Movement - simple diffusion

• Net movement of particles ( molecules and ions ) from a region of high to low concentration
• Difference in concentration is called the concentration gradient
• Diffusion is passive and doesn’t require energy , it occurs by random thermal motion of particles
• Continues down concentration gradient until the particles are randomly distributed until equilibrium has been reached
• Any small , uncharged ( non-polar ) particle can pass between the phospholipid molecules and readily diffuse through the membrane

  • such as oxygen and carbon dioxide which can dissolve in the hydrophobic bilayer