40 General Science (GS) Practice Questions & Answers

1. 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.

   Ref QB-U89U6WSource: 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. 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.

   Ref QB-CREZRWSource: 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. 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.

   Ref QB-V8M6CXSource: 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. 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.

   Ref QB-DRSBXXSource: 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. 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.

   Ref QB-W8YGHYSource: 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. 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.

   Ref QB-ER5P4ZSource: 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. 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.

   Ref QB-X8BUPZSource: Ecology: trophic roles — producers, consumers, decomposers in nutrient cycling; ASVAB GS Life Science (ecology)Report a problem with this question

8. 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.

   Ref QB-7RNBWQSource: 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. 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.

   Ref QB-Q8UGGRSource: 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. 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.

    Ref QB-VRQRPTSource: 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. 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.

    Ref QB-C9JK4TSource: 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. 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.

    Ref QB-URCEHSSource: 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. 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.

    Ref QB-B979XRSource: 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. 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.

    Ref QB-XREE2WSource: 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. 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.

    Ref QB-E999FVSource: Newton's second law of motion, F = ma; ASVAB GS Physical Science (force and motion)Report a problem with this question

16. 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.

    Ref QB-WR34VUSource: 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. 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.

    Ref QB-D9WW9USource: 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. 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.

    Ref QB-RRAEZNSource: 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. 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.

    Ref QB-8959ENSource: Ohm's law, V = IR; ASVAB GS Physical Science (electricity)Report a problem with this question

20. 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.

    Ref QB-YTQW7XSource: 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

21. 21. Which cell structure controls which substances enter and leave the cell?

    • A.The mitochondrion
    • B.The cytoplasm
    • C.The cell membrane✓ Answer
    • D.The chromosome

    The cell membrane is selectively permeable: it lets some substances pass while blocking others, so it regulates everything that enters or leaves the cell. The mitochondrion releases energy, the cytoplasm is the cell's internal fluid, and chromosomes carry genetic information.

    Ref QB-GBW3TXSource: Standard high-school cell biology: the plasma membrane is selectively permeable (ASVAB GS life science domain, officialasvab.com)Report a problem with this question

22. 22. In pea plants, tall (T) is dominant over short (t). What height will a plant with genotype Tt show?

    • A.It will be tall✓ Answer
    • B.It will be variable
    • C.It will be short
    • D.It will be medium

    When one dominant allele is present, it masks the recessive allele, so a heterozygous Tt plant shows the dominant trait: tall. Traits do not blend into a medium form in simple Mendelian dominance, and the phenotype is fixed by the genotype, not random.

    Ref QB-XTCK2WSource: Mendelian genetics: a heterozygote expresses the dominant allele (law of dominance)Report a problem with this question

23. 23. Which level of biological classification is the most specific?

    • A.Species✓ Answer
    • B.Genus
    • C.Kingdom
    • D.Family

    The classification hierarchy narrows from kingdom down through phylum, class, order, family, and genus to species, so species is the smallest, most specific group — its members can interbreed and produce fertile offspring.

    Ref QB-FBJRMWSource: Linnaean taxonomy hierarchy: kingdom → phylum → class → order → family → genus → speciesReport a problem with this question

24. 24. Which of these animals is a reptile?

    • A.The salamander
    • B.The toad
    • C.The frog
    • D.The snake✓ Answer

    Reptiles have dry, scaly skin and lay shelled eggs on land, which describes the snake. Frogs, salamanders, and toads are amphibians: they have moist skin without scales and typically lay their eggs in water.

    Ref QB-WTZ8VUSource: Vertebrate class traits: reptiles = scaly skin, amniotic eggs; amphibians = moist skin, eggs in waterReport a problem with this question

25. 25. In the human digestive system, most nutrients are absorbed into the blood in:

    • A.The esophagus
    • B.The small intestine✓ Answer
    • C.The stomach
    • D.The large intestine

    The small intestine is lined with millions of finger-like villi that create an enormous surface area, so it is where most digested nutrients pass into the bloodstream. The stomach mainly breaks food down, the large intestine mainly absorbs water, and the esophagus only transports food.

