PNG Grade 10 Science key terms

The smallest living unit of an organism, bounded by a membrane and containing cytoplasm and genetic material. Some organisms are single cells; others, such as humans, are built from many specialised cells working together.

The process by which green plants, algae and some bacteria use light energy trapped by chlorophyll to convert carbon dioxide and water into glucose, releasing oxygen as a waste product.

The release of energy from glucose inside cells using oxygen, producing carbon dioxide and water. The energy released powers life processes such as growth, movement and keeping body temperature steady.

A protein that speeds up one specific chemical reaction in living things without being used up itself. Enzymes work best at particular temperatures and pH values and are destroyed by high heat.

The movement of water molecules through a partially permeable membrane from a region of higher water concentration to a region of lower water concentration, for example when water enters plant root hair cells.

The net movement of particles from an area of higher concentration to an area of lower concentration, caused by their random motion. It needs no energy input and explains gas exchange in lungs and leaves.

The green pigment held in chloroplasts that absorbs mainly red and blue light and reflects green light, which is why leaves look green. It captures the light energy used in photosynthesis.

A diagram showing the direction in which energy flows through organisms, starting with a producer and passing to consumers. Each arrow means 'is eaten by', and decomposers recycle nutrients from every level.

A community of living organisms interacting with one another and with the non-living parts of their surroundings, such as soil, water, light and temperature, within a defined area.

The maintenance of a steady internal environment in an organism, such as constant body temperature, blood glucose and water balance, even when conditions outside the body change.

A section of DNA on a chromosome carrying the instructions for making a particular protein or characteristic. Genes are passed from parents to offspring and exist in alternative forms called alleles.

The smallest particle of an element that can take part in a chemical reaction. It has a nucleus of protons and neutrons surrounded by electrons arranged in shells.

A pure substance made of only one kind of atom that cannot be broken into simpler substances by chemical means. Elements are listed in the periodic table in order of atomic number.

A pure substance formed when two or more different elements are chemically joined in fixed proportions, such as water or sodium chloride. Its properties differ from those of its elements.

Two or more substances combined without chemical bonding, in any proportion. Each substance keeps its own properties and the parts can usually be separated by physical methods such as filtration, evaporation or distillation.

The strong attraction between oppositely charged ions, formed when a metal transfers electrons to a non-metal. Ionic compounds usually form crystals and conduct electricity when molten or dissolved in water.

A bond formed when two atoms share one or more pairs of electrons, usually between non-metals. Covalent substances such as water and carbon dioxide generally have low melting points.

A scale from 0 to 14 showing how acidic or alkaline a solution is. Below 7 is acidic, 7 is neutral and above 7 is alkaline; each whole step means a tenfold change in hydrogen ion concentration.

The reaction between an acid and a base or alkali that produces a salt and water and moves the pH towards 7. It is used to treat acid spills, soothe indigestion and make fertilisers.

A reaction in which a substance gains oxygen or loses electrons. The rusting of iron and the burning of fuels are everyday examples, and oxidation is always accompanied by reduction.

A chart in which elements are arranged in order of increasing atomic number so that elements with similar properties line up in vertical columns called groups and horizontal rows called periods.

A push or pull that can change an object's speed, direction or shape. Force is a vector measured in newtons, and the net force decides how the motion of an object changes.

The rate at which velocity changes with time, measured in metres per second squared. An object accelerates when it speeds up, slows down or changes direction, and a net force causes it.

The energy transferred when a force moves an object through a distance along the line of the force, measured in joules. Work done equals force multiplied by distance moved.

The rate at which work is done or energy is transferred, measured in watts. One watt is one joule per second, so a more powerful device transfers the same amount of energy in less time.

The energy an object has because it is moving, calculated as one half of its mass multiplied by the square of its speed and measured in joules. Doubling the speed quadruples this energy.

The rule that the current through a conductor is directly proportional to the voltage across it, provided the temperature stays constant. Voltage equals current multiplied by resistance.

A measure of how strongly a component opposes the flow of electric current, measured in ohms. Resistance rises with greater length and higher temperature and falls when the wire is made thicker.

The number of complete waves or vibrations passing a fixed point each second, measured in hertz. Frequency is the reciprocal of the period and sets the pitch of a sound.

The bending of light as it passes from one transparent material into another of different optical density, caused by a change in speed. It explains lenses, prisms and why pools look shallower.

The force acting at right angles per unit area of a surface, measured in pascals. Pressure increases when the force increases or the area shrinks, which explains sharp knives and wide snowshoes.

The theory that Earth's outer shell is broken into large plates that slowly move, carrying continents and ocean floor. Their collisions, separations and slides cause earthquakes, volcanoes and mountain building.

A sudden shaking of the ground caused by the rapid release of energy when rocks along a fault break and move. The energy travels as seismic waves and is recorded by instruments called seismographs.

The continuous set of processes by which igneous, sedimentary and metamorphic rocks are formed, worn down and changed into one another through heat, pressure, weathering and melting.

The continuous movement of water between oceans, the atmosphere and the land through evaporation, condensation, precipitation and runoff, driven by energy from the Sun and by gravity.

The trapping of heat in the lower atmosphere by gases such as carbon dioxide and methane, which absorb outgoing infrared radiation and warm Earth's surface. Adding more of these gases causes global warming.

The wearing away and removal of rock or soil by agents such as running water, wind, ice and gravity, after weathering has already broken the material into smaller pieces.

The Sun together with every object held to it by gravity, including eight planets, their moons, dwarf planets, asteroids and comets, all travelling around the Sun in the same direction.