ACT Science Question and Answers — Questions 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?
- 4.05 mg/mL (Correct answer)
- 2.85 mg/mL
- 1.70 mg/mL
- 6.10 mg/mL
Correct answer: 4.05 mg/mL
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?
- The enzyme denatures at high temperatures (Correct answer)
- The reaction requires more substrate at higher temperatures
- Temperature has no effect on enzyme activity
- The enzyme is most active at 20°C
Correct answer: The enzyme denatures at high temperatures
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?
- Species A and Species B populations are negatively correlated (Correct answer)
- Species A is preying on Species B
- Species B is being outcompeted for food by Species A
- A disease is killing Species B
Correct answer: Species A and Species B populations are negatively correlated
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?
- Buffers maintain stable pH, controlling for metabolic byproducts (Correct answer)
- Buffers increase bacterial growth rate
- Buffers eliminate the need for a control group
- Buffers sterilize the growth medium
Correct answer: Buffers maintain stable pH, controlling for metabolic byproducts
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?
- 20.3% (Correct answer)
- 25.5%
- 17.8%
- 15.6%
Correct answer: 20.3%
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.
Question 6: Scientist 1 claims that global temperatures are rising due to increased CO₂. Scientist 2 claims natural solar cycles are responsible. Which evidence would MOST strongly support Scientist 1's view?
- A strong correlation between CO₂ levels and temperature independent of solar output changes (Correct answer)
- Increased solar activity over the past century
- Rising sea levels in coastal cities
- Melting glaciers in mountainous regions
Correct answer: A strong correlation between CO₂ levels and temperature independent of solar output changes
Strong evidence for CO₂-driven warming would be a strong statistical correlation between atmospheric CO₂ concentration and global temperature over time, especially if this correlation holds during periods of stable solar output. This directly addresses the competing hypothesis about solar cycles.
ACT Science Question and Answers
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?