20 General Science (GS) Practice Questions & Answers
Every General Science (GS) practice question from the ASVAB Practice Test, with the correct answer and a short explanation.
Start practice test →1. Which organelle produces most of a cell's ATP through cellular respiration?
- A.Mitochondrion✓ Answer
- B.Golgi apparatus
- C.Nucleus
- D.Ribosome
Mitochondria carry out aerobic cellular respiration, breaking glucose down with oxygen and storing the released energy in ATP, which is why they are called the cell's powerhouses. Ribosomes assemble proteins, the Golgi packages them, and the nucleus stores DNA.
Source: Standard cell biology (mitochondrion = site of aerobic cellular respiration/ATP synthesis); ASVAB GS Life Science content area, DoD ASVAB Technical Bulletin No. 1, Ch. 3Report a problem with this question
2. Which structure is found in plant cells but not in animal cells?
- A.Mitochondrion
- B.Cell wall✓ Answer
- C.Ribosome
- D.Cell membrane
Plant cells are enclosed by a rigid cell wall made of cellulose that lies outside the cell membrane and gives the cell shape and support; animal cells have only the flexible membrane. Membranes, mitochondria and ribosomes occur in both cell types.
Source: Standard cell biology: plant-specific structures are the cellulose cell wall, chloroplasts and a large central vacuole; ASVAB GS Life Science content areaReport a problem with this question
3. During photosynthesis, plants take in carbon dioxide and release which gas?
- A.Nitrogen
- B.Oxygen✓ Answer
- C.Hydrogen
- D.Methane
Photosynthesis follows 6CO2 + 6H2O + light energy -> C6H12O6 + 6O2: light energy splits water molecules, and the oxygen atoms left over are released as O2 gas. Cellular respiration runs the opposite way, consuming oxygen and releasing carbon dioxide.
Source: Photosynthesis overall equation 6CO2 + 6H2O + light -> C6H12O6 + 6O2 (oxygen derived from photolysis of water); ASVAB GS Life Science content areaReport a problem with this question
4. Blood vessels that carry blood away from the heart are called:
- A.Arteries✓ Answer
- B.Veins
- C.Venules
- D.Capillaries
Arteries are defined by the direction of flow — away from the heart — not by whether the blood is oxygen-rich; the pulmonary artery, for example, carries oxygen-poor blood to the lungs. Veins return blood to the heart and capillaries are where gas and nutrient exchange occurs.
Source: Human circulatory anatomy: arteries conduct blood away from the heart, veins toward it; ASVAB GS Life Science (human body systems)Report a problem with this question
5. In the human respiratory system, oxygen passes into the bloodstream in the:
- A.Alveoli✓ Answer
- B.Trachea
- C.Diaphragm
- D.Bronchi
The alveoli are microscopic air sacs with walls one cell thick, wrapped in capillaries, so oxygen and carbon dioxide diffuse directly between air and blood there. The trachea and bronchi only conduct air, and the diaphragm is the muscle that drives breathing.
Source: Human respiratory anatomy: alveolar-capillary membrane is the site of gas exchange; ASVAB GS Life Science (human body systems)Report a problem with this question
6. Two parents heterozygous for a trait (Aa x Aa) are crossed. What fraction of offspring is expected to show the recessive trait?
- A.1/2
- B.None
- C.3/4
- D.1/4✓ Answer
A Punnett square for Aa x Aa gives genotypes 1 AA : 2 Aa : 1 aa, and only the homozygous recessive aa expresses the recessive trait, so 1/4 of the offspring show it. That is the classic 3:1 dominant-to-recessive phenotype ratio.
Source: Mendelian genetics: monohybrid cross of two heterozygotes yields 1:2:1 genotypic and 3:1 phenotypic ratios; ASVAB GS Life Science (genetics)Report a problem with this question
7. In a food chain, organisms that break down dead matter and return nutrients to the soil are called:
- A.Producers
- B.Decomposers✓ Answer
- C.Predators
- D.Herbivores
Decomposers such as bacteria and fungi digest dead organisms and waste, releasing nitrogen, carbon and other nutrients back into the soil where producers can absorb them again. Without this recycling step, nutrients would stay locked in dead tissue and the ecosystem's cycles would stall.
