- 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.
Rate of Diffusion
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.