ASVAB General Science — Life Science and Biology Questions

The cell is the basic structural and functional unit of all living organisms. Cell theory (one of biology's foundational principles): (1) All living things are composed of one or more cells; (2) The cell is the basic unit of life; (3) All cells come from pre-existing cells. Levels of biological organization (smallest to largest): atom → molecule → organelle → cell → tissue → organ → organ system → organism → population → community → ecosystem → biome → biosphere. Cell types: (1) Prokaryotic — bacteria and archaea; no membrane-bound nucleus; smaller, simpler; circular DNA in nucleoid; (2) Eukaryotic — plants, animals, fungi, protists; membrane-bound nucleus containing DNA in chromosomes; membrane-bound organelles (mitochondria, ER, Golgi, lysosomes, chloroplasts in plants). Major cell structures: cell membrane (boundary, selectively permeable), cytoplasm (interior), nucleus (control center, DNA), mitochondria (powerhouse, ATP production), ribosomes (protein synthesis). Plant cells additionally have: cell wall (rigid, cellulose), chloroplasts (photosynthesis), large central vacuole.

Photosynthesis occurs in plants, algae, and some bacteria, converting light energy into chemical energy stored in glucose. Equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. Plants take in CO₂ through stomata in leaves; absorb water through roots; capture light using chlorophyll in chloroplasts (green pigment); produce glucose (food) and release oxygen as byproduct. Two main stages: (1) Light-dependent reactions — occur in thylakoid membranes; produce ATP and NADPH; split water releasing O₂; (2) Light-independent reactions (Calvin cycle) — occur in stroma; use ATP and NADPH to fix CO₂ into glucose. Photosynthesis is the foundation of nearly all food chains; provides oxygen for aerobic respiration. Cellular respiration is essentially the reverse: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP. Plants do BOTH photosynthesis (during light) and respiration (all the time). Net effect during day: photosynthesis dominates, plants produce O₂ and consume CO₂. At night: only respiration, plants consume O₂ and produce CO₂.

Arteries carry blood AWAY from the heart (think: A for Away, A for Artery). Veins carry blood TOWARD the heart. Capillaries are tiny vessels between arteries and veins where exchange of gases, nutrients, and waste occurs. Arterial vs venous characteristics: (1) Arteries — thick muscular walls (withstand high pressure), elastic, carry oxygenated blood (except pulmonary arteries which carry deoxygenated blood from heart to lungs), no valves; (2) Veins — thinner walls, lower pressure, carry deoxygenated blood (except pulmonary veins carrying oxygenated blood from lungs to heart), have valves preventing backflow; (3) Capillaries — single-cell thick walls allow diffusion of gases, nutrients, waste between blood and tissues. Circulation paths: Systemic circulation — heart pumps oxygenated blood from left ventricle through aorta to body, returns deoxygenated through superior/inferior vena cava to right atrium. Pulmonary circulation — right ventricle pumps deoxygenated blood through pulmonary arteries to lungs, returns oxygenated through pulmonary veins to left atrium. Heart chambers: right atrium, right ventricle (pulmonary), left atrium, left ventricle (systemic).

Atomic number = number of protons in the nucleus; uniquely identifies the element. Carbon has 6 protons (atomic number 6); oxygen has 8; iron has 26. The periodic table is organized by atomic number, increasing left-to-right and top-to-bottom. Atoms also contain: (1) Neutrons — in the nucleus, no charge, similar mass to protons; mass number = protons + neutrons; isotopes are atoms of the same element with different neutron counts; (2) Electrons — orbit the nucleus in shells; negative charge; mass much less than protons/neutrons; in a neutral atom, electrons = protons. Periodic table organization: Periods (rows) — elements have same number of electron shells. Groups (columns) — elements have similar chemical properties due to same number of valence (outer-shell) electrons. Group 1: alkali metals (highly reactive). Group 2: alkaline earth metals. Groups 3-12: transition metals. Group 17: halogens (highly reactive nonmetals). Group 18: noble gases (very unreactive). Metals on left side; nonmetals upper right; metalloids on the diagonal between.

Water = H₂O = 2 hydrogen atoms + 1 oxygen atom. Common chemical formulas to know: H₂O (water); CO₂ (carbon dioxide); O₂ (oxygen gas); N₂ (nitrogen gas); H₂ (hydrogen gas); NaCl (sodium chloride/salt); HCl (hydrochloric acid); NaOH (sodium hydroxide/lye); H₂SO₄ (sulfuric acid); NH₃ (ammonia); CH₄ (methane); C₆H₁₂O₆ (glucose); H₂O₂ (hydrogen peroxide); O₃ (ozone); CaCO₃ (calcium carbonate/limestone). Water properties making it essential for life: (1) Polar molecule — oxygen attracts electrons more than hydrogen, creating partial negative on O and partial positive on H; this polarity allows water to dissolve many substances ('universal solvent'); (2) Hydrogen bonding — partial charges attract neighboring water molecules; gives water high surface tension, cohesion, adhesion, high specific heat, high heat of vaporization; (3) Density anomaly — water expands when freezing, so ice floats on liquid water; insulates aquatic life in winter; (4) Three states common at Earth temperatures (solid, liquid, gas).

