Cambridge Lower Secondary Science Stage 9 Vocabulary

Vocabulary flashcards covering key biology, chemistry, physics, and Earth/space concepts from Stage 9 Lower Secondary Science.

Chlorophyll

A green pigment found inside chloroplasts in plant cells that captures energy from sunlight for photosynthesis.

Photosynthesis

The chemical reaction in plants that uses water, carbon dioxide, and light energy captured by chlorophyll to produce glucose and oxygen.

Stomata

Tiny holes in the lower epidermis of a leaf that allow carbon dioxide to diffuse in and oxygen and water vapour to diffuse out.

Carbon cycle

The pathway by which carbon atoms continuously move between the atmosphere, living organisms, decomposers, and fossil fuels.

Atomic number

The number of protons contained in the nucleus of an atom of an element.

Mass number

The total number of protons and neutrons in the nucleus of an atom.

Density

The mass per unit volume of a substance, calculated using the equation $\text{density} = \frac{\text{mass}}{\text{volume}}$.

Ionic bond

A chemical bond formed by the electrostatic attraction between oppositely charged ions.

Covalent bond

A chemical bond formed when two non-metal atoms share one or more pairs of electrons.

Macromolecule

A giant 3D structure composed of many atoms held together by strong covalent bonds, such as diamond or graphite.

Heat

The total thermal energy of all the vibrating particles in an object, measured in joules ($\text{J}$).

Temperature

A measure of the average thermal energy of the particles in an object.

Absolute zero

The lowest possible theoretical temperature ($-273\,^{\circ}\text{C}$), at which particles completely stop moving.

Law of conservation of energy

The scientific principle stating that energy cannot be created or destroyed, only changed from one store to another or transferred.

Conduction

The transfer of thermal energy through a material by the passing on of vibrations from particle to neighbouring particle.

Convection

The transfer of thermal energy in liquids and gases where warmer, less dense fluid rises and cooler, denser fluid sinks.

Radiation

The transfer of thermal energy by electromagnetic waves that does not require particles and can travel through a vacuum.

Transpiration

The loss of water vapour from the leaves of a plant through evaporation and diffusion via stomata.

Excretion

The removal of metabolic waste materials and excess substances that have been produced inside the cells of an organism.

Urea

A toxic waste substance made in the liver from excess proteins/amino acids and filtered out of the blood by the kidneys.

Reactivity series

A list of metals arranged in order of their chemical reactivity, from most reactive at the top to least reactive at the bottom.

Displacement reaction

A chemical reaction in which a more reactive metal takes the place of a less reactive metal in its compound or salt.

Law of conservation of mass

The principle stating that no mass is lost or gained during a chemical reaction because no atoms are created or destroyed.

Exothermic reaction

A chemical reaction that transfers energy to the surroundings, releasing thermal energy.

Endothermic reaction

A chemical reaction that absorbs thermal energy from the surroundings.

Amplitude

The maximum distance moved by a particle in a wave from its rest position, which determines the loudness of a sound wave.

Frequency

The number of complete vibrations or waves produced per second, measured in hertz ($\text{Hz}$), which determines the pitch of a sound.

Interference

The effect produced when two or more waves of the same type meet and overlap, reinforcing or cancelling each other.

Collision theory

The hypothesis proposing that the Moon formed from debris produced when a Mars-sized planet named Theia collided with the early Earth.

Nebula

A giant cloud of dust and gas (mainly hydrogen and helium) in space, which can act as a stellar nursery for new star formation.

Natural selection

The process by which organisms with advantageous features are more likely to survive, reproduce, and pass on their advantageous genes.

Rate of reaction

A measure of how quickly reactants are used up or products are formed in a chemical reaction over time.