Science Glossary

The branch of chemistry concerned with acids and bases and how they react. In the Brønsted–Lowry model, an acid donates a proton (H⁺) and a base accepts one. For example, hydrochloric acid donates protons in water, making the solution acidic.

The minimum amount of energy that colliding particles must have for a chemical reaction to occur. A higher activation energy means a slower reaction, and catalysts work by providing a pathway with lower activation energy.

A feature or behaviour that improves an organism's chance of surviving and reproducing in its environment. Adaptations develop over many generations through natural selection, such as a polar bear's thick fur or a cactus's water-storing stem.

The planning and carrying out of complex experimental procedures that involve multiple steps, controls, and careful management of variables. Advanced design allows scientists to investigate more challenging questions reliably.

The characteristics of air, the mixture of gases that surrounds the Earth. Air has mass, takes up space, can be compressed, and exerts pressure; it is mainly nitrogen and oxygen and is organised into atmospheric layers.

The application of the forces of flight and the principles of aerodynamics to building aircraft. Designers balance lift, weight, thrust, and drag, shaping wings and bodies so that an aircraft can take off, fly, and land safely.

Organic compounds that contain a hydroxyl group (–OH) bonded to a carbon atom. The –OH group makes alcohols more soluble in water and reactive; ethanol, found in alcoholic drinks and fuels, is a common example.

Saturated hydrocarbons that contain only single carbon–carbon bonds, with the general formula CₙH₂ₙ₊₂. They are relatively unreactive and include common fuels such as methane, propane, and butane.

Hydrocarbons that contain at least one carbon–carbon double bond, with the general formula CₙH₂ₙ. The double bond makes alkenes more reactive than alkanes and allows addition reactions, including the formation of polymers.

Physical or behavioural features that help an animal survive and reproduce in its environment. Physical adaptations include camouflage, thick fur, or sharp claws, while behavioural adaptations include migration and hibernation.

The grouping of animals based on shared traits such as body structure, how they reproduce, and whether they have a backbone. Major groups include mammals, birds, reptiles, amphibians, fish, and invertebrates. Classification helps scientists study relationships among species.

The observable parts and characteristics of an animal, such as legs, wings, fur, scales, beaks, or claws. These features are clues to how an animal moves, what it eats, and the environment it lives in. Comparing them helps us classify animals into groups.

Major categories of animals based on shared characteristics. Vertebrates—mammals, birds, reptiles, amphibians, and fish—have backbones, while invertebrates such as insects and worms do not. Each group shares features in body structure and life processes.

The stages an animal passes through from birth or hatching to adulthood and reproduction. The stages differ among species—some animals undergo metamorphosis while others simply grow larger—but all cycles allow the species to continue.

The historical scientific models that describe the structure of the atom and how they developed as evidence accumulated. From Dalton's solid sphere to Thomson's, Rutherford's, and Bohr's models, each refined our picture of how protons, neutrons, and electrons are arranged.

The internal makeup of an atom, consisting of a tiny central nucleus of positively charged protons and neutral neutrons, surrounded by negatively charged electrons. The number of protons defines the element, while the arrangement of electrons determines how it bonds and reacts.

Forces acting on an object that are equal in size and opposite in direction, so they cancel out. When forces are balanced, the net force is zero and the object stays still or keeps moving at a steady speed.

Adjusting the coefficients in a chemical equation so that the same number of atoms of each element appears on both the reactant and product sides. Balancing reflects the law of conservation of mass, since atoms are neither created nor destroyed in a reaction.

The use of standard units and instruments to determine quantities such as length, mass, volume, and temperature. Accurate, repeatable measurement lets scientists compare results and communicate findings clearly.

The fundamental ideas or rules that underlie a topic and on which more detailed understanding is built. Identifying the basic principles helps make sense of how a system or field of study works.

The essential things a living organism needs to survive, such as food (or sunlight for plants), water, air, and a suitable habitat with space and shelter. If any requirement is not met, the organism cannot survive.

Simple implements used to perform tasks, make measurements, or observe the world, such as rulers, magnifiers, and hand tools. Choosing and using the right tool safely is a fundamental science and design skill.

Actions or patterns of behaviour that help an organism survive and reproduce in its environment. Examples include birds migrating to warmer regions, animals hibernating through winter, and hunting in groups.

A ring-shaped hydrocarbon with the formula C₆H₆ that is the simplest aromatic compound. Its carbon atoms share delocalised electrons in a stable ring, giving benzene distinctive chemistry and making it a building block of many compounds.

The variety of living things in an area, including the range of different species, the genetic differences within them, and the variety of ecosystems. High biodiversity makes ecosystems more stable and resilient.

The blood and the network of vessels that carry it around the body. Arteries carry blood away from the heart, veins return it, and tiny capillaries allow the exchange of oxygen, nutrients, and wastes with the body's cells.

A solution that resists changes in pH when small amounts of acid or base are added. Buffers usually contain a weak acid and its conjugate base, and they are important in keeping the pH of blood and other systems stable.

A substance that speeds up a chemical reaction without being used up itself, by lowering the activation energy. Because it is not consumed, a small amount of catalyst can be used repeatedly, as enzymes do in living cells.

Natural objects found in space, such as stars, planets, moons, asteroids, and comets. Studying celestial bodies and their movements helps us understand the structure and history of the universe.

The internal structures of a cell, each with a specific role. The nucleus controls the cell's activities, the cytoplasm holds the contents, and the cell membrane controls what enters and leaves; plant cells also have a wall and chloroplasts.

The tasks that cells carry out to stay alive, such as taking in nutrients, releasing energy through respiration, removing wastes, growing, and reproducing. Specialised cells also perform particular jobs for the whole organism.

