absolute zero. The lowest theoretical temperature (0K = -273.16°C) where all molecular activity ceases.
acceleration. Rate of change of velocity.
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.
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.
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.
cation. A positive ion.
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.
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
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 molecules within 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.
electrolyte. An ion solution that is an electrical conductior.
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.
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.
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.
fusion. 1. Change of state of a substance from a solid to a liquid. 2. The joining together of two atomic nuclei.
gauge bosons. Particles that mediate the transfer of energy between other particles: protons, gravitons, W and Z particles.
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.
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.
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.
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.
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.
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.
metals. Elements characterised by their opacity, malleability and thermal and electrical conductivity.
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.
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.
organelles. Specialized organs within cells.
ozone. An isotope of oxygen that blocks ultra-violet radiation. Normally found in the stratosphere.
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.
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 chemical reaction.
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.
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.
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.
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.