ACT Science Question and Answers

Question 1

A researcher measures the absorbance of three protein solutions at 280 nm and obtains values of 0.42, 0.85, and 1.27 respectively. If the relationship between concentration and absorbance is linear, what concentration corresponds to an absorbance of 0.85 if the 0.42 value represents 2 mg/mL?

Accepted Answer

4.05 mg/mL

Answer

Using Beer-Lambert law, absorbance is directly proportional to concentration. If 0.42 absorbance = 2 mg/mL, then 0.85 ÷ 0.42 × 2 = approximately 4.05 mg/mL. The relationship is linear, so doubling the absorbance approximately doubles the concentration.

Question 2

In an experiment studying enzyme activity, the reaction rate doubles when temperature increases from 20°C to 30°C but drops sharply at 50°C. Which conclusion is best supported by this data?

Accepted Answer

The enzyme denatures at high temperatures

Answer

Enzymes are proteins that denature at high temperatures. The doubling of reaction rate between 20°C and 30°C follows the general rule that reaction rates approximately double for every 10°C rise. The sharp drop at 50°C indicates enzyme denaturation, where the protein's 3D structure is disrupted.

Question 3

A graph shows the population of two species over 20 years. Species A increases while Species B decreases. Which hypothesis is MOST supported by this data alone?

Accepted Answer

Species A and Species B populations are negatively correlated

Answer

Without additional data, the most cautious and supported hypothesis is that there is a negative correlation between the two populations. This could indicate predator-prey relationships, competition, or other interactions, but the data alone only shows the correlation, not causation.

Question 4

Two experiments test the effect of pH on bacterial growth. Experiment 1 uses a buffer; Experiment 2 does not. Why is Experiment 1 the better experimental design?

Accepted Answer

Buffers maintain stable pH, controlling for metabolic byproducts

Answer

A buffer maintains a stable pH throughout the experiment by neutralizing acids and bases produced during bacterial metabolism. Without a buffer (Experiment 2), bacterial byproducts can shift the pH over time, making it impossible to isolate pH as an independent variable.

Question 5

A student measures the mass of a sample before and after heating and records values of 15.62 g and 12.45 g. What percentage of the original mass was lost?

Accepted Answer

20.3%

Answer

Percentage mass lost = (mass lost ÷ original mass) × 100. Mass lost = 15.62 − 12.45 = 3.17 g. Percentage = (3.17 ÷ 15.62) × 100 ≈ 20.3%. This type of calculation is common in ACT Science data interpretation questions.

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ACT Science Question and Answers