Source: Ecology: trophic roles — producers, consumers, decomposers in nutrient cycling; ASVAB GS Life Science (ecology)Report a problem with this question
8. A prolonged deficiency of vitamin C causes which disease?
- A.Rickets
- B.Scurvy✓ Answer
- C.Goiter
- D.Beriberi
Vitamin C is required to build collagen, the protein that holds connective tissue, gums and blood-vessel walls together, so a long shortage produces scurvy with bleeding gums and poor wound healing. Rickets comes from lack of vitamin D, beriberi from thiamine (B1) and goiter from iodine.
Source: Nutrition: vitamin C (ascorbic acid) deficiency disease is scurvy, via impaired collagen synthesis; ASVAB GS Life Science (health and nutrition)Report a problem with this question
9. Which layer of the Earth is liquid?
- A.Inner core
- B.Crust
- C.Outer core✓ Answer
- D.Mantle
The outer core is molten iron and nickel, and the movement of that liquid metal generates Earth's magnetic field. The inner core is just as hot but stays solid because of the enormous pressure, and the mantle is solid rock that only flows very slowly.
Source: Earth's internal structure: crust, solid mantle, liquid outer core, solid inner core (seismic S-wave shadow zone evidence); ASVAB GS Physical Science (earth science)Report a problem with this question
10. Marble forms when limestone is changed by heat and pressure. Marble is therefore what kind of rock?
- A.A mineral ore
- B.Igneous
- C.Sedimentary
- D.Metamorphic✓ Answer
Metamorphic rock is existing rock whose minerals are recrystallized by heat and pressure without the rock ever fully melting, which is exactly how limestone becomes marble and shale becomes slate. Igneous rock forms from cooled magma or lava, and sedimentary rock forms when sediment is compacted and cemented.
Source: Rock cycle: metamorphic rocks form from pre-existing rock altered by heat and pressure (limestone -> marble); ASVAB GS Physical Science (geology)Report a problem with this question
11. Earth's seasons are caused mainly by:
- A.The 23.5-degree tilt of Earth's axis✓ Answer
- B.Its changing distance from the Sun
- C.The Moon's gravitational pull
- D.Changes in the Sun's energy output
Because Earth's axis is tilted 23.5 degrees, each hemisphere is angled toward the Sun for part of the year and away for the rest, changing how directly sunlight strikes the surface and how long the days are. Distance is not the cause — Earth is actually closest to the Sun in early January, during Northern Hemisphere winter.
Source: Astronomy: seasons result from Earth's 23.5-degree axial tilt (obliquity), not orbital distance; ASVAB GS Physical Science (earth and space science)Report a problem with this question
12. Approximately what percentage of dry air is nitrogen?
- A.50%
- B.96%
- C.78%✓ Answer
- D.21%
Dry air is about 78% nitrogen, 21% oxygen and roughly 1% argon plus trace gases such as carbon dioxide, so nitrogen is by far the most abundant gas in Earth's atmosphere. Test-takers often pick 21% because they are thinking of oxygen, the gas we actually use.
Source: Atmospheric composition of dry air: N2 ~78%, O2 ~21%, Ar ~0.93%; concept of official ASVAB GS sample question on the principal atmospheric gasReport a problem with this question
13. A solar eclipse occurs when:
- A.The Moon passes between the Sun and Earth✓ Answer
- B.The Sun passes between Earth and the Moon
- C.The Moon is at its farthest point from Earth
- D.Earth passes between the Sun and the Moon
In a solar eclipse the Moon moves directly between the Sun and Earth and casts its shadow on Earth's surface, blocking the Sun from view. When the order is reversed and Earth's shadow falls on the Moon, the event is a lunar eclipse instead.
