Model Gut

• Visking tubing is a fine smooth membrane with small holes in it. These holes are large enough to allow water and other small molecules through. They are too small to allow large molecules through.
• What was the purpose of taking samples from the Visking tubing and surrounding water immediately after water was poured around the tubing?

  To check whether the rinsing had been adequate and the tube was not leaking its contents.
• From your results, do you think that starch can get through the holes in the Visking tubing membrane?

  There is no starch outside the Visking tubing, but starch on both occasions inside. It looks like starch cannot get through the Visking membrane.
• From your results, do you think that glucose can get through the holes in the membrane?

  There is no glucose outside the Visking at the beginning, but there is after 15 minutes. It looks like glucose does move through the Visking membrane.
• What does this tell you about starch and glucose molecules?

  Starch molecules are too big to pass through the holes in the Visking membrane. Glucose molecules are small enough to pass through the holes in the Visking tubing.
• How is this length of Visking tubing containing starch and glucose similar to the gut of a multicellular organism?

  The similarities between Visking tubing and a real gut are:

  • the food molecules are contained in a tube whose walls are permeable only to small molecules
  • the food in the tube is a mixture of large and small molecules
  • the tube is surrounded by liquid which contains a low concentration of food molecules.
• What features of a real gut are missing from this model?

  The differences between Visking tubing and a real gut are:

  • the Visking tubing membrane is smooth, a gut lining is folded and folded again with a larger surface area for its length
  • a real gut is surrounded by blood flowing in vessels that take away the soluble products of digestion and maintain a concentration gradient between the gut contents and the surroundings
  • there are active transport mechanisms that will draw food molecules through the wall of a real gut.
• 1. Use syringes to add 5 cm3 of starch suspension and 5 cm3 of glucose solution.
  2. Rinse the tubing under the tap and suspend in the boiling tube.
  3. Remove 1 cm3 of the gut contents. 1 drop on dimple tile, the rest in a test tube.
  4. Put water into the boiling tube level with gut contents.
  5. Immediately remove 1 cm3 of the water. 1 drop on dimple tile, the rest in a test tube.
  6. Add one drop of iodine solution to the dimple tiles. Blue-black = starch.
  7. Add an equal volume of B’s reagent into the test tubes and put them in boiling water for 2-3 minutes. Orange = glucose.
  8. Repeat after 15 minutes.
• 𝗚𝗨𝗧 𝗖𝗢𝗡𝗧𝗘𝗡𝗧𝗦 𝗔𝗧 𝗧𝗛𝗘 𝗕𝗘𝗚𝗜𝗡𝗡𝗜𝗡𝗚: starch & glucose are present

  𝗪𝗔𝗧𝗘𝗥 𝗔𝗥𝗢𝗨𝗡𝗗 𝗚𝗨𝗧 𝗔𝗧 𝗕𝗘𝗚𝗜𝗡𝗡𝗜𝗡𝗚: no starch or glucose present

  𝗚𝗨𝗧 𝗖𝗢𝗡𝗧𝗘𝗡𝗧𝗦 𝗔𝗙𝗧𝗘𝗥 𝟭𝟱 𝗠𝗜𝗡𝗨𝗧𝗘𝗦: starch & glucose are present

  𝗪𝗔𝗧𝗘𝗥 𝗔𝗥𝗢𝗨𝗡𝗗 𝗚𝗨𝗧 𝗔𝗙𝗧𝗘𝗥 𝟭𝟱 𝗠𝗜𝗡𝗨𝗧𝗘𝗦: no starch but glucose is present