CLEP® practice test

Free CLEP Natural Sciences Practice Test (2026)

This is a set of 25 original practice questions that follow the official CLEP Natural Sciences content outline and its topic weights, each with a short explanation.

  • 25 questions
  • 10 topics from the official outline
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The practice test

25 questions

Question 1 of 25In the ABO blood group system, alleles A and B are codominant and both are dominant to allele O. A woman with type A blood and a man with type B blood have a child with type O blood. What must the genotypes of the woman and the man be, in that order?
Question 2 of 25Along the west coast of South America there is a deep ocean trench just offshore, a chain of volcanoes on land, and earthquakes that occur at greater depths the farther inland they are. What best explains these features?
Question 3 of 25A sample of double-stranded DNA is 30% adenine. What percentage of its bases are guanine?
Question 4 of 25After an antibiotic has been used heavily in a hospital for several years, most bacteria of one species found there are resistant to it. Which explanation fits natural selection?
Question 5 of 25A loaded truck and a small car collide head-on. During the collision, how does the force the truck exerts on the car compare with the force the car exerts on the truck?
Question 6 of 25Iodine-131 has a half-life of about 8 days. If a sample contains 40 mg of iodine-131, about how much iodine-131 remains after 24 days?
Question 7 of 25Which blood vessels carry oxygen-poor blood away from the heart?
Question 8 of 25In a lake, algae capture 50,000 kilocalories of energy per square meter each year. If about 10% of the energy at each feeding level passes to the next level, about how much reaches the tertiary consumers, per square meter each year?
Question 9 of 25What will a star with about the same mass as the Sun most likely become after it has used up its nuclear fuel and shed its outer layers?
Question 10 of 25Water (molar mass 18 g/mol) boils at 100 °C, but methane (molar mass 16 g/mol) boils at about −162 °C. What best explains the difference?
Question 11 of 25Which observation best supports the idea that mitochondria evolved from bacteria that were engulfed by an ancient host cell?
Question 12 of 25In vertebrate embryos, the brain and spinal cord develop from which germ layer?
Question 13 of 25A spaceship travels at 0.6c (60% of the speed of light) on a trip that takes 10 years as measured by observers on Earth. According to special relativity, how much time passes on the ship's own clock during the trip? (Use γ = 1/√(1 − v²/c²).)
Question 14 of 25During aerobic cellular respiration, which stage makes the most ATP?
Question 15 of 25Two 3-ohm resistors are connected in series to a 12-volt battery. Ignoring the battery's internal resistance, what current flows in the circuit?
Question 16 of 25A cliff shows three flat rock layers: sandstone at the bottom, shale above it, and limestone at the top. A dike of igneous rock cuts up through the sandstone and the shale; its top was eroded flat before the limestone was deposited, so the limestone lies unbroken across it. The layers have never been overturned. What is the order of events, from oldest to youngest?
Question 17 of 25In a plant, purple flowers (P) are dominant to white flowers (p). A purple-flowered plant is crossed with a white-flowered plant, and about half of the 120 offspring have white flowers. What is the genotype of the purple parent?
Question 18 of 25Uranium-238 (atomic number 92) decays by emitting an alpha particle. What are the atomic number and mass number of the nucleus that forms?
Question 19 of 25Archaea look much like bacteria under a microscope, yet biologists place them in a separate domain. What evidence first led to this?
Question 20 of 25A wildfire kills all the trees in a forest but leaves the soil in place. Over the next decades, grasses, then shrubs, then young trees grow back. What is this process called?
Question 21 of 25Light from distant galaxies is shifted toward longer, redder wavelengths, and the farther away a galaxy is, the larger its redshift. What does this mainly tell astronomers?
Question 22 of 25A single-celled organism has a cell membrane, a cell wall, and a circular chromosome, but no nucleus. Which structure must it also have?
Question 23 of 25A pot of ice and water is heated slowly on a stove, and a thermometer shows the mixture stays at 0 °C until all the ice has melted. What happens to the energy added during this time?
Question 24 of 25How does the hydrogen ion concentration of a solution with pH 3 compare with that of a solution with pH 5?
Question 25 of 25Why can a vaccine protect a person for years after it is given?

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