Facilitated Diffusion

Facilitated Diffusion

• Most substances in the cell are too large or too polar to cross membranes by simple diffusion.
• Facilitated diffusion is needed in such cases.
• Solutes move along their concentration gradient.
• It doesn't require energy (passive transport).
• It uses transport proteins to help move solutes through the membrane.

Types of Transport Proteins

• Two types of transport proteins are used in facilitated diffusion:
  • Channel proteins
  • Carrier proteins

Channel Proteins

• Provide a tunnel through the membrane for substances to pass through.

Carrier Proteins

• Change their shape to move solutes through the membrane.
• Membrane fluidity is important to allow these proteins to change shape.

Types of Channel Proteins

• Ion channels
• Porins
• Aquaporins