| Diffusion definition | - The net movement of molecules from a region of high concentration to a region of low concentration
- Until evenly distributed
- Passive |
| Key points of diffusion | - No energy needed
- Particles diffuse down concentration gradient
- Only free particles can diffuse through cell membranes |
| Simple diffusion meaning | - When molecules diffuse directly through a cell membrane |
| Facilitated diffusion | - When large or charged particles diffuse through carrier or channel proteins in the membrane |
| Carrier proteins | - Large molecules attach to carrier proteins
- The protein changes shape
- This releases molecule on the opposite side of the membrane
- Different carrier proteins for different molecules |
| Channel proteins | - Pores in the membrane for charged particles to move through
- Different channel proteins for different molecules |
| Factors that affect the rate of simple diffusion | - Concentration gradient
- The thickness of exchange surface
- The surface area |
| Concentration gradient and simple diffusion | - The higher it is the faster the rate
- Difference in concentration decreases as equilibrium is reached |
| The thickness of exchange surfaces and simple diffusion | - The thinner the exchange surface the faster the rate |
| Surface area and simple diffusion | - The larger the surface area the the faster the rate e.g. microvilli |
| Factors that affect the rate of facilitated diffusion | - The concentration gradient
- The number of channel or carrier proteins |
| The concentration gradient and facilitated diffusion | - The higher it is the faster the rate
- Difference in concentration decreases as equilibrium is reached |
| The number of channel or carrier proteins and facilitated diffusion | - The more proteins the faster the rate
- Once all proteins are in use, facilitated diffusion cant happen any faster |
