Science continuum glossary

Air resistance
Air resistance is a frictional force experienced by objects as they move through air or as air flows around them. It generally opposes the motion of the object or the air flow around it, and is created by the air rubbing on the outside surface of the object. Students often neglect its influence because it is difficult to calculate and only of significance with high relative speeds or large surface areas. It is responsible for the operation of parachutes and important in the design of aircraft and cyclone tolerant buildings.

Arteries
Arteries are muscular blood vessels in the body that transport blood away from the heart to capillaries or the lungs. Most arteries convey blood rich in oxygen or, in the case of the pulmonary arteries that carry blood from the heart to the lungs, carbon dioxide. Arteries have elastic walls that allow the pressure from the heart’s pumping to be transmitted along the artery.

Artificial light source
A luminous object which is manufactured or controlled by humans. E.g. incandescent and fluorescent light bulbs, light emitting diodes (LED’s), torches and electroluminescent devices.

Assimilation
is taking on the traits of another culture, leaving the culture of origin behind while embracing the new one.

Atmospheric pressure
Atmospheric pressure is the weight force exerted on an area by the weight of a vertical column of air rising above the surface area to the upper reaches of the Earth’s atmosphere. Sometimes referred to as ‘barometric pressure’ or simply as ‘air pressure’ it varies due to changes in local weather conditions. At sea level it is approximately equal to a weight of 1kg per square cm or 10 tonnes per square metre. We only notice the effects of this potentially very large force when the air is acting on only one side of a surface.

Atom
Atoms are a fundamental building block of matter; a small number (less than 90) of different types of atoms make up the very large number of substances we encounter. Atoms are neither created nor destroyed in (non-nuclear) physical and chemical changes – they merely rearranged, with the total number not changing. The substances we call elements are those that contain only one kind of atom. Students find it very difficult to imagine how small atoms are. Atoms are composed of more fundamental particles, the most important being electrons, protons and neutrons. The positively charged protons and the neutrally charged neutrons reside in a relatively small nucleus at the centre of the atom where nearly all the mass of an atom is concentrated.

Atomic mass
The atomic mass is the sum of the individual masses of all the protons and neutrons found in the nucleus of an atom. Because the mass of an individual atom is so small it is more convenient to express it as a relative mass using the mass of a carbon 12 atom as equivalent to 12 units of atomic mass.

Attractive force
‘Attractive force’ is a term applied to non contact forces which result in objects being ‘drawn together’. These forces may be electrostatic, magnetic or gravitational. The attractive forces between atoms and molecules that hold liquid and solid particles together are electrostatic.

Big Bang
a cosmological theory in which the expansion of the universe is presumed to have begun with a primeval explosion referred to as the ‘Big Bang’. This giant explosion around 14 billion years ago expanded rapidly, cooled and coalesced into the universe we observe today.

Biochemical
A biochemical refers to particular products of chemical reactions associated with biological functions in living organisms. It is also used as an adjective for the (typically complex) chemical reactions that occur in living things.

Blood Vessels
The blood vessels are flexible tubular canals through which blood circulates throughout the body. The blood vessels are part of the circulatory system. Arteries, veins, and capillaries are all kinds of blood vessels. Arteries carry blood from the heart to capillaries which are the smallest type of blood vessels. Capillaries have very thin walls which allow liquids and gases to exchange between cells and the blood. Veins then return blood containing wastes to organs for its removal and then on to the heart for circulation.

Brownian motion
Brownian motion is the random movement of molecules in a liquid or gas due to their thermal energy. This term is named after the botanist Robert Brown who observed the random motion of tiny pollen grains as they were nudged by their collision with water molecules.

Calorie
a unit of energy widely used to measure the chemical energy in food. It is equal to the amount of heat energy required to raise the temperature of 1 gram of water 1°C and is equivalent to 4.184 joule. Some confusion exists when this term is used in the context of food where the kilocalorie is also used, but is often written as Calorie or Cal. One Calorie (or ‘large’ calorie - capital C) is equal to one kilocalorie (or 1000 calories – small c).

Capillaries
Capillaries are the smallest of a body's blood vessels which connect arteries and veins. They are important for the exchange of gases, such as oxygen and carbon dioxide, and other substances between the blood and cells. The walls of capillaries are very thin and are often composed of only a single layer of cells. This allows molecules such as oxygen and water and waste products such as carbon dioxide and urea to pass through them. This property of capillary walls is critical to the role that the circulatory system has in collecting and transporting different substances to and from different parts of our bodies.

