Surface area/gas exchange

• As organisms increase in size, they have more cells and more volume, and a higher requirement for oxygen. As size increases, volume increases more than surface area. This means their surface area to volume ratio decreases.
• What affects the rate of diffusion?

  -surface area

  -diffusion pathway

  -concentration gradient
• How does surface area affect the rate of diffusion?

  The larger the surface area, the faster the rate of diffusion.

  Folded surfaces, e.g. microvilli, increase surface area
• How does diffusion pathway affect the rate of diffusion?

  The shorter the diffusion pathway, the less distance substances have to travel, so the faster rate of diffusion.

  Flattened cells and tissues that are 1 cell thick shorten diffusion pathways
• How does concentration gradient affect the rate of diffusion?

  The higher the concentration gradient, the faster the rate of diffusion.
• How can concentration gradients be maintained?

  -ventilation mechanisms/circulatory systems bring fresh oxygen and remove carbon dioxide

  -use of oxygen in respiration and production of carbon dioxide in cells
• How is concentration gradient maintained in aquatic organisms?

  -movement of aquatic organisms can increase the flow of oxygenated water and help maintain concentration gradients

  -turbulence in water increases oxygenation and therefore the concentration gradient
• As organisms increase in size, their volume increases faster than their surface area
• Organisms with a larger surface area to volume ratio can obtain more oxygen
• How can concentration gradients be maintained?

  • ventilation & circulation: brings fresh oxygen and removes carbon dioxide
  • use of oxygen in respiration and production of carbon dioxide in cells
  • movement of aquatic organisms increases the flow of oxygenated water
  • turbulence in water increases oxygenation