Your FREE Praxis 5435 Flashcards 2026 – 200+ Cards

The factor a researcher deliberately changes to test its effect; plotted on the x-axis as the suspected cause.

The outcome that is measured; it depends on (responds to) the independent variable and is plotted on the y-axis.

A condition kept the same across all groups so it cannot influence the results.

The group that does not receive the experimental treatment; it provides a baseline for comparison.

A testable, falsifiable, proposed explanation, often stated as an 'if/then' prediction about how variables relate.

A claim is falsifiable if there is a possible observation or experiment that could prove it wrong; a requirement for a scientific hypothesis.

A broad, well-substantiated explanation supported by a large body of evidence (e.g., evolution, plate tectonics) — far stronger than a guess.

A statement (often mathematical) describing a consistent natural pattern, such as Newton's laws; it describes what happens but not why.

Accuracy = closeness to the true value; precision = closeness of repeated measurements to each other. Measurements can be precise but inaccurate.

A consistent error that shifts every measurement in the same direction (e.g., a balance reading high), reducing accuracy but not precision.

Unpredictable scatter in measurements from trial to trial; reduced by averaging many trials.

Independent (manipulated) variable goes on the x-axis; dependent (measured/responding) variable goes on the y-axis.

Repeating an experiment to confirm results are reliable and not due to chance; central to the self-correcting nature of science.

Evaluation of research by independent experts before publication; a key check on the quality and validity of scientific claims.

An observation is information gathered directly with the senses or instruments; an inference is a conclusion drawn from observations.

Qualitative = descriptive (color, texture); quantitative = numerical/measured (mass, length, time).

Meter (length), kilogram (mass), second (time), kelvin (temperature), ampere (current), mole (amount), candela (luminous intensity).

A valid controlled experiment changes only one independent variable so any change in the outcome can be attributed to it.

Question → hypothesis → experiment → analyze data → conclusion; results often loop back to new questions, so it is iterative, not one-time.

Two variables changing together (correlation) does not prove one causes the other; only a controlled experiment can establish causation.

A simplified representation (physical, mathematical, or conceptual) used to explain or predict phenomena, e.g., the atomic model.

Always wear goggles; flush eyes/skin with water for 15 minutes and notify the instructor if a chemical contacts them.

Define the problem and constraints → brainstorm → design → build a prototype → test → evaluate → redesign (iterate).

Science seeks to understand the natural world; engineering applies that understanding to design solutions under real-world constraints.

Scientific and engineering advances shape society (medicine, energy, communication) and raise ethical, economic, and environmental questions.

The digits in a measurement that carry meaning about its precision; the result of a calculation should reflect the least precise measurement.

Mean = average; median = middle value of ordered data; mode = most frequent value. The median resists outliers.

A limit on a design solution, such as cost, time, materials, safety, or available space.

Information acquired through observation or experiment; the basis for testing scientific claims.

Claims presented as scientific but lacking testability, falsifiability, or supporting evidence (e.g., astrology).

Protons (+, in nucleus), neutrons (neutral, in nucleus), electrons (−, orbit nucleus). Nearly all the atom's mass is in the nucleus.

The number of protons in an atom; it defines the element's identity.

The sum of protons and neutrons in an atom's nucleus.

Atoms of the same element (same protons) with different numbers of neutrons, and thus different mass numbers.

An atom that has gained or lost electrons, giving it a net negative (anion) or positive (cation) charge.

Columns of elements with similar chemical properties because they have the same number of valence electrons.

Horizontal rows; properties change gradually from left (metals) to right (nonmetals) across a period.

Generally decreases left-to-right across a period (more nuclear charge pulls electrons in) and increases down a group.

Increases up and to the right; fluorine is the most electronegative element.

The energy required to remove an electron from a neutral atom; increases left-to-right across a period.

Electrons in the outermost shell; they determine an element's bonding behavior and reactivity.

A bond formed by the transfer of electrons from a metal to a nonmetal, producing oppositely charged ions that attract.

A bond formed when two nonmetal atoms share electrons.

Bonding in metals where positive ions sit in a 'sea' of delocalized electrons, explaining conductivity and malleability.

Mass is neither created nor destroyed in a chemical reaction; the mass of reactants equals the mass of products.

A chemical equation with equal numbers of each type of atom on both sides, satisfying conservation of mass.

A fuel reacts with oxygen to release energy, e.g. $\ce{CH4 + 2O2 -> CO2 + 2H2O}$.

Two or more reactants combine to form one product: $\ce{A + B -> AB}$.

