GLOSSARY OF SCIENTIFIC TERMS

absolute zero. The lowest theoretical temperature (0K = -273.16°C) where all molecular activity ceases.
acceleration. Rate of change of velocity.
acid. A compound that yields hydrogen ions (H+) when in aqueous solution. Acids have a sour taste and turn blue litmus red.
activation energy. The energy required to initiate a chemical reaction.
adiabatic system. A system that neither gains or looses heat.
alcohol. Organic compound used in gums, resins, dyes and perfumes. Fermentation produces ethanol not alcohol.
alkali. A base that is soluble in water.
allele. Gene variant.
allotrope. Element with more than one natural form.
alloy. A substance formed by the combination of two or more elements, at least one of which must be a metal.
amino acids. Carbon, hydrogen, oxygen and nitrogen compounds the composition of which are determined by genes.
anion. A negative ion.
atomic number. The number of protons in an atom..
atomic symbol. The letters representing each of the elements.
atomic weight. The average weight of an atom.
atoms. Composite particles of protons, neutrons and electrons. The smallest part of a substance that can take part in a chemical reaction. Click here for more information.
baryon. A three quark hadron. The most common baryons are protons and neutrons.
base. A compound that yields hydroxide (OH- ) ions when in aqueous solution. Bases have a bitter taste, feel greasy and turn red litmus blue.
biosynthesis. The production of cellular material.
boiling point. The temperature at which a liquid turns to a vapour.
bond. A chemical link between atoms.
capacitance. The ability to store an electric charge.
carbohydrates. The major energy source within plants and animals: sugars, starches and glucose polymers.
carbon. The basic element in all organic compounds.
catalyst. A substance that reduces the activation energy of a reaction.
cation. A positive ion.
cell. The smallest independent part of an organism.
chain reaction. Polymerisation initiated by the bonding of a free radical with a monomer.
charge. The amount of unbalanced electricity in a system. Either positive or negative.
chemical equation. The mathematical representation of a chemical reaction.
chemical (empirical) formula. The ratio of elements in a substance. For example: the chemical formula of common salt is NaCl, sodium and chlorine in a ratio of 1:1.
chemical reaction. The transformation of substances by the rearrangement of their atoms.
chromosomes. DNAmolecules that contain the set of instructions required to build and maintain cells.
compound. A substance containing more than one element.
conduction. Heat or electricity transfer through molecular interaction, eg: heat passing along a metal bar.
convection. Heat transfer through the movement of a fluid, eg: warm air rising.
coulomb attraction. Electrostatic attraction between bodies of opposite charge
covalent bond. A bond formed between atoms that share electrons.
crystal. Solid substance with a regular geometirc arrangement of atoms.
cytosol. Jelly-like substance within cells.
density. The mass per unit volume in a substance.
diffraction. The deviation in the path of a wave that encounters the edge of an obstacle.
diffusion. The random movement of moleculeswithin a fluid.
DNA: Deoxyribonucleic acid. Twisted helical polymer chains. See chromosomes.
elasticity. The ability of a body to regain its original shape after deformation.
electric current. A flow of electrons through a conductor, the size of the current is proportional to the rate of electron flow.
electrons. Negatively charged atomic particles.
electromagnetic waves. Waves with both an electric and magnetic component. They are: radio, micro, infra-red, visible light, ultraviolet, X and gamma rays.
electrolyte. An ion solution that is an electrical conductior.
element. A substance composed of atoms all with the same atomic number. A substance that cannot be split chemically into smaller substances.
endothermic reaction. A reaction in which heat is absorbed ie: melting or boiling.
energy. The capacity to do work. Work is done by transferring energy from one form to another. For example the chemical energy in a fuel is converted to thermal energy as it burns. See also Laws of Thermodynamics.
entropy. The state of disorder in a thermodynamic system: the more energy the higher the entropy.
enzymes. Biological catalysts, proteins that control specific processes within the body.
equilibrium. A stable situation in which products and reactants are balanced.
evaporation. The change of state of a substance from a liquid to a gas below its boiling point.
evolution. Natural selection, the survival of the fittest, is the driving force behind evolution and is measured by a species viability and fecundity. Governed by Darwin's theory of evolution by natural selection:
1. The distinguishing features (characters) of an organism may affect it fitness.
2. The design of an species (its morphology) differs within a population and may improve its fitness.
3. An organism may be susceptible to a lack of vital resources, predation and disease reducing its fitness.
4. The characters that improve fitness must be inherited. Individuals that inherit these characters will survive at the expense of those who do not.
