A student places a sprig of the aquatic plant Elodea in a beaker of water and shines a 100-watt incandescent lamp on it from different distances. She counts the oxygen bubbles released per minute. Lamp distance (cm) Bubbles per minute 10 38 20 24 30 15 40 9 She did not measure the water temperature during any trial. Which change to the procedure would most improve the validity of her conclusion that light intensity controls the rate of photosynthesis?

Place a clear water heat shield between lamp and beaker and record the water temperature in each trial

Add a fifth trial at 50 cm so the data table covers a wider range of lamp distances

Use a brighter lamp so that the bubble counts at the greatest distance become easier to see

Count bubbles for only 30 seconds in each trial so the plant has less time to adjust to the light

A team built four solar oven prototypes and wants to compare how well each one heats water. Which testing procedure gives the fairest comparison of the designs?

Test all four ovens side by side at the same time with equal masses of water and the same thermometers

Test each oven with an amount of water scaled to its size so that larger ovens are not penalized

Test one oven per day at noon for four days, using the same mass of water in each oven

Test the team's favorite design for the longest time so its full heating ability is shown

A lab isolates an infectious particle from a sick patient. Observations: it has an RNA genome inside a protein coat, it has no ribosomes or cytoplasm, and it reproduces only after entering a host cell. Which conclusion is best supported by these observations?

It is a virus, so drugs that block bacterial ribosomes will not affect it.

It is a eukaryotic parasite, because it must live inside a host to survive.

It is a bacterium, so drugs that block cell wall synthesis will stop it.

It is a prokaryote, because it lacks a nucleus and membrane-bound organelles.

A student tests whether garlic extract slows bacterial growth. She soaks paper disks in garlic extract made with ethanol, lets them dry and places them on agar plates spread with bacteria. After 48 hours she measures the clear zone around each disk. Which disk is the most appropriate negative control?

A disk soaked in ethanol alone and dried

A disk soaked in a commercial antibiotic

A disk soaked in double-strength extract

A disk with extract on a plate of no bacteria

A team adjusts the launch angle of a classroom catapult to find the angle that gives the greatest distance. Launch angle Distance (m) 30° 4.1 40° 4.6 45° 4.7 50° 4.6 60° 4.0 What is the best plan for the next round of tests to optimize the angle?

Test angles between 40° and 50° in small steps, with repeated trials at each angle

Test angles between 10° and 30°, since the lower angles have not been tested yet

Test angles above 60°, since distance changed most sharply at the higher angles

Test only 45° many more times, since it already gave the greatest distance measured

Which property of carbon best explains why it forms the backbone of carbohydrates, lipids, proteins, and nucleic acids?

It forms four stable covalent bonds, building chains and rings

It forms metallic bonds that carry electric signals in cells

It forms ionic bonds that dissolve readily in cell fluids

It has a full outer shell, so it resists all chemical change

Earth is closest to the Sun in early January, yet January is winter in California. Which explanation best accounts for this?

Axial tilt gives lower sun angles and shorter days

Earth's axis flips to point away from the Sun in winter

The Sun's energy output drops each year during January

Clouds reflect more sunlight when Earth is near the Sun

CSET Science Subtest I (215) Foundational-Level General Science

Free CSET Science Subtest I (215) Practice Questions

10 sample questions for the CSET Science Subtest I (215) Foundational-Level General Science, with the correct answer and an explanation for each. No account needed. Try each one before you open the answer.

Sections covered on the exam: Scientific Practices, Engineering Design, and Crosscutting Concepts, Physical Sciences, Life Sciences, Earth and Space Sciences.

