Diffusion — Cambridge IGCSE Combined Science
Diffusion is the net movement of particles down a concentration gradient; learn why it matters and what changes its rate.
Revision notes
2 short notes, in the order of the specification. Each one in short:
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.
The rate of diffusion depends on four factors: surface area, temperature, concentration gradient and distance. Diffusion is faster with a larger surface area, a higher temperature, a steeper concentration gradient and a shorter distance. In agar cubes containing indicator placed in dilute acid, the smallest cube, with the largest surface area compared with its volume, loses its colour first.
Exam questions
4 exam-style questions (10 marks), each with its mark scheme.
Answer the questionsFlashcards
6 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of movement into and out of cells on one page, so you can see where this subtopic fits.
Open the mind mapPractical sheet
Method, variables, risks and a results table, with questions to answer.
Print it
Free PDFs to print or save.
Quick check questions
Describe diffusion.
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The net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement.
Name two substances that move into or out of cells by diffusion.
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Any two from: oxygen, carbon dioxide, urea, digested food molecules.
Supplement Name the four factors you investigate that affect the rate of diffusion.
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Surface area, temperature, concentration gradient and distance.
Written and checked against the Cambridge IGCSE Combined Science (0653) specification · Updated October 2026