5. Mutation is essential for evolution: the inheritance of non-standard genes that improve fitness.
Note: Fitness is the ability to survive and reproduce, not necessarily a measure of physical fitness.
exothermic reaction. A reaction from which heat is lost eg: combustion.
fats. Molecules of fatty acids or glycerol. Used as a food store, insulation and for shock absorption.
fecundity. The ability to breed.
field. A region in space that is defined by a vector function. Common fields are: gravitational, electric and magnetic.
fission. Splitting the nucleus of an atom into smaller units.
fluid. A liquid or gas.
force. An action (transfer of energy) that will accelerate a body in the direction of the applied force. See Newtons Laws of Motion.
free radical. A highly reactive molecule used to start the production of a polymer chain.
frequency. The rate as which periodic motion repeats itself.
friction. The interaction between surfaces: a measure of the resistance felt when sliding one body over another.
fundamental particles. Those particles that are not known to contain any smaller components: leptons, quarks and gauge bosons.
fusion. 1. Change of state of a substance from a solid to a liquid. 2. The joining together of two atomic nuclei.
gametes. Sex cells (spermatozoa or ova) that carry the genes donated by each parent.
gauge bosons. Particles that mediate the transfer of energy between other particles: protons, gravitons, W and Z particles.
gene. A unit of inheritance. A section of DNA. comprising a sequence of four bases: adenine, guanine, cytosine and thymine.
genome. The collective noun for a set of genes. The human genome contains 100 000 genes.
gravity. The attraction that all bodies have for one another.
hadrons. Quark composites: mesons and baryons. Protons and neutrons are the most common hadrons.
half-life. The time taken for the level of radioactivity in an element to halve.
halogen. Highly reactive gases forming group 7 of the periodic table.
heat. The internal energy of a body (substance).
hydrocarbon. Compounds containing only hydrogen and carbon atoms.
ideal gas. One which obeys the ideal gas law. At low pressures, real gases behave like ideas gases.
inertia. Tendency of a body to remain at rest or move in straight line.
inheritance. The features of an organism are determined by a set of chromosomes. These originate in the parents and are passed on to an offspring during fertilisation. It follows then that since chromosomes are inherited, all the features of an organism must be inherited.
ion. Atom with an unbalanced electrical charge caused by the loss or gain of one or more electrons.
ionic bond. An bond formed by the electro-magnetic attraction between ions of opposite charge.
isomer. Chemical compounds with the same composition but different shapes.
isomeric structure. The shape of a molecule. The isomeric structure is determined by the order in which the atoms are bonded together.
isotope. An element that has more or less neutrons than normal. Many isotopes are radioactive.
kinetic energy. The energy possessed by a body in motion.
latent heat. The amount of energy required to change a solid to a liquid or liquid to a gas.
Laws of Themodynamics.
1. The amount of energy in the universe is fixed. It cannot be created or destroyed only changed from one state to another.
2. Heat cannot pass from a cold to a hot body. The opposite condition where heat always flows from a hot to a cold body is valid for the whole universe.
lens. Light modifier. Convex lenses focus and concave lens diffuse light waves.
leptons. Fundamental particles that are relatively non-reactive and capable of an independent existence: electrons, muons, tau particles and neutrinos.
light. The visible part of the electromagnetic spectrum: red, orange, yellow, green, blue, indigo and violet. White light is a combination of all the above colours.
magnet. A body which produces a magnetic field. All magnets are di-pole and follow the rule that like poles repel and unlike poles attract.
mass. The quantity of matter in a body.
mesons. Two quarkhadrons, the product of radioactive decay.
metals. Elements characterised by their opacity, malleability and thermal and electrical conductivity.
mitochondria. Organelles that convert glucose into energy.
molecular formula. The number and types of atom in a molecule. For example the molecular formula of methane is CH4, one atom of carbon and four atoms of hydrogen.
molecule. A group of atoms bonded together. It is the smallest part of a substance that retains the chemical properties of the whole.
moment. A rotating effect. See torque.
momentum. The product of mass times velocity. Momentum is conserved in any system of particles.
monomers. Small molecules that link together to form a polymer.
neutralization. A reaction in which the characteristics of an acid or base disappear.
neutrons. Particles with zero charge forming part of an atomic nuclei. 3 quarkhadrons.
