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

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?

Accepted Answer

Global temperatures have increased significantly since 1960

Answer

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:

Accepted Answer

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

Answer

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?

Accepted Answer

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

Answer

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?

Accepted Answer

Altitude (atmospheric pressure)

Answer

The independent variable that was deliberately changed is altitude, which affects atmospheric pressure and therefore the boiling point of water.

ACT Practice Test

ACT Practice Test

ACT Science Question and Answers 2