Praxis® Elementary Education:
Science Subtest (5005)
Practice Test & Study Guide

Category I

Earth and Space Sciences

Earth's Structure: the four layers — inner core (solid iron-nickel, ~5,000°C), outer core (liquid iron-nickel, generates Earth's magnetic field), mantle (mostly solid silicate rock; upper mantle = lithosphere + asthenosphere), crust (oceanic crust: thin/dense/dark basalt; continental crust: thick/less dense/lighter granite); types of rocks — igneous (formed from cooling magma/lava: intrusive cools slowly underground forming large crystals like granite; extrusive cools quickly at surface forming small crystals like basalt or obsidian), sedimentary (formed from compressed layers of sediment — most common at Earth's surface; may contain fossils; examples: sandstone, limestone, shale), metamorphic (existing rocks transformed by heat and/or pressure — marble from limestone, slate from shale); the rock cycle — how rocks continuously transform between all three types; minerals and their identifying properties (luster, hardness, streak, cleavage, fracture, crystal form).

Weathering, Erosion, and Deposition: mechanical/physical weathering (breaking rock into smaller pieces without changing chemical composition — frost wedging, abrasion, root pressure, salt crystal growth) vs. chemical weathering (rock composition changed by chemical reactions — oxidation/rusting, carbonation/acid rain, hydration); erosion (transport of weathered material by water, wind, ice, or gravity); deposition (laying down of transported sediment when the agent loses energy); how erosion and deposition shape landforms — river deltas, alluvial fans, sand dunes, moraines; soil profile — O horizon (organic/humus), A horizon (topsoil), B horizon (subsoil), C horizon (weathered parent rock), R horizon (bedrock).

Plate Tectonics: Earth's lithosphere divided into ~15 major tectonic plates that move on the asthenosphere (driven by convection currents in the mantle); plate boundary types — convergent (plates collide: subduction zones, volcanoes, mountain ranges, ocean trenches; e.g., Himalayas from Indian Plate colliding with Eurasian Plate), divergent (plates move apart: mid-ocean ridges, rift valleys, new crust created; e.g., Mid-Atlantic Ridge), transform (plates slide past each other: earthquakes, no crust created or destroyed; e.g., San Andreas Fault in California); evidence for plate tectonics — matching fossils and rock formations across continents, continental fit (Pangaea ~225 million years ago), paleomagnetism (striped magnetic reversals on ocean floor), seafloor spreading.

Hydrosphere and Water Cycle: Earth's water distribution — oceans contain ~97% of all water; freshwater distribution: glaciers/ice caps ~69%, groundwater ~30%, surface water (lakes, rivers, swamps) ~1%, atmosphere small fraction; the hydrologic/water cycle — evaporation (liquid water → water vapor, driven by solar energy), transpiration (plants release water vapor through stomata), condensation (water vapor → liquid droplets forming clouds when warm, moist air cools to the dew point), precipitation (water falls as rain, snow, sleet, or hail depending on atmospheric temperature), runoff (water flows across land surface into streams and rivers), infiltration (water soaks into the ground, replenishing aquifers/groundwater); tides (caused by gravitational pull of the Moon primarily, and the Sun secondarily); ocean currents and their influence on regional climates.

Atmosphere, Weather, and Climate: layers of Earth's atmosphere — troposphere (0–12 km, where weather occurs and temperatures decrease with altitude), stratosphere (12–50 km, contains the ozone layer that absorbs harmful UV radiation), mesosphere (50–80 km, where meteors burn up), thermosphere (80–700 km, very low density, very high temperature), exosphere (700+ km, merges into space); atmospheric composition — nitrogen ~78%, oxygen ~21%, argon ~0.9%, CO₂ ~0.04%, water vapor (variable), trace gases; weather vs. climate (weather = short-term local atmospheric conditions; climate = long-term average pattern of weather for a region); factors influencing climate — latitude (distance from equator), altitude (elevation above sea level), proximity to large bodies of water (moderating effect), ocean currents, prevailing winds; major cloud types — cumulus (puffy, fair weather), stratus (flat layers, may produce drizzle), cirrus (high, wispy, ice crystals), cumulonimbus (towering thunderstorm clouds); greenhouse effect — CO₂ and other greenhouse gases trap heat in Earth's atmosphere; enhanced greenhouse effect driving global climate change.

