HiSET Science cheat sheet

A hypothesis must be testable and falsifiable; an untestable statement is not a scientific hypothesis.

Independent variable: the factor deliberately changed by the experimenter; dependent variable: the factor measured in response.

Controlled variables are kept constant across groups to reduce alternative explanations; a control group receives no treatment or a standard condition.

Correlation means two variables change together; it does not by itself establish causation.

Repeated trials and larger samples reduce random error; peer review checks methods, evidence, and conclusions.

Mean = sum of values ÷ number of values; median = middle value when ordered; mode = most frequent value.

Line graphs display continuous change, bar graphs compare categories, and scatterplots show relationships between two variables.

In scientific notation, a number is written as a coefficient between 1 and 10 multiplied by a power of 10.

Newton's first law: an object at rest stays at rest and a moving object keeps constant velocity unless a net force acts.

Newton's second law: net force = mass × acceleration (F = ma); greater force or smaller mass gives greater acceleration.

Speed = distance ÷ time; acceleration = change in velocity ÷ time.

Kinetic energy = ½mv²; gravitational potential energy = mgh near Earth's surface.

Density = mass ÷ volume; an object denser than its fluid sinks, and one less dense floats.

Atomic number equals protons; mass number equals protons plus neutrons; neutral atoms have equal protons and electrons.

In a chemical reaction, atoms are rearranged but not created or destroyed, so mass is conserved.

pH below 7 is acidic, pH 7 is neutral, and pH above 7 is basic; each whole pH unit is a tenfold change in hydrogen ion concentration.

Wave speed = frequency × wavelength; higher frequency means shorter wavelength if speed is constant.

Cell theory states that all living things are made of cells, cells are the basic unit of life, and new cells arise from existing cells.

Prokaryotic cells lack a nucleus and membrane-bound organelles; eukaryotic cells have a nucleus and membrane-bound organelles.

Photosynthesis uses light energy to convert carbon dioxide and water into glucose and oxygen: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

Cellular respiration releases energy from glucose: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.

Mitosis produces two genetically identical diploid cells for growth and repair; meiosis produces four genetically varied haploid gametes.

DNA carries genetic information; genes are DNA segments that code for proteins or traits.

Natural selection: individuals with inherited traits better suited to the environment tend to survive and reproduce more.

In a food chain, producers make food, consumers eat other organisms, and decomposers break down dead matter; about 10% of energy passes to the next level.

Homeostasis is the maintenance of stable internal conditions, often regulated by negative feedback loops.

Earth's internal layers are crust, mantle, outer core, and inner core; the outer core is liquid and the inner core is solid.

Plate tectonics: lithospheric plates move over the asthenosphere; divergent boundaries separate plates, convergent boundaries collide, and transform boundaries slide past.

The rock cycle transforms igneous, sedimentary, and metamorphic rocks through melting, cooling, weathering, erosion, deposition, compaction, and heat or pressure.

Water cycle: evaporation and transpiration add water vapor, condensation forms clouds, precipitation returns water, and runoff collects in bodies of water.

Seasons are caused by Earth's axial tilt as it orbits the Sun, not by changes in Earth's distance from the Sun.

Moon phases result from the changing angle between Earth, the Moon, and the Sun as the Moon orbits Earth.

Solar system order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

Earth's atmosphere is mostly nitrogen and oxygen; it protects life from harmful radiation and helps regulate temperature.

The greenhouse effect occurs when atmospheric gases absorb and re-emit infrared radiation, warming Earth's surface.