Characteristic
A characteristic is a distinguishing feature or quality of an organism that helps to define, identify or describe it.

Chemical bond
A chemical bond is a non contact force holding atoms together in a combined state. This force may result from the attraction of opposite charges (ionic bond), the magnetic and electrical attraction of shared electrons (covalent bond), or a combination of these attractions.

Chromosome
Chromosomes are thread-like bodies, usually x shaped and usually found in pairs in the nuclei of living cells. They carry genetic information that determines the inherited characteristics of an organism. Chromosomes consist of deoxyribonucleic acid (DNA) and proteins and each chromosome can be regarded as comprising a number of genes. Each species can be characterised by the number of chromosomes that its cells contain, for example, humans usually have 46 chromosomes per cell (23 pairs).

Circulatory system
The circulatory system contains the blood vessels (arteries, veins and capillaries) and heart which moves blood throughout the body. Among other things this system provides oxygen and nutrients to cells and aids them in the removal of waste products, fighting infection and general repair.

Closed system
A closed system is a continuous predetermined or prescribed pathway. It may be useful to think of the analogy of trains on a railway line where the trains move around the same track and goods can be transported around the pathway. In the human body the circulatory system is an example of a closed system. The blood travels along a defined, closed pathway of tubular blood vessels comprising a complex system of arteries, capillaries and veins. The blood is contained within this connected system and circulates continuously, never leaving this pathway. Some invertebrate animals such as molluscs, arthropods (such as insects and spiders) have an 'open' circulatory system where organs are bathed in a surrounding fluid which is not contained by tubular vessels. In such an open circulatory system there is no predetermined pathway and there is no distinction between blood and other tissue fluid.

Colloid
A colloid is formed by the suspension of droplets of liquid or solid particles which are small enough to be kept in constant motion by the molecular movement of the suspending medium. The particles may be suspended in either a liquid or a gas and will not settle out of suspension under the action of gravity alone. Examples are smoke, milk, mayonnaise, whipped cream and aerosols.

Combustion
Combustion describes the process of burning (rapid oxidation) in which oxygen is chemically combined with a fuel to release energy in the form of light and heat. Combustion occurs in the gaseous state for example, when a candle or wooden log is burning, for example, the reaction (and hence the flame) is always just above the fuel. The variation in ignition temperatures of different fuels reflect the different temperatures needed to get either the fuel or (in cases such as wood) decomposition products of the fuel into the gas state.

Conductor
any material that does allow electricity to flow through it easily because the electrons in their atoms are able to easily from atom to atom. Most metals are very good conductors. A poor electrical conductor is said to be a good electrical insulator.

Compound
A compound is formed by the combination of two or more atoms from different elements in a fixed proportion. The elements in a compound combine to lose their individual properties and to form a substance with new physical and chemical properties.

Compression force
The application of a compression force to an object causes it to become squashed or compacted. Some solid materials like stone and ceramics are able to withstand very large compressive forces with very little measurable deformation which make them a suitable building material for the construction of high walls and columns.

Concentrate
A concentrate is a mixture that has had the majority of its base component, or solvent, removed. Typically this will be the removal of water from a solution or suspension such as the removal of water from fruit juice. The term is also used to describe the removal of much of the unwanted solid matter from a mined ore. The benefit of producing a concentrate is that this reduces the weight of the ore for transportation.

Consumer
The term consumer is used in biology to refer to an organism that cannot produce its own sources of energy, but feeds on other living organisms. Animals and parasitic plants would be considered consumers. In a food chain, herbivores (animals that eat green plants) are primary consumers and carnivores (that eat herbivores or other carnivores) are secondary consumers.

Continuous view of matter
A continuous view of matter advocates that matter remains divisible into smaller and smaller quantities which continue to maintain the physical and chemical properties of the original sample. This view stands in contrast to the particulate model of matter that advocates that matter is constructed from tiny particles called atoms which are not divisible without the loss of their chemical properties. A continuous view of matter also commonly does not recognise any empty space in matter.

Coulomb
Is the standard unit of electric charge and can be either positive or negative. It is equal to the amount of charge contained on 6.25 X 1018 electrons or the amount of charge that flows past a point in a conducting wire when a current of 1 amp flows for one second.

Diffusion
Diffusion is the movement of molecules in a gas or liquid by random thermal agitation from a region of high concentration to a region of lower concentration.