The different kinds of cells, such as plant and animal cells, or the specialised cells of the body like nerve, muscle, and blood cells. Cells differ in shape and structure according to the functions they perform.

The levels of organisation in living things, from cells to tissues, organs, and organ systems. Similar cells form tissues, tissues form organs, and organs work together as systems, allowing complex organisms to function.

Conditions that arise from changes in the normal functioning of cells. Cancer, for example, results from cells dividing uncontrollably due to mutations. Studying disease at the cellular level helps explain how illnesses develop and how they might be treated.

Symbolic representations of chemical reactions using formulas for reactants and products. Equations are balanced so that the same number of atoms of each element appears on both sides, reflecting the conservation of mass.

A process in which substances called reactants are transformed into new substances called products by the breaking and forming of chemical bonds. Reactions are often accompanied by signs such as colour change, gas production, or a change in temperature.

A property of a molecule that is not superimposable on its mirror image, much like left and right hands. Chiral molecules exist as two mirror-image forms, which can behave very differently in biological systems.

The parts that make up an electric circuit, such as a cell or battery (energy source), wires (conductors), switches (to control flow), and devices like bulbs or motors that use the electrical energy.

The main ways components are connected in a circuit. In a series circuit there is a single path for the current, while in a parallel circuit there are multiple paths, which affects how current and voltage are shared.

Long-term shifts in temperature and weather patterns across the globe. Recent rapid change is driven largely by human activities such as burning fossil fuels, which release greenhouse gases that trap heat in the atmosphere.

Regions of the Earth that share similar long-term weather patterns, such as tropical, temperate, and polar zones. Climate zones are shaped mainly by latitude, which affects how much solar energy an area receives.

The fraction of the sky covered by clouds at a given time, used to describe and predict weather. Meteorologists estimate cloud cover because it affects temperature, the chance of precipitation, and how much sunlight reaches the ground.

In ecology, all the populations of different species that live and interact in the same area. The species in a community depend on one another through relationships such as feeding, competition, and cooperation.

The shared environment in which local populations of different plants and animals live together and interact. Within a community habitat, organisms compete for and share resources such as food, water, and space.

The study of similarities and differences among organisms using anatomical and genetic evidence. Comparing body structures, embryos, and DNA reveals how closely species are related and supports the idea that they share common ancestors.

Machines made by combining two or more simple machines to perform work. A bicycle, for example, combines wheels and axles, levers, and gears. Complex machines let people accomplish tasks that would be difficult with a single simple machine.

The protection and careful use of natural resources and the environment to prevent waste and loss. Conservation includes actions such as saving water and energy, protecting habitats, and recycling, helping ensure resources remain for the future.

The principle that energy cannot be created or destroyed, only transformed from one form to another, so the total energy of an isolated system stays constant. For example, a falling object converts gravitational potential energy into kinetic energy.

A chemical bond formed when two atoms share one or more pairs of electrons. Covalent bonding typically occurs between non-metal atoms and holds together molecules such as water and carbon dioxide.

The traditional ways in which a culture uses plants and animals, such as for food, medicine, clothing, tools, or ceremony. Studying cultural uses shows the close relationship between people and the living things in their environment.

The rate of flow of electric charge through a conductor, measured in amperes. Conventional current is treated as the flow of positive charge, and it is driven by a voltage across the circuit.

Regular events that repeat each day as a result of Earth's rotation, such as sunrise, sunset, and predictable changes in temperature and shadows. Recognising daily patterns helps learners connect observations to the movement of the Sun.

The process of examining collected data to find patterns, relationships, and meaning. Analysis may involve organising data into tables and graphs, calculating averages, and interpreting results to answer the original question.

The gathering of measurements and observations during an investigation. Careful, organised data collection ensures that the evidence is accurate and complete enough to support valid conclusions.

Organising observations and measurements clearly using tables, charts, and graphs. Recording data in an orderly way makes patterns easier to see and allows results to be checked and shared with others.

The cycle of light and darkness caused by the Earth rotating once on its axis about every 24 hours. The side of Earth facing the Sun experiences day, while the side facing away experiences night.

A step-by-step approach to solving problems by planning, building, testing, and improving a solution. The cycle is repeated, using the results of each test to refine the design until it meets the goal.

The spreading out of waves as they pass through a narrow opening or around the edge of an obstacle. Diffraction is greatest when the opening is similar in size to the wavelength, and it provides evidence that light behaves as a wave.

The breakdown of food into smaller molecules that the body can absorb and use. It begins in the mouth and continues in the stomach and intestines, where mechanical action and enzymes turn food into nutrients.

Using the evidence gathered in an investigation to make reasoned, supported statements that answer the original question. Sound conclusions are based on data rather than opinion and may suggest new questions to explore.

A state in a reversible reaction where the forward and reverse reactions occur at the same rate, so the concentrations of reactants and products stay constant. The reaction has not stopped; both directions continue at equal speed.

The two main motions of the Earth: its rotation on its axis, which causes day and night, and its revolution around the Sun once a year, which together with the axial tilt produces the seasons.

The layered interior of the Earth, made up of the thin outer crust, the thick mantle beneath it, and the dense core of mostly iron and nickel. These layers differ in composition, temperature, and state.

The living and non-living parts of an ecosystem that interact with one another. Living (biotic) parts include plants, animals, and microbes, while non-living (abiotic) parts include sunlight, water, soil, and temperature.

Communities of living organisms interacting with one another and with the non-living parts of their environment, such as water, soil, and air. Energy and nutrients flow through an ecosystem, linking all its parts together.

The proportion of input energy that a system converts into useful output, usually expressed as a percentage. No machine is perfectly efficient because some energy is always lost, most often as heat due to friction.

