Practice Test 5 - ACT Science

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

A student investigated how salt concentration affects the boiling point of water. She prepared four 250 mL beakers, each containing 200 mL of distilled water. She added table salt to make solutions of 0%, 2%, 4%, and 6% salt by mass. Each beaker was heated on the same hot plate setting, starting at room temperature (22°C). The student stirred each solution at a constant rate with the same glass rod and recorded the temperature when the liquid reached a steady rolling boil for 30 seconds. She used the same thermometer for all trials and measured boiling point to the nearest 0.1°C. Which of the following is the independent variable?
A research team investigated the effect of soil moisture on root development in plants. Soil moisture levels were varied while plant species and nutrient levels were kept constant. Root length was measured. The experimenter manipulated [blank] and measured [blank].
Student A argues that the primary benefit of exercise is cardiovascular health. Student B believes it's mental health improvement. How do the hypotheses differ?
In Study 1, the animals were kept "at rest." This was an important experimental control because:
During an experiment to determine if a specific diet affects weight loss, participants' weights are recorded weekly. What is the dependent variable?
Scientists examined how the angle of sunlight affects solar panel efficiency. Sunlight angle was varied while keeping panel type and environmental conditions constant. The electricity generated was measured. In this experiment, the dependent variable is:
Which change would make a study about the effect of noise on concentration more reliable?
Researchers aimed to discover the impact of different exercise intensities on cardiovascular health. The intensity of exercise was varied, and blood pressure was measured. Diet and age of participants were kept constant. Which factor was controlled?
According to Figure 1, over the 8 weeks the mass gained on Diet B was approximately how many times the mass gained on Diet A?
Based on Table 2, which surface material created the greatest resistance (friction) to the movement of the block?
Researchers conducted an experiment to test the effect of different fertilizers on tomato yield. The type of fertilizer was varied while the amount of sunlight and water received by the plants was kept constant. The number of tomatoes produced was recorded. In this experiment, the dependent variable is:
A biology class investigated whether light color affects the growth of bean seedlings. Identical seedlings were placed in 4 boxes lined with colored plastic: clear (white light), red, blue, or green. Each box contained 10 seedlings in the same potting soil. All boxes were kept at $22^\circ\text{C}$ , watered with 20 mL daily, and placed the same distance from identical lamps for 12 hours per day. After 14 days, students measured the average seedling height in each box using a ruler. In this experiment, the dependent variable is:
Which of the following is the strongest reason to doubt that prediction?
An experiment tests the effect of water salinity on fish respiration rate by altering salinity levels. What is the independent variable?
A student investigated whether stretching a rubber band changes its electrical resistance when coated with graphite. Hypothesis: increasing stretch length increases resistance. Procedure: (1) Rub a soft graphite pencil along a 6 cm section of a rubber band until the surface appears uniformly gray. (2) Attach two alligator clips 4.0 cm apart along the coated section; connect to a digital multimeter set to ohms. (3) Measure resistance with the band unstretched. (4) Stretch the band to lengths of 7 cm, 8 cm, and 9 cm (measured with a ruler) while keeping clip spacing fixed at 4.0 cm, and record resistance at each length. (5) Repeat the entire procedure with 5 rubber bands and average results. What is the independent variable in this experiment?
Student X believes that the primary driver of technological progress is government funding. Student Y argues it is private sector investment. How do the hypotheses differ?
A telescope detects fast radio bursts (FRBs): brief, intense radio flashes from space. Astrophysicists debate their origin. Scientist 1: Scientist 1 proposes FRBs come from magnetars (highly magnetized neutron stars) releasing sudden energy. This model predicts some FRBs should repeat from the same location, and bursts may be associated with high-energy emissions in X-rays. Scientist 2: Scientist 2 argues FRBs are produced by mergers of compact objects, such as neutron star collisions. Mergers are one-time events, so this model predicts FRBs should not repeat from the same source. Scientist 2 also predicts some FRBs might coincide with gravitational-wave detections. Scientist 3: Scientist 3 proposes FRBs are caused by interactions between a pulsar and material from a nearby companion star. This model predicts bursts may show periodicity tied to the orbital period of the binary system. Which statement is consistent with Scientist 2's viewpoint but not Scientist 1's?
Which measurement shows the least precision in the data set?
A student notices that a metal spoon placed in hot soup quickly becomes hot at the handle, while a wooden spoon does not. Scientists discuss what property best explains the difference. Scientist 1: Scientist 1 claims the key factor is thermal conductivity. He argues metals have free electrons that transfer energy efficiently, so heat moves rapidly from the hot end to the handle. He predicts that among metals, a copper spoon will heat the handle faster than a stainless-steel spoon of the same shape. Scientist 2: Scientist 2 claims the key factor is heat capacity. She argues materials with higher specific heat require more energy to raise temperature, so the handle warms more slowly. She predicts that if the spoons have equal mass and receive the same heat input, the one with higher specific heat will show a smaller temperature rise. Scientist 3: Scientist 3 claims the key factor is surface color and radiation. He argues darker surfaces absorb more heat from the hot soup and surrounding steam via radiation, so a dark spoon warms faster. He predicts that painting a spoon black will significantly increase how fast the handle warms, even if the material stays the same. How do the hypotheses differ?
Based on Figure 1, what would the sustained swimming speed most likely be at 35 °C?

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