Transport in cells

• Diffusion


  The net movement of particles from an area of high concentration to an area of low concentration
• Diffusion


  Particles move randomly
• Factors affecting diffusion


  • Concentration gradient
  • Membrane surface area
  • Temperature
• Concentration gradient


  The difference in concentration between two areas
• Concentration gradient


  The bigger the difference, the greater the rate of diffusion
• Membrane surface area


  The larger the surface area of the membrane, the faster the rate of diffusion
• Temperature


  The higher the temperature, the faster the rate of diffusion
• Surface area to volume ratio

  The ratio of the surface area to the volume of a structure
• Structures with a large surface area to volume ratio

  • Alveoli
  • Red blood cells
• How alveoli are specialised to transfer gases in the lungs

  • Large surface area
  • Thin membrane
• A large surface area allows more of a substance to diffuse at the same time
• A thin membrane reduces the diffusion distance