A region around a charged object in which another charge experiences a force. The field's strength and direction describe how a charge would be pushed or pulled, and field lines are used to picture it.

The practices that prevent injury and damage when working with electricity, such as avoiding water near outlets, not overloading circuits, and using insulation and fuses. These measures guard against electric shock and fire.

The arrangement of electrons in an atom's shells and subshells. Electrons fill the lowest available energy levels first, and the configuration of the outermost electrons largely determines an element's chemical properties and its place in the periodic table.

A measure of how strongly an atom attracts the shared pair of electrons in a chemical bond. Electronegativity increases across a period and decreases down a group, and differences in electronegativity between atoms determine whether a bond is ionic, polar, or non-polar.

The absorption or release of energy during a chemical reaction. Exothermic reactions release energy, usually as heat, raising the temperature of the surroundings, while endothermic reactions absorb energy and feel cold.

Using less energy to perform the same task, so that less is wasted. Improving efficiency—such as using LED bulbs or better insulation—reduces energy loss, usually as heat, and lowers costs and environmental impact.

The energy that is not transferred usefully in a process and is usually given off as heat. At each step of a food chain or in any machine, some energy is lost, which is why no process is perfectly efficient.

Sources of energy used by people, grouped as renewable or non-renewable. Renewable sources such as solar, wind, and hydro are naturally replenished, while non-renewable sources such as coal, oil, and gas are limited and release pollution when burned.

The movement of energy from one object, organism, or place to another. Energy can be transferred by heat, light, sound, electricity, or movement, and along a food chain it passes from producers to consumers.

Alterations in the environment caused by natural events such as floods and fires or by human activity such as pollution and clearing land. These changes can affect the living things that depend on the environment.

Interconnected natural systems that cycle matter and energy through the environment, such as the water cycle, carbon cycle, and nutrient cycles. A change in one part of a system can affect the others.

Common technological solutions and devices used in daily life, such as tools, appliances, and machines. Studying everyday technology shows how scientific ideas are applied to meet human needs and solve practical problems.

Observations that show how species and the Earth have changed over time, such as fossils, rock layers, and similarities in anatomy and DNA. This evidence supports scientific explanations like evolution.

Devices used to study space, such as telescopes that gather light from distant objects, satellites that orbit Earth, and space probes that travel to other planets. These tools extend human observation far beyond what the eye can see.

The outside characteristics of an organism that can be observed without dissection, such as shape, size, colour, and body coverings. These features help organisms survive and are often used to identify and classify living things.

Everyday substances such as wood, metal, plastic, glass, and fabric, each recognised by its properties. Knowing the properties of familiar materials helps explain why each is chosen for particular objects, such as glass for windows because it is transparent.

Interconnected food chains that show how energy and nutrients flow among the organisms in an ecosystem. Because most animals eat more than one kind of food, food webs give a more complete picture than a single food chain.

The study of forces as vector quantities, taking into account both their size and direction. By adding forces together, scientists find the net force on an object, which determines whether and how the object accelerates.

The real-world uses and effects of forces acting on objects. Understanding forces explains everyday situations such as why seatbelts protect passengers, how bridges bear loads, and why friction lets us walk without slipping.

The process of quantifying forces, typically measured in newtons (N) using a device such as a spring scale. Measuring force lets scientists compare pushes and pulls and analyse how forces affect the motion of objects.

The size or magnitude of a force, which together with its direction determines how much it changes an object's motion. A greater force produces a greater change in speed or direction for a given mass.

Categories of forces, including contact forces such as friction and applied pushes, and field forces that act at a distance such as gravity, magnetism, and electric force. Identifying the forces acting on an object is the first step in analysing its motion.

The four forces that act on an aircraft: lift, which holds it up; weight, which pulls it down; thrust, which moves it forward; and drag, which resists its motion. Flight is controlled by balancing these forces.

The natural processes by which landforms, rocks, and other features are created over time, such as volcanic activity, deposition of sediment, and erosion. Understanding them explains how Earth's surface took its present shape.

The collection of fossils preserved in rock layers that provides physical evidence of life in the past. By studying the fossil record, scientists can trace how organisms have changed over millions of years and learn about species that are now extinct.

A force that opposes the relative motion, or attempted motion, between two surfaces in contact. Static friction prevents motion from starting, while kinetic friction acts on surfaces that are already sliding, converting energy into heat.

Vast systems of stars, gas, and dust held together by gravity. Galaxies contain millions to billions of stars and come in shapes such as spiral, elliptical, and irregular; our Solar System lies within the Milky Way galaxy.

The movement of oxygen into the blood and carbon dioxide out of it, which in humans takes place in the lungs. Oxygen passes into the blood for the body's cells, while carbon dioxide waste is breathed out.

The differences in genes among individuals within a population. Variation arises from mutation and the mixing of genes during reproduction, and it provides the raw material that natural selection acts upon, allowing populations to adapt over time.

Natural processes that shape the Earth, such as earthquakes, volcanic eruptions, and erosion. Some events are sudden and dramatic, while others act slowly over long periods, reshaping the planet's surface.

The attractive force that acts between any two objects with mass. Newton's law of universal gravitation states that this force increases with the masses and decreases with the square of the distance between them, governing the motion of planets and satellites.

The attractive force that pulls objects with mass toward one another. On Earth, gravity pulls everything toward the ground, giving objects weight, and on a larger scale it keeps moons and planets in their orbits.

The results of gravity, the force that pulls objects with mass toward one another. Gravity keeps planets in orbit around the Sun, holds the Moon near Earth, and gives objects weight by pulling them toward the ground.

The process by which living things increase in size and develop over their lifetime. Plants and animals pass through predictable stages from young to mature forms. Studying growth and change helps us understand life cycles and how organisms develop.