Astronomy: the solar system — the Sun is a G-type main-sequence (yellow dwarf) star composed primarily of hydrogen (~73%) and helium (~25%); energy produced by nuclear fusion in the Sun's core (hydrogen nuclei fuse to form helium, releasing enormous energy as light and heat); eight planets in order from Sun (My Very Educated Mother Just Served Us Nachos): Mercury, Venus, Earth, Mars (inner rocky terrestrial planets), Jupiter, Saturn, Uranus, Neptune (outer gas giants); moons, asteroids (rocky, concentrated in asteroid belt between Mars and Jupiter), comets (icy bodies from Oort Cloud or Kuiper Belt), dwarf planets (Pluto, Eris, Ceres). Earth-Moon-Sun system — Moon phases (new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent; ~29.5-day cycle; caused by changing relative positions); solar eclipses (Moon directly between Earth and Sun — total solar eclipse visible from narrow path); lunar eclipses (Earth between Moon and Sun — Earth's shadow falls on Moon — visible from any location where Moon is above the horizon); seasons caused by Earth's axial tilt of 23.5° (NOT distance from Sun — Earth is actually closest to the Sun in January, Northern Hemisphere winter); stars — classification by temperature: blue-white (hottest), yellow (medium, like our Sun), red (coolest); stellar life cycle; the Milky Way galaxy; the observable universe and the Big Bang theory.

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Category II

Life Sciences

Cell Structure and Function: cells as the basic unit of life; prokaryotic cells (no membrane-bound nucleus — bacteria and archaea; simpler structure; single circular chromosome) vs. eukaryotic cells (membrane-bound nucleus — plants, animals, fungi, protists; more complex structure); major organelles and their functions — cell membrane (selective permeability, controls what enters and exits; phospholipid bilayer with embedded proteins), cell wall (structural support and protection; found in plants, fungi, and bacteria — NOT in animal cells; plant cell walls made of cellulose), nucleus (contains DNA, controls cell activities, contains nucleolus which makes ribosomes), mitochondria (cellular respiration → produces ATP energy; "powerhouse of the cell"; has its own DNA, suggesting endosymbiotic origin), chloroplasts (photosynthesis — converts light energy to chemical energy stored in glucose; found only in plant cells and algae; has own DNA), ribosomes (protein synthesis — found in all cells; either free in cytoplasm or attached to rough ER), endoplasmic reticulum (rough ER: studded with ribosomes, transports proteins; smooth ER: no ribosomes, synthesizes lipids and detoxifies), Golgi apparatus (packages proteins in vesicles and ships them to destinations inside or outside the cell — "cell's post office"), vacuoles (storage; large central vacuole in plant cells stores water, maintaining turgor pressure), lysosomes (contain digestive enzymes that break down waste materials — found mainly in animal cells).

Photosynthesis and Cellular Respiration: Photosynthesis (in chloroplasts, plant cells only): 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂ — converts light energy into chemical energy stored in glucose; takes place in two stages: light-dependent reactions (in thylakoid membranes — uses light to split water, releasing O₂, and produces ATP and NADPH) and Calvin cycle/light-independent reactions (in stroma — uses ATP and NADPH to convert CO₂ into glucose). Cellular respiration (in mitochondria, all living cells): C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP energy — releases chemical energy from glucose; three stages: glycolysis (in cytoplasm, no oxygen needed, produces 2 ATP), Krebs cycle (in mitochondrial matrix, aerobic), electron transport chain (in inner mitochondrial membrane, produces most ATP). Key relationship: photosynthesis and cellular respiration are complementary — photosynthesis uses CO₂ and produces O₂; cellular respiration uses O₂ and produces CO₂. All living organisms (including plants) perform cellular respiration; only organisms with chloroplasts perform photosynthesis.

