GACE® Middle Grades Science (4–8) (705)
Practice Test

Physical and chemical properties of matter; the periodic table:physical properties are measurable without changing the substance’s chemical identity — density, melting point, boiling point, solubility, conductivity, hardness, color; chemical properties describe a substance’s ability to change into a different substance — flammability, reactivity with acid, oxidation; the periodic table is organized by increasing atomic number (protons); periods (horizontal rows) represent the number of electron shells; groups/families (vertical columns) share similar chemical properties because of the same number of valence electrons; key groups to know: Group 1 (alkali metals — 1 valence electron, highly reactive with water), Group 2 (alkaline earth metals), Group 17 (halogens — 7 valence electrons, highly reactive nonmetals), Group 18 (noble gases — 8 valence electrons, chemically inert); metals (left side: good conductors, malleable, ductile, lustrous), metalloids (staircase line: silicon, germanium; semiconductors), and nonmetals (right side: poor conductors, brittle in solid form); protons = atomic number; neutrons = mass number − atomic number; electrons = protons in a neutral atom; isotopes differ in number of neutrons.

Characteristics of elements, compounds, and mixtures; conservation of matter in chemical reactions:elements are pure substances made of only one type of atom; compounds are pure substances made of two or more elements chemically bonded in fixed ratios (water is always H₂O; carbon dioxide is always CO₂); mixtures combine two or more substances physically — the composition varies and components can be separated by physical means; homogeneous mixtures (solutions): uniform composition throughout (saltwater, air); heterogeneous mixtures: non-uniform composition (salad, granite); the law of conservation of mass: in a chemical reaction, matter is neither created nor destroyed — the total mass of reactants equals the total mass of products; balancing chemical equations to reflect conservation of mass; evidence of a chemical reaction (color change, gas production, precipitate formation, energy change, odor).

Phase changes; kinetic molecular theory:kinetic molecular theory (KMT): all matter is made of particles in constant motion; temperature is a measure of average kinetic energy; particles in solids vibrate in fixed positions (definite shape, definite volume); particles in liquids move more freely past each other (no definite shape, definite volume); particles in gases move rapidly and are far apart (no definite shape, no definite volume); phase changes and the energy involved: melting (solid → liquid, endothermic — absorbs energy), vaporization/boiling (liquid → gas, endothermic), condensation (gas → liquid, exothermic — releases energy), freezing (liquid → solid, exothermic), sublimation (solid → gas directly, e.g., dry ice), deposition (gas → solid directly, e.g., frost); temperature does NOT change during a phase change (plateau on a heating/cooling curve).

Law of conservation of energy; forms and transfer of energy; waves and optics:the law of conservation of energy: energy cannot be created or destroyed, only converted from one form to another; forms of energy: kinetic (energy of motion), potential (stored energy — gravitational, elastic, chemical, nuclear), thermal/heat, light/radiant, electrical, sound; energy transfers (conduction, convection, radiation); electromagnetic spectrum (radio waves, microwaves, infrared, visible light [ROYGBIV], ultraviolet, X-rays, gamma rays) — higher frequency = shorter wavelength = higher energy; wave characteristics: amplitude (height; related to energy), wavelength (distance between crests), frequency (waves per second; measured in Hz), wave speed = frequency × wavelength; behavior of light: reflection (bouncing off a surface; angle of incidence = angle of reflection), refraction (bending when passing from one medium to another; light slows in denser media; a prism separates white light into its component colors), diffraction (bending around obstacles or through openings); mirrors (plane mirrors create virtual, upright images; concave mirrors can focus light; convex mirrors create smaller, wider-field images) and lenses (convex/converging lenses focus light; used in cameras and magnifying glasses; concave/diverging lenses spread light; used in correcting nearsightedness).

Newton’s laws of motion; force, mass, motion; work and power:Newton’s First Law (Law of Inertia): an object at rest remains at rest, and an object in motion remains in motion at constant velocity, unless acted on by a net external force; Newton’s Second Law: F = ma (net force equals mass times acceleration; a greater force produces greater acceleration; a greater mass requires greater force for the same acceleration); Newton’s Third Law: for every action there is an equal and opposite reaction; net force: the vector sum of all forces acting on an object; balanced forces produce zero net force and no change in motion; unbalanced forces produce acceleration; friction (static friction resists the start of motion; kinetic/sliding friction acts during motion; air resistance is friction with air); gravity as a universal attractive force (F = Gm₁m₂/r²); work = force × displacement (in the direction of the force); measured in joules (J); power = work/time = energy/time; measured in watts (W); simple machines (lever, pulley, wheel and axle, inclined plane, wedge, screw) reduce the force needed to do work by increasing the distance over which the force is applied (trade-off between force and distance; work done remains the same).

