SHS Science Foundations: Integrated Chemistry, Biology, and Physics

SI (International System of Units)

A globally agreed system of measurement used in science, based on base units like meter (m), kilogram (kg), second (s), kelvin (K), mole (mol), and ampere (A).

Scientific notation

A way of writing numbers as a × 10ⁿ, where 1 ≤ a < 10 and n is an integer, used for very large or very small values.

Significant figures

The digits in a measurement that are known with certainty plus one estimated digit, showing the precision of the measurement.

Independent variable

The variable that is deliberately changed in an experiment to test its effect on another variable.

Dependent variable

The variable that is measured in an experiment; it may change when the independent variable changes.

Controlled variables

Factors kept constant in an experiment so they do not influence the dependent variable.

Matter

Anything that has mass and takes up space.

Particle model of matter

A model that explains matter as tiny particles that are always moving, with spaces and forces between them.

Physical change

A change in form or state where no new substance is formed (for example, melting, boiling, cutting).

Chemical change

A change where one or more new substances with different properties are formed (a chemical reaction).

Density

Mass per unit volume; calculated as density = mass / volume.

Element

A pure substance made of only one kind of atom; listed on the periodic table.

Atom

The smallest unit of an element that still has that element's properties; made of protons, neutrons, and electrons.

Proton

Positively charged subatomic particle in the nucleus; atomic number equals the number of protons.

Neutron

Neutral subatomic particle in the nucleus; adds mass and helps stabilize the nucleus.

Electron

Negatively charged, very light particle moving in the electron cloud; controls chemical behavior.

Atomic number (Z)

Number of protons in an atom's nucleus; defines the element.

Mass number (A)

Total number of protons plus neutrons in the nucleus of a specific atom.

Ionic bond

A chemical bond formed by the transfer of electrons from one atom to another, producing oppositely charged ions that attract each other. Typically between a metal and a non-metal.

Covalent bond

A chemical bond formed when two atoms share one or more pairs of electrons. Usually occurs between non-metal atoms and forms molecules.

Molecule

A group of two or more atoms joined by covalent bonds, acting as a single particle. Example: H2O, CO2, O2.

Chemical formula

A shorthand way to show which elements and how many atoms of each are in a substance. Example: H2O has 2 hydrogen atoms and 1 oxygen atom.

Word equation

A way of describing a reaction using words: reactants → products. Example: magnesium + oxygen → magnesium oxide.

Symbol equation

A chemical equation using formulas instead of words. Example: 2H2 + O2 → 2H2O.

Cell theory

Biology rulebook stating that: (1) all living things are made of one or more cells, (2) the cell is the basic unit of structure and function, and (3) all cells come from pre-existing cells.

Prokaryotic cell

A small, simple cell without a nucleus or membrane-bound organelles; examples include bacteria and archaea.

Eukaryotic cell

A larger, more complex cell with a nucleus and membrane-bound organelles; found in plants, animals, fungi, and protists.

Cell membrane

Thin, flexible boundary made mainly of phospholipids and proteins that controls what enters and leaves the cell.

Nucleus

Membrane-bound organelle that stores DNA and controls the cell’s activities.

Mitochondrion (plural: mitochondria)

Organelle that releases energy from food molecules to produce ATP; often called the powerhouse of the cell.

Photosynthesis (word equation)

carbon dioxide + water + light energy → glucose + oxygen

Cellular respiration (aerobic, word equation)

glucose + oxygen → carbon dioxide + water + energy (ATP)

Chloroplast

Organelle in plant and algal cells where photosynthesis happens; contains chlorophyll to absorb light.

Mitochondrion (plural: mitochondria)

Organelle in most eukaryotic cells where cellular respiration releases energy from glucose to make ATP.

Producer

An organism (usually using photosynthesis) that makes its own food from simple substances; entry point of energy into most food chains.

Consumer

An organism that must eat other organisms to obtain energy and nutrients (herbivores, carnivores, omnivores).

DNA

DeoxyriboNucleic Acid; the molecule that stores genetic information in cells, organized into genes and chromosomes.

Gene

A segment of DNA that contains instructions for making a specific protein or functional RNA, influencing a trait.

Chromosome

A long, tightly coiled piece of DNA wrapped around proteins. Humans usually have 46 in body cells, arranged in 23 pairs.

Allele

A different version of the same gene, such as a brown-eye allele vs. a blue-eye allele.