Genetics and Evolution: DNA (deoxyribonucleic acid) — the hereditary material in virtually all living organisms; DNA structure — double helix made of nucleotides; each nucleotide contains a phosphate group, a deoxyribose sugar, and one of four nitrogenous bases: adenine (A), thymine (T), guanine (G), or cytosine (C); complementary base pairing: A pairs with T, G pairs with C; genes are segments of DNA that encode instructions for making specific proteins; chromosomes — condensed DNA wrapped around histone proteins; humans have 46 chromosomes (23 pairs); somatic cells are diploid (2n = 46); gametes (eggs and sperm) are haploid (n = 23) produced by meiosis. Mendelian genetics — dominant alleles (expressed when present, uppercase) and recessive alleles (only expressed when homozygous, lowercase); genotype (actual alleles: TT, Tt, tt) vs. phenotype (expressed trait: tall or short); 3:1 phenotypic ratio from a monohybrid cross of two heterozygous parents (Tt × Tt); sex-linked traits (carried on X chromosome, more commonly expressed in males XY); common genetic disorders. Natural selection and evolution — Darwin's theory: organisms with heritable traits that increase survival and reproduction in a given environment leave more offspring, passing those traits to the next generation; over many generations, beneficial traits become more common in populations (populations evolve — not individual organisms); evidence: fossil record, comparative anatomy (homologous structures: same bone structure in different limbs; analogous structures: similar function, different origin; vestigial structures: remnants of structures that had a function in ancestors), molecular evidence (DNA similarity).

Classification and Organisms: taxonomic classification system (Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species — "Dear King Philip Came Over For Good Soup"); three domains of life — Bacteria (prokaryotes, no nucleus, cell walls of peptidoglycan), Archaea (prokaryotes, no nucleus, different cell wall chemistry, extremophiles), Eukarya (eukaryotes with membrane-bound nucleus — includes kingdoms Animalia, Plantae, Fungi, Protista); binomial nomenclature — genus + species name, italicized (e.g., Homo sapiens); dichotomous keys for organism identification; viral structure and why viruses are not considered living (not cellular, cannot reproduce independently, have no metabolism — they hijack host cell machinery to replicate). Vascular plants (have xylem and phloem for water and nutrient transport — ferns, gymnosperms, angiosperms) vs. nonvascular plants (lack vascular tissue — mosses, liverworts, hornworts); plant organ functions — roots (anchor plant, absorb water and dissolved minerals), stems (support, transport water and nutrients), leaves (photosynthesis — chlorophyll in mesophyll cells; gas exchange through stomata), flowers (attract pollinators for sexual reproduction), fruits (protect seeds and aid dispersal).

Animal Physiology and Ecology: major body systems — digestive (mechanical and chemical breakdown of food into absorbable nutrients), circulatory (heart pumps blood through arteries, capillaries, veins; delivers O₂ and nutrients, removes CO₂ and wastes), respiratory (gas exchange: O₂ enters blood, CO₂ exits through lungs or gills), skeletal (structural support, protection, mineral storage, blood cell production in red bone marrow), muscular (cardiac muscle: involuntary, heart; smooth muscle: involuntary, internal organs; skeletal muscle: voluntary, attached to bones by tendons), nervous (brain, spinal cord, peripheral nerves; coordinates responses to stimuli), immune (defends against pathogens — innate and adaptive immunity), endocrine (hormones regulate body functions — insulin regulates blood glucose, thyroid hormone regulates metabolism); homeostasis — maintaining stable internal environment (temperature, blood pH, blood glucose). Ecology — levels of organization: organism → population (same species, same area) → community (all populations in an area) → ecosystem (community + abiotic factors) → biome → biosphere; biomes: tropical rainforest (high temperature, very high rainfall, highest biodiversity), desert (low rainfall, extreme temperatures), grassland/savanna (seasonal rainfall, grasses dominate), temperate deciduous forest (four seasons, moderate rainfall, broadleaf trees), taiga/boreal forest (cold winters, coniferous trees), tundra (very cold, treeless, permafrost); food chains, food webs, and energy pyramids — 10% rule (only ~10% of energy transfers to the next trophic level, the other ~90% lost as heat); producers (autotrophs — make own food), primary consumers (herbivores), secondary and tertiary consumers (carnivores/omnivores), decomposers (break down dead organic matter, returning nutrients to soil — fungi and bacteria); ecological relationships — predation, competition, mutualism (+/+), commensalism (+/0), parasitism (+/−); biogeochemical cycles — carbon cycle, nitrogen cycle, water cycle; primary succession (starts on bare rock, no soil — pioneer species begin process), secondary succession (starts after disturbance on existing soil — faster than primary).