Digestive system
The digestive system is a series of connected organs from mouth to anus whose purpose is to break down, digest and excrete wastes from the food we eat. The digestive system breaks down complex food molecules into simple molecules, so that they can easily be absorbed into the bloodstream. These molecules are transported in the blood to the body's cells, where they are used for maintenance, growth and reproduction.

DNA
DNA is an abbreviation for deoxyribonucleic acid, a complex molecular chain found in the nucleus or cytoplasm of all living cells. DNA acts as a sequence of genetic instructions that encodes proteins and enables cells to reproduce and perform their functions.

Ecosystem
An ecosystem is a biological community and its environment. All the dynamic interactions between plants, animals, and the physical environment in which they live make up an ecosystem. No community can carry more organisms than its food, water, and physical environment can accommodate therefore for an ecosystem to be self sustaining these interactions must remain in balance. In an ecosystem, each organism has its own niche, or role, to play. Food and territory are often balanced by natural phenomena such as fire, disease, and the number of predators. Ecosystems may change in function, structure and composition over time due to natural or human disturbance such as drought, flooding, mowing and herbicides.

Elastic collision
An elastic collision describes a collision in which particles rebound without loss of kinetic energy or conversion of this energy into heat, sound or deformation of the particles. For macroscopic objects, no collision is perfectly elastic, however the collisions which occur between molecules in gases, liquids and solids are. If the collisions were not perfectly elastic the motion of the gas molecules would eventually reduce allowing them to be attracted by the weak attractive forces of other molecules and resulting in a change of state to a liquid.

Electrical energy
The term electrical energy refers to energy that is attributed to the movement or position of electrical charges within an electric field. This could include energy derived from both current carrying and static electricity.

Electrical insulator
Any material that does not allow electricity to flow through it easily because the electrons in their atoms do not move easily from atom to atom (i.e. the material has high resistance). Glass, rubber, ceramics and some plastics are good insulators. A poor electrical insulator is said to be a good electrical conductor.

Electromagnetic spectrum
- the complete range of energies of electromagnetic waves from the lowest (largest wavelengths) to the highest (smallest wavelengths) including, in order, electric power transmission, radio waves, infrared, visible light, ultraviolet, X-ray, and gamma ray radiation.

Electrostatic forces
Electrostatic forces are engaging for students because they are examples of a non-contact force that can be easily explored. For example, rubbing balloons or plastic rods create pushes and pulls that can be experienced by objects without making contact. An electrostatic force can either attract or repel other charged objects. All materials are influenced by electrostatic fields although special sensitive equipment is needed to detect its effects. Electrostatic forces are strongly connected to magnetic forces; the fundamental force of ‘electromagnetism’ comprises both these forces.

Element
An element is a pure substance composed of atoms of only one type in that they all have the same number of protons in their nucleus. Each element can be found positioned on the Periodic Table. As the largest number of protons found in the nucleus of any stable atom found on Earth is 92 and not all of these 92 different atoms are stable, there are less than 90 elements that occur naturally on the Earth and 15 or so that have been produced briefly or in small quantities in laboratories. These elements combine into the extremely large number of compounds that we encounter in the world around us.

Endocrine system
The endocrine system uses secretions (hormones) to regulate mood, growth and development and tissue function and to maintain overall metabolism. The endocrine system consists of endocrine glands: the pituitary, thyroid, and adrenal glands. These glands release hormones directly into the circulatory system where they act as chemical messengers coordinating cell behaviour and regulating body functions. All multicellular organisms produce hormones for this purpose.

Ferromagnetism
Ferromagnetism is the common form of magnetism exhibited by metals containing either iron, nickel or cobalt or alloys containing two or more of these metals. These metals become magnetised when they experience a strong magnetic field nearby and are still able to retain this property when the nearby field is removed.

Field
The term field is used to describe a region around a central object in which a second object experiences a force from the central object without being touched by it. Examples are gravitational, magnetic and electric fields. The strength of both electric and magnetic fields reduces very quickly as one moves away from the central object. Although gravity is a relatively weak force in comparison with the other forces, the effects of a gravitational field can extend over astronomical distances. The concept of a field is difficult for students because fields are invisible and their presence can only be inferred by noting how the field influences other objects.

Food web
A food web is a simplified diagrammatic representation of feeding relationships between organisms within an ecosystem. Food webs can be described for a particular environment and generally consist of a series of interconnecting food chains usually beginning with organisms capable of producing ‘food’ (such as green plants) from an energy source (usually the Sun) and connected to organisms that eat them, then organisms that eat those and so on. It is important for students to understand that food webs are diagrams representing only some of the many possible relationships that exist in any given ecosystem.

