Diffusion

• What is diffusion?

  Net movement of particles from high to low concentration
• What happens to particles during diffusion?

  They move until evenly distributed
• What is a concentration gradient?

  Path from high to low concentration
• How does diffusion occur across cell membranes?

  Particles diffuse freely if they can move through
• What is simple diffusion?

  Diffusion directly through a cell membrane
• Why can oxygen and carbon dioxide diffuse easily through cell membranes?

  They are small and non-polar
• What factors affect the rate of diffusion?

  • Concentration gradient
  • Thickness of exchange surface
  • Surface area
• How does a higher concentration gradient affect diffusion?

  The rate of diffusion increases
• What happens to diffusion as equilibrium is reached?

  Diffusion slows down over time
• What are microvilli?

  Projections that increase surface area
• How do microvilli affect the rate of diffusion?

  They increase the surface area for exchange
• What is facilitated diffusion?

  Diffusion through carrier or channel proteins
• How do carrier proteins function in facilitated diffusion?

  They change shape to move molecules across
• What do channel proteins do?

  Form pores for charged particles to diffuse
• What factors affect the rate of facilitated diffusion?

  Concentration gradient and number of proteins
• What happens when all carrier proteins are in use?

  Facilitated diffusion cannot happen faster
• What are aquaporins?

  Channel proteins for water diffusion
• How do kidney cells utilize aquaporins?

  They reabsorb water efficiently
• How do you calculate the rate of diffusion from a graph?

  Find the gradient of the line
• What do you do for a curved graph to find the rate of diffusion?

  Draw a tangent and find its gradient
• What is the difference between diffusion and facilitated diffusion?

  • Diffusion: Direct movement through membranes
  • Facilitated diffusion: Uses proteins for larger/charged molecules