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Category III

Physical Sciences

Properties of Matter: states of matter — solid (definite shape and volume, particles closely packed in regular arrangement, low kinetic energy), liquid (definite volume but takes shape of container, particles close but can flow past each other), gas (no definite shape or volume, particles far apart and move rapidly and randomly), plasma (ionized gas at extremely high temperatures — most common state of matter in the universe, found in stars); physical properties (observable without changing chemical composition — mass, volume, density, color, solubility, conductivity, magnetism, melting/boiling point) vs. chemical properties (describe how a substance reacts to form new substances — flammability, reactivity with acids, ability to rust/corrode, toxicity); physical changes (form or appearance changes but chemical composition remains the same — cutting, tearing, dissolving, melting, boiling, condensation, freezing — the original substance can be recovered) vs. chemical changes (new substances with different chemical compositions are formed — burning/combustion, rusting/oxidation, cooking, baking, decomposition — signs: temperature change, color change, gas production with bubbles, precipitate formation, light emission); elements (pure substances made of only one type of atom — cannot be broken down further by chemical means; ~118 elements in the periodic table), atoms (smallest unit of an element that retains its chemical properties), compounds (two or more elements chemically bonded in fixed ratios — properties differ from component elements; e.g., H₂O has very different properties than hydrogen gas or oxygen gas), molecules (two or more atoms bonded together — can be elements like O₂ or N₂, or compounds like H₂O or CO₂), mixtures (two or more substances physically combined — each retains its own properties; can be separated by physical means: filtration, distillation, evaporation, magnetism; homogeneous mixture = solution, uniform throughout; heterogeneous mixture = non-uniform, components visible). Atomic structure — protons (positive charge, in nucleus), neutrons (no charge, in nucleus), electrons (negative charge, in electron shells/orbitals outside nucleus); atomic number = number of protons (defines the element); mass number = protons + neutrons; isotopes = same element, different number of neutrons (same atomic number, different mass number; may be radioactive); the periodic table — organized by increasing atomic number; periods (horizontal rows — same number of electron shells); groups/families (vertical columns — same number of valence electrons, similar chemical properties).

Energy and Matter Relationships: Law of Conservation of Energy — energy cannot be created or destroyed, only converted from one form to another (applies to all physical and chemical processes); forms of energy — kinetic energy (energy of motion; KE = ½mv²; depends on both mass and velocity), potential energy (stored energy; gravitational PE = mgh, depends on mass, height, and gravitational acceleration; elastic PE stored in stretched/compressed springs; chemical PE stored in chemical bonds — released in combustion, respiration), thermal/heat energy (total kinetic energy of all particles in a substance), light/radiant energy (electromagnetic radiation), sound energy (mechanical wave energy), electrical energy (energy of moving electric charges), nuclear energy (stored in atomic nuclei — released in fission and fusion); heat transfer methods — conduction (transfer through direct contact between materials in physical contact; metals are good conductors because free electrons can move easily; wood and air are insulators; example: metal spoon in hot coffee), convection (transfer through fluid motion — warm fluid is less dense and rises, cool fluid sinks, creating convection currents; examples: boiling water, atmospheric wind circulation, oceanic circulation, mantle convection driving plate tectonics), radiation (transfer through electromagnetic waves without any medium needed — works in a vacuum; example: solar radiation traveling through space to warm Earth; infrared radiation from a campfire); temperature vs. heat — temperature measures average kinetic energy of particles; heat is the transfer of thermal energy between substances at different temperatures (always flows from higher to lower temperature); phase changes — melting (solid → liquid, absorbs heat), freezing (liquid → solid, releases heat), vaporization/evaporation (liquid → gas, absorbs heat), condensation (gas → liquid, releases heat), sublimation (solid → gas directly, absorbs heat — dry ice, frost on cold days), deposition (gas → solid directly, releases heat — frost formation on windows); Law of Conservation of Mass — matter is neither created nor destroyed in physical or chemical changes (reactant mass = product mass).

Chemical Reactions: chemical bonds — ionic bonds (metal transfers electrons to nonmetal; results in oppositely charged ions that attract each other; e.g., NaCl — table salt), covalent bonds (nonmetals share electrons; e.g., H₂O, CO₂, O₂); balancing simple chemical equations; identifying reaction types — synthesis (A + B → AB), decomposition (AB → A + B), single replacement (A + BC → AC + B), double replacement (AB + CD → AD + CB), combustion (fuel + O₂ → CO₂ + H₂O + energy); acids (pH < 7; donate H⁺ ions; taste sour; examples: lemon juice pH ~2, vinegar pH ~3, stomach acid pH ~1.5; turn blue litmus paper red; react with metals to produce hydrogen gas) and bases (pH > 7; accept H⁺ ions or donate OH⁻; taste bitter; feel slippery; examples: baking soda pH ~8.5, ammonia pH ~11, bleach pH ~12; turn red litmus paper blue); the pH scale — runs from 0–14; is logarithmic (each unit = 10× change in H⁺ concentration); 7 = neutral (pure water); neutralization reaction: acid + base → salt + water (product pH approaches 7).