One reactant breaks into two or more products: $\ce{AB -> A + B}$.

A substance that donates H⁺ ions (or accepts electrons); has a pH below 7 and turns litmus red.

A substance that accepts H⁺ (or donates OH⁻); has a pH above 7 and turns litmus blue.

Measures acidity from 0–14; 7 is neutral, below 7 acidic, above 7 basic. Each unit is a tenfold change in H⁺ concentration.

Solid (fixed shape/volume), liquid (fixed volume, takes shape of container), gas (fills container), plasma (ionized gas).

Melting, freezing, vaporization (boiling/evaporation), condensation, sublimation (solid→gas), deposition (gas→solid).

Endothermic reactions absorb energy (surroundings cool); exothermic reactions release energy (surroundings warm).

Physical change alters form but not identity (melting, cutting); chemical change forms new substances (burning, rusting).

Element = one kind of atom; compound = atoms chemically bonded in fixed ratio; mixture = physically combined, separable substances.

A homogeneous mixture of a solute dissolved in a solvent (e.g., salt water).

Mass per unit volume: $\rho = \dfrac{m}{V}$. An object floats if its density is less than the fluid's.

An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted on by a net force.

Net force equals mass times acceleration: $F = ma$.

For every action there is an equal and opposite reaction; forces come in pairs on different objects.

Speed is distance per time (scalar); velocity is speed with direction (vector).

The rate of change of velocity: $a = \dfrac{\Delta v}{\Delta t}$. It occurs when speed or direction changes.

Energy of motion: $KE = \tfrac{1}{2}mv^2$. It increases with the square of speed.

Stored energy due to position: $PE = mgh$.

Energy cannot be created or destroyed, only transformed from one form to another; total energy stays constant.

Force applied over a distance in the direction of motion: $W = Fd$. Measured in joules.

The rate of doing work: $P = \dfrac{W}{t}$. Measured in watts.

The product of mass and velocity: $p = mv$; conserved in collisions in a closed system.

A force that opposes motion between surfaces in contact; converts kinetic energy to heat.

An attractive force between masses; near Earth's surface it gives free-falling objects an acceleration of about $9.8\ \text{m/s}^2$.

Mass is the amount of matter (constant, kg); weight is the force of gravity on that mass ($W = mg$, varies by location).

Lever, pulley, wheel and axle, inclined plane, wedge, and screw; they change the size or direction of a force.

How much a machine multiplies input force; it does not multiply work or energy (those are conserved).

Radio, microwave, infrared, visible light, ultraviolet, X-rays, gamma rays — increasing frequency and energy, decreasing wavelength.

Wavelength (crest-to-crest distance), frequency (waves per second), amplitude (height), and speed ($v = f\lambda$).

Transverse: medium moves perpendicular to wave travel (light); longitudinal: medium moves parallel (sound).

Reflection = bouncing off a surface; refraction = bending when entering a new medium; diffraction = spreading around obstacles.

A longitudinal mechanical wave that requires a medium; pitch depends on frequency and loudness on amplitude.

Voltage equals current times resistance: $V = IR$.

Series: one path, current is the same everywhere; parallel: multiple paths, voltage is the same across branches.

Conductors (metals) let charge flow easily; insulators (rubber, glass) resist charge flow.

A magnet created by current flowing through a coil of wire; its strength depends on current and number of coils.

Conduction (direct contact), convection (fluid movement), and radiation (electromagnetic waves, no medium needed).

Temperature measures the average kinetic energy of particles; heat is the energy transferred between objects at different temperatures.

Fission splits a heavy nucleus releasing energy (nuclear plants); fusion joins light nuclei (powers the Sun), releasing even more energy.

Unstable nuclei emit alpha, beta, or gamma radiation, transforming into more stable elements over time.

The time for half of a radioactive sample to decay; constant for a given isotope.

Mechanical, thermal, chemical, electrical, nuclear, electromagnetic, and sound — all interconvertible.

The vector sum of all forces on an object; zero net force means no acceleration (equilibrium).

Buildup of electric charge on a surface, often from friction; like charges repel and opposite charges attract.

Every magnet has a north and south pole; like poles repel, opposite poles attract, and poles cannot be isolated.

The amount of solute per amount of solution; higher concentration means more dissolved solute.

A substance that speeds a reaction by lowering activation energy without being consumed.

The minimum energy needed to start a chemical reaction.

Moles of solute per liter of solution; a common measure of concentration.

At constant temperature, the pressure and volume of a gas are inversely related: $P_1 V_1 = P_2 V_2$.

