Diffusion
Particles spread from high to low concentration.
About this topic
Diffusion is the net movement of particles from a region of higher concentration to lower concentration, down the concentration gradient, due to random motion. It is passive, requiring no energy. Rate increases with steeper gradient, higher temperature, smaller distance and larger surface area.
Oxygen diffuses from the lungs into blood, and carbon dioxide the other way. Cells have adaptations to speed diffusion, such as folded membranes, thin walls and good blood supply. Diffusion works well over short distances but not across large organisms.
Smell is a daily example: when someone opens a bag of popcorn across the room, particles spread out until you notice the scent. In your lungs, oxygen diffuses from the alveoli into the blood because oxygen concentration is higher in the air than in the capillaries, and carbon dioxide diffuses the other way. Rate rises with a steeper gradient, higher temperature, greater surface area and shorter distance.
Body structures are shaped by these rules: the thin walls of alveoli and the folded surface of the small intestine speed up diffusion. A classic experiment drops a coloured crystal in water and times how fast the colour spreads, hot versus cold. Students often think particles stop moving at equilibrium; they keep moving, but there is no net movement because it is equal in both directions.
Key ideas
- Passive, needs no energy
- Faster when hot or steep gradient
- Gas exchange uses diffusion
Quick check
Use cases: where Diffusion helps
- Homework: review the key idea behind Diffusion before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Diffusion without notes.
- Visual learning: play with the interactive lab to see how Diffusion changes when you adjust its inputs.
- Teaching a friend: explain Diffusion in your own words, then compare your version with the key ideas.
Biology underpins medicine, farming, conservation and biotechnology.
Frequently asked questions
What is Diffusion?
Particles spread from high to low concentration.
What will I learn in Diffusion?
Passive, needs no energy. Faster when hot or steep gradient. Gas exchange uses diffusion.
Is Diffusion part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Diffusion lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Diffusion?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.