Mechanics — Motion and Forces: position, displacement, distance, speed (distance/time, scalar), velocity (speed + direction, vector), acceleration (change in velocity/time — can be change in speed or direction); Newton's Three Laws of Motion — First Law (Law of Inertia): an object at rest remains at rest and an object in motion continues moving at constant velocity unless acted upon by a net external force (explains seatbelt necessity, objects drifting in space); Second Law: F = ma (net force equals mass times acceleration; larger force = greater acceleration for same mass; larger mass = less acceleration for same force; explains why heavy objects need more force to move); Third Law (Action-Reaction): for every action force, there is an equal and opposite reaction force acting on a different object (rocket propulsion, swimming, walking, jumping); gravity (universal attractive force between any two masses; F = Gm₁m₂/d²; directed toward center of Earth; weight = mg where g ≈ 9.8 m/s² on Earth's surface); weight vs. mass — mass is constant (amount of matter, measured in kg); weight varies with gravitational field strength (a force measured in Newtons); friction (force opposing relative motion between surfaces in contact; always opposes motion; converts kinetic energy to thermal energy); buoyancy (upward force on an object partially or fully submerged in a fluid; Archimedes' principle: buoyant force = weight of fluid displaced; objects float when buoyant force ≥ weight); simple machines (lever, pulley, wheel and axle, inclined plane, screw, wedge — all trade force for distance; mechanical advantage = output force / input force).

Electricity, Magnetism, Waves, and Optics: static electricity — buildup of electric charge on the surface of a material (like charges repel, unlike charges attract); current electricity — flow of electrons through a conductor; series circuits (single path; if one component fails, all fail; current same throughout; total voltage divided among components) vs. parallel circuits (multiple paths; if one fails, others continue; voltage same across each branch; current varies by branch; household wiring is parallel); conductors (allow free electron flow — metals, especially copper and silver) vs. insulators (resist electron flow — rubber, plastic, wood, glass); Ohm's Law: V = IR (voltage = current × resistance); magnets — north and south poles; like poles repel, opposite poles attract; Earth has a magnetic field (magnetic north ≈ geographic north); electromagnets (electric current flowing through a coil of wire produces a magnetic field — strength increases with more coil turns or more current; turning off current eliminates the magnetic field). Waves — transverse waves (particles oscillate perpendicular to wave travel direction — light, water surface waves) vs. longitudinal waves (particles oscillate parallel to wave travel direction — sound waves, compressions and rarefactions); wave properties: wavelength (distance between successive crests, in meters), frequency (number of complete waves per second, in Hertz), amplitude (height of wave from equilibrium — determines loudness for sound, brightness for light), wave speed (v = frequency × wavelength); electromagnetic spectrum in order of increasing frequency (decreasing wavelength): radio waves → microwaves → infrared → visible light (ROY G BIV: red, orange, yellow, green, blue, indigo, violet) → ultraviolet → X-rays → gamma rays (highest frequency, most energy, most penetrating); sound waves — longitudinal mechanical waves requiring a medium; travel fastest in solids, slower in liquids, slowest in gases (because particle density affects vibration transmission); optics — reflection (angle of incidence = angle of reflection, measured from normal to surface), refraction (bending of light as it passes from one medium to another of different density — light slows when entering denser medium; explains why a straw appears bent in water), lenses (convex/converging lenses focus light — used in magnifying glasses, cameras, eyes; concave/diverging lenses spread light — used in correcting nearsightedness).