The predictable ways in which living things grow and develop through stages. Some organisms change gradually, while others transform dramatically, as in metamorphosis. Recognising these patterns helps scientists compare how different species develop.

The parts of an environment that an organism needs to survive: food, water, shelter, and space. A habitat provides all of these in the right amounts for a particular species. If one component is missing or limited, organisms may not survive there.

Actions taken to preserve the natural environments that organisms depend on, such as creating parks and reserves and limiting harmful development. Protecting habitats helps prevent species from declining or becoming extinct.

Different kinds of natural environments that support particular communities of living things, such as forests, deserts, wetlands, grasslands, and oceans. Each habitat has its own climate, soil, and resources, which determine the plants and animals that can live there.

The role of the heart as a muscular pump that circulates blood throughout the body. By contracting rhythmically, it sends oxygen-rich blood to the tissues and returns oxygen-poor blood to the lungs.

A form of energy that is transferred between objects because of a difference in temperature, always flowing from warmer to cooler. Adding heat energy can raise temperature or cause a change of state, such as melting ice.

Things that produce heat, such as the Sun, fire, electrical appliances, and friction. Identifying heat sources helps explain how objects and environments are warmed and how thermal energy moves.

The movement of thermal energy from a warmer object or region to a cooler one. It occurs in three ways: conduction through direct contact, convection through moving fluids, and radiation through electromagnetic waves.

The effects of human activity on the environment and living things, both positive and negative. Activities such as farming, building, and burning fuels can cause pollution and habitat loss, while conservation efforts can repair and protect ecosystems.

Using experiments and evidence to support or reject a hypothesis, a proposed explanation for an observation. A fair test is designed to see whether the predicted outcome actually occurs, helping decide if the idea is well supported.

The change in momentum produced when a force acts on an object over a period of time, equal to force multiplied by time. Increasing the time over which a force acts, as in a car's crumple zone, reduces the force needed for a given change in momentum.

Traditional ecological knowledge and practices developed by Indigenous peoples through long observation of the local environment. This knowledge includes sustainable ways of harvesting, managing land, and understanding seasonal cycles, and is increasingly valued alongside Western science.

Materials or methods that slow the transfer of heat, helping keep objects warm or cool. Insulators such as foam, wool, and air trap heat and reduce its flow, which is why they are used in clothing and buildings.

The attractive forces that act between molecules, rather than within them. These forces, which include hydrogen bonding and van der Waals forces, are weaker than chemical bonds but determine properties such as boiling point, melting point, and solubility.

An opening overview of a topic that provides background and introduces the key ideas to be studied. It sets the context for more detailed learning that follows.

The planning of a fair experiment, including identifying variables, choosing materials and steps, and deciding what to measure. A well-designed investigation changes only one variable at a time so results can be trusted.

A type of chemical bond formed when one atom transfers one or more electrons to another, creating positively and negatively charged ions that attract each other. Ionic bonds usually form between metals and non-metals, as in sodium chloride (table salt).

The existence of two or more compounds that share the same molecular formula but differ in the arrangement of their atoms. Isomers can have different structures or different spatial orientations, which often gives them different properties.

Atoms of the same element with the same number of protons but different numbers of neutrons, giving them different mass numbers. Isotopes share chemical properties; for example carbon-12 and carbon-14 are both carbon, but carbon-14 is radioactive and used in dating.

The branch of physics that describes motion—position, velocity, and acceleration—without considering the forces that cause it. Kinematic equations relate these quantities and allow the motion of objects to be predicted.

The principle that when a system at equilibrium is disturbed by a change in concentration, temperature, or pressure, it shifts to partly counteract the change and restore equilibrium. It allows chemists to predict how conditions affect a reaction's yield.

Diagrams that show how atoms are bonded in a molecule and where any lone pairs of electrons are located, using dots and lines to represent electrons. Lewis structures help predict the shape and reactivity of molecules.

A form of energy that travels as electromagnetic waves and allows us to see. Light can be reflected, absorbed, or refracted, and plants capture it during photosynthesis to make food.

Characteristics of light, including that it travels in straight lines, can be blocked by objects to form shadows, and can be reflected off surfaces or bent when passing through materials. These properties explain how we see and use light.

Electromagnetic waves, including visible light, that carry energy and can travel through a vacuum. Light waves can be reflected, refracted, and absorbed, and the visible spectrum is only a small part of the full electromagnetic spectrum.

The reactant that is completely used up first in a chemical reaction, which therefore limits the amount of product that can form. Once the limiting reagent runs out the reaction stops, leaving any other reactants in excess.

The distinction between things that are alive and things that are not. Living things grow, use energy, reproduce, and respond to their surroundings, while non-living things such as rocks or water do not. Recognising this difference is one of the first steps in studying biology.

The natural surroundings of a particular area, including its living things (plants, animals) and non-living parts (soil, water, air, climate). Studying the local environment helps learners understand the relationships between organisms and their surroundings.

Understanding of the local environment built up from community experience and careful observation over time. Local knowledge can reveal patterns in weather, wildlife, and plants that complement formal scientific study.

The different categories of machines, from simple machines such as levers and pulleys to complex machines that combine several simple machines. Each type changes the size or direction of a force to make work easier.

The push or pull exerted by magnets. Magnets attract certain metals such as iron, and their poles attract or repel the poles of other magnets. Magnetic force acts at a distance, without the objects needing to touch.

The characteristics of a material that determine how it can be used, such as hardness, colour, texture, flexibility, and whether it floats or conducts heat. Comparing properties helps us choose the right material for a purpose, like using rubber for its flexibility.

