ASVAB General Science Study Guide: Everything You Need to Know
The General Science (GS) section of the ASVAB covers a wide range of topics — biology, earth science, chemistry, physics, and more. While it doesn't count toward your AFQT score, it feeds into critical line scores like the ST (Skilled Technical) and GM (General Maintenance) composites that determine whether you qualify for technical and medical jobs.
This guide covers every major topic you'll see on the GS section, organized from most to least commonly tested.
Why General Science Matters
The GS section has 15 questions and a 10-minute time limit on the CAT-ASVAB. It may not affect your AFQT, but it affects these important line scores:
- Army ST (Skilled Technical): GS + WK + PC + MK + MC
- Army GM (General Maintenance): GS + AS + MK + EI
- Marines GT: Includes GS for some calculations
- Navy/Coast Guard: GS is part of several rating qualifications
Jobs that need GS include combat medic (68W), lab technician, dental specialist, and many maintenance roles. Check the job explorer to see which careers need strong GS scores.
Biology
Biology is the most heavily tested topic on the GS section. Expect 4-5 questions on human biology and life science.
Human Body Systems
Circulatory System:
- The heart pumps blood through arteries (away from heart) and veins (toward heart)
- Arteries carry oxygenated blood (except pulmonary arteries)
- Red blood cells carry oxygen using hemoglobin
- White blood cells fight infection
- Platelets help blood clot
Respiratory System:
- Oxygen enters through the nose/mouth, passes through the trachea, bronchi, and into the lungs
- Gas exchange happens in the alveoli — oxygen enters the blood, carbon dioxide exits
- The diaphragm contracts to expand the lungs during inhalation
Digestive System:
- Mouth (mechanical and chemical digestion) → Esophagus → Stomach (acid breaks down food) → Small intestine (nutrients absorbed) → Large intestine (water absorbed) → Excretion
- The liver produces bile for fat digestion
- The pancreas produces enzymes and insulin
Nervous System:
- Central nervous system: brain and spinal cord
- Peripheral nervous system: nerves throughout the body
- Neurons transmit electrical signals called impulses
- Reflex arcs bypass the brain for faster response
Skeletal and Muscular Systems:
- Adults have 206 bones
- Joints are where bones meet — ball-and-socket (shoulder), hinge (elbow), pivot (neck)
- Three types of muscle: skeletal (voluntary), smooth (involuntary), cardiac (heart)
- Tendons connect muscle to bone; ligaments connect bone to bone
- Cell membrane: controls what enters and exits the cell
- Nucleus: contains DNA, controls cell activity
- Mitochondria: produces ATP (energy) — "powerhouse of the cell"
- Ribosomes: produce proteins
- Cell wall: found in plant cells only, provides structure
- Chloroplasts: found in plant cells, perform photosynthesis
Cell Biology
Mitosis vs Meiosis:
- Mitosis: cell division producing 2 identical cells (growth and repair)
- Meiosis: cell division producing 4 sex cells with half the chromosomes (reproduction)
- DNA is a double helix made of nucleotide base pairs: A-T and C-G
- Genes are segments of DNA that code for traits
- Dominant alleles (AA or Aa) override recessive alleles (aa)
- A Punnett square predicts offspring trait probabilities
- Producers: plants (make food via photosynthesis)
- Consumers: animals (eat other organisms)
- Decomposers: fungi and bacteria (break down dead matter)
- Food chain: producer → primary consumer → secondary consumer → tertiary consumer
- Ecosystem: all living (biotic) and non-living (abiotic) factors in an environment
Genetics Basics
Ecology
Earth Science
Expect 2-3 questions on earth science topics.
