ACT Science Question and Answers 2 — Questions and Answers
Question 1: In an experiment studying enzyme activity, a researcher increases substrate concentration while keeping enzyme concentration constant. What happens to the reaction rate beyond a certain point?
- It levels off because all enzyme active sites are saturated (Correct answer)
- It continues to increase proportionally
- It decreases as the enzyme becomes overwhelmed
- It drops to zero as the enzyme denatures
Correct answer: It levels off because all enzyme active sites are saturated
Once all active sites on enzyme molecules are occupied (saturation), additional substrate cannot increase the rate further. This maximum rate is called Vmax.
Question 2: A scientist records average global temperature anomalies from 1880–2020. The data shows a steady upward trend after 1960. Which conclusion is best supported?
- Global temperatures have increased significantly since 1960 (Correct answer)
- Temperatures were constant before 1960
- The temperature rise will continue at the same rate indefinitely
- Human activity is the sole cause of the temperature change
Correct answer: Global temperatures have increased significantly since 1960
The data directly supports that temperatures rose significantly after 1960. Cause attribution and future projections require additional data beyond what is described.
Question 3: Two scientists disagree about the cause of a mass extinction event 66 million years ago. Scientist A argues it was caused by an asteroid impact; Scientist B argues volcanic activity was the primary cause. A discovery of a thin iridium-rich layer worldwide at the 66-million-year boundary most supports:
- Scientist A, because iridium is rare on Earth but common in asteroids (Correct answer)
- Scientist B, because volcanic eruptions release iridium
- Both scientists equally
- Neither scientist, as iridium is unrelated to extinctions
Correct answer: Scientist A, because iridium is rare on Earth but common in asteroids
Iridium is extremely rare in Earth's crust but is abundant in meteorites and asteroids. A global iridium layer at the extinction boundary strongly supports the asteroid impact hypothesis (Scientist A).
Question 4: In a table showing photosynthesis rates at different light intensities, the rate doubles from 200 to 400 lux but only increases by 10% from 800 to 1,600 lux. What does this indicate?
- Light is becoming a limiting factor at lower intensities but another factor limits rate at higher intensities (Correct answer)
- The plant uses less light at higher intensities
- CO₂ concentration doubles the rate at 200 lux
- Temperature is the only limiting factor
Correct answer: Light is becoming a limiting factor at lower intensities but another factor limits rate at higher intensities
The rapid rate increase at low light intensity shows light is limiting there. The plateau at high intensity indicates another factor (CO₂ or temperature) has become the new limiting factor.
Question 5: A researcher measures the boiling point of water at sea level (100°C) and at 3,000 m elevation (90°C). Which variable was manipulated?
- Altitude (atmospheric pressure) (Correct answer)
- Temperature of the water
- Volume of water used
- Chemical composition of water
Correct answer: Altitude (atmospheric pressure)
The independent variable that was deliberately changed is altitude, which affects atmospheric pressure and therefore the boiling point of water.
Question 6: A graph shows that as soil nitrogen content increases from 0 to 50 ppm, plant growth increases. From 50 to 100 ppm, plant growth declines. What can be concluded?
- Excessive nitrogen is toxic to plants beyond a certain optimal level (Correct answer)
- Plants do not need nitrogen to grow
- More nitrogen always improves plant growth
- The relationship between nitrogen and growth is random
Correct answer: Excessive nitrogen is toxic to plants beyond a certain optimal level
The data shows an optimal nitrogen level (~50 ppm). Beyond this, growth declines, indicating that excessive nitrogen is harmful — a phenomenon of nutrient toxicity.
ACT Science Question and Answers 2
In an experiment studying enzyme activity, a researcher increases substrate concentration while keeping enzyme concentration constant.
What happens to the reaction rate beyond a certain point?