Diffusion

What is facilitated diffusion?

Diffusion for large molecules and charged particles. Proteins help to “facilitate” the movement of particles through membrane. It is faster than simple diffusion.

Why is facilitated diffusion used?

Some particles/molecules would move very slowly through the membrane so they need to diffuse through specialised carrier or channel proteins instead.

Is facilitated diffusion passive or active?

It’s a passive process as no energy is involved, it’s moving down the concentration gradient.

How do carrier proteins work?

They move large molecules, different proteins facilitate the diffusion of different large molecules. Large molecules attach and then protein changes shape releasing molecule on other side of membrane.

How do channel proteins work?

They form pores for charged particles to diffuse through, different protein channels facilitate the diffusion of different charged particles. They don’t change shape, it’s a simple ‘tunnel’ which allows charged particles to cross membrane.

What are the factors affecting facilitated diffusion?

• concentration gradient - greater concentration difference is the faster rate of facilitated diffusion. As particles still moving down concentration gradient, true until all proteins are in use. Equilibrium reached.

• number of channel/carrier proteins - greater number of channel/carrier protein the faster the rate of facilitated diffusion. True until point, once all proteins are in use they can’t happen faster. Becomes limiting factor.