GCSE Combined Science Key Terms & Vocabulary

Every key term and definition you need for GCSE Combined Science, organised by topic. 781 definitions across 27 topics (AQA · Edexcel · Eduqas · OCR · WJEC), free to read and practise with spaced-repetition flashcards.

Forces Ecology Waves Homeostasis & Response Quantitative Chemistry Organic Chemistry Electricity Infection & Response Inheritance, Variation & Evolution Atomic Structure and the Periodic Table Energy Chemical Changes Organisation Bonding, Structure and the Properties of Matter Cell Biology Magnetism and Electromagnetism Particle Model of Matter Chemical Analysis Using Resources Atomic Structure Chemistry of the Atmosphere Rate and Extent of Chemical Change Energy Changes Working Scientifically Bioenergetics Space Physics Required Practicals

Practise these terms free →

Forces

Practise Forces →Practise →

Acceleration: measured in metres per second squared (m/s²).
Distance: a scalar quantity; displacement is a vector quantity.
Elastic deformation: reversible; plastic deformation is permanent.
Work done against friction: transferred to thermal energy.
Gravitational field strength: defined as the gravitational force per unit mass and is measured in N/kg.
Inertia: the resistance of an object to a change in its state of motion. Mass is a measure of inertia.
Joule: the unit of work done; it equals one newton of force applied over one metre.
Mass: the amount of matter in an object (kg); weight is the gravitational force on it (N) and depends on g.
Moment: measured in newton metres (N·m).
Momentum: measured in kg m/s.
Upthrust: the resultant upward force on an object in a fluid, caused by the pressure on its bottom surface being greater than the pressure on its top surface.
Resultant force: the single force equivalent to all the forces acting on an object combined.
Speed: a scalar quantity; velocity is a vector quantity because it includes direction.
Velocity: a vector (speed in a direction); speed is a scalar (magnitude only).
Spring constant k: the stiffness of a spring (force needed per unit extension).
Total stopping distance: the sum of thinking distance and braking distance.
Terminal velocity: the maximum constant speed a falling object reaches when the drag (air resistance) exactly balances its weight.
Thinking distance: the distance travelled while the driver reacts before braking; braking distance is the distance travelled while the brakes are decelerating the car.
Terminal velocity: reached when the object's weight is balanced by the upward drag (air resistance) force.
Force: a vector: it has both magnitude and direction. Resultants must account for direction, not just size.
Work done: measured in joules, the same unit as energy.
Work done: equivalent to energy transferred.
Work done: measured in joules (J).; A 200 m journey in 50 s gives an average speed of 4 m/s.; A car accelerating from 0 to 20 m/s in 5 s has a = 20 ÷ 5 = 4 m/s².; A car going from 10 m/s to 30 m/s in 5 s has a = 20 ÷ 5 = 4 m/s².; A car accelerating from 5 m/s to 25 m/s in 4 s has a = (25 − 5) ÷ 4 = 5 m/s².; a = (v − u) ÷ t; equivalently a = Δv ÷ t.; Acceleration a = (v − u) ÷ t, where u is the initial velocity, v is the final velocity, and t is the time taken.; The SI unit symbol for acceleration is m/s².

Showing 30 of 174. Practise the full Forces set →

Ecology

Practise Ecology →Practise →

Abiotic factors: non-living environmental factors: light intensity, temperature, water/ moisture, oxygen concentration, soil pH, and mineral content.
Abiotic factors: the non-living components of an ecosystem, such as temperature, light intensity, and pH.
Bioaccumulation: the build-up of pollutants in the tissues of organisms, increasing in concentration up the food chain.
Biodiversity: the variety of life in an area, including species and genetic variation.
Biotic factors: living factors in an ecosystem: food availability, competition, predation, pathogens, and mates.
Biotic factors: the living components of an ecosystem, such as predators, prey, and competitors.
Carbon: locked into plants when they absorb CO₂ during photosynthesis.
Decomposers: microorganisms — chiefly bacteria and fungi — that break down dead organisms and waste, releasing carbon as CO₂.
Community: all the populations of different species living together in one area.
Community: all living organisms in an area; an ecosystem adds the abiotic (non-living) environment.
Competition: when two or more organisms compete for the same limited resource (food, water, light, mates, territory).
Conservation: the practice of maintaining biodiversity and protecting habitats and species, especially those at risk of extinction.
Decomposers: essential for releasing nutrients from dead matter.
Dry mass: used in pyramids of biomass because water content varies, making fresh mass unreliable for comparison.
Food webs: more realistic than chains because most organisms eat or are eaten by many species.
Food web: more stable than a single food chain because multiple pathways let predators switch prey if one species declines.
Light intensity: an abiotic factor; it limits the rate of photosynthesis in plants.
Carbon: stored long-term as fossil fuels (coal, oil, natural gas) underground.
Microplastics: ingested by marine animals, blocking digestion and reducing feeding success.
Mutualism: a relationship where both species benefit, e.g. oxpeckers feed on parasites on a rhino's skin, gaining food while the rhino loses parasites.
Nature reserves: protected areas of land or sea managed primarily for wildlife conservation.
Nitrogen: essential for plants because they need it to make amino acids and proteins.
Nitrogen fixation: the conversion of atmospheric N₂ gas into ammonia or ammonium ions.
Peat bogs: major terrestrial carbon stores; destruction (for fuel or agriculture) releases stored CO₂ as peat decomposes or burns.
Pooter: used to collect small ground/leaf insects; it is not designed to capture flying insects (use nets for those).
Population: all organisms of one species in an area.
Population: all individuals of one species in an area; a community is all species combined.
Producers: plants or algae that make their own food by photosynthesis.
Quadrat: used to estimate plant numbers in a sample area.
Quadrat: the square frame used to sample stationary plants.

Showing 30 of 143. Practise the full Ecology set →

Waves

Practise Waves →Practise →

Amplitude: the maximum displacement of a particle from its rest (equilibrium) position.
Perfect black body: also the best possible emitter of radiation at any given temperature.
Critical angle: the angle of incidence at which the refracted ray runs along the boundary (refraction angle = 90°).
Diffraction: the spreading out of waves as they pass through a gap or around an obstacle.
TIR: used in endoscopes because it transmits images along flexible (optical-fibre) cables.
Frequency: the number of waves passing a point each second.
Infrared: used in thermal imaging cameras, toasters/grills, and TV remote controls.
Convex lens: a converging lens: it bends parallel rays of light inwards so they meet at the principal focus.
Concave lens: a diverging lens: it spreads parallel rays of light apart so they appear to come from a single point.
Focal length: the distance from the centre of the lens to the principal focus.
Real image: formed where light rays actually meet and can be projected onto a screen.
Virtual image: formed where rays only appear to come from; it cannot be projected onto a screen.
Magnification: calculated as image height divided by object height and has no units.
Light: an example of a transverse wave: electric and magnetic fields oscillate perpendicular to the direction of propagation.
Light: an example of a transverse wave.
Light: a transverse wave.
Light: a transverse EM wave that can travel through a vacuum.
Microwaves: used in mobile-phone communication because they pass through the atmosphere and reach receivers.
Normal: an imaginary line drawn at 90° (perpendicular) to a surface at the point where a ray meets it.
Optical fibres: the technology that uses TIR to transmit data.
P-waves (primary waves): longitudinal seismic waves: particles vibrate parallel to the direction of wave travel.
Period: measured in seconds (s) and represents the time for one full oscillation of the wave.
Higher-frequency sound waves: heard as higher-pitched notes.
Radio waves: used for television and radio broadcasting.
Refraction: the change in direction of a wave when it crosses a boundary between media because the wave's speed changes.
S-waves (secondary waves): transverse seismic waves: particles vibrate at right angles to the direction of wave travel.
Sound: a longitudinal wave.
Sound: a longitudinal mechanical wave: particles vibrate parallel to the direction of energy transfer.
Sound waves: longitudinal — the air particles vibrate parallel to the direction in which the sound travels.
Sound: a longitudinal wave of pressure variations — particles vibrate parallel to the direction of travel (unlike transverse light waves).

