Diffusion
Cards (6)
- Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration
- The concentration gradient is the path from an area of higher concentration to an area of lower concentration. Particles diffuse down a gradient
- Diffusion is a passive process - when molecules diffuse directly through a cell membrane its also known as simple diffusion
- The rate of diffusion depends on
- The concentration gradient - the higher it is the faster the rate of diffusion. As diffusion takes a place the difference between the two sides decrease until it reaches an equilibrium
- The thickness of the exchange surface - the thinner the exchange surface the shorter the distance for diffusion - faster rate of diffusion
- The surface area - the larger the surface area, the faster the rate of diffusion
- Facilitated diffusion moves down a concentration gradient, from a higher to lower concentration. It is also a passive process - it doesn't use energy. There are two types of proteins involved: channel proteins, carrier proteins
- Carrier proteins moves large molecules across the membrane down their concentration gradient. Different carrier proteins facilitate the diffusion of different molecules
- First a large molecule attaches to a carrier proteins binding site in the membrane
- Then the protein changes shape
- This releases the molecule on the opposite side of the membrane
- Channel proteins form pores in the membrane for charged particles to diffuse through.Different channel proteins facilitate the diffusion of different charged particles
- Factors affecting the rate of facilitated diffusion
- The concentration gradient - the higher the concentration gradient the faster the rate of facilitated diffusion. As equilibrium is reached the rate of facilitated diffusion will level off
- The number of channel or carrier proteins - once all the proteins in a membrane are in use, facilitated diffusion can't happen any faster even if you increase the concentration gradient