure?

The digital thermometer reads 36.58 °C. The precision of the thermometer is:

PASSAGE VI

Fruit Fly Genetics

Introduction

In the fruit fly Drosophila melanogaster, eye color is a sex-linked trait determined by a gene on the X chromosome. The allele for the wild-type red eye color ($X^R$) is dominant, while the allele for the mutant white eye color ($X^r$) is recessive.

Females (XX): Inherit one X chromosome from each parent. A female will have white eyes only if she is homozygous recessive ($X^r X^r$).

Males (XY): Inherit an X chromosome from the mother and a Y chromosome from the father. Because the Y chromosome does not carry the eye color gene, a male expresses whichever allele is present on his single X chromosome (X^R Y \= Red; X^r Y \= White).

Students conducted two studies to observe these inheritance patterns.

Study 1

The students crossed a homozygous red-eyed female ($X^R X^R$) with a white-eyed male ($X^r Y$). To predict the genotypes of the offspring, they constructed a Punnett square (Figure 1).

They then collected 100 offspring (the F1 generation) and recorded the results in Table 1.

Study 2

The students performed the reciprocal cross. They crossed a white-eyed female ($X^r X^r$) with a red-eyed male ($X^R Y$). A second Punnett square was constructed to predict the outcome (Figure 2).

They collected 100 offspring and recorded the results in Table 2.

A student hypothesized that the gene for eye color is located on an autosome (a non-sex chromosome). Do the results of Study 1 and Study 2 support this hypothesis?

A psychology experiment tested whether a brief mindfulness session reduces test anxiety. Sixty students were randomly assigned to either 10 minutes of guided mindfulness or quiet sitting. Anxiety was rated (0–100) immediately before and immediately after the session.

Based on the data, which conclusion is most strongly supported?

PASSAGE III

EARTH SCIENCE / BIOLOGY: Conflicting Viewpoints

Introduction

Approximately 66 million years ago, a mass extinction event occurred at the boundary between the Cretaceous and Paleogene periods (the K-Pg boundary), wiping out roughly 75% of all plant and animal species on Earth, including all non-avian dinosaurs. Geologists have discovered a distinct layer of sedimentary rock worldwide at the K-Pg boundary that contains unusually high levels of iridium, a metal rare in Earth’s crust. Two scientists present different hypotheses for the cause of the extinction and the source of the iridium.

Scientist 1

The mass extinction was caused by the impact of a massive asteroid, approximately 10 kilometers in diameter. Asteroids are naturally rich in iridium. When the asteroid struck the Earth, the immense force of the collision vaporized the asteroid and a large portion of Earth's crust, ejecting a massive cloud of iridium-rich dust and debris into the atmosphere. This dust cloud enveloped the planet for months or even years, blocking out incoming sunlight. The lack of sunlight halted photosynthesis globally, causing the collapse of marine and terrestrial food webs.

Furthermore, the impact would have triggered global wildfires, acid rain, and massive tsunamis. The presence of shocked quartz (quartz crystals deformed by intense, sudden pressure) and tektites (glassy spheres formed by rapidly cooling, ejected rock) in the K-Pg boundary layer alongside the iridium firmly points to a high-velocity extraterrestrial impact as the sole trigger of the extinction.

Scientist 2

The mass extinction was not caused by a sudden impact, but rather by intense, prolonged volcanic activity. Around 66 million years ago, a massive volcanic region in what is now India, known as the Deccan Traps, experienced a series of colossal eruptions that lasted for tens of thousands of years. These eruptions released millions of cubic kilometers of lava.

While iridium is rare in Earth's surface crust, it is present in high concentrations in the deep mantle. The massive magma plumes from the Deccan Traps brought this deep-Earth iridium to the surface, where volcanic ash plumes spread it globally. The prolonged eruptions released massive quantities of sulfur dioxide ($SO_2$) and carbon dioxide ($CO_2$) into the atmosphere. The $SO_2$ caused severe short-term global cooling and acid rain, while the $CO_2$ led to long-term extreme global warming. This resulting climate instability severely stressed ecosystems over thousands of years, leading to a gradual, rather than instantaneous, mass extinction. Shocked quartz can also be formed by the explosive pressures of massive volcanic eruptions.

Suppose a geological study proved that tektites can only form when rock is subjected to temperatures and instantaneous impact pressures far exceeding those generated by even the most explosive volcanic eruptions. This finding would:

A food scientist tested the hypothesis that higher oven temperature shortens cookie baking time. She baked identical cookie dough balls (20 g each) on the same metal tray lined with the same parchment paper. She used three oven settings: $160^\circ\text{C}$, $180^\circ\text{C}$, and $200^\circ\text{C}$. For each temperature, she timed how long it took for the cookie edges to turn golden brown, using the same oven rack position and the same stopwatch. Which variable was held constant?

PASSAGE VI PHYSICS: This passage is adapted from a study on the forces acting on an object on an inclined plane. Introduction A student conducted experiments to determine the factors that affect the force required to pull a block up an inclined plane at a constant velocity. The force ($F$) required depends on the mass of the block ($m$), the angle of the incline ($\theta$), and the friction between the block and the surface. The experimental setup consisted of a wooden board (the inclined plane) and a spring scale attached to a rectangular block. The student pulled the block up the incline at a steady speed and recorded the force in Newtons (N). Study 1 To test how the angle of the incline affects the force, the student used a standard wooden block with a mass of 1.0 kg. The surface of the inclined plane was smooth wood. The student varied the angle of the incline from 10° to 60°. Results were recorded in Table 1. Study 2 To test how the surface material (friction) affects the force, the student fixed the angle of the incline at 30° and used the same 1.0 kg block. The student covered the wooden board with different materials: Sandpaper, Rubber, and Plastic. The force was measured for each surface. Results were recorded in Table 2. Study 3 To test how the mass of the block affects the force, the student used the smooth wood surface and fixed the angle at 30°. The student added weights to the block to increase its total mass. Results were recorded in Table 3.

In Study 1, the independent variable (the factor intentionally changed by the student) was:

A robotics team tested how battery voltage affects motor speed. They measured the motor’s rotational speed after 30 seconds of operation at each voltage setting.

Comparing Trial 2 and Trial 4, which variable increased?

Student X claims that the internet is the primary driver of globalization. Student Y believes it's international trade. On which point would Student X and Student Y most likely disagree?

A class compared the electrical resistance of wires of different lengths. Procedure: (1) Cut copper wire into lengths of 10 cm, 20 cm, 30 cm, and 40 cm. (2) Measure each length with a ruler. (3) Connect each wire to a digital multimeter set to ohms, using alligator clips. (4) Record resistance and plot resistance vs. length. The alligator clips sometimes gripped oxidized sections of wire; students did not sand the wire ends. The ruler had millimeter marks, and most students estimated to the nearest millimeter. Expected pattern: resistance increases linearly with length. Which procedural error would have the greatest effect on the results?

Two scientists propose different mechanisms for the sudden extinction of dinosaurs. Scientist A suggests a massive asteroid impact, while Scientist B points to gradual volcanic activity. Fossil records show a sudden extinction event. Which hypothesis is more consistent with the fossil evidence?