Showing 30 of 132. Practise the full Waves set →

Homeostasis & Response

Practise Homeostasis & Response →Practise →

ADH: released by the pituitary gland.
ADH: the hormone that controls water reabsorption in the kidney.
Auxin: the plant hormone that controls cell elongation and growth direction.
Auxin: used commercially as a rooting powder to encourage stem cuttings to grow roots.
Brain: made of billions of interconnected neurones and controls complex behaviour.
Cerebral cortex: the brain region responsible for consciousness, intelligence, memory and language.
Cerebellum: the brain region that controls muscular coordination and balance.
Medulla: the brain region that controls unconscious activities such as heartbeat and breathing.
Cerebral cortex: the highly folded outer layer of the brain.
Brain: extremely complex and delicate, which makes investigating and treating brain disorders very difficult.
Cerebral cortex: divided into two halves called cerebral hemispheres.
Cerebellum: the brain region that controls balance and fine motor coordination.
Effector: a muscle or gland that produces a response to a nerve impulse.
Ethene (ethylene): a gaseous hormone used to ripen fruit during storage.
Cornea: the transparent front layer of the eye that does most of the focusing (refraction) of incoming light.
Iris: the coloured muscular ring that controls the size of the pupil and therefore how much light enters the eye.
Accommodation: the process of changing the shape of the lens to focus on near or distant objects.
Myopia (short-sightedness): when distant objects are focused in front of the retina, corrected using a concave (diverging) lens.
Hyperopia (long-sightedness): when near objects are focused behind the retina, corrected using a convex (converging) lens.
Pupil size: controlled by two sets of iris muscles: circular muscles and radial muscles working antagonistically.
FSH: produced by the pituitary gland and stimulates the development of follicles in the ovary.
Gibberellins: plant hormones that promote stem elongation by cell stretching.
Glucose: fully reabsorbed in healthy kidneys by active transport.
Hormonal communication: slower than nervous because hormones travel in blood; nerves transmit electrical impulses.
Hypothalamus: the brain region that monitors and regulates core body temperature.
Urea: produced in the liver from the deamination of excess amino acids and is excreted by the kidneys.
Osmoregulation: the control of the water content (water balance) of the body, and is carried out by the kidneys.
ADH (anti-diuretic hormone): released by the pituitary gland and increases the permeability of the kidney tubules so that more water is reabsorbed into the blood.
Kidney transplant: a long-term cure but the recipient must take immunosuppressant drugs for life to stop their immune system rejecting the donor kidney.
Ovulation: triggered by a surge in LH (luteinising hormone) from the pituitary gland.

Showing 30 of 130. Practise the full Homeostasis & Response set →

Quantitative Chemistry

Practise Quantitative Chemistry →Practise →

Actual yield: almost always less than theoretical yield because: the reaction may be reversible, the reaction may be incomplete, side reactions may produce unwanted by-products, and some product is lost during separation/purification.
Atom economy: a measure of the proportion of reactant atoms that end up in the desired product, expressed as a percentage.
Atoms: rearranged but never created or destroyed in a chemical reaction.
Mass: conserved because no atoms are created or destroyed — they are only rearranged.
Avogadro constant: approximately 6.02 × 10²³ (per mole).
Concentration: calculated as moles divided by volume.
Concentration: also expressed in grams per cubic dm³ (g/dm³).
Limiting reactant: the one completely used up first; it determines the maximum amount of product.
Limiting reactant: the reactant used up first in the reaction.
Relative formula mass (Mr): found by adding the relative atomic masses of all atoms in the formula.
Percentage composition: useful in industry because it predicts the yield from a given mass of compound.
Theoretical yield: calculated using the moles of the limiting reactant.
Phenolphthalein: pink in alkali and colourless in acid, so it turns colourless at the end-point when acid is added to alkali.
Universal indicator: not suitable for titration because its gradual colour range gives no sharp end-point.
Rough (trial) titration: done first, then accurate repeats are taken until concordant results within 0.10 cm³ are achieved.
Reactants not used up: described as being in excess.
Actual yield: almost always less than theoretical yield because reactions may be reversible or incomplete, side reactions make by-products, and some product is lost during transfer and purification.
High atom economy: economically and environmentally favourable because more of the reactant mass becomes useful product, wasting fewer finite raw materials and producing less waste to dispose of.; Adding water to a solution decreases its concentration.; Adding more of the excess reactant to a reaction does not increase the amount of product formed (it stays limited by the limiting reactant).; Addition polymerisation has a 100% atom economy because every reactant atom ends up in the polymer — no by-products are formed.; Atom economy = (Mr of desired product ÷ sum of Mr of all products) × 100.; The Avogadro constant 6.02 × 10²³ is the number of particles in one mole of any substance.; One mole of any substance contains Avogadro's number (6.02 × 10²³) of particles.; The symbol for the Avogadro constant is Nₐ.; Equal volumes of different gases at the same temperature and pressure contain equal numbers of molecules (Avogadro's law).; In a balanced chemical equation, the number of atoms of each element must be the same on both sides.; A balanced equation conserves mass and the number of atoms of each element.; In CaCO₃: Mr = 40 + 12 + 48 = 100; %Ca = 40/100 × 100 = 40%.; When calcium carbonate is heated in an open container, CO₂ escapes into the surroundings, so the mass of the remaining solid falls.

Showing 30 of 130. Practise the full Quantitative Chemistry set →

Organic Chemistry

Practise Organic Chemistry →Practise →

Addition polymerisation: when many alkene monomers join to form a polymer.
Addition polymers: difficult to dispose of because their strong C–C bonds resist biodegradation.
Alcohols: named with the suffix -ol; their functional group is –OH (e.g. methanol, ethanol).
Alcohols: soluble in water and form solutions with a neutral pH (pH 7).
Ethanol: produced industrially by fermentation, in which yeast converts sugar (glucose) into ethanol and carbon dioxide.
Alkanes: described as saturated because they contain only single bonds (no double bonds); every carbon holds the maximum number of hydrogens possible.
Alkanes: saturated hydrocarbons because they contain only single bonds between carbon atoms.
Alkanes: relatively unreactive except in combustion (they burn in air to release energy).
Alkenes: more reactive than alkanes because the C=C double bond easily opens to allow addition of new atoms.
Alkenes from cracking: used to make polymers.
Alkenes: more reactive than alkanes due to their double bond.
Alkenes: described as unsaturated because they contain a carbon–carbon double bond and can undergo addition reactions.
Alkenes: unsaturated hydrocarbons because they contain a reactive carbon–carbon double bond (C=C).
Alkenes: more reactive than alkanes because the C=C double bond readily opens to allow new atoms to add across it.
First four alkenes: ethene (C₂H₄), propene (C₃H₆), butene (C₄H₈) and pentene (C₅H₁₀).
Carboxylic acids: weak acids: only a small fraction of their molecules ionise (dissociate) in aqueous solution.
Carboxylic acids: named with the suffix -anoic acid and contain the functional group –COOH.
Carbon monoxide: dangerous because it binds tightly to haemoglobin in red blood cells, blocking oxygen transport and causing potentially fatal poisoning.
Cracking: breaking long-chain alkanes into shorter alkanes and alkenes, matching supply to demand for petrol and useful feedstocks.
Cracking: industrially important because it makes useful smaller alkanes and alkenes from less-useful long-chain ones.
Cracking: important because fractional distillation yields too many long-chain alkanes; demand is for petrol and alkenes (shorter chains).
Crude oil: separated into alkane fractions by fractional distillation.
Crude oil: separated into alkane fractions by fractional distillation, which exploits differences in boiling point.
Ethanol from fermentation: renewable because the glucose comes from recently grown plants.
Fermentation: a slow, batch process using renewable sugar at low temperature, giving an impure product; industrial hydration of ethene is a continuous, fast process giving a pure product.
Ethanol: produced by fermentation when yeast acts on sugars without oxygen.
Ethanol: also produced industrially by hydration of ethene: ethene + steam (with a phosphoric acid catalyst) → ethanol.
Combustion: the reaction of a hydrocarbon (or other fuel) with oxygen — releasing energy as heat and light.
Monomer: a small molecule that joins with others to form a polymer.
Nylon: not an addition polymer; it is a condensation polymer made from two different monomers.

Showing 30 of 113. Practise the full Organic Chemistry set →

Electricity

Practise Electricity →Practise →

Ammeter: connected in series with the component whose current is being measured, so it carries the full current it is measuring.
Cell: shown by a long thin line (positive terminal) and a short thicker line (negative terminal), close together.
Circuit breaker: a switch that trips off when current is too high and can be reset after the fault is fixed; a fuse must be replaced once it has blown.
Electric current: the rate of flow of electric charge — the charge passing a point per second.
Diode: the component that allows current to flow in one direction only.
Electrons: the subatomic particles transferred during charging by friction.
Light-dependent resistor (LDR): a resistor rectangle enclosed in a circle with two arrows pointing inward, showing light falling on the component.
Live wire: brown.
Milliamp (mA): one-thousandth of an ampere, so to convert milliamps to amps you divide by 1000 (not 100); e.g. 250 mA = 0.25 A.
Electrical resistance: measured in ohms, symbol Ω.
Resistance: proportional to wire length: a longer wire has more electron–atom collisions and so a higher resistance.
Resistance: the property that opposes the flow of electric current in a circuit.
Resistance: inversely proportional to cross-sectional area: a thicker wire of the same length and material has lower resistance.
Resistor: shown by a plain rectangle in modern schematics (or a zigzag in older diagrams).
Thermistor (NTC): a resistor whose resistance decreases as its temperature rises — opposite to a standard resistor.
Thermistors: used in thermostats because their resistance varies predictably with temperature, so a circuit can sense temperature changes.
UK mains electricity supply: alternating current (AC) at 230 V and 50 Hz.
UK mains: not direct current — it is AC.
Voltmeter: connected in parallel across the component whose potential difference is being measured.; Alternating current (AC) reverses direction periodically; direct current (DC) flows in one direction only.; DC flows one way; AC reverses direction periodically.; A 60 W bulb left on for 2 h (7200 s): energy = 60 × 7200 = 432 000 J = 0.12 kWh.; The SI unit of electric charge is the coulomb (C), equal to one ampere flowing for one second.; Conventional current flows from positive to negative terminal; electrons (negative carriers) flow the opposite way.; Cost of electricity = number of kilowatt-hours used × price per unit.; Rearranging V = IR: I = V ÷ R; 12 V across 4 Ω gives 3 A.; The SI unit of electric current is the ampere (A).; Direct current (DC) flows in only one direction.; A diode's I-V graph shows zero current below a forward-bias threshold voltage (~0.7 V for silicon), then current rises steeply.; A diode allows current to flow in one direction only; it has very high resistance in the reverse direction.