Force
For students a force is best thought of as a push or pull between objects which may cause one or both objects to change speed and/or the direction of their motion (i.e. accelerate). Most pushes and pulls involve establishing contact between objects using electrostatic forces. All forces are measured in newtons (N) and have a direction associated with them. Physicists identify four fundamental forces: gravitational, electromagnetic (involving both electrostatic and magnetic forces), weak nuclear forces and strong nuclear forces. All interactions between matter can be explained as the action of one or a combination of the four fundamental forces.

Friction
Students are very familiar with the effects of friction in retarding an object's motion but less able to identify situations where it is of benefit or essential in aiding motion. Although not completely understood by scientists, it originates from the interaction of electrostatic forces between the surface particles. Friction is a force which opposes the relative motion of two surfaces in contact, and resists or retards their sliding over each other. It can be reduced by applying lubricants and increased with the application of resin or waxes to the surfaces.

Galaxy
A galaxy is a term that describes a complex system of stars held in orbit by mutual gravitational attraction. They may contain upward of 100 billion stars and associated dark matter (i.e. non luminous gas and dust). The Milky Way is the name given to our local galaxy containing the sun. The Milky Way is one of billions of similar galaxies in the observable universe.

Gel
A gel is a semi-solid, jellylike material formed from a colloidal solution. By weight, gels are mostly liquid, yet they behave like a cross between a solid and a liquid. Examples are gelatine, hair gel and toothpaste.

Gene
Genes are the fundamental units of heredity that are passed from parent to offspring during reproduction. They are constructed from a segment of deoxyribonucleic acid (DNA) and encode information essential for the construction and regulation of proteins (such as enzymes) and other molecules that determine the growth and functioning of the organism.

Glands
A gland is a cell or group of cells which have the ability to manufacture a secretion which acts as a chemical signal or is used by another organ in the organism. Endocrine glands in the human body secrete hormones and discharge these directly into the bloodstream where they are used in other parts of the body. Salivary glands produce saliva in response to eating and sweat glands produce salt and urea in solution to evaporate from the skin to assist the body with temperature control.

Glucose
Glucose is a simple form of sugar and one of the most important carbohydrates in biological processes. In the human body it is transported by the blood and used as a source of energy in cell function. We maintain a small store of free glucose in our blood (sugar levels) that can be used by cells very quickly as well as a bigger store of chains (polymers) of glucose that we call on during sustained periods of exertion. In plants, glucose is one of the main products of photosynthesis and an important source of chemical energy for plant cellular function as well as for animals that eat plants.

The term glutinous describes a substance that is very sticky and displays similar properties to an adhesive or glue, such as ‘glutinous rice’.

Gondwana
a name given to the southern hemisphere`super continent' consisting of South America, Africa, Madagascar, India, Arabia, Malaya and the East Indies, New Guinea, Australia, New Zealand and Antarctica prior to its break up under the forces causing continental drift.

Hormones
Hormones are chemicals produced by various glands in the endocrine system which have the effect of changing or controlling the activities of systems or organs in other parts of the body.

Horsepower
a non-metric unit of power. One horsepower is equivalent to 745.7 watts.

Immersion
Immersion is the act of completely wetting something by allowing it to sink or pushing it below the surface of a liquid.

Ion
An ion is an atom or a molecule which becomes charged because of an imbalance of electrons and protons. If the atom or molecule loses a negatively charged electron then its overall charge becomes positive and if it gains an electron then its overall charge becomes negative.

Joule
a metric unit of energy. One joule is equal to the energy transformed by the power of one watt operating for one second. 4.184 joule of heat energy (or one Calorie) is required to raise the temperature of 1 gram of water 1°C. There are 3.6 million joule in one kilowatt-hour. The joule is named after an English brewer, James Joule (1818 – 1889), who first quantified the relationship between heat and mechanical energy.

Kilowatt hour
a common unit of energy used for metering electricity. It is equivalent to the use of 1000 watts of electricity for one full hour. 1 kWh = two 500 watt bulbs lit for 1 hour. (10 bulbs x 100 watts each x 2 hours = 2000 watts hours or 2kWh).

Kinetic energy
The term kinetic energy refers to energy attributed to the movement of an object relative to a reference point. The greater the movement and/or the greater the mass of the object the more kinetic energy that can be stored. If an object is stationary then its kinetic energy relative to that point is always zero.  

