Diffusion and facilitated diffusion

• What is diffusion?

  Movement from higher to lower concentration
• What is the nature of the diffusion process?

  It is a passive process
• When does diffusion stop?

  When equilibrium is reached
• Which molecules can diffuse through the bilayer?

  Small, non-polar, lipid soluble molecules
• What factors affect the rate of diffusion?

  Concentration gradient, temperature, surface area, properties of molecules
• Which molecules cannot directly diffuse through the phospholipid bilayer?

  Large, polar, hydrophilic molecules and ions
• What is facilitated diffusion?

  Diffusion requiring transport proteins
• What are the two types of transport proteins?

  Channel proteins and carrier proteins
• What are the characteristics of channel proteins?

  • Water-filled pores
  • Fixed in shape
  • Allow charged substances to diffuse
  • Most are gated
  • Do not carry out active transport
• What are the characteristics of carrier proteins?

  • Can switch between two shapes
  • Binding site opens to one side first
  • Can carry out active or passive transport
• How is diffusion defined?

  Movement from higher to lower concentration