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Glossary

A glossary of science-related words.

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Glossary terms A–Z definitions

obesity

An excessively high amount of body fat in relation to lean body mass. It is measured using a system known as body mass index (BMI).

ocean acidification

Decrease in ocean pH due to higher levels of dissolved carbon dioxide.

ocean basin

The large depressions of the sea floor. Sediments can accumulate and build up here.

oceanographer

Someone who studies the properties and processes of the ocean.

octahedral

A molecular structural shape in which six atoms or groups of atoms are symmetrically arranged around a central atom. The positions of the six surrounding atoms define the vertices of an octahedron.

odorant

A substance or product that has a lot of odour (smell).

oesophagus

A thin muscular-walled tube that runs from mouth to stomach. Also known as the gullet, it allows food to be transported to the stomach by peristaltic muscular movement.

olfactory

Relating to the sense of smell.

Oligocene

A geological epoch forming part of the Neogene period that extends over the time division 34–23 million years ago. It follows on from the Eocene epoch 56–34 million years ago.

omega-3 fatty acids

Although the body is capable of synthesising saturated and monounsaturated fatty acids, it cannot produce the essential fatty acids such as ω-3 (omega-3) and ω-6 (omega-6). These acids are required for the construction of cell membranes and as precursors for the production of hormones.

oolites

Small rounded balls of calcium carbonate (also known as ooids) that form in warm, supersaturated, shallow, highly agitated tropical marine water. The limestone rock that is formed from oolites is called oolite.

opaque

A substance that does not allow light to pass through it.

ophthalmology

The study of the anatomy, physiology and diseases of the eye. An ophthalmologist is a medical and surgical specialist trained to perform operations on the eye.

opportunistic pathogen

Bacteria that do not usually cause disease but can become a health threat when the body’s immune system is compromised.

optical microscope

A microscope that uses a glass lens (or lenses) to magnify small objects that are illuminated with visible light.

orbit

The path of an object as it revolves around another object. For example, the path the Moon takes as it moves around the Earth is its orbit.

order

A division used in the Linnean system of classification or taxonomy.

Ordovician

A geologic period covering the time division 488–444 million years ago.

organelle

Structure within a cell that has a specific function such as the nucleus, mitochondria and ribosomes.

organic

Organic matter has biological (living) origins containing carbon.

organic chemistry

The study of the compounds of carbon, excluding the oxides of carbon and the inorganic metal compounds known as bicarbonates, carbonates and cyanides.

organic compounds

Substances based on a carbon framework. They vary greatly in size and complexity and contain other elements, most commonly hydrogen and oxygen.

organic photovoltaics

(OPV) Photovoltaic cells that use organic substances to transform light energy into electrical energy.

organism

A living thing.

organochloride

A compound containing carbon, hydrogen and chlorine atoms bonded together.

ornithologists

People who study birds.

orrery

A mechanical device for representing the relative positions, motions and phases of the Sun, planets and their satellites in the solar system.

oscilloscope

An electronic instrument used to observe and measure changing electrical signals.

osteoarthritis

A condition involving the breakdown and eventual loss of cartilage that serves as a cushion between the bones of the joints.

osteomalacia

Softening of the bones. Known as ‘rickets’ in children.

osteoporosis

A disease that develops when bones lose calcium and other minerals. It results in bones that are porous and brittle.

otolith

A structure made of calcium carbonate found in the inner ear, especially in fish. Used to detect gravity and/or linear acceleration.

ovary

1. (Flowering plants) Contains the ovules in the female part of the flower. 2. (Animals) The female egg-producing organ involved in sexual reproduction.

ovule

1. (Plants) In seed plants, contains female sex cells (gametes) inside an ovary. An ovule develops into a seed after fertilisation. 2. (Animals) A small egg (ovum).

oxidation

Any chemical process involving the removal of electrons from an element or compound.

oxide

A chemical compound made up of oxygen combined with at least one other element. Most of the Earth’s crust consists of oxides.

oxygen

A non-metal – symbol O, atomic number 8. Oxygen is a gas found in the air. It is needed for aerobic respiration in cells.

oxyntomodulin

A hormone produced in the large intestine that has the effect of suppressing appetite.

ozone

Ozone is made up of three atoms of oxygen (O3). It is a highly reactive pale blue gas with a noticeable odour. Ozone forms a thin layer in the stratosphere. This layer protects life on Earth from ultraviolet rays. Ultraviolet radiation is a known cause of skin cancer.

ozone depletion

This term commonly refers to a reduction of ozone molecules in the atmosphere, which protect life on Earth from UV radiation. This is most prevalent over the poles and along the equator.

ozonesonde

An instrument for measuring the concentration of ozone in the atmosphere. Usually attached to a hydrogen-filled balloon and a parachute.

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