Showing 30 of 103. Practise the full Electricity set →

Infection & Response

Practise Infection & Response →Practise →

Antibodies: proteins that bind to specific antigens on a pathogen, marking it for destruction.
Athlete's foot: a fungal disease affecting the skin (especially between the toes) and nails.
Clinical trials: the stage at which a drug is first tested on people, after passing preclinical safety screens.
Communicable disease: one that can be passed from one organism to another.
Aseptic technique: a set of procedures that prevents unwanted microorganisms from contaminating a culture.
Agar: a solidifying jelly extracted from seaweed onto which microorganisms are grown; nutrient broth is the equivalent liquid medium.
Inoculating loop: sterilised by holding it in a Bunsen flame until it glows red hot, then allowing it to cool before use.
Double-blind trial: one in which neither the patient nor the doctor/researcher knows which participant received the drug or the placebo.
Gonorrhoea: a bacterial sexually transmitted infection that can cause infertility if untreated.
HIV: difficult to defeat because it attacks white blood cells (CD4⁺ T helpers) of the immune system.
HIV: a virus that attacks white blood cells, specifically T-helper lymphocytes, weakening the immune system; untreated infection progresses to AIDS.
Influenza (flu): caused by a virus.
Monoclonal antibodies: produced from a single clone of genetically identical cells.
Monoclonal antibody: an identical antibody produced by cloning a single B-cell.
Monoclonal antibodies: identical antibodies cloned from a single B-cell.
Malaria: caused by a protist (Plasmodium) spread by mosquitoes.
Malaria: caused by a protist (Plasmodium) and spread by the bite of infected female Anopheles mosquitoes.
Measles: a viral infection in humans.
Measles: caused by a virus and is spread by droplets inhaled from the coughs or sneezes of infected people.
Monoclonal antibodies: antibodies that are all identical and produced from a single clone of cells, so they bind to one specific antigen.
Monoclonal antibodies: made by combining a mouse B-lymphocyte (which makes a specific antibody) with a tumour cell to form a hybridoma.
Hybridoma: the cell formed by fusing a B-lymphocyte and a tumour cell; it both makes the antibody and divides many times to produce large quantities.
Mice: injected with the chosen antigen so their B-lymphocytes produce antibodies against that specific antigen before fusion.
Monoclonal antibodies: specific because each binds to only one type of antigen, allowing them to target one substance or one type of cell.
Monoclonal antibodies: used in laboratory diagnostic assays (such as ELISA) to detect or measure the level of a specific molecule, hormone, or pathogen.
MRSA: the hospital "superbug" famously resistant to many antibiotics.
Developing new antibiotics: difficult and slow because bacteria evolve resistance quickly after release.
Pathogen: a microorganism that causes disease: a virus, bacterium, fungus, or protist.
Placebo: a dummy treatment with no active drug, designed to look identical to the real treatment.
Tobacco mosaic virus (TMV): a plant pathogen that produces a mosaic pattern of discolouration on leaves, reducing photosynthesis and growth.

Showing 30 of 99. Practise the full Infection & Response set →

Inheritance, Variation & Evolution

Practise Inheritance, Variation & Evolution →Practise →

Linnaeus: credited with creating the binomial naming system.
Cystic fibrosis: autosomal recessive because it is caused by a recessive allele on a non-sex chromosome (CFTR on chromosome 7).
Cystic fibrosis: caused by a recessive allele, meaning a person must inherit two copies to be affected.
Cystic fibrosis: inherited recessively; two copies (one from each parent) are needed for the condition to appear.
Chromosomes: the structures inside the nucleus that carry the DNA molecules.
DNA: transcribed into mRNA; ribosomes then translate the mRNA into protein.
Dominant allele: always expressed in the phenotype, even if only one copy is present.
Environmental variation: variation caused by the organism's surroundings (e.g. diet, sunlight, training).
Gene: a section of DNA that codes for a specific protein.
Genetic engineering: the process of transferring genes between organisms.
Genome: the complete set of genetic information (all the DNA) in an organism.
Genotype: the combination of alleles an organism carries; phenotype is the observable trait.
Geographic isolation: when physical barriers split populations apart.
Genetic engineering: controversial because of unknown long-term impacts on human health and on ecosystems.
GM (genetically modified) crop: a crop whose DNA has been altered for improved traits.
Bacteria-made human insulin: preferred to animal-extracted insulin because GM bacteria produce large quantities of identical human insulin.
Golden rice: genetically engineered to contain a precursor of vitamin A, intended to prevent vitamin-A-deficiency blindness.
Human Genome Project: an international effort to sequence the entire human DNA.
Human insulin: now mostly produced by genetically modified bacteria.
Human insulin: produced by inserting the insulin gene into a bacterial plasmid for expression.
Kingdom: the broadest of the Linnaean classification groups.
Mutation: a random change in the DNA base sequence of a gene.
DNA nucleotide: made of a sugar, a phosphate, and a base.
Polydactyly: caused by a dominant allele, so one copy is enough to show the condition.
Polydactyly: the inherited disorder that causes extra fingers or toes; it is dominantly inherited.
Scientific names: written with the genus and species in italics.
Sickle cell anaemia: caused by a recessive allele.
Speciation: the formation of a new species after isolation and divergence.
Speciation: the formation of new species through evolution, often when populations become reproductively isolated.
Biological sex: determined by the father because sperm carry either an X or a Y chromosome.

Showing 30 of 95. Practise the full Inheritance, Variation & Evolution set →

Atomic Structure and the Periodic Table

Practise Atomic Structure and the Periodic Table →Practise →

Alkali metals: stored under oil to prevent them reacting with air and water.
Argon: used in (incandescent) light bulbs as an inert filler that stops the hot tungsten filament burning.
Argon: used in light bulbs because the inert atmosphere protects the filament from oxidising.
Bromine: a liquid at room temperature.
Electron's mass: about 1/1836 (≈ 1/2000) of a proton's; treated as ≈ 0 at GCSE.
Helium: the noble gas used in helium balloons.
Helium: used to fill weather balloons safely because it is inert and less dense than air.
Isotopes: atoms of the same element with the same number of protons but different numbers of neutrons.
Mendeleev's table: accepted because the properties of later-discovered elements (gallium, germanium) matched his predictions.
Metals: on the left and centre; non-metals are on the right of the periodic table.
Modern periodic table: arranged in order of increasing atomic number.
Noble gases: unreactive because they have a full outer shell of electrons.
Noble gases: unreactive because their outer electron shells are full.
Noble gases: unreactive because they have a full outer electron shell.
Noble gases: monatomic because their full outer shells leave no reason to bond with other atoms.
Isotopes: written with the mass number as a superscript before the element symbol: ¹²C, ¹⁴C, ²³⁵U.
Group 1 metals: stored under oil because they react vigorously with oxygen and water vapour in air.
Protons: found in the nucleus.
Relative atomic mass (Ar): the weighted average mass of an element's naturally occurring isotopes, where the "weight" is the percentage abundance.
Transition metals: the block of elements found between Group 2 and Group 3 in the centre of the periodic table.
Transition metals: typically denser than Group 1 metals; iron, copper and most others sink in water whereas lithium, sodium and potassium float.
Transition metal compounds: typically coloured, such as blue copper(II) sulfate and orange-brown iron(III) compounds.
Transition metals: much less reactive than Group 1 metals; they react slowly or not at all with water and oxygen at room temperature.
Transition metals: generally harder and stronger than the soft Group 1 alkali metals, which can be cut with a knife.; An atom has no overall charge because the number of protons (+1 each) equals the number of electrons (−1 each).; Atomic number = number of protons (= electrons in neutral atom); mass number = protons + neutrons.; Atomic number Z equals the number of protons in an atom.; Ordering by atomic number resolved anomalies that mass-order produced (e.g. tellurium/iodine).; The atomic number of an atom is the number of protons it contains.; Niels Bohr placed electrons in fixed orbits at quantised energy levels around the nucleus.

