diffusion through membranes

• We use the visking tubing at school because it's similar to the small intestine
• we can call the small holes in the visking tubing pores
• the walls of the visking tubing have pores that are small and only allow small molecules to pass through
• to mimic the small intestine, we fill a visking 'sauasage' with a solution of starch and glucose
• when the water is tested is tested at the start, we find that it contain neither glucose or starch
• when the water is tested after 20 minutes, we find that it contains glucose only
• visking tube lets glucose molecules through because the glucose molecules are much smaller than starch molecules
• a selectively permeable membrane lets through small molecules only
• Letter: B

  
• Letter: D

  
• Letter: A

  
• Letter: C

  
• As a model of a living membrane, we sometimes use visking tubing
• We can think of visking tubing being selectivley permeable
• Diffusion in and out of a call is controlled by its cell membrane
• Letter: D