Subtopic 2

Facilitated Diffusion

1.The movement of hydrophilic molecules or ions across the plasma membrane with the help of transport proteins.

2.Substances that are not soluble in lipids do not pass readily through the phospholipid bilayer.

3.Substances such as glucose, amino acids, proteins and nucleic acids pass through the membrane by facilitated diffusion.

Facilitated diffusion involves 2 types of protein

1. Channel proteins

Provide functional pore in the membrane for the diffusion of ions. The pore are selective about which ions can pass through.

2. Carrier proteins

Pick up the diffusion molecules on one side of the membrane and release them on the other side.

- Absorption of certain nutrients through the villi of the small intestine.

- Carrier proteins found on the membrane of cells that line the intestinal wall transport small    molecules such as amino acids and glucose into the blood capillaries of the villi