Module 3- Exchange and Transport

• Why do multicellular animals need a specialized exchange surface?

  • Large organisms have a very small SA:V ratio
  • There is a large diffusion distance from the outside to cells inside the organism
  • diffusion is too slow to meet metabolic needs
• What are the key features of an efficient exchange system?

  • large surface area
  • thin walls/ 1 cell thick
  • good blood supply and ventilation
• Why is it important to have a large surface area in an exchange system?

  • there is more space for molecules to diffuse across the membrane which increases the rate of diffusion
• Why is it important to have thin walls in an exchange system?

  • it decreases the diffusion distance which increases the rate of diffusion
• Why is it important to have a good blood supply and ventilation in an exchange system?

  • increases the concentration gradient which increases the rate of diffusion
• What is the function of the cartilage?

  supports the trachea and bronchi
• What is the function of the ciliated epithelium?


  a layer of cells that have many hair like extensions called cilia
• What is the function of goblet cells?

  secretes mucus
• What is the function of mucus?

  traps pathogens
• What is the function of the cilia?

  moves mucus to the mouth
• What is the function of the smooth muscle?

  it contracts which causes the airways to constrict
• what is the function of elastic fibres?

  stretch and recoil
• What is the function of the squamous epithelium?

  it provides a short diffusion distance
• Why do the lungs have lots of small alveoulus?

  so there is a large SA:V ratio
• Why do the lungs have lots of alveoli?

  so there is a large surface area