Exchanging Substances

• What is the significance of surface area to volume ratio in single-celled organisms?

  It allows substances to pass easily
• Why do multicellular organisms require exchange surfaces and transport systems?

  Cells are too far from the outer surface
• What are the four organs adapted for exchange in multicellular organisms?

  • Leaves: gas exchange
  • Small intestine: absorption of food
  • Gills: gas exchange in fish
  • Alveoli: gas exchange in lungs
• How do leaves facilitate gas exchange?

  They have a flat shape and stomata
• What is the role of the small intestine in exchange?

  Absorption of food molecules
• What features do exchange surfaces usually have?

  A large surface area, thin membrane, efficient blood supply, ventilation
• What is the function of gills in fish?

  Gas exchange between water and blood
• What adaptations do gills have for efficient gas exchange?

  Lots of gill filaments and lamellae
• What is the role of alveoli in the lungs?

  Gas exchange
• How do alveoli facilitate gas exchange?

  They have thin walls and a capillary network
• How many alveoli are present in the lungs?

  Millions
• What happens to air in the alveoli?

  Air moves in and out
• What are the key features of effective exchange surfaces in organisms?

  • Large surface area for diffusion
  • Thin membranes for short diffusion distance
  • Efficient blood supply in animals
  • Ventilation for gas exchange