Genotype

The combination of alleles an organism has for a gene, often written as letter pairs (for example, BB, Bb, or bb).

Phenotype

The observable traits of an organism, such as eye color or blood type, resulting from genotype and environment.

Ecosystem

All the living (biotic) and nonliving (abiotic) things in an area and how they interact.

Biotic factor

A living or once-living part of an ecosystem, such as plants, animals, fungi, or bacteria.

Abiotic factor

A nonliving part of an ecosystem, such as sunlight, temperature, water, soil, or air.

Population

All the individuals of the same species living in a specific area.

Community

All the different populations that live together in an area.

Homeostasis

The process by which an organism maintains a stable internal environment despite external changes.

Reference point

A fixed place used to describe position and motion, e.g., your house, the starting line, or the ground.

Distance

The total path length an object travels, always positive and without direction.

Displacement

The straight-line change in position from start to finish, including direction (a vector).

Speed

How fast distance changes; distance traveled per unit time, without direction.

Average speed

Total distance divided by total time for a trip.

Velocity

Speed with direction; how fast displacement changes (a vector).

Force

A push or pull that can change an object's motion. Measured in newtons (N).

Balanced forces

Forces that cancel out so the net force is 0 N. The object's motion does not change.

Unbalanced forces

Forces that do not cancel. Net force is not 0 N, so the object's motion changes (it accelerates).

Newton's First Law (Inertia)

An object keeps its state of motion (rest or constant straight-line motion) unless a net external force acts on it.

Newton's Second Law

The acceleration of an object depends on the net force and its mass. Conceptually: F = m × a.

Newton's Third Law

For every action force, there is an equal and opposite reaction force acting on a different object.

Energy

The ability to cause change or do work. It appears in many forms (kinetic, potential, thermal, chemical, etc.) but is conserved in total.

Law of conservation of energy

Energy cannot be created or destroyed; it can only be transferred or transformed from one form to another. Total energy stays constant.

Kinetic energy

Energy of motion. Moving objects (like cars or rolling balls) have kinetic energy; faster or more massive objects have more.

Gravitational potential energy

Energy stored due to an object's height in a gravitational field. Higher positions have more gravitational potential energy.

Work (physics)

Energy transferred when a force causes an object to move in the direction of the force. In simple cases, work = force × distance and is measured in joules (J).

Power

The rate of doing work or transferring energy. Power = work ÷ time and is measured in watts (W), where 1 W = 1 J/s.

Wave

A repeating disturbance that carries energy from one place to another without transporting matter the whole distance.

Amplitude

The size of a wave; for transverse waves, the height from rest to crest. Larger amplitude means more energy.

Wavelength (λ)

The distance between two matching points on a wave, such as crest to crest or compression to compression.

Frequency (f)

The number of wave cycles that pass a point each second, measured in hertz (Hz).

Mechanical wave

A wave that requires a medium (solid, liquid, or gas) to travel, such as sound or water waves.

Electromagnetic wave

A wave of vibrating electric and magnetic fields that can travel through a vacuum, such as light or radio waves.

Electric charge

A basic property of matter that causes electric forces; can be positive or negative. Moving charge creates electric current.

Electric field

The invisible region around a charged object where other charges feel a force. Explains attraction and repulsion at a distance.

Electric current (I)

The rate of flow of electric charge, measured in amperes (A). In metals, it is mainly moving electrons.

Voltage (V)

Electric potential difference; the "push" that drives current through a circuit, measured in volts (V).

Resistance (R)

How much a material or component opposes current, measured in ohms (Ω). Higher resistance means less current for the same voltage.

Ohm's law

The relationship `V = I × R`, linking voltage (V), current (I), and resistance (R) in many simple circuits.

Conservation of energy

A law stating that energy cannot be created or destroyed, only transferred from one object to another or transformed from one form to another in a closed system.

Conservation of mass

In ordinary chemical and biological processes, the total mass of a closed system remains constant; atoms are rearranged but not created or destroyed.

System

The part of the universe you are focusing on in an experiment or problem. Everything outside it is the surroundings.

Independent variable

The variable that is deliberately changed in an experiment to see its effect on the dependent variable.

Dependent variable

The variable that is measured in an experiment; it changes in response to the independent variable.

Controlled variable

A variable that is kept constant during an experiment to make the test fair and ensure valid results.