At constant pressure, a gas's volume is directly proportional to its absolute temperature.

$6.022 \times 10^{23}$ particles per mole; links the number of particles to the amount of substance.

Plants convert carbon dioxide and water into glucose and oxygen using light energy: $\ce{6CO2 + 6H2O -> C6H12O6 + 6O2}$.

In the chloroplasts of plant cells, using the green pigment chlorophyll to capture light.

Cells break down glucose with oxygen to release energy (ATP): $\ce{C6H12O6 + 6O2 -> 6CO2 + 6H2O}$.

Mostly in the mitochondria of eukaryotic cells.

They are roughly reverse processes: photosynthesis stores energy in glucose; respiration releases it. Products of one are reactants of the other.

Adenosine triphosphate — the cell's main energy-carrying molecule, produced by respiration.

Energy release without oxygen; in muscle it produces lactic acid, in yeast it produces alcohol and $\ce{CO2}$.

All living things are made of cells, the cell is the basic unit of life, and all cells come from pre-existing cells.

Prokaryotes (bacteria) lack a nucleus and membrane-bound organelles; eukaryotes (plants, animals) have both.

The organelle that contains the cell's DNA and controls cell activities.

The 'powerhouse' organelle where most cellular respiration and ATP production occur.

The organelle in plant cells where photosynthesis takes place; contains chlorophyll.

The selectively permeable boundary controlling what enters and leaves the cell.

A rigid outer layer in plant, fungal, and bacterial cells that provides support and protection; absent in animal cells.

The site of protein synthesis (translation) in the cell.

Movement of particles from high to low concentration; passive, requiring no energy.

Diffusion of water across a selectively permeable membrane from low to high solute concentration.

Movement of substances against a concentration gradient, requiring energy (ATP).

Deoxyribonucleic acid — a double helix of nucleotides (A-T, G-C base pairs) that stores genetic information.

A segment of DNA that codes for a protein or trait.

A condensed structure of DNA and protein; humans have 23 pairs (46 total).

Cell division producing two genetically identical diploid cells, used for growth and repair.

Cell division producing four genetically varied haploid gametes (sex cells) with half the chromosome number.

A dominant allele is expressed when present; a recessive allele is masked unless two copies are inherited.

Genotype is the genetic makeup (e.g., Bb); phenotype is the observable trait (e.g., brown eyes).

Homozygous = two identical alleles (BB or bb); heterozygous = two different alleles (Bb).

A diagram predicting offspring genotype and phenotype ratios from the parents' alleles.

The semiconservative copying of DNA before cell division; each new molecule keeps one original strand.

Transcription copies DNA into mRNA; translation uses mRNA at the ribosome to build a protein.

A change in DNA sequence; it can be harmful, beneficial, or neutral and is the ultimate source of genetic variation.

Individuals with traits better suited to the environment survive and reproduce more, passing those traits on.

Change in the inherited traits of a population over generations; descent with modification.

An inherited trait that improves an organism's survival or reproduction in its environment.

Fossils, homologous structures, embryology, DNA/molecular similarities, and observed natural selection.

A group of organisms that can interbreed and produce fertile offspring.

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species — broadest to most specific.

An autotroph that makes its own food via photosynthesis (or chemosynthesis); the base of a food chain.

A heterotroph that eats other organisms; classified as herbivore, carnivore, or omnivore.

An organism (bacteria, fungi) that breaks down dead matter and recycles nutrients into the ecosystem.

Interconnected food chains showing energy flow through an ecosystem from producers up to top consumers.

Only about 10% of energy passes from one trophic level to the next; the rest is lost as heat.

Carbon moves among the atmosphere, organisms, oceans, and rocks via photosynthesis, respiration, decay, and combustion.

Bacteria convert atmospheric nitrogen into usable forms (fixation) that organisms use to build proteins and DNA.

Evaporation, condensation, precipitation, and collection circulate water through the environment.

The maximum population size an environment can sustain given its resources.

A resource or condition (food, water, space, predators) that limits a population's growth.

A large region defined by its climate and characteristic plants and animals (e.g., desert, tundra, rainforest).

A community of living organisms interacting with their nonliving (abiotic) environment.

Mutualism (both benefit), commensalism (one benefits, other unaffected), parasitism (one benefits, host harmed).

Predator and prey populations cycle: prey rises, predators rise, prey falls, predators fall.

The maintenance of stable internal conditions (temperature, pH, water) despite a changing environment.

A protein catalyst that speeds biological reactions; specific to its substrate and sensitive to temperature and pH.

