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Browse key terms and definitions across all GCSE subjects. Search by keyword or filter by subject and exam board.
23,110 key terms
Photochromic material
A material that changes colour in response to light, commonly ultraviolet light.
Photochromic pigment
A colouring substance that changes colour in response to exposure to ultraviolet (UV) light.
Photocopying
Reproducing an existing document or design onto suitable sheets using a copying machine.
Photo etching
A manufacturing process that uses a light-sensitive coating, patterned light exposure and chemical etching to create a pattern in metal, such as copper tracks on a PCB.
Photoresist
A light-sensitive coating used to create a protective pattern over copper during PCB manufacture.
Photosynthesis
The process by which plants use sunlight to make sugars from carbon dioxide and water, transferring carbon into living material.
Photosynthesis
The process in which green plants and algae use light energy to make glucose from carbon dioxide and water, releasing oxygen.
Photosynthesis
The process in which algae and plants use light energy to make glucose from carbon dioxide and water, releasing oxygen.
Photosynthesis
The process by which plants use light energy to make glucose from carbon dioxide and water.
Photosynthetic organism
A living organism that carries out photosynthesis, such as a plant or an alga.
Phototropism
A directional growth response to light.
Photovoltaic cell
A device that transfers energy from sunlight directly into an electrical pathway without a turbine.
Photovoltaic cell
A device that converts energy from sunlight directly into electrical energy.
pH probe
An electronic sensor used to measure the pH of a solution and give a numerical reading.
Phrase
A group of related words that functions as a unit within a sentence.
Phratry
A kinship association in ancient Athens involved in recognising family membership and descent.
pH scale
A numbered scale, usually from 0 to 14, that measures the acidity or alkalinity of a solution.
pH titration curve
A graph showing how pH changes as measured volumes of an acid or alkali are added during a titration.
Phylogenetic tree
A branching diagram representing a hypothesis about evolutionary relationships.
Phylogeny
The evolutionary history and relationships of an organism or group of organisms.
Physical activity
Movement of the body that uses energy, including activities such as walking, cycling, exercise and sport.
Physical activity level (PAL)
How physically active a person is; it influences how much energy they need from food.
Physical Activity Readiness Questionnaire (PARQ)
A screening questionnaire completed before starting or increasing physical activity to identify health concerns that may require medical advice or changes to training.
Physical barrier
A structure that helps stop pathogens entering the body.
Physical barrier
A layer that prevents substances such as oxygen and water from reaching a metal surface.
Physical barrier
A structure that blocks pathogen entry or traps and removes pathogens.
Physical change
A change between physical states in which no new substance is produced.
Physical change
A change in which no new substance is formed and the material can recover its original properties when the change is reversed.
Physical change
A change in which no new substance forms. When a change of state is reversed, the material recovers its original properties.
Physical change
A change in a material’s size, shape or physical state without forming a new substance, such as chopping vegetables or melting butter.
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