ACT Science Question and Answers 2

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?

Accepted Answer

It levels off because all enzyme active sites are saturated

Answer

It continues to increase proportionally

Answer

It decreases as the enzyme becomes overwhelmed

Answer

It drops to zero as the enzyme denatures

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?

Accepted Answer

Global temperatures have increased significantly since 1960

Answer

Temperatures were constant before 1960

Answer

The temperature rise will continue at the same rate indefinitely

Answer

Human activity is the sole cause of the temperature change

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:

Accepted Answer

Scientist A, because iridium is rare on Earth but common in asteroids

Answer

Scientist B, because volcanic eruptions release iridium

Answer

Both scientists equally

Answer

Neither scientist, as iridium is unrelated to extinctions

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?

Accepted Answer

Light is becoming a limiting factor at lower intensities but another factor limits rate at higher intensities

Answer

The plant uses less light at higher intensities

Answer

CO₂ concentration doubles the rate at 200 lux

Answer

Temperature is the only 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?

Accepted Answer

Altitude (atmospheric pressure)

Answer

Temperature of the water

Answer

Volume of water used

Answer

Chemical composition 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?

Accepted Answer

Excessive nitrogen is toxic to plants beyond a certain optimal level

Answer

Plants do not need nitrogen to grow

Answer

More nitrogen always improves plant growth

Answer

The relationship between nitrogen and growth is random