Topic 2b- Exchange across cell membranes- diffusion Flashcards
What is diffusion?
Net movement of particles from high to low concentration.
No energy required.
Particles diffuse down concentration gradient.
Facilitated diffusion uses carrier proteins and protein channels.
What is facilitated diffusion?
Some larger molecules would diffuse extremely slowly through the phospholipid bilayer because they’re so big. Charged particles would also diffuse slowly. So too speed things up large or charged particles diffuse through carrier proteins or channel proteins in the membrane instead- this is called facilitated diffusion.
In facilitated diffusion, what are carrier and channel proteins?
Carrier proteins- move large molecules across membranes, down their concentration gradient.
First, a large molecule attaches to a carrier protein 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.
Describe the mechanism for the absorption of amino acids in the ileum.
- Facilitated diffusion of amino acid
- Co-transport
- Sodium ions actively transported from cell to blood/ tissue fluid.
- Creating sodium ion concentration/ diffusion gradient
- Facilitated diffusion of amino acid into blood/ capillary.