Showing 30 of 90. Practise the full Atomic Structure and the Periodic Table set →

Energy

Practise Energy →Practise →

GCSE energy stores: kinetic, gravitational potential, elastic potential, thermal, chemical, nuclear, electrostatic, and magnetic.
Energy: measured in joules (J).
Heating: a transfer pathway, not an energy store; the eight GCSE stores do not include "heat" as a separate store.
Kilowatt-hour (kWh): the energy used when a 1 kW device runs for 1 hour. It is the unit used on electricity bills.
LED lamps: more efficient than filament lamps.
LED lights: more efficient than filament bulbs because they waste much less heat through dissipation.
LED bulbs: more efficient than filament bulbs because filaments waste much energy as infrared heat.
Metals: better thermal conductors than plastics or wood because free (delocalised) electrons carry energy through the metal lattice.
Nuclear power: low-carbon because reactors don't burn fuel and emit no CO₂ during generation.
Nuclear fuels (uranium): non-renewable resources.
Power: the rate of energy transfer (or work done per unit time).
Specific heat capacity: the energy needed to raise the temperature of 1 kg of a substance by 1 °C.
Insulation: placed around the block to reduce heat loss to the surroundings and improve accuracy.
Solar power: a renewable resource.
Water: used as a coolant because it has a very high specific heat capacity (4200 J/kg°C), so it absorbs lots of heat per kg.
Water: not a coolant because of low specific heat capacity — its capacity is high.
Power: measured in watts (W). One watt equals one joule per second (1 W = 1 J/s).; Black matt surfaces emit and absorb infrared radiation better than white shiny surfaces, which reflect.; Cavity wall insulation (foam) reduces heat loss by stopping convection currents in the cavity and reducing conduction across it.; Conduction transfers thermal energy through solids.; Conduction transfers energy by vibrating particles in contact; convection transfers energy by bulk fluid movement.; Energy cannot be created or destroyed, only transferred between stores.; A convection current forms when heated fluid expands, becomes less dense and rises while cooler fluid sinks to replace it.; Convection only occurs in liquids and gases because the particles need to be free to move and carry thermal energy.; Doubling the speed of an object quadruples its kinetic energy, because v is squared.; A device with efficiency 1.0 (100%) would transfer all input energy into useful output with no waste energy.; A machine with efficiency greater than 1.0 (more than 100%) is impossible — it would create energy.; As a decimal, efficiency = useful output energy transfer ÷ total input energy transfer.; Efficiency = useful output energy ÷ total input energy × 100%.; An electric heater has the highest efficiency among GCSE-typical comparison devices, because almost all the input electrical energy becomes useful heat output.

Showing 30 of 89. Practise the full Energy set →

Chemical Changes

Practise Chemical Changes →Practise →

Aluminium: deposited at the cathode because Al³⁺ ions are attracted to the negative electrode.
Carbon (graphite) anodes: replaced regularly because oxygen produced at the anode reacts with the hot carbon, burning it away as CO₂.
Brine: concentrated sodium chloride solution.
Sodium hydroxide: left in solution after brine electrolysis.
Copper sulfate crystals: prepared in school by adding excess copper(II) oxide to warm dilute sulfuric acid, filtering, then crystallising.
Aluminium oxide: dissolved in cryolite because cryolite lowers the melting point, saving energy.
Pure salt crystals: obtained from the filtered salt solution by evaporating off some water and allowing the solution to cool and crystallise.
Metal: reactive because it loses electrons readily; e.g. iron is more reactive than copper because it loses electrons more easily.
Excess unreacted base: removed from the salt solution by filtration before crystallisation.
Gold: found as a native (pure) metal in nature because it is unreactive; iron is found as an ore because it reacts with oxygen and water.
Hydrogen: the non-metal included in the reactivity series so its reactivity can be compared with metals.
Insoluble salts: made by mixing two soluble salt solutions so the insoluble product precipitates; the precipitate is then filtered, washed, and dried.
Iron: extracted with carbon (carbon is more reactive than iron) but aluminium needs electrolysis (aluminium is more reactive than carbon).
Potassium: the most reactive metal in the GCSE reactivity series (group 1, towards the top of the table).
Oxidation: the loss of electrons.
Reduction: the gain of electrons.
Strength: degree of ionisation; concentration describes moles per dm³ of solution.; The acid used determines the salt's anion: HCl → chloride; H₂SO₄ → sulfate; HNO₃ → nitrate.; Acid + metal carbonate → salt + water + carbon dioxide.; Acid + reactive metal → salt + hydrogen gas.; Acidic solutions have a pH below 7 (range 0–6.9).; Acid + base → salt + water is the core neutralisation reaction used to make most soluble salts — e.g. HCl + NaOH → NaCl + H₂O.; Acids release hydrogen ions (H⁺) when dissolved in water.; In a redox reaction, the oxidising agent is itself reduced, and the reducing agent is itself oxidised.; Aluminium must be extracted by electrolysis (not reduction with carbon) because it is above carbon in the reactivity series, so carbon cannot displace it.; Alkalis release hydroxide ions (OH⁻) when dissolved in water.; During electrolysis, negative ions (anions) move towards the anode and positive ions (cations) move towards the cathode.; At the anode (positive electrode), ions lose electrons — this is called oxidation.; The positive electrode in electrolysis is the anode.; At the anode, hot O₂ reacts with the carbon electrode, burning it away as CO₂; the anode therefore shrinks and must be replaced.

Showing 30 of 84. Practise the full Chemical Changes set →

Organisation

Practise Organisation →Practise →

Alveoli: adapted for efficient gas exchange by their large surface area, thin walls (one cell), and rich blood supply.
Atria: the upper chambers that receive blood returning to the heart from the veins.
Bile: not an enzyme; it emulsifies fats physically by lowering surface tension.
Bile: produced in the liver.
Bile: stored in the gall bladder before release into the small intestine.
Capillaries: one endothelial cell thick to minimise the diffusion distance for gases and nutrients between blood and tissues.
Coronary heart disease (CHD): caused by fatty plaques (atheroma) building up inside the coronary arteries, narrowing them and restricting blood flow to the heart muscle.
Enzymes: biological catalysts (proteins) that speed up reactions in living organisms.
Pepsin: the protein-digesting enzyme secreted in the stomach.
Peristalsis: the wavelike muscular contractions that move food along the gut.
Phloem: the plant tissue that transports sugars made by photosynthesis around the plant.
Plasma: the liquid component of blood and transports dissolved glucose, amino acids, carbon dioxide, urea, hormones, antibodies, and heat around the body.
Small intestine: the main site of both digestion completion and absorption of nutrients.
Statins: drugs that lower blood LDL cholesterol levels, reducing the rate at which fatty plaques build up in arteries.
Stent: a small wire-mesh tube inserted into a narrowed coronary artery and expanded to hold the artery open, restoring blood flow.
Stent: a wire-mesh tube inserted into a narrowed coronary artery to hold it open and restore blood flow.
Transpiration: the loss of water vapour from a plant's leaves.
Villi: finger-like projections in the small intestine that increase surface area for absorption.
Xylem: not a living tissue; mature xylem vessels are dead cells with thick lignified walls.
Xylem: the plant tissue that transports water (and dissolved mineral ions) from roots to leaves.; The region of the enzyme where the substrate binds is called the active site.; The tiny air sacs in the lungs are called alveoli.; Alveoli give the lungs a large surface area because there are millions of tiny air sacs.; The wall of an alveolus is one cell thick, minimising diffusion distance.; Amylase breaks down starch into simple sugars (maltose / glucose).; Amylase digests starch into maltose (a sugar).; Arteries carry blood away from the heart at high pressure; veins carry blood back towards the heart at low pressure.; Artificial (mechanical) hearts avoid donor-rejection issues and waiting-list delays, but mechanical parts can fail and the patient typically needs anticoagulant medication. They are usually a temporary bridge to transplant.; A positive Benedict's test changes the blue reagent to green, then yellow, then brick-red / orange as more reducing sugar is present.; Benedict's reagent tests for reducing sugars (e.g. glucose); the sample is heated in a water bath.