L

Lithosphere
the rigid outer layers of the Earth’s crust and the upper mantle. The tectonic plates are composed of parts of the lithosphere. The lithosphere ranges in thickness from 6-12 km underneath the oceans to more than 200 km under the continents.

Magnetic Force
Magnetic forces are examples of non-contact forces that can be easily explored in the classroom. For example, bar magnets experience pushes and pulls without making contact with each other. Strongly magnetic materials include iron, nickel and cobalt, which can exert either attractive or repulsive forces on other similar materials. However all materials are influenced by magnetic fields, but sensitive equipment is needed to detect these effects (such as medical imaging using Magnetic Resonance Imaging - MRI). Magnetic forces are strongly connected to electrostatic forces; the fundamental force of electromagnetism combines both these forces.

Mammals
Mammals are one of the families that make up vertebrate animals. Most mammals give birth to live young which are nourished by milk produced in specialised mammary glands in the female. Mammals are warm blooded and usually have some hair or fur (whales have thick layers of blubber) which assists them to maintain a constant body temperature. An additional characteristic of all mammals is that their heart contains four chambers.

Mass
Mass is best described as a measure of the amount of stuff (or matter) in an object and is very hard to define for students because it is such a fundamental property. To determine the mass of an object you can measure how strongly it is attracted by the Earth's gravitational field (i.e. weigh it on a scale and find its mass). Another method to determine mass, although rarely used in practice, is to measure the object's acceleration when a known force is applied to cause it to accelerate; much bigger forces are required to accelerate a heavily loaded truck compared with a motorbike accelerating at the same rate. Mass is measured in kilograms (kg). The ‘everyday weight’ of an object on the Earth is considered equivalent to its mass simply for convenience; however, this can be a source of confusion in upper levels of school because weight is really a force (see weight force) and should be measured in newtons (N) not kilograms (kg).

Metabolism
In a biological system, metabolism refers to the ongoing interrelated series of chemical reactions taking place in living organisms that provide the energy and nutrients needed to sustain life.

Millennium
A millennium is a period of one thousand years. Millennia is the plural term used to describe a period of many thousands of years.

Mixture
A mixture is the result of combining two or more substances together physically without resulting in a chemical bonding. The components of mixtures can usually be easily separated.

Molecular mass
The molecular mass (less accurately referred to as molecular weight) is equal to the sum of the atomic masses of all atoms in a molecule, based on a scale in which the atomic mass of the carbon 12 isotope is set as being exactly 12.

Molecule
A molecule is formed by the combination of two or more atoms held together by chemical bonds. It may contain combinations of atoms from either the same element or a variety of elements. Unlike the small number of different atoms, there are a huge number of different molecules and the number and type of molecules changes in chemical reactions.

Mutation
Mutations describe any change in the DNA ( deoxyribonucleic acid) contained in a cell. Mutations may be caused by copying errors during cell division, or by exposure to DNA-damaging agents in the environment, such as chemicals or ionising radiation. Some mutations can be harmful, while others may be of benefit to an organism. Mutations in most types of cells are not inherited, however if they occur in sex cells, they can be passed on to offspring and can influence a whole population. The appearance of mutations is central to evolution; if the individual with the mutation is better able to survive and reproduce then the mutation may spread through a population.

Naphthalene
Naphthalene is a white crystalline hydrocarbon solid at normal room temperature which passes slowly from the solid state to a gas without becoming a liquid (see sublimation). It is also known as camphor (or moth balls) and is sometimes placed in clothes drawers where it slowly emits a gas toxic to most insects without wetting the clothes.

Natural light source
A natural light source is a luminous object which emits light without any human intervention or control. E.g. the Sun and other stars, fire, lightening, chemical luminescence from glow worms, glow sticks or rotting organic matter and very hot objects.

Nervous system
The nervous system is sometimes referred to as the ‘communication system’ because it coordinates the activity of the muscles, monitors organs, controls input from the senses, and regulates the body's responses to internal and external stimuli. There are two main parts; the central nervous system comprising the brain, spinal cord and retinas and the peripheral nervous system which includes most sensory and muscle connections.

Newton (N) – the unit
The newton is the common unit used for measuring force. It was named in memory of Isaac Newton (1642-1727) who did much to clarify our understanding of forces and motion. Most students and adults have no understanding of the size of a force of one newton (1 N). It is similar to the force needed to support the weight of one apple.