Question 1 · Scientific Practices, Engineering Design, and Crosscutting Concepts
A student places a sprig of the aquatic plant Elodea in a beaker of water and shines a 100-watt incandescent lamp on it from different distances. She counts the oxygen bubbles released per minute.
Lamp distance (cm) Bubbles per minute
10 38
20 24
30 15
40 9
She did not measure the water temperature during any trial.
Which change to the procedure would most improve the validity of her conclusion that light intensity controls the rate of photosynthesis?
- A.Place a clear water heat shield between lamp and beaker and record the water temperature in each trial
- B.Add a fifth trial at 50 cm so the data table covers a wider range of lamp distances
- C.Use a brighter lamp so that the bubble counts at the greatest distance become easier to see
- D.Count bubbles for only 30 seconds in each trial so the plant has less time to adjust to the light
Show answer and explanation
Answer: A. Place a clear water heat shield between lamp and beaker and record the water temperature in each trial
An incandescent lamp warms the water more at short distances, so temperature changes along with light intensity and is a confounding variable. A heat shield and temperature records let her hold temperature constant. Adding more distances or a brighter lamp does nothing to separate the effect of light from the effect of heat.
Question 2 · Scientific Practices, Engineering Design, and Crosscutting Concepts
A team built four solar oven prototypes and wants to compare how well each one heats water.
Which testing procedure gives the fairest comparison of the designs?
- A.Test each oven with an amount of water scaled to its size so that larger ovens are not penalized
- B.Test one oven per day at noon for four days, using the same mass of water in each oven
- C.Test the team's favorite design for the longest time so its full heating ability is shown
- D.Test all four ovens side by side at the same time with equal masses of water and the same thermometers
Show answer and explanation
Answer: D. Test all four ovens side by side at the same time with equal masses of water and the same thermometers
Running the ovens together controls sunlight, air temperature and wind, and equal water masses and identical thermometers keep the comparison fair. Testing on different days lets the weather vary. Giving one design more time, or changing the water mass, changes more than one variable at once.
Question 3 · Physical Sciences
A student heats 10.0 g of calcium carbonate in an open crucible until it fully decomposes by CaCO3 → CaO + CO2. The solid left behind has a mass of 5.6 g. What mass of carbon dioxide escaped?
- A.4.4 g
- B.5.6 g
- C.10.0 g
- D.15.6 g
Show answer and explanation
Answer: A. 4.4 g
Mass is conserved, so the reactant mass equals the total product mass, and the gas accounts for the missing mass. The CO2 mass is 10.0 g − 5.6 g = 4.4 g. Adding the masses (15.6 g) assumes the gas adds mass instead of leaving the crucible.
Question 4 · Life Sciences
A lab isolates an infectious particle from a sick patient. Observations: it has an RNA genome inside a protein coat, it has no ribosomes or cytoplasm, and it reproduces only after entering a host cell.
Which conclusion is best supported by these observations?
- A.It is a eukaryotic parasite, because it must live inside a host to survive.
- B.It is a virus, so drugs that block bacterial ribosomes will not affect it.
- C.It is a bacterium, so drugs that block cell wall synthesis will stop it.
- D.It is a prokaryote, because it lacks a nucleus and membrane-bound organelles.
Show answer and explanation
Answer: B. It is a virus, so drugs that block bacterial ribosomes will not affect it.
A nucleic acid genome in a protein coat with no ribosomes or cytoplasm, reproducing only inside host cells, describes a virus. Viruses have no ribosomes or cell walls for antibiotics to target. Lacking a nucleus does not make it a prokaryote, because prokaryotes are cells with their own ribosomes and metabolism.
Question 5 · Earth and Space Sciences
A newly discovered dwarf planet orbits the Sun at an average distance of 4 AU. Using Kepler's third law, P² = a³ (P in years, a in AU), what is its orbital period?
- A.2 years
- B.64 years
- C.8 years
- D.16 years
Show answer and explanation
Answer: C. 8 years
Kepler's third law gives P² = 4³ = 64, so P = √64 = 8 years. Choosing 64 years forgets the square root, and 16 years comes from setting the period equal to the distance squared (4² = 16) instead of taking the square root of the distance cubed.