pH scale measures acidity/alkalinity from 0 to 14: pH < 7 = acidic; pH = 7 = neutral; pH > 7 = basic/alkaline. Pure water has pH 7. Logarithmic scale: each integer change is a 10-fold change in H+ concentration. So pH 4 is 10× more acidic than pH 5, 100× more than pH 6. Common substances and approximate pH: stomach acid 1-2; lemon juice 2; vinegar 2-3; orange juice 3-4; coffee 5; rain (natural) 5.6; milk 6.5; pure water 7; blood 7.4; baking soda solution 9; ammonia 11; bleach 12; lye (sodium hydroxide) 14. Acids: substances that donate H+ ions (Brønsted-Lowry definition) or accept electron pairs (Lewis definition). Strong acids fully dissociate (HCl, H₂SO₄); weak acids partially dissociate. Bases: substances that accept H+ ions or donate hydroxide (OH-). Strong bases fully dissociate (NaOH, KOH); weak bases partially. Acid-base reactions produce salt and water. Buffers resist pH change — blood pH maintained 7.35-7.45 by bicarbonate buffer system. pH affects enzyme function; small changes can disrupt metabolism.

Newton's three laws of motion: (1) FIRST LAW (Inertia): An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted on by a net external force. Objects 'want' to keep doing what they're doing; inertia is the resistance to change in motion. Mass measures inertia — more massive objects are harder to start, stop, or change direction. Example: a book on a table stays still until you push it; a hockey puck on frictionless ice would slide forever. (2) SECOND LAW (F = ma): The net force on an object equals its mass times its acceleration. F = ma. Force is measured in Newtons (kg·m/s²). Acceleration is the change in velocity over time. Mass is constant for an object. Example: more force on the same mass = more acceleration; same force on more mass = less acceleration. (3) THIRD LAW (Action-Reaction): For every action, there is an equal and opposite reaction. When object A exerts force on object B, B exerts equal but opposite force on A. Example: when you push against a wall, the wall pushes back with equal force; a rocket pushes hot gas out the back, the gas pushes the rocket forward. Newton's laws apply to non-relativistic, non-quantum scales — everyday physics. Einstein's relativity modifies them at near-light speeds; quantum mechanics modifies them at atomic scales.

Newton's Second Law: F = ma. Force = mass × acceleration. Units: Force in Newtons (N); mass in kilograms (kg); acceleration in meters per second squared (m/s²). 1 Newton = 1 kg·m/s² (the force needed to accelerate 1 kg at 1 m/s²). Other common physics formulas: (1) Weight = mg (mass × gravitational acceleration; g = 9.8 m/s² on Earth); weight is a force, mass is a quantity of matter; (2) Velocity = displacement/time; (3) Acceleration = change in velocity/time; (4) Kinetic energy = ½mv²; (5) Gravitational potential energy = mgh; (6) Work = force × distance (when in the same direction); (7) Power = work/time; (8) Momentum = mv; (9) Density = mass/volume; (10) Pressure = force/area. Solving F = ma problems: identify what's given (typically 2 of 3), solve for unknown. Example: a 2 kg object accelerates at 5 m/s²; force = 2 × 5 = 10 N. Example: a 50 N force on a 10 kg object; acceleration = 50/10 = 5 m/s². Net force: when multiple forces act, sum them as vectors; F = ma applies to the NET force.

Kinetic energy is the energy of motion. Any moving object has KE: KE = ½mv². Examples: a moving car, falling water, wind, a thrown ball, atoms vibrating (thermal energy), electrons flowing (electricity). Forms of energy: (1) Kinetic — motion energy (mechanical, thermal, sound, electrical); (2) Potential — stored energy (gravitational, elastic, chemical, nuclear); (3) Radiant — electromagnetic waves (light, radio, X-rays). Energy conversions: (1) Falling object: gravitational PE → KE; (2) Pendulum: KE ↔ PE alternately; (3) Burning fuel: chemical PE → thermal KE → light + heat; (4) Battery → electrical current: chemical PE → electrical KE; (5) Photosynthesis: radiant → chemical PE in glucose. Conservation of Energy: energy cannot be created or destroyed, only transformed (First Law of Thermodynamics). The total energy of an isolated system is constant. In real systems, some energy is lost as heat (entropy increase — Second Law). 'Lost' energy isn't gone — it just becomes less useful (dispersed as low-grade thermal energy). Mechanical energy = KE + PE; in conservative systems (no friction), mechanical energy is conserved.

Order from Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Mnemonics: 'My Very Educated Mother Just Served Us Noodles' (replacing 'Nachos' since Pluto's reclassification). Pluto was reclassified as a dwarf planet in 2006. Planet categories: (1) Terrestrial (inner, rocky): Mercury, Venus, Earth, Mars — smaller, rocky surface, fewer or no moons, no rings; (2) Gas giants: Jupiter, Saturn — large, mostly hydrogen and helium, many moons, rings (Saturn most prominent); (3) Ice giants: Uranus, Neptune — large but smaller than gas giants, contain water/ammonia/methane ices, also have rings and many moons. Asteroid belt between Mars and Jupiter. Kuiper belt beyond Neptune (where Pluto resides). Key planet facts: Mercury — smallest, closest to Sun, extreme temperatures; Venus — hottest (runaway greenhouse), backwards rotation, brightest planet; Earth — only known life, liquid water; Mars — red from iron oxide, evidence of past water; Jupiter — largest, Great Red Spot, 95 moons; Saturn — most prominent rings, second largest, 146 moons; Uranus — tilted on side, rotates 'sideways'; Neptune — windiest, blue from methane. Sun is a yellow dwarf star; solar system formed ~4.6 billion years ago.