Diffusion

• What is diffusion?

  net movement of particles from an area of high concentration to an area of low concentration along a concentration gradient – this is a passive process (does not require energy from respiration)
• Name three factors that affect the rate of diffusion. 

  concentration gradient, temperature, membrane surface area
• How are villi adapted for exchanging substances?

  • long and thin – increases surface area

  • one-cell-thick membrane – short diffusion pathway

  • good blood supply – maintains a steep concentration gradient
• How are the lungs adapted for efficient gas exchange?

  • alveoli – large surface area

  • moist membranes – increases rate of diffusion

  • one-cell-thick membranes – short diffusion pathway

  • good blood supply – maintains a steep concentration gradient
• How are fish gills adapted for efficient gas exchange?

  • large surface area for gases to diffuse across

  • thin layer of cells – short diffusion pathway

  • good blood supply – maintains a steep concentration gradient
• The difference in concentration between 2 areas is called the concentration gradient.

  The larger the difference in concentration - the faster the rate of diffusion.
• Examples of diffusion (4)

  • oxygen & glucose into cells of the body from the bloodstream for respiration
  • carbon dioxide into actively photosynthesising plant cells
  • gas exchange in the lungs
  • simple sugars & amino acids from the gut through cell membranes