Newton's First Law of Motion
This first law of motion is often stated as: a body remains at rest or in motion with a constant velocity unless acted upon by a net force. This type of language often remains confusing to students unless they are given opportunities to discuss and interpret its meaning using everyday language. It is best considered by an analysis of two situations. The first situation is intuitive. A stationary object will remain stationary unless you provide it with a push or a pull. The second situation is not so intuitive. An object travelling with a constant speed in a constant direction will continue unaltered unless you provide it with a push or a pull. If you do give it a push or pull, it will either change its speed or direction or both. For example, an ice hockey puck experiences minimal friction while moving on the ice and so continues moving at a constant speed in the same direction unless it experiences a push from a hockey stick.

Newton's Second Law of Motion
This second law of motion is often stated as: the resultant force acting on a body results in an acceleration which is in the same direction as the resultant force and is directly proportional to the magnitude of this force and inversely proportional to the mass of the object. This language is very unhelpful to students and does little to improve their understanding of the ideas being expressed. The second law builds on the qualitative understanding of the first law by providing a quantitative relationship between mass, force and acceleration. For expediency it is often taught mathematically as F = ma (where F = force, m = mass and a = acceleration), but although most students learn to successfully manipulate the equation, it does little to assist their understanding of the concepts involved. Consider a description using everyday language. We know that applying a push to an object that is free to move will cause it to accelerate. The second law suggests that doubling the push on the same object will result in twice the acceleration and that the same push given to an object with half the mass will also double its acceleration.

Nuclear reaction
A nuclear reaction involves the collision of individual particles or combinations of particles, or the emission of particles from the nucleus, to form nuclei that are different from the original. This will often result in the production of new elements due to heavy nuclei being broken apart (i.e. nuclear fission) or light nuclei being bonded together (i.e. nuclear fusion). The vast majority of nuclear reactions occur in stars where the extremely high temperatures encourage high energy collisions between nuclei to create new elements. Students often consider nuclear reactions to involve similar processes to chemical reactions, but new elements can never be created by chemical reactions.

Ohm
An ohm is a unit of electrical resistance named in honour of Georg Ohm (1789 -1854), a German scientist who started to investigate the properties of electrical resistance while teaching as a high school physics teacher. He is recognised for discovering the relationship between voltage, current flow and resistance known as Ohm’s Law.

Oobleck
Oobleck is a popular name used to refer to a stiff mixture of corn starch and water (1 part water to 1.5-2 parts corn starch) often used as a demonstration aid when teaching about the properties of solids and liquids. Oobleck is not readily categorised as a liquid or solid as it behaves as a ‘runny’ liquid if poured slowly but behaves much like a solid if forced to move or change shape quickly. Substances which display similar behaviour are called ‘dilatants’. The name Oobleck originates from a green slime invented by children's author Dr Seuss in the book Bartholomew and the Oobleck.

Orbit
For most students the term orbit generally refers to the path taken by an artificial satellite around the Earth, for example, the International Space Station orbits around the Earth. However the term refers generally to the path taken by both artificial and natural satellites around any central object under the influence of gravity. Hence the moon orbits the Earth and the Earth orbits the sun. Most orbits are described as being circular but are more precisely an ellipse.

Organism
An organism is a living thing composed of either a single cell or multiple cells that has (or can develop) the ability to act or function independently. Five forms of organisms are often proposed: plants, animals, fungi, protists (such as algae) and bacteria. Organisms are the smallest biological unit needed for reproduction, so while a single cell organism such as bacteria may be autonomous, the majority of individual cells in multicellular organisms are not. This means that, while many individual cells in an organism that has recently died may be carrying on their metabolic processes, the organism is regarded as dead.

Particle model of light
This model suggests light is composed of huge numbers of tiny particles which are emitted from a light source and travel outward independently in straight paths in all directions.

Peer review
This is a public process that requires peers – other scientists – to accept ideas or reject ideas in a consensus making process. In this consensus making it will mean that some scientists will agree, some will partially agree and others will disagree. In reaching a consensus, there may be some modification of the ideas presented. For example, when proposing a theory such as ‘Natural Selection’ it is impossible to ‘prove’ or ‘disprove’ the theory, but rather it may be supported, rejected or modified.

Photosynthesis
Photosynthesis is the process used by plants, algae and some bacteria to change carbon dioxide and water into carbohydrates using energy from sunlight. The process usually releases oxygen into the atmosphere as a by-product. A common misconception by students is that green plants require only carbon dioxide and that all the oxygen they produce during photosynthesis is a net gain for the atmosphere. Plants also require some oxygen for respiration.

