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Edexcel GCSE Combined Science key terms

Abiotic component
The non-living parts of an ecosystem, such as air, water and soil.
From: Ecosystem material cycling and the carbon cycle
Abiotic factor
A non-living feature of the environment, such as light intensity, temperature or water availability.
From: Ecological Fieldwork and Population Estimates

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Absolute zero

The lowest possible temperature, taken as $-273\,°\text{C}$ or $0\,\text{K}$ . In the GCSE particle model, particles have no movement and zero kinetic energy at this temperature.

From: Gas pressure and temperature

Absorption

The taking in of radiation by a material, transferring energy to that material.

From: Effects and uses of EM waves

Acceleration

The rate of change of velocity, measured in $\text{m/s}^2$ .

From: Newton’s laws and changes in motion

Acid

A substance that produces hydrogen ions, $\mathrm{H^+}$ , in aqueous solution.

From: Acids, alkalis, pH and acid strength

Acid rain

Rain made more acidic by atmospheric pollutants such as sulfur dioxide and nitrogen oxides.

From: Fuel combustion, pollution and hydrogen alternatives

Acquired characteristic

A characteristic that develops during an organism’s lifetime because of environmental influences, rather than being inherited through its alleles.

From: Polygenic features and phenotypic variation

Acrosome

A cap on the head of a sperm cell containing digestive enzymes that help the sperm penetrate an egg's outer layers.

From: Cell Structures and Specialised Cells

Activation energy

The minimum energy that colliding particles must have for a reaction to occur.

From: Heat energy changes in chemical reactions

Active site

The region of an enzyme where a substrate binds and the reaction takes place.

From: Enzymes

Active transport

The movement of substances across a cell membrane against their concentration gradient, using energy released by respiration.

From: Transport and Water Uptake in Plants

Activity

The number of nuclear decays per second in a radioactive source.

From: Activity and half-life

Adaptation

Action that reduces harm from climate change by adjusting to its effects, such as constructing flood defences.

From: The greenhouse effect and climate change

Adrenalin

A hormone produced by the adrenal glands that prepares the body for fight or flight.

From: Hormones and Metabolic Rate

Adult stem cell

A stem cell found in particular tissues of the body that can differentiate into a limited range of related specialised cells.

From: Stem Cells and Their Use in Medicine

Aerobic respiration

Cellular respiration that uses oxygen to break down glucose completely, producing carbon dioxide and water and releasing energy.

From: Respiration

AIDS

Acquired immune deficiency syndrome: a condition in which HIV has severely weakened the immune system, allowing life-threatening infections and other illnesses to develop.

From: Health and Communicable Diseases

Alkali

A soluble base that forms an alkaline solution in water, with a pH greater than 7.

From: Group 1

Alkali metal

A Group 1 metal, such as lithium, sodium or potassium, that reacts with water to produce an alkaline metal hydroxide solution and hydrogen.

From: Group 1

Alkane

A saturated hydrocarbon containing only single bonds between carbon atoms.

From: Crude oil, fractional distillation and cracking

Alkene

An unsaturated hydrocarbon containing a carbon–carbon double bond.