Modelling absorption

• We should eat a balanced diet suitable for our age and lifestyle
• Overeating can lead to obesity
• Nutrients have to be digested before we can absorb and use them
• Visking tubing


  An artificial, partially-permeable membrane used in osmosis and diffusion experiments
• Modelling absorption in the small intestine


  1. Set up apparatus with Visking tubing

  2. Sample and test liquid inside and outside tubing at regular intervals

  3. Test for starch using iodine

  4. Test for glucose using Benedict's reagent
• The tubing still contains all the starch after two minutes, as starch molecules are too big to pass through the holes in the Visking tubing
• Glucose appears in the water because starch is digested (broken down) by the enzyme amylase to glucose, and glucose molecules are small enough to pass through the holes in the Visking tubing to the liquid in the beaker
• The model of the absorption of digested food in the small intestine

  Has limitations
• Similarities between model and small intestine


  • Selectively permeable
• Differences between model and small intestine


  • Smaller surface area due to lack of villi
  • Does not flow so concentration gradient is not maintained