The heart, blood, and vessels that transport oxygen, nutrients, and wastes throughout the body.

Lungs and airways that exchange oxygen and carbon dioxide between the body and the air.

Organs that break down food into nutrients the body can absorb and use.

The brain, spinal cord, and nerves that sense stimuli and coordinate responses.

Carbohydrates (energy), lipids (storage/membranes), proteins (structure/enzymes), and nucleic acids (genetic info).

Asexual produces genetically identical offspring from one parent; sexual combines two parents' genes, increasing variation.

The variety of life in an ecosystem; greater biodiversity generally makes an ecosystem more stable and resilient.

The gradual change in a community over time — primary (bare rock) or secondary (after a disturbance like fire).

Crust, mantle, outer core (liquid), inner core (solid).

The thick layer beneath the crust that behaves as a slowly flowing solid; convection currents here drive plate movement.

The outer core is liquid (molten iron and nickel) and generates Earth's magnetic field; the inner core is solid due to immense pressure.

The theory that Earth's rigid outer shell is broken into plates that slowly move over the softer mantle below.

Plates pull apart; magma rises to form new crust, creating mid-ocean ridges and rift valleys.

Plates collide; the denser plate subducts, forming volcanoes, mountains, and deep ocean trenches.

Plates slide past each other horizontally, producing earthquakes (e.g., the San Andreas Fault).

Convection currents in the mantle, powered by Earth's internal heat, move the plates.

Wegener's hypothesis that continents were once joined in a single landmass (Pangaea) and have since drifted apart.

Concentrated along plate boundaries, especially the Pacific 'Ring of Fire.'

Forms from the cooling and solidifying of molten magma or lava (e.g., granite, basalt).

Forms when sediments are compacted and cemented over time (e.g., sandstone, limestone); may contain fossils.

Forms when existing rock is changed by heat and pressure (e.g., marble from limestone).

The continuous transformation among igneous, sedimentary, and metamorphic rock through melting, weathering, and pressure.

Weathering breaks rock down in place (physical or chemical); erosion transports the pieces away by wind, water, or ice.

A naturally occurring, inorganic solid with a definite chemical composition and crystal structure.

Preserved remains or traces of past life, most often found in sedimentary rock.

In undisturbed rock layers, the oldest layers are at the bottom and the youngest at the top.

Relative dating orders events (older/younger); absolute dating gives a numeric age, often via radioactive decay.

Troposphere, stratosphere (ozone), mesosphere, thermosphere, exosphere — from the surface upward.

A region in the stratosphere that absorbs most of the Sun's harmful ultraviolet radiation.

Atmospheric gases (CO₂, water vapor, methane) trap heat, warming Earth's surface; excess gas intensifies warming.

Evaporation, transpiration, condensation, precipitation, and runoff continually move water through Earth's systems.

Weather is short-term atmospheric conditions; climate is the long-term average weather of a region.

A front is the boundary between air masses; cold fronts often bring storms, warm fronts bring gradual precipitation.

Large-scale movements of seawater driven by wind, temperature, and salinity that redistribute heat around the globe.

The regular rise and fall of sea level caused mainly by the Moon's gravitational pull, with the Sun contributing.

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune — inner rocky planets, then outer gas/ice giants.

Rotation (spin on its axis, ~24 h) causes day and night; revolution (orbit around the Sun, ~365 days) defines a year.

The tilt of Earth's axis (about 23.5°), not its distance from the Sun, causes the seasons.

New, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent — driven by Sun-Earth-Moon geometry.

Solar: Moon passes between Sun and Earth, blocking the Sun. Lunar: Earth passes between Sun and Moon, casting a shadow on the Moon.

Stars form from gas/dust nebulae, fuse hydrogen as main-sequence stars, then expand and end as white dwarfs, neutron stars, or black holes.

A medium-sized star that produces energy by nuclear fusion of hydrogen into helium; the source of Earth's energy.

A vast system of stars, gas, and dust bound by gravity; our solar system lies in the Milky Way galaxy.

The leading explanation that the universe began ~13.8 billion years ago from an extremely hot, dense state and has been expanding since.

Gravity holds planets in orbit around the Sun and moons around planets; orbital paths are ellipses.

Renewable resources (solar, wind, hydro) replenish naturally; nonrenewable (coal, oil, gas) form over millions of years.

A map using contour lines to show elevation; closely spaced lines indicate steep terrain.

Comets are icy bodies with tails; asteroids are rocky bodies (mostly between Mars and Jupiter); a meteor is debris burning up in the atmosphere.