Question 6 · Scientific Practices, Engineering Design, and Crosscutting Concepts
A student tests whether garlic extract slows bacterial growth. She soaks paper disks in garlic extract made with ethanol, lets them dry and places them on agar plates spread with bacteria. After 48 hours she measures the clear zone around each disk.
Which disk is the most appropriate negative control?
- A.A disk soaked in a commercial antibiotic
- B.A disk soaked in double-strength extract
- C.A disk with extract on a plate of no bacteria
- D.A disk soaked in ethanol alone and dried
Show answer and explanation
Answer: D. A disk soaked in ethanol alone and dried
A negative control receives everything except the factor being tested, so it shows whether the solvent or the disk alone affects growth. The ethanol-only disk does this. An antibiotic disk is a positive control that shows the method can detect inhibition, and double-strength extract is just another treatment level.
Question 7 · Scientific Practices, Engineering Design, and Crosscutting Concepts
A team adjusts the launch angle of a classroom catapult to find the angle that gives the greatest distance.
Launch angle Distance (m)
30° 4.1
40° 4.6
45° 4.7
50° 4.6
60° 4.0
What is the best plan for the next round of tests to optimize the angle?
- A.Test angles between 10° and 30°, since the lower angles have not been tested yet
- B.Test angles above 60°, since distance changed most sharply at the higher angles
- C.Test angles between 40° and 50° in small steps, with repeated trials at each angle
- D.Test only 45° many more times, since it already gave the greatest distance measured
Show answer and explanation
Answer: C. Test angles between 40° and 50° in small steps, with repeated trials at each angle
The data peak somewhere between 40° and 50°, so optimization means narrowing the search there with finer steps and repeated trials to reduce random error. Testing only 45° cannot reveal whether a nearby angle is better. Angles below 30° and above 60° lie in regions where distance is already falling.
Question 8 · Physical Sciences
Which property of carbon best explains why it forms the backbone of carbohydrates, lipids, proteins, and nucleic acids?
- A.It forms metallic bonds that carry electric signals in cells
- B.It forms ionic bonds that dissolve readily in cell fluids
- C.It forms four stable covalent bonds, building chains and rings
- D.It has a full outer shell, so it resists all chemical change
Show answer and explanation
Answer: C. It forms four stable covalent bonds, building chains and rings
With four valence electrons, carbon shares electrons to form four covalent bonds, including bonds to other carbon atoms, so it can build long chains, branches, and rings. Carbon does not have a full valence shell (that describes noble gases), and biological molecules are covalent, not ionic or metallic.
Question 9 · Life Sciences
During translation, a tRNA with the anticodon 3'-UAC-5' binds to a codon on the mRNA at the ribosome.
Partial codon table (mRNA codons):
AUG = Met | UAC = Tyr | AUC = Ile | GUA = Val
Which amino acid does this tRNA carry?
- A.Isoleucine
- B.Tyrosine
- C.Valine
- D.Methionine
Show answer and explanation
Answer: D. Methionine
The anticodon pairs with its complementary codon: 3'-UAC-5' pairs with 5'-AUG-3', and the codon table assigns AUG to methionine. Reading the anticodon itself as a codon gives tyrosine, which is the most common error, because codon tables list mRNA codons, not anticodons.
Question 10 · Earth and Space Sciences
Earth is closest to the Sun in early January, yet January is winter in California. Which explanation best accounts for this?
- A.Earth's axis flips to point away from the Sun in winter
- B.The Sun's energy output drops each year during January
- C.Axial tilt gives lower sun angles and shorter days
- D.Clouds reflect more sunlight when Earth is near the Sun
Show answer and explanation
Answer: C. Axial tilt gives lower sun angles and shorter days
Earth's axis is tilted about 23.5° and keeps pointing the same direction in space, so in January the Northern Hemisphere receives sunlight at a low angle for fewer hours. The small change in Earth-Sun distance matters far less, and the axis does not flip during the year.

Lamp distance (cm)	Bubbles per minute
10	38
20	24
30	15
40	9

Launch angle	Distance (m)
30°	4.1
40°	4.6
45°	4.7
50°	4.6
60°	4.0

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