Surface Area to Volume Ratio

• Why do multicellular organisms require exchange surfaces and a transport system?

  Due to their low surface area to volume ratio
• What is the function of gills in fish?

  To transport gases into and out of fish
• What is diffusion?

  Movement of molecules from high to low concentration
• What is the surface area to volume ratio?

  It compares the surface area of an object to its volume
• How does the surface area to volume ratio affect diffusion in single-celled organisms?

  Higher ratio allows efficient diffusion of molecules
• What is the surface area of a cube with side length 1 mm?

  6 square mm
• What is the volume of a cube with side length 1 mm?

  1 cubic mm
• What is the surface area to volume ratio of a cube with side length 1 mm?

  6:1
• What is the surface area of a cube with side length 2 mm?

  24 square mm
• What is the volume of a cube with side length 2 mm?

  8 cubic mm
• What is the surface area to volume ratio of a cube with side length 2 mm?

  3:1
• What is the surface area of a cube with side length 3 mm?

  54 square mm
• What is the volume of a cube with side length 3 mm?

  27 cubic mm
• What is the surface area to volume ratio of a cube with side length 3 mm?

  2:1
• Why does the surface area to volume ratio decrease as organisms get larger?

  Because volume increases faster than surface area
• How do multicellular organisms solve the problem of low surface area to volume ratio?

  By developing specialized structures for gas exchange
• What are the adaptations of gills in fish for gas exchange?

  Massive surface area, thin membranes, efficient blood supply
• How does oxygen diffuse in fish gills?

  From water into deoxygenated blood
• What happens to oxygenated blood in fish gills?

  It returns to the body after gas exchange
• What are the key adaptations of fish gills for efficient gas exchange?

  • Large surface area from filaments
  • Thin membranes for short diffusion pathway
  • Efficient blood supply to maintain concentration gradient
• What are the implications of a low surface area to volume ratio for multicellular organisms?

  • Insufficient diffusion for internal cells
  • Need for specialized exchange surfaces
  • Requirement for transport systems to circulate gases
• How do single-celled organisms like amoebas rely on diffusion?

  • High surface area to volume ratio
  • Oxygen diffuses directly through the membrane
  • Efficient transport of molecules in and out