Diffusion

 Diffusion is a mechanism used to transport materials across cell membranes, using no energy (ATP).

There are three types of diffusion:

• simple diffusion
• facilitated transport
• co-transport

Simple Diffusion

The movement of ions and molecules from an area of high concentration to a low concentration across a cell membrane.

Molecules which are transported by simple diffusion include:

• oxygen
• carbon dioxide
• steroid hormones
  

Facilitated Transport

Facilitated diffusion is the diffusion of ions, water or hydrophilic molecules across a membrane with the help of channel proteins. Of these channel proteins there are two types; gated and non-gated channels.

Molecules which are transported via facilitated diffusion include:

• glucose
• amino acids
• water
• some ions