Modelling the digestive system

This is a common experiment used to model the digestive system and should help you understand how to work scientifically.

Aim of the experiment

To use Visking tubing to model the digestive system and show what substances can pass through its lining.

Method

  1. Set up two sets of the apparatus as in the diagram.
  2. Put 1cm3 of amylase enzyme into tube 1 but not tube 2.
  3. Leave at room temperature for five minutes.
  4. Test for starch using iodine and glucose using Benedict’s reagent inside and outside both tubes.
Two beakers with a Visking tube inside each. In the first Visking tube is 5cm3 of starch solution and 1cm3 of amylase solution, and in the second tube is 5cm3 of starch solution.A Visking tubing experiment

Variables

  • Independent variable - the presence or absence of amylase.
  • Dependent variable - the presence or absence of glucose inside and outside the tubing.
  • Controlled variables - the quantities of the solutions used, the time taken before testing and the temperature of the water.

Risks

Care must be taken with glassware, iodine solution and Benedict’s solution.

Expected results

Tube 1 (with amylase)

InsideOutside
Starch presentYesNo
Glucose presentYesYes

Tube 2 (without amylase)

InsideOutside
Starch presentYesNo
Glucose presentNoNo

What the results mean

  1. There is no starch outside the Visking tubing. It is too large to pass through it.
  2. Glucose is present in the solution containing amylase, but not in the solution that doesn't contain amylase. Amylase breaks down starch into glucose.
  3. There is glucose outside the Visking tubing. Glucose is small enough to pass through it.

Evaluation

  • Your measurements are accurate if they are close to their true value.
  • This experiment only gives yes or no results so accuracy is not relevant here.
  • Your measurements are precise if they are similar when completed again.
  • Your experiment is repeatable if you get precise measurements when it is repeated.
  • Your experiment is reproducible if others get precise measurements when they repeat it.
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