3.1: adaptations for gas exchange

• What is the definition of gas exchange?

  When oxygen and/or carbon dioxide moves by simple diffusion in opposite directions across an exchange surface
• Why can oxygen and carbon dioxide move across cell membranes by simple diffusion?

  they are small, non-polar and lipid-soluble
• What adaptations do exchange surfaces have?

  -large surface area

  -short diffusion distance/pathway

  -good blood supply

  -ventilation mechanism

  -permeable

  -moist (oxygen and carbon dioxide diffuse best in solution)
• What types of molecule can enter cells through simple diffusion?

  Gases: small, non-polar, lipid-soluble molecules

  e.g. oxygen, carbon dioxide enter the cell through the phospholipid bilayer
• How can large and polar molecules enter cells?

  -Through specific protein carriers/channels by facilitated diffusion

  -active transport (if going against a concentration gradient)

  -endocytosis or exocytosis