Diffusion

• Particles are constantly moving due to their kinetic energy.
• Motion is random.
• Particles bouncing off each other. 

• Net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower. 
• Passive diffusion means that no metabolic energy is required.
• It's the difference in concentration that matters, not the concentration.
• When there is no concentration gradient, dynamic equilibrium is achieved.

Three factors that affect the rate of diffusion:

1. Concentration gradient - larger concentration gradient = faster rate.

2. Area over which diffusion takes place - larger exchange surface = faster rate.

3. Thickness of exchange surface - Thinner exchange surface = faster rate. 

• There are two types of intrinsic proteins - protein channels and carrier proteins.
• They facilitate diffusion.
• Protein channels are water filled, they allow ions to diffuse and are selective.
• Carrier proteins are specific to a small molecule e.g. glucose.