Gas exchange in animals

For an organism to function, substances must move into and out of cells. Three processes contribute to this movement – diffusion, osmosis and active transport.

Part of

Biology (Single Science)

Exchange and transport in animals

Diffusion

Particles - molecules and ions - in a liquid and a gas are continuously moving. Because of this movement, particles will spread themselves evenly throughout a liquid or a gas.

If there is a situation where particles of a substance are in a higher concentration, they will move from this region to where they are in a lower concentration. This is called diffusion.

It is important to remember that the particles:

will move in both directions, but there will be a net movement from high to low concentration
will end up evenly spread throughout the liquid or gas, but will continue to move