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 role of gills in fish?

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

  Movement of molecules from high to low concentration
• How do single-celled organisms like amoebas transport molecules?

  They rely on diffusion through their membrane
• How do you calculate 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 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 having specialized structures and transport systems
• What do fish use to obtain oxygen from water?

  Gills
• How does oxygen-rich water flow in fish?

  It passes into the mouth and over gills
• What adaptations do gill filaments have to increase diffusion rate?

  Large surface area, thin membrane, efficient blood supply
• Why is a high concentration gradient important for diffusion in gills?

  It ensures efficient oxygen uptake into the blood
• What are the adaptations of gill filaments for gas exchange?

  • Massive surface area
  • Thin membrane for short diffusion pathway
  • Efficient blood supply to maintain concentration gradient
• What are the implications of low surface area to volume ratio for multicellular organisms?

  • Insufficient diffusion for internal cells
  • Need for specialized exchange surfaces
  • Requirement for transport systems