Cells: structure, function, and types:the cell is the basic unit of life; prokaryotic cells (bacteria and archaea): no membrane-bound nucleus, no membrane-bound organelles, circular DNA in the cytoplasm; simpler and smaller than eukaryotic cells; examples: E. coli, Streptococcus, cyanobacteria; eukaryotic cells (plants, animals, fungi, and protists): have a membrane-bound nucleus containing DNA, and membrane-bound organelles; specialized cells reflect their function — red blood cells are biconcave, anucleate, and full of hemoglobin to maximize oxygen transport; neurons have long axons and dendrites for signal transmission; muscle cells (myocytes) are elongated and contain contractile proteins; guard cells in plants control gas exchange through stomata by changing shape; key organelles and functions: nucleus (contains DNA; directs cell activities), mitochondria (aerobic cellular respiration; ATP production; “powerhouse of the cell”), chloroplasts (photosynthesis; in plant cells only; contain chlorophyll), ribosomes (protein synthesis; found in all cells), endoplasmic reticulum (rough ER: protein synthesis and packaging; smooth ER: lipid synthesis and detoxification), Golgi apparatus (modifies, packages, and ships proteins), cell membrane (phospholipid bilayer; controls what enters and exits; present in all cells), cell wall (rigid outer layer in plant cells and bacteria; made of cellulose in plants; provides structure and protection), vacuole (large central vacuole in plant cells provides structural support and stores water).

Body systems and their interactions; homeostasis:major body systems and their interactions (the GACE tests understanding of how systems work together): digestive system (breaks down food into nutrients that enter the bloodstream) → circulatory system (transports nutrients, oxygen, hormones, and waste products throughout the body) → respiratory system (exchanges O₂ and CO₂ between blood and air in the lungs) → urinary/excretory system (filters nitrogenous waste from blood and excretes it as urine); skeletal system (provides structure and protection; makes blood cells in red bone marrow; works with muscular system for movement); nervous system and endocrine system (coordinate and regulate body functions); skin/integumentary system (barrier against pathogens; temperature regulation; vitamin D synthesis); homeostasis is the maintenance of a stable internal environment despite external changes — key examples: body temperature regulation (shivering to warm up; sweating to cool down — both are negative feedback mechanisms that oppose a change to restore the set point); blood glucose regulation by insulin (lowers blood glucose) and glucagon (raises blood glucose) — both secreted by the pancreas; negative feedback is the primary mechanism of homeostasis (the response opposes the change).

Heredity, variation, and biological evolution:DNA carries genetic information in the sequence of bases (adenine-thymine, guanine-cytosine base pairing in double-stranded DNA); genes are segments of DNA that code for proteins; chromosomes are organized structures of DNA and protein in the cell nucleus; humans have 46 chromosomes (23 pairs); Mendelian genetics: dominant alleles mask recessive alleles in the heterozygous (Aa) condition; Punnett squares are used to predict the probability of offspring genotypes and phenotypes; genotype is the genetic makeup (AA, Aa, aa); phenotype is the expressed trait; codominance (both alleles are fully expressed in the heterozygote — AB blood type; roan cattle) and incomplete dominance (the heterozygote shows a blended phenotype — red + white = pink in snapdragons) are exceptions to simple dominance; mutations (changes in DNA sequence) are the ultimate source of genetic variation; variation within a species is the raw material for natural selection; natural selection: individuals with traits better suited to their environment are more likely to survive and reproduce, passing those traits to offspring; over time, this leads to adaptation and, eventually, speciation; evidence for evolution: fossil record (chronological sequence of organisms), biogeography (related species found in geographically connected regions), comparative anatomy (homologous structures: same underlying structure, different function; analogous structures: different underlying structure, same function), comparative embryology, and molecular evidence (DNA and protein sequence similarities).

Ecosystems: biomes, population dynamics, human impacts, and matter/energy flow:terrestrial biomes and their key characteristics: tropical rainforest (high temperature, extremely high precipitation, high biodiversity), savanna (warm, seasonal rainfall, grassland with scattered trees), desert (low precipitation, extreme temperature fluctuations; hot deserts like Sahara; cold deserts like Gobi), temperate grassland/prairie (moderate precipitation, seasonal temperature changes, few trees), temperate deciduous forest (moderate precipitation, four seasons, deciduous trees that lose leaves in fall), taiga/boreal forest (cold, coniferous forests; largest land biome by area), tundra (very cold, permafrost, extremely low precipitation, low biodiversity; arctic and alpine); aquatic biomes: freshwater (lakes, rivers, wetlands — low salinity), marine (ocean — high salinity; includes coral reefs, estuaries, open ocean); food chains and food webs: producers (autotrophs) → primary consumers (herbivores) → secondary consumers → tertiary consumers → decomposers; energy flow is unidirectional and decreases at each trophic level (approximately 10% of energy is transferred to the next level — the 10% rule); matter (carbon, nitrogen, water, phosphorus) cycles through ecosystems; biotic factors (living: predators, prey, competitors, decomposers) and abiotic factors (non-living: temperature, rainfall, sunlight, soil nutrients, pH) both affect population dynamics; carrying capacity (K) is the maximum population a given environment can sustainably support; human impacts: habitat destruction (the leading cause of biodiversity loss worldwide), invasive species, overexploitation, pollution, and climate change all reduce biodiversity and alter ecosystem function; sustainable practices can mitigate these impacts.