Showing 30 of 84. Practise the full Organisation set →

Bonding, Structure and the Properties of Matter

Practise Bonding, Structure and the Properties of Matter →Practise →

Alloys: harder than pure metals because atoms of different sizes distort the regular layers, so the layers can no longer slide over each other easily.
Alloys: harder than pure metals because different-sized atoms disrupt the lattice, stopping layers sliding over each other.
Alloys: harder than pure metals because different-sized atoms stop layers sliding.
Alloys: harder than pure metals because different-sized atoms disrupt layer sliding.
Brass: made of copper and zinc.
Bronze: the alloy made by mixing copper and tin.
Covalent bond: a chemical bond formed when two atoms share a pair of electrons.
Graphene: a single layer of carbon atoms arranged in a hexagonal lattice; it is very strong and conducts electricity.
Graphite: soft and slippery because weak intermolecular forces between the layers allow them to slide over each other.
Forces between separate molecules: intermolecular forces, distinct from the covalent bonds holding atoms within each molecule.
Metallic bond: the strong attraction between positive metal ions and a "sea" of delocalised electrons.
Metals: good conductors because delocalised electrons are free to move through the lattice and carry charge.
Metals: malleable because layers of ions can slide past each other.
Nanoparticles: used in sunscreen (e.g. zinc oxide) and as catalysts.
Nanoparticles: 1 to 100 nanometres in diameter.
Pure metals: malleable because identical-sized ion layers slide over each other without breaking the metallic bond.
Pure metals: softer than alloys because regular layers of identical ions can slide over each other.
Silver nanoparticles: added to wound dressings for their antibacterial properties.
Stainless steel: useful for cutlery and surgical tools because iron is mixed with chromium and nickel; the chromium oxide layer resists corrosion.
Stainless steel: the alloy that resists corrosion in kitchen knives.
Steel: iron + carbon; brass is copper + zinc; bronze is copper + tin.
Steel: an alloy of iron with small amounts of carbon.; A chloride ion (Cl⁻) carries a charge of −1.; Covalent bonds form between non-metal atoms. Ionic bonds form between a metal and a non-metal.; Metals conduct electricity because delocalised electrons carry charge.; In diamond, each carbon atom forms four strong covalent bonds to four neighbouring carbon atoms in a rigid 3D tetrahedral lattice.; Diamond has a very high melting point and is very hard because of the many strong covalent bonds running throughout the structure.; Diamond does not conduct electricity: all four outer electrons of each carbon are used in bonds, so there are no delocalised charge carriers.; Diamond does not have a free electron per atom (that is graphite): all four outer electrons of each carbon are used in covalent bonds.; A double covalent bond involves the sharing of four electrons (two pairs).

Showing 30 of 81. Practise the full Bonding, Structure and the Properties of Matter set →

Cell Biology

Practise Cell Biology →Practise →

Adult stem cells: found in tissues like bone marrow and can differentiate into a more limited range of cell types — e.g. bone marrow stem cells form the various blood cell types but not nerves.
Cancer: uncontrolled cell division caused by mutations to genes that regulate the cell cycle, producing tumours.
Concentration gradient: a difference in concentration between two regions.
Cytoplasm: the jelly-like substance where most of the cell's chemical reactions take place.
Fish gills: efficient for gas exchange because the lamellae give a huge surface area and thin walls (short diffusion distance).
Iodine solution: used to stain plant cells so that structures show up more clearly under the microscope.
Magnification: image size; resolution is detail clarity — the smallest distance between two points still seen as separate.
Meiosis: cell division that produces four genetically different haploid gametes (sperm or eggs).
Mitochondria: the site of aerobic respiration.
Mitosis: cell division that produces two genetically identical diploid daughter cells. The body uses it for growth, repair, and asexual reproduction.
Nerve cells: long (not short and wide); the long axon allows electrical impulses to travel between distant parts of the body.
Potato strips: blotted dry before weighing to remove surface water, which would otherwise add to the mass.
Osmosis: the net movement of water through a partially permeable membrane down its water-potential gradient.
Plant cell walls: made of cellulose, which gives them strength.
Red blood cells: adapted to carry oxygen by being biconcave (large surface area), lacking a nucleus (more haemoglobin space), and flexible enough to squeeze through capillaries.
Resolution: the smallest distance between two points that can still be seen as separate.
Ribosomes: the site of protein synthesis.
Sperm cells: adapted with a long tail for swimming, many mitochondria for energy, and an acrosome containing enzymes that digest the egg's outer layer.
Stem cell: an undifferentiated cell that can divide and specialise into one or more types of cell.; Active transport can move substances against a concentration gradient using cellular energy.; Active transport moves substances against a concentration gradient and requires energy.; Active transport requires energy released by respiration in the cell.; Actual size = image size ÷ magnification; a 4 mm image at ×400 represents an actual size of 0.01 mm.; Adult stem cells (found in bone marrow and other tissues) can only become a narrower set of cell types — they are multipotent.; An animal cell placed in a hypotonic solution gains water by osmosis and may burst (cytolysis).; Animal cells do not have a cell wall (cellulose walls are a plant-cell feature).; In adult humans, stem cells are found in bone marrow.; The cell membrane controls which substances enter and leave the cell.; Chloroplasts carry out photosynthesis using light energy.; Ciliated epithelial cells line the trachea and bronchi; their cilia sweep mucus and trapped debris away from the lungs.

Showing 30 of 81. Practise the full Cell Biology set →

Magnetism and Electromagnetism

Practise Magnetism and Electromagnetism →Practise →

Electromagnets: used in relays, electric bells, loudspeakers, scrapyard cranes, MRI scanners, and motors.
Electromagnet: a coil of wire (a solenoid), often wrapped around a soft iron core, that becomes magnetic only when current flows.
Magnetic field: strongest at the poles of a bar magnet.
Generator effect: also called electromagnetic induction.
Electromagnetic induction: a potential difference induced in a conductor by changing magnetic flux.
Motor effect: the force experienced by a current-carrying conductor placed in a magnetic field.
Induced voltage: increased by moving the magnet faster (raising the rate of change of flux).
Generator's output: increased by a stronger magnetic field, more turns on the coil, and faster rotation.
Soft iron: used (not steel) because it magnetises and demagnetises easily — it loses its magnetism the moment current stops. Steel retains magnetism, making it unsuitable for a controllable electromagnet.
Solenoid: a long coil of wire that produces a magnetic field when current flows through it.
Magnetic flux density B: measured in tesla (T).; The National Grid transmits at very high voltage (up to 400 kV) because higher voltage means lower current, reducing I²R heat loss in cables.; A simple AC generator works because a coil rotates in a magnetic field, inducing an alternating PD.; AC generators output an alternating current that reverses direction every half-turn.; An AC generator uses slip rings rather than a split-ring commutator so the connection stays continuous and the current alternates.; AC generators (alternators) use slip rings; DC generators (dynamos) use a split-ring commutator.; An alternator uses slip rings to produce AC; a dynamo uses a split-ring commutator to produce DC.; Magnetic field lines run from the north pole to the south pole outside a bar magnet.; A compass detects magnetic field direction.; A DC motor uses a split-ring commutator to reverse the current through the coil every half turn, keeping the coil rotating in one direction.; Earth itself acts like a giant bar magnet.; An electric bell uses an electromagnet to repeatedly pull a striker against a bell.; The magnitude of the force on the conductor is F = BIL, where B is magnetic flux density (T), I is current (A), and L is the length of conductor in the field (m).; Rotating an AC generator's coil faster increases both the frequency and the peak voltage of the output.; Magnetic field lines show the direction a free north pole would move and, by their density, the strength of the field (closer lines = stronger field).; Magnetic field lines never cross each other where two magnetic fields interact.; Field lines around a magnet always point from north to south (outside the magnet).; Fleming's left-hand rule predicts the force direction on a current in a magnetic field: thumb = thrust (force), first finger = field, second finger = current. All three at right angles.; A device that produces electricity from rotation is called a generator.; The National Grid uses high voltage for transmission because this reduces current and the heat lost in cables (P = I²R).

Showing 30 of 77. Practise the full Magnetism and Electromagnetism set →

Particle Model of Matter

Practise Particle Model of Matter →Practise →

Absolute zero: approximately −273 °C (precisely −273.15 °C).
Absolute zero: 0 K (−273 °C), where particles have minimum internal energy.
Deposition: the change of state in which a gas turns directly into a solid (without passing through the liquid state).
Heat: energy; temperature measures the intensity (average KE), not the total amount of energy.
Ice: less dense than liquid water because water molecules form a hexagonal lattice with gaps (hydrogen bonding).
Internal energy: the total kinetic and potential energy of all the particles in a system.
Internal energy: measured in joules (J).
Temperature: a measure of the average kinetic energy of particles; internal energy is the total energy of all particles. They are related but not identical.
Latent heat: the energy needed to change state without a change in temperature.
Specific latent heat: the energy needed to change the state of 1 kg of a substance without changing its temperature.
Gas pressure: caused by particles colliding with the walls of the container.
Gas pressure: caused by particles colliding with the container walls.; 100 °C = 100 + 273 = 373 K.; 25 °C = 25 + 273 = 298 K.; Absolute zero (0 K) corresponds to −273 °C (more precisely −273.15 °C).; At absolute zero, gas particles theoretically have no kinetic energy.; A 2 m³ gas at 100 kPa compressed to 0.5 m³ at constant T gives p₂ = p₁V₁/V₂ = 100 × 2 / 0.5 = 400 kPa.; Boyle's Law: at constant temperature, p × V is constant for a fixed mass of gas (p₁V₁ = p₂V₂).; To convert Celsius to kelvin, add 273 (more precisely 273.15).; Gas exerts pressure on container walls because particles collide with the walls, each exerting a force per collision.; Compressing a gas increases pressure because particles experience more collisions per area per second.; Doing work on a gas by compression raises its internal energy.; Doing work on a gas by compression raises its temperature.; Compressing a gas does work on it, raising its temperature.; Decreasing the volume of a fixed mass of gas at constant temperature increases its pressure.; A 240 g block with a volume of 30 cm³ has a density of 8 g/cm³.; A 540 g block with volume 200 cm³ has a density of 540 ÷ 200 = 2.7 g/cm³.; Density equals mass divided by volume.; Density ρ = m / V, with units kg/m³ or g/cm³.; The SI unit of density is kg/m³.

