JC Science key terms

A testable, specific prediction about what will happen in an investigation, based on prior knowledge. It must be stated so that evidence collected could show it to be wrong.

Any factor in an investigation that can change or be changed. Scientists identify the independent variable they alter, the dependent variable they measure, and others they hold constant.

An investigation in which only the independent variable is changed while all other relevant factors are kept the same, so any effect measured can be attributed to that one cause.

A comparison setup or group in which the treatment is absent or a known standard is used, allowing the effect of the tested factor to be judged against a baseline.

The extent to which repeated measurements or trials give consistent results. Reliability is improved by repeating readings and calculating a mean, reducing the influence of random variation.

How close a measured value is to the true value. Accuracy differs from precision: a set of readings can agree closely with each other yet all be far from the correct value.

A result that does not fit the pattern shown by the other data. Anomalies are identified and may be excluded from a mean, but the reason for them should be investigated.

A statement judging whether the evidence supports the hypothesis, supported by the data collected. A good conclusion also notes limitations and suggests further work.

The smallest unit of life, bounded by a membrane and containing genetic material and cytoplasm. Some organisms are single cells; others are built from many specialised cells.

A protein that speeds up a specific chemical reaction in living things without being used up. Enzymes work best at particular temperatures and pH values and are denatured by extremes.

The breakdown of large food molecules into smaller, soluble ones that can be absorbed into the blood. It involves mechanical action and chemical action by enzymes.

The net movement of particles from a region of higher concentration to a region of lower concentration, driven by random motion. It needs no energy input from the cell.

The controlled release of energy from food molecules inside cells, using oxygen in aerobic respiration and producing carbon dioxide and water. Anaerobic respiration releases less energy without oxygen.

The transport of blood around the body by the heart and blood vessels, delivering oxygen and nutrients to cells and carrying away carbon dioxide and other wastes.

The removal from the body of waste products made by cells, such as carbon dioxide and urea. Excretion is different from egestion, which removes undigested food.

A section of DNA on a chromosome that carries the instructions for a particular characteristic or protein. Genes are passed from parents to offspring during reproduction.

One of the alternative versions of a gene. An organism inherits two alleles for each gene, one from each parent, and their combination determines the observable characteristic.

Describing an allele whose effect appears in the phenotype even when only one copy is present. A recessive allele shows only when two copies are inherited.

The passing of genetic information from parents to offspring through gametes, explaining why offspring resemble their parents but are not identical to them.

A feature or behaviour that improves an organism's chance of surviving and reproducing in its environment. Adaptations arise over generations through natural selection.

The process by which individuals with variations better suited to their environment survive and reproduce more successfully, so those inherited features become more common in later generations.

A community of living organisms interacting with each other and with the non-living parts of their environment, such as soil, water and light, within a defined area.

A diagram showing the transfer of energy from one organism to the next, beginning with a producer and ending with a top predator. Arrows show the direction of energy flow.

An organism, usually a green plant or alga, that makes its own food by photosynthesis. Producers form the base of every food chain and supply energy to consumers.

The variety of living things present in an area, measured as the number of different species and the range of variation within them. High biodiversity generally makes ecosystems more stable.

The particular place where an organism lives, providing the food, water, shelter and conditions it needs. Loss of habitat is a major cause of species decline.

A pure substance made of only one kind of atom, which cannot be split into simpler substances by chemical means. Elements are listed in the periodic table.

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

A substance formed when two or more different elements are chemically joined in fixed proportions, for example water. A compound has properties unlike those of its elements.

Two or more substances combined without chemical bonding, in any proportions, which can usually be separated by physical methods such as filtration or distillation.

A separation technique that uses a filter to trap insoluble solid particles while a liquid or gas passes through, separating an insoluble solid from a liquid.

A separation technique that boils a liquid mixture and condenses the vapour, used to separate a solvent from a solution or to separate liquids with different boiling points.

A substance that releases hydrogen ions in water, has a pH below 7, turns blue litmus red and reacts with bases to form a salt and water.

A substance that reacts with an acid to form a salt and water. A soluble base is called an alkali and has a pH above 7.

The reaction between an acid and a base that produces a salt and water, bringing the pH towards 7. It is used to treat acid spills and to reduce soil acidity.

A scale from 0 to 14 measuring how acidic or alkaline a solution is. Values below 7 are acidic, 7 is neutral and values above 7 are alkaline.

How quickly reactants are used up or products are formed during a chemical change. It increases with higher temperature, greater concentration, smaller particle size or a catalyst.

A substance that increases the rate of a chemical reaction without being used up itself. In living organisms, biological catalysts are called enzymes.

A chemical reaction that releases energy to the surroundings, usually as heat, so the temperature rises. Combustion and neutralisation are common examples.

A push or pull acting on an object, measured in newtons. Forces can change an object's speed, direction or shape, and they occur in pairs.

The force of gravity acting on an object, measured in newtons and equal to mass multiplied by gravitational field strength. Weight changes with location; mass does not.

The capacity to do work or cause change, measured in joules. Energy can be transferred or stored in different forms but is conserved in any closed system.

The energy transferred when a force moves an object through a distance, calculated as force multiplied by distance moved in the direction of the force.

The rate at which energy is transferred or work is done, measured in watts. One watt equals one joule of energy transferred each second.

The rate of flow of electric charge around a circuit, measured in amperes. Current is the same at every point in a single series loop.

The energy transferred per unit charge as charge passes through a component, measured in volts. It is also called potential difference.

A measure of how strongly a component opposes the flow of current, measured in ohms. For a fixed resistor, voltage equals current multiplied by resistance.

The change in direction of a wave as it passes from one medium into another where its speed differs, for example light bending as it enters glass or water.

The number of complete waves passing a point each second, measured in hertz. Higher frequency means higher pitch for sound and different colour for light.

A disturbance that transfers energy from place to place without transferring matter. Waves have wavelength, frequency and amplitude, and may be transverse or longitudinal.

The day-to-day state of the atmosphere in a particular place, including temperature, rainfall, wind and cloud cover. Weather changes over hours and days.

The average pattern of weather in a region over many years. Climate is determined by factors such as latitude, altitude, distance from the sea and prevailing winds.

The warming of a planet's surface as certain gases in the atmosphere absorb and re-emit outgoing infrared radiation. Human emissions are intensifying it and changing climate.

The Sun and everything bound to it by gravity, including eight planets, dwarf planets, moons, asteroids and comets. Planets orbit the Sun in elliptical paths.

Meeting present needs without compromising the ability of future generations to meet theirs, by conserving resources, reducing pollution and protecting biodiversity.

Moral principles used to judge whether a scientific or technological application is right or acceptable, weighing benefits against risks to people, animals and the environment.