Stars, galaxies, and the solar system:stars are classified by surface temperature, luminosity, and color using the Hertzsprung-Russell (H-R) diagram — the main sequence runs from hot, luminous blue stars (upper left) to cool, dim red stars (lower right); our Sun is a medium-sized, yellow main-sequence star (G-type); stellar life cycles: low-mass stars (like the Sun) follow the sequence nebula → protostar → main-sequence star → red giant → planetary nebula → white dwarf; high-mass stars: nebula → protostar → main-sequence star → red supergiant → supernova → neutron star OR black hole; galaxies contain billions of stars; the Milky Way is a barred spiral galaxy; the universe is approximately 13.8 billion years old (Big Bang theory); the Doppler effect and redshift of distant galaxies provide evidence that the universe is expanding; the solar system: the Sun contains 99.8% of the solar system’s mass; inner rocky (terrestrial) planets: Mercury, Venus, Earth, Mars; outer gas and ice giants: Jupiter, Saturn, Uranus, Neptune; Earth’s rotation on its axis (once every ~24 hours) creates day and night; Earth’s revolution around the Sun (once every ~365.25 days) combined with its 23.5° axial tilt creates seasons; lunar phases result from the Moon’s position relative to the Earth and Sun; solar eclipses occur when the Moon is between the Earth and the Sun (new moon); lunar eclipses occur when the Earth is between the Moon and the Sun (full moon); tides are caused primarily by the Moon’s gravitational pull on Earth’s oceans.

Earth’s geologic history, tectonic processes, the rock cycle, and surface-shaping processes:Earth’s age (~4.6 billion years) is determined by radiometric dating using the decay of radioactive isotopes (e.g., uranium-lead, carbon-14 for recent materials); the geologic time scale divides Earth’s history into eons, eras, periods, and epochs based on fossil evidence and rock layers; the law of superposition: in undisturbed rock layers, older rocks are on the bottom and younger rocks are on top; index fossils help establish the age of rock layers; plate tectonics: Earth’s lithosphere is divided into tectonic plates that move on the asthenosphere; convergent boundaries (plates collide: oceanic-continental → subduction zone, volcanic arc, ocean trench; continental-continental → mountain building like the Himalayas); divergent boundaries (plates move apart: mid-ocean ridges, rift valleys like the East African Rift); transform boundaries (plates slide laterally: earthquakes, no volcanoes; San Andreas Fault, CA); the rock cycle: igneous rocks form from cooling magma or lava (intrusive/plutonic, e.g., granite — slow cooling, large crystals; extrusive/volcanic, e.g., basalt — fast cooling, small crystals); sedimentary rocks form from compaction and cementation of sediments (e.g., sandstone, limestone, shale); metamorphic rocks form from existing rocks changed by heat and/or pressure (e.g., marble from limestone; slate from shale); weathering (physical: breaking rocks into smaller pieces without changing chemical composition; chemical: altering chemical composition — oxidation, hydrolysis, carbonation) and erosion (transport of weathered material by water, wind, ice, gravity) shape Earth’s surface; major landforms and their formation: mountains (tectonic uplift), valleys (river and glacial erosion), deltas (deposition at river mouths), sand dunes (wind deposition).

The hydrologic cycle, marine and freshwater systems, Earth’s atmosphere, weather, and climate change:the hydrologic/water cycle: evaporation (liquid → vapor; solar energy-driven), transpiration (water vapor released by plants; evaporation + transpiration = evapotranspiration), condensation (vapor → liquid; forms clouds; requires condensation nuclei), precipitation (rain, snow, sleet, hail), surface runoff (water flows over land into streams and rivers), infiltration (water soaks into the ground → groundwater), collection (water accumulates in oceans, lakes, aquifers); layers of Earth’s atmosphere (from surface upward): troposphere (weather occurs here; temperature decreases with altitude; 0–12 km), stratosphere (contains ozone layer that absorbs UV radiation; temperature increases with altitude; 12–50 km), mesosphere (temperature decreases with altitude; meteors burn up here; 50–80 km), thermosphere (very high temperatures; auroras; 80–700 km); atmospheric conditions that produce weather: air masses are large bodies of air with uniform temperature and humidity (continental polar = cold dry; maritime tropical = warm moist); fronts are boundaries between air masses (cold front: cold air pushes under warm air → cumulonimbus clouds, heavy precipitation; warm front: warm air glides over cold air → stratus clouds, light precipitation); factors affecting local weather: proximity to water bodies (marine vs. continental climates), elevation (temperature decreases ~3.5°F per 1,000 ft), prevailing winds, ocean currents; global warming and climate change: greenhouse gases (carbon dioxide, methane, nitrous oxide, water vapor) trap infrared radiation in the atmosphere (enhanced greenhouse effect); primary human causes: burning fossil fuels, deforestation, agriculture, and industrial processes; observed impacts: rising global average temperatures, melting ice caps and glaciers, rising sea levels, more frequent and intense extreme weather events, shifting biome boundaries, ocean acidification (CO₂ dissolves in seawater to form carbonic acid, threatening marine ecosystems particularly coral reefs and shell-forming organisms).