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Seasons — the most commonly tested Earth science misconception: Seasons are caused by Earth's axial tilt of 23.5° — NOT by Earth's distance from the Sun. In Northern Hemisphere summer, Earth's axis tilts toward the Sun, causing: (1) more direct sunlight (concentrated over smaller area = more energy per square meter), (2) longer days (more hours of sunlight). In Northern Hemisphere winter, Earth's axis tilts away from the Sun, causing less direct sunlight and shorter days. Earth is actually CLOSEST to the Sun (perihelion) in early January — Northern Hemisphere winter. Southern Hemisphere seasons are opposite because when the Northern Hemisphere tilts toward the Sun, the Southern Hemisphere tilts away

Moon phases — cause, sequence, and eclipses: Moon phases are caused by the changing angle between the Moon, Earth, and Sun as the Moon orbits Earth (~29.5 days). The Moon does NOT emit its own light — we see reflected sunlight. The illuminated portion we see depends on the Moon's position relative to Earth and Sun. New Moon: Moon between Earth and Sun (we see the unlit side — dark). Full Moon: Earth between Moon and Sun (we see the fully lit side). Solar eclipse: Moon directly between Earth and Sun — Moon's shadow falls on Earth (total eclipse visible from narrow path). Lunar eclipse: Earth between Moon and Sun — Earth's shadow falls on Moon (visible from any location where the Moon is above the horizon). Know these relationships cold — they are consistently tested

Plate tectonics — boundaries and associated features: Convergent (two plates collide) → subduction zones (denser oceanic plate dives under less dense continental plate), volcanoes (magma rises through subduction zone), mountain ranges (continental-continental convergence), deep ocean trenches; Divergent (plates move apart) → mid-ocean ridges (new seafloor created as magma wells up), rift valleys (on continents — e.g., Great Rift Valley of Africa), gradual widening of oceans; Transform (plates slide horizontally past each other) → earthquake-prone fault zones (no volcanoes, no mountains, no trenches; e.g., San Andreas Fault). Know which type of boundary produces which geologic features

Rock types and the rock cycle: Igneous rocks form from cooling magma (intrusive/plutonic: cools slowly underground → large interlocking crystals, e.g., granite) or lava (extrusive/volcanic: cools rapidly at surface → small or no crystals, e.g., basalt, obsidian). Sedimentary rocks form from compaction and cementation of sediment layers (most common rock type at Earth's surface; only type that typically contains fossils; examples: sandstone, limestone, shale, coal). Metamorphic rocks form when existing rocks are subjected to heat and pressure (marble comes from limestone; slate comes from shale; quartzite comes from sandstone). The rock cycle shows how each type can transform into the others over geologic time — know the transformation pathways

Star properties and the electromagnetic spectrum: Stars are classified by color based on surface temperature — blue/white stars are the HOTTEST (O-type stars, ~30,000+ K), yellow stars are medium temperature (G-type like our Sun, ~5,800 K), orange and red stars are the COOLEST (M-type red dwarfs, ~3,000 K). This is counterintuitive for many students who associate red with heat. The electromagnetic spectrum from lowest to highest frequency/energy: radio waves (lowest) → microwaves → infrared → visible light (ROYGBIV) → ultraviolet → X-rays → gamma rays (highest). Know that visible light is only a small slice of the full spectrum, and that higher frequency = higher energy = shorter wavelength

Photosynthesis vs. cellular respiration — the most tested Life Science relationship: Photosynthesis (chloroplasts, plant cells and algae only): 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂ — uses light energy to convert CO₂ and water into glucose and oxygen. Cellular respiration (mitochondria, ALL living cells including plants): C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP — releases energy from glucose. CRITICAL MISCONCEPTION: "Plants don't need to respire because they photosynthesize." FALSE — ALL living organisms (plants, animals, fungi, bacteria) perform cellular respiration continuously to produce ATP. Plants photosynthesize during daylight hours and respire continuously 24/7. Know which organelle performs each process (chloroplast vs. mitochondria) and the inputs/outputs of each

Cell organelles most frequently tested on the 5005: Mitochondria — cellular respiration, produces ATP (energy currency); "powerhouse of the cell"; has its own DNA suggesting ancient endosymbiotic bacterial origin. Chloroplasts — photosynthesis; found only in plant cells and algae; also has own DNA. Cell membrane — in ALL cells; selectively permeable (phospholipid bilayer with embedded proteins); controls what enters and exits. Cell wall — in plant, fungal, and bacterial cells ONLY (NOT in animal cells); provides structural support; plant cell walls are made of cellulose. Nucleus — "control center"; contains DNA; bounded by nuclear envelope with pores. Vacuole — large central vacuole in plant cells stores water and maintains turgor pressure (keeps plant cells firm); much smaller vacuoles in animal cells. Ribosomes — found in ALL cells (prokaryotic and eukaryotic); site of protein synthesis

