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Glossary

A glossary of science-related words.

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Glossary terms A–Z definitions

lab scale

Done or set-up on a small scale, typically in a laboratory.

labyrinth

Inner-most part of the ear containing the cochlea (for hearing) and the vestibular system (for balance).

lactic acid

Acid produced by muscles exercising anaerobically. Accumulation can cause pain.

lamina

The flat, green leafy blade of a fern frond.

laminar flow

When the layers of air (or another fluid) move over an object smoothly, without turbulent mixing of the layers.

lapilli

A subdivision of tephra (ash). Refers to material ejected from a volcano that is between 2 mm and 64 mm in diameter.

Large Hadron Collider (LHC)

A gigantic scientific instrument 27 km in diameter, constructed 100 m underground near Geneva, on the border between Switzerland and France. It is a particle accelerator used by physicists to study the smallest known particles – the fundamental building blocks of all things.

large intestine

The end part of the gastrointestinal tract that includes the caecum, colon and rectum.

larval

The immature or juvenile form of some animals.

latent heat

The heat necessary to transform from one state of matter (i.e. solid) to another (i.e. liquid) without a rise in temperature until the change is completed.

lateral

Side.

lateral line

A sense organ in fish used to detect movement and vibration in the surrounding water. Runs around the head and along the side of the body.

lava

Magma that has erupted from a volcano and has come to the surface.

leachate

The liquid product of leaching.

leaching

When a compound becomes dissolved in water and moves from one place to another, for example, a fertiliser in the soil dissolves in rain water and ends up in a stream.

LED

Light emitting diode. A semiconductor device that gives off light when current passes through it in one direction only.

legume

A plant having fruits that are developed from a simple superior ovary and usually dehiscing into two valves. Legumes bear nodules on the roots, which contain nitrogen-fixing bacteria. Examples are peas, beans and clovers.

lens

A piece of glass or other transparent material with at least one curved surface. Lenses are used to change the direction of light rays that pass through them (focusing or dispersing the rays).

lesion

Almost any abnormality involving any tissue or organ due to any disease or any injury.

lethal

Capable of causing death.

lethal dose (LD50)

Also written as LD50. This is the amount of or length of exposure to a substance that causes death in 50% of the species studied under experimental conditions.

leukocytes

White cells (or immune cells) in the blood that help protect the body from infection and disease.

lever

A simple machine consisting of a rigid bar (a bone) that rotates about a pivot and is used to transmit a force.

leverage

An alternative name for torque.

lichen

A mutualistic relationship between a fungi and an algae. The two species are so intertwined that they appear to be one organism.

lift

In aerodynamics, upward force produced by a difference in pressure due to airflow.

light energy

Electromagnetic radiation, particularly radiation of a wavelength that is visible to the human eye.

light microscope

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

light spectrum (visible)

Electromagnetic waves in the range visible to the human eye. These waves have a wavelength from about 400 nanometres in the violet to about 770 nanometres in the red. Light behaves both as a particle and a wave. A particle of light is known as a photon.

light year

A unit of distance. Approximately 9.5 trillion kilometres (9 500 000 000 000 km), which is how far light travels in a year.

lightning

A large-scale natural spark discharge, visible as a flash of blue-white light, that occurs within the atmosphere or between the atmosphere and the Earth’s surface. The lightning channel consists of extremely high-temperature plasma.

lignin

A natural substance found in the cell walls of wood that binds the wood fibres together, making them rigid and strong.

lime

Chemically, lime is the compound calcium oxide. Commercially, lime could refer to ground-up calcium carbonate marketed as AgLime.

limelight

If a marble-sized piece of lime is heated to a high temperature, it emits a very bright white light. In the 1820s, British Army officer Thomas Drummond used this property of lime to develop a light that could be used in lighthouses and on the battlefield. Called Drummond lights, they eventually replaced the gas lights used in music halls and theatres. Performers and actors were now ‘in the limelight’ when on stage.

limestone

Sedimentary rocks formed mainly from the minerals calcite or dolomite. Many limestones are derived from the shells of dead marine organisms. Others are formed by chemical precipitation.

Linnean classification system

Developed by Swedish botanist Carl Linneaus in the 1700s, this system groups organisms into kingdoms, phyla, classes, orders, families, genera and species depending on their relationship to other organisms.

lipase

An enzyme that breaks down fats.

lipid

Any of a group of organic (carbon-containing) compounds, including fats, oils and waxes, that are insoluble in water, oily to the touch and, together with carbohydrates and proteins, constitute the principal structural material of living cells.

liquid chromatography-mass spectrometry (LC-MS)

A powerful technique used for many applications that has very high sensitivity and selectivity. Generally, its application is towards the general detection and potential identification of chemicals in the presence of other chemicals (in a complex mixture).

lithification

The set of geologic processes that changes loose sedimentary materials into hard sedimentary rock over a long time period.

lithosphere

The outer solid part of the Earth, made up of the crust and upper mantle. It varies in thickness and composition.

litre

(L) The special name for the unit of volume known as the cubic decimetre. There are exactly 1000 litres in 1 cubic metre – 1000 L = 1 m3.

littoral zone

The area of a coastal shore between the low tide mark and the high tide mark. Sometimes called the intertidal zone.

liver

A vital organ situated beside the stomach. It is the body’s largest internal organ and plays a major role in metabolism as well as other important and complex functions.

locus

In genetics, the specific site of a particular gene on its chromosome.

lotic

Pertains to or lives in flowing waters. Generally refers to flowing water ecosystems and comes from the Latin word ‘lotus’ meaning ‘washed’.River ecosystems are prime examples of lotic ecosystems.

low pressure

In aerodynamics, low pressure is formed over the top of an aerofoil (wing) as it moves through the air because the air particles become 'stretched' out as they travel faster over the upper surface towards the wing.

Lumbricidae

A family of earthworms.

luminescence

A process in which energy stored in a material is given off as light when suitably stimulated.

luminous intensity

The quantity of visible light emitted from a source, such as a light bulb, in unit time per unit solid angle.

lustre

The way light interacts with the surface of a mineral. For example, if the mineral has a polished metal appearance, its lustre is described as ‘metallic’. Terms like dull, greasy, waxy, pearly and adamantine (diamond) are used to describe lustre.

lycophyte

The oldest living vascular plant division at around 410 million years old; includes some of the most primitive living species such as Selaginella.

lymph nodes

Small, bean-shaped structures that are part of the lymphatic system. They filter the lymph to remove bacteria and other harmful agents, such as cancer cells.

lymph vessels

Very thin vessels that branch into every part of the body and are part of the lymphatic system.

lymphatic system

Part of the immune system that protects the body against 'invaders', like bacteria and parasites. It is a network of small lymph nodes connected by lymph vessels.

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