ACT Science Easy practice

Based on Experiment 1, what factor was held constant across all four pots?

Based on the data in Experiment 1, what best describes the relationship between temperature and reaction rate from $10°\text{C}$ to $40°\text{C}$?

Based on Experiment 2, in which year did the trees grow rings widest, and how does that year's rainfall compare?

Based on Experiment 3, what is the most likely salinity at $12$ km from the river mouth?

Set 1 — Two scientists explain a decline in pond fish populations.

At Lake Marisol, populations of native fish have fallen by roughly $30\%$ over the past decade. Water samples and biological surveys are available.

Scientist 1. The decline is driven by rising water temperatures. Average summer surface temperatures have risen by $1.6°\text{C}$ over the same period. Most of the native species spawn within a narrow temperature window, and warmer water also reduces dissolved oxygen. Surveys show that during the hottest summers, native fish are concentrated near a cool deep-water spring rather than in their usual shallow-water habitat, consistent with thermal stress.

Scientist 2. The decline is driven by an invasive predator fish introduced from a connected stream around the same time. Stomach contents from sampled invasive individuals contain juvenile native fish in roughly $60\%$ of dissections, and the invasive population grew $4\times$ over the decade. The same native species that declined in Lake Marisol have remained stable in a nearby lake where the invasive species is not present, despite similar temperature trends.

According to Scientist 1, which observation most directly supports the claim that temperature drives the native fish decline?

Experiment 1. A botany student tested how soil pH affects the growth of tomato seedlings. She prepared four identical pots with sterile potting soil, watered each with the same volume of water buffered to a specific pH, and recorded the seedling height after $14$ days under identical light and temperature.

In Experiment 1, what is the independent variable?

Experiment 1. A biology student measured the reaction rate of an enzyme at six different temperatures while keeping pH and substrate concentration constant. The data are shown below.

According to the data, at what temperature was the reaction rate highest?

Set 2 — Two researchers explain why a battery's voltage declines faster in cold weather.

Field technicians have noticed that car batteries lose voltage faster on cold mornings than on warm ones, especially when the temperature drops below $-5°\text{C}$.

Researcher 1. The decline is caused by reduced chemical reaction rates at low temperatures. Battery chemistry depends on ions moving through an electrolyte; at lower temperatures the ions move more slowly, so the rate at which the battery can deliver current is reduced. Lab measurements of identical batteries at temperatures from $-20°\text{C}$ to $30°\text{C}$ show that the achievable peak current drops smoothly as temperature falls. This effect is fully reversible — when the battery warms up, it works normally again.

Researcher 2. The decline is caused by increased mechanical load on the engine in the cold. Engines are harder to crank in the cold because oil is more viscous and internal friction is higher, drawing far more current from the battery during a cold start than during a warm start. The battery is not failing chemically; it is being asked to deliver much more energy per start. As soon as engines start more easily (warmer weather, lighter oil), the same battery performs normally.

According to Researcher 1, what is the underlying cause of poor cold-weather battery performance?

Experiment 2. An environmental scientist studied how tree-ring width varies with rainfall in the year the ring grew. She sampled trees from a single forest, measured ring widths for $5$ different years, and looked up that year's total rainfall.

Which of the following best characterizes Experiment 2's design?

Experiment 2. A physics class hung known masses from a vertical spring and measured the resulting extension. The setup was kept in a temperature-controlled room.

According to the data in Experiment 2, what is the extension when a $250\text{ g}$ mass is hung?