Mendelian genetics — Punnett squares and inheritance patterns: A Punnett square predicts the probability of offspring genotypes from a cross. Monohybrid cross of two heterozygous parents (Tt × Tt): TT (25%), Tt (50%), tt (25%) → genotypic ratio 1:2:1; phenotypic ratio 3 tall: 1 short. Sex-linked traits are carried on the X chromosome — males (XY) who inherit one recessive allele on the X chromosome will express the trait (no second X to mask it); females (XX) must inherit two recessive alleles to express it; females with one recessive allele are carriers. Common sex-linked traits: color blindness, hemophilia. Autosomal dominant disorders (one copy of allele causes disease — Huntington's disease). Autosomal recessive disorders (two copies needed — cystic fibrosis, sickle cell anemia, phenylketonuria)

Food webs and the 10% energy rule — a consistently tested ecology concept: In any food chain or web, approximately 10% of the energy at one trophic level is transferred to the next — the other ~90% is lost as heat through metabolic processes. This explains: why food chains are typically limited to 4–5 links (too little energy remains after 5 transfers to support another level), why there are far fewer top predators than herbivores or producers in any ecosystem, and why eating lower on the food chain is more energy-efficient (vegetarian diets use far less agricultural land than meat-heavy diets). Energy pyramid: the bottom (producers) has the most energy and biomass; each level above has ~10% of the level below it. Know how to calculate energy available at different trophic levels using the 10% rule

Natural selection — commonly misunderstood concepts: Natural selection acts on existing heritable variation — it does NOT create new variation. Individual organisms do NOT evolve — populations change allele frequencies over many generations. Evolution is NOT directed toward a goal or "improvement" — it is non-directed change in allele frequencies. Acquired characteristics are NOT inherited (a giraffe cannot pass on a longer neck from stretching — Lamarckian inheritance is incorrect). Natural selection has three requirements: (1) variation must exist in the population, (2) variation must be heritable (passed from parents to offspring), (3) variation must affect survival and reproduction (selection pressure). Evolution can also occur through genetic drift (random allele frequency changes in small populations) and gene flow (movement of alleles between populations)

Newton's Three Laws — with specific real-world examples: First Law (Inertia): objects resist changes in their state of motion. Examples — a car that suddenly stops throws passengers forward (inertia keeps them moving); satellites stay in orbit without fuel (no friction in space to slow them); a tablecloth pulled quickly leaves dishes behind (dishes' inertia keeps them in place). Second Law (F = ma): a loaded truck needs a more powerful engine than an empty truck to achieve the same acceleration (more mass requires more force). The same force applied to a tennis ball vs. a bowling ball produces very different accelerations. Third Law (Action-Reaction): a rocket engine expels gas downward (action) → rocket is pushed upward (reaction); a swimmer pushes water backward (action) → swimmer is pushed forward (reaction); a gun recoils when fired (action: bullet pushed forward; reaction: gun pushed backward)

Physical vs. chemical changes — the most tested Physical Science distinction: Physical changes alter form without changing chemical composition. Examples: cutting paper (smaller pieces, same chemical composition); melting ice (liquid water — still H₂O); dissolving sugar in water (sugar molecules disperse but sugar can be recovered by evaporating the water — PHYSICAL even though it looks like a transformation); bending a wire; mixing sand and salt. Chemical changes form new substances with different chemical compositions. Examples: burning paper (produces CO₂, H₂O, ash — cannot un-burn paper); rusting iron (iron + oxygen → iron oxide = new substance); cooking an egg (proteins denature — irreversible); baking bread (many chemical reactions — CO₂ bubbles cause rising). Signs of a chemical change: temperature change, color change, gas production (bubbles), precipitate formation, light emission. Note: temperature change alone is not always sufficient — dissolving NaOH in water produces heat but is a physical change (dissolution)

Heat transfer methods — conduction, convection, and radiation with examples: Conduction: direct contact between materials; electrons or molecular vibrations transfer thermal energy. Best example: holding a metal spoon in hot soup — the spoon handle gets warm. Metals conduct well (free electrons); wood and plastic are insulators. Convection: heat transfer through fluid movement; warm fluid is less dense and rises, cool fluid sinks, creating circular currents. Best examples: boiling water (bottom heats, rises, cooler water sinks); weather patterns (warm air rises near equator, creating wind); ocean currents; mantle convection driving plate tectonics. Radiation: electromagnetic wave energy transfer requiring NO medium — works through a vacuum. Best example: solar energy reaching Earth through space. Unlike conduction and convection, radiation does not require matter — it is the only heat transfer method that works in a vacuum

