2B.2 Diffusion

• how do you calculate the rate of diffusion from a straight line and curved graph?

  find the gradient (draw a tangent for a curve) and calculate by change in Y/change in X (rise over run).
• how does the number of channel and carrier proteins affect the rate of facilitated diffusion?

  the more proteins, the faster the rate. once all the proteins are in use the rate cannot further increase.
• name an example in the body when facilitated diffusion is used?

  glucose being absorbed from blood plasma into red blood cells.
• what two factors affect the rate of facilitated diffusion?

  • the concentration gradient. • the number of carrier and channel proteins.
• how do channel proteins work?

  they form pores in the membrane for charged particles to diffuse through.
• how do carrier proteins work?

  • large/charged molecules attach to a carrier protein in the membrane.• the protein changes shape.• the molecule is released on the other side.
• are carrier and channel proteins specific?

  yes. they are only complimentary to certain molecules.
• what is facilitated diffusion?


  the net movement of larger or polar molecules passively down a concentration gradient with the use of carrier and channel proteins.
• why do we need facilitated diffusion?

  large and charged (polar) molecules diffuse extremely slowly through the phospholipid bilayer.
• what are the two types of diffusion?

  simple and facilitated.
• how does surface area affect rate of simple diffusion?

  the larger the surface area (length of membrane) the faster the rate of diffusion.
• how does thickness of the exchange surface affect rate of simple diffusion?

  the thinner the exchange area (the shorter the distance to travel) the faster the rate.
• how does the concentration gradient affect the rate of simple and facilitated diffusion?

  the higher the gradient, the faster the rate until equilibrium is reached.
• what three factors affect rate of simple diffusion?

  • concentration gradient• thickness of exchange surface • surface area
• name two examples of molecules that move via simple diffusion.

  oxygen and carbon dioxide.
• what does passive movement mean?


  particles do not require energy to move.
• what is simple diffusion?

  the net movement of particles passively down a concentration gradient.