Cells B

• Diffusion distance:

  
  

  Faster when smaller

  Exchange in the body only over 1 cell
• Density (diffusion):

  
  

  Gases diffuse faster

  greater density = slower rate of diffusion
• Concentration gradient (diffusion) :

  
  

  steep concentration gradient = faster diffusion
• Active transport:

  
  

  Energy-requiring process that moves material across a cell membrane against a concentration difference
• Osmosis (diffusion):

  
  

  Diffusion of water through a semi - permeable membrane