Source: Astronomy: solar eclipse geometry (Sun-Moon-Earth alignment at new moon); ASVAB GS Physical Science (earth and space science)Report a problem with this question
14. A light-year is a unit of:
- A.Speed
- B.Time
- C.Brightness
- D.Distance✓ Answer
A light-year is the distance light travels in one year at about 300,000 km per second — roughly 9.5 trillion kilometers — so it measures length, not elapsed time. The word 'year' in the name is what makes this a classic trap.
Source: Astronomical units: 1 light-year = distance light travels in one Julian year (~9.46 x 10^12 km); ASVAB GS Physical Science (astronomy)Report a problem with this question
15. According to Newton's second law, if the net force on an object doubles while its mass stays the same, its acceleration:
- A.Is cut in half
- B.Doubles✓ Answer
- C.Is four times greater
- D.Stays the same
Newton's second law states F = ma, which rearranges to a = F/m, so with mass held constant acceleration is directly proportional to the net force. Doubling the force therefore doubles the acceleration.
Source: Newton's second law of motion, F = ma; ASVAB GS Physical Science (force and motion)Report a problem with this question
16. An astronaut travels from Earth to the Moon. Which quantity stays the same?
- A.Mass✓ Answer
- B.Both mass and weight
- C.Neither one
- D.Weight
Mass is the amount of matter in an object and does not change with location, while weight is the force of gravity on that mass and depends on where you are. The Moon's surface gravity is about one-sixth of Earth's, so the astronaut weighs far less there but has exactly the same mass.
Source: Mass vs. weight: weight = mg varies with gravitational field strength; mass is invariant; ASVAB GS Physical Science (force and motion)Report a problem with this question
17. Why can sound not travel through a vacuum?
- A.It needs a material medium to carry vibrations✓ Answer
- B.It travels too slowly
- C.A vacuum absorbs sound
- D.It is an electromagnetic wave
Sound is a mechanical longitudinal wave: it moves by making particles of a solid, liquid or gas compress and expand against each other, so with no particles present there is nothing to vibrate. That is also why sound travels faster in solids than in air, where particles are packed closer together, while light is electromagnetic and crosses a vacuum freely.
Source: Wave physics: sound is a mechanical (longitudinal) wave requiring a material medium; ASVAB GS Physical Science (waves and sound)Report a problem with this question
18. Heat from the Sun reaches Earth across empty space mainly by:
- A.Insulation
- B.Radiation✓ Answer
- C.Convection
- D.Conduction
Radiation transfers energy as electromagnetic waves and therefore needs no matter at all, which is the only way heat can cross the vacuum between the Sun and Earth. Conduction requires direct contact between particles and convection requires a moving fluid, so neither works in space.
Source: Heat transfer mechanisms: conduction (contact), convection (fluid motion), radiation (electromagnetic waves, no medium required); ASVAB GS Physical Science (heat)Report a problem with this question
19. A 12-volt source drives a current of 3 amperes through a resistor. The resistance is:
- A.4 ohms✓ Answer
- B.0.25 ohms
- C.15 ohms
- D.36 ohms
Ohm's law states V = I x R, so resistance is R = V / I = 12 / 3 = 4 ohms. Multiplying instead of dividing gives the 36-ohm trap answer, and adding gives 15.
Source: Ohm's law, V = IR; ASVAB GS Physical Science (electricity)Report a problem with this question
20. Noble gases such as helium and neon rarely react chemically because:
- A.They are all metals
- B.Their nuclei are unstable
- C.Their outermost electron shells are full✓ Answer
- D.They contain no electrons
Chemical bonding happens when atoms gain, lose or share valence electrons to reach a full outer shell, but noble gases already have full outer shells, so they have no energetic incentive to bond. They sit in the far-right column of the periodic table, and their inertness is why helium is used in balloons and argon in welding.
Source: Periodic table Group 18 (noble gases): chemical inertness from a filled valence electron shell (octet rule); ASVAB GS Chemistry content areaReport a problem with this question
Practice questions modeled on the ASVAB content domains. Not affiliated with or endorsed by the U.S. Department of Defense, USMEPCOM, or any branch of the U.S. Armed Forces. Study the official practice materials at officialasvab.com. Official ASVAB →