Geology
Three types of rocks:
- Igneous: formed from cooled magma/lava (granite, basalt, obsidian)
- Sedimentary: formed from compressed sediments (sandstone, limestone, shale)
- Metamorphic: formed from existing rocks changed by heat/pressure (marble, slate, quartzite)
- The rock cycle: rocks can transform between all three types
Earth's Layers:
- Crust: thin outer layer (5-70 km thick)
- Mantle: thick, semi-solid layer (2,900 km thick)
- Outer core: liquid iron and nickel
- Inner core: solid iron and nickel (hottest layer)
Plate Tectonics:
- Earth's crust is divided into tectonic plates
- Plates move due to convection currents in the mantle
- Convergent boundaries: plates collide (mountains, trenches)
- Divergent boundaries: plates separate (mid-ocean ridges)
- Transform boundaries: plates slide past each other (earthquakes)
Weather and Atmosphere
Atmosphere layers (from surface up):
- Troposphere (weather happens here, 0-12 km)
- Stratosphere (ozone layer, 12-50 km)
- Mesosphere (50-80 km)
- Thermosphere (80-700 km)
- Exosphere (outermost, transitions to space)
Weather concepts:
- High pressure systems bring clear skies
- Low pressure systems bring clouds and precipitation
- Warm fronts: warm air moves over cold air (gradual rain)
- Cold fronts: cold air pushes under warm air (thunderstorms)
- Humidity: amount of water vapor in the air
- Solar system order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
- Inner planets: rocky (Mercury, Venus, Earth, Mars)
- Outer planets: gas/ice giants (Jupiter, Saturn, Uranus, Neptune)
- Earth's rotation: causes day and night (24 hours)
- Earth's revolution: orbit around the sun causes seasons (365.25 days)
- Moon phases: New Moon → Waxing Crescent → First Quarter → Waxing Gibbous → Full Moon → Waning Gibbous → Third Quarter → Waning Crescent
- Tides: caused by the gravitational pull of the moon and sun
- Atoms are made of protons (positive, in nucleus), neutrons (neutral, in nucleus), and electrons (negative, orbit nucleus)
- Atomic number = number of protons (defines the element)
- Atomic mass = protons + neutrons
- Isotopes = same element, different number of neutrons
- Ions = atoms with gained or lost electrons (positive = cation, negative = anion)
- Elements are organized by atomic number
- Groups (columns): elements with similar properties
- Periods (rows): elements with same number of electron shells
- Metals: left side (conduct electricity, malleable)
- Nonmetals: right side (poor conductors, brittle)
- Noble gases: far right column (unreactive, full outer shell)
- Reactants (left side of arrow) become products (right side)
- Law of Conservation of Mass: matter cannot be created or destroyed
- Exothermic: releases heat (combustion, explosion)
- Endothermic: absorbs heat (photosynthesis, melting ice)
- Scale of 0-14 measuring acidity/basicity
- 0-6: Acidic (lemon juice = 2, vinegar = 3)
- 7: Neutral (pure water)
- 8-14: Basic/alkaline (baking soda = 9, bleach = 13)
- Solid: fixed shape and volume (molecules tightly packed)
- Liquid: fixed volume, takes shape of container
- Gas: no fixed shape or volume (molecules spread out)
- Plasma: ionized gas (stars, lightning)
- Phase changes: melting, freezing, evaporation, condensation, sublimation
- Newton's First Law (Inertia): An object at rest stays at rest; an object in motion stays in motion unless acted on by a force
- Newton's Second Law: Force = Mass × Acceleration (F = ma)
- Newton's Third Law: Every action has an equal and opposite reaction
- Gravity: 9.8 m/s² on Earth's surface
- Friction: force that opposes motion between surfaces
- Kinetic energy: energy of motion (KE = ½mv²)
- Potential energy: stored energy (gravitational PE = mgh)
- Conservation of Energy: energy cannot be created or destroyed, only transformed
- Types: mechanical, thermal, chemical, electrical, nuclear, light, sound
- Wavelength: distance between wave peaks
- Frequency: number of waves per second (measured in Hertz)
- Amplitude: height of a wave (determines loudness for sound)
- Sound travels faster through solids than liquids, and faster through liquids than gases
- Speed of sound in air: approximately 343 m/s
- Conduction: heat transfer through direct contact (metal spoon in hot soup)
- Convection: heat transfer through fluid movement (boiling water)
- Radiation: heat transfer through electromagnetic waves (sun warming Earth)
Astronomy
Chemistry
Expect 2-3 chemistry questions.
Atomic Structure
Periodic Table Basics
Chemical Reactions
pH Scale
States of Matter
Physics
Expect 2-3 physics questions, focusing on mechanics and energy.
Forces and Motion
Energy
Waves and Sound
Heat Transfer
Quick Reference: Most Common GS Questions
Based on frequency on recent ASVAB tests:
1. Human body systems (circulatory, respiratory, digestive) — 3-4 questions 2. Cell biology and genetics — 1-2 questions 3. Earth science (rocks, atmosphere) — 2 questions 4. Chemistry basics (atoms, pH, states of matter) — 2 questions 5. Physics (forces, energy) — 2 questions 6. Ecology and environment — 1 question 7. Astronomy — 1 question
Study Tips for General Science
Tip 1: Prioritize biology. It's the most heavily tested topic. If you're short on time, spend 50% of your GS study on human body systems and cell biology.
Tip 2: Use mnemonics. "My Very Educated Mother Just Served Us Nachos" for planet order. "King Philip Came Over For Good Spaghetti" for taxonomy (Kingdom, Phylum, Class, Order, Family, Genus, Species).
Tip 3: Don't go deep. The ASVAB tests breadth, not depth. You need to know what mitochondria DO, not the Krebs cycle. Know what tectonic plates ARE, not the names of specific plates.
Tip 4: Practice with real questions. Understanding concepts is step one. Applying them under time pressure is step two. Use the General Science practice section for timed practice.
Tip 5: Connect topics. Chemistry explains biology (pH affects enzymes). Physics explains earth science (convection drives plate tectonics). Seeing connections makes everything easier to remember.
Next Steps
1. Take a practice test to see your current GS score 2. Review the topics above, starting with biology 3. Practice with GS questions daily 4. Check which military jobs need strong GS scores 5. Use the study guides for deeper topic review