surface area : volume

• Surface area to volume ratio

  The relationship between the size of an organism and the surface area available for exchange processes
• Importance of surface area to volume ratio in biology

  • Explains how many exchange surfaces (e.g. for gas exchange or absorption) organisms have
  • Organisms have similar adaptations to make transport across exchange surfaces more efficient
• Calculating surface area to volume ratio

  1. Calculate surface area of shape

  2. Calculate volume of shape

  3. Divide surface area by volume
• Relationship between size of organism and surface area to volume ratio

  Larger organisms have smaller surface area to volume ratios
• Diffusion


  The process by which smaller organisms can efficiently exchange substances across their surface without additional adaptations
• Adaptations of larger organisms

  • Have smaller surface area to volume ratios
  • Have higher metabolic rates and greater demands for gas exchange and absorption
  • Need adaptations to increase surface area without reducing volume too much
• Adaptations to increase surface area

  • Villi and microvilli in digestive system
  • Alveoli and bronchioles in respiratory system
  • Spiracles and tracheal system in insects
  • Gill filaments and lamellae in fish
  • Broad, thin leaves in plants
  • Capillary networks
• Larger plants have adaptations to maximise gas exchange, such as broad, thin leaves
• Capillary networks provide a large surface area for gas exchange at the cellular level