PSSA Grade 8 Science flashcards
PSSA Grade 8 Science · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Hypothesis
- A testable, falsifiable prediction that explains an observation and can be supported or rejected by the results of a controlled experiment.
- Independent variable
- The factor the experimenter deliberately changes or manipulates between groups so that its effect on the measured outcome can be determined.
- Dependent variable
- The factor that is measured or observed in an experiment; it is expected to respond to changes made in the independent variable.
- Control group
- The group in an experiment that does not receive the treatment; it provides a baseline for judging the effect of the independent variable.
- Scientific theory
- A well-tested explanation for a broad set of observations, supported by large amounts of evidence from many investigations and accepted by most scientists.
- Percent error
- A measure of accuracy found by subtracting the accepted value from the measured value, dividing by the accepted value, and multiplying by 100.
- Repetition and sample size
- Repeating trials and testing many subjects reduces the effect of random error and makes experimental results more reliable and trustworthy.
- Scientific model
- A physical, mathematical, or computer representation of something too large, small, slow, or dangerous to observe directly; every model has limitations.
- Cell theory
- All living organisms are made of one or more cells, the cell is the basic unit of life, and new cells arise from existing cells.
- Eukaryotic cell
- A cell that contains a nucleus and membrane-bound organelles; found in plants, animals, fungi, and protists but not in bacteria.
- Chloroplast
- The plant cell organelle that captures light energy and uses it to make glucose from carbon dioxide and water during photosynthesis.
- Mitochondrion
- The organelle where cellular respiration releases usable energy from food molecules and stores it in ATP for cell activities.
- Osmosis
- The diffusion of water across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.
- Natural selection
- Individuals with inherited traits better suited to their environment survive and reproduce more, so those traits become more common in later generations.
- Mitosis versus meiosis
- Mitosis makes two genetically identical body cells for growth and repair; meiosis makes four genetically different sex cells, each with half the chromosome number.
- Energy pyramid
- A diagram showing that only about ten percent of the energy at each feeding level passes to the next level; most is lost as heat.
- Physical change
- A change in the size, shape, or state of matter that does not alter the identity of the substance; examples include melting and tearing.
- Chemical change
- A change in which one or more new substances form with different properties; evidence includes unexpected color change, gas, precipitate, or temperature change.
- Newton's second law
- The acceleration of an object equals the net force on it divided by its mass, written as F = ma; greater force or smaller mass means greater acceleration.
- Density
- Mass per unit volume, calculated as density equals mass divided by volume; an object denser than its fluid sinks and a less dense object floats.
- Speed and velocity
- Speed is distance divided by time and has no direction; velocity is speed in a stated direction, so a change in direction changes velocity.
- Law of conservation of energy
- Energy cannot be created or destroyed, only transformed from one form to another or transferred between objects; the total amount stays constant.
- Wave speed relationship
- Wave speed equals frequency multiplied by wavelength; if speed is constant, a longer wavelength means a lower frequency and vice versa.
- Balanced forces
- Equal forces acting in opposite directions on an object, producing a net force of zero so the object's motion does not change.
- Plate tectonics
- The theory that Earth's lithosphere is broken into plates that move slowly over the asthenosphere, causing earthquakes, volcanoes, and mountain building.
- Convergent boundary
- A plate boundary where two plates move toward each other; oceanic crust may subduct, forming trenches and volcanoes, or continents may collide and form mountains.
- Earthquake epicenter
- The point on Earth's surface directly above the focus of an earthquake, where shaking is usually strongest.
- Rock cycle
- The continuous processes of melting, cooling, weathering, erosion, compaction, and heat and pressure that change rock among igneous, sedimentary, and metamorphic forms.
- Earth's axial tilt
- Earth's axis is tilted about 23.5 degrees, so different hemispheres receive more direct sunlight at different times of year, producing the seasons.
- Moon phases
- The changing apparent shape of the Moon seen from Earth, caused by the relative positions of the Sun, Earth, and Moon as the Moon orbits.
- Erosion and deposition
- Erosion is the transport of weathered rock and soil by water, wind, ice, or gravity; deposition is the dropping of those materials in a new location.
- Solar system structure
- The Sun is the central star; rocky inner planets orbit closer and gas and ice giants orbit farther out, all held in elliptical orbits by gravity.