Showing 30 of 74. Practise the full Particle Model of Matter set →

Chemical Analysis

Practise Chemical Analysis →Practise →

Filtration: the separation method that removes insoluble solids from a liquid.
Instrumental methods: analytical techniques carried out by machines rather than by manual chemical tests.
Flame emission spectroscopy: an instrumental method used to analyse metal ions in solution.
Solvent front: the furthest point the solvent reaches up the paper before the experiment is stopped.; Damp red litmus paper turns blue near ammonia gas (because ammonia is alkaline).; Ammonia gas (NH₃) is identified by turning damp red litmus paper blue.; Calcium gives a brick-red (orange-red) flame in a flame test.; Test for carbonate (CO₃²⁻): add dilute acid; carbon dioxide is released. Pass the gas through limewater — it turns cloudy/milky, confirming CO₂ and thus carbonate.; Test for chloride (Cl⁻): acidify with dilute nitric acid, then add silver nitrate solution. A white precipitate of silver chloride confirms chloride.; Chlorine gas bleaches damp litmus paper white — used as the diagnostic test for chlorine.; The test for chlorine: damp litmus paper is bleached (turns white).; Damp litmus paper near chlorine first turns red (chlorine is acidic in water) then white (bleached).; Chromatography identifies an unknown substance by running it alongside known references; a matching Rf indicates the same compound.; Paper chromatography separates the substances in a mixture according to how far each travels up the paper with the solvent.; The test for carbon dioxide is to bubble it through limewater; the limewater turns milky if CO₂ is present.; Copper gives a green (blue-green) flame in a flame test.; Adding sodium hydroxide to a solution of copper(II) ions produces a blue precipitate of copper(II) hydroxide.; Crystallisation separates a soluble solid from its solution.; Evaporation or crystallisation separates a soluble solid from its solvent.; The liquid that passes through a filter paper is called the filtrate.; Filtration separates an insoluble solid from a liquid.; Flame tests identify metal cations by colour: Li⁺ red, Na⁺ yellow, K⁺ lilac, Ca²⁺ orange-red, Cu²⁺ blue-green.; Flame tests identify the metal ion present in a compound.; Lithium compounds give a crimson-red colour in a flame test.; Sodium compounds give a yellow colour in a flame test.; Potassium compounds give a lilac (light purple) colour in a flame test.; Calcium compounds give an orange-red colour in a flame test.; Copper compounds give a green colour in a flame test.; A flame test can only identify one metal ion in a mixture, because a strong colour (e.g. sodium yellow) masks the colours of any others present.; Adding sodium hydroxide solution to a metal-ion solution gives a coloured hydroxide precipitate: copper(II) blue, iron(II) green, iron(III) brown.

Showing 30 of 72. Practise the full Chemical Analysis set →

Using Resources

Practise Using Resources →Practise →

Aluminium: extracted by electrolysis rather than carbon reduction because aluminium is more reactive than carbon, so carbon cannot reduce its oxide.
Aluminium: extracted by electrolysis instead of carbon reduction because aluminium is more reactive than carbon.
Ammonium sulfate: made by reacting ammonia with sulfuric acid (H₂SO₄).
Chlorine: added to drinking water to kill microorganisms.
Crude oil: a finite resource.
Crude oil: classed as a finite resource because it forms over millions of years, far slower than we extract it.
Desalination: not used routinely in the UK because of very high energy cost.
Desalination: removing dissolved salts from seawater.
Distilled water: not normally used as drinking water because it has no minerals, tastes flat, and lacks beneficial calcium and magnesium.
Finite resources: used faster than they form; renewable resources replenish naturally.
Zinc: used in galvanising iron.
Balanced Haber-process equation: N₂ + 3H₂ ⇌ 2NH₃.
Iron: extracted in a blast furnace, where carbon (coke) reduces iron oxide at high temperature, releasing molten iron.
Iron: extracted from iron oxide by reduction with carbon in a blast furnace.
Marketing campaign reach: NOT a stage in a life cycle assessment (the genuine stages are raw-material extraction, manufacturing, use, disposal).
LCAs: not fully objective because some impacts are hard to quantify in numbers (allocation, weighting).
Potable water: water that is safe to drink.
Potable water: safe to drink and may contain dissolved minerals; pure water is only H₂O.
Renewable resources: replenished as fast or faster than they are used.
Starch-based plastics: considered renewable because they are made from crops that can be regrown, unlike oil-based plastics.; Aluminium does not corrode away even though it is reactive because a thin oxide layer (Al₂O₃) forms on its surface and prevents further oxidation.; Ammonia from the Haber process is mainly used to make nitrogen fertilisers.; Ammonium nitrate (NH₄NO₃) is a common nitrogen-rich fertiliser, made by reacting ammonia with nitric acid.; Industrial route: NH₃ is oxidised (Ostwald process) to HNO₃; then NH₃ + HNO₃ → NH₄NO₃.; Painting and oiling iron prevent rusting by acting as physical barriers that keep water and oxygen away from the metal.; Bioleaching uses bacteria to extract metals from low-grade ores by producing an acidic leachate that dissolves the metal.; Bioleaching uses bacteria to extract metals from low-grade ores.; Coating iron with oil or paint prevents rust by blocking water and oxygen from reaching the iron surface.; Distillation turns salty water into drinking water: heat to boiling, then condense the steam into a separate container.; Examples of finite resources: crude oil, metal ores. Examples of renewable resources: timber, cotton, wool.

Showing 30 of 70. Practise the full Using Resources set →

Atomic Structure

Practise Atomic Structure →Practise →

Activity: measured in becquerels (Bq), where 1 Bq is one decay per second.
Alpha radiation: dangerous if inhaled or ingested because the alpha source sits inside the body where the strong ionisation directly damages cells.
Alpha particles: large (2 protons + 2 neutrons), carry a 2+ charge, and are strongly ionising — they lose energy quickly to surrounding atoms, so they only travel a few cm in air and are stopped by paper or skin.
Alpha particles: the most ionising type of nuclear radiation but have the shortest range in air.
Alpha radiation: stopped by a sheet of paper.
Background radiation: the low-level ionising radiation that is always present around us, from natural and artificial sources.
Activity: measured in becquerels (Bq), where 1 Bq = one decay per second.
Beta particles: high-speed electrons emitted from the nucleus.
Beta radiation: stopped by a thin (≈ 5 mm) sheet of aluminium.
Nuclear fission: the splitting of a large, unstable nucleus (e.g. U-235) into two smaller nuclei, releasing neutrons and energy.
Fusion: difficult on Earth because positive nuclei repel each other (electrostatically), so extreme temperature and pressure are required to bring them close enough to fuse.
Nuclear fusion: the energy source of the Sun and other stars.
Gamma rays: electromagnetic radiation with very high penetrating power and low ionising power.
Gamma rays: used in radiotherapy to kill cancer cells.
Gamma radiation: used to sterilise medical equipment because it passes through sealed packaging and kills bacteria inside.
Medical tracers: radioisotopes that emit gamma radiation, which exits the body and can be detected by cameras outside.
Half-life: the time taken for the number of radioactive nuclei (or the activity / count rate) in a sample to halve.
Radioisotope's half-life: fixed — it cannot be changed by temperature, pressure, or chemical state.
Radioactive decay: random for any individual nucleus, but statistically reliable over a large sample of nuclei.; An alpha particle (helium nucleus) carries a charge of +2.; Alpha decay reduces the mass number by 4 and the atomic number by 2.; Domestic smoke detectors use a small alpha source (e.g. americium-241) that ionises air inside a detector chamber; smoke disrupts the current and triggers the alarm. Alpha is preferred because it can't penetrate the detector casing.; When measuring a radioactive source, the background count rate must be subtracted from the total measured count to find the source's true activity.; The typical UK background-radiation dose is about 2.7 millisieverts (mSv) per year — well below the level that causes detectable harm.; In beta decay the element changes because the atomic number increases by one (a neutron becomes a proton).; Beta-minus decay leaves the mass number unchanged but increases the atomic number by 1.; Carbon-14 has a half-life of about 5,730 years; it is taken up by living organisms and decays predictably after death, allowing radiocarbon dating of once-living material.; A chain reaction in a fission reactor is when released neutrons trigger further fissions, sustaining the reaction.; Control rods absorb neutrons to control the rate of fission.; The chain reaction in a reactor is controlled by control rods (often boron) that absorb excess neutrons.