Series vs. parallel circuits — and why household wiring is parallel: Series circuit: single path for current; one broken component stops all current flow; total resistance = sum of individual resistances; voltage divided among components proportionally to resistance; current is the same at every point. Parallel circuit: multiple independent paths for current; if one branch fails, others continue (removing one lightbulb doesn't extinguish others); voltage is the same across each branch; total current = sum of branch currents; adding more branches decreases total resistance. Household electrical wiring uses parallel circuits for two critical reasons: (1) each device operates at the same voltage (standard 120V in the U.S.); (2) each device can be turned on or off independently — turning off one lamp doesn't affect others. This is why a burned-out light bulb doesn't cause all other lights in your home to go out

Conservation of energy — energy transformations to know: Energy is NEVER created or destroyed — only converted from one form to another. Common transformations: chemical → electrical → light/heat (battery powers a flashlight); chemical → thermal → mechanical (fuel burned in engine produces motion); gravitational potential → kinetic (ball falling: gains speed, loses height); kinetic → thermal (friction slows a sliding object and warms the surfaces); electrical → mechanical + sound + heat (electric motor driving a fan — most energy goes to motion, some to heat from resistance, some to sound). In ALL real energy transformations, some energy is "lost" as low-grade heat — this does NOT violate conservation of energy; the energy still exists, it's just in a less useful form. This is the Second Law of Thermodynamics: in any energy conversion, the total entropy (disorder) of the system increases

Experimental design — variables and fair testing: in a controlled experiment: the independent variable (IV) is the factor the experimenter deliberately changes (manipulates) — one at a time; the dependent variable (DV) is the factor that is measured or observed as a result of the IV change; controlled variables (constants) are all other factors kept the same to ensure any observed change in the DV is caused only by the IV change. A "fair test" has only one IV. Example: testing whether sunlight affects plant growth — IV = amount of sunlight; DV = plant height after 2 weeks; controlled = same soil, same amount of water, same temperature, same plant species, same size pots. A control group provides a baseline with no manipulation of the IV for comparison

Appropriate science tools for elementary classrooms: thermometer (measures temperature in Celsius and Fahrenheit; lab vs. outdoor vs. body thermometers); hand lens/magnifying glass (magnifies small objects 2–10×; for examining rocks, insects, seeds); microscope (magnifies very small objects 40–1000×; compound microscope for cells; stereo microscope for 3D objects); graduated cylinder (measures liquid volume in mL; always read at the bottom of the meniscus at eye level); triple-beam balance or digital balance (measures mass in grams; more accurate than a spring scale for mass); spring scale (measures force/weight in Newtons; also used to measure gravitational force on an object); ruler or meter stick (measures length in cm and mm); stopwatch (measures time); barometer (measures atmospheric pressure — rising pressure = improving weather; falling pressure = worsening weather); anemometer (measures wind speed). Know which tool is appropriate for which measurement task

Scientific theory vs. scientific law — a commonly tested nature of science concept: in everyday language, "theory" means a guess or hunch. In science, a scientific theory is a well-substantiated, thoroughly tested explanation of a body of observations and experimental evidence — NOT a guess. Examples: cell theory (all living things are made of cells), germ theory (diseases are caused by microorganisms), theory of evolution by natural selection, atomic theory, plate tectonic theory. A scientific law describes WHAT happens consistently in nature under given conditions (usually expressed mathematically) — Newton's Law of Universal Gravitation, Law of Conservation of Energy, Boyle's Law, Law of Conservation of Mass. Laws describe patterns; theories explain WHY the patterns exist. Neither is more "proven" than the other — they answer different kinds of questions

Reading and interpreting scientific data displays: data table — organized rows and columns; identify the IV (usually left column) and DV (usually right column); look for trends as IV changes; identify anomalies (data points that don't fit the pattern — may indicate experimental error or a real phenomenon worth investigating). Bar graph — compare quantities across discrete categories; heights of bars represent values; useful for comparing groups. Line graph — show continuous change over time or in response to a continuous variable; slope indicates rate of change; flat line = no change. Scatterplot — shows relationship between two continuous variables; trend line (line of best fit) shows direction of relationship; upward slope = positive correlation; downward slope = negative correlation; scattered points with no pattern = no correlation. Correlation vs. causation: two variables can be correlated without one causing the other