High School Equivalency Test (HiSET) Science Syllabus

What is the difference between a dominant and a recessive allele?

A dominant allele is expressed whenever present; a recessive allele is only expressed when two copies are present (homozygous recessive).

In a Punnett square cross of two heterozygous parents (Bb x Bb), what is the genotype and phenotype ratio?

Genotype ratio 1 BB : 2 Bb : 1 bb; phenotype ratio 3 dominant : 1 recessive.

What determines biological sex in humans by chromosomes?

XX produces a female and XY produces a male; the father's sperm carries the X or Y that determines sex.

What is a genetic mutation?

A change in the DNA sequence, which can be harmful, beneficial, or neutral and may be passed to offspring if it occurs in gametes.

What is the main function of the circulatory system?

To transport blood, carrying oxygen, nutrients, hormones, and wastes throughout the body.

What is the function of the respiratory system, and where does gas exchange occur?

It brings oxygen into the body and removes carbon dioxide; gas exchange occurs in the alveoli of the lungs.

What is the function of the nervous system?

To detect stimuli and rapidly transmit electrical signals (via neurons) to coordinate body responses and process information.

What is homeostasis?

The maintenance of a stable internal environment (e.g., temperature, pH, glucose) despite external changes.

What is the role of the digestive system?

To break down food into nutrients the body can absorb and to eliminate solid waste.

What is natural selection?

The process by which organisms with traits better suited to their environment survive and reproduce more, passing those traits on (survival of the fittest).

What is biological evolution?

The change in the heritable characteristics (allele frequencies) of a population over successive generations.

Name three types of evidence that support evolution.

Fossil record, comparative anatomy (homologous structures), and molecular/DNA similarities (also embryology).

What is an adaptation?

An inherited trait that increases an organism's chance of survival and reproduction in its environment.

What is the source of new genetic variation that natural selection acts upon?

Mutation (and, in sexually reproducing organisms, genetic recombination).

In an ecosystem, what is the difference between a producer and a consumer?

Producers (autotrophs) make their own food via photosynthesis; consumers (heterotrophs) obtain energy by eating other organisms.

What is the role of decomposers in an ecosystem?

They break down dead organisms and waste, recycling nutrients back into the environment.

Roughly what percentage of energy is passed to the next trophic level in a food chain?

About 10%; the other ~90% is lost mainly as heat through life processes.

What is the difference between a food chain and a food web?

A food chain shows a single linear path of energy flow; a food web shows many interconnected food chains in an ecosystem.

What is the difference between an element, a compound, and a mixture?

An element is one type of atom; a compound is two or more elements chemically bonded; a mixture is substances physically combined and not chemically bonded.

What are the three subatomic particles and their charges?

Protons (positive) and neutrons (neutral) in the nucleus, and electrons (negative) orbiting it.

What does the atomic number of an element tell you?

The number of protons in the atom's nucleus, which identifies the element.

What distinguishes a physical change from a chemical change?

A physical change alters form but not identity (e.g., melting); a chemical change forms new substances (e.g., burning).

What is 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.

In a chemical equation, what are reactants and products?

Reactants are the starting substances (left of the arrow); products are the substances formed (right of the arrow).

On the pH scale, what values indicate acids, bases, and neutral?

Below 7 is acidic, exactly 7 is neutral, and above 7 is basic (alkaline).

What is Newton's first law of motion (the law of inertia)?

An object at rest stays at rest and an object in motion stays in motion at constant velocity unless acted on by an unbalanced (net) force.

State Newton's second law of motion as a formula.

Force = mass × acceleration (F = ma).

What is the formula for speed?

Speed = distance ÷ time.

What is the difference between kinetic and potential energy?

Kinetic energy is the energy of motion; potential energy is stored energy due to position or condition (e.g., gravitational PE).

What is the law of conservation of energy?

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

What are the three main types of rocks and how does each form?

Igneous (cooled magma/lava), sedimentary (compacted/cemented sediments), and metamorphic (existing rock changed by heat and pressure).

What are the three layers of Earth's interior from outside to center?

Crust, mantle, and core (the core has a liquid outer core and solid inner core).

What is the theory of plate tectonics?

Earth's lithosphere is broken into plates that move on the mantle, causing earthquakes, volcanoes, and mountain building at their boundaries.

What are the main steps of the water cycle?

Evaporation, condensation, precipitation, and collection/runoff (with transpiration from plants).

What is weathering versus erosion?

Weathering is the breaking down of rock in place; erosion is the transport of those weathered materials by wind, water, or ice.

What is the difference between weather and climate?

Weather is the day-to-day state of the atmosphere; climate is the average weather pattern of a region over many years.

What gas in the atmosphere is most responsible for protecting Earth from harmful UV radiation?

Ozone (O3), found in the stratosphere's ozone layer.

What causes the greenhouse effect?

Greenhouse gases (like CO2, water vapor, and methane) trap heat radiated from Earth's surface, warming the atmosphere.

What causes Earth's seasons?

The tilt of Earth's axis (about 23.5°) as it orbits the Sun, changing the angle and duration of sunlight received by each hemisphere.

What causes the phases of the Moon?

The changing relative positions of the Moon, Earth, and Sun, which change how much of the Moon's sunlit side we see from Earth.

What is the difference between rotation and revolution for Earth?

Rotation is Earth spinning on its axis (one day); revolution is Earth orbiting the Sun (one year).

List the planets of the solar system in order from the Sun.

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

What force keeps the planets in orbit around the Sun?

Gravity, the attractive force between masses.