How the properties of a material determine the purposes it is suited for. A material's hardness, flexibility, or ability to conduct heat or electricity makes it useful for specific jobs—metal for cooking pots because it conducts heat well, for example.

The study of the properties of materials and how those properties make them suitable for different uses. It combines ideas from physics and chemistry to develop and improve materials such as metals, plastics, and ceramics.

The selection and application of materials based on their properties. Engineers and designers match a material's characteristics, such as strength or waterproofing, to the demands of a task in order to build effective and safe products.

The process of determining the size of a quantity using standard units and instruments, such as measuring length with a ruler or mass with a balance. Accurate measurement allows results to be compared and repeated.

The factor by which a machine multiplies an input force, found by comparing the output force to the effort applied. A machine with a high mechanical advantage lets a small force move a large load, though usually over a greater distance.

Waves that transfer energy through the vibration of a medium such as air, water, or a solid. Sound and water waves are examples; because they need particles to vibrate, mechanical waves cannot travel through a vacuum.

Life cycles in which an animal changes its body form dramatically as it develops. In complete metamorphosis (as in butterflies) the stages are egg, larva, pupa, and adult, while incomplete metamorphosis (as in grasshoppers) skips the pupa stage.

The physical and chemical characteristics used to identify minerals, such as hardness, colour, lustre, streak, and crystal shape. Because each mineral has a consistent set of properties, geologists use them to tell minerals apart.

Naturally occurring minerals that are extracted from the Earth and used by people, such as metal ores, salt, and gemstones. They are non-renewable on human timescales, so their use raises questions about conservation and sustainability.

Combinations of two or more substances that are physically blended but not chemically joined, so each keeps its own properties. Mixtures can be homogeneous, looking the same throughout (like salt water), or heterogeneous, with visibly different parts (like a salad).

The SI unit for the amount of a substance, defined as the number of particles equal to about 6.022 × 10²³ (Avogadro's number). The mole allows chemists to count atoms and molecules by weighing, linking the mass of a substance to the number of particles it contains.

The three-dimensional arrangement of the atoms in a molecule, determined largely by the repulsion between electron pairs around the central atom. Geometry affects a molecule's polarity and how it interacts with other molecules.

The product of an object's mass and velocity, a vector quantity that describes its quantity of motion. A heavy or fast-moving object has large momentum and requires a large force to stop.

The changing appearance of the Moon over about a month as different portions of its sunlit half face the Earth. The cycle runs from new moon to full moon and back, caused by the Moon's orbit around the Earth.

The different ways objects can move, such as in a straight line, along a curve, back and forth, or by spinning. Describing types of movement is a first step toward understanding motion and the forces that cause it.

Materials and energy from nature that people use, such as water, air, soil, minerals, forests, and fossil fuels. Some are renewable while others are limited, so their use raises questions of conservation.

The process by which organisms with traits better suited to their environment tend to survive and reproduce more successfully, passing those traits to offspring. Over many generations, this gradually changes the characteristics of a population—the basis of evolution.

The principle that an object stays at rest or moves at a constant velocity unless acted on by an unbalanced (net) force. Also called the law of inertia, it explains why objects resist changes to their state of motion.

The principle that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass, written as F = ma. It explains how the size of a force determines how quickly an object speeds up.

The principle that for every action force there is an equal and opposite reaction force. When one object pushes on a second, the second pushes back with equal strength in the opposite direction, as when a rocket expels gas and is pushed forward.

Life cycles in which the young develop directly into adults without a major change in body form. Animals such as mammals and birds grow larger and mature but keep the same basic body plan from birth, unlike insects that undergo metamorphosis.

The uptake of digested nutrients into the bloodstream, which in humans occurs mainly in the small intestine. Its lining is folded and covered in tiny projections that increase the surface area for absorbing nutrients efficiently.

The ability to use the senses and appropriate tools carefully to notice and record details about objects and events. Good observation is the foundation of science, providing the evidence used to ask questions and test ideas.

The law stating that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance, written as V = IR. It is a fundamental relationship for analysing electric circuits.

The regular paths that objects in space follow as they move around larger bodies under the pull of gravity. Planets orbit the Sun and moons orbit planets, generally along elliptical paths.

Groups of organs that work together to carry out a major body function, such as the digestive system or circulatory system. The body's systems cooperate to keep the whole organism alive and healthy.

The branch of chemistry that studies carbon-containing compounds, their structures, properties, and reactions. Carbon's ability to form four bonds and long chains gives rise to millions of compounds, including those that make up living things.

A value assigned to an atom that shows how many electrons it has apparently gained or lost in a compound. Oxidation numbers help track electron transfer in redox reactions and are used to balance redox equations.

The relationship in which living things produce young that resemble their parents. Offspring inherit characteristics from their parents and often depend on them for food and protection early in life. This passing on of traits is the basis of heredity.

A chart that arranges all the chemical elements in order of increasing atomic number into rows (periods) and columns (groups). Elements in the same group have similar properties because they have the same number of outer electrons, which makes the table a powerful tool for predicting chemical behaviour.

Patterns in the properties of elements that appear across periods and down groups of the periodic table, such as atomic radius, ionization energy, and electronegativity. These trends arise from the arrangement of electrons and help predict how elements behave.

Logarithmic scales used to express how acidic or basic a solution is. pH measures the concentration of hydrogen ions and pOH the concentration of hydroxide ions; a low pH is acidic, a high pH is basic, and the two values always add up to 14 in water at 25°C.

Changes in a substance's form or appearance that do not produce a new substance, such as melting, freezing, cutting, or dissolving. The material's identity stays the same, and many physical changes can be reversed.

Characteristics of a substance that can be observed or measured without changing what it is, such as mass, colour, density, and state of matter. Physical properties are used to identify and compare substances and do not involve forming a new substance.