Showing 30 of 55. Practise the full Atomic Structure set →

Chemistry of the Atmosphere

Practise Chemistry of the Atmosphere →Practise →

Sulfur dioxide: the pollutant that causes acid rain.
Carbon footprint: the total greenhouse-gas emissions across the life cycle of an activity or product.
Carbon offsetting: paying for activities that absorb the same amount of CO₂ as you have emitted.
Carbon footprint: the total greenhouse gases produced by an activity or product.
Carbon monoxide: a colourless pollutant that binds far more strongly than oxygen to haemoglobin, reducing oxygen transport.
Carbon monoxide: produced by incomplete combustion of carbon-containing fuels when the oxygen supply is limited.
Today's atmosphere: approximately 78% nitrogen, 21% oxygen, 1% argon, and 0.04% carbon dioxide.
Carbon offsetting: controversial because the reductions claimed may not reliably match the emissions they're meant to cancel.
Acid rain: caused by sulfur dioxide and nitrogen oxides dissolving in water vapour to form sulfuric and nitric acids.; Argon makes up most (~0.93 %) of the remaining 1 % of air.; The Earth's earliest atmosphere formed about 4 billion years ago, as the planet itself was still cooling.; Carbon capture and storage (CCS) separates CO₂ from power-station flue gas and injects it into deep geological formations.; Carbon capture and storage (CCS) can reduce industrial carbon footprints by trapping CO₂ before it reaches the atmosphere.; Individual actions that reduce a carbon footprint include flying less, eating less meat, insulating the home, and using public transport.; Reducing meat consumption and flying less are among the actions that most reduce an individual's carbon footprint.; Carbon monoxide forms from incomplete combustion and binds far more strongly than oxygen to haemoglobin, reducing oxygen transport.; Both carbon dioxide and methane are greenhouse gases that contribute to a carbon footprint.; CO₂ levels fell as the oceans cooled enough to dissolve large amounts of CO₂.; The proportion of carbon dioxide in today's atmosphere is less than 1 % (about 0.04 %).; CO₂ was locked into rock as limestone (calcium carbonate from marine shells) and into fossil fuels (from photosynthesising plants and plankton that died and were buried).; Two parallel processes reduced atmospheric CO₂: dissolution in oceans, and photosynthesis followed by burial of biomass.; Consequences of global warming include rising sea levels from melting polar ice and thermal expansion, and more frequent extreme weather events.; Photosynthesising cyanobacteria began producing oxygen around 2.7 billion years ago, leading to the Great Oxygenation Event ~2.4 billion years ago.; Deforestation contributes to rising atmospheric CO₂ because fewer trees remain to absorb CO₂ via photosynthesis.; Earth's earliest atmosphere (about 4 billion years ago) was mainly carbon dioxide and water vapour, with small amounts of methane, ammonia, and very little oxygen.; Oxygen levels rose on early Earth because photosynthesising cyanobacteria evolved, used CO₂ and released O₂ as a by-product.; Burning fossil fuels (coal, oil, natural gas) for electricity, heat, and transport is the largest human source of atmospheric CO₂.; Greenhouse gases absorb outgoing long-wavelength (infrared) radiation emitted by Earth's surface and re-radiate it in all directions, trapping heat in the lower atmosphere.; Switching to a heat pump and a renewable electricity tariff is among the actions that most reduce the carbon footprint of a household.; A product's carbon footprint includes emissions from manufacture, transport, use, and disposal.

Showing 30 of 51. Practise the full Chemistry of the Atmosphere set →

Rate and Extent of Chemical Change

Practise Rate and Extent of Chemical Change →Practise →

Catalyst: a substance that speeds up a reaction without being used up.
Catalyst: not used up during a chemical reaction.
Catalysts: important in industry because they speed up reactions at lower temperatures, saving energy and cost.
Catalysts: important in industry because they save energy and time, increasing profit.
Collision theory: the theory that explains how reactant collisions lead to a reaction.
Enzymes: the biological catalysts that speed up reactions in living things.
Enzymes: the biological catalysts in living organisms.
Gas syringe: used to measure the volume of gas produced in a rates-of-reaction experiment.
Dependent variable: the volume of gas produced (or the loss in mass) over time.
Reversible reaction: shown with the symbol ⇌ instead of →.; A catalyst provides an alternative reaction pathway with a lower activation energy; reactants find a route that requires less energy to reach the transition state.; A catalyst increases the rate of both the forward and reverse reactions in a reversible reaction by the same amount, so the equilibrium position is unchanged.; A catalyst speeds up a reaction by providing an alternative reaction pathway with a lower activation energy.; A catalyst speeds up a reaction without being used up — it lowers the activation energy and can be recovered chemically unchanged at the end.; Catalysts do not appear in the overall reaction equation (they are usually written above the arrow).; Colorimetry measures how much light is absorbed by a coloured solution.; Increasing concentration in solution increases rate because more particles per unit volume means more frequent collisions.; Increasing concentration speeds up a reaction because particles collide more frequently.; Increasing the concentration of a reactant shifts the equilibrium toward the products (and vice versa).; Increasing the concentration of a reactant in solution increases the reaction rate because more reactant particles per unit volume means more successful collisions per second.; At dynamic equilibrium, the forward and reverse reactions are both still occurring, but at equal rates, so net concentrations stay constant.; If the forward reaction is endothermic, raising the temperature favours the forward direction, increasing yield.; If the forward reaction is exothermic, the reverse reaction is endothermic, with the same magnitude of energy change.; Dynamic equilibrium can only be reached in a closed system, where reactants and products cannot escape.; If the forward reaction is exothermic, raising the temperature shifts equilibrium backwards (the endothermic direction), decreasing yield.; Gas production rate can be measured using a gas syringe or an inverted measuring cylinder.; Two common methods for measuring the rate of a gas-producing reaction are: gas syringe volume against time, and mass loss on a balance.; Le Chatelier's principle: if a system at equilibrium is disturbed, the equilibrium shifts to oppose the change.; Rate can be measured by mass loss when a gas is released from the reaction vessel.; Using powder instead of lumps increases rate because more particles are exposed at the surface, giving more collisions per second.

Showing 30 of 47. Practise the full Rate and Extent of Chemical Change set →

Energy Changes

Practise Energy Changes →Practise →

Activation energy: shown as a hump on a reaction profile.
Activation energy: the minimum energy needed for a reaction to occur.
Bond energies: measured in kilojoules per mole (kJ/mol).
Breaking bonds: endothermic; making bonds is exothermic.
Activation energy: the minimum energy colliding particles must have to react.
Reaction: exothermic when the energy released by making bonds is greater than the energy needed to break bonds.
Fuel cells: cleaner than petrol engines because they produce only water (no CO₂, no particulates) at the point of use.
Polystyrene cup: used in calorimetry instead of a metal beaker because it is a good insulator and minimises heat loss to the surroundings.; Overall energy change = energy to break bonds − energy released forming bonds.; Breaking chemical bonds requires energy (endothermic step); forming bonds releases energy (exothermic step).; Breaking chemical bonds requires (absorbs) energy; forming bonds releases energy.; A calorimetry experiment measures the heat energy released or absorbed in a chemical reaction by recording the temperature change of the solution.; The heat energy change in calorimetry is calculated using Q = mcΔT (mass × specific heat capacity × temperature change).; Catalysts affect activation energy by providing an alternative reaction path with a lower activation energy.; On an energy profile diagram, a catalyst lowers the activation energy peak by providing an alternative reaction pathway.; A catalyst lowers activation energy by providing an alternative reaction pathway.; Cold packs use endothermic reactions to absorb heat from the surroundings.; ΔH = (sum of bond energies broken) − (sum of bond energies formed).; Most reactions need activation energy even if exothermic overall because reactant bonds must first be broken before new bonds can form.; On an energy profile diagram for an exothermic reaction, the activation energy is the energy difference from reactants up to the peak — the minimum energy required to react.; On an energy profile diagram, an endothermic reaction has products at a higher energy level than reactants.; On a reaction profile, an endothermic reaction is shown with products higher in energy than reactants.; In an endothermic reaction the temperature of the surroundings decreases because energy is absorbed from them.; In an endothermic reaction, the overall energy change ΔH is positive.; An energy profile diagram shows the energies of reactants and products and the activation energy between them.; Everyday exothermic reactions include combustion, hand warmers (iron oxidation), neutralisation, and respiration; endothermic examples include cold packs, photosynthesis, and thermal decomposition.; For an exothermic reaction, ΔH is negative.; In an exothermic reaction, the products have less energy than the reactants.; In an exothermic reaction the temperature of the surroundings increases because energy is transferred to them.; Exothermic reactions release energy (temperature rises); endothermic reactions absorb energy (temperature falls).

