Fiducia TogetherOsmosis, diffusion and active transport
Three ways substances move in and out of cells, and the differences examiners test.
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.
What it is
Diffusion is net movement of particles from high to low concentration, passive. Osmosis is diffusion of water across a partially permeable membrane, from dilute to concentrated solution. Active transport moves substances against the gradient and requires energy from respiration.
Where it applies
GCSE biology and combined science, with a required practical on osmosis.
How it works
Diffusion and osmosis need no energy; active transport does, which is why cells doing a lot of it have many mitochondria — root hair cells absorbing minerals, for example.
Surface area, distance and concentration gradient all affect rate, which is why exchange surfaces are folded, thin and well supplied with blood.
How to use it in your work
Be precise about water in osmosis: from a dilute solution to a concentrated one, or from high water potential to low. Vague answers lose the mark.
In the practical, calculate PERCENTAGE change in mass, not raw change, because the starting masses differ.
Where to get help
Your teacher, your board's specification for the depth required at your tier, and Bitesize for the diagrams. The subject song runs the topics in order.
Revise this with a song
These are ours. We write revision songs because a lot of people remember a tune when they cannot remember a page, and because revising out loud in the kitchen beats staring at a highlighter.
- The Biology Song The GCSE biology specification, set to music.
Where to read more
Last reviewed 2026-08-28 by Fiducia Together · Next review due 2027-08-28
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.