Diffusion

• Diffusion is the net movement of molecules or ions from a region of high concentration to low concentration until an equilibrium is reached
• Diffusion is a passive process so doesn't require extra input of energy
• Increase rate of diffusion by

  • increasing temperature
  • higher concentration gradient
  • higher surface area
  • shorter diffusion pathway
• Rate of diffusion is calculated by surface area x concentration gradient all divided by diffusion distance
• Other factors that affect rate of diffusion

  • molecular mass/size
  • charge/polarity
• Water-filled channel proteins can be described as aquaporins
• Facilitated diffusion is the movement of molecules across a membrane with the help of a protein
• Channel proteins increase the permeability of the plasma membrane to water and other molecules
• Carrier proteins changes shape and rotates through the membrane and deposits the molecule on the other side