specialised exchange surfaces

• metabolic activity of a multicellular organism is high so oxygen demands are high.
• Increased surface area

  = provides area needed for exchange and overcomes limitations of SA:V.
• thin layers

  = distances that substances have to diffuse are short- process is fast and efficient.
• good blood supply

  = steeper concentration gradient means faster diffusion- substances are constantly delivered to and removed- maintains gradient.
• ventilation

  = maintains diffusion gradient for gases- maintains concentration gradient, process is more efficient.