Newtons Laws of Motion. Classical laws which enable the prediction of the path of any object from a grain of sand to entire galaxies:
1. A body will remain at rest or move with a constant velocity unless acted upon by an outside force.
2. The acceleration of a body is proportional to the applied force. This is expressed by the universal formula: Force = mass × acceleration.
3. For every action there is an equal and opposite reaction.
noble gases. Elements with zero valency. They form group 0 in the periodic table and are non-reactive.
nucleus. 1. Organelle containing the chromosomes. 2. That part of an atom containing the protons and neutrons.
organelles. Specialized organs within cells.
organic compounds. Substances that contain Carbon.
ozone. An isotope of oxygen that blocks ultra-violet radiation. Normally found in the stratosphere.
pH Scale. The strength of acids and bases. Pure water has a pH value of 7, acids have a lower value and bases higher.
phase changes. Freezing or boiling.
photo-synthesis. The conversion of water and carbon-dioxide by plants into glucose and oxygen. Light is used as an energy source.
photons. Fundamental quantum particles. It is the interaction of photons with other particles that drives the universe.
polymerisation. The repetitive bonding of small molecules (monomers) to produce large molecules (polymers).
polymers. Long chain molecules such as PVC, nylon or DNA produced by the polymerisation of monomers.
potential difference. The voltage difference between two points. Electricity flows from a high to low level of potential.
potential energy. Amount of useable energy within a body at rest.
power. Amount of work done per second.
products. The substances produced in a chemicalreaction.
proteins. Amino acid polymers with specific biological functions, especially the growth, regeneration and repair of cells.
protons. Positively charged particles forming part of atomic nuclei. 3 quarkhadrons.
quantum theory. The theory that energy can only be absorbed or radiated in discrete values or quanta. All particles are subject to quantum theory. Click here to find out more.
quarks. Fundamental particles, incapable of independent existence, that combine to form particles such as protons and neutrons.
radiation. 1. Transfer of heat between bodies without a change in the temperature of the intervening medium. 2. Any release of energy from its source.
radioactivity. The spontaneous release of energy from atomic nuclei.
reactants. The substances that take part in a chemical reaction.
refraction. The deflection of a wave as it passes from one medium to another, eg through a lens.
relative atomic mass (RAM). The mass of an atom relative to one atom of carbon. Carbon has a RAM of 12.
relativity. The relative values of time, motion, mass and energy of a body in motion. Click here for more information
reproduction. Reproduction is the process by which a new organism is produced. The first stage in the production of any organism is the fertilisation of an ova by spermatozoa (or spores on the case of plants). Fertilisation produces a single cell called a zygote which contains all the information required to build the adult organism. The progression (growth) from zygote to adult is achieved through cell division.
resistance. Opposition to current flow in a conductor.
resonance. A state where the natural frequency of a body equals an applied frequency.
respiration. The production of energy by the oxidisation of glucose.
scalar. A quantity that is defined by its magnitude only (ie energy, temperature).
simple harmonic motion. A repeating motion about a central equilibrium point (pendulum, weighted spring).
special relativity. The observable effects on a body in motion. As velocity increases, time slows down, mass increases and lengths contract.
speciation. A group of organisms that are able to interbreed all belong to the same species. It follows then that organisms that are unable to interbreed belong to separate species.
specific heat. The heat capacity of a body.
standard model. The organization and relationships between fundamental particles. Click here for more information.
strain. The deformation of a body under an applied load.
stress. The measure of the force acting on a body.
temperature. How hot one body is when compared to another.
torque. The tendency of a body to rotate under an applied force..
uncertainty. It is impossible to know exactly where something is and where it is going. This is a fundamental law of nature has a major effect on quantum theory.
valency. A measure of the reactivity of an element.
vector. A quantity that is determined by its magnitude and direction: forces and fields (see scalar).
velocity. The rate of change of distance with respect to time.
viability. The ability to survive to adulthood.
viscosity. The internal friction of a fluid, thick fluids have a high viscosity and thin fluids low.
weight. The gravitational force exerted on a mass.
work. The amount of energy transferred to a system.
zygote. A fertilised egg, the fusion of a male and female gamete.