The movement of planets as they orbit the Sun and rotate on their axes. Orbits are shaped by gravity, and a planet's rotation produces day and night while its revolution around the Sun produces its year.

Structural features that help a plant survive in its particular environment. Examples include waxy leaves that reduce water loss in deserts, deep roots that reach underground water, and broad leaves that capture light in shady forests.

The grouping of plants according to shared characteristics, such as whether they produce flowers, seeds, or cones. Scientists use features like leaf shape, reproduction method, and structure to sort plants into categories such as flowering plants, conifers, ferns, and mosses.

The observable parts of a plant, such as roots, stems, leaves, flowers, and seeds. Each part has a job: roots absorb water, stems provide support and transport, leaves capture sunlight, and flowers and seeds enable reproduction.

Major categories of plants based on shared features. Common groups include flowering plants, which reproduce using flowers and seeds, conifers, which bear cones, and non-seed plants such as ferns and mosses. Grouping plants makes their diversity easier to study.

The stages a plant passes through during its life, typically from seed to germination, growth, flowering, pollination, and seed production. The cycle then repeats as new seeds are dispersed and grow into new plants.

The main structures of a plant and their functions. Roots anchor the plant and take in water and minerals, the stem carries water and holds the plant up, leaves make food using sunlight, and flowers produce seeds for reproduction.

The ways plants react to their surroundings. Plants grow toward light, their roots grow downward in response to gravity, and some plants respond to touch or the changing seasons. These responses help plants survive even though they cannot move from place to place.

The two main groups of living things, distinguished by how they obtain food. Plants make their own food from sunlight through photosynthesis, while animals must eat plants or other animals for energy. They also differ in movement, growth, and structure.

The theory that the Earth's outer shell is divided into large plates that slowly move over the mantle. The interactions of these plates at their boundaries cause earthquakes, volcanoes, and the formation of mountains.

The study of how the size and structure of a population change over time. Populations grow or shrink depending on births, deaths, and migration, and are limited by factors such as food, space, and predators.

The study of groups of organisms of the same species living in an area, including their size, growth, density, and how they change over time. Such studies help explain how populations respond to resources and environmental pressures.

Water that falls from the atmosphere to the ground as rain, snow, sleet, or hail. Precipitation forms when water vapour in clouds condenses into droplets or ice crystals heavy enough to fall, and it is a key stage of the water cycle.

The process of finding solutions to challenges using reasoning, evidence, and testing. In science and design it involves identifying the problem, exploring possible solutions, trying them out, and evaluating the results.

The curved path followed by an object that is launched into the air and then moves under the influence of gravity alone. Its motion can be analysed as a combination of constant horizontal velocity and vertical acceleration due to gravity.

A liquid has a fixed volume but takes the shape of its container, because its particles are close together yet able to slide past one another. This is why liquids flow and can be poured but cannot be easily compressed.

A solid has a fixed shape and a fixed volume because its particles are packed tightly together in fixed positions and can only vibrate. This explains why solids keep their shape and do not flow, unlike liquids and gases.

Forces that change the motion of objects by moving them away (a push) or toward you (a pull). Pushes and pulls can start or stop motion, change its direction, or change its speed, and they vary in strength and direction.

The skill of developing clear, focused, and testable questions that can guide a scientific investigation. A good question is specific enough to be answered through observation or experiment and forms the starting point of inquiry.

A measure of how quickly reactants are converted into products, often expressed as the change in concentration over time. The rate is influenced by temperature, concentration, surface area, and catalysts.

Basic types of chemical reactions, such as combination (substances join), decomposition (a substance breaks apart), and combustion (a substance burns in oxygen). Classifying reactions helps predict the products that will form.

How quickly a chemical reaction proceeds, measured by how fast reactants are used up or products are formed. The rate is affected by factors such as temperature, concentration, surface area, and the presence of a catalyst.

Processes in which substances interact to form new substances with different properties. Signs that a chemical reaction has occurred include colour change, gas bubbles, a temperature change, or the formation of a solid (precipitate).

Reactions involving the transfer of electrons between substances, in which one species is oxidised (loses electrons) and another is reduced (gains electrons). Redox reactions power batteries, cause corrosion, and drive respiration.

The bouncing back of light when it strikes a surface. For a smooth surface, the angle of reflection equals the angle of incidence, which is why mirrors form clear images.

The bending of light as it passes from one transparent medium into another of different density, caused by a change in the light's speed. Refraction explains how lenses focus light and why objects in water appear displaced.

The systematic techniques scientists use to collect and analyse information, chosen to suit the question being investigated. Methods range from controlled experiments to careful observation, such as astronomical observation of distant objects.

The systematic steps used to gather, organise, and interpret information in order to answer a question. It typically includes asking a question, collecting and recording data, analysing results, and drawing evidence-based conclusions.

A measure of how strongly a material opposes the flow of electric current, measured in ohms. Higher resistance reduces current for a given voltage, and resistance often converts electrical energy into heat.

Two or more Lewis structures that together represent the bonding in a molecule whose electrons are actually delocalised. The real molecule is a hybrid of these structures, which explains its stability, as in benzene.

The responsible and planned use of natural resources so they last and the environment is protected. It involves balancing human needs with conservation, for example by limiting harvesting, recycling materials, and restoring damaged areas.

The ways people extract and consume natural resources to meet their needs. How resources are used affects their availability for the future and can impact the environment, which is why sustainable use is important.

Physical changes that can be undone to return a material to its original state, such as melting ice back from water or dissolving and then evaporating salt. They contrast with chemical changes, which usually cannot be reversed.

The results of a planet revolving, or orbiting, around the Sun. Combined with the tilt of its axis, a planet's revolution produces the yearly cycle of seasons and changing lengths of day.