    Ref QB-EB7EFVSource: Human digestive system: villi of the small intestine perform most nutrient absorptionReport a problem with this question

26. 26. The central nervous system consists of the:

    • A.Spinal cord and body nerves
    • B.Brain and cranial nerves
    • C.Brain and spinal cord✓ Answer
    • D.Sensory and motor nerves

    The nervous system is divided into two parts: the central nervous system, made of the brain and spinal cord, which processes information; and the peripheral nervous system, made of the cranial, sensory, and motor nerves that carry signals to and from it.

    Ref QB-VTNWPTSource: Human nervous system anatomy: CNS = brain + spinal cord; all other nerves form the PNSReport a problem with this question

27. 27. In the human body, tendons connect:

    • A.Muscle to bone✓ Answer
    • B.Bone to cartilage
    • C.Muscle to muscle
    • D.Bone to bone

    Tendons are tough cords of connective tissue that anchor muscles to bones, transmitting the pull of a contracting muscle so the bone moves. Ligaments are the structures that connect bone to bone at joints — the classic point of confusion.

    Ref QB-DBU3AUSource: Musculoskeletal anatomy: tendons attach muscle to bone; ligaments attach bone to boneReport a problem with this question

28. 28. A childhood deficiency of vitamin D can cause which disease?

    • A.Anemia
    • B.Rickets✓ Answer
    • C.Goiter
    • D.Beriberi

    Vitamin D is needed for the body to absorb calcium and harden growing bones; without it, children's bones stay soft and bend, a disease called rickets. Anemia is linked to iron deficiency, goiter to iodine deficiency, and beriberi to vitamin B1 deficiency.

    Ref QB-UTAKHSSource: Nutrition/deficiency diseases: vitamin D deficiency → rickets (impaired calcium absorption)Report a problem with this question

29. 29. A solution with a pH of 9 is best described as:

    • A.Acidic
    • B.Basic✓ Answer
    • C.Saturated
    • D.Neutral

    On the pH scale, 7 is neutral, values below 7 are acidic, and values above 7 are basic (alkaline); since 9 is above 7, the solution is basic. Saturation describes how much solute is dissolved and has nothing to do with pH.

    Ref QB-CBGR4TSource: pH scale: 7 neutral, <7 acidic, >7 basicReport a problem with this question

30. 30. Which of the following is a chemical change?

    • A.Iron rusting✓ Answer
    • B.Sugar dissolving
    • C.Water boiling
    • D.Ice melting

    A chemical change produces a new substance with different properties: rusting combines iron with oxygen to form iron oxide, a new compound. Melting, dissolving, and boiling are physical changes — the substance changes state or mixes but remains chemically the same and can be recovered.

    Ref QB-MXR4ZUSource: Physical vs chemical change: chemical change forms a new substance (rusting = oxidation of iron)Report a problem with this question

31. 31. The atomic number of an element equals the number of:

    • A.Protons plus neutrons
    • B.Neutrons in the nucleus
    • C.Protons in the nucleus✓ Answer
    • D.Electrons plus neutrons

    The atomic number counts only the protons in the nucleus, and it is what defines the identity of an element on the periodic table. Protons plus neutrons give the mass number instead — the classic trap — while neutron count alone can vary between isotopes of the same element.

    Ref QB-4FKXDUSource: Atomic structure: atomic number = proton count; mass number = protons + neutronsReport a problem with this question

32. 32. A cork floats on water because the cork's density is:

    • A.Equal to that of water
    • B.Unrelated to that of water
    • C.Less than that of water✓ Answer
    • D.Greater than that of water

    An object floats when it is less dense than the fluid it is placed in, because the buoyant force from the displaced water exceeds the object's weight. If its density were greater than water's it would sink, and if equal it would hover suspended rather than float on top.

    Ref QB-H66T53Source: Density and buoyancy (Archimedes' principle): objects less dense than the fluid float — applied style of officialasvab.com GS samplesReport a problem with this question

33. 33. Dry ice changing directly from a solid into a gas is an example of:

    • A.Deposition
    • B.Evaporation
    • C.Sublimation✓ Answer
    • D.Condensation

    Sublimation is the phase change in which a solid turns directly into a gas without ever becoming a liquid, which is exactly what dry ice (solid CO2) does. Evaporation goes from liquid to gas, condensation from gas to liquid, and deposition is the reverse of sublimation — gas straight to solid.

