1. Practical 1 The Model Gut

2. Mammalian Nutrition Learning objectives: By the end of the lesson you should be able to: State the need for digestion. Describe the movement of molecules across the small intestine to the blood using your experience of a model gut.

3. Introduction The process of ___________ can be demonstrated with a model gut. Starch is a _________________ made up of many _______ ___________ _____ joined together ______________turns _____ when __________ is present. ___________ turns _________ when _______ is present _______________ turns _________ when ____________ is present absorption large moleculesmall glucose molecules Iodine solutionblackstarch Clinistixpurpleglucose Benedict’s solutionorangeglucose

4. Represents the __________ Represents __________ ____________ in the gut Represents the blood Visking Tubing Glucose/ starch mixture Water “gut wall” “food” “molecules”

5. Aim To show the effect of the size of molecule on absorption

6. Method 1. Tie a knot at one end of a soaked piece of visking tubing and use a dropper to half fill with the glucose/starch mixture 2. Seal the bag by tying a knot in the other end of the visking tubing and rinse the bag under the tap. 3. Place the bag in a boiling tube and cover with water. 4. Remove a few drops of water from the tube and place onto a dimple tray. 5. Test for sugar using Benedicts Reagent. Test for starch using iodine. 6. Leave for 30 minutes and then retest the surrounding water for glucose and starch. Record your results.

7. Results Glucose Starch At start of experiment At end of experiment X X X

8. Interpretation Why are only glucose molecules found in the “blood” at the end of the experiment? They are very small and pass through the “gut wall” What must happen to starch molecules before they can be absorbed into the “blood” They must be broken down into small molecules

9. Conclusion Which size of molecule is absorbed from the “gut” into the “blood” Only the small molecules

10. Evaluation Why is the visking tubing bag washed before being placed in the boiling tube? Any glucose or starch on the outside of the bag will give false positive results