The continuous process by which rocks are formed, broken down, and reformed over long periods of time. Through melting, cooling, weathering, and pressure, one type of rock can gradually become another, recycling Earth's materials.

The three main categories of rock classified by how they form: igneous rock from cooled molten material, sedimentary rock from compacted sediments, and metamorphic rock changed by heat and pressure. Each type gives clues about Earth's history.

Naturally occurring solid materials of the Earth. Minerals are pure substances with a definite composition and structure, while rocks are made of one or more minerals combined together.

The results of a planet spinning, or rotating, on its axis. The Earth's rotation causes the cycle of day and night and the apparent movement of the Sun and stars across the sky.

The practices and rules followed to prevent accidents and injury during scientific work, such as wearing protective equipment, handling materials carefully, and following instructions. Safety procedures protect both the investigator and others.

Two ways of describing physical quantities. A scalar has only magnitude, such as mass or temperature, while a vector has both magnitude and direction, such as velocity or force. Distinguishing them is essential for analysing motion correctly.

Mathematical or conceptual representations used to explain and predict natural phenomena. Models simplify complex systems so they can be studied and tested, such as a diagram of the water cycle or an equation describing motion.

A well-supported explanation of some aspect of the natural world, based on a large body of evidence and repeatedly confirmed through observation and experiment. Unlike everyday use of the word, a scientific theory is reliable, though it can be refined as new evidence emerges.

Instruments used to observe and measure the natural world, such as rulers, thermometers, microscopes, and balances. Each tool extends our senses or improves accuracy, allowing more detailed and reliable observations.

The regular changes in weather, daylight hours, temperature, and the behaviour of living things that occur as the seasons cycle through the year. These changes are caused by the tilt of the Earth as it orbits the Sun.

The links between seasonal changes and the behaviour of living things and the environment, such as animal migration, plant flowering, and changing daylight. Recognising these connections helps explain how organisms respond to the cycle of the seasons.

The four periods of the year—spring, summer, autumn, and winter—caused by the tilt of the Earth's axis as it orbits the Sun. The tilt changes how directly sunlight strikes each hemisphere, producing yearly cycles of temperature and daylight.

Techniques used to separate the components of a mixture based on differences in their properties. Filtration separates solids from liquids, evaporation recovers a dissolved solid, and distillation separates liquids with different boiling points.

A repetitive back-and-forth motion in which the restoring force is proportional to the displacement from the rest position and always directed toward it. A swinging pendulum and a mass on a spring are classic examples.

Basic devices that make work easier by changing the size or direction of a force, including the lever, pulley, wheel and axle, inclined plane, wedge, and screw. They do not reduce the total work but allow a task to be done with less effort.

A law that describes how light bends, or refracts, when it passes from one medium into another. It relates the angles of incidence and refraction to the refractive indices of the two media, explaining effects such as a straw appearing bent in water.

The mixture of materials that make up soil, including weathered minerals, organic matter (humus), water, and air. The proportions of these materials affect how fertile a soil is and what can grow in it.

Characteristics of a solution, such as concentration (how much solute is dissolved) and solubility (how much can dissolve). These properties describe the mixture of a solute dissolved evenly in a solvent, like salt dissolved in water.

Grouping materials according to shared properties such as texture, hardness, colour, or whether they float or sink. Sorting is an early science skill that helps learners observe carefully and recognise that materials can belong to more than one group.

A form of energy carried by vibrations that travel as waves through a medium such as air, water, or solids. Sound energy is produced when objects vibrate and is detected by our ears as sound.

Characteristics of sound, which is produced by vibrations and travels as waves through a medium such as air, water, or solids. Sounds vary in loudness (volume) and pitch, and they cannot travel through a vacuum.

Longitudinal mechanical waves produced by a vibrating source that travel through a medium as compressions and rarefactions. Their frequency determines pitch and their amplitude determines loudness.

The scientific study and exploration of objects and phenomena beyond Earth. It uses tools such as telescopes, satellites, and probes to investigate planets, stars, and galaxies, and to test ideas about the origin and structure of the universe.

Tools and devices used to explore and study space, such as satellites that orbit Earth, telescopes that gather distant light, and probes that travel to other worlds. This technology extends human observation far beyond Earth.

The variety and number of different species within a community or ecosystem. Greater species diversity generally makes an ecosystem more stable and better able to recover from disturbances.

The physical forms in which matter exists—solid, liquid, and gas—determined by how its particles are arranged and how much energy they have. Solids hold their shape, liquids flow and take their container's shape, and gases spread to fill any space.

The use of statistics to interpret data, identify patterns, and judge whether results are meaningful rather than due to chance. Scientists rely on statistical analysis to draw reliable conclusions and to decide how much confidence to place in their findings.

The life cycle of a star, from its formation in a cloud of gas and dust to its eventual death. A star's path depends on its mass, ending as a white dwarf, neutron star, or black hole, and the process forms many chemical elements.

The responsible care and protection of the environment and its resources. Stewardship involves making choices—both individual and collective—that conserve nature and keep it healthy for future generations.

The branch of chemistry that uses balanced equations to calculate the relative amounts of reactants and products in a reaction. Stoichiometry lets chemists predict how much product will form or how much reactant is needed.

Physical features of an organism's body that improve its chances of survival, such as a camel's hump, a bird's beak shape, or a cactus's spines. These features develop over generations through natural selection.

The particles that make up an atom: positively charged protons and neutral neutrons in the nucleus, and negatively charged electrons surrounding it. Their numbers determine an element's atomic number, mass, and chemical properties.

The apparent path of the Sun across the sky from east to west during the day. This movement is caused by the Earth rotating on its axis, not by the Sun itself moving, and it produces shadows that change through the day.