Physical environment
The physical environment refers to the external, tangible surroundings in which an organism exists and which can influence its behaviour and development. It includes landforms, soil types and climate.

Plasma
In biological systems the term plasma is used to describe the liquid component of blood in which the blood cells and the proteins that form blood clots are suspended. Plasma is a yellow coloured fluid and the largest single component of blood, making up about 55% of total blood volume.

In physics the term plasma is often used to refer to a fourth state of matter in which a substance is in the form of a super heated gas.

Plastic flow
The slow deformation of a material’s shape due to the continued application of a force allowing it to change shape by bending without fracture or decomposition.

Polymerisation
Polymerisation is a chemical reaction in which two or more small molecules are combined to form much longer connected chains ( polymers) of repeated molecules.

Population
In biological systems a population refers to a collection of organisms of a particular species living and interacting in the same geographic region.

Potential energy
The energy possessed by an object by virtue of its location or position in a field. As an example, consider a gravitational field. The higher an object is when compared with another, the greater its gravitational ‘potential’ energy. This gravitational energy is converted into kinetic energy (energy of motion) as it falls. An object which is distorted (compressed or stretched) also has potential energy.

Power
Is the rate at which energy is transformed. It is usually measured in the international unit called the watt and occasionally with the unit horsepower when concerned with cars or electric motors.

Precipitation
In the chemical sciences, precipitation refers to the formation (condensation) of a solid from a solution during a chemical reaction. Commonly two dissolved substances react to form a new substance that does not remain in solution. The precipitate usually settles out of solution on the bottom of the container but can form a suspension or colloid. During these changes, the solution changes from being translucent to opaque (i.e. ‘clear’ to ‘cloudy’).

Private science
The ideas and understanding scientists have about science as they go about their daily work.

Producer
The term producer is used in biology to describe an organism, generally a plant or algae, that can produce organic food molecules (usually glucose) using the sun's energy (by photosynthesis) or by other chemical reactions (chemosynthesis). Most producers are a source of food for other organisms.

Product
This term is used to describe the substances that are produced by a chemical reaction. Reactants undergo a chemical change to produce products with different properties.

Reactants
A term used to describe the substances that take part in a chemical reaction. The reactants undergo a chemical change to produce products with different properties.

Reliability
Reliability is the degree to which an assessment instrument or protocol consistently and repeatedly measures an attribute achieving similar results for the same population.

Renal System
The renal system is responsible for the regulation of bodily fluids and the elimination of wastes from the human body. The key organs of this system are the kidneys which filter wastes (such as urea) from the blood and excrete them, along with water and other waste, as urine. The body is able to regulate the operation of a number of organs to help it adapt and accommodate to changes in environmental conditions that may adversely affect body functions. The kidneys play a vital role in this process by regulating acid-base balance, electrolyte concentrations and blood pressure and controlling blood volume.

Respiration
Respiration is a process with both physical and metabolic aspects, whereby an organism exchanges oxygen and carbon dioxide with its external environment. It is this exchange of gases that allows an organism to supply its cells and tissues with the oxygen needed for metabolism and relieves them of the carbon dioxide formed in energy-producing chemical reactions.

Selection
Selection is the process where organisms with advantageous traits are more successful reproductively than those without the traits. This results in them producing more offspring to succeeding generations which have an increased chance of expressing a similar trait. Selection can occur from the pressures of natural environmental conditions or from human intervention in selective breeding programs.

Solar system
The solar system is usually thought by students to be just the planets in orbit around the sun, but it also includes all the moons, periodic comets, meteors, asteroids, dust and debris which are held in orbit by the sun's gravitational attraction. The solar system is far bigger than the orbit of the outermost planet.

Solution
A solution is formed by combining one or more substances by dissolving them into another substance. A common example would be a solid (solute) dissolving into a liquid (solvent), like salt into water. Gases may also dissolve into liquids, like carbon dioxide or oxygen in water, and liquids and gases into themselves.

Solvent
A solvent is the substance doing the dissolving that results in a solution. Water is a good solvent for many, but not all substances. In everyday speech, the term solvent is sometimes used for non-aqueous liquids such as turpentine and acetone that are useful for dissolving substances such as oil that cant be dissolved in water.

Spring balance
A spring balance is a common laboratory device used to measure the weight of an attached object by recording the resulting extension or stretching of a steel spring. The spring extension is proportional to the stretching weight force so it can be calibrated to measure either force in newtons (N) or equivalent mass in kilograms (kg).

