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A glossary of science-related words.

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The specific area in which in organism lives.


‘Heavy’ subatomic particles each made up of three quarks. Protons and neutrons are the most well known hadrons.


The oxygen-carrying substance in red blood cells.

hair cell

A sensory receptor within the ear. A cell structure that contains small extensions similar in appearance to fine hairs.


The time required for half of a given sample to undergo radioactive decay.


A very stable and unreactive chemical commonly used in fire extinguishment.


Having one copy of each chromosome, or having a single set of chromosomes. Gametes (egg and sperm cells) are haploid.


A division of a Māori tribe or iwi. Māori clans or subtribes.


New Zealand flax (Phormium tenax).

Haversian canals

Small interconnecting, longitudinal channels in compact bone that carry blood vessels and nerve fibres.


A situation that poses a level of threat to life, health or the environment.

Heat energy (heat)

Energy in materials that relates to the random movement of the particles in that material. The greater the random movement of particles the more heat energy the material has. Temperature is a measure of the heat energy of a material.

heat pump

A device that can move heat energy either into (heating) or out of (cooling) an enclosed space such as a house. For example, a household heat pump, when placed in heating mode, transfers heat energy present in the cold outside air to the warm inside air.

heavy metals

Elements that exhibit metallic properties. Often refers to toxic heavy metals that can cause serious illness in organisms. Waste-derived fuels are especially prone to containing toxic heavy metals.


Heirloom plant breeds have been around for generations, often only in small numbers. They are passed down within a family or community and generally not used in large-scale agriculture. They reflect a much greater genetic diversity than the breeds currently grown on a large scale.


(He) A colourless, odourless inert gaseous element occurring in natural gas and with radioactive ores.

Helmholtz resonator

A structure where pressure fluctuations over the opening causes the fluid or air inside to resonate, forming an audible sound, for example, the sound generated by blowing across the top of a bottle.


A plant, such as mistletoe, that obtains water and nutrients from its host but makes some of its own food by photosynthesis. Unlike a parasite, a hemiparasite does not normally kill its host.

hepatic portal vein

A blood vessel in the abdominal cavity that drains blood from the gastrointestinal tract and transports it to the liver.


A collection of dried plants mounted and classified for botanical study; the building or container that holds the plant collection.


An animal that only eats plants, compared to carnivores, which only eat meat, or omnivores, which eat plants and meat.

herd shelter

A generic term to describe an area where cows can be removed from the pasture for a period of time. It collects effluent, which can later be applied to the land as needed. It also shelters cows from wind and rain.


An animal having both male and female sexual organs.


A zoologist who studies reptiles and amphibians.


The study of amphibians and reptiles.

hertz (Hz)

The SI unit of frequency. For sound, this is reported as the number of waves per second.


Made up of a mixture of different parts or substances.


An animal that is unable to make its own food and relies on consuming nutrients from other organisms.

high-tech start-up

A newly created company working in a high-tech industry. These companies are usually in a phase of research and development.

Hikurangi Margin

An active subduction zone extending off the east coast of the North Island where the Pacific and Australian plates collide – the Pacific plate is forced down under the Australian plate.


A chemical that plays a major role in many allergic reactions. It triggers the inflammatory response to pathogens. It dilates blood vessels and makes the vessel walls abnormally permeable.


Human immunodeficiency virus (HIV) causes the immune system to fail. This gives opportunity for life-threatening infections to become established in the body.


Emphasising the importance of the whole and the interdependence of its parts.


The single specimen chosen as the type of a new species or subspecies in the original description. The description usually occurs in a scientific publication. Also known as a type specimen.


The tendency of a system to maintain internal stability.


Hominids are usually humans and their extinct ancestors. They are characterised by an upright gait, increased brain size and intelligence. In the last few years, the category has been extended to include the great apes. To make the distinction in this broader category, researchers often refer to the human branch as ‘hominins’ to mean just the Homo and Australopithecus genus.


Composed of parts or elements that are uniform in structure throughout.


A sweet syrup produced by scale insects living in beech forests. Used by birds, fungi and insects as a food source.


A chemical substance secreted by an endocrine gland into the bloodstream. It acts on specific target cells to produce a given response.


Originally defined to compare the output of steam engines with the power of draught horses, the horsepower (hp) is still commonly used. The SI unit for power is the watt (W), and 1 horsepower equates to 746 W.

host cell

A living cell in which a virus reproduces.


In geology, a hotspot is a location on the Earth's surface that has experienced active volcanism for a long period of time.

Hubble Space Telescope (HST)

A 2.4 m reflecting telescope in orbit approximately 590 km above the surface of the Earth.


Māori word for a gathering, meeting or assembly.

Human Genome Project

An international project to identify all the genes in human DNA and to determine the sequence of the 3 billion nucleotides that make up human DNA.


Organic matter in soils consisting of decaying plants or animals.


In general terms, husbandry is the care of animals, including breeding and raising them.


A chemical compound made up of hydrogen and carbon only. Mainly obtained from petroleum.


A condition often associated with spina bifida. Hydrocephalus is an excess of cerebrospinal fluid (CSF) that has accumulated in the brain. The term is from the Greek hydro (water) and cephali (head).

hydrofluoric acid

One of the strongest inorganic acids. It is very corrosive, and geologists use it to break down rock samples. It also attacks glass so is stored in plastic containers.


A network of polymer chains that attract water molecules. Due to their significant water content, hydrogels have a degree of flexibility very similar to natural tissue. Soft contact lenses are a good example.


First element on the periodic table - ­ symbol H, with the atomic number of 1, meaning that it has a single proton in its nucleus.

hydrogen bonds

A chemical bond of enormous importance in biochemical processes that forms between hydrogen atoms and another strongly electronegative atom, for example oxygen, nitrogen and fluorine.

hydrogen sulfide

A colourless gas with a characteristic rotten-egg smell that is highly toxic. Exposure to high levels (>100 ppm) can cause convulsions, coma and death.


An enzyme that catalyses the hydrolysis (breakdown using water) of a chemical bond. For example, sucrase found in the small intestine hydrolyses the glycosidic bond in sucrose, releasing glucose and fructose.


The study of movement, distribution or quality of water throughout the Earth’s systems.


A chemical reaction with water that results in the break up of a molecule into two parts.


An underwater microphone used to listen for and record sound under water.


All the water on Earth, whether it is liquid, solid (ice and snow) or vapour (in the atmosphere).


From ‘hydro’ meaning water and ‘thermal’ meaning hot.

hydrothermal vent

A region on the ocean floor where geothermally heated fluids escape from cracks in the Earth’s crust. It is essentially a hot spring on the ocean floor, found mostly along mid-oceanic ridges.


A form of calcium phosphate that occurs as a mineral. It is the chief structural component of bone and teeth.


A straightening movement that goes beyond the joint’s normal boundaries to extension.


Undesirable reactions produced by the immune system, including allergies and autoimmunity. These reactions may be damaging and are occasionally fatal.


Anything travelling faster than five times the speed of sound (faster than about 1650 m/s or 6000 km/h in air).


Small threads that are part of a fungus. These thin strands stretch out to gather food and nutrients to allow the fungus to grow.