The physical characteristics of the surface of a planet or moon, such as craters, mountains, valleys, and plains. Studying surface features gives clues about a world's history and the processes that shaped it.

Techniques that use resources in ways that meet present needs without harming the ability of future generations to meet theirs. Examples include renewable energy, recycling, and responsible harvesting.

Ways of living and using resources that protect the environment over the long term. They reduce waste and pollution and conserve resources so that ecosystems and communities can thrive into the future.

Common health problems that affect the normal functioning of body systems, such as the respiratory, circulatory, or digestive systems. Understanding these disorders shows how the parts of a system depend on one another to keep the body healthy.

The way separate systems connect and work together to form a larger functioning whole. In the body, for example, the digestive, circulatory, and respiratory systems cooperate to keep cells supplied with energy and oxygen.

The ways different systems affect one another and work together. In the body, organ systems interact to keep cells supplied; in the environment, natural systems exchange matter and energy.

An approach that examines how the parts of a system are connected and influence one another, rather than studying them in isolation. It helps explain how a change in one part can affect the whole system.

The systems scientists use to classify and name living things based on shared characteristics. Organisms are grouped into ranks such as kingdom, phylum, class, and species, which shows how they are related.

A measure of how hot or cold something is, related to the average energy of the particles in a substance. Temperature is measured with a thermometer in units such as degrees Celsius, and differences in temperature cause heat to flow.

The ways changes in temperature affect materials and processes, such as causing substances to expand, contract, or change state. For example, heating usually makes materials expand, while cooling makes them contract.

Characteristics that describe how a material responds to heat, such as how well it conducts thermal energy and how much heat it can store. These properties determine whether a material is useful as a conductor or an insulator.

Groups of similar specialised cells that work together to perform a particular function. In animals, the main types include muscle, nervous, epithelial, and connective tissue, which combine to form organs.

A laboratory technique for finding an unknown concentration by reacting a solution with a measured volume of another solution of known concentration. An indicator or pH meter signals the endpoint, when the reactants have combined in exact proportions.

The instruments and substances chosen to carry out an investigation or build a design. Selecting suitable tools and materials, and using them safely, is essential to gathering reliable evidence and creating effective solutions.

A turning effect produced by a force applied at a distance from a pivot, equal to the force multiplied by that distance. Torque causes rotation, which is why a longer wrench makes it easier to turn a stiff bolt.

The feeding positions in a food chain, such as producers, primary consumers, secondary consumers, and decomposers. Energy passes from one trophic level to the next, but much is lost as heat at each step.

The distinction between physical changes, which alter a substance's form without making a new substance, and chemical changes, which produce new substances. Melting ice is physical, while burning wood is chemical and cannot be easily reversed.

The different forms energy can take, such as mechanical (motion and position), thermal, electrical, chemical, light, and sound energy. Energy can be transformed from one form to another but is never created or destroyed.

The various natural features of the Earth's surface, such as mountains, valleys, plateaus, plains, and coastlines. Landforms are created and changed by processes like tectonic activity, erosion, and deposition.

Categories of movement including linear (in a straight line), circular (around a centre), reciprocating (back and forth), and rotational (spinning). Recognising the type of motion helps describe and predict how an object will move.

Forces acting on an object that do not cancel out, producing a net force. Unbalanced forces cause an object to change its motion—starting, stopping, speeding up, slowing down, or changing direction.

The large-scale organisation of the universe, from planets and stars up to galaxies and clusters of galaxies separated by vast distances. Understanding this structure helps explain the scale and history of the cosmos.

Keeping all conditions in an experiment constant except the one being tested, so that any change in the result can be linked to that single variable. Controlling variables is what makes an experiment a fair test.

The difference in electric potential energy per unit charge between two points in a circuit, measured in volts. Voltage acts like the 'push' that drives electric current through a conductor.

Practices that reduce water use and protect water supplies, such as fixing leaks, using water-efficient appliances, and avoiding waste. Conserving water helps ensure there is enough clean water for people and ecosystems.

The continuous movement of water through the environment by evaporation, condensation, precipitation, and collection. Powered by the Sun and gravity, the water cycle recycles Earth's water between the oceans, atmosphere, and land.

The places from which water is obtained, such as rivers, lakes, groundwater, glaciers, and rainfall. Understanding water sources is important for supplying communities and for managing this limited resource wisely.

The ways waves behave when they meet a boundary or obstacle, including reflection (bouncing back), refraction (bending as they change speed), and diffraction (spreading around edges). These interactions explain effects such as echoes and rainbows.

The effects that weather conditions have on the environment and on human activity, such as how storms, droughts, or temperature changes affect ecosystems, farming, and daily life.

The use of instruments to record weather conditions, such as thermometers for temperature, rain gauges for precipitation, and anemometers for wind speed. Accurate measurements allow weather to be tracked, compared, and forecast.

Recurring conditions in the atmosphere over an area, including temperature, precipitation, wind, and cloud cover. Observing weather patterns over time allows forecasts and helps distinguish day-to-day weather from long-term climate.

The movement of air across the Earth's surface, caused by differences in air pressure as air moves from high-pressure to low-pressure areas. Wind varies in speed and direction and plays a major role in shaping weather and climate.

The relationship in which work is done when a force moves an object through a distance. Work is calculated as force multiplied by the distance moved in the direction of the force, and it transfers energy to the object.

Work is the energy transferred when a force moves an object through a distance, measured in joules, while power is the rate at which that work is done, measured in watts. A more powerful machine does the same work in less time.

The relationship between the work done and the time taken to do it, which defines power. Doing the same work in less time requires more power, so power measures how quickly energy is transferred or transformed.