Stalactites
The word stalactites comes from the Greek word for ‘drip’ and means ‘that which drips’. Stalactites are a type of thin cone-shaped rock formation that hangs from the ceiling or roof of limestone caves. They are usually produced by the deposition of minerals from solution as it drips.

Stalagmites
Stalagmites are a cone-shaped rock formation found on the floor of a cave that are usually but not always found below a stalactite. Stalagmites are usually produced by the deposition of minerals from solution from the drips falling from above.

Star
The term star has many everyday meanings. When used to describe an astronomical object, it generally refers to massive spherical balls of very hot gas that are visible in the night sky as only points of light due to their immense distances. Stars are so massive that the compression of their gases by gravity initiates sustained nuclear reactions which result in the production of new elements and the release of energy in the form of light and heat.

Subduction
The term subduction describes the movement of the Earth’s tectonic plates where one plate collides with another forcing one plate to ride up over the other. The plate forced below usually suffers considerable melting as it is forced deep below the Earth’s surface.

Sublimation
Sublimation is the physical change of state of a substance from a solid to a gas without passing through the liquid state or the reverse process of passing from a gas to a solid. Examples of substances that sublime at room temperatures are carbon dioxide (dry ice), iodine and naphthalene (camphor or moth balls). In conditions of low humidity, ice will sublime directly to water vapour at temperatures below 0 degrees Celsius.

Synthetic
The term synthetic refers to a substance that has been manufactured, processed or chemically altered after being extracted from naturally occurring plant, animal or mineral sources. The term is not usually applied to substances produced by naturally occurring biological processes.

Tectonic plates
rigid parts of the Earth's crust and upper mantle that move very slowly and adjoin each other along zones of seismic activity. These plates form a part of the lithosphere.

Trace elements
The term trace elements is used to describe a range of chemical elements that occur in very low concentrations which are vital for the growth, development and physiology of plants.

Urea
Urea is a product of protein breakdown that can be safely removed from the body. Urine is the waste solution that contains dissolved urea. An average person excretes about 30 grams of urea per day. The ability of the liver to convert products of protein breakdown into urea is essential to human health.

Validity
Validity is the state of being authentic or genuine. Validity describes the extent to which a test measures the skills it intends to measure and the extent to which inferences and actions made on the basis of this assessment are appropriate and accurate.

Veins
A vein is a blood vessel in the body that returns blood from organs toward the heart. Most veins carry blood with small amounts of dissolved gases, but the pulmonary veins carry blood rich in oxygen from the lungs to the heart. Because the pressure of the heartbeat is dissipated in the capillaries, veins do not have elastic walls; they are essentially hollow tubes that collapse when not filled with blood and have one-way flaps called ‘venous valves’ to prevent gravity from causing blood to backflow and pool in the lower extremities of the body. Veins rely on pressure from adjacent contracting muscles to push the blood back to the heart.

Vertebrates
Vertebrate is a term commonly used to describe animals that have backbones or spinal columns. The name comes from the bones of the spinal column, the vertebrae. Vertebrates contain many familiar groups (families) of large animals such as reptiles, birds, mammals, fish and amphibians. This group is characterized by a muscular system as well as a central nervous system. Vertebrates are most easily distinguished by having an easily identified head, with sensory organs (especially eyes concentrated at the fore end of the body. In comparison some examples of animals that do not fit this category (invertebrates) are jellyfish, worms and insects.

Watt
The watt is a metric unit of power equal to the rate of transformation of one joule of energy per second. It is named after the Scottish engineer and inventor James Watt (1736-1819) who did much to develop and popularize the steam engine.

Wave model of light
This model suggests light is composed of continuous waves which travel outwards from the light source much like water waves radiate from the impact of a stone thrown into a pond.

Weight force
Weight is often confused with mass, but it is not the same thing. The weight of an object on Earth is the gravitational force of Earth acting on the object and will vary depending on the position of the object and the strength of Earth's gravitational field. The weight of an object will change if it is placed on the surface of a different planet because the gravitational force of that planet on the object will be different, but the object's mass (i.e. the amount of matter it contains) remains the same. Weight is what a scale reads and is measured in newtons (N).  

Work
The word work is often used in everyday speech with a variety of meanings. To the scientist the word ‘work’ is used with a very precise meaning. It defines a mathematical measure of the ‘effort’ needed to move an object by applying a force to it. The work completed is a product of the force applied to the object and the resulting distance it was moved. If an object is not moved by a ‘push’ or ‘pull’ then no work has been done.