Showing 30 of 45. Practise the full Energy Changes set →

Working Scientifically

Practise Working Scientifically →Practise →

Accuracy: how close a measured value is to the true value.
Anomalous result: a point that does not follow the trend of the other points.
Control experiment: an identical experiment run without the independent variable, used for comparison.
Control variables: the variables kept the same throughout the experiment.
Dependent variable: the variable that is measured as the outcome of the experiment.
Independent variable: the variable that the experimenter deliberately changes.
Mean: found by adding all the values together and dividing by the number of readings.
Observation: something you directly see, hear or measure (e.g. fizzing, a colour change, a solid forming) — not the explanation of why it happens or a vague "a reaction occurred".
Precision: how close repeated measurements are to each other.
Random error: unpredictable variation that affects readings differently each time.
Rate: inversely proportional to the time taken, so if the time halves (e.g. 24 s to 12 s) the rate doubles — a factor of 2 increase.
Random errors: reduced by taking more repeat measurements and calculating the mean.
Results: reliable (repeatable) if repeating the experiment gives consistent, similar results.
Standard deviation: a measure of how spread out the values in a dataset are around the mean.
Systematic error: a consistent error that affects all measurements in the same way (often the same size and direction).
Experiment: valid if it tests what it claims to test, with no confounding (uncontrolled) variables.
Control variables: kept constant so that only the independent variable can affect the dependent variable.
Repeat measurements: taken to identify anomalies and to calculate a more reliable mean.
Independent variable: plotted on the x-axis (horizontal).
Dependent variable: plotted on the y-axis (vertical).; A balance that always reads 0.5 g too high is a systematic error — all readings are shifted by the same amount.; A categoric (label) variable such as colour is plotted as a bar chart; a continuous (numerical) variable such as wavelength is plotted as a line graph.; A directly proportional relationship shows as a straight line passing through the origin.; On a distance–time graph the gradient represents speed (or velocity).; Anomalous results should be identified and excluded when drawing the line of best fit and calculating means.; In a fair test only the independent variable is changed; all other variables are controlled.; The gradient of a straight-line graph = change in y ÷ change in x.; For the same absolute uncertainty (±0.5 cm), a larger measurement (50.0 cm) has a smaller percentage uncertainty than a smaller one (5.0 cm).; A line of best fit is a line or curve drawn as close as possible to all the plotted points, showing the trend.; Percentage change = (change ÷ original value) × 100.

Showing 30 of 42. Practise the full Working Scientifically set →

Bioenergetics

Practise Bioenergetics →Practise →

Chlorophyll: the green pigment in chloroplasts that absorbs light energy for photosynthesis.
Limiting factor: a factor whose low level prevents the rate of photosynthesis from increasing further.
Oxygen: released as a by-product of photosynthesis.
Oxygen debt: the extra oxygen consumed after exercise to break down accumulated lactic acid.
Water temperature: kept constant because temperature affects enzyme activity and would otherwise act as an uncontrolled variable.
Dependent variable: the number of oxygen bubbles per minute (or the volume of gas collected).
Photosynthesis: endothermic — it takes in energy (from light) and stores it as chemical energy in glucose.; Balanced symbol equation for aerobic respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.; Aerobic respiration releases more energy per glucose molecule than anaerobic respiration.; Aerobic respiration uses oxygen and releases much more energy per glucose molecule than anaerobic respiration.; Aerobic respiration: glucose + oxygen → carbon dioxide + water (+ energy released).; Anaerobic respiration releases less energy because glucose is only partially broken down without oxygen.; Photosynthesis takes place inside chloroplasts, organelles found in the cells of green plant tissue (mainly leaves), not in root cells.; Rate increases with CO₂ concentration up to a point where another factor becomes limiting and the rate plateaus.; Above approximately 40–45°C the enzymes catalysing photosynthesis begin to denature, so the rate falls sharply.; Light intensity falls with the square of distance from the source (inverse square law) — so doubling the distance quarters the intensity.; Until another factor becomes limiting, the rate of photosynthesis is roughly proportional to light intensity.; The three main factors that limit the rate of photosynthesis are light intensity, carbon dioxide concentration, and temperature.; In human muscle cells, anaerobic respiration breaks glucose down to produce lactic acid.; Oxygen debt after vigorous exercise is the extra oxygen needed to oxidise the lactic acid that has built up.; In a light-intensity photosynthesis experiment the independent variable is the distance of the light source from the pondweed.; Word equation: carbon dioxide + water → glucose + oxygen (light is the energy input, not a reactant).; The pondweed (Cabomba/Elodea) practical measures the rate of photosynthesis by counting oxygen bubbles released.; Plants use glucose from photosynthesis for respiration, storage as starch, and for building amino acids, proteins, fats and cellulose.; Anaerobic respiration in yeast produces ethanol and carbon dioxide (fermentation).; Anaerobic respiration in yeast does not produce lactic acid; lactic acid is the product in animal muscle.

Space Physics

Practise Space Physics →Practise →

Natural satellite: a naturally occurring body in orbit (e.g. the Moon orbiting Earth), whereas an artificial satellite is a human-made object placed in orbit (e.g. a communications satellite).
Light from distant galaxies: observed to be shifted towards the red (longer-wavelength) end of the spectrum, an effect called red shift.
Red shift: evidence that the universe is expanding and supports the Big Bang theory, that the universe began from a small, hot, dense region.
Moon: a natural satellite that orbits a planet, and our Solar System lies within the Milky Way galaxy.
Elements heavier than iron: formed only during the explosion of a supernova, then scattered into space.; Gravity provides the centripetal force that keeps a satellite or planet in a circular orbit, acting towards the centre of the orbit.; An object in a circular orbit moves at a constant speed but its velocity constantly changes because its direction is always changing.; For a stable orbit at a fixed radius there is only one possible speed; if the speed increases the orbital radius decreases, so a faster satellite orbits closer in.; The more distant a galaxy is, the greater its red shift, meaning more distant galaxies are moving away from us faster.; The cosmic microwave background radiation (CMBR) is low-temperature radiation from all directions and is the main evidence supporting the Big Bang theory.; Dark matter and dark energy are not understood, but were proposed to explain observations of how galaxies move and how the expansion of the universe is changing.; Our Solar System contains one star, the Sun, which has eight planets orbiting it.; The Sun formed from a nebula, a cloud of dust and gas pulled together by gravity.; As well as planets, the Solar System contains dwarf planets such as Pluto.; A star begins to form when gravity pulls together a cloud of dust and gas called a nebula, which contracts into a protostar.; A protostar becomes a main sequence star when its core gets hot enough for nuclear fusion of hydrogen into helium to begin.; During the main sequence stage a star is stable because the outward pressure from fusion balances the inward force of gravity.; A star much more massive than the Sun ends its life by exploding as a supernova, leaving a neutron star or, if massive enough, a black hole.; A star about the size of the Sun expands into a red giant, then collapses to form a white dwarf at the end of its life.

Required Practicals

Practise Required Practicals →Practise →

Aseptic technique: a set of methods used to prevent contamination of cultures by unwanted microorganisms.
Petri dish lid: fixed with two or three short pieces of tape but is NOT sealed all the way round, so that oxygen can enter and harmful anaerobic bacteria are not encouraged to grow.
Burette volumes: read at eye level from the bottom of the meniscus, to the nearest 0.05 cm³, to avoid parallax error.
Concordant results: titre readings that agree within 0.10 cm³ of each other; only concordant titres are averaged.
End point: reached when the indicator permanently changes colour, showing neutralisation is complete.
Conical flask: placed on a white tile during a titration so the indicator's colour change at the end point can be seen clearly.; In aseptic technique the inoculating loop is sterilised by holding it in a Bunsen flame until it glows red hot, and the Petri dish lid is lifted as little as possible to stop airborne microbes contaminating the culture.; In school labs agar plates are incubated at no more than 25 °C to prevent the growth of pathogens that could harm humans.; A clear zone (zone of inhibition) around a disc shows that the antiseptic or antibiotic has stopped bacteria growing there, i.e. it is effective.; A larger zone of inhibition indicates that the antibiotic is more effective at killing or inhibiting that bacterium.; The effectiveness of an antibiotic is measured from the diameter (or area) of the zone of inhibition around the disc.; All equipment is sterilised before the practical to prevent contamination from unwanted microorganisms.; Phenolphthalein and methyl orange are the indicators used for acid–alkali titrations (they give a sharp single colour change, unlike universal indicator).; When 25.0 cm³ of NaOH is neutralised by 20.0 cm³ of 0.5 mol/dm³ HCl (1:1 ratio), moles HCl = 0.5 × 0.020 = 0.010 mol, so the NaOH concentration = 0.010 ÷ 0.025 = 0.4 mol/dm³.; A titration finds the exact volume of acid needed to neutralise a known volume of alkali (and hence its concentration).; The first "rough" titration gives only an approximate end point and is discarded; the accurate concordant readings are used for the mean titre.

Try it for four weeks. Free.

One school. Unlimited classes. No card limit. No teacher limit. If your students aren't practising daily by the end of the trial, you owe us nothing.

Start free trial Talk to us first