GLOSSARY OF KEY TERMS
Density: How tightly packed atoms are in an object. Density is mass divided by volume.
Dependent variable: The variable in an investigation that changes because the independent variable has been changed.
Diaphragm: A large sheet of muscle below the lungs, at the bottom of the ribcage.
Diffusion: The spreading out of particles to fill the space they are in.
Digestion: The breakdown of food in the body.
Digital caliper: Used to measure small, curved objects, e.g. the diameter of pipes or coins.
Dilute solution: A solution that contains a small amount of solute dissolved in a large amount of solvent.
Diode: A component that only allows current to flow in one direction.
Disposal: Getting rid of something when it can no longer be used.
Dissipation: When energy is wasted and does not convert to a useful form.
Distance-time graph: Used to calculate an object’s speed.
Distillation: The method used to separate a liquid and a soluble solid when you want to keep the solvent (liquid) or when separating two miscible liquids (liquids that mix).
DNA: A chemical called deoxyribonucleic acid that is wrapped around a protein and makes up chromosomes.
Dominant: A dominant trait will show even if only one parent passes the gene for it on to their offspring.
Ductile: A metal that can be stretched into wire.
Ecology: The study of how communities of plants and animals interact with each other and their environment.
Ecosystem: All the communities in an area interacting with each other and their environment.
Effervescence: Bubbles of gas being produced in a liquid.
Efficiency: How well a device uses or converts the energy that flows into it.
Electron: A negatively charged subatomic particle, which orbits the nucleus of an atom.
Electron microscope: A piece of laboratory equipment that allows biologists to study cells in great detail by passing a beam of electrons through the specimen.
Electronic configuration: Describes the location of electrons in an atom.
Element: A substance that contains only one type of atom.
Embryo: The name given to the developing offspring in the early stages of pregnancy.
Endothermic: Describes a chemical reaction that takes in heat from the environment.
Energy: The ability to do work. The SI unit of energy is the joule (J).
Energy efficiency: The percentage of electrical energy that is converted to a useful form.
Energy profile diagram: A diagram showing the energy transfer that takes place in a chemical reaction.
Enhanced greenhouse effect: If the concentration of greenhouse gases in the atmosphere increases beyond the normal level, extra heat is trapped close to the Earth’s surface.
Enzyme: A protein that helps to speed up chemical reactions.
Error: A mistake that is introduced into a reading or an investigation.
Evaporation: When the particles that gain the correct amount of energy leave a surface, spread out and change state from a liquid to a gas.
Evolution: The gradual change in the inherited characteristics (controlled by genes) of a species over time.
Exhalation: Breathing out, which gives out carbon dioxide and water vapour to the atmosphere.
Exothermic: Describes a chemical reaction that gives out heat to the environment.
Extinction: When a species no longer exists.
Faeces: Undigested food and waste matter that is egested by the body.
Fertile period: The short time during the menstrual cycle when a sexually mature female body can become pregnant.
Fertilisation: The fusion of the male sperm and the female egg to form a zygote.
Filtration: The method used to separate insoluble solids from liquids.
Elements of Science 397
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