exchanging substances

• Specialized exchange surfaces


  Parts of an organism over which they exchange substances with their environment
• Specialized exchange surfaces in humans

  • Alveoli
  • Villi
• Alveoli


  • Small sac-like things found in the lungs at the very ends of the bronchioles
  • Exchange oxygen and carbon dioxide between the air and the blood
• Villi


  • Finger-like things found on the inside lining of the small intestines
  • Help absorb nutrients like glucose and amino acids
• Specialized exchange surfaces in plants


  • Root hair cells
  • Leaves
• Root hair cells


  • Help absorb water and mineral ions from the soil
• Leaves


  • Help absorb the carbon dioxide they need from the air
• Common features of specialized exchange surfaces


  • Large surface area
  • Thin surfaces
  • Permeable to substances they need to exchange
  • Good blood supply (internal medium)
  • Good supply of external medium
• Large surface area


  Allows more molecules to diffuse across at the same time, increasing the rate of diffusion
• Thin surfaces


  Short diffusion distance, allowing faster diffusion
• Permeable


  Allows substances to diffuse across rather than blocking them
• Good blood supply (internal medium)


  Helps maintain a concentration gradient for substances being absorbed
• Good supply of external medium


  Helps maintain a concentration gradient for substances being absorbed, e.g. air for alveoli, food for villi