exchange

• factors affecting the need for an exchange system:

  • size - larger diffusion distance
  • SA:V - large volume calm later to SA, which is too small to supply cells with sufficient oxygen
  • activity level - increased metabolic activity requires greater level of oxygen and glucose for respiration
• features for efficient exchange

  • large surface area
  • constant supply of molecules on one side keeps concentration high
  • constant removal of molecules on other side keeps concentration low
  • thin barrier reduces diffusion distance