Praxis General Science flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Hypothesis

A testable, falsifiable prediction about the relationship between variables, stated before data collection so that results can either support or refute it.

Scientific theory

A well-substantiated explanation of some aspect of nature, supported by extensive and repeated evidence, broader than a hypothesis, and still open to revision if conflicting evidence appears.

Scientific law

A concise statement, often mathematical, describing a consistent pattern observed in nature, such as Newton's second law; it describes what happens rather than explaining why.

Independent variable

The factor that the experimenter deliberately changes or manipulates in order to test its effect on the measured outcome, which is called the dependent variable.

Control group

The comparison group that does not receive the experimental treatment, used to show that observed changes come from the manipulated variable rather than other factors.

Peer review

Evaluation of a study's methods and conclusions by independent experts in the same field before publication, screening for flaws, bias, and unsupported claims.

Engineering design process

An iterative cycle of defining a problem, specifying criteria and constraints, designing and building prototypes, testing them, and optimizing the solution against trade-offs such as cost and safety.

Significant figures

Digits in a measurement that carry meaningful information about its precision; calculation rules require rounding answers to match the least precise input value.

Newton's second law

The net force acting on an object equals its mass multiplied by its acceleration; acceleration points in the direction of the net force and is inversely proportional to mass.

Conservation of energy

Energy cannot be created or destroyed, only transformed between forms; in a closed system the total energy before and after any process remains unchanged.

Ohm's law

The current through a conductor equals the voltage across it divided by its resistance; doubling voltage doubles current, while doubling resistance halves current.

Wave equation

Wave speed equals frequency multiplied by wavelength; within a given medium where speed is fixed, higher frequency corresponds to shorter wavelength and vice versa.

Density

Mass per unit volume of a substance; an object denser than its surrounding fluid sinks while a less dense object floats, and density can help identify pure substances.

Specific heat capacity

The energy required to raise one gram of a substance by one degree Celsius, used in the equation q = mc delta T to calculate heat absorbed or released.

pH scale

A logarithmic measure of hydrogen ion concentration in which each unit represents a tenfold change; values below 7 are acidic and values above 7 are basic.

Covalent bond

A chemical bond formed when two atoms share one or more pairs of electrons, typically between nonmetals, producing discrete molecules or extended network solids.

Cell theory

The principle that all living organisms are made of one or more cells, that the cell is the basic unit of life, and that all cells arise from preexisting cells.

Mitosis

Nuclear division that produces two genetically identical diploid daughter cells, used for growth, repair, and asexual reproduction in somatic cells rather than gametes.

Meiosis

Two successive nuclear divisions that produce four genetically distinct haploid gametes, halving the chromosome number and generating variation through crossing over and independent assortment.

Photosynthesis

The process by which autotrophs use light energy to convert carbon dioxide and water into glucose and oxygen, storing energy in the chemical bonds of sugar.

Cellular respiration

The breakdown of glucose to release usable ATP energy, using oxygen in aerobic pathways and producing carbon dioxide and water as waste products.

Natural selection

The process by which individuals with heritable traits better suited to their environment reproduce more successfully, causing those traits to increase in frequency over generations.

Homeostasis

The maintenance of a stable internal environment, such as temperature or blood glucose, through negative feedback loops that counteract deviations from a set point.

Dominant allele

An allele whose trait appears in the phenotype whenever at least one copy is present, masking the expression of a recessive allele at the same gene locus.

Plate tectonics

The theory that Earth's rigid lithosphere is broken into plates that move over the asthenosphere, causing earthquakes, mountain building, and volcanism at plate boundaries.

Rock cycle

The ongoing transformation of rock among igneous, sedimentary, and metamorphic types through melting, cooling, weathering, erosion, deposition, compaction, and heat and pressure.

Water cycle

The continuous movement of water through evaporation, transpiration, condensation, precipitation, and runoff, redistributing water among oceans, the atmosphere, and land.

Cause of seasons

Earth's 23.5-degree axial tilt changes the angle and duration of sunlight at each latitude as Earth orbits the Sun, producing seasonal temperature differences.

Kepler's first law

Each planet orbits the Sun along an ellipse with the Sun at one focus, so the planet-Sun distance varies over the course of a single orbital year.

Greenhouse effect

Atmospheric gases such as carbon dioxide and water vapor absorb and re-emit outgoing infrared radiation, warming Earth's surface above its otherwise expected temperature.

Seismic P waves

The fastest earthquake waves, longitudinal compressions that travel through both solids and liquids and therefore arrive first at a seismograph station.

Nebular hypothesis

The model that the solar system formed from a rotating cloud of gas and dust that collapsed, flattened into a disk, and accreted into the Sun and planets.