1Particles spread out
Diffusion is the overall movement of particles from a high concentration (lots of them) to a low concentration (fewer), until they are evenly spread.
diffusionconcentration
Lesson 1.4 notes
Diffusion
Explain how oxygen, carbon dioxide and other substances move into, out of and between cells by diffusion.
2Random movement
Each particle moves randomly, bumping into others. Where there are more particles, more of them move out than in, so overall they spread out. Nothing pushes them.
3Into and out of cells
Small particles diffuse through the cell membrane. Oxygen and glucose diffuse into a cell, where they are used up. Carbon dioxide, made by respiration, diffuses out.
4Blood and body cells
Blood brings oxygen to the body's cells. Oxygen diffuses from the blood, where there is a lot, into the cells, where it's used up. Carbon dioxide diffuses the other way.
5In the lungs
In the lungs, oxygen diffuses from the air in tiny air sacs (alveoli) into the blood, and carbon dioxide diffuses out. The walls are very thin, so it's a short way to go.
alveoli
6In a leaf
In daylight, carbon dioxide diffuses into a leaf through tiny holes, and into its cells for photosynthesis. The oxygen they make diffuses out.
7Faster diffusion
Diffusion is faster when it's warmer (the particles move faster), when the difference in concentration is bigger, over a shorter distance and across a bigger surface.
Explore: Diffusion lab
Particles start on one side of a cell membrane. Change the temperature, the number of particles and their size, then count how many get through.
Common mistake: Particles spread out because they move randomly
They don't want to spread out, and nothing pushes them. Where there are more particles, more of them move away than move in. Once they are evenly spread they keep moving, but there's no overall change.
Remember
- Diffusion is the overall movement of particles from a high concentration (lots of them) to a low concentration (fewer).
- Oxygen and glucose diffuse into cells through the cell membrane, and carbon dioxide diffuses out.
- Diffusion is faster when it's warmer, when the difference in concentration is bigger, over a shorter distance and across a bigger surface.
Going further at GCSE