    Ref QB-ZNYMJ2Source: States of matter / phase changes: sublimation = solid → gas (dry ice, CO2)Report a problem with this question

34. 34. An object's resistance to any change in its state of motion is called:

    • A.Momentum
    • B.Friction
    • C.Inertia✓ Answer
    • D.Acceleration

    Newton's first law states that an object at rest stays at rest and an object in motion keeps moving in a straight line unless acted on by an outside force; this built-in resistance to change is inertia, and it increases with mass. Momentum is a quantity (mass times velocity), not a resistance, friction is an external force, and acceleration is the change itself.

    Ref QB-J6H5B4Source: Newton's first law of motion (law of inertia)Report a problem with this question

35. 35. A rocket rises because the gases it pushes downward push back up on the rocket, an example of Newton's:

    • A.Third law of motion✓ Answer
    • B.Law of gravitation
    • C.First law of motion
    • D.Second law of motion

    Newton's third law says that for every action there is an equal and opposite reaction: the rocket pushes exhaust gases down, and the gases push the rocket up with equal force. The first law concerns inertia, the second relates force to mass and acceleration, and gravitation describes attraction between masses.

    Ref QB-2PBYQ3Source: Newton's third law of motion: action-reaction force pairsReport a problem with this question

36. 36. The freezing point of water, 0 degrees Celsius, is equal to:

    • A.0 °F
    • B.273 °F
    • C.100 °F
    • D.32 °F✓ Answer

    The conversion formula is F = (9/5)C + 32, so 0 °C gives (9/5)(0) + 32 = 32 °F. The Fahrenheit and Celsius scales have different zero points — 0 °F is well below freezing — and 273 is the Kelvin value (273 K), not Fahrenheit.

    Ref QB-K6VFG5Source: Temperature scales: F = (9/5)C + 32; water freezes at 0 °C = 32 °F = 273 K (officialasvab.com sample-question topic)Report a problem with this question

37. 37. In a pot of water heating on a stove, heat spreads through the water mainly by:

    • A.Convection✓ Answer
    • B.Radiation
    • C.Evaporation
    • D.Conduction

    In liquids and gases, heat moves mainly by convection: warm water at the bottom expands, becomes less dense, and rises while cooler water sinks, creating circulating currents that carry heat through the pot. Conduction dominates in solids (like the metal pot itself), radiation transfers heat by waves, and evaporation is a phase change, not a heat-transfer mode within the water.

    Ref QB-3PPAW4Source: Heat transfer modes: convection = heat carried by circulating currents in fluidsReport a problem with this question

38. 38. In the water cycle, clouds form when water vapor cools and turns into tiny liquid droplets, a process called:

    • A.Precipitation
    • B.Evaporation
    • C.Transpiration
    • D.Condensation✓ Answer

    Condensation is the change from gas to liquid: as rising water vapor cools in the atmosphere, it condenses onto tiny particles to form the droplets that make up clouds. Evaporation is the opposite change (liquid to gas), precipitation is water falling as rain or snow, and transpiration is water vapor released by plants.

    Ref QB-M68TN6Source: Water cycle stages: condensation (gas → liquid) forms cloudsReport a problem with this question

39. 39. Day and night on Earth are caused by:

    • A.Earth's rotation on its axis✓ Answer
    • B.The Moon's orbit around Earth
    • C.Earth's orbit around the Sun
    • D.The tilt of Earth's axis

    Earth spins once on its axis about every 24 hours, so any given location turns into sunlight (day) and then away from it (night). Revolution around the Sun takes a full year and defines the year, the Moon's orbit causes tides and moon phases, and the axial tilt is responsible for the seasons.

    Ref QB-4P2N36Source: Earth's motions: rotation (≈24 h) causes day/night; revolution (1 year) defines the year — rotation-vs-revolution distinctionReport a problem with this question

40. 40. In the scientific method, a hypothesis is best described as:

    • A.A testable explanation✓ Answer
    • B.A final research conclusion
    • C.A fact proven beyond doubt
    • D.A law that cannot change

    A hypothesis is a proposed explanation for an observation that can be tested by experiment — it is made before the evidence is in, which is why it must be testable and can be rejected. It is not a proven fact or a final conclusion, and it differs from a law, which summarizes what consistently happens.

    Ref QB-K8TMG5Source: Scientific method: hypothesis = testable proposed explanation, distinct from theory and lawReport a problem with this question

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