gas exchange surfaces

• surface area to volume ratio

  • SA=total area of an organism exposed to environment
  • v=total internal vol of an organism
  • as size of organism increases, SA:V ratio decreases
  • because volume increases more rapidly than surface area as size increases
• single-celled organisms

  • large SA:V ratio
  • exchange of substances by simple diffusion
  • large surface area allows for max absorption of nutrients and gases+removal of waste products
  • small V within cell means diffusion distances to all organelles is short
• large multi-cellular organisms

  • adaptions- gas exchange system
  • adapted to increase surface area available for gas exchange eg aveoli increase SA is lungs
• diffusion pathways

  • surface often contains one cell layer of epithelial cells
  • gives a very short diffusion pathway
• concentration gradient

  • the difference in concentration of exchange substances on either side of exchange surfaces
  • increased diffusion conc= greater rate of diffusion
  • mocement of exchange substances away from exchange surface means conc gradient is maintained

  -alveoli have a good blood supply, removed 02 from cappilary side and supplies C02

  -constant inhalation and exhalation supplies 02 and removed C02 from alveoli side of exchange surface
• ficks law of diffusion

  rate of diffusion=(surface area x conc different)/diffusion distance(thickness of membrane)
• alveoli

  • epithelium forms alveolar wall(one cell thick)= thin and permeable for easy diffusion
  • surrounded by large capillary network(maintains steep conc gradient) C02 to the alveoli and 02 out of alveoli
  • capillary wall one cell thick
  • good blood supply, steep conc gradient
  • ventilation keeps steep conc gradient