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Glossary

A glossary of science-related words.

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Glossary terms A–Z definitions

data logger

A device that can read various types of electrical signals and log the data in internal memory for later download to a computer.

deadly nightshade

(Also called belladonna.) One of the most poisonous plants found in the western hemisphere. All parts of the plant are toxic, containing tropane alkaloids.

decant

To draw off a liquid without disturbing the sediment or the lower liquid layers.

decibel (dB)

A logarithmic unit used to describe the loudness of sound (amongst other things).

decomposer

An organism that breaks down dead matter.

deforestation

Deforestation is the long-term or permanent loss of forest cover when trees are removed to clear land for another use.

deform

To change shape.

degenerative disease

A disease in which the function or structure of the affected tissues or organs progressively deteriorates over time.

degrade in orbit

When an object in orbit about another object, for example a satellite around the Earth, slowly loses altitude and moves closer to the central object (e.g. the Earth), this is known as a degrade in orbit. In the example of a satellite moving about the Earth, a degrade in orbit can be caused by drag from the Earth’s atmosphere.

dehydration

Loss of water from the body through breathing, perspiration and waste removal. If this loss is not counterbalanced through consumption of water, the body’s physical and mental functions can be degraded.

delta wing

A wing in the form of a triangle. It is named for its similarity in shape to the Greek upper case letter delta (Δ).

dementia

Deterioration of intellectual faculties, such as memory, concentration, and judgment, resulting from disease or a disorder of the brain. It is sometimes accompanied by emotional disturbance and personality changes.

denaturation

A process in which the structure and shape of large biomolecules such as proteins or nucleic acids are altered due to exposure to some external stress such as heat or changing pH.

dendrite

A long extension of a neuron that receives nerve signals and transmits them to the main body of the cell.

denitrification

Part of the nitrogen cycle. A process where bacteria in soil breaks down nitrates into atmospheric nitrogen gas.

denitrification bed

A bed or wall composed of organic material and soil that is dug into the ground. The bed intercepts shallow groundwater, providing anaerobic conditions in which denitrification can take place.

density

Density describes how tightly a certain amount of matter (atoms or molecules) of a substance is compacted in a given volume. Density is commonly measured in grams per millilitre (g/ml) or cubic centimetre (g/cm3).

dentine

Most of a human tooth is made of dentine. It is a strong, hard material laid down by cells lining the pulp cavity. The outer surface is covered with enamel.

dentition

The arrangement, type and number of teeth in a particular species.

deoxyribose nucleic acid (DNA)

The genetic material that contains the ‘blueprint’ of all living matter.

deposition

A geologic process referring to the settling out or placement of sediments following transport from one place to another.

depressant

A drug or substance that slows down the normal function of a specific part of the brain (the central nervous system).

dermis

The inner layer of the two main layers that make up the skin. Contains the roots of hairs, glands (that make sweat, which helps regulate body temperature, and sebum, which is an oily substance that helps keep the skin from drying out), blood vessels, lymph vessels and nerves.

desalination

The process of removing salt, especially from seawater.

design thinking

A set of skills, competencies or dispositions relating to the highly iterative collaborative process designers employ when conceiving, planning and producing an object or system.

desorption

Molecules or particles are released from a surface – the reverse of adsorption.

detritus

In biology, particulate matter from dead organisms.

diagenesis

The hardening of loose sediment into sedimentary rock. It is the sum of the physical, chemical and biological changes that take place in sediments as they become consolidated into rocks.

diagnosis

The identification of disease through the examination of the symptoms.

diammonium phosphate (DAP)

The world’s most widely used phosphate fertiliser. It contains 46% phosphate and 18% nitrogen.

diapause

A state of dormancy in which all development is suspended. A pupa entering diapause will cease development, and the metamorphosis of the insect inside will halt until conditions become more favourable to the survival of the insect.

diatom

A microscopic algae that has silicon ‘boxes’ instead of a cell membrane.

dicotyledon

A plant of one of the two major groups of flowering plants (angiosperms) characterised by a seed with two seed leaves called cotyledons.

dietary fibre

The portion of fruits, vegetables, nuts and grains we eat that is resistant to digestion and absorption in the small intestine. Fibre is an important ingredient of a healthy diet.

diffraction

The bending of waves as they pass small obstacles and the spreading out of waves after passing through small openings.

diffuse

Spread out.

diffuse reflection

The reflection of light from a rough surface in which the incident light rays are reflected from the surface at many different angles.

diffusion

The movement of atoms or molecules from an area of higher concentration to an area of lower concentration. Atoms and small molecules can move across a cell membrane by diffusion.

digestion

The mechanical and chemical breaking down of food into smaller components that can be absorbed into a bloodstream.

dimorphism

Occurring in two different forms.

dinoflagellate

Microscopic single-celled organism that lives in freshwater and seawater. Under warm conditions, marine species can grow and spread to cause a red ‘bloom’ visible in the sea.

dioxin

A general term that describes a group of chemicals that are highly toxic and persistent in the environment. They can be produced through industrial processes or naturally (for example, through forest fires).

diploid

Having two copies of each chromosome. These cells have twice the haploid number of chromosomes as they inherit one set of chromosomes from each haploid gamete (egg and sperm).

diseases

An abnormal condition of an organism that impairs bodily functions.

disinfection

When a substance is applied to a non-living surface in order to kill microorganisms.

dispersal

Movement of an organism to a new place. Seeds in plants and spores in ferns and fungi help dispersal by floating on the wind to new habitats. This allows stationary species to colonise new areas.

divergent boundaries

Tectonic plate boundaries, where new crust is generated as the plates pull away from each other.

dizygotic twins

Twins that derive from two separately fertilised eggs.

DNA

DNA or deoxyribonucleic acid is a very big molecule, found primarily in the nucleus of cells. It is the main component of chromosomes and is the material that transfers genetic characteristics in all known living organisms.

DNA fingerprint

A unique pattern of bands that is produced from an organism’s DNA.

DNA sequencing

A technique used to determine the exact sequence of nucleotides in a sample of DNA.

Dobson unit (DU)

A unit of measurement of atmospheric ozone. One Dobson unit refers to a layer of ozone that would be 10 millionths of a metre thick under standard temperature and pressure.

doline

A closed depression, also known as a sinkhole, draining underground in karst landscape areas. It can be cylindrical, conical, bowl or dish shaped and vary in size from a few metres to hundreds of metres across.

dolomite

A carbonate mineral that has the chemical name calcium magnesium carbonate – Ca(MgCO3)2. Dolomitic limestone is an important agricultural fertiliser.

dope

The addition of a small amount of an impurity to a semiconductor to increase its conductivity.

Doppler effect

An apparent shift in the frequency of sound or light. This is due to relative motion between the source of the sound or light and the observer.

dormant

Not active but capable of renewed activity.

dose

The amount of a substance that comes into contact with a living organism or some part of a living organism.

downlink

A link used to transmit a data signal from a remote source to a local receiver. For satellites, this is the radio connection that carries electromagnetic signals from a satellite down to a ground station.

drag

Sometimes called air resistance or fluid resistance, drag refers to forces that oppose the relative motion of an object through a fluid (a liquid or gas).

drug

A pharmaceutical drug could be a medicine or chemical substance intended for use in the medical diagnosis, cure, treatment or prevention of disease.

dry steam power plants

These use hydrothermal fluids that are primarily steam (not a water/steam mixture).

ductile

Able to change shape without breaking.

duodenum

The first section of the human small intestine. It is about 25–30 cm